Dissertations / Theses on the topic 'Two dimensional visible spectroscopy'
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1
Townsley, Christopher Mark. "Optical spectroscopy of two-dimensional hole systems in the quantum limit." Thesis, University of Exeter, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312067.
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Harris, Janet Caroline. "Optical spectroscopy of correlated two-dimensional electrons." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390497.
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Zhang, Xu Ph D. Massachusetts Institute of Technology. "Two-dimensional crystals : spectroscopy and electronic applications." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112036.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 159-177).
The success in creating atomically thin and mechanically robust two-dimensional (2D) crystals, starting with graphene, has unveiled new possibilities for next generation of ultrafast and ubiquitous electronics. One critical distinction between 2D crystals and 3D crystals is that 2D crystals are all-surface materials. Therefore, it is essential to understand how 2D materials interact with their environments and how this interaction impacts their electronic properties. From a practical perspective, it also provides us with a unique tool to tailor the electronic properties of 2D materials through surface functionalization. In the first half of this thesis, a suite of X-ray techniques is used to investigate how the surface functionalizing dopants will impact the electronic and chemical states of graphene. Based on this study, we develop an effective and non-invasive doping method for graphene through plasma-based chlorination. In order to make system-level 2D electronics successful, a flexible and ubiquitous energy harvesting solution is indispensable. Therefore, the second part of this thesis is dedicated to the development of a MoS₂ 2H-1T phase heterojunction-based GHz flexible rectifier as an enabling component for wireless energy harvester. It is the first flexible rectifier operating up to the X-band and it covers most of the unlicensed industrial, scientific and medical (ISM) radio band, including the Wi-Fi channels. By integrating this rectifier with an antenna, the MoS₂-enabled rectenna successfully demonstrates direct energy harvesting of electromagnetic (EM) radiation in the Wi-Fi band and lights up a commercial light-emitting diode (LED) with zero external bias (battery-free). Moreover, our MoS₂ rectifier also realizes successful frequency conversion as a mixer beyond 10 GHz on flexible substrates. This work provides a universal energy harvesting building block that can be integrated with various wearable electronic systems and paves the way towards using the existing Wi-Fi infrastructure as an energy hotspot for wireless charging.
by Xu Zhang.
Ph. D.
4
Kraft, Robert A. (Robert Arthur) 1970. "In vivo two-dimensional NMR correlation spectroscopy." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85271.
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Gardner, Elizabeth Mary. "Two-dimensional infrared spectroscopy for protein analysis." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/5602.
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A number of forms of coherent multi-dimensional vibrational spectroscopy (CMDVS) have been identified as being useful for addressing a range of biological problems. Here a particular member of this family of spectroscopies, electronvibration- vibration two-dimensional infrared (EVV 2DIR) spectroscopy (also known as DOubly-Vibrationally Enhanced InfraRed (DOVE-IR)), is explored for its possible utility for two particular bioanalytical applications; protein identification and the study of enzyme mechanisms. The main focus of this work is on the development of EVV 2DIR as a tool for high-throughput, label-free proteomics, in particular for protein identification and absolute quantification. The protein fingerprinting strategy is based on the identification of proteins through their spectroscopically determined amino acid compositions. To this end, spectral signatures of amino acid side chains (tyrosine, phenylalanine and tryptophan) have been identified, as well as those from CH2 and CH3 groups which have been found to be appropriate for use as internal references. The intensities of these cross peaks are measured to give proteins’ amino acid compositions in the form of amino acid / CHx ratios. Specialised databases comprising the amino acid / CHx ratios of proteins have been developed for achieving protein identifications using the EVV 2DIR data. The second strand of this research considers the potential of triply resonant EVV 2DIR for studying protein structures and mechanisms. It is possible to use the electronic polarising properties of EVV 2DIR to good effect to achieve significant enhancement of the signal size when probing a chromophore. Here this effect is demonstrated for the case of bacteriorhodopsin (bR) membranes isolated from Halobacterium salinarium. The signal enhancement that is achievable from the retinal chromophore at the heart of bR makes it possible to study this whilst avoiding the surrounding protein.
6
Paul, Jagannath. "Coherent Response of Two Dimensional Electron Gas probed by Two Dimensional Fourier Transform Spectroscopy." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6738.
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Advent of ultrashort lasers made it possible to probe various scattering phenomena in materials that occur in a time scale on the order of few femtoseconds to several tens of picoseconds. Nonlinear optical spectroscopy techniques, such as pump-probe, transient four wave mixing (TFWM), etc., are very common to study the carrier dynamics in various material systems. In time domain, the transient FWM uses several ultrashort pulses separated by time delays to obtain the information of dephasing and population relaxation times, which are very important parameters that govern the carrier dynamics of materials. A recently developed multidimensional nonlinear optical spectroscopy is an enhanced version of TFWM which keeps track of two time delays simultaneously and correlate them in the frequency domain with the aid of Fourier transform in a two dimensional map. Using this technique, the nonlinear complex signal field is characterized both in amplitude and phase. Furthermore, this technique allows us to identify the coupling between resonances which are rather difficult to interpret from time domain measurements. This work focuses on the study of the coherent response of a two dimensional electron gas formed in a modulation doped GaAs/AlGaAs quantum well both at zero and at high magnetic fields.
In modulation doped quantum wells, the excitons are formed as a result of the inter- actions of the charged holes with the electrons at the Fermi edge in the conduction band, leading to the formation of Mahan excitons, which is also referred to as Fermi edge singularity (FES). Polarization and temperature dependent rephasing 2DFT spectra in combination with TI-FWM measurements, provides insight into the dephasing mechanism of the heavy hole (HH) Mahan exciton. In addition to that strong quantum coherence between the HH and LH Mahan excitons is observed, which is rather surprising at this high doping concentration. The binding energy of Mahan excitons is expected to be greatly reduced and any quantum coherence be destroyed as a result of the screening and electron-electron interactions. Such correlations are revealed by the dominating cross-diagonal peaks in both one-quantum and two-quantum 2DFT spectra. Theoretical simulations based on the optical Bloch Equations (OBE) where many-body effects are included phenomenologically, corroborate the experimental results. Time-dependent density functional theory (TD-DFT) calculations provide insight into the underlying physics and attribute the observed strong quantum coherence to a significantly reduced screening length and collective excitations of the many-electron system. Furthermore, in semiconductors under the application of magnetic field, the energy states in conduction and valence bands become quantized and Landau levels are formed. We observe optical excitation originating from different Landau levels in the absorption spectra in an undoped and a modulation doped quantum wells. 2DFT measurements in magnetic field up to 25 Tesla have been performed and the spectra reveal distinct difference in the line shapes in the two samples. In addition, strong coherent coupling between landau levels is observed in the undoped sample. In order to gain deeper understanding of the observations, the experimental results are further supported with TD-DFT calculation.
7
Johnson, Mark Thomas. "Photoelectron spectroscopy of two-dimensional materials and surfaces." Thesis, University of Cambridge, 1987. https://www.repository.cam.ac.uk/handle/1810/250898.
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Mignuzzi, Sandro. "Near-field optical spectroscopy of two-dimensional materials." Thesis, King's College London (University of London), 2017. https://kclpure.kcl.ac.uk/portal/en/theses/nearfield-optical-spectroscopy-of-twodimensional-materials(2e5e7a6b-d2b5-4242-bab7-3a66bd6c8c25).html.
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Real materials contain structural defects which significantly affect their properties. Defects, in a general sense, are ubiquitous and encompass the diverse variety of elements capable of disrupting the continuity and translational symmetry of a crystalline lattice, both in terms of its structural morphology, and in terms of local modulation of its electrical and optical properties. In this perspective, atomic vacancies, line vacancies, atomic rearrangements, local doping inhomogeneity, chemically adsorbed adatoms, all fall within the broad category of defects. Thus, the nanoscale details of surface structure plays a pivotal role in understanding the impact defects may have on the overall properties of the material, and this is particularly true for "all-surface" materials such as two-dimensional (2-D) crystals. Even the interface between two atomically thin layers has a strong impact on the electronic and optical properties of few-layered stacks; therefore, also the interface associated with stacking and layer orientation can be viewed as an extend defect in two dimensions. While macroscopic morphological characterization methods can provide averaged information over a lateral extent defined by their spatial resolution, high resolution (i.e. nanoscale) imaging has the potential to unveil important insights into the role of defects that dominate several aspects of surface chemistry and physics. On the one hand, defects in 2-D materials can be seen as deleterious as they may alter their electrical, chemical, magnetic and mechanical properties. On the other hand, the intentional creation of nanoscale defects may offer an additional degree of freedom for engineering their properties. In this perspective, having structural defects can be either detrimental or beneficial, depending on the targeted application. Despite the ever expanding literature on the study of the interplay between defects and the optical, electrical and mechanical properties of two dimensional materials, direct and non-destructive imaging of defect formation at the nanoscale remains a significant challenge. Although techniques such as electron microscopies or scanning tunnelling microscopy can be used to resolve individual lattice defects, they may be destructive or restricted to specific (e.g. conductive) substrates. This thesis presents a nanoscale optical investigation of 2-D materials, such as graphene and single-layer MoS2, with a particular focus on the characterisation of defects. The field enhancement at the tip-apex of a metal-coated atomic force microscopy (AFM) tip is used to decrease the spatial resolution beyond the diffraction limit. In the case of the investigation of Raman scattering, this near-field optical technique is known as tip-enhanced Raman spectroscopy (TERS). TERS is here demonstrated to be a valid technique to probe the distribution of point-like defects at the nanoscale, especially in the case of barely defective graphene. An analytical model to describe near-field imaging of pointlike Raman scatterers, which is of general applicability to zero-dimensional scatterers such as molecules, is presented. The near-field image, constructed from the Raman intensity, is found to depend on the Raman tensor and the orientation of the scatterer. The model can be also used to explain the different values of near-field Raman enhancement observed for different Raman bands. Motivated by the successful optical characterization of defects in graphene by means of Raman spectroscopy, it is now timely to expand the study of structural defects to other 2-D materials, such as semiconducting transition metal dichalcogenides. MoS2 is one of the most prominent members of this newly discovered category of chalcogenide monolayers. Defect-induced Raman scattering of single-layer MoS2 is studied by means of a controlled introduction of defects using ion-bombardment. Phonon confinement is used to explain the evolution of peak widths and shifts, and a metric based on Raman intensities is proposed to quantify defects. To gain insight into the defect-induced Raman processes, polarised and resonance Raman spectroscopy are employed.
9
Chan, Ho Bun 1969. "Tunneling spectroscopy of the two-dimensional electron gas." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9387.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1999.Includes bibliographical references (p. 155-161).
We measure the single particle density of states (DOS) of a two-dimensional electron system (2DES) in a GaAs/AlGaAs heterostructure. Using a technique that we call "Time Domain Capacitance Spectroscopy" (TDCS), we measure the complete current-voltage characteristics for tunneling into the 2DES without making ohmic contacts to it. TDCS detects the tunneling current in regimes difficult to access by conventional methods, such as when the in-plane conductance is low. For the first time we detect the contributions of localized states to the tunneling current. The DOS of an interacting 2DES in the diffusive limit displays logarithmic energy dependence near the Fermi level. Using TDCS, we measure the voltage dependence of the tunneling conductance of a semiconductor 2DES and observe the logarithmic Coulomb anomaly for the first time in 2D systems other than thin metal films. As we increase the density, this suppression in tunneling conductance narrows and recedes. Nevertheless suppression reappears when we apply a magnetic field perpendicular to the 2D plane. We find that the tunneling conductance depends linearly on voltage near zero bias for all magnetic field strengths and electron densities. Moreover, the slopes of this linear gap are strongly field dependent. The data are suggestive of a new model of the tunneling gap in the presence of disorder and screening. We also use TDCS to study the interactions among electronic spins. By applying excitations less than kT, we observe that equilibrium tunneling into spin-polarized quantum Hall states (v=l, 3, 1/3) occurs at two distinct tunneling rates for samples of very high mobility. Some electrons tunnel into the 2DES at a fast rate while the rest tunnel at a rate up to 2 orders of magnitude slower. Such novel double-rate tunneling is not observed at even-integer filling fractions where the 2DES is not spin-polarized. The dependence of the two rates on magnetic field, temperature and tunnel barrier thickness suggests that slow in-plane spin relaxation, possibly related to formation of Skyrmions, leads to a bottleneck for tunneling of electrons.
by Ho Bun Chan.
Ph.D.
10
Zhang, Tianhao. "Optical two-dimensional Fourier transform spectroscopy of semiconductors." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3315815.
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Nagata, Yuki. "Two-dimensional spectroscopy in solid, liquid, and surface." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136791.
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Harris, C. Thomas (Charles Thomas). "Terahertz waveguide spectroscopy of two-dimensional plasmons in GaAs." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62452.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 85-88).
The electrical characteristics of high-mobility, two-dimensional electron gas (2DEG) systems, such as GaAs quantum wells, have been well-studied at low frequencies and in extreme conditions of high magnetic fields and ultralow temperatures. While high-frequency excitations of 2DEGs have been examined to some extent from microwave to terahertz (THz) frequencies, a fundamental understanding of the physical properties of 2DEGs in this range have by no means been mastered. To address this matter, this thesis focused on studying a fundamental, high-frequency collective excitation, known as the plasmon, to better understand plasmon damping and coupling mechanisms in GaAs quantum well 2DEGs. The experiments utilized THz waveguide spectroscopy to study the low-temperature behavior of 2D plasmons.
by C. Thomas Harris.
S.M.
13
Docherty, Callum James. "Terahertz spectroscopy of graphene and other two-dimensional materials." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:98c03952-dc3f-442b-bbc0-d8397645cc1b.
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In this thesis, two-dimensional materials such as graphene are tested for their suitability for opto-electronic applications using terahertz time domain spectroscopy (THz-TDS). This ultrafast all-optical technique can probe the response of novel materials to photoexcitation, and yield information about the dynamics of the material systems. Graphene grown by chemical vapour deposition (CVD) is studied using optical-pump THz-probe time domain spectroscopy in a variety of gaseous environments in Chapter 4. The photoconductivity response of graphene grown by CVD is found to vary dramatically depending on which atmospheric gases are present. Adsorption of these gases can open a local bandgap in the material, allowing stimulated emission of THz radiation across the gap. Semiconducting equivalents to graphene, molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), grown by CVD, are investigated in Chapter 5. These members of the transition metal dichalcogenide family show sub-picosecond responses to photoexcitation, suggesting promise for use in high-speed THz devices. In Chapter 6, an alternative production route to CVD is studied. Liquid-phase exfoliation offers fast, easy production of few-layer materials. THz spectroscopy reveals that the dynamics of these materials after photoexcitation are remarkably similar to those in CVD-grown materials, offering the potential of cheaper materials for future devices. Finally in Chapter 7, it is shown that carbon nanotubes can be used to make ultrafast THz devices. Unaligned, semiconducting single walled carbon nanotubes can be photoexcited to produce an ultrafast, dynamic THz polariser. The work in this thesis demonstrates the potential for these novel materials in future opto-electronic applications. THz spectroscopy is shown to be an important tool for the characterisation of new materials, providing information that can be used to understand the dynamics of materials, and improve production methods.
14
He, Keliang. "Optical Spectroscopy of Two-Dimensional Transition Metal Dichalcogenides (TMDCs)." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1387468973.
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Zhang, Yaqing Ph D. Massachusetts Institute of Technology. "Two-dimensional terahertz rotational spectroscopy in the gas phase." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122715.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2019Cataloged from PDF version of thesis.
Includes bibliographical references.
Two-dimensional (2D) coherent spectroscopy has been developed to study molecular dynamics and structures for decades, but its extension into the terahertz (THz) regime remains rare. In this thesis, I describe several experiments using two-dimensional terahertz rotational spectroscopy. Employing intense THz electromagnetic fields and the differential chopping technique, we have extended multi-dimensional coherent spectroscopy into the THz regime. We have observed rotational dynamics of linear, symmetric-top, and asymmetric-top molecular species, indicating that 2D THz spectroscopy is an incisive tool for investigating collective quantum effects of the rotational degree of freedom. Based on the quantum mechanical rigid rotor model, we have developed simulation and calculation approaches to disentangling spectroscopic signals from molecular rotations.
We have shown ultrafast 2D THz photon echo spectroscopy of gaseous acetonitrile samples, revealing J-state-resolved rotational dynamics in symmetric-top molecular rotors. We have revealed nonlinear rotational couplings and many-body interactions in water vapor, uncovering the strongly correlated nature of rotational quantum states in water molecules. Additionally, experimental evidence of linear and nonlinear THz spectroscopy of stable water dimers in the vicinity of atmospheric conditions has been observed. We have reported dual-type rotational couplings and a propensity for the K-state-dependent cross-peaks in sulfur dioxide, highlighting distinct rotational properties in slightly asymmetric-top molecules. We have measured the quartic THz effect using two-dimensional THz-Raman hybrid spectroscopy, opening the way for understanding and applications of higher-even-order THz-matter coherences beyond the linear and quadratic THz field effects.
Utilizing the density matrix and time propagation approaches, we have developed a set of simulation and calculation methodologies to characterize rotational dynamics in the gas phase based on the quantum mechanical rigid-rotor model. Our work shows the remarkable capability of 2D THz spectroscopy to interrogate rotational dynamics in the gas phase, laying a foundation for understanding and manipulation of nonlinear light-molecule interactions via multi-dimensional coherent THz spectroscopy.
by Yaqing Zhang.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Chemistry
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Golla, Dheeraj, and Dheeraj Golla. "Ultrafast Dynamics of Two Dimensional Materials." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/626303.
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Two dimensional (2D) materials are poised to revolutionize the
future of optics and electronics. The past decade saw intense research
centered around graphene. More recently, the tide has shifted to a bigger
class of two-dimensional materials including graphene but more
expansive in their capabilities. The so called ‘2D material zoo’ includes
metals, semi-metals, semiconductors, superconductors and insulators.
The possibility of mixing and matching 2D materials to fabricate
heterostructures with desirable properties is very exciting.
To make devices with superior electronic, optical and thermal
properties, we need to understand how the electrons, phonons and other
quasi particles interact with each other and exchange energy in the
femtosecond and nanosecond timescales. To measure the timescales of
energy distribution and dissipation, I used ultrafast pump-probe
spectroscopy to perform time-domain measurements of optical
absorption. This approach allows us to understand the impact of manybody
interactions on the bandstructure and carrier dynamics of 2D
materials.
After a brief introduction to femtosecond laser spectroscopy, I will
explore the transient absorption dynamics of three classes of 2D
materials: intrinsic graphene, graphene-hBN heterostructures and
Transition Metal Dichalcogenides (TMDs). We will see that using pumpprobe
measurements around the high energy M-point of intrinsicgraphene, we can extract the value of the acoustic deformation potential
which is vital in characterizing the electron-acoustic phonon
interactions. In the next part of the thesis, I will delineate the role of the
substrate in the cooling dynamics in graphene devices. We will see that
excited carriers in graphene on hBN substrates cool much faster that on
SiO2 substrates due to faster decay of the optical phonons in graphenehBN
heterostructures. These results show that graphene-hBN
heterostructures can solve the hot phonon bottleneck that plagues
graphene devices at high power densities. In the last part, I will
demonstrate the role of phonon induced bandgap renormalization in the
carrier dynamics of TMD materials and measure the timescale of
phonon decay through the generation of low-energy phonons and
transfer to the substrate. This study will help us understand carrier
recombination in TMD devices under high-bias conditions which show
great potential in opto-electronic applications such as photovoltaics,
LEDs etc.
17
DeFlores, Lauren P. "Multi-mode two-dimensional infrared spectroscopy of peptides and proteins." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43732.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Vita.
Includes bibliographical references.
In this thesis, a methodology for understanding structural stability of proteins through multi-mode two-dimensional infrared (2D IR) spectroscopy is developed. The experimental framework for generation of broadband infrared lasers and robust new approaches to 2D IR spectroscopy are demonstrated. Long-term phase stability is achieved through the development of a passively stabilized diffractive optic and wedge interferometer. A new approach for acquisition of 2D IR spectra in the pump-probe geometry reduces overall experimental complexity. These technological advances extend the capabilities of 2D IR to further resolve inter- and intramolecular couplings, relaxation pathways and structural kinetics in complex systems. Characterization of multi-mode spectra is first performed on model protein systems to reveal detailed information on the effects of solvation and structure on the amide vibrations. Differences in vibrational coupling, transition dipole angles and the anharmonic potential of the amide vibrations of isotopologues of N-methylacetamide arise from significant change in the local mode composition of the amide II band due to isotopic substitution of the peptide group. Extension of multi-mode 2D IR to study the amide I'-II' spectra of an ideal protein system, poly-L-lysine, provides direct evidence for the structural sensitivity of the amide II' vibration, particularly to the !-helix moiety. This structural sensitivity arises from through bond coupling and structure induced symmetry and orientation of adjacent residues. Integration of these tools with hydrogen exchange techniques allows for the protein structural kinetics and stability to be observed through protein-solvent interactions with enhanced structural sensitivity relative to amide I spectroscopy alone.
The amide II' diagonal provides a measure of the degree of exchange and the cross peaks between the structurally sensitive amide I/I' vibration and the solvent exposure sensitive amide II and II' modes reveal the location of exchange. Partial exchange of the secondary structure of ubiquitin is revealed by correlation of the different amide signatures through analysis of cross peak line shapes, positions and amplitudes. Results provide direct evidence for a highly stable helix and labile "-sheet structure.
by Lauren P. DeFlores.
Ph.D.
18
Demirdöven, Nurettin 1974. "Coherent two-dimensional infrared spectroscopy : a study of coupled vibrations." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17653.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2003.Vita.
Includes bibliographical references.
This thesis provides an introduction to experimental techniques used in two-dimensional (2D) infrared (IR) spectroscopy, outlines how third-order nonlinear response of a multi-level vibrational system is calculated, and provides a detailed methodology of line shape analysis in 2D spectroscopy. Specific emphasis is given to inherent sensitivity of 2D spectroscopy to correlated spectral broadening. The signatures of highly correlated transition energy fluctuations in a model system of two strongly coupled carbonyl stretching vibrations are reflected by the elongation of the cross peaks along the diagonal of the 2D spectrum. The dynamics of this correlation is monitored by the changes in the 2D line shapes and successfully modeled using a correlated spectral diffusion model. The sensitivity of 2D IR spectroscopy to interactions between multiple vibrational coordinates is also explored in conformationally complex polypeptides and proteins with well-defined secondary structures. 2D IR spectroscopy of β-hairpins and globular proteins with antiparallel (AP) β-sheet domains is studied to identify 2D markers of AP β-sheet conformation. The experiments on β-hairpins and proteins with varying percentage of β-sheet character showed that the formation of cross peaks between the two characteristic vibrational modes of AP β-sheets is a marker of AP β-sheet secondary structure. The intensity, location and line shapes of the cross peaks are qualitatively related to the size, geometry and the conformational variations in the AP β-sheet structure.
by Nurettin Demirdöven.
Ph.D.
19
Yankowitz, Matthew Abraham. "Local Probe Spectroscopy of Two-Dimensional van der Waals Heterostructures." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/594649.
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A large family of materials, collectively known as "van der Waals materials," have attracted enormous research attention over the past decade following the realization that they could be isolated into individual crystalline monolayers, with charge carriers behaving effectively two-dimensionally. More recently, an even larger class of composite materials has been realized, made possible by combining the isolated atomic layers of different materials into "van der Waals heterostructures," which can exhibit electronic and optical behaviors not observed in the parent materials alone. This thesis describes efforts to characterize the atomic-scale structural and electronic properties of these van der Waals materials and heterostructures through scanning tunneling microscopy measurements. The majority of this work addresses the properties of monolayer and few-layer graphene, whose charge carriers are described by massless and massive chiral Dirac Hamiltonians, respectively. In heterostructures with hexagonal boron nitride, an insulating isomorph of graphene, we observe electronic interference patterns between the two materials which depend on their relative rotation. As a result, replica Dirac cones are formed in the valence and conduction bands of graphene, with their energy tuned by the rotation. Further, we are able to dynamically drag the graphene lattice in these heterostructures, owing to an interaction between the scanning probe tip and the domain walls formed by the electronic interference pattern. Similar dragging is observed in domain walls of trilayer graphene, whose electronic properties are found to depend on the stacking configuration of the three layers. Scanning tunneling spectroscopy provides a direct method for visualizing the scattering pathways of electrons in these materials. By analyzing the scattering, we can directly infer properties of the band structures and local environments of these heterostructures. In bilayer graphene, we map the electrically field-tunable band gap and extract electronic hopping parameters. In WSe₂, a semiconducting transition metal dichalcogenide, we observe spin and layer polarizations of the charge carriers, representing a coupling of the spin, valley and layer degrees of freedom.
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Knighton, Brittany E. "Nonlinear Ultrafast Excitation and Two-Dimensional Terahertz Spectroscopy of Solids." BYU ScholarsArchive, 2021. https://scholarsarchive.byu.edu/etd/9190.
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Ultrafast spectroscopy allows us to probe and understand material properties. With it, we can measure phonon-polaritons (optical phonons coupled with light) and the resulting dispersion curve in lithium niobate. Customizing the excitation source in ultrafast measurements can excite phonon modes to large amplitudes, allowing the experimental exploration of the Potential Energy Surface in solids. However, stronger pump fluences and bigger signal isn't always the answer in ultrafast spectroscopy. When sample signals and their nonlinear and mechanisms cannot be distinguished with 1D measurements, simple 2D THz measurements are a great place to start searching for distinct factors as was the case in cadmium tungstate. 2D measurements when paired with modeling and first principles calculations can reveal cutting edge information about exciting materials.
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Folpini, Giulia. "Exploring Nonresonant Interactions in Condensed Matter by Two-Dimensional Terahertz Spectroscopy." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/18860.
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Zur Untersuchung nichtlinearer Reaktionen von kondensierten Materie-Systemen wird die multidimensionale Terahertz-Spektroskopie genutzt.
Ein mehrere Oktaven umfassende THz-Quelle, die auf der Frequenzmischung in organischen Kristallen basiert, wird entwickelt und zur Erforschung der Librationsbande von Wasser-Nanotröpfchen in DOPC-Micellen verwendet.
Die nichtresonante THz-Strahlung wird genutzt, um die Emission im mittleren Infrarotbereich eines Intersubband-Übergangs von GaAs-Quantentöpfen kohärent zu steuern.
Schließlich wird die 2D-THz-Spektroskopie verwendet, um die nichtlineare Antwort einer "soft-mode" in einem Aspirin-Molekül-Kristall zu studieren.Multidimensional Terahertz spectroscopy is used to investigate the nonlinear response of condensed matter systems. A multioctave-spanning THz source based on frequency mixing in organic crystals is developed and used to study the libration band of water nanodroplets confined in DOPC micelles. Nonresonant THz radiation is used to coherently control the mid-infrared emission of an intersubband transition of GaAs quantum wells. Finally, 2D THz spectroscopy is used to study the nonlinear response of a soft mode in an aspirin molecular crystal.
22
Rödel, Tobias. "Two-dimensional electron systems in functional oxides studied by photoemission spectroscopy." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS197/document.
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De nombreux oxydes de métaux de transition (TMOs) possèdent des propriétés physiques complexes (ferroélectricité, magnétisme, supraconductivité à haute Tc ou magnétorésistance colossale). Les différents degrés de liberté (le réseau, la charge, le spin ou l'ordre orbitalaire) interagissent pour donner des phases différentes, très proches en énergie, qui vont former une grande variété d'états fondamentaux accessibles. La possibilité de fabriquer des hétérostructures de TMOs a encore accru la complexité de ces systèmes, de nouveaux phénomènes apparaissant aux interfaces. Un exemple typique est le gaz d'électrons bidimensionnel (2DEG) créé à l'interface entre deux oxydes isolants, LaAlO3 et SrTiO3, qui montre une transition métal-isolant, du magnétisme ou de la supraconductivité (contrôlée par une tension de grille). Le point de départ de cette thèse a été la découverte d'un 2DEG similaire à la surface nue de SrTiO3 fracturée sous vide, rendant possible l'étude de sa structure électronique par photoémission angulaire.Dans cette thèse, l'étude de surfaces préparées, plutôt que de petites facettes fracturées, a permis l'obtention de données spectroscopiques possédant des largeurs de raie proches des valeurs intrinsèques. Il est alors possible d'étudier les effets à N corps comme la renormalisation de la self-énergie due à l'interaction électron-phonon.Ces recherches sur la structure électronique du 2DEG à la surface de SrTiO3 ont pris un tour nouveau lorsqu'une texture de spin complexe y a été mesurée par photoémission résolue en spin. Nous présentons des résultats qui contredisent ces conclusions et nous discutons des raisons pouvant expliquer ce désaccord.Une des motivations de cette thèse était de savoir si la structure électronique et les propriétés du 2DEG pouvaient être contrôlées. L'étude du 2DEG sur des surfaces (110) et (111) de SrTiO3 révèle que sa structure de bandes (ordre orbitalaire, symétrie de la surface de Fermi, masses effectives) peut être ajustée en confinant les électrons sur des surfaces de différentes orientations du même matériau.Un succès majeure est la mise en évidence de 2DEGs à la surface de nombreux autres TMOs (TiO2-anatase, CaTiO3, BaTiO3) ou d'oxydes plus simples utilisés dans les applications (ZnO). Dans tous ces oxydes, nous avons identifié les lacunes en oxygène comme étant à l'origine de la création des 2DEGs.Dans l'anatase, ou d'autres TMOs en configuration électronique initiale d0, les lacunes en oxygène produisent à la fois des électrons localisés ou itinérants (le 2DEG). Il peut être subtile de prévoir quel est le cas est le plus favorable énergétiquement comme le démontre l'étude de deux polymorphes de TiO2, anatase et rutile. Dans CaTiO3, l’octaèdre formé par les atomes d'oxygène autour du Ti est incliné. Cette rupture de symétrie provoque un mélange des orbitales d et modifie le 2DEG. Dans BaTiO3, la création d'un 2DEG entraîne la coexistence de deux phénomènes normalement incompatibles, la ferroélectricité et la métallicité, dans deux zones spatialement distinctes du même matériau. Ce travail démontre qu'un 2DEG existe aussi à la surface de ZnO qui est, contrairement aux oxydes à base de Ti, plutôt un semiconducteur conventionnel, le caractère des orbitales pour les électrons itinérants étant alors de type s et non de type d.Le principal résultat est la mise au point d'une méthode simple et versatile pour la création de 2DEGs en évaporant de l'aluminium sur des surfaces d'oxydes. Une réaction d'oxydo-réduction entre le métal et l'oxyde permet de créer un 2DEG à l'interface entre le métal oxydé et l'oxyde réduit. Dans cette thèse, les 2DEGs ont été étudiés uniquement par photoémission sous ultra-vide. Cette méthode ouvre la possibilité d'étudier ces 2DEGs dans des conditions de pression ambiante en utilisant, par exemple, des techniques de transport, un pas important vers la production de masse et à bas coûts de 2DEGs dans les oxydes pour de futures applicationsMany transition metal oxides (TMOs) show complex physics, ranging from ferroelectricity to magnetism, high-Tc superconductivity and colossal magnetoresistance. The existence of a variety of ground states often occurs as different degrees of freedom (e.g. lattice, charge, spin, orbital) interact to form different competing phases which are quite similar in energy. The capability to epitaxially grow heterostructures of TMOs increased the complexity even more as new phenomena can emerge at the interface. One typical example is the two-dimensional electron system (2DES) at the interface of two insulating oxides, namely LaAlO3/SrTiO3, which shows metal-to-insulator transitions, magnetism or gate-tunable superconductivity. The origin of this thesis was the discovery of a similar 2DES at the bare surface of SrTiO3 fractured in vacuum, making it possible to study its electronic structure by angle-resolved photoemission spectroscopy (ARPES).In this thesis, the study of well-prepared surfaces, instead of small fractured facets, results in spectroscopic data showing line widths approaching the intrinsic value. This approach allows a detailed analysis of many-body phenomena like the renormalization of the self-energy due to electron-phonon interaction.Additionally, the understanding of the electronic structure of the 2DES at the surface of SrTiO3(001) was given an additional turn by the surprising discovery of a complex spin texture measured by spin-ARPES. In this thesis data is presented which contradicts these conclusions and discusses possible reasons for the discrepancy.One major motivation of this thesis was the question if and how the electronic structure and the properties of the 2DES can be changed or controlled. In this context, the study of 2DESs at (110) and (111) surface revealed that the electronic band structure of the 2DES (orbital ordering, symmetry of the Fermi surface, effective masses) can be tuned by confining the electrons at different surface orientations of the same material, namely SrTiO3.A major achievement of this thesis is the generalization of the existence of a 2DES in SrTiO3 to many other surfaces and interfaces of TMOs (TiO2 anatase, CaTiO3, BaTiO3) and even simpler oxides already used in modern applications (ZnO). In all these oxides, we identify oxygen vacancies as the origin for the creation of the 2DESs.In anatase and other doped d0 TMOs, both localized and itinerant electrons (2DES) can exist due to oxygen vacancies. Which of the two cases is energetically favorable depends on subtle differences as demonstrated by studying two polymorphs of the same material (anatase and rutile).In CaTiO3, the oxygen octahedron around the Ti ion is slightly tilted. This symmetry breaking results in the mixing of different d-orbitals demonstrating again why and how the electronic structure of the 2DES can be altered.In BaTiO3, the creation of a 2DES results in the coexistence of the two, usually mutual exclusive, phenomena of ferroelectricity and metallicity in the same material by spatially separating the two.Moreover, this work demonstrates that the 2DES also exists in ZnO which is - compared to the Ti-based oxides - rather a conventional semiconductor as the orbital character of the itinerant electrons is of s and not d-type.The main result of this thesis is the demonstration of a simple and versatile technique for the creation of 2DESs by evaporating Al on oxide surfaces. A redox reaction between metal and oxide results in a 2DES at the interface of the oxidized metal and the reduced oxide. In this thesis the study of such interfacial 2DESs was limited to photoemission studies in ultra high vacuum. However, this technique opens up the possibility to study 2DESs in functional oxides in ambient conditions by e.g. transport techniques, and might be an important step towards cost-efficient mass production of 2DESs in oxides for future applications
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Draeger, Simon [Verfasser], and Tobias [Gutachter] Brixner. "Rapid Two-Dimensional One-Quantum and Two-Quantum Fluorescence Spectroscopy / Simon Draeger ; Gutachter: Tobias Brixner." Würzburg : Universität Würzburg, 2020. http://d-nb.info/1203068247/34.
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Robyr, Pierre Stéphane. "Two-dimensional polarization-transfer NMR spectroscopy for studying ordered and disordered solids /." [S.l.] : [s.n.], 1994. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10968.
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Lymer, Katherine. "Two-dimensional spectroscopy of γ-aminobutyric acid on a clinical MRI scanner." Thesis, University of Edinburgh, 2005. http://hdl.handle.net/1842/28462.
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This work evaluates three implementations of 2D MRS for both in-vitro and in-vivo GABA measurement on a clinical MRI scanner. Existing spectroscopy sequences were used to develop a protocol for performing 2D J-resolved MRS without a dedicated sequence. GABA was measured in-vitro at concentrations approaching normal physiological levels and volunteer results allowed assignment of the 3.01ppm GABA resonance at its J-coupling frequency (7.4Hz). However, the prolonged scan time of over two hours prevented practical application of this approach. A far more efficient method of acquiring 2D J-resolved spectra is achieved with a dedicated 2D J-resolved sequence. An optimised set of acquisition parameters was produced to allow GABA measurement with maximum SNR, and without macromolecule contamination, in 35 minutes. Since the reproducibility of the sequence must be sufficient to detect physiological changes, a formal reproducibility study was performed acquiring three measures of reproducibility at six concentrations of GABA, using a standard volume head coil, 3”- and 5”- surface coils. To our knowledge, this is the first such reproducibility study dedicated to 2D J-resolved GABA measurement, and as such, could have significant implications on the interpretation of in-vivo results. In-vivo 2D J-resolved spectra were acquired and compared well to the published results, allowing assignment of the 3.01ppm GABA (plus macromolecule) peak (J = 7.4Hz). In the first reported 2D J-resolved spectra specifically designed to reduce the macromolecular contribution by optimising the echo time range, assignment of the in-vivo 3.01ppm GABA peak was less convincing.
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Smith, K. I. "The two-dimensional nuclear magnetic resonance spectroscopy analysis of peptides in solution." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377720.
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Zhao, Liang. "Optical properties of two-dimemsional Van der Waals crystals: from terahertz to visible." Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1433378350.
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Baniasadi, Fazel. "Structure Characterization and Electronic Properties Investigation of Two-Dimensional Materials." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/103904.
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This dissertation will have three chapters. In chapter one, a comprehensive review on defects in two dimensional materials will be presented. The aim of this review is to elaborate on different types of defects in two dimensional (2D) materials like graphene and transition metal dichalcogenides (TMDs). First, different types of point and line defects, e.g. vacancies, anti-sites, guest elements, adatoms, vacancy clusters, grain boundaries, and edges, in these materials are categorized in terms of structure. Second, interactions among defects are discussed in terms of their rearrangement for low-energy configurations. Before studying the electronic and magnetic properties of defective 2D materials, some of the structures are considered in order to see how defect structure evolves to a stable defect configuration. Next, the influence of defects on electronic and magnetic properties of 2D materials is discussed. Finally, the dynamic behavior of defects and 2D structures under conditions such as electron beam irradiation, heat treatment, and ambient conditions, is discussed. Later as a case study, defects in a two dimensional transition metal dichalcogenide will be presented. Among two-dimensional (2D) transition metal dichalcogenides (TMDs), platinum diselenide (PtSe2) stands at a unique place in the sense that it undergoes a phase transition from type-II Dirac semimetal to indirect-gap semiconductor as thickness decreases. Defects in 2D TMDs are ubiquitous and play crucial roles in understanding and tuning electronic, optical, and magnetic properties. Here intrinsic point defects in ultrathin 1T-PtSe2 layers grown on mica were investigated through the chemical vapor transport (CVT) method, using scanning tunneling microscopy and spectroscopy (STM/STS) and first-principles calculations. Five types of distinct defects were observed from STM topography images and the local density of states of the defects were obtained. By combining the STM results with first-principles calculations, the types and characteristics of these defects were identified, which are Pt vacancies at the topmost and next monolayers, Se vacancies in the topmost monolayer, and Se antisites at Pt sites within the topmost monolayer. Our study shows that the Se antisite defects are the most abundant with the lowest formation energy in a Se-rich growth condition, in contrast to cases of 2D molybdenum disulfide (MoS2) family. Our findings would provide critical insight into tuning of carrier mobility, charge carrier relaxation, and electron-hole recombination rates by defect engineering or varying growth condition in few-layer 1T-PtSe2 and other related 2D materials. Also, in order to investigate the layer dependency of vibrational and electronic properties of two dimensional materials, 2M-WS2 material was selected. Raman spectroscopy and DFT calculation proved that all Raman active modes have a downshift when material is thinned to few layers (less than 5 layers). It was proven that there is a strong interaction between layers such that by decreasing the number of layers, the downshift in Raman active modes is mostly for the ones which belong to out-of-plane atomic movements and the most downshift is for the Ag2 Raman active mode. Also, I investigated the effect of number of layers on the band structure and electronic properties of this material. As the number of layers decreases, band gap does not change until the materials is thinned down to only a single monolayer. For a single monolayer of 2M-WS2, there is an indirect band gap of 0.05eV; however, with applying in-plane strain to this monolayer, the material takes a metallic behavior as the strain goes beyond ±1%.Doctor of Philosophy
Graphite (consisting of graphene as building blocks) and TMDS in bulk form are layered and with exfoliation one can reach to few layers which is called two-dimension. Two dimensional materials like graphene have been used in researches vastly due to their unique properties, e.g. high carrier mobility, and tunable electronic properties. Transition metal dichalcogenides (TMDs) with a general formula of MX2, where M represents transition metal elements (groups 4-10) and X represents chalcogen elements (S, Se or Te), are another family of two-dimensional materials which have been extensively studied in the past few years. Besides exfoliation, there are also synthesis methods to produce two dimensional materials, e.g. chemical vapor deposition and chemical vapor transport. Normally, after synthesizing these materials, researchers investigate structure and electronic properties of these materials. There might be some atoms which no longer exist in the structure; hence, those are replaced by either vacancies or other elements which all of them are called defects. In chapter 1, defects in graphene and transition metal dichacolgenides were investigated, carefully. Later, dynamic behavior of defects in these materials were investigated and finally, the effect of defects on the electronic properties of the two dimensional materials were investigated. Chapter two talks about a case study which is two dimensional 1T-PtSe2. In this chapter, 5 different kinds of defects were studied using scanning tunneling microscopy and spectroscopy investigations and density functional theory was used to prove our assumptions of the origin of defects. Also, another thing which is investigated by researcher is that how atoms in two dimensional materials vibrate and how the number of layers in the two dimensional material influences vibrations of atoms. Other than this, electronic properties of these materials is dependent upon the number of layers. When these materials are synthesized, there is a stress applied to the material due the mismatch between the material and its substrate, so it is worth investigating the effect of stress (strain) on the structure, and electronic properties of the material of interest. For this purpose, 2M-WS2 was exfoliated on Si/SiO2 substrate and the layer dependency of its vibrational modes was investigated using Raman spectroscopy and density functional theory calculation. Also, in order to investigate the influence of stress (strain) on the electronic properties of two dimensional 2M-WS2, a single monolayer of this materials underwent a series of strains in density functional theory calculations and the effect of strain on the electronic properties of this material was investigated.
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Klix, Christian Ludwig [Verfasser]. "Spectroscopy of displacements in a two-dimensional colloidal glass former / Christian Ludwig Klix." Konstanz : Bibliothek der Universität Konstanz, 2014. http://d-nb.info/1096333554/34.
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Kehoe, Thomas Bernard. "Optical spectroscopy of two-dimensional hole systems in the integer quantum hall regime." Thesis, University of Exeter, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249084.
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De, Marco Luigi Ph D. Massachusetts Institute of Technology. "The molecular dynamics of hydrogen-bonding explored with broadband two dimensional infrared spectroscopy." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/105022.
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Thesis: Ph. D. in Physical Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2016.Cataloged from PDF version of thesis. Vita
Includes bibliographical references (pages 317-352).
It is no overstatement to claim that hydrogen bonding is the most important intermolecular interaction. On a day-to-day basis, we encounter the peculiar effects of hydrogen bonding in liquid water; however, it is well appreciated that hydrogen bonding is immensely important in many contexts and, in particular, in biological ones. Despite this apparent significance, a general molecular picture of the dynamics of hydrogen-bonding systems is lacking. Over the last two decades, ultrafast multidimensional infrared spectroscopy has emerged as powerful technique for studying molecular dynamics in the condensed phase. By taking advantage of the complex relationship between a molecular oscillator's frequency and its environmental structure, we may understand molecular dynamics from an experimental perspective. However, the study of hydrogen bonding poses a significant technical challenge in that the interaction gives rise to broad resonances in the mid-infrared absorption spectrum. Traditional methods for generating short pulses of mid-infrared light are fundamentally limited in the bandwidth they can produce. Oftentimes, the width of a hydrogen-bonded oscillator's absorption resonance exceeds the broadest bandwidth mid-infrared laser pulse. In this thesis, I describe our development and use of a novel source of short, broadband mid-infrared light pulses that span the entire region of high-frequency molecular vibrations. We use this source as a probe in two-dimensional infrared spectroscopy experiments to study a wide variety hydrogen-bonding systems, including hydrogen-bonded dimers and protein films, with a particular emphasis on liquid water. Across these systems, we observe fascinating trends in the changes in molecular dynamics with increasing complexity of hydrogen bonding. In particular, we find experimental evidence for large deformations of the nuclear potential energy surface, giving rise to extremely anharmonic and collective dynamics. The effect is most dramatic in liquid water, where the rapidly fluctuating hydrogen-bond network results in vibrational excitons wherein O-H stretching motion is delocalized over multiple molecules. In this case, the nuclear potential energy surface is so complex that even simple changes in the mass of the oscillators result in qualitatively different dynamics.
Funding from U.S. Department of Energy DE-FG02-99ER14988 and DE-SC0014305
by Luigi De Marco.
Ph. D. in Physical Chemistry
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Vaughan, Joshua Charles. "Two-dimensional ultrafast pulse shaping and its application to coherent control and spectroscopy." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32492.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2005.Vita.
Includes bibliographical references (p. 167-182).
This thesis develops powerful new methods for shaping femtosecond laser pulses in two dimensions and explores their application to coherent control of propagating lattice excitations and degenerate four-wave mixing spectroscopy. Pulse shaping in two dimensions is achieved by manipulating the spectral components of ultrashort laser pulses within many horizontal slices of the pulse. Each horizontal slice is independently shaped by means of a two-dimensional liquid crystal spatial light modulator, and taken together the shaped regions form sophisticated optical waveforms with time-dependent spatial profiles. Automated optical control over coherent lattice responses that are both time- and position-dependent across macroscopic length scales is demonstrated. Two- dimensional (2D) femtosecond pulse shaping was used to generate excitation light fields that were directed toward distinct regions of crystalline samples, producing terahertz-frequency lattice vibrational waves that emanated outward from their multiple origins at lightlike speeds. Interferences among the waves resulted in fully specified far-field responses, including tilted, focusing, or amplified wavefronts. Generation and coherent amplification of terahertz travelling waves and terahertz phased-array generation are also demonstrated. A novel approach to coherent nonlinear optical spectroscopy based on 2D femtosecond pulse shaping is introduced. Multiple phase-stable output beams are created and overlapped at the sample in a phase-matched boxcars geometry via 2D femtosecond pulse shaping.
(cont.) The pulse timing, shape, phase, and spectral content within all beams may be specified, yielding an unprecedented level of control over the interacting fields in nonlinear spectroscopic experiments. Heterodyne detection and phase cycling of the nonlinear signal is easily implemented due to the excellent phase stability between each output beam. This approach combines the waveform generation capabilities of magnetic resonance spectroscopy with the wavevector specification and phase-matching of nonlinear optical spectroscopy, yielding the signal selectivity and control capabilities of both. Results on three prototype systems will be used to illustrate the exciting possibilities with this method.
by Joshua Charles Vaughan.
Ph.D.
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Valduga, De Almeida Camargo Franco. "Unravelling vibrational and electronic coherences via two-dimensional electronic spectroscopy of zinc-porphyrins." Thesis, University of East Anglia, 2017. https://ueaeprints.uea.ac.uk/63645/.
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Two-dimensional electronic spectroscopy (2D-ES) is a cutting edge experimental method to probe ultrafast phenomena such as energy transfer, chemical reactions, coherent wavepacket motion, etc. It is an extension of transient absorption methods which recovers the signal as a function of the excitation frequency, resolving signals that are overlapped in traditional techniques, and allowing simultaneous high spectral resolution in excitation frequency and high temporal resolution of the dynamics. 2D-ES studies of light-harvesting systems from photosynthetic organisms reported coherent wavepacket motion, attributed to electronic coherences between different exciton states. Vibrational and vibronic coherences can also be observed with 2D-ES, and it is thus important to study the specific signatures of each. In this thesis, we present an experimental setup that is well suited to recover coherent wavepacket motion and employ it to study vibrational coherences in a zinc-porphyrin monomer. A first experiment is analyzed with the traditional convention of using only the real part of the complex-valued 2D-ES signal, and interference between neighboring oscillatory features is revealed, explained and modeled. We also find that when the full complex-valued signal is analyzed, the most pronounced interference features disappear, and in this case an analysis based on double-sided Feynman diagrams suffices to describe all observations. We then report an experiment with a blue-shifted laser spectrum, which matches the molecular absorption in a way that is more commonly found in 2D-ES studies, and observe signatures that closely resemble the features expected for a purely electronic coherence, which we explain considering the laser spectrum for all three field-matter interactions. Finally, we demonstrate a 2D-ES experiment with a red-shifted spectrum which exclusively probes coherences in the ground state, complementing experiments with the blue-shifted spectrum. We argue that a combination of the two suffices for unambiguous interpretation of coherences in 2D-ES, lifting the need for an ultrabroadband laser.
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Yang, Ming. "Ultrafast two-dimensional infrared spectroscopy of hydrogen-bonded base pairs and hydrated DNA." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16561.
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Die Struktur von DNS Molekülen und ihre Wechselwirkung mit Wasser werden seit langer Zeit heiß diskutiert. In der vorliegenden Arbeit wird nichtlineare Spektroskopie zur Untersuchung dieser Systeme angewendet. Oligomere, die aus 23 alternierenden Adenin-Thymin-Basenpaaren bestehen und eine Doppelhelix bilden, wurden mit Hilfe von 2D IR Spektroskopie für verschiedene Hydratisierungsgrade untersucht. Für DNS-Filme bei 0% relativer Feuchte (r.F.) erlauben die transienten Spektren eine Unterscheidung der NH Streckschwingung von Thymin ((NH)), der symmetrischen und asymmetrischen NH2 Streckschwingung von Adenin (s(NH2) and a(NH2)) sowie die Bestimmung der jeweiligen Linienprofile. Die Spektren zeigen eine homogene Verbreiterung für die (NHT) wohingegen die s(NH2) and a(NH2) eine ausgeprägte und zeitunabhängige inhomogene Verbreiterung zeigen, welche auf Unordnungen in der DNS-Struktur hinweisen. Außerdem kann Energietransfer von der a(NH2) zur (NH) beobachtet werden. Bei Erhöhung der r.F. hat die erhöhte Anzahl von Wassermolekülen nur einen geringen Einfluss auf die Positionen und Linienprofile der NH Streckschwingungen. Dadurch wird nahegelegt, dass die spektrale Dynamik vom DNS Molekül selbst und nicht vom umgebenen Wasser bestimmt ist. Im Gegensatz dazu zeigt die OH Streckmode der Wasserhülle um die DNS spektrale Diffusion auf einer 500 fs Zeitskala. Guanosin-Cytidin(GC)-Basenpaare wurden in Chloroformlösung untersucht, um die Wechselwirkung zwischen Basenpaaren zu verstehen. Dabei wurden die NH Schwingungen in einer local mode Darstellung betrachtet, die zwei freie NH Gruppen von G und C und drei wasserstoffverbrückte NH Gruppen beeinhaltet. Die Kopplungen und Relaxationsdynamik der NH Streckanregungen wurden mit Femtosekunden-Pump-Probe und 2D IR Experimenten studiert. Die Ergebnisse zeigen eine Verringerung der Lebensdauer mit der Bildung von Wasserstoffbrücken sowie Energietransfer zwischen zwei wasserstoffverbrückten NH Streckschwingungen.The structure of DNA molecule and the interactions with its surrounding water is a hot topic for long time. In this thesis, we employ the nonlinear spectroscopy, including femtosecond pump-probe and two-dimensional infrared (2D IR) experiment, to study the vibrational dynamics of the systems. Double-stranded DNA short oligomers containing 23 alternating adenine-thymine base pairs were studied at different hydration levels by femtosecond 2D IR spectroscopy. For a DNA film at 0% relative humidity, the transient spectra enable a separation of the NH stretching mode of thymine from the symmetric and asymmetric NH2 stretching modes of adenine and determine the individual line shapes. For the NH stretch of thymine, the spectra demonstrate an essential homogeneous broadening, whereas for the symmetric and asymmetric NH2 stretches a pronounced and time-independent inhomogeneous broadening suggests a disorder in DNA structure. An energy transfer from the asymmetric NH2 stretch of adenine to the NH stretch of thymine is also observed. When the relative humidity increases, the increased water molecules have limited influence on the positions and line shapes of NH stretching frequencies, suggesting the spectral dynamics governed by DNA rather than water fluctuations. In contrast, the OH stretching mode of water shell around hydrated DNA undergoes a spectral diffusion on a 500 fs time scale, which is slower than the neat water. The guanosine-cytidine (GC) base pairs in chloroform solution were investigated to understand the interactions within base pairs. A local mode representationof NH stretching mode is adopted, consisting two free NH groups of G and C and three hydrogen bonded NH groups. The coupling and relaxation dynamics of the NH stretching excitations are studied by femtosecond pump-probe and 2D IR experiments. The results demonstrate a lifetime shortening upon the formation of hydrogen bonds, and an energy transfer between two hydrogen-bonded NH stretches.
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Lin, Yu-Pu. "Functionalization of two-dimensional nanomaterials based on graphene." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4727.
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Cette étude de la fonctionnalisation de graphène se base principalement sur la monocouche de graphène épitaxiée sur SiC. Les propriétés électroniques, structurales et les compositions chimiques du graphène fonctionnalisé sont étudiées. L'incorporation d'azote dans le graphène réalisée par les procédures à base de plasma montre un décalage de niveaux inoccupés du graphène vers EF , obtenue par les analyses spectroscopie de photoémission inverse en résolution angulaire. Ce dopage-n est attribué à la présence de graphitique-N. De plus, la configuration des espèces de N substitués dans le graphène peut être contrôlée efficacement par l'énergie, les espèces d'azote incidentes, et l'épaisseur du graphène de départ. L'hydrogénation de la couche tampon de graphène (BLG) à température variante sature les liaisons pendantes de Si de l'interface différemment, soit par la formation de nouvelles liaisons C-Si à température ambiente, soit par les hydrogènes intercalés. Le BLG devient fortement-isolant dans le premier cas, et devient une monocouche de graphène quasi-autoportante (QFSG) dans le second, permettant un nouveau concept de fabrication des dispositifs à base de graphène sur SiC. La réaction/couplage entre des molécules pi-conjugué et les graphène vierge ou fonctionnalisé est aussi étudiée. Les états inoccupés des molécules à base de perylene sont légèrement modiffiées sur le graphène dopé N à cause d'un renforcement de transfert de charge. Des réactions chimiques entre les molécules perylenes et le graphène sont observées aprés l'exposition aux électrons de basse énergie. En résumé, cette étude permettra une meilleure maîtrise des propriétés des matériaux 2D comme le graphèneIn order to promote 2D materials like graphene to their numerous applications, new methodsaltering their electronic and chemical properties have to be mastered. In this thesis, theprocesses of chemical doping and hydrogenation of monolayer graphene grown on SiC are investigated. Nitrogen atoms are successfully substituted in the graphene lattice using plasma-basedmethods. The bonding configurations of the incorporated N can be controlled via the nature and energy of exposing species and the thickness of the pristine graphene. An n-type doping, revealed by angle-resolved inverse photoemission spectroscopy (ARIPES), is found in most N-doped graphene and is assigned to the presence of graphitic-N. Hydrogenations of the buffer layer of graphene (BLG) on SiC at ambient or high temperatures saturate the remaining Si dangling bonds at BLG/SiC interface in two different ways, either by inducing additional C-Si bonds or by H intercalation. This results in 2D materials with distinct characters, an insulating, graphane-like H-BLG or a quasi-free-standing graphene, which may be used as a new concept for the engineering of graphene-based devices. The interactions between pi-conjugated molecules and the functionalized graphene are also investigated. The unoccupied states of molecules are altered by the presence of incorporated N, but the degradation of molecules due to low-energy electron exposure seems not enhanced by the doping nitrogen under the studied conditions. Nevertheless, the functionalization of graphene is demonstrated and its electronic and chemical properties are carefully studied, which should help to faster further applications employing functionalized graphene
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Rule, Kirrily. "Magnetic ordering in the two dimensional antiferromagnet, FePS₃." Monash University, School of Physics and Materials Engineering, 2004. http://arrow.monash.edu.au/hdl/1959.1/9725.
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Khan, Assad Ullah. "Thin-Film Polymer Nanocomposites Composed of Two-Dimensional Plasmonic Nanoparticles and Graphene." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/101942.
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Plasmonic polymer nanocomposites contain plasmonic nanoparticles that are dispersed within a polymer. The polymer matrix strongly influences the optical properties of plasmonic nanoparticles. It is imperative to understand the interaction between plasmonic nanoparticles and polymers so that one can develop functional devices using nanocomposites. The utilization of plasmonic nanoparticles as fillers has great potential to transform critical nanotechnologies where light management is crucial, such as refractive index based nanosensors, optical coatings, and light actuated devices. Despite the great potential, effective integration of plasmonic nanoparticles with polymers remains challenging. This dissertation presents i) the effects of dielectric media on the optical properties of plasmonic nanoparticles, ii) the sensing of polymer brush formation on nanoparticles, iii) the fabrication of plasmonic nanocomposite thin-films with controlled optical properties, and iv) the development of electrically conductive membranes for electrostatic speakers.
The optical response of plasmonic nanoparticles (referred to as wavelength of localized surface plasmon resonance, λLSPR) is sensitive to changes in refractive index of the medium. The sensitivity (S) plays a critical role in determining the performance of nanoparticles in sensing applications. In this dissertation, I have conducted a systematic study on the sensitivity of plasmonic nanoparticles as a function of various parameters: shape, size, composition, initial plasmonic resonance wavelength, cross-sectional area, and aspect ratio. Among the parameters investigated, aspect ratio (R) is determined to be the key parameter that controls S, following an empirical equation, S = 46.87 R + 109.37. This relationship provides a guideline for selecting fillers in plasmonic polymer nanocomposites, and it predicts the final effect of plasmonic nanoparticles on the optical properties of polymer nanocomposites.
Plasmonic nanoparticles are employed to probe polymer grafting on the surfaces of metal nanoparticles. Using ultraviolet-visible (UV-vis) spectroscopy, I have demonstrated the quantification of polymer grafting density on the surface of plasmonic nanoparticles. The λLSPR of plasmonic nanoparticles red-shifts as the polymer concentration near the nanoparticle surface increases. I have investigated the formation of polymer brush by grafting the nanoparticles with thiolated polyethylene glycol (PEG-SH) and revealed the three–regime kinetics in situ. Importantly, this study suggests that a latent regime arises due to fast polymer adsorption and prolonged chain rearrangement on nanoparticle surfaces. When the polymer chains rearrange and chemically tether to the surface, they contract and allow more polymer chains to graft onto the particle surface until saturation. This analytical method provides a new surface probing technique for polymer brush analysis, complementary to conventional methods such as quartz crystal microbalance, atomic force microscope, and microcantilivers.
Commercial tinted glass employs expensive metalized films to reduce light transmittance but has limited spectral selectivity. To reduce the cost of metalized films and to improve the spectral selectivity, I have employed plasmonic nanoparticles in polymers to fabricate spectral-selective tinted films. First, I have synthesized two-dimensional (2D) plasmonic silver nanoparticles (AgNPs) using multi-step growth. The nanoparticles have a tunable plasmon resonance and provide spectral selectivity. The multi-step growth forgoes polymeric ligands such as poly(vinylpyrrolidone) (PVP) and solely relies on a small molecule sodium citrate. Briefly, small citrate-capped Ag seeds are first grown into small 2D AgNPs. The small 2D AgNPs are then used to grow large 2D AgNPs via multiple growth steps. The PVP-free method allows for fast synthesis of 2D AgNPs with large sizes and tunable plasmon resonance across the visible and NIR region. The 2D AgNPs are integrated with polymers to produce thin-film plasmonic nanocomposites. By controlling the planar orientation of the 2D AgNPs through layer-by-layer assembly, the polymer nancomposites have achieved reduced light transmittance and enhanced reflectance across the visible and NIR range. In contrast to conventional polymer nanocomposites where the AgNPs are randomly oriented, the thin-film polymer nanocomposites exhibit excellent control over nanoparticle density and hence the optical properties, that is, tunable light transmittance and reflectance across the visible and NIR.
Lastly, graphene is used to prepare conductive free-standing polymer thin-films. Graphene, an ultralight weight 2D material with excellent electrical and mechanical properties, has potential for use in thin-film composites essential for photovoltaics, electrostatic speakers, sensors, and touch displays. Current graphene-based composite films contain graphene flakes randomly mixed in a polymer matrix and usually possess poor mechanical and electrical properties. In this dissertation, I have developed thin-film nanocomposites comprised of chemical vapor deposited (CVD) graphene and high-performance polyetherimide (PI). The CVD-grown graphene is polycrystalline, and it cannot be used as a free-standing film. By enforcing the polycrystalline graphene with a thin layer of PI, I have prepared free-standing thin-film composites with a high aspect ratio of 105. Mechanical and electrical property characterization reveals a Young's modulus of 3.33 GPa and a resistance of 200 - 500 Ω across the membrane. A typical spring constant of the membrane is ~387 N/m. Dynamic electromechanical actuation shows that the membrane vibrates at various input frequencies. The polymer/graphene film has excellent acoustic properties, and when used as a speaker membrane, it reduces the electrical power consumption by a factor of 10-100 over the frequency range of 600–10,000 Hz.Doctor of Philosophy
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Kozawa, Daichi. "Behavior of photocarrier in atomically thin two-dimensional semiconducting materials for optoelectronics." Kyoto University, 2015. http://hdl.handle.net/2433/199420.
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Magill, Brenden A. "Microwave spectroscopy of edge and bulk modes of two dimensional electrons in magnetic field." Thesis, The Florida State University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3564920.
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Edge magnetoplasmons (EMPs) and pinning mode resonances in two dimensional electron systems (2DESs) can both be thought of as lower hybrid modes of cyclotron and plasma resonances. This dissertation describes low temperature microwave spectroscopy of both of these modes. EMPs have oscillating charge confined at the 2DES edge by the combination of the perpendicular magnetic field and the electrostatic potential that produces the edge. Pinning mode resonances are from electron solids oscillating against confinement provided by disorder in the bulk of the 2DES.
The first part of this dissertation concerns the search for a mode similar to an EMP but confined solely by a linear magnetic inhomogeneity in the perpendicular magnetic field (Bz). While we do not observe such an excitation, we do observe a marked reduction in the velocity of an EMP in the presence of a Bz-inhomogeneity.
In the second part of this dissertation, we investigate pinning modes in “wide'' quantum well samples, for which the effective electron-electron interaction is softened at short range due to the vertical extent of the wavefunction. We observe a pinning mode resonance whose peak frequency (fpk ) vs Landau level filling (ν) shows an anomalous increase as ν moves away from ν = 1 under roughly the same conditions as anomalous quantum Hall effects observed previously in DC transport. A region of ν with enhanced fpk is interpreted as evidence for a new electron solid phase.
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Khalil, Munira 1975. "A tale of coupled vibrations in solution told by coherent two-dimensional infrared spectroscopy." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/16607.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2004.Vita.
Includes bibliographical references.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Coherent two-dimensional infrared (2D IR) spectroscopy is used as a tool for investigating the molecular structure and dynamics of coupled vibrations in solution on a picosecond timescale. The strongly coupled asymmetric and symmetric carbonyl stretches of Rh(CO)₂C₅H₇0₂ (RDC) dissolved in hexane serve as a convenient model system. Fourier transform 2D IR spectra are obtained from heterodyne-detected third-order nonlinear signals using a sequence of broad bandwidth femtosecond IR pulses. A 2D IR correlation spectrum with absorptive lineshapes results from the addition of 2D rephasing and non-rephasing spectra, which sample conjugate frequencies in the evolution time period. The 2D IR correlation spectrum contains peaks with different positions, signs, amplitudes and lineshapes. The positions of the peaks map the transition frequencies between the ground, singly, and doubly excited states of the system, and thus describe the anharmonic vibrational potential. Peak amplitudes reflect the relative magnitudes and orientations of the transition dipole moments in the molecular frame, the electrical anharmonicity of the system, and the vibrational relaxation dynamics. The 2D line shapes are sensitive to the complicated system-bath interactions in solution. 2D IR spectra taken with varying polarization conditions and as a function of a variable waiting time can be used to isolate and quantify these spectroscopic observables. The polarization-selective 2D IR spectra of RDC in hexane are analyzed in terms of two coupled local coordinates to obtain their mutual orientation and the magnitude of the coupling between them. Evidence of vibrational coherence transfer between close-lying transition frequencies is indicated by the presence of extra induced peaks in 2D IR
(cont.) rephasing spectra. The data is modeled by using Redfield theory to account for coherence transfer, vibrational dephasing and population relaxation in a multilevel vibrational system. Building on the studies of the RDC model system, 2D IR spectroscopy is used to study the thermal denaturation of RNase A by characterizing the temperature-dependent Amide I band. A nonlinear IR probe is used to study the early events in the laser temperature-jump initiated denaturation of RNase A.
by Munira Khalil.
Ph.D.
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Stone, Katherine Walowicz. "Coherent multi-exciton dynamics in semiconductor nanostructures via two-dimensional Fourier transform optical spectroscopy." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/49554.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 139-149).
The Coulomb correlations between photoexcited charged particles in materials such as photosynthetic complexes, conjugated polymer systems, J-aggregates, and bulk or nanostructured semiconductors produce a hierarchy of collective electronic excitations (i.e. excitons, biexcitons, etc.) which may be harnessed for applications in quantum optics, light-harvesting, or quantum information technologies. These excitations represent correlations among successively greater numbers of electrons and holes, and their associated multiple-quantum coherences could reveal detailed information about complex many-body interactions and dynamics. However, unlike single-quantum coherences involving excitons, multiple-quantum coherences do not radiate and they have largely eluded direct observation and characterization. In this work, I present a novel optical technique, two-quantum two-dimensional Fourier transform optical spectroscopy, which allows direct observation of the dynamics of multiple-exciton states that reflect the correlations of their constituent electrons and holes. The approach is based on closely analogous methods in nuclear magnetic resonance, in which multiple phase-coherent fields are used to drive successive transitions such that multiple-quantum coherences can be accessed and probed. A spatiotemporal femtosecond pulse shaping technique has been used to overcome the challenge of control over multiple, noncollinear phase-coherent optical Fields in the experimental geometries that are used to isolate selected signal contributions through wavevector matching.
(cont.) Results from a GaAs quantum well system reveal distinct coherences of biexcitons that are formed from two identical excitons or from two excitons whose holes are in di®erent spin sublevels ("heavy-hole" and "light-hole" excitons). The biexciton binding energies and dephasing dynamics are determined, and changes in the dephasing rates as a function of the excitation density are observed, revealing still higher-order correlations due to exciton-biexciton interactions. Two-quantum coherences due to four-particle correlations that do not involve bound biexciton states but that in°uence the exciton properties are also observed and characterized. I also present one-quantum two-dimensional Fourier transform optical spectroscopy measurements which show that the higher-order correlations isolated by two-quantum techniques are highly convolved with two-particle correlations in the conventional one-quantum measurements.
by Katherine Walowicz Stone.
Ph.D.
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Wickramasinghe, Thushan E. "Growth Techniques and Optical and Electrical Characterization of Quantum Confined Zero-Dimensional and Two-Dimensional Device Structures." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou156631995093606.
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Pannell, Daniel K. (Daniel Kirk). "A Study of Intra- and Interaggregate Exchange Processes of Alkyllithium Compounds Using One- and Two- Dimensional NMR Spectroscopy." Thesis, University of North Texas, 1992. https://digital.library.unt.edu/ark:/67531/metadc278360/.
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One- and two-dimensional NMR spectroscopy, including 13C{6Li}{1H} triple resonance techniques, were used to characterize a series of mixed alkyllithium aggregates and to study their exchange processes.
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Froehlicher, Guillaume. "Optical spectroscopy of two-dimensional materials : graphene, transition metal dichalcogenides and van der Waals heterostructures." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAE033/document.
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Au cours de ce projet, nous avons utilisé la microspectroscopie Raman et de photoluminescence pour étudier des matériaux bidimensionnels (graphène et dichalcogénures de métaux de transition) et des hétérostructures de van der Waals. Tout d’abord, à l’aide de transistors de graphène munis d’une grille électrochimique, nous montrons que la spectroscopie Raman est un outil extrêmement performant pour caractériser précisément des échantillons de graphène. Puis, nous explorons l’évolution des propriétés physiques de N couches de dichalcogénures de métaux de transition semi-conducteurs, en particulier de ditellurure de molybdène (MoTe2) et de diséléniure de molybdène (MoSe2). Dans ces structures lamellaires, nous observons la séparation de Davydov des phonons optiques au centre de la première zone de Brillouin, que nous décrivons à l’aide d’un modèle de chaîne linéaire. Enfin, nous présentons une étude toute optique du transfert de charge et d’énergie dans des hétérostructures de van der Waals constituées de monocouches de graphène et de MoSe2. Ce travail de thèse met en évidence la riche photophysique de ces matériaux atomiquement fins et leur potentiel en vue de la réalisation de nouveaux dispositifs optoélectroniquesIn this project, we have used micro-Raman and micro-photoluminescence spectroscopy to study two-dimensional materials (graphene and transition metal dichalcogenides) and van der Waals heterostructures. First, using electrochemically-gated graphene transistors, we show that Raman spectroscopy is an extremely sensitive tool for advanced characteri-zations of graphene samples. Then, we investigate the evolution of the physical properties of N-layer semiconducting transition metal dichalcogenides, in particular molybdenum ditelluride (MoTe2) and molybdenum diselenide (MoSe2). In these layered structures, theDavydov splitting of zone-center optical phonons is observed and remarkably well described by a ‘textbook’ force constant model. We then describe an all-optical study of interlayer charge and energy transfer in van der Waals heterostructures made of graphene and MoSe2 monolayers. This work sheds light on the very rich photophysics of these atomically thin two-dimensional materials and on their potential in view of optoelectronic applications
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Peng, Chunte Sam. "Two-dimensional infrared spectroscopy of nucleic acids : application to tautomerism and DNA aptamer unfolding dynamics." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91113.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2014.Cataloged from PDF version of thesis. Vita.
Includes bibliographical references.
The structural dynamics of nucleic acids are intimately related to their biological functions; however, our ability to study these molecular dynamics has been largely impeded by the lack of techniques that possess both high time resolution and structural sensitivity. The motivation for the work in this thesis was to develop and apply two-dimensional infrared spectroscopy (2D IR) as a new experimental tool to investigate nucleic acid dynamics. Infrared spectroscopy is sensitive to structural changes of nucleic acids and 2D IR offers sub-picosecond time resolution. 2D IR spectroscopy is advantageous over the linear infrared absorption spectroscopy because the vibrational spectrum is spread onto two frequency axes, giving rise to the structurally sensitive cross-peaks. These cross-peaks allow the determination of vibrational couplings, which encode chemical bond connectivity, distance and orientation. However, 2D IR spectroscopy of nucleic acids is underdeveloped due to the difficulties in modeling highly delocalized and coupled vibrations of nucleobases. This thesis initiated the efforts to develop 2D IR spectroscopy of nucleic acids by first characterizing the 2D IR spectra and vibrational eigenstates of nucleobases, using a model of multiple anharmonically coupled oscillators. With pronounced cross-peaks existing between all the vibrations for a give nucleobase, 2D IR spectroscopy was shown to be capable of distinguishing between different tautomers, using pyridone as a model system. Coupled with a laser-induced temperature-jump (T-jump), 2D IR was used to monitor rapidly exchanging tautomers in real time under physiological conditions on the nanosecond timescale. Systematically characterizing the tautomer exchange rates as a function of various experimental variables lead to a two-state concerted mechanism involving bridging water wires for the lactam-lactim tautomerization of 6-chloro-2-pyridone. This method was then applied to study the tautomerism of a deoxycytidine analog, KP1212, which is an anti-HIV drug. Multiple tautomers, including the normally rare enol tautomers, were found under physiological conditions. This observation supports the rare tautomer hypothesis, which states that each tautomer displays a distinct base-pairing preference, eventually leading to mutations and population collapse of the HIV viruses. Beyond studies on the single nucleotide level, 2D IR was used to characterize the structural dynamics of thrombin-binding aptamer (TBA), which is a 15mer DNA folded into a guanine-quadruplex (G-quadruplex). The 2D IR spectral signatures of G-quadruplex were established, and T-jump transient 2D IR was employed to investigate the unfolding dynamics of TBA. A mechanism of the early unfolding of TBA was proposed: A ~100 nanosecond response was attributed to the local deformation of the G-quadruplex, and a few-microsecond response was ascribed to be the fraying of the 3'-tail of TBA. This observation was consistent with a mechanism suggested by molecular dynamics simulations. Finally, the dissociation of double-stranded DNA formed by TBA and its complementary strand was found to be on the timescale of tens to hundreds of microseconds. The experiments in this thesis demonstrate the capability of 2D IR to investigate nucleic acid dynamics spanning a wide range of timescales.
by Chunte Sam Peng.
Ph. D.
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Guan, Shenheng. "Fourier transform ion cyclotron resonance mass spectrometry: Personal computer-based instrument and two-dimensional spectroscopy." Scholarly Commons, 1989. https://scholarlycommons.pacific.edu/uop_etds/3367.
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A personal computer based Fourier transform ion cyclotron resonance mass spectrometer has been designed and constructed. An IBM PC AT compatible computer is used to host the interface of the instrument. The advantages of using a personal computer to host the FT-ICR instrument include: (1) very low cost of the computer; (2) extensive graphic and mathematic capabilities; (3) easy performance alteration or expansion; (4) an abundance of application software; and (5) support for a wide range of output devices. A dedicated digital hardware interface, which provides high speed data transfer and accurate timing control, was assembled on the computer's extension board. The extension board is used to replace the frequency synthesizers and waveform recorders normally used for arbitrary waveform generation and data acquisition at a speed of several mega Hertz. The unique features of the digital hardware design include: (1) common memory for both excitation and data acquisition; (2) control logic for critical timing steps; (3) system memory mapping for fast data transfer. This design has not only led to great reduction in construction cost but has increased the flexibility of the instrument to perform complex experiments as well. A general phase modulation algorithm for the stored waveform inverse Fourier transform (SWIFT) excitation has been developed. The method can be used to generate arbitrary excitation waveforms with optimal dynamic range reduction. The maximum entropy spectral analysis (MEM) has been investigated. When the broad-band MEM method was demonstrated in the host computer, resolution and signal-to-noise ratio improvement was observed. New preamplifier, electron beam circuits, and the sample inlet system of the instrument were designed and constructed with computer control. This provides the instrument with reliability, stability, and functionality. A theoretical model for two dimensional Fourier transform ion cyclotron resonance mass spectrometry has been proposed. The model interprets the physical significance of the modulation of the ion signals in the additional dimension. According to the model, the additional time dimension (which is introduced as the duration between the pair of 2D excitation pulses) determines the speed of the primary ions just before the reaction period. The speed modulation may result in primary ion population modulation. In general, the speed modulation will transfer into ion signal modulation through a variety of channels, such as reactions and ion loss. The model also predicts that the ion modulation in the additional dimension is not sinusoidal (therefore, harmonics exist) and the ion signal modulation has definite phase relationships. The implementation of the 2D technique is developed and demonstrated.
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Rai, Rachel H. "Crystallization of Two-Dimensional Transition Metal Dichalcogenides for Tailored Optical Properties." University of Dayton / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1565191101735252.
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Eichel, Rüdiger-Albert. "New concepts in two-dimensional pulse electron paramagnetic resonance spectroscopy : resolution enhancement by magnetic field modulation /." Zürich : [s.n.], 2001. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=14394.
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Grainger, David S. "The application of the maximum entropy method to one- and two-dimensional nuclear magnetic resonance spectroscopy." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291092.
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Jo, Ju-Yeon. "Full molecular dynamics simulations of molecular liquids for single-beam spectrally controlled two-dimensional Raman spectroscopy." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263491.
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