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Dissertations / Theses on the topic 'Molecular diode'

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Published: 25 May 2024

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1

Deeny, J. A. "Tunable diode laser spectroscopy." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253325.

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2

Johnson, Simon Anthony. "Trace gas detection using diode lasers." Thesis, University of Cambridge, 1986. https://www.repository.cam.ac.uk/handle/1810/290026.

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3

Loroño, G. Marcos Antonio. "High resolution infrared diode laser spectroscopy of jet-cooled polyatomic molecules and molecular clusters." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621626.

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4

Hultell, Andersson Magnus S. "A Molecularly Switchable Polymer-Based Diode." Thesis, Linköping University, Department of Science and Technology, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-1571.

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Despite tremendous achievements, the field of conjugated polymers is still in its infancy, mimicking the more mature inorganic, i.e. silicon-based, technologies. We may though look forward to the realisation of electronic and electrochemical devices with exotic designs and device applications, as our knowledge about the fundamentals of these promising materials grow ever stronger.

My own contribution to this development, originating from an idea first put forward by my tutor, Professor Magnus Berggren, is a design for a switchable polymer-based diode. Its architecture is based on a modified version of a recently developed highly-rectifying diode,12 where an intermediate molecular layer has been incorporated in the bottom contact. Due to its unique ability to switch its internal resistance during operation, this thin layer can be used to shift the amount of (forward) current induced into the rectifying structure of the device, and by doing so shift its electrical characteristics between an insulating and a rectifying behaviour (as illustrated below). Such a component should be of great commercial interest in display technologies since it would, at least hypothetically, be able to replace the transistors presently used to address the individual matrix elements.

However, although fairly simple in theory, it proved to be quite the challenge to fabricate the device structure. Machinery errors and contact problems aside, several process routes needed to be evaluated and only a small fraction of the batches were successful. In fact, it was not until the very last day that I detected the first indications that the concept might actually work. Hence, several modifications might still be necessary to undertake in order to get the device to work properly.

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5

Rothwell, W. J. M. "Infrared diode laser spectroscopy of free radicals and molecular ions." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355508.

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6

Liu, Zhuan. "Infrared diode laser absorption spectroscopy of gas phase molecular ions." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627231.

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7

Denton, Bryan John. "The application of diode lasers to atomic spectroscopy." Thesis, University of Newcastle Upon Tyne, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316100.

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8

Norton, Peter Robert. "The molecular beam epitaxy technique for PbSe-based lead chalcogenide diode lasers." Thesis, University of Bath, 1986. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370994.

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9

Chan, Kit-ying Anna. "Near-ir tunable diode laser absorption spectroscopy of gaseous pollutants /." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19905014.

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10

Brown, Philip Robert. "Diode laser spectroscopy of molecular ions and excited atoms in alternative current discharges." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315821.

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11

陳潔瑩 and Kit-ying Anna Chan. "Near-ir tunable diode laser absorption spectroscopy of gaseous pollutants." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31214940.

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12

Ning, Ya Nong. "A study of optical fibre interferometric systems using multimode laser diode light sources." Thesis, City University London, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316037.

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13

Park, Jeongho. "Molecular Beam Epitaxy (MBE) Growth of Rare Earth Doped Gallium Nitride for Laser Diode Application." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1148273402.

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14

Sicard, Lambert. "Assemblages linéaires et cycliques d’unités fluorènes pour l’électronique organique : relations structure-propriétés." Thesis, Rennes 1, 2018. http://www.theses.fr/2018REN1S066/document.

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Les oligophénylènes constituent une classe de molécules centrale dans la conception de semi-conducteurs organiques pour des applications optoélectroniques. Ces travaux portent sur la synthèse et l’étude approfondie de dérivés linéaires et cycliques du fluorène (un biphényle rigidifié par un pont méthylène), fragment constitutif essentiel dans l’électronique organique. Nous nous intéressons en particulier aux relations structure-propriétés de ces systèmes π-conjugués. Dans une première partie, avec comme cadre le développement de matériaux hôtes pour diodes électroluminescentes (PhOLEDs), nous présentons une étude de la régioisomérie de phényl-fluorènes et de phényl-spirobifluorènes. Ses résultats ont permis la préparation de quatre matériaux hôtes purs hydrocarbures, dimères de spirobifluorène, intégrés dans des PhOLEDs bleues à hautes performances. Dans une seconde partie, nous nous intéressons au domaine récent des nano-anneaux moléculaires, objets cycliques présentant une conjugaison π de nature singulière. Après une revue bibliographique portant sur les cycloparaphénylènes et leurs propriétés, nous présentons nos études concernant plusieurs exemples de leurs analogues pontés : les cycloparafluorènes
Oligophenylenes constitute a major class of molecules in the design of organic semiconductors for optoelectronics applications. This work involves the synthesis and in-depth study of linear and cyclic derivatives of fluorene (a biphenyl rigidified by a methylene bridge), an essential building block in organic electronics. We focus our attention on the structure-property relationships of these π-conjugated systems. In a first part, within the framework of host materials for phosphorescent organic light-emitting diodes (PhOLEDs), we present a regioisomerism study of phenyl-fluorenes and phenyl-spirobifluorenes. Its results enabled the preparation of four pure hydrocarbon host materials, spirobifluorene dimers, used in high-performance blue PhOLEDs. In a second part, we take interest in the emerging field of molecular nanorings, cyclic objects presenting a singular nature of π-conjugation. After a bibliographical review covering cycloparaphenylenes and their properties, we present our studies regarding several examples of their bridged analogues: cycloparafluorenes
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15

Crow, Martin Brian. "High resolution diode laser spectroscopy of transient species." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:64bd9688-fdb3-4d05-ac2b-2a9bb621bb7c.

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This thesis presents applications of near infrared diode lasers to high resolution spectroscopy of transient radical species. Firstly, time resolved near infrared laser gain versus absorption is utilised in Chapter 2 to determine the I∗ quantum yield following ultraviolet photolysis of iodobenzene and its fluorinated analogues. The experimental method is first confirmed by comparison with literature values of the quantum yield for iodomethane photolysis, returning a quantum yield of Φ(I∗) = 0.71 ± 0.04 in good agreement with the literature, before being applied to determine the I∗ quantum yield following 248 nm and 266 nm photolysis of iodobenzene (Φ(I∗) = 0.28 ± 0.04) and pentafluoroiodobenzene (Φ(I∗) = 0.32 ± 0.05). The I∗ quantum yields for 4-fluoroiodobenzene, 2,4-difluoroiodobenzene and 3,5-difluoroiodobenzene are also reported in order to determine the effect of selective fluorination on the dynamics of the photodissociation process. This work complements velocity-map ion imaging studies and spin-orbit resolved ab initio calculations of the ultraviolet photolysis of these compounds. Chapter 3 details the development of a narrow-bandwidth tunable continuous wave ultraviolet radiation source, through sum frequency mixing of tunable near infrared diode lasers with a fixed frequency, high powered, solid state laser. The application of the UV radiation source to spectroscopy of the A 1A2 − X 1A1 electronic band of formaldehyde is explored, where absolute absorption cross sections are determined for rotational transitions within the 220410 and 220430 vibronic bands. The sub-Doppler resolution has allowed refinement of the rotational constants for the slowly predissociating excited state of the 220430 vibronic band. The lifetimes of several rotational levels is determined to be in the range 0.74 ns to 1.46 ns. In Chapter 4 the UV radiation source developed in Chapter 3 is applied to the A 2Σ+ − X 2Π electronic band of the OH radical. Firstly, this source is utilised to probe a continuous supply of hydroxyl radicals using cavity-enhanced absorption spectroscopy and wavelength modulation spectroscopy. Pressure induced broadening parameters for the Q1(2) rotational transition for He, Ne, Ar and N2 buffer gases are also measured. Following the successful application of this source to probe a continuous OH source at atmospheric pressure, the UV spectrometer is used to probe OH radicals from nitric acid photolysis at 193 nm, where the nascent speed distribution and Doppler lineshape is shown to be in excellent agreement with the literature. Time resolved absorption spectroscopy of the nascent OH fragment also returns a translational relaxation constant of ktrans = (3.85±1.06)×10−10cm3molecule−1s−1, which is in good agreement with literature values. These preliminary results indicate the potential of this narrow-bandwidth tunable UV source as an absorption-spectroscopy-based probe of nascent Doppler profiles. Chapter 5 presents the application of frequency-modulated radiation from a near infrared diode laser as a probe of the angular momentum polarisation of the nascent CN fragments, produced by 266 nm photolysis of ICN. These CN fragments are probed in the high rotational states of both the ground and first excited vibrational level on the A 2Π − X 2Σ+ electronic transition; in particular these constitute the first measurements of alignment and orientation in the first excited vibrational level at this photolysis wavelength. The alignment parameters reported for both vibrational levels are comparable, indicating that the incoherent dynamics contributing to their formation are the same. In contrast, the orientation of the v = 1 CN fragment is shown to be of opposite sign to that of v = 0 at this photolysis wavelength, although the absolute differences in their orientation parameters are similar to that observed for photolysis at 248 nm. This observation is consistent with coherent orientation arising from phase differences between wavepackets propagating on multiple excited potential energy surfaces.
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16

Liang, Yu-Han. "Deep Ultraviolet Light Emitters Based on (Al,Ga)N/GaN Semiconductor Heterostructures." Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/1008.

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Deep ultraviolet (UV) light sources are useful in a number of applications that include sterilization, medical diagnostics, as well as chemical and biological identification. However, state-of-the-art deep UV light-emitting diodes and lasers made from semiconductors still suffer from low external quantum efficiency and low output powers. These limitations make them costly and ineffective in a wide range of applications. Deep UV sources such as lasers that currently exist are prohibitively bulky, complicated, and expensive. This is typically because they are constituted of an assemblage of two to three other lasers in tandem to facilitate sequential harmonic generation that ultimately results in the desired deep UV wavelength. For semiconductor-based deep UV sources, the most challenging difficulty has been finding ways to optimally dope the (Al,Ga)N/GaN heterostructures essential for UV-C light sources. It has proven to be very difficult to achieve high free carrier concentrations and low resistivities in high-aluminum-containing III-nitrides. As a result, p-type doped aluminum-free III-nitrides are employed as the p-type contact layers in UV light-emitting diode structures. However, because of impedance-mismatch issues, light extraction from the device and consequently the overall external quantum efficiency is drastically reduced. This problem is compounded with high losses and low gain when one tries to make UV nitride lasers. In this thesis, we provide a robust and reproducible approach to resolving most of these challenges. By using a liquid-metal-enabled growth mode in a plasma-assisted molecular beam epitaxy process, we show that highly-doped aluminum containing III-nitride films can be achieved. This growth mode is driven by kinetics. Using this approach, we have been able to achieve extremely high p-type and n-type doping in (Al,Ga)N films with high aluminum content. By incorporating a very high density of Mg atoms in (Al,Ga)N films, we have been able to show, by temperature-dependent photoluminescence, that the activation energy of the acceptors is substantially lower, thus allowing a higher hole concentration than usual to be available for conduction. It is believed that the lower activation energy is a result of an impurity band tail induced by the high Mg concentration. The successful p-type doping of high aluminum-content (Al,Ga)N has allowed us to demonstrate operation of deep ultraviolet LEDs emitting at 274 nm. This achievement paves the way for making lasers that emit in the UV-C region of the spectrum. In this thesis, we performed preliminary work on using our structures to make UV-C lasers based on photonic crystal nanocavity structures. The nanocavity laser structures show that the threshold optical pumping power necessary to reach lasing is much lower than in conventional edge-emitting lasers. Furthermore, the photonic crystal nanocavity structure has a small mode volume and does not need mirrors for optical feedback. These advantages significantly reduce material loss and eliminate mirror loss. This structure therefore potentially opens the door to achieving efficient and compact lasers in the UV-C region of the spectrum.
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17

Eriksson, Mirjam. "Tunable diode laser absorptionspectroscopy of atomic potassium in a KOH-seeded flat flame." Thesis, Umeå universitet, Institutionen för fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-146503.

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Potassium (K) is the main ash-forming element released from biomass during thermochemical conversion. A better understanding of K chemistry and monitoring of K species is needed to optimize combustion systems. Since K species are highly reactive and prevailing concentrations depend on the conversion conditions, accurate quantification requires in situ measurement techniques. Tunable diode laser absorption spectroscopy with a single-mode distributed feedback laser is used to probe the D1 transition of atomic potassium, K(g), at 769.9 nm. The large current tuning range of the diode laser (5 cm-1) enables monitoringthe wings of the absorption profile. Fitting to the acquired line shape wings is used as astrategy to enhance the dynamic range of the sensor and measure K(g) concentrations even under optically thick condition. A potassium-rich combustion environment is simulated by converting KOH salt in a premixed methane/air flat flame. Quantitative measurements of K(g) are made at 75 positions in the flame. This yields radial K(g) profiles at three different heightsin the plume above the KOH salt and an axial profile at the burner center. The acquired average K(g) concentrations are corrected for effective plume size, i.e. the absorption pathlength determined from the radial profiles. Knowledge of the K(g) distribution in flames can lead to a better understanding of K release and primary reaction kinetics.
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18

Jangid, Vikas. "Rectenna device on coupling of molecular diodes and plasmonic nano-antennas to convert light into electricity." Electronic Thesis or Diss., Aix-Marseille, 2022. http://www.theses.fr/2022AIXM0032.

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L'utilisation massive de combustibles fossiles provoque un changement climatique et un réchauffement de la planète à un rythme alarmant. Ce travail de thèse se concentre sur le développement d'un dispositif de cellule solaire de troisième génération qui exploite la nature ondulatoire de la lumière en dépassant la limite de Schockley-Queisser. Le dispositif est appelé rectenna (antenne redresseuse) et est composé d'un couplage de nano-antennes plasmoniques et de diodes moléculaires. Le principe de fonctionnement du dispositif est le suivant : absorption de la lumière incidente par des nanocubes d'argent servant d'antennes (en haut), canalisation du flux électronique de charges par des redresseurs moléculaires à base de ferrocène (entre les deux) et substrat d'or ultra-lisse (en bas) pour réaliser l'assemblage Ag-SAM-Au. Des nanocubes d'argent fonctionnalisés avec des molécules redresseuses à base de dithiol sont auto-assemblés sur un film d'or. Lorsqu'elle est éclairée, une telle architecture rectenna permet le couplage d'un mode cavité plasmonique fortement confiné entre les nano-cubes d'argent et le plan d'or. La structure électronique et supramoléculaire des molécules est étudiée de manière approfondie, de même que la synthèse de nanocubes d'argent monodispersés et la fabrication d'un substrat d'or ultra-lisse. L'auto-assemblage Ag-SAM-Au est optimisé avec des caractéristiques électriques et optiques pour l'application de la conversion de la lumière en électricité
Massive use of fossil fuel is causing climate change and global warming at an alarming rate. The development of alternative and renewable energy resources is an urgent need of the hour. This thesis work focuses on development of a third generation solar cell device which exploits the wave nature of light surpassing the Schockley-Queisser limit. The device is called rectenna (rectifying antenna) and composed of coupling of plasmonic nano-antennas and molecular diodes. The working principle of the device is as follows: absorbing incident light by silver nanocubes as antennas (on top), channeling the electronic flow of charges by ferrocene based molecular rectifiers (in between) and ultra-smooth gold substrate (at the bottom) to make Ag-SAM-Au assembly. Silver nano-cubes functionalized with dithiol rectifying molecules are self-assembled onto a gold film. When illuminated, such a rectenna architecture allows the coupling of a strongly confined plasmon cavity mode between silver nano-cubes and the gold plane. The plasmonic coupling results in an electromagnetic field intensity enhancement up to four orders of magnitude within the cavity, exactly where the rectifying molecules are localized. The electronic and supramolecular structure of the molecules is extensively studied along with synthesis of monodispersed silver nanocubes and fabrication of ultra-smooth gold substrate, the Ag-SAM-Au self-assembly is optimized with electrical and optical characteristics for the application of light to electricity conversion
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19

Baran, Stuart George. "Gas-phase detection methods using diode lasers." Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:43e8ec07-9e1a-4060-bc8b-be75c8565600.

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Diode lasers are a convenient and economical source of near-infrared radiation, which may usefully be applied to a host of different sensitive detection methods; this thesis presents novel extensions of these methods, making use of the favourable characteristics of this type of light source. The first part of this thesis details the development of an optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) apparatus, including the development of the optical system, the sample handling, and the electronics for feedback phase control. A preliminary demonstration of the system is reported, presenting the detection of atmospheric water absorptions close to 1596 nm. Optimisation and application of the OF-CEAS spectrometer are then demonstrated, after which the spectrometer is applied to the sensitive detection of carbon dioxide absorptions suitable as a diagnostic aid in identifying Heliobacter pylori infection. A time-normalised α-min value of 5.8 × 10−9 cm−1s1/2 was measured for these spectra. Further optimisation of the system leads to an ultimate detection sensitivity of 1.42 × 10−9 cm−1s1/2, measured on absorption transitions in acetylene close to 1532 nm. In order further to characterise the performance of the OF-CEAS system, analogous experiments are presented using the OF-CEAS setup and a standard diode-laser cavity-enhanced absorption spectroscopy (CEAS) apparatus. Detection is carried out on the P(6) line of the ν1 + ν3 vibrational band of the mixed isotopologue of acetylene, 12-C13-CH2. Direct comparison is made between the sensitivities of the two methods, and in light of this the suitability of each technique for detection in different environments is considered. The well-characterised and consistent frequency scale which is inherent to the OF-CEAS technique is then applied to a line shape analysis for the presented absorption spectra. Pressure-broadening coefficients are determined for selected absorptions in the ν1 + ν3 band of acetylene. In spite of the low resolution associated with this technique, this accurate frequency scaling allows observation of subtle line shape effects such as Dicke collisional narrowing using the data presented in Chapter 3 for the R(60) line in the 3ν1 + ν3 vibrational band of CO2. These effects are quantified through use of a Galatry fit to each absorption spectrum. The statistical significance associated with the use of such a model, and the physical meaning of the results, are examined and discussed. An alternative strategy for increasing the sensitivity of a diode-laser-based gas monitoring technique lies in moving detection to the mid-infrared region, where the absorption cross-sections are generally larger. With this motivation, difference frequency generation is presented, to produce radiation close to 3.5 µm which is then applied to a series of different enhanced spectroscopy techniques. The optimal sensitivity, of 32 ppb NO2 at 45 Torr total sample pressure, was achieved using wavelength modulation spectroscopy. The different techniques are compared and possible improvements to them are put forward. Finally, proof-of-principle work is presented seeking to combine the enhanced circulating power associated with the optical-feedback-locked techniques and non-linear optical techniques to move detection to a more favourable spectral region. Light close to 429 nm is generated by second harmonic generation in a crystal of potassium niobate, with resonance-enhancement afforded by a feedback V-cavity of the sort employed in OF-CEAS. The potential of such a system for diode-laser-based generation of blue and ultraviolet light is demonstrated and discussed, along with improvements that might be implemented to increase the efficiency of the system.
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20

SILVA, Cícero Moezio da. "Travamento da freqüência de um diodo laser nas asas da ressonância de uma linha atômica." Universidade Federal de Campina Grande, 2013. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/1947.

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Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-10-10T17:10:14Z No. of bitstreams: 1 CICERO MOEZIO DA SILVA – DISSERTAÇÃO (PPGFísica) 2013.pdf: 1359216 bytes, checksum: 450c592c37b5fc9ef90ce40e270eaaae (MD5)
Made available in DSpace on 2018-10-10T17:10:14Z (GMT). No. of bitstreams: 1 CICERO MOEZIO DA SILVA – DISSERTAÇÃO (PPGFísica) 2013.pdf: 1359216 bytes, checksum: 450c592c37b5fc9ef90ce40e270eaaae (MD5) Previous issue date: 2013-08-16
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Este trabalho reporta o desenvolvimento experimental de um sistema de travamento da frequência de um diodo laser nas asas de uma linha atômica. Como sinal de erro, utilizamos a transmissão por uma célula com janelas paralelas (contendo vapor de césio) para o travamento da frequência. Mostramos que o sinal de erro é estável durante 1 hora e meia. Este sinal contemos citações nas asas da ressonância que podem ser usadas para a estabilização da frequência. Travamos a frequência entre 1860 a 2817 MHz fora da ressonância e obtemos uma estabilidade de 30MHz. A técnica descrita não necessita de campo magnético ou de detecção sensível a polarização,que simplifi ca substancialmente em relação às técnicas existentes.
In this work we demonstrate the experimental development of a system of frequency- locking of a diode laser on the wings of an atomic line. As an error signal, we use the transmission through a cell with parallel windows (containing cesium vapor) for the frequency-locking. We show that the error signalis stable for one hour and a half and has oscillations in the wings of the resonance that can be used tostabilize the frequency. We locked the frequency between 1860-2817 MHz out of resonance and obtained a stability of 30MHz. The described technique does not require a magnetic field or polarization-sensitive detection, whichs impli es substantially over existing techniques.
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21

Gravelle, Simon. "Nanofluidics : a theoretical and numerical investigation of fluid transport in nanochannels." Thesis, Lyon 1, 2015. http://www.theses.fr/2015LYO10238.

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Cette thèse décrit diverses situations liées au transport fluidique aux nano-échelles. Le premier chapitre est une introduction à la nanofluidique qui contient une revue des longueurs caractéristiques, des forces et des phénomènes présents aux nano-échelles. Le deuxième chapitre est une étude de l'impact de la géométrie sur la perméabilité hydrodynamique d'un nanopore. Inspirée par la forme des aquaporines, cette étude suggère une optimisation possible pour des canaux biconiques. Le troisième chapitre est une étude du remplissage capillaire dans des canaux sub-nanométriques en carbone. Cette étude montre l'importance de la pression de disjonction induite par la structure du fluide sur le remplissage. Le quatrième chapitre est une étude d'une diode nanofluidique, un composant connu pour imiter le comportement d'une diode à semi-conducteur. On montre qu'un fort couplage entre l'eau et la dynamique des ions entraîne une rectification du flux d'eau à l'intérieur de la diode. Le cinquième et dernier chapitre est une étude de l'origine du bruit rose (1=f) communément observé lors des mesures de courant ionique dans les nanopores
This thesis discusses various situations linked to transport at the nanoscale. The first chapter is an introduction to nanofluidics, containing a review of characteristic lengths, forces, or phenomena existing at the nanoscale. The second chapter is a study of the impact of geometry on the hydrodynamic permeability of a nanopore. This study, inspired by the shape of aquaporins, suggests a possible optimisation of permeability for bi-conical channels. The third chapter is a study of capillary filing inside subnanometric carbon channels which highlights the importance of the disjoining pressure induced by the fluid structuring inside the nanochannel. The fourth chapter is a study of nanofluidic diode, a component known to mimic the behaviour of semiconductor diode. The study highlights a strong coupling between water and ion dynamics which leads to a water flow rectification inside the diode. The fifth and last chapter is a study of the origin of commonly observed pink noise (1=f) in ionic current measurements through nanopores
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22

McBride, Patrick M. "The Effect of Polarization and InGaN Quantum Well Shape in Multiple Quantum Well Light Emitting Diode Heterostructures." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/822.

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Previous research in InGaN/GaN light emitting diodes (LEDs) employing semi-classical drift-diffusion models has used reduced polarization constants without much physical explanantion. This paper investigates possible physical explanations for this effective polarization reduction in InGaN LEDs through the use of the simulation software SiLENSe. One major problem of current LED simulations is the assumption of perfectly discrete transitions between the quantum well (QW) and blocking layers when experiments have shown this to not be the case. The In concentration profile within InGaN multiple quantum well (MQW) devices shows much smoother and delayed transitions indicative of indium diffusion and drift during common atomic deposition techniques (e.g. molecular beam epitaxy, chemical vapor deposition). In this case the InGaN square QW approximation may not be valid in modeling the devices' true electronic behavior. A simulation of a 3QW InGaN/GaN LED heterostructure with an AlGaN electron blocking layer is discussed in this paper. Polarization coefficients were reduced to 70% and 40% empirical values to simulate polarization shielding effects. QW shapes of square (3 nm), trapezoidal, and triangular profiles were used to simulate realistic QW shapes. The J-V characteristic and electron-hole wavefunctions of each device were monitored. Polarization reduction decreased the onset voltage from 4.0 V to 3.0 V while QW size reduction decreased the onset voltage from 4.0 V to 3.5 V. The increased current density in both cases can be attributed to increased wavefunction overlap in the QWs.
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23

Mohib, Abdul. "Molecular diodes." Thesis, Cranfield University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439279.

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24

Siladie, Alexandra-Madalina. "Nanofils AlxGa1-xN et AlN pour la réalisation de diodes émettant dans l'UV-C." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY059.

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La thèse sera consacrée à la croissance par épitaxie par jets moléculaires d’hétérostructures AlGaN/GaN de type filaire, incluant leur dopage de type n et de type p. La caractérisation des propriétés structurales et optiques de ces hétérostructures sera menée à bien en combinant des expériences de microscopie électronique à balayage, de spectroscopie de la photoluminescence, de diffraction de RX. Dans le cadre d’un partenariat national et international, des études de nanocathodoluminescence à haute résolution et de Kelvin probe seront également menées. Finalement, on réalisera des structures complètes de LEDs émettant dans la gamme de l’UV C (environ 250-280 nm), en collaboration étroite (dans le cadre d’un projet ANR) avec le CNRS/Institut Néel qui prendra en charge le dépôt d’une électrode conductrice en diamant, l’étape de processing et les caractérisations électriques
Because of their band gap value extending from 0.68 eV (for InN) up to 3.5 eV (GaN) and 6.2 eV (AlN), nitride family is potentially well adapted to the realization of light emitting diodes (LEDs) or detectors in a wavelength range spanning from infrared to ultraviolet. In particular, the possibility to realize devices emitting in the UV C range (200-280 nm) is a current subject of interest, in relation with numerous applications such as air and water sanitization, counterfeiting detection, sensors etc… Contrary to the visible LEDs which exhibit an excellent efficiency (at least for blue emission, which, coupled to a yellow phosphor is at the base of standard white LEDs currently available on the market), UV LEDs efficiency is currently limited to a few percent, as a consequence of the lack of suitable substrates, which results in defective material, and of doping difficulties, which limit current injection. One innovative solution to overcome these difficulties consists of using nanowires (NWs): the remarkable geometry (small diameter) and aspect ratio (height/diameter) of these objects make them favorable to the realization of heterostructures free of extended defects, therefore limiting carrier non radiative recombination. Furthermore, as a major advantage, electrical doping of NWs (type n with Si, type p with Mg) is considerably eased in NWs, as a result of an improved elastic strain relaxation, which significantly pushes away the dopant incorporation limit to values higher than in 2D layers used for conventional UV LEDs to date. The combination of these advantages make UV emitting NWs a subject of intense interest, with the prospect of realizing a breakthrough in efficiency. We are partially funded by an ANR project to explore this road. In this context, the proposed PhD project will consist of growing and fully characterizing the structural and optical properties of AlxGa1-xN/ AlyGa1-yN / AlxGa1-xN NW heterostructures (cathodo- and photo-luminescence, high resolution electron microscopy, atom probe and Kelvin probe measurement, etc…) with the prospect of realizing innovative, highly efficient UV LEDs in the range 240-270 nm. The process of the final structures and their electrical characterization will be performed by CNRS-Néel, after deposition of a doped-diamond upper contact. The work will be mostly performed in the Nanophysics and semiconductor CNRS/CEA group in CEA-INAC, which has an internationally recognized expertise in the academic studies on nitride materials, in close collaboration with several academic groups in France and abroad (CNRS-Néel, CNRS-LPS, University of Valencia….)
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25

Bernard, Alice. "Towards an electrically-injected optical parametric oscillator." Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC104/document.

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Le travail présenté dans cette thèse porte sur la conception, la fabrication et la caractérisation de sources prévues pour fonctionner à la fois comme diode laser et comme oscillateur paramétrique optique. Ces lasers sont conçus pour émettre sur un mode d’ordre supérieur afin de permettre une conversion de fréquence paramétrique avec les modes fondamentaux du guide à la fréquence moitié. La diode laser et l’OPO partagent la même cavité optique ; pour assurer l’accord de phase et corriger les écarts à la structure nominale induits lors de l’élaboration par épitaxie, la largeur de ruban est utilisée comme paramètre de contrôle des indices efficaces. Les diodes proposées sont donc étroites (3-5 µm) et gravées profondément. En conséquence, il est potentiellement intéressant d’utiliser des boîtes quantiques pour limiter les recombinaisons non radiatives sur les flancs. Dans le cadre de ce travail, nous avons conçu des diodes basées sur ce principe pour les deux systèmes GaAs/AlGaAs et InGaAsP/InP, qui permettent respectivement d’obtenir potentiellement une émission OPO au voisinage de 2 µm ou de 3 µm. Dans le cas de l’InGaAsP/InP, nous avons étudié au préalable l’indice de réfraction des alliages InGaAsP dans une plage de longueur d’onde jusque-là non couverte par la littérature. Ces données ont été acquises via des mesures d’indice efficace (m-lines) de couches guidantes d’InGaAsP épitaxiées en accord de maille sur un substrat d’InP. Pour des structures laser-OPO optimisées, les simulations montrent que le seuil OPO devrait être obtenu pour une puissance de pompe intracavité de quelques centaines de mW, qu’il est réaliste d’atteindre pour des diodes laser à l’état de l’art. Nous avons étudié les propriétés électro-optiques de diodes lasers à puits quantiques GaAs/AlGaAs réalisées sur la base de nos dessins; l’observation de l’effet laser sur le mode TE2 valide le dessin vertical original de nos diodes lasers. En vue de la fabrication de laser-OPO à ruban étroit, nous avons développé des procédés de fabrication nouveaux sur la Plateforme Technologique Amont (CEA – Grenoble), notamment la gravure profonde (>10 µm) par ICP-RIE. Enfin, nous avons proposé un concept alternatif de diode-OPO, comprenant des cavités laser et OPO distinctes couplées par un taper adiabatique
The work presented in this thesis deals with the design, fabrication and characterization of sources intended to function as both laser diodes and optical parametric oscillators. These lasers are designed to emit on a higher order mode to allow parametric frequency conversion with fundamental modes of the guide at half frequency. The laser diode and OPO share the same optical cavity; to ensure phase matching and correct nominal structure deviations induced during epitaxial processing, the ridge width is used as a control parameter of the effective indices. The proposed diodes are therefore narrow (3-5 μm) and etched deeply. Consequently, it is potentially interesting to use quantum dots to limit non-radiative recombination on the sidewalls. In the context of this work, we have designed diodes based on this principle for the two GaAs/AlGaAs and InGaAsP/InP systems, which respectively allow to potentially obtain an OPO emission in the vicinity of 2 μm or 3 μm. In the case of InGaAsP/InP, we previously studied the refractive index of InGaAsP alloys in a wavelength range not covered by literature to this day. This data was acquired via effective m-line index measurements of InGaAsP guiding layers epitaxially grown on and lattice-matched to an InP substrate. For optimized laser-OPO structures, simulations show that the OPO threshold should be obtained for an intracavity pump power of a few hundred mW, which is realistic to achieve for state-of-the-art laser diodes. We have studied the electro-optical properties of GaAs/AlGaAs quantum well laser diodes made on the basis of our designs; the observation of the laser effect on the TE2 mode validates the original vertical design of our laser diodes. For the manufacture of narrow-ridge lasers-OPOs, we have developed new manufacturing processes on the Plateforme Technologique Amont (Upstream Technology Platform, CEA - Grenoble), including deep etching (> 10 μm) by ICP-RIE. Finally, we have proposed an alternative diode-OPO concept, comprising distinct laser and OPO cavities coupled by an adiabatic taper
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26

Zhou, Xin. "Towards voltage-gated ion channels, molecular diodes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape16/PQDD_0012/NQ32730.pdf.

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27

Kwong, Chin Fai. "Molecularly doped organic electroluminescent diodes." HKBU Institutional Repository, 2000. http://repository.hkbu.edu.hk/etd_ra/254.

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28

Apostol, Petru. "Synthèse et propriétés de cristaux liquides et magnétiques de 1,8,15,22-tétraalkoxy-phtalocyanines de métaux (II) et (III)." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0109/document.

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Cette thèse décrit dans un premier temps la synthèse entièrement régiosélective de phtalocyanines tétra-(endo-alcoxy)-fonctionnalisées puis la formation de leurs complexes avec des ions métalliques. Dans un second temps sont étudiées leurs propriétés magnétiques, l'induction de mésophases colonnaires dans des gammes de températures convenables et avec des tailles modérées de substituants, ainsi que leur utilisation dans des diodes organiques. L'approche synthétique à suivre est la cyclo-tétramérisation de 3-(2-alkylalcoxy)-phtalonitriles suivie de la coordination d'un ion métallique. La symétrisation des chaînes aliphatiques dans le précurseur 3-alcoxy-phtalonitrile, en allant de 2 butyloctyl à 2-pentylheptyl, maintient la régiosélectivité et le mésomorphisme, tandis que les courtes chaînes 2-butylhexyl mènent à la formation d'un mélange de phtalocyanines régioisomères et à une plus grande tentance à la crystallisation. La combinaison de températures de clarification raisonnables avec un empilement colonnaire à température ambiante et avec une proportion assez importante de centres conjurés au sein de la masse moléculaire rend les deux premières séries de matériaux, c'est-à-dire MPc(OCH2CHBuHex)4, and MPc(OCH2CHPent2)4, potentiellement utiles comme transporteurs de charges uniformément orientables dans des dispositifs électroniques organiques. Nous démontrons que ces matériaux phtalocyanines tétra-α-alcoxy-substitués, représentés par H2Pc(OCH2CHBuHex)4, NiPc(OCH2CHBuHex)4 et CuPc(OCH2CHBuHex)4, mènent à des performances originales des dispositifs quand ils sont utilisés comme couche active organique dans des structures simples de diode ITO/PEDOT :PSS/PC/Al. Un redressement prononcé du courant est obtenu dans des diodes malgré l’alignement planaire prépondérant des colonnes dans les couches. Le ligand Pc tétra-α-alcoxy-substitué très soluble donne des molécules-aimants mononucléaires originales par coordination avec MnIII et DyIII. Remarquablement, l’isomère de symétrie C4h du complexe sandwich octa-alcoxy se forme sélectivement grâce aux subsistants encombrants sur les deux cycles Pc
This thesis describes the fully regioselective synthesis of symmetric all-endo tetra-alkoxy-functionalized phthalocyanines and their metal ion complexes accompanied by induction of columnar mesophases in convenient temperature ranges at moderate substituent sizes, as well as their use in organic diodes and the study of their magnetic properties. The synthetic approach to follow is lithium-induced macrocyclization of 3-(2-alkylalkoxy)-phthalonitriles prior to transition meatl ion insertion. Symmetrization of the aliphatic chains in the 3-alkoxy-phthalonitrile precursor from 2-butylocytyl to 2-pentylheptyl maintains both the regioisomeric mixture during the cyclo-tetramerization and to a somewhat greater tendency to crystallization. The combination of attainable clearing temperatures with room temperature columnar stacking and with a relatively high content of conjugated core within the molecular mass makes the first two series of materials, i.e. MPc(OCH2CHBuHex)4, and MPc(OCH2CHPent2)4, potentially useful as uniformly orientable charge transposters in organic electronic devices. We establish that these tetra-α-alkoxy substituted phthalocyanine materials, as exemplified with H2Pc(OCH2CHBuHex)4, NiPc(OCH2CHBuHex)4 and CuPc(OCH2CHBuHex)4, lead to original device performances when applied as an active organic layer in simple ITO/PEDOT:PSS/PC/Al diode structures. A pronounced current rectification of the diodes is obtained despite the preponderantly planar alignment of the columns in the films. The highly soluble tetra-α-alkoxy-substituted Pc ligand, when combined with MnIII and DyIII, gives rise to original mononuclear single molecule magnets. Remarkably, the C4h-symmetric isomer of the octa-alkoxy double decker complex is formed selectively due of presence of the bulky substituents on both Pc rings
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29

Jami, Avinash. "Fused-Molecular Systems for Organic Light Emitting Diodes." TopSCHOLAR®, 2015. http://digitalcommons.wku.edu/theses/1543.

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Organic light emitting diodes (OLEDs) are electronic devices made by sandwitching organic light emissive materials between two electrodes. When voltage is applied across the two conductors, a bright light is generated. The color of the emitting light depends on the band gap of the semiconducting material. The work described here focuses on designing and synthesizing narrow band gap molecular systems derived from fused-arene derivatives for producing organic blue light emitting diodes. Three molecular systems derived from anthracene, pyrene, and carbazole, were designed and synthesized. Two molecular systems of anthracen-9-ylmethyl anthracene-9- carboxylate and pyren-1-ylmethyl 4-bromobenzoate were synthesized through Steglich esterification reaction and the third, pyren-1-ylmethyl 4-(9-hexyl-6-{4-[(pyren-1- ylmethoxy) carbonyl] phenyl}-9H-carbazol-3-yl) benzoate was synthesized by Grignard metathesis followed by Kumada coupling reaction. Structural characterizations were performed using 1H, 13C NMR and FTIR analysis. Photophysical properties of these systems were studied in chloroform (CHCl3) solution using UV-visible and Fluorescence spectroscopies. The absorption and fluorescence emission spectra revealed the potential applicability of these three systems as blue and blue-green emitters for OLEDs. The future work of this project will focus on utilizing these three molecular systems to fabricate OLED devices.
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30

Hansford, Graeme Mark. "Diode laser infrared spectroscopy of jet-cooled polyatomic molecules." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321031.

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31

O'Sullivan, Paul John. "Infrared diode laser spectroscopy of transient phosphorus-bearing molecules." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613757.

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AL-SHADEEDI, AKRAM. "LATERAL AND VERTICAL ORGANIC TRANSISTORS." Kent State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=kent1492441683969202.

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33

Tai, Feng-i. "Photochromic molecules in polymer switch diodes." Thesis, Linköping University, Department of Science and Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-6810.

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Photochromism has been investigated extensively during recent years. The large interest for information storage in memory applications is associated with the bi-stable character of the photochromism phenomena. In molecular photochromics, two isomers with different absorption spectrum can be obtained according to the specific wavelength of the light exposure. This reversible transformation process can be considered as optical writing/erasing step of a memory.

Here we first report the absorption spectra of solid-state films based on the blends consisting of PC molecules, the spirooxazine 1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3’-[3H]phenanthr[9,10-b](1,4)oxazine] (PIII, Sigma-Aldrich, 32,256-3) and a polymer matrix host, poly(2-methoxy-5(2’-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV). The bi-stability in conjugated polymer matrix is studied by following the time evolution of the optical properties of the blends.

Thereafter, the electrical performance of PC-polymer diodes is characterized and reported. While the PIII molecules in the blend bulks are switched to their low energy gap state, forming external energy levels above the valence band of MEH-PPV, the injected charges (hole-dominated) will be trapped by the low energy gap isomer of PIII and that leads to current modulation. PIII molecules can be switched between two energy gap states upon the photo-stimulation, and the I-V characteristics of the device can also be controlled reversibly via the photoisomerization. The retention time of the diode’s electrical switching fits quite well with the absorption characteristics of the blend films; this correspondence builds a good link between the film property and the device behavior.

Furthermore, we observed a two-trap system in the blend diodes from the I-V curves, and a model is proposed which can explain the schematic concept of the trap-limited current modulation. To combine the knowledge and information from the investigations above, we tested a novel device design based on a bi-layer of the PC and polymer materials, and the promising result for future work is presented in the end.

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Tai, Feng-I. "Photochromic molecules in polymer switch diodes." Thesis, Linköpings universitet, Institutionen för teknik och naturvetenskap, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-6810.

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Photochromism has been investigated extensively during recent years. The large interest for information storage in memory applications is associated with the bi-stable character of the photochromism phenomena. In molecular photochromics, two isomers with different absorption spectrum can be obtained according to the specific wavelength of the light exposure. This reversible transformation process can be considered as optical writing/erasing step of a memory. Here we first report the absorption spectra of solid-state films based on the blends consisting of PC molecules, the spirooxazine 1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3’-[3H]phenanthr[9,10-b](1,4)oxazine] (PIII, Sigma-Aldrich, 32,256-3) and a polymer matrix host, poly(2-methoxy-5(2’-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV). The bi-stability in conjugated polymer matrix is studied by following the time evolution of the optical properties of the blends. Thereafter, the electrical performance of PC-polymer diodes is characterized and reported. While the PIII molecules in the blend bulks are switched to their low energy gap state, forming external energy levels above the valence band of MEH-PPV, the injected charges (hole-dominated) will be trapped by the low energy gap isomer of PIII and that leads to current modulation. PIII molecules can be switched between two energy gap states upon the photo-stimulation, and the I-V characteristics of the device can also be controlled reversibly via the photoisomerization. The retention time of the diode’s electrical switching fits quite well with the absorption characteristics of the blend films; this correspondence builds a good link between the film property and the device behavior. Furthermore, we observed a two-trap system in the blend diodes from the I-V curves, and a model is proposed which can explain the schematic concept of the trap-limited current modulation. To combine the knowledge and information from the investigations above, we tested a novel device design based on a bi-layer of the PC and polymer materials, and the promising result for future work is presented in the end.
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35

Worthing, Philip Thomas. "Molecular fluorescence from microcavities." Thesis, University of Exeter, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302668.

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36

Trasobares, Sánchez Jorge. "High frequency electronics on nanodot molecular junctions : interaction between molecules, ions and waves." Thesis, Lille 1, 2015. http://www.theses.fr/2015LIL10168/document.

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Une combinaison entre l’assemblage de monocouches au sommet de nano-cristaux d’or et la microscopie à sonde locale permet d’explorer l’interaction entre les molécules actives et son milieu, mais aussi démontrer expérimentalement une diode moléculaire peut travailler à haute fréquence. La fabrication des nanocristaux d’or par lithographie électronique rapide nous a permis leur caractérisation par des techniques nécessitant des surfaces millimétrique, mais également par des techniques en champ proche. La détection electrochimique d’un petit nombre de molécules par nanocrystal prévoit d’intéressantes recherches futures sur l’attache et la détection de molécules uniques sur la nano-particule d’or. D’un côté, cette étude confirme une théorie récente: les effets coopératifs entre les molécules ont un effet d’asymétrie sur « la courbe d’histogramme de conductance ». D’un autre côté, des théories d’électrochimie ont été utilisées pour investiguer les effets d’interaction entre molécules avec groupe redox et l’écart-type de l’énergie moléculaire. Cette étude nous a permis d’extraire des gammes d’énergie de couplage entre molécules, un premier pas vers une estimation quantitative expérimentale de ce paramètre clé pour les applications en électronique organique. A l’aide d’un AFM couplé à un système de mesure en hyperfréquences, nous mesurons les propriétés électroniques à l’échelle nanométrique. Nous prouvons une diode moléculaire à 18 GHz avec un ratio de redressement de 12 dB (facteur 4) à cette fréquence. Des petites capacitances, dans la gamme de l’aF ont en particulier permis d’observer ce comportement à hautes fréquences
An attractive combination of self-assembled monolayers on top of “Au” single crystal Nanoparticles (AuNp) and Scanning Probe Microscopies permits to explore the interaction between active molecules in the junction, as well as with the media. At the same time, we demonstrate the experimental proof of a molecular rectifying diode working at gigahertz frequency. Device fabrication by fast e-beam lithography allows their characterization by techniques that may need millimeter scale surfaces as well as by near field Scanning Probe Microscopies. Detection of a little number of molecules per AuNP promises interesting future research in the challenge of grafting and detecting single molecules per nanoparticle. On the one hand, this investigation confirms a recent theoretical prediction that cooperative effects between molecules may have an effect on the asymmetry of the conductance histogram line shape. On the other hand, established electrochemical theories are exploited to investigate similar factors such as interaction between redox molecules and the modification of the energy level of molecular orbitals. This study permits extracting a range of coupling energies between molecules that may be a first step towards the quantitative experimental estimation of this key parameter in molecular electronics. Thanks to an AFM connected to Network analyzer, we characterize a molecular diode operating at high frequency to 18 GHz with a rectification ratio of 12 dB (factor 4) at this frequency. Small capacitances in the order of few aF permit to see this behavior at high frequencies
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Selvaranjan, Selvadurai. "Processable molecular lanthanide chelates for organic light emitting diodes (OLEDs)." Thesis, London South Bank University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.618667.

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38

Bell, I. S. "Novel phosphorus-bearing transient molecules studied by infrared diode laser spectroscopy." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596544.

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Studies of the reaction of white phosphorus vapour with oxygen are of considerable fundamental and practical interest. The reaction produces an intense chemiluminescence, although the identity of the emitting species has been controversial. In the experiments reported in this thesis, the phosphorus glow has been probed directly using infrared diode laser absorption spectroscopy to detect some of the transient intermediates present. The introductory chapter presents a review of the advantages of using lasers over conventional sources as spectroscopic tools. Lasers output light of a monochromatic nature, enabling extremely high resolution measurements to be made, whilst their high power engenders excellent sensitivity. The development of tunable infrared sources, especially the semiconductor diode laser, is also described. A review of previous spectroscopic measurements of transient phosphorus-bearing species is then presented, along with a discussion of some of the applications associated with their observation. A diode laser spectrometer equipped with a multi-pass (White) cell has been used to study such short-lived species in the experiments reported in this thesis, and is described in chapter 2. The transient species PO and PO2 have previously been observed in this laboratory. Chapter 3 presents the first reliable rotational assignment of P2O molecule, observed in the reaction of oxygen atoms with white phosphorus vapour. The addition of NO to this reaction mixture was then found to produce PNO, another analogue of N2O, as described in chapter 4. The upper state of the N=O stretching fundamental of the PNO molecule was found to be perturbed, enabling an absolute assignment of the infrared spectrum of this band to be made. This reaction opens the door to a range of novel species that may be produced in this system. The next two chapters describe the addition of halogen molecules to the phosphorus glow, producing the ClPO and BrPO molecules. Their infrared spectra have been assigned with the aid of a Loomis-Wood spectral display program.
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39

Collet, Tim David [Verfasser], and J. [Akademischer Betreuer] Schmalian. "Electronic transport through correlated nanostructures: molecular diodes and steady state currents = Elektronischer Transport durch korrelierte Nanostrukturen: molekulare Dioden und Ströme in stationären Zuständen / Tim David Collet. Betreuer: J. Schmalian." Karlsruhe : KIT-Bibliothek, 2014. http://d-nb.info/1063027500/34.

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40

Kleemann, Hans. "Organic Electronic Devices - Fundamentals, Applications, and Novel Concepts." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-105059.

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This work addresses two substantial problems of organic electronic devices: the controllability and adjustability of performance, and the integration using scalable, high resolution patterning techniques for planar thin-film transistors and novel vertical transistor devices. Both problems are of particular importance for the success of transparent and flexible organic electronics in the future. To begin with, the static behavior in molecular doped organic pin-diodes is investigated. This allows to deduce important diode parameters such as the depletion capacitance, the number of active dopant states, and the breakdown field. Applying this knowledge, organic pin-diodes are designed for ultra-high-frequency applications and a cut-off-frequency of up to 1GHz can be achieved using optimized parameters for device geometry, layer thickness, and dopant concentration. The second part of this work is devoted to organic thin-film transistors, high resolution patterning techniques, as well as novel vertical transistor concepts. In particular, fluorine based photo-lithography, a high resolution patterning technique compatible to organic semiconductors, is introduced fielding the integration of organic thin-film transistors under ambient conditions. However, as it will be shown, horizontal organic thin-film transistors are substantially limited in their performance by charge carrier injection. Hence, down-scaling is inappropriate to enlarge the transconductance of such transistors. To overcome this drawback, a novel vertical thin-film transistor concept with a vertical channel length of ∼50nm is realized using fluorine based photo-lithography. These vertical devices can surpass the performance of planar transistors and hence are prospective candidates for future integration in complex electronic circuits.
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Qian, Haibo. "Diode laser spectroscopy of free radicals and other transient molecules in the gas phase." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627118.

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42

Chau, Nga Yuen. "Molecular design, synthesis and luminescent properties of new functional metallophosphors of iridium (III) and platinum (II)." HKBU Institutional Repository, 2015. https://repository.hkbu.edu.hk/etd_oa/220.

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Organic light-emitting diode (OLED) technology has found multitudinous applications in the development of solid-state lighting, flat-panel displays and flexible screens. Nowadays, the phosphorescent OLEDs based on metallophosphors can reach sufficiently high efficiencies for practical application. Recently, red, green and blue (RGB) platforms of highly efficient phosphorescent emitters have been achieved and OLEDs TV is now commercialized in the marketplace. However, the design and synthesis of innovative emitter materials play an important role in commercialization of the OLED technology. The basic concept of OLED is herein discussed in chapter 1 putting main focus on phosphorescent iridium(III) complexes. In chapter 2, a series of cyclometalated iridium(III) complexes containing 2-(4-benzylphenyl)pyridine have been synthesized and different electron-donating and electron-withdrawing substituents were attached on the pyridyl ring in the ligand. The device D6 doped with 8 wt% B4 gave the excellent OLED performance with a peak of external quantum efficiency (ext) of 21.4%, power efficiency (P) of 51 lm/W and current efficiencyL) of 76.3 cd/A, which is much higher than that of commercial available fac-Ir(ppy)3 under the same operation condition. These findings draw our attention to the fact that a weak electron-donating benzyl group could alleviate intermolecular aggregation in the solid state, thus improving the device performance. The bulky moiety introduced on 2-phenylpyridine through a CH2 spacer in the ligands could suppress the triplet-triplet annihilation in their metal complexes. Cylcometalating ligands and their respective metal complexes have been fully characterized by 1H and 13C NMR spectroscopy and matrix-assisted laser desorption inoization-time of flight (MALDI-TOF) mass spectrometry. In chapter 3, a series of thiazole-based iridium(III) complexes have been synthesized and characterized. It is considered that the thiazole moiety is infrequently used for organic semiconducting materials. To have a better understanding on this functional unit, different hole-transporting groups (eg, carbazole or fluorene) are attached to the thiazole ring in the cyclometalating ligands in order to tune the HOMO and LUMO levels of the complexes. Device D29 doped with 8 wt% T2 gave the highest L of 35.8 cd/A and ext of 11.1%. This result implied that thiazole moiety is an alternative option to afford a new class of cyclometalating ligands for OLED research. In chapter 4, a series of cationic iridium(III) complexes bearing diimine ligand have been synthesized and characterized. The diimine ligands were decorated with the sterically bulky groups. As self-aggregation could deteriorate the device efficiency, this molecular design strategy can diminish the aggregation-caused quenching problems, which has been supported by the aggregation-induced emission enhancement present in complexes E2 and E3. In Chapter 5, a series of bis-tridentate iridium(III) complexes have been synthesized and characterized. Our challenging is to design two types of tridentate chelates (ie. monoanionic and dianionic ligands) for balancing the charge on the metal center. Besides, these chelates should be a good cyclometallate to coordinate with the iridium metal. Four compounds with different dianionic tridentate chelates were designed to achieve distinct color emission. Compound K4 exhibited extremely high quantum yield of 85.5%. This finding revealed that the metal complex featuring two tridentate chelates is a promising phosphorescent dye in OLED. Lastly, the concluding remarks and the experimental details of all the compounds in the previous chapters were included in Chapters 6 and 7.
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43

Matta, Samuel. "AlGaN quantum dots grown by molecular beam epitaxy for ultraviolet light emitting diodes." Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTS042/document.

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Ce travail porte sur la croissance par épitaxie sous jets moléculaires (EJM) et sur les propriétés structurales et optiques de boîtes quantiques (BQs) AlyGa1-yN insérées dans une matrice AlxGa1-xN (0001). L’objectif principal est d’étudier le potentiel des BQs en tant que nouvelle voie pour la réalisation d’émetteurs ultraviolets (UV) efficaces.Tout d'abord, nous avons étudié la croissance des BQs GaN en utilisant soit une source plasma (N2, appelée PAMBE) soit une source ammoniac (NH3, appelée NH3-MBE) afin de choisir la meilleure approche pour former les BQs les plus efficaces. Il a été montré que le procédé de croissance est mieux contrôlé en utilisant l’approche PAMBE, conduisant à la croissance de BQs GaN avec des densités plus élevées, une meilleure uniformité en taille et des intensités de photoluminescence (PL) jusqu’à trois fois plus élevées. En outre, l'influence de la contrainte épitaxiale sur le processus d'auto-assemblage des BQs a été étudiée en fabriquant des BQs GaN sur différentes couche tremplins d’AlxGa1-xN (avec 0,5 ≤ x ≤ 0,7). Nous avons montré que des BQs avec des densités plus élevées et des hauteurs plus faibles sont formées en augmentant le désaccord de paramètre de maille (c.à.d en utilisant des tremplins avec xAl plus élevé). Cependant, les mesures de photoluminescence (PL) indiquent un fort décalage de l'énergie d'émission vers le rouge lorsque xAl augmente, en raison de l'augmentation de la discontinuité du champ électrique interne de 3 à 5,3 MV/cm.Ensuite, des études approfondies sur les conditions de croissance et les propriétés optiques des BQs Al0,1Ga0,9N / Al0,5Ga0,5N ont été présentées, montrant les différents défis pour fabriquer des BQs efficaces. L’optimisation de la procédure de croissance, notamment l’étape de recuit post-croissance, a montré une modification de la forme des BQs. Plus précisément, un changement d’une forme allongée (pour un recuit à 740 °C), à une forme symétrique (pour un recuit à une température proche de ou supérieure à 800°C) a été observé. En plus, une bande d’émission supplémentaire vers les plus grandes longueurs d’onde a également été observée pour les BQs formées avec un recuit à 740°C. Cette bande a été attribuée à une fluctuation de composition des BQs, induisant la formation d’une famille additionnelle de BQs avec des hauteurs plus grandes et une compostions en Al inférieure à 10 %, estimée proche de l’alliage binaire GaN. Enfin, il a été démontré qu’en faisant un recuit à plus haute température (≥ 800°C), l’émission de PL de cette famille supplémentaire de BQs (BQs riche en Ga ou (Al)GaN) diminue très fortement. De plus, cette étape de recuit impacte fortement la forme des BQs et a conduit à une amélioration de leur efficacité radiative d’un facteur 3. Ensuite, la variation de la composition en Al des BQs AlyGa1-yN (0,1 ≤ y ≤ 0,4), ainsi que la quantité de matière déposée ont permis d’évaluer la gamme de longueurs d’onde d’émission accessibles. En ajustant les conditions de croissance, l’émission des BQs a été déplacée de l’UVA vers l’UVC, atteignant une émission autour de 270 - 275 nm (pour les applications de purification de l’eau et de l’air) avec des rendements radiatifs élevés. Les mesures de photoluminescence résolue en temps (TRPL), combinées avec les mesures de PL en fonction de la température, nous ont permis de déterminer les efficacités quantiques internes (IQE) des BQs GaN / AlxGa1-xN (0001). Des valeurs d’IQE comprises entre 50 % et 66 % ont été obtenues à basse température, avec la possibilité d’atteindre un rapport d’intensité intégré de PL, entre 300 K et 9 K, allant jusqu’à 75 % pour les BQs GaN et 46 % pour les BQs AlyGa1-yN (contre 0,5 % pour des structures équivalents à base de puits quantiques).Enfin, nous avons montré la possibilité de fabriquer des DELs à base de BQs (Al,Ga)N couvrant une grande gamme de longueurs d’onde allant du bleu-violet jusqu’à l’UVB (de 415 nm à 305 nm)
This PhD deals with the epitaxial growth, structural and optical properties of AlyGa1-yN quantum dots (QDs) grown on AlxGa1-xN (0001) by molecular beam epitaxy (MBE), with the aim to study their potential as a novel route for efficient ultraviolet (UV) emitters.First, we have studied the growth of GaN QDs using either plasma MBE (PAMBE) or ammonia MBE (NH3-MBE) to find the most adapted nitrogen source for the fabrication of UV emitting QDs. It was shown that the growth process is better controlled using PAMBE, leading to the growth of GaN QDs with higher densities, better size uniformity and up to three times higher photoluminescence (PL) intensities. Also, the influence of the epitaxial strain on the QD self-assembling process was studied by fabricating GaN QDs on different AlxGa1-xN surfaces (with 0.5 ≤ x ≤ 0.7). We showed that QDs with higher densities and smaller sizes (heights) are formed by using a larger lattice-mismatch (i.e. a higher xAl composition). However, photoluminescence (PL) measurements indicated a strong redshift in the emission energy as the Al content of the AlxGa1-xN template increases due to the increase of the internal electric field discontinuity from 3 to 5.3 MV/cm.Next, in-depth investigations of the growth conditions and optical properties of Al0.1Ga0.9N QDs / Al0.5Ga0.5N were done presenting the different challenges to be solved to grow efficient QDs. Changing the growth procedure, especially the post-growth annealing step, has shown a modification of the QD shape from elongated QDs, formed with an annealing at 740°C, to symmetric QDs, formed with an annealing at a temperature around or above 800°C. An additional band emission at lower energies was also observed for QDs grown with a lower annealing temperature (740°C). This additional band emission was attributed to the formation of QDs with higher heights and a reduced Al composition less than the nominal one of 10 % (i.e. forming Ga-rich QDs). The influence of the annealing step performed at higher temperature has been shown to strongly decrease the PL emission from this additional QD family. In addition, this annealing step strongly impacted the QD shape and led to an improvement of the QD radiative efficiency by a factor 3. Then, the AlxGa1-xN barrier composition (0.5 ≤ x ≤ 0.7), the AlyGa1-yN QD composition (0.1 ≤ y ≤ 0.4) as well as the deposited amount were varied in order to assess the range of accessible emission energies. Also, the influence of varying the AlxGa1-xN barrier composition on the QD formation was studied. By varying these growth conditions, the QD wavelength emission was shifted from the UVA down to the UVC range, reaching a minimum wavelength emission of 270 - 275 nm (for water and air purification applications) with a high radiative efficiency. Time resolved photoluminescence (TRPL) combined with temperature dependent PL measurements enabled us to determine the internal quantum efficiencies (IQE) of AlyGa1-yN QDs / AlxGa1-xN (0001). IQE values between 50 % and 66 % were found at low temperature, combined with the ability to reach a PL integrated intensity ratio, between 300 K and 9 K, up to 75 % for GaN QDs and 46 % for AlyGa1-yN QDs (versus 0.5 % in a similar quantum well structure emitting in the UVC range).Finally, the demonstration of AlyGa1-yN QD-based light emitting diode prototypes, emitting in the whole UVA range, using GaN and Al0.1Ga0.9N QDs, and in the UVB range down to 305 nm with Al0.2Ga0.8N QDs active regions, was shown
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44

Jansson, Emil. "Electronicharacterization of molecules with application to organic light emitting diodes." Licentiate thesis, KTH, School of Biotechnology (BIO), 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4349.

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The presented thesis is devoted to the field of organic light emitting

diodes (OLEDs). Time-dependent Kohn-Sham density functional theory

(TDDFT) is applied

in order to eludicate optical properties such as fluorescence and

phosphorescence for some of the most important materials. The

accuracy of TDDFT is evaluated with respect to the calculated absorption

and emission spectra for commonly used light emitting polymers.

A continuation of this work is devoted to Polyfluorene as this polymer

has proven to be very promising. In this study the chain

length dependence of its singlet and triplet excited states is

analyzed as well as the excited state structures.

Understanding the phosphorescence mechanism of tris(2-phenylpyridine)Iridium is

of importance in order to interpret the high efficiency of OLEDs

containing these specimens. The mechanism is analyzed by calculating

the electric transition dipole moments by means of TDDFT using

quadratic response functions.

As not only the optical properties are essential for effective

devices, electron transfer properties are addressed. The electron

transfer capability of the sulfur and nitrogen analogues of Oxadiazole

is evaluated through their internal reorganization energy.

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45

Hauksson, Isak Sverrir. "Investigation of spontaneous and stimulated emission from ZnSe epilayers and ZnCdSe-ZnSe quantum well systems grown by molecular beam epitaxy." Thesis, Heriot-Watt University, 1996. http://hdl.handle.net/10399/749.

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46

Karabaeva, Kanykey E. "Photochemistry of Masked Pyrene-4,5-Dione." Bowling Green State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1371083757.

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47

Horne, Kyle S. "Nano-scale Thermal Property Prediction by Molecular Dynamics Simulation with Experimental Validation." DigitalCommons@USU, 2014. https://digitalcommons.usu.edu/etd/3089.

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Quantum cascade laser (QCL) diodes have potential applications in many areas including emissions analysis and explosives detection, but like many solid-state devices they suer from degraded performance at higher temperatures. To alleviate this drawback, the thermal properties of the QCL diodes must be better understood. Using molecular dynamics (MD) and photothermal radiometry (PTR), the thermal conductivity of a representative QCL diode is computed and measured respectively. The MD results demonstrate that size eects are present in the simulated systems, but if these are accounted for by normalization to experimental results the thermal conductivity of the QCL can be reasonably obtained. The cross-plane conductivity is found to be in the range of 1.8 to 4.3 W=m K, while the in-plane results are in the range of 3.7 to 4.0 W=m K. These values compare well with experimental results from the literature for both QCL materials and for AlInAs and GaInAs, which the QCL is composed of. The cross-plane conductivity results are lower than those of either AlInAs or GaInAs, which demonstrates the phonon scattering at the interfaces. The in-plane results are between AlInAs and GaInAs, which is to be expected. The PTR results are less concrete, as there seem to be heat transfer eects active in the samples which are not included in the models used to t the frequency scans. These effects are not 2D heat transfer artifacts nor are they the result of volumetric absorption. It is possible that they are the results of plasmon induction, but this is only supposition. As the data stand, the PTR and MD results are within an order of magnitude of each other and follow reasonable trends, which suggests that both results are not too far o from reality. While the experimental results are not entirely conclusive, the simulations and experiments corroborate each other suciently to warrant further investigation using these techniques. Additionally, the simulations present sucient internal consistency so as to be useful for thermal property investigation independent of the PTR results.
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48

Uejima, Motoyuki. "Theoretical Design of Light-Emitting Molecules Based on Vibronic Coupling Density Analysis." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188601.

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49

Carnevale, Santino D. "Catalyst-free III-nitride Nanowires by Plasma-assisted Molecular Beam Epitaxy: Growth, Characterization, and Applications." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1374066626.

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50

Jansson, Emil. "Electronic characterization of molecules with application to organic light emitting diodes." Licentiate thesis, Stockholm : Theoretical Chemisty, School of Biotechnology, Royal Institute of Technology, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4349.

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