Дисертації з теми "Atomically thin"
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Bandurin, Denis. "Electron transport in atomically thin crystals." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/electron-transport-in-atomically-thin-crystals(e184d9d8-ad44-41e0-8be9-bd381d6a21d6).html.
Повний текст джерелаPearce, Alexander James. "Electromechanical properties of atomically thin materials." Thesis, University of Exeter, 2014. http://hdl.handle.net/10871/15294.
Повний текст джерелаBaugher, Britton William Herbert. "Electronic transport in atomically thin layered materials." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91393.
Повний текст джерела125
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 101-110).
Electronic transport in atomically thin layered materials has been a burgeoning field of study since the discovery of isolated single layer graphene in 2004. Graphene, a semi-metal, has a unique gapless Dirac-like band structure at low electronic energies, giving rise to novel physical phenomena and applications based on them. Graphene is also light, strong, transparent, highly conductive, and flexible, making it a promising candidate for next-generation electronics. Graphene's success has led to a rapid expansion of the world of 2D electronics, as researchers search for corollary materials that will also support stable, atomically thin, crystalline structures. The family of transition metal diclialcogenides represent some of the most exciting advances in that effort. Crucially, transition metal dichalcogenides add semiconducting elements to the world of 2D materials, enabling digital electronics and optoelectronics. Moreover, the single layer variants of these materials can posses a direct band gap, which greatly enhances their optical properties. This thesis is comprised of work performed on graphene and the dichalcogenides MoS 2 and WSe2. Initially, we expand on the family of exciting graphene devices with new work in the fabrication and characterization of suspended graphene nanoelectromnechanical resonators. Here we will demonstrate novel suspension techniques for graphene devices, the ion beam etching of nanoscale patterns into suspended graphene systems, and characterization studies of high frequency graphene nanoelectromechanical resonators that approach the GHz regime. We will then describe pioneering work on the characterization of atomically thin transition metal dichalcogenides and the development of electronics and optoelectronics based on those materials. We will describe the intrinsic electronic transport properties of high quality monolayer and bilayer MoS 2 , performing Hall measurements and demonstrating the temperature dependence of the material's resistivity, mobility, and contact resistance. And we will present data on optoelectronic devices based on electrically tunable p-n diodes in monolayer WSe2 , demonstrating a photodiode, solar cell, and light emitting diode.
by Britton William Herbert Baugher.
Ph. D.
Ye, Fan. "HIGHLY TUNABLE ATOMICALLY THIN RESONANTNANOELECTROMECHANICAL SYSTEMS (NEMS)." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1589392684740436.
Повний текст джерелаFarrokhi, M. Javad. "ELECTRONIC PROPERTIES OF ATOMICALLY THIN MATERIAL HETEROSTRUCTURES." UKnowledge, 2019. https://uknowledge.uky.edu/physastron_etds/67.
Повний текст джерелаReale, Francesco. "Chemical vapour deposition of atomically thin tungsten disulphide." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/56620.
Повний текст джерелаVenanzi, Tommaso. "Optical and infrared properties of atomically thin semiconductors." Technische Universität Dresden, 2020. https://tud.qucosa.de/id/qucosa%3A73364.
Повний текст джерелаManca, Marco. "Study of the optoelectronic properties of atomically thin WSe2." Thesis, Toulouse, INSA, 2019. http://www.theses.fr/2019ISAT0030.
Повний текст джерелаTransition Metal Dichalcogenides (TMDs) are a family of layered materials with potential applications in optics and electronics. Following the discovery of graphene, TMDs were characterized and extraordinary physical properties were discovered: when thinned down to a monolayer, TMDs become direct band gap materials, therefore strongly facilitating light emission. The direct bandgap of these semiconductors is situated on the edge of the Brillouin zone, at the K-point. This is different from standard semiconductors for optoelectronics like GaAs where the bandgap is in the centre of the Brillouin zone. The optical properties are dominated by excitons, and light-matter interaction is extremely strong with up to 20% of light absorption per monolayer. In addition to a bandgap, TMDs present strong spin-orbit coupling and broken inversion symmetry. As a result, the optical transitions across the bandgap have chiral selection rules. The spin states in the valence and conduction bands are well separated in energy by the spin-orbit interaction. This makes it possible to optically address specific spin and valley states in momentum space and monitor their dynamics. As a result monolayer TMDs are exciting model systems for spin and valley physics: these research fields are termed spintronics and valleytronics. This motivated our work on the exact understanding of the optical transitions, their polarization selections rules and the different exciton states
Lorchat, Étienne. "Optical spectroscopy of heterostructures based on atomically-thin semiconductors." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAE035.
Повний текст джерелаDuring this thesis, we have fabricated and studied by optical spectroscopy, van der Waals heterostructures composed of semiconductor monolayers (transition metal dichalcogenides, TMD) coupled to a graphene monolayer or to a plasmonic resonator. We have observed significant changes in the dynamics of the TMD optically excited states (excitons) when it is in direct contact with graphene. Graphene neutralizes the TMD monolayer and enables non-radiative transfer of excitons within less than a few picoseconds. This energy transfer process may be accompanied by a considerably less efficient, extrinsic photodoping. The reduced lifetime of TMD excitons in the presence of graphene has been exploited to show that their valley pseudo-spin maintains a high degree of polarization and coherence up to room temperature. Finally, by strongly coupling TMD excitons to the modes of a geometric phase plasmonic resonator, we have demonstrated, at room temperature, that the momentum of the resulting chiral polaritons (chiralitons) is locked to their valley pseudo-spin
Hudson, David Christopher. "Two dimensional atomically thin materials and hybrid superconducting devices." Thesis, University of Exeter, 2014. http://hdl.handle.net/10871/16034.
Повний текст джерелаHan, Kyung-Eun. "Transport of n-alkanes through graphene nanoporous atomically thin membrane." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/123294.
Повний текст джерелаCataloged from PDF version of thesis.
Includes bibliographical references (pages 67-68).
Accurately characterizing molecular transport through a nanoporous atomically thin graphene membrane is important in determining potential for graphene's application as a filter. Amongst many factors that affect the transport, the effect of size of molecules is analyzed in this paper. Diffusion of n-alkanes between C10 and C18 was analyzed to isolate the effect of molecule size in transport trends. The n-alkanes are chosen as the solutes for their similar long-chains but differing lengths. Differently branched structures cause variable interactions with graphene between molecules. Thus, this structural consistency in n-alkanes make them optimal solutes. Additionally, these molecules are comprised of only carbon and hydrogen, allowing the same functional groups and polarities. However, their distinct boiling points allow detection in the gas chromatography-mass spectrometry (GCMS).
A diffusion cell with feed and permeate chambers, separated by a semipermeable membrane, was used to induce diffusion with difference in solute concentration between the chambers. Diffusion concentration and rates were calculated using GCMS analysis of samples taken over 6-hour period during the diffusion. The calculations were done for diffusion with and without graphene membrane for comparison. When integrating the GCMS peaks, two types of integration methods - wide-peak and narrow-peak integrations - were used to estimate the error due to difficulties in identifying peak boundaries. These results were further compared to the inherent diffusivity coefficients of the molecules, in order to quantify the selectivity imparted by graphene for diffusion. The diffusion trends from each data set were compared to the diffusion trend from inherent diffusivity coefficients, which shows that diffusiyity should decrease with larger and heavier n-alkanes.
The experimentally obtained data shows that smaller molecules diffused at faster rates, and there was a noticeable drop in the diffusion transport between C 12 and C 14. This is consistent with the expected trend. Studies that minimize sources of errors are recommended to further understand the transport of alkanes through graphene.
by Kyung-Eun Han.
S.B.
S.B. Massachusetts Institute of Technology, Department of Mechanical Engineering
Unal, Selim. "Field-effect transistors and optoelectronic devices based on emerging atomically thin materials." Thesis, University of Exeter, 2017. http://hdl.handle.net/10871/27140.
Повний текст джерелаMalina, Evan. "Mechanical Behavior of Atomically Thin Graphene Sheets Using Atomic Force Microscopy Nanoindentation." ScholarWorks @ UVM, 2011. http://scholarworks.uvm.edu/graddis/145.
Повний текст джерелаKozawa, Daichi. "Behavior of photocarrier in atomically thin two-dimensional semiconducting materials for optoelectronics." Kyoto University, 2015. http://hdl.handle.net/2433/199420.
Повний текст джерелаNicolas, Rana. "Squeezing light in nanoparticle-film plasmonic metasurface : from nanometric to atomically thin spacer." Thesis, Troyes, 2015. http://www.theses.fr/2015TROY0028/document.
Повний текст джерелаSurface plasmon polariton (SPP) and Localized surface plasmon (LSP) have attracted numerous researchers due to their high technological potential. Recently, strong attention was paid to the potential of SPP and LSP combinations by investigating metallic nanoparticles (NPs) on top of metallic thin films. Several studies on such systems have shown the coupling and hybridization between localized and delocalized modes. In this work, we propose a full systematic study on coupled NP/film systems with Au NPs and Au films. We investigate both experimentally and theoretically the influence of an ultra-thin SiO2 dielectric spacer layer, as well as the evolution of the plasmonic modes as the spacer thickness increases. We show that coupled systems exhibit enhanced optical properties and larger tunability compared to uncoupled systems. We also compare these results with those measured for coupled interfaces using graphene as a non-dielectric sub-nanometer spacer. Introducing graphene adds complexity to the system. We show that such coupled systems also exhibit enhanced optical properties and larger tunability of their spectral properties compared to uncoupled systems as well as unexpected optical behavior. We explain this behavior by evidencing graphene doping by metallic NPs, which can be a first step towards graphene based optoelectronic devices. After establishing a deep understanding of coupled systems we perform both SERS and RI sensing measurements to validate the high potential of these plasmonic interfaces
Sundararajan, Abhishek. "A STUDY ON ATOMICALLY THIN ULTRA SHORT CONDUCTING CHANNELS, BREAKDOWN, AND ENVIRONMENTAL EFFECTS." UKnowledge, 2015. http://uknowledge.uky.edu/physastron_etds/27.
Повний текст джерелаNeumann, Andre [Verfasser], and Alexander [Akademischer Betreuer] Högele. "Cryogenic hyperspectroscopy of nanoemitters and atomically thin semiconductors / Andre Neumann ; Betreuer: Alexander Högele." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2017. http://d-nb.info/1160876320/34.
Повний текст джерелаSperber, Jared L. "Investigations of hexagonal boron nitride: bulk crystals and atomically-thin two dimensional layers." Thesis, Kansas State University, 2016. http://hdl.handle.net/2097/32509.
Повний текст джерелаDepartment of Chemical Engineering
James H. Edgar
Hexagonal boron nitride has been used as an inert, refractory material with excellent resistance to thermal decomposition and oxidation for more than fifty years. In the past few years, hBN has been targeted for potential electrical and optical devices such as neutron detectors, ultraviolet light emitters, deep ultraviolet light detectors, and substrates for graphene and other atomically-thin two-dimensional materials. All of these potential applications benefit from high quality, single crystals, with thicknesses varying from nanometers to microns. This research was undertaken to investigate four aspects of hBN crystal growth and recovery. (1) In an effort to optimize hBN crystal growth from a nickel-chromium flux, a series of stepped cooling experiments were undertaken. The temperature profile was stepped in a way as to promote growth in both the a and c directions, at their optimal growth conditions. Crystals were found to be typically 100-500 µm across and thickness of approximately 20-30 µm with a pyramid-like crystal habit. (2) A method for the removal of hBN crystals prior to freezing of the metal flux was demonstrated using a specialized hot pressed boron nitride crucible capable of removing hBN crystals from the flux in situ. (3) Growth of isotopically pure hBN crystals was undertaken. By modifying the crucible material for solution growth, enrichment of hBN crystals over 90% was accomplished. (4) Exfoliation of hBN has many potential applications, specifically as graphene-hBN heterostructures where layers approaching thicknesses of single atoms are most effective surface to interact with graphene as an electronic device. Several methods were tested toward exfoliating a single crystal resulting in few-layered hexagonal boron nitride nanosheets. As a result of these investigations a greater understanding of hBN bulk growth, its isotopic enrichment, its recovery, and its exfoliation was obtained.
Trainer, Daniel Joseph. "INVESTIGATION OF THE QUASIPARTICLE BAND GAP TUNABILITY OF ATOMICALLY THIN MOLYBDENUM DISULFIDE FILMS." Diss., Temple University Libraries, 2019. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/559773.
Повний текст джерелаPh.D.
Two dimensional (2D) materials, including graphene, hexagonal boron nitride and layered transition metal dichalcogenides (TMDs), have been a revolution in condensed matter physics and they are at the forefront of recent scientific research. They are being explored for their unusual electronic, optical and magnetic properties with special interest in their potential uses for sensing, information processing and memory. Molybdenum disulfide (MoS2) has been the flagship semiconducting TMD over the past ten years due to its unique electronic, optical and mechanical properties. In this thesis, we grow mono- to few layer MoS2 films using ambient pressure chemical vapor depositions (AP-CVD) to obtain high quality samples. We employ low temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) to study the effect of layer number on the electronic density of states (DOS) of MoS¬2. We find a reduction of the magnitude of the quasiparticle band gap from one to two monolayers (MLs) thick. This reduction is found to be due mainly to a shift of the valence band maxima (VBM) where the conduction band minimum (CBM) does not change dramatically. Density functional theory (DFT) modeling of this system shows that the overlap of the interfacial S-pz orbitals is responsible for shifting the valence band edge at the Γ-point toward the Fermi level (EF), reducing the magnitude of the band gap. Additionally, we show that the crystallographic orientation of monolayer MoS2 with respect to the HOPG substrate can also affect the electronic DOS. This is demonstrated with five different monolayer regions having each with a unique relative crystallographic orientation to the underlying substrate. We find that the quasiparticle band gap is closely related to the moiré pattern periodicity, specifically the larger the moiré periodicity the larger the band gap. Using DFT, we find that artificially increasing the interaction between the film and the substrate means that the magnitude of the band gap reduces. This indicates that the moiré pattern period acts like a barometer for interlayer coupling. We investigate the effect of defects, both point and extended defects, on the electronic properties of mono- to few layer MoS¬2 films. Atomic point defects such including Mo interstitials, S vacancies and O substitutions are identified by STM topography. Two adjacent defects were investigated spectroscopically and found to greatly reduce the quasiparticle band gap and arguments were made to suggest that they are Mo-Sx complex vacancies. Similarly, grain boundaries were found to reduce the band gap to approximately ¼ of the gap found on the pristine film. We use Kelvin probe force microscopy (KPFM) to investigate the affect of annealing the films in UHV. The work function measurements show metastable states are created after the annealing that relax over time to equilibrium values of the work function. Scanning transmission electron microscopy (STEM) is used to show that S vacancies can recombine over time offering a feasible mechanism for the work function changes observed in KPFM. Lastly, we report how strain affects the quasiparticle band gap of monolayer MoS2 by bending the substrate using a custom built STM sample holder. We find that the local, atomic-scale strain can be determined by a careful calibration procedure and a modified, real-space Lawler Fujita algorithm. We find that the band gap of MoS2 reduces with strain at a rate of approximately 400 meV/% up to a maximum strain of 3.1%, after which the film can slip with respect to the substrate. We find evidence of this slipping as nanoscale ripples and wrinkling whose local strain fields alter the local electronic DOS.
Temple University--Theses
Golalikhani, Maryam. "Structure and electronic properties of atomically-layered ultrathin nickelate films." Diss., Temple University Libraries, 2015. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/353844.
Повний текст джерелаPh.D.
This work presents a study on stoichiometry and structure in perovskite-type oxide thin films and investigates the role of growth–induced defects on the properties of materials. It also explores the possibility to grow thin films with properties close or similar to the ideal bulk parent compound. A novel approach to the growth of thin films, atomic layer-by-layer (ALL) laser molecular beam epitaxy (MBE) using separate oxide targets is introduced to better control the assembly of each atomic layer and to improve interface perfection and stoichiometry. It also is a way to layer materials to achieve a new structure that does not exist in nature. This thesis is divided into three sections. In the first part, we use pulsed laser deposition (PLD) to grow LaAlO3 (LAO) thin films on SrTiO3 (STO) and LAO substrates in a broad range of laser energy density and oxygen pressure. Using x-ray diffraction (θ-2θ scan and reciprocal space mapping), transmission electron microscopy (TEM) and x-ray fluorescence (XRF) we studied stoichiometry and structure of LAO films as a function of growth parameters. We show deviation from bulk–like structure and composition when films are grown at oxygen pressures lower than 10-2 Torr. We conclude that the discussion of LAO/STO interfacial properties should include the effects of growth–induced defects in the LAO films when the deposition is conducted at low oxygen pressures, as is typically reported in the literature. In the second part, we describe a new approach to atomically layer the growth of perovskite oxides: (ALL) laser MBE, using separate oxide targets to grow materials as perfectly as possible starting from the first atomic layer. We use All laser MBE to grow Ruddlesden–Popper (RP) phase Lan+1NinO3n+1 with n = 1, 2, 3 and 4 and we show that this technique enables us to construct new layered materials (n=4). In the last and main section of this thesis, we use All laser MBE from separate oxide targets to build the LaNiO3 (LNO) films as near perfectly as possible by depositing one atomic layer at a time. We study the thickness dependent metal-insulator transition (MIT) in ultrathin LNO films on an LAO substrate. In LNO, the MIT occurs in thin films and superlattices that are only a few unit cells in thickness, the understanding of which remains elusive despite tremendous effort devoted to the subject. Quantum confinement and structure distortion have been evoked as the mechanism of the MIT; however, first-principle calculations show that LaNiO3 remains metallic even at one unit cell thickness. Here, we show that thicknesses of a few unit cells, growth–induced disorders such as cation stoichiometry, oxygen vacancies, and substrate-film interface quality will impact the film properties significantly. We find that a film as thin as 2 unit cells, with LaO termination, is metallic above 150 K. An oxygen K-edge feature in the x-ray absorption spectra is clearly inked to the transition to the insulating phase as well as oxygen vacancies. We conclude that dimensionality and strain are not sufficient to induce the MIT without the contribution of oxygen vacancies in LNO ultrathin films. Dimensionality, strain, crystallinity, cation stoichiometry, and oxygen vacancies are all indispensable ingredients in a true control of the electronic properties of nanoscale strongly–correlated materials.
Temple University--Theses
Matoba, Tomohiko. "Fabrication of transition-metal oxide thin films with atomically smooth surface for spintronics application." 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/174948.
Повний текст джерелаVenanzi, Tommaso [Verfasser], Manfred [Gutachter] Helm, and Rudolf [Gutachter] Bratschitsch. "Optical and infrared properties of atomically thin semiconductors / Tommaso Venanzi ; Gutachter: Manfred Helm, Rudolf Bratschitsch." Dresden : Technische Universität Dresden, 2021. http://d-nb.info/1231845791/34.
Повний текст джерелаNur, Baizura Binti Mohamed. "Study on photoluminescence quantum yields of atomically thin-layered two-dimensional semiconductors transition metal dichalcogenides." Kyoto University, 2018. http://hdl.handle.net/2433/233854.
Повний текст джерелаDel, Pozo Zamudio Osvaldo. "Optics of atomically thin films and van der Waals heterostructures made from two-dimensional semiconductors." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/11975/.
Повний текст джерелаLindlau, Jessica [Verfasser], and Alexander [Akademischer Betreuer] Högele. "Optical spectroscopy of charge-tunable atomically thin semiconductors at cryogenic temperatures / Jessica Lindlau ; Betreuer: Alexander Högele." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1196009414/34.
Повний текст джерелаGhosh, Sujoy. "SYNTHESIS, ELECTRONIC AND OPTO-ELECTRONIC TRANSPORT PROPERTIES OF ATOMICALLY THIN 2D LAYERS OF MoS2, WSe2 and CuIn7Se11." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/dissertations/1308.
Повний текст джерелаPachuta, Kevin. "Compositional Changes Associated with the Exfoliation of Lithium Cobalt Oxide into Atomically Thin CoO2 Nanosheets." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1522969523294786.
Повний текст джерелаHuffstutler, Jacob Danial. "AN ANALYSIS OF ELECTROCHEMICAL ENERGY STORAGE USING ELECTRODES FABRICATED FROM ATOMICALLY THIN 2D STRUCTURES OF MOS2, GRAPHENE AND MOS2/GRAPHENE COMPOSITES." OpenSIUC, 2014. https://opensiuc.lib.siu.edu/theses/1583.
Повний текст джерелаMurray, Clifford David Hughes [Verfasser], Thomas [Gutachter] Michely, and Paul van [Gutachter] Loosdrecht. "Local spectroscopy of atomically thin MoS2: electronic states at 1D defects, charge transfer and screening / Clifford David Hughes Murray ; Gutachter: Thomas Michely, Paul van Loosdrecht." Köln : Universitäts- und Stadtbibliothek Köln, 2020. http://d-nb.info/1225478510/34.
Повний текст джерелаCantley, Lauren. "Biomimetic nanopores from atomically thin membranes." Thesis, 2017. https://hdl.handle.net/2144/23567.
Повний текст джерела2018-07-09T00:00:00Z
Kao, R. H., and 高榮輝. "Ultra-thin Oxide with Atomically Smooth Interfaces." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/15934356417162502798.
Повний текст джерела中華大學
電機工程研究所
85
Native oxide is an important issue for ultra-thin oxide, which is strongly related to the gate oxide integrity such as QBD, interface scattering, etc. We have designed a leak-tight low-pressure oxidation system to desorb the native oxide in-situ. Atomically flat interfaces between oxide and Si are obtained for oxide thickness of 11 and 38 A. Because of the smooth interface and good thickness uniformity of oxide, both high-field electron mobility and oxide breakdown behavior are much improved, significant mobility improvement is obtained from these oxides with smoother interface than that from conventional furnace oxidation. Mobility reduction in ultra-thin oxide has been observed for the first time, which may be due to the remote coulomb scattering from gate electrode. In our study, the thickness variation of a 23 A N2O-oxide, grown on a 4-inch substrate, is less than 1 A, that is attributed to the increased mean-free-path of N2O-molecules under low pressure environment, only one Si atomic plane distorted beneath the N2O-oxide/Si interface suggests that thermal stress is not the limiting factor to obtain the atomically smooth interface. Direct relationship of electron mobility to interface roughness was obtained from the measured mobility of MOSFET and high resolution TEM.
Zhang, Xiaoxiao. "Excitonic Structure in Atomically-Thin Transition Metal Dichalcogenides." Thesis, 2016. https://doi.org/10.7916/D8639Q01.
Повний текст джерелаLin, Che-Yi, and 林哲儀. "Explore intrinsically electrical characteristics of atomically thin SnS2 flake." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/57669934010113348197.
Повний текст джерела國立中興大學
物理學系所
103
Here, fakes made of a few layers of SnS2 were obtained by mechanical exfoliation of a semiconducting SnS2 bulk crystal grown by chemical vapor transport and then deposited on a heavily doped Si substrate covered with a 285-nm-thick SiO2 layer. The number of layers was quickly determined by examining the difference in the contrast of the color images and the grayscale images. To study the electrical properties of SnS2 flakes, field-effect transistors (FETs) were fabricated using standard e-beam lithography and thermal evaporation. Atomically thin SnS2 FETs displayed a clear n-type demeanor in charge transport with a current modulation of up to 105 and mobility of ~3.2 cm2V-1s-1. Through careful analysis of temperature dependent resistance between two- and four-terminal FETs, we found the contact resistance extracted was small than ~5 % of total FET resistance, implying the contact resistance can be eliminated in our device fabrication process. Besides, low-frequency noise of intrinsic SnS2 flakes can be uncovered. Our result not only gives atomic insights into the electrical properties of SnS2 FETs for the first time, but also bring a big impact to the development of 2D optoelectronics.
Chuang, Zong-Ying, and 莊宗穎. "Mechanical Exfoliation of Atomically Thin, Large Area Transition Metal Dichalcogenides." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/4t93g3.
Повний текст джерела國立交通大學
光電工程研究所
107
The discovery of the two-dimensional (2D) layered semiconductors, such as transition metal dichalcogenides (TMDCs), has gained interests owing to their remarkable electronic and optical properties. While the ML TMDC flakes prepared by mechanical exfoliation method has a good crystal quality compared to those fabricated by chemical vapor deposition (CVD), atomically thin, large-area sample is difficult to obtain. In this work, we employed an ultrathin gold film to efficiently exfoliate the TMDC layers and successfully obtained a large-area ultrathin TMDC with excellent optical properties. These large-area ultrathin layers can also be transferred to any substrate without any cracks. The effect of thermal annealing in vacuum on the optical and electrical properties of TMDC samples is investigated by using the luminescence spectroscopy, atomic force microscopy, and the micro-four-point probe technique. Annealing in vacuum not only ameliorates the threshold voltage, but also enhances the contact between the electrode and samples, increasing the current and carrier mobility. The concomitant sample transfer to the substrates on a hot plate can effectively reduce wrinkles and further improve the threshold voltage, but the minimal changes of current and carrier mobility are observed.
"Electronic Transport Studies of Atomically Thin van der Waals Materials." Tulane University, 2018.
Знайти повний текст джерелаSince the discovery of unconventional superconductivity in iron pnictides and iron chalcogenides, they are of great interest for both fundamental physics and high-field applications. Among the iron-based superconductors, the layered iron chalcogenide Fe(Te1-xSex) is structurally the simplest, and present unusual superconducting and magnetic properties. In particular, the existence of weak van der Waals (vdW) bonding between charge-neutral layers makes it easy to exfoliate Fe(Te1-xSex) crystals down to atomically thin sheets like graphene and transition metal dichalcogenides. In this thesis work, we discovered a series of new phenomenons and implemented electronic transport studies on these novel vdW materials. For iron chalcogenide superconductor Fe(Te1-xSex), it has been speculated from bulk studies that nanoscale inhomogeneous superconductivity may inherently exist in this system. However, this has not been directly observed from nanoscale transport measurements. Thus we prepared Fe(Te0.5Se0.5) nanoflakes with various thickness and systematically studied the correlation between the thickness and superconducting phase transition through micromechanical exfoliation and high-precision low-energy ion milling thinning. Our result revealed a systematic thickness-dependent evolution of superconducting transition. When the thickness of the Fe(Te0.5Se0.5) thin flake is reduced to less than the characteristic inhomogeneity length (around 12nm), both the superconducting current path and the metallicity of the normal state in the Fe(Te0.5Se0.5) atomic sheets are suppressed. This observation provides the first transport evidence for the nanoscale inhomogeneity nature of superconductivity in Fe(Te1-xSex). Our follow-up studies on inhomogeneous superconductivity in another ratio of Te/Se for thinner flakes further revealed the underlying physics behind the broadened phase transition. With the reduction of thickness (d < 9nm), strain free Fe(Te0.7Se0.3) nanoflakes have exhibited characters of two dimensional (2D) superconductivity according to Ginzburg – Landau (GL) fluctuation. We also observed the typical Berezinskii-Kosterlitz-Thouless (BKT) signatures which lead to the broadening of phase transition. With the combination measurements of temperature-dependent resistance (R-T) and magnetoresistance (R-H), it can be clearly identified that four distinct transition regions, including GL fluctuation, BKT transition, intrinsic inhomogeneity and superconducting region, exist in the atomically thin Fe(Te1-xSex) sheets at different temperature range. Furthermore, the dynamic evolution of random-resistor-network due to the inhomogeneous superconductivity has been explicitly revealed through I – V measurements. In addition, we found an exotic switching effect which may be associated with the induced Joule heating in the Fe(Te0.7Se0.3) nanoflakes by performing I – V sweep. We also expanded our study on the newly discovered topological nodal-line semimetal (TNLSM) ZrSiSe which can be treated as another vdW material with vdW bonding between adjacent Se layers. In this thesis work, we systematically studied the thickness dependence of quantum oscillations in ZrSiSe nanoflakes. With the reducing thickness below 50nm, an additional quantum oscillation emerges. This new quantum oscillation corresponds to a 2D surface state, evidenced by the angular dependence of cos(θ) in magnetoresistance measurements. The analysis of Landau level (LL) fan diagram and the directly fitting of Lifshitz-Kosevich (LK) formula both suggest a trivial surface state. In addition, the estimated size of Fermi surface is in good agreement with the reported angular-resolved photoemission spectroscopy (ARPES) result. Our study on the ZrSiSe surface state verifies exceptional case of bulk-edge correspondence principle in TNLSM. And also our experimental demonstrates a new way of probing surface state in TNLSM with nanoscale transport.
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Chunlei Yue
Lin, B. C., and 林柏村. "From low temperature Si epitaxy to atomically smooth ultra-thin oxide." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/72013835653885263096.
Повний текст джерела國立交通大學
電子工程系
87
Abstract: We have designed a leak-tight low pressure hot wall furnace system, which can be used to grow Si epitaxy layer, selective epitaxial Si and ultra-thin silicon dioxide (<30A). The residual native oxide not only degrades the quality of epitaxial material but also extremely important for ultra-thin gate oxide. In contrast to previous ultra-high-vacuum chemical-vapor-deposition or molecular beam epitaxy, we have used a leak-tight design and hydrogen bake to reduce the background moisture and oxygen. We have first successfully grown epitaxial Si at 550oC and the quality of epitaxial film has been found comparable to that of Si substrate. The low temperature of 550 oC is especially chosen because it is suitable for future SiGe epitaxy. The selective epitaxy is achieved at low temperatures by using Dichlorosilane (SiH2Cl2) and a minimum temperature of 750 oC is achieved that is low enough for process integration consideration. The native oxide can strongly influence the gate oxide integrity. By removing the native oxide and re-growing thermal oxide, atomically smooth oxide-Si interface can be achieved. Significant mobility improvement was obtained from these oxides than that from conventional furnace oxidation. The trap generation rate and stress-induced leakage current (SILC) are also much reduced using the atomically smooth oxide. The gate oxide quality of ultra-thin oxide can be further improved by using deuterium annealing instead of traditional forming gas annealing. A factor of five times reduction of SILC is obtained by deuterium annealing.
Chen, Hui-Yuan, and 陳薈元. "Probing Elastic Properties of Atomically-thin Interfacial Layer by Femtosecond Acoustics." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/91772253942514860460.
Повний текст джерела國立臺灣大學
光電工程學研究所
103
While the developing trend of modern electronic devices is toward scaling down, heat removal is a critical issue since thermal effect becomes seriously significant as dimensions shrink. Besides, many complex and denser structures such as 3D integrated circuits or FinFET were designed to exploit the limited space and optimize the overall device performance, which is a trend well-characterized by Moore’s law. However, it is well-known that an interfacial layer (IL) is usually formed between two adjacent heterogeneous materials. The existence of this unavoidable interfacial layer might hinder the heat conduction in those fabricated devices, and thus certainly diminishes their operational lifetime. Since heat is mainly carried by acoustic phonons, elastic property of materials is among the essential information for thermal management. Unfortunately, a proper technology to probe the elastic property of this atomically-thin interfacial layer has not yet been documented. In this thesis, we designed an interfacial layer (IL) model system between bulk GaN and Al2O3 film, and conducted femtosecond acoustic measurement to obtain the elastic properties of the IL. The acoustic impedance, mass density and a cross-plane elastic constant of the IL were successfully obtained. We further evaluated a 16% reduction in thermal energy transmission owing to the IL from a theoretical calculation. With the capability of probing the elastic properties across layers of only several atoms thick, our demonstration could be deemed as the first step to deal with heat dissipation issue stemming from the ILs. Hopefully, our approach will provide a better thermal management for nano-scaled devices in the future.
Fuchigami, Kenji. "Atomically resolved STM studies of the perovskite manganite thin-film surfaces." 2009. http://etd.utk.edu/2009/Spring2009Dissertations/FuchigamiKenji.pdf.
Повний текст джерелаMotmaen, Dadgar Abdollah. "Strain Engineering, Quantum Transport and Synthesis of Atomically-thin Two-dimensional Materials." Thesis, 2017. https://doi.org/10.7916/D8XD1D8G.
Повний текст джерелаLIN, CHUNG-WEI, and 林忠緯. "Atomically thin metal oxide Titania as electrontransporting layer for Perovskite Solar Cells." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/31629514907756147120.
Повний текст джерела國立臺灣大學
材料科學與工程學研究所
105
A recently emerging class of solid-state hybrid organic–inorganic perovskite-based solar cells,using CH3NH3PbX3(X=Cl,Br,I) as light harvesting materials, had demonstrated remarkably high power conversion efficiencies of nearly 21%. Most state-of-the-art perovskite solar cells typically have a device structure that is based on a hightemperature sintered metal oxide(compact TiO2) as electron transporting layer(ETL) which may cause the limitation of perovskite solar cells to be deposited on flexible substrates and affect their compatibility with fabrication processes in multi-junction solar cells. In this work, the utilization of atomically thin titania (atomic Ti0.87O2) deposited at room temperature as an ultra-thin electron transporting layer in perovskite solar cell was demonstrated.Through Langmuir-Blodgett deposition process at room temperature,atomic Ti0.87O2 was conformally deposited on FTO substrate with a high coverage and eliminated the requirement of high temperature process (over 500C) to deposit compact TiO2. The incorporation of multi-layer Ti0.87O2 (around 5 nm) effectively decreased the recombination of electron and hole and leaded to a reduced leakage current. This resulted in a promising device performance (14.05%) that is compatible to the device fabricated using high-temperature sintered metal oxide as electron selection layer. More importantly, we find devices using atomic Ti0.87O2 as electron transporting layer have a better stability in atomsphere. After 30 days, the atomic Ti0.87O2 devices remain about 70% of their original efficiency, unlike compact TiO2 devices, which remain 10% of original efficiency. With the atomic Ti0.87O2 electron transporting layer, we can successfully make a whole low temperature solution process, an atomically thin film ETL, and a stable deivces.
Lloyd, David. "Engineering with atomically thin materials: making crystal grains, strains, and nanoporous membranes." Thesis, 2020. https://hdl.handle.net/2144/41023.
Повний текст джерелаChristopher, Jason Woodrow. "Riveting two-dimensional materials: exploring strain physics in atomically thin crystals with microelectromechanical systems." Thesis, 2018. https://hdl.handle.net/2144/27857.
Повний текст джерелаTsai, Yung-Han, and 蔡詠涵. "Two-dimensional atomically thin perovskite oxide as electron transport layer for perovskite solar cells." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/as64kv.
Повний текст джерела國立臺灣大學
材料科學與工程學研究所
106
Two-dimensional (2D) oxides are a large group of 2D materials. These 2D oxides can be divided into two subgroups: 2D metal oxides and 2D perovskite oxides. They are rich in structural diversity, electronic properties, and have novel physical and chemical properties from quantum confinement or surface effects comparing to their bulk states. 2D oxides are widely applied in the nanocapacitors, secondary batteries, and photocatalysts fields. Among the 2D perovskite oxides, Ca2Nb3O10 (CNO) atomic sheet is an n-type wide bandgap semiconductor. It has well aligned conduction band minimum with that of the lead halide perovskite, which is an efficient light absorber for solar cell application. These properties make CNO a promising electron transport material to extract electrons and block holes from lead halide perovskite light absorber. On the other hand, comparing to the conventional high temperature (> 500 ˚C) sintered compact-TiO2 electron transport layer, CNO can be deposited with relative low temperature (< 150 ˚C) solution process. In this work, we deposited CNO with low temperature Langmuir-Blodgett deposition method as electron transport layer to fabricate perovskite solar cell. The resultant devices showed best efficiency of 14.10%, which is compatible to the conventional high-temperature sintered compact-TiO2 device (14.07%). Moreover, the CNO based devices showed better electron transport ability than the conventional ones. Our work showed that CNO atomic sheet is a highly promising electron transport material for low-temperature solution processed all perovskite structure solar cells.
"Photovoltaics large and small: atomically thin semiconductor growth and kilowatt-scale transmissive photovoltaic systems." Tulane University, 2019.
Знайти повний текст джерелаThis dissertation describes several key developments in semiconductor devices and technologies designed for solar power conversion and other applications. The first development is of two new growth techniques for producing large-area two-dimensional molybdenum disulfide (MoS2). Such two-dimensional materials have the potential to miniaturize photovoltaic volume and mass by orders of magnitude without sacrificing performance. While large-scale 2D-material-based photovoltaics have not yet been realized, large-area growths such as those described in this dissertation provide meaningful progress toward that goal. The described techniques enable 2D MoS2 thickness control on the order of angstroms and increase 2D MoS2 growth speed by two orders of magnitude relative to the current state of the art. Furthermore, the grown materials are developed into preliminary optoelectronic devices, with performance characterization, as a step toward more advanced photovoltaic devices. The second development presented in this dissertation is the design, fabrication, test, and analysis of a kW-scale hybrid spectrum-splitting photovoltaic module. The module is designed to be transmissive to incident infrared radiation, allowing for infrared light to be separately collected by a thermal receiver, while simultaneously collecting high-energy visible and ultraviolet light via photovoltaics. A system is built and tested on an outdoor testbed and shows 75% total power conversion efficiency (thermal and electric) of the incident solar spectrum, surpassing the capability of conventional photovoltaics. This high efficiency and combination of electrical and thermal power accelerates solar energy penetration into new applications requiring multiple power streams. Across these varied length scales, this dissertation gives glimpses into new innovations throughout the photovoltaic and semiconductor fields and aims to share this knowledge and outlook with the next generation of researchers.
1
John Robertson
Sharma, Ankur. "Engineering the Exciton Dynamics and Transport in Atomically Thin Organic and Inorganic Semiconductor Materials." Phd thesis, 2020. http://hdl.handle.net/1885/197201.
Повний текст джерелаWurdack, Matthias. "Strong light-matter coupling and room temperature exciton polaritons in atomically-thin WS2 crystals." Phd thesis, 2022. http://hdl.handle.net/1885/266953.
Повний текст джерелаVutukuru, Mounika. "Straining the flatland: novel physics from strain engineering of atomically thin graphene and molybdenum disulfide." Thesis, 2021. https://hdl.handle.net/2144/43097.
Повний текст джерелаMecouch, William J. "Preparation and characterization of thin, atomically clean GaN(0001) and AlN(0001) films and the deposition of thick GaN films via iodine vapor phase growth." 2005. http://www.lib.ncsu.edu/theses/available/etd-06142005-212822/unrestricted/etd.pdf.
Повний текст джерела