Bibliografie tematiche / Molecular interdiffusion

Letteratura scientifica selezionata sul tema "Molecular interdiffusion"

Autore: Grafiati

Pubblicato: 22 giugno 2024

Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili

Scegli il tipo di fonte:

Consulta la lista di attuali articoli, libri, tesi, atti di convegni e altre fonti scientifiche attinenti al tema "Molecular interdiffusion".

Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.

Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.

Articoli di riviste sul tema "Molecular interdiffusion":

Tahani, Masoud, Eligiusz Postek e Tomasz Sadowski. "Molecular Dynamics Study of Interdiffusion for Cubic and Hexagonal SiC/Al Interfaces". Crystals 13, n. 1 (27 dicembre 2022): 46. http://dx.doi.org/10.3390/cryst13010046.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

The mechanical properties of the SiC/Al interface are crucial in estimating the overall strength of this ceramic-metal composite. The present work investigates the interdiffusion at the SiC/Al interface using molecular dynamics simulations. One cubic and one hexagonal SiC with a higher probability of orientations in contact with Al are examined as two samples of metal-matrix nanocomposites with whisker and particulate reinforcements. These reinforcements with the Si- and C-terminated surfaces of the SiC/Al interfaces are also studied. The average main and cross-interdiffusion coefficients are evaluated using a single diffusion couple for each system. The effect of temperature and annealing time are analysed on the self- and interdiffusion coefficients. It is found that the diffusion of Al in SiC is similar in cubic and hexagonal SiC and as expected, the interdiffusion coefficient increases as the temperature and annealing time increase. The model after diffusion can be used to evaluate the overall mechanical properties of the interface region in future studies.

Tahani, Masoud, Eligiusz Postek, Leili Motevalizadeh e Tomasz Sadowski. "Effect of Vacancy Defect Content on the Interdiffusion of Cubic and Hexagonal SiC/Al Interfaces: A Molecular Dynamics Study". Molecules 28, n. 2 (11 gennaio 2023): 744. http://dx.doi.org/10.3390/molecules28020744.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

The mechanical properties of ceramic–metal nanocomposites are greatly affected by the equivalent properties of the interface of materials. In this study, the effect of vacancy in SiC on the interdiffusion of SiC/Al interfaces is investigated using the molecular dynamics method. The SiC reinforcements exist in the whisker and particulate forms. To this end, cubic and hexagonal SiC lattice polytypes with the Si- and C-terminated interfaces with Al are considered as two samples of metal matrix nanocomposites. The average main and cross-interdiffusion coefficients are determined using a single diffusion couple for each system. The interdiffusion coefficients of the defective SiC/Al are compared with the defect-free SiC/Al system. The effects of temperature, annealing time, and vacancy on the self- and interdiffusion coefficients are investigated. It is found that the interdiffusion of Al in SiC increases with the increase in temperature, annealing time, and vacancy.

Tahani, Masoud, Eligiusz Postek e Tomasz Sadowski. "Diffusion and Interdiffusion Study at Al- and O-Terminated Al2O3/AlSi12 Interface Using Molecular Dynamics Simulations". Materials 16, n. 12 (12 giugno 2023): 4324. http://dx.doi.org/10.3390/ma16124324.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

The equivalent characteristics of the materials’ interfaces are known to impact the overall mechanical properties of ceramic–metal composites significantly. One technological method that has been suggested is raising the temperature of the liquid metal to improve the weak wettability of ceramic particles with liquid metals. Therefore, as the first step, it is necessary to produce the diffusion zone at the interface by heating the system and maintaining it at a preset temperature to develop the cohesive zone model of the interface using mode I and mode II fracture tests. This study uses the molecular dynamics method to study the interdiffusion at the interface of α-Al2O3/AlSi12. The hexagonal crystal structure of aluminum oxide with the Al- and O-terminated interfaces with AlSi12 are considered. A single diffusion couple is used for each system to determine the average main and cross ternary interdiffusion coefficients. In addition, the effect of temperature and the termination type on the interdiffusion coefficients is examined. The results demonstrate that the thickness of the interdiffusion zone is proportional to the annealing temperature and time, and Al- and O-terminated interfaces exhibit similar interdiffusion properties.

Griesche, Axel, Bo Zhang, Jürgen Horbach e Andreas Meyer. "Interdiffusion and Thermodynamic Forces in Binary Liquid Alloys". Materials Science Forum 649 (maggio 2010): 481–86. http://dx.doi.org/10.4028/www.scientific.net/msf.649.481.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

A novel X-ray radiography method is used to measure chemical diffusion in a long-capillary in liquid Al95Ni5 at.-%. Molecular dynamics simulations provide interdiffusion coefficients and thermodynamic factors for the whole composition range in Al-Ni. The data are compared to literature data in Sb-Sn and Ag-Sn. The relation between interdiffusion coefficient and thermodynamic forces is discussed in the context of the Darken equation. In systems with common ordering tendency (Al-Ni, Sb-Sn) the thermodynamic factor is larger than one and enhances interdiffusion. In systems with common demixing tendency (Ag-Sn) the thermodynamic factor is smaller than one and reduces interdiffusion.

Ouyang, Yifang, Jizheng Wu, Jiangxia Wen, Hongmei Chen, Yulu Zhou, Xiaoma Tao e Yong Du. "Molecular dynamics simulation of diffusion for Ni–Zr interface". International Journal of Modern Physics B 34, n. 25 (4 settembre 2020): 2050217. http://dx.doi.org/10.1142/s0217979220502173.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

The molecular dynamics simulation has been performed to study the effects of temperature on interdiffusion of Ni–Zr system. The simulated results indicate that the thickness of Ni/Zr diffusion layer increased with increasing diffusion time, and interdiffusion results in disordered or amorphization in the diffusion zone. During the diffusion process, Ni atoms diffuse crossing the interface more easily and deeply into Zr side than Zr atoms into Ni side. The activation energies of Ni and Zr are 1.25 and 1.28 eV for Ni(100)//Zr(0001) interface, 1.33 and 1.42 eV for Ni(110)//Zr(0001) interface at the temperature range of 950–1100 K, respectively. The microscopic diffusion mechanisms for Ni atoms in Zr lattice have been studied, and the results show that the most possible diffusion mechanism is the interstitial hopping mechanism, while for Zr diffusing in Ni, the vacancy diffusion mechanism is favored. The interdiffusion for case of Ni(110)//Zr(0001) interface is more easy than that of Ni(100)//Zr(0001) interface due to the lower surface energy for the former. In the diffusion zone of Ni–Zr, some typical clusters have been identified, which are similar to those extracted from the Ni–Zr intermetallic compounds, and which are generally consistent with the experimental observations in diffusion couples.

Wang, Li, Tsung-Tse Lin, Mingxi Chen, Ke Wang e Hideki Hirayama. "Terahertz quantum cascade laser considering compositional interdiffusion effect". Applied Physics Express 16, n. 3 (1 marzo 2023): 032007. http://dx.doi.org/10.35848/1882-0786/acc568.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Abstract This study presents an experimental demonstration of the crucial role of compositional interdiffusion at interfaces in GaAs/AlGaAs alternating superlattices for developing the terahertz quantum cascade lasers operating at high temperatures. By growing GaAs/Al0.3Ga0.7As superlattices using the molecular beam epitaxy technique, an aluminum interdiffusion width of 0.95 nm (equivalent to ∼3.4 monolayers) is estimated. Incorporating this interdiffusion width as an additional design parameter has resulted in a 20 K improvement in the maximum operating temperature of the laser. To quantify the magnitude of the interdiffusion scattering effects on electron dynamics, an independent self-energy that functions based on the axial correlation length is introduced in the non-equilibrium Green’s function model. It clarifies that changes in the lifetime of quantum states and also the population fractions are primarily influenced by the deformation of wave functions at the injector when the interfaces become interdiffused.

Le, Anh-Duc, André Chateau Akué Asséko, Benoît Cosson e Patricia Krawczak. "Investigating the Effect of Interface Temperature on Molecular Interdiffusion during Laser Transmission Welding of 3D-Printed Composite Parts". Materials 16, n. 18 (7 settembre 2023): 6121. http://dx.doi.org/10.3390/ma16186121.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

The present study investigated the influence of temperature on molecular interdiffusion at the interface during the laser transmission welding of 3D-printed continuous carbon-fiber-reinforced thermoplastic composites. In order to accurately measure the temperature at the weld interface, a series of thermocouples were embedded in the laser-absorbent composite part. Two different molecular interdiffusion models were implemented to calculate the degree of healing and to predict the effects of temperature on the welding process. The degree of healing and the weld line width were computed and compared with microscopy observations. The discrepancy between the two proposed numerical models was less than 6%. Both models showed good agreement with the experimental data, with an average error of 13.28% and 7.26%, respectively. The results revealed a significant correlation between the thermal history and molecular interdiffusion at the interface. Furthermore, the relationship between the welding parameters (laser beam scanning speed) and weld line width was established. The findings of this study provide a comprehensive understanding of the underlying mechanisms involved in the laser welding of 3D-printed composites and offer insights to optimize the welding process for enhanced weld quality and superior mechanical properties in the final product.

Tsige, Mesfin, e Gary S. Grest. "Molecular dynamics simulation of solvent–polymer interdiffusion: Fickian diffusion". Journal of Chemical Physics 120, n. 6 (8 febbraio 2004): 2989–95. http://dx.doi.org/10.1063/1.1640347.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Bastrakova, M. V., K. R. Mukhamatchin, Yu M. Kuznetsov e M. V. Dorokhin. "The study of Si/Ge interdiffusion using molecular dynamics simulation". Journal of Physics: Conference Series 1695 (dicembre 2020): 012036. http://dx.doi.org/10.1088/1742-6596/1695/1/012036.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Borkovska, L. V., R. Beyer, M. Hoffmann, A. Holzhey, N. Korsunska, Yu G. Sadofyev e Joerg Weber. "Role of Cation Vacancy-Related Defects in Self-Assembling of CdSe Quantum Dots". Defect and Diffusion Forum 230-232 (novembre 2004): 55–66. http://dx.doi.org/10.4028/www.scientific.net/ddf.230-232.55.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

In this chapter we present the results of the photoluminescent and optical investigations of the influence of cation vacancy-related defects on CdSe/ZnSe quantum dot organization. Selfassembling growth was achieved under molecular beam epitaxy with subsequent annealing step. Number of cation vacancies was controlled by the intensity of the emission band connected with complex that includes cation vacancy and shallow donor. For the first time it is shown that increase of number of cation vacancy related defects results in the reduction of potential fluctuations in the QD layer. In this case a relatively uniform dense array of QDs with shallow localization potential is organized. It is proposed that generation of cation vacancies during the growth suppresses both Cd segregation and Cd surface diffusion as well as facilitates Cd/Zn interdiffusion. Interdiffusion process is proved by the changes in the photoluminescence and optical reflection spectra of ZnSe layers. It is showned that Cd/Zn interdiffusion can play an important role in CdSe/ZnSe intermixing during the QD formation at least under such growth conditions which can stimulate generation of cation vacancies.

Più fonti

Tesi sul tema "Molecular interdiffusion":

Binder, Kurt, Subir K. Das, Michael E. Fisher, Jürgen Horbach e Jan V. Sengers. "Interdiffusion in critical binary mixtures by molecular dynamics simulation". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193274.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

A simulation study of the static and dynamic critical behavior of a symmetric binary Lennard-Jones mixture is briefly reviewed. Using a combination of semi-grand-canonical Monte Carlo (SGMC) and molecular dynamics (MD) methods near the critical temperature of liquid-liquid unmixing, the correlation length and “susceptibility” related to the critical concentration fluctuations are estimated, as well as the self- and interdiffusion coefficients. While the self-diffusion coefficient does not show a detectable critical anomaly, the interdiffusion coefficient is found to vanish when one approaches the critical temperature at fixed critical concentration. It is shown that in the corresponding Onsager coefficient both a divergent singular part and a nonsingular background term need to be taken into account. With appropriate finite-size scaling analysis (the particle numbers studied for the dynamics lie only in the range from N = 400 to 6400), the critical behavior of the interdiffusion coefficient is found to be compatible both with the theoretically predicted behavior and with corresponding experimental evidence.

Binder, Kurt, Subir K. Das, Michael E. Fisher, Jürgen Horbach e Jan V. Sengers. "Interdiffusion in critical binary mixtures by molecular dynamics simulation". Diffusion fundamentals 6 (2007) 10, S. 1-12, 2007. https://ul.qucosa.de/id/qucosa%3A14184.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Yaneva, Jaklin, Burkhard Dünweg e Andrey Milchev. "Non-fickian interdiffusion of dynamically asymmetric species: a molecular dynamics study". Diffusion fundamentals 2 (2005) 40, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14370.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Laot, Christelle Marie III. "Spectroscopic Characterization of Molecular Interdiffusion at a Poly(Vinyl Pyrrolidone) / Vinyl Ester Interface". Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36944.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Mechanical properties of (woven carbon fiber / vinyl ester matrix) composites can be greatly improved if the interphase between the reinforcing high-strength low-weight fiber and the thermoset resin is made more compliant. In order to improve the adhesion of the vinyl ester matrix to the carbon fiber, a thermoplastic coating such as poly(vinyl pyrrolidone) (PVP) can be used as an intermediate between the matrix and the fiber. The extent of mutual diffusion at the (sizing material / polymer matrix) interphase plays a critical role in determining the mechanical properties of the composite.

In this research, the molecular interdiffusion across a poly(vinyl pyrrolidone))/vinyl ester monomer (PVP/VE) interface is being investigated by Fourier Transform Infrared Attenuated Total Reflectance (FTIR-ATR) spectroscopy. The ATR method which can be used to characterize the transport phenomena, offers several advantages, such as the ability to monitor the diffusion in situ or to observe chemical reactions. In order to separate the effects of the vinyl ester monomer diffusion and the crosslinking reaction, ATR experiments were carried out at temperatures below the normal curing temperature. Diffusion coefficients were determined by following variations in infrared bands as a function of time, and fitting this data to a Fickian model. The values of the diffusion coefficients calculated were consistent with values found in the literature for diffusion of small molecules in polymers. The dependence of diffusion coefficients on temperature followed the Arrhenius equation. Hydrogen bonding interactions were also characterized. The diffusion model used in this study, however, does not seem to be appropriate for the particular (PVP/VE) system. Because the glass transition temperature of the PVP changed as diffusion proceeded, one would expect that the mutual diffusion coefficient did not stay constant. In fact, it was shown that the Tg can drop by 140oC during the diffusion process. A more suitable model of the (PVP/VE) system should take into account plasticization, hydrogen bonding, and especially a concentration dependent diffusion coefficient. Further analysis is therefore needed.
Master of Science

Gopal, Anamika. "Effects of Thickness, Morphology and Molecular Structure of Donor and Acceptor Layers in Thermally Interdiffused Polymer Photovoltaics". Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/27279.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

An in-depth study of concentration gradients in thermally-interdiffused polymer – fullerene photovoltaic devices, with a focus on thickness and heat treatments, is presented in this thesis. Device performance is improved from the bilayer by the creation of a concentration gradient of the donor and acceptor materials throughout the active layer of the device. Concentration gradients are expected to improve device performance by optimizing the charge transfer, transport and collection processes. This is achieved through heat-induced interdiffusion of the two materials at temperatures above the glass transition temperature of the polymer. Investigation of the poly(3-octylthiophene) (P3OT) – C₆₀ system show a three-fold improvement in the external quantum efficiencies (EQE) as compared with bilayer devices. Auger spectroscopy, combined with argon-ion beam milling, serves to record the concentration depth profile and identify concentration gradients in the device through detection of the sulfur in the P3OT backbone. Concentration gradients are optimized to yield the best devices through a thickness variation study conducted on the P3OT – C₆₀ system for fixed thermal interdiffusion conditions at 118 °C for 5 minutes. An optimum thickness of 40 to 60 nm is obtained for the two materials that yields the ideal morphology of a concentration gradient as recorded by Auger spectroscopy. For such devices, the concentration gradient is seen to extend through the device, ending in a thin layer of pure material at each electrode. A monochromatic power conversion efficiency of 2.05% is obtained for 5.3 mW/cm²⁺ illumination at 470 nm. A brief study is also presented to optimize the concentration gradient profile through variations of the thermal parameters. The dependence of the concentration gradient on the interdiffusion time and temperature is investigated. The merits of heat treatment on the crystallinity of P3OT and the overall device performance are also discussed. It is shown in some case that devices with annealed P3OT layers show almost twice the EQE as non-annealed P3OT layer devices. Potential alternatives for C₆₀ in interdiffused devices with P3OT have been presented. [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM), a well-investigated acceptor for blend devices, is studied as an acceptor in concentration gradient devices. A method for spin-coating uniform bilayers of P3OT and PCBM, without solution damage to either layer, is presented. A thermal variation study of the interdiffusion conditions on this system indicated higher interdiffusion temperatures and times are preferred for P3OT – PCBM systems. For interdiffusion at 150 °C for ten minutes, EQE values approaching 35 % at 500 nm are obtained. Auger spectroscopy studies on this system yielded the same conclusions about the concentration gradient device morphology that gives optimum device output. 1:1 and 1:2 blends of P3OT – PCBM are also studied. The influence of various thermal treatments on these devices is described. The endohedral fullerene Sc₃N@C₈₀ is introduced as a new acceptor material. The endohedral fullerene consists of Sc₃N cluster enclosed in a C₈₀ cage. An order of magnitude increase is seen in device performance upon sublimation of these molecules on a P3OT layer confirming its effectiveness as an acceptor. Preliminary studies done on this system indicated the need for greater thermal treatment to produce optimum concentration gradients. An in depth study for varying temperatures and times is presented. The best device performance was seen for interdiffusion at 160 °C for 25 minutes. The endohedral fullerene devices also show a long-term deterioration and so best result are presented from a set of devices fabricated within the same time period. The study of these three donor-acceptor systems confirms that the conclusions on the thickness dependence and device performance study conducted for the P3OT – C₆₀ system extend to other acceptors. A model of EQE for varying thicknesses based on absorption in the interdiffused concentration gradient regions is also presented. This model effectively highlights the influence of P3OT layer thickness on the trends observed in the EQE. It did not, however, reproduce the experimental thickness variation results for varying C₆₀ thicknesses. Incorporation of the effects of the electric field intensity distribution is expected to correct for this. Suggestions have been given on how this might be achieved.
Ph. D.

Jabeen, Rowshni. "Laser transmission welding of natural fibre reinforced thermoplastic composites". Electronic Thesis or Diss., Ecole nationale supérieure Mines-Télécom Lille Douai, 2022. http://www.theses.fr/2022MTLD0011.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Le soudage par transmission laser des thermoplastiques nécessite l’optimisation de l’adhérence interfaciale au niveau du joint de soudure. A cet égard, la modélisation du procédé et le développement d'outils de simulation numériques sont indispensables pour optimiser la résistance mécanique du joint de soudure. La tâche est plus difficile dans le cas de matériaux composites très hétérogènes et anisotropes. De plus, la transmission laser est encore difficile dans le cas de milieux opaques ou semi-transparents tels que les composites thermoplastiques renforcés de fibres naturelles. Les propriétés thermiques et optiques des composites dépendent des propriétés et de la morphologie des constituants tels que les fibres et le polymère, qui peuvent affecter le spectre de transmission dans le domaine infrarouge. L’absorption et la réfraction de la propagation du rayon laser dans les matériaux composites conduisent à une réduction de l’énergie transmise arrivant à l’interface da soudure, ce qui influence directement la qualité de la soudure et ses performances mécaniques.Dans cette thèse, l'effet des phénomènes d'absorption et de diffusion sur le développement du champ de température à l'interface de la soudure est analysé numériquement et expérimentalement. Compte tenu de l’orientation, de la forme, de la longueur et de la fraction volumique des fibres, des géométries numériques 3D représentant les matériaux composites sont générées pour simuler la propagation des rayons laser avec l'algorithme "Ray tracing". Des modèles numériques pour estimer la résistance de la soudure sont présentés tout en tenant compte de l'influence des paramètres de soudage (tels que la puissance du laser, la vitesse d’alimentation et la position du foyer), les propriétés du matériau et l'interdiffusion moléculaire à l'interface de la soudure. La résistance de la soudure est mesurée par des essais mécaniques et leurs résultats sont comparés aux résultats de la modélisation numérique
Laser transmission welding of thermoplastics requires the optimisation of interfacial adhesion at the weld joint. In this regard, the process modelling, and the development of numerical simulation tools are indispensable to optimize the mechanical strength of the weld joint. The task is more difficult in the case of highly heterogeneous and anisotropic composite materials. Moreover, the laser transmission is still difficult in the case of opaque or semi-transparent media such as natural fibre reinforced thermoplastic composites. The thermal and optical properties of composites depend on the properties and morphology of the constituents such as fibres and polymer, which can affect the transmission spectrum in the infrared range. The absorption and refraction of laser ray propagation in the composite materials lead to a reduction of the transmitted energy arriving at the weld interface, which directly influences the quality of the weld and its mechanical performance. In this dissertation, the effect of absorption and diffusion phenomena on the development of temperature field at the weld interface is analysed numerically and experimentally. Considering the fibre orientation, shape, length and volume fraction, numerical 3D geometries representing composite materials are generated to simulate the propagation of laser rays with “Ray tracing” algorithm. Numerical models to estimate the strength of weld are presented while considering the influence of welding parameters (such as laser power, feeding speed and focus position), material properties and molecular interdiffusion at the weld interface. The weld bonding strength is measured by mechanical tests and their results are compared with numerical modelling results

Tardot, Alain. "Diffraction de rayons X et interdiffusion dans les superréseaux CdTe/CdZnTe et CdTe/HgTe". Grenoble 1, 1993. http://www.theses.fr/1993GRE10090.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Ce travail concerne la caracterisation structurale et l'etude de l'interdiffusion dans les superreseaux contraints cdte/cdznte et cdte/hgte, elabores par epitaxie par jets moleculaires, au moyen de la double diffraction de rayons x. Les parametres structuraux (composition, epaisseur, etat de deformation) sont obtenus de facon precise en utilisant conjointement l'experience et la simulation en theorie cinematique. Les coefficients d'interdiffusion des couples cd/zn (400c) et cd/hg (200c) sont mesures par diffraction x. Ils permettent de calculer les profils de concentration des superreseaux en fonction de la temperature et du temps de recuit. Par extrapolation, nous precisons les conditions de croissance pour obtenir des interfaces raides, qui sont necessaires pour des dispositifs optoelectroniques performants

Baron, Thierry. "Dopage des semiconducteurs II-VI à base de tellure et réalisation de structures quantiques". Université Joseph Fourier (Grenoble ; 1971-2015), 1996. http://www.theses.fr/1996GRE10060.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Nous avons etudie le dopage des semiconducteurs ii-vi a base de tellure. Concernant le dopage de type n, nous avons montre que l'impurete iode est mieux adaptee que l'impurete indium, pour atteindre de fortes concentrations de porteurs dans cdte et cdznte. Le dopage de type p est realise en utilisant une cellule dc plasma, permettant d'obtenir de l'azote sous forme atomique. En comparant les proprietes electriques, optiques et structurales de znte:n et de cdte:n, nous avons mis en evidence un phenomene de compensation limitant le niveau maximum de dopage accessible pour cdte:n. Afin de comprendre l'origine de ce phenomene, nous avons entrepris l'etude du dopage des alliages cdznte et des alliages cdmgte et znmgte. A partir de cette etude, nous avons elabore un modele fonde sur la comparaison des enthalpies de formation des composes nitrures a#3n#2 (a=cd, zn, mg). La formation de tels composes limiterait la solubilite limite de l'azote en site substitutionnel actif. Ainsi, la compensation interviendrait preferentiellement dans les materiaux contenant du mg puis du cd, et serait faible pour le materiau znte. Un mecanisme complementaire, faisant intervenir le parametre de maille, a egalement ete propose. Maitrisant le dopage des tellurures, nous avons realise des heterostructures dopees par modulation afin d'etudier des gaz d'electrons bidimensionnels. En epitaxiant des puits quantiques dopes de type p, nous avons montre que la localisation de l'impurete azote dans la structure modifie les energies de liaison (i) de l'exciton lie sur un accepteur neutre et (ii) de l'accepteur. Nous avons mis en evidence, par des mesures optiques, structurales et chimiques, une acceleration de l'interdiffusion dans les superreseaux contenant a la fois du mg et de l'azote. Enfin, nous avons realise des dispositifs optoelectroniques tels que des modulateurs optiques ou des emetteurs et des detecteurs de rayonnement dans l'infrarouge

Arnoult, Alexandre. "Dopage par modulation d'hétérostructures de semiconducteurs II-VI semimagnétiques en épitaxie par jets moléculaires". Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10237.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Une etude theorique preliminaire a cette these a prevu que lorsque l'on introduit un gaz de trous bidimensionnel (2d) dans un puits quantique de semiconducteur semimagnetique, l'interaction entre les spins localises et les porteurs de charges induit une transition de phase ferromagnetique. Nous avons mis au point l'elaboration d'un tel systeme a base de tellurures en epitaxie par jets moleculaires, ainsi que la caracterisation au niveau microscopique des interfaces, du dopage et du transfert de porteurs dans le puits quantique. Ceci nous a permis d'elaborer des echantillons ayant donne lieu a toute une serie d'etudes physiques. Le dopage par modulation d'heterostructures de semiconducteurs ii-vi a base de tellure en epitaxie par jets moleculaires n'avait ete realise jusqu'a notre etude que pour un dopage de type n, sur des structures comportant du cdmgte comme materiau barriere, avec peu de magnesium. Or cet alliage est la clef de la realisation d'un bon confinement quantique dans les tellurures, surtout pour le dopage de type p ou la concentration en mg doit etre augmentee. L'utilisation d'une source d'azote ecr, dopant de type p, et l'optimisation des parametres de la croissance ont permis l'obtention d'un gaz de trous 2d de bonne densite, comme le montrent la spectroscopie optique, l'effet hall et la capacite-tension. L'etude de structures interdiffusees par sims, diffraction de rayon x et spectroscopie optique, nous a de plus permis de mieux comprendre les mecanismes de degradation en cours de croissance de nos couches comportant du magnesium, et dopees a l'azote. Un modele base sur la diffusion de l'azote a ete propose. Il a ensuite ete possible de realiser des structures semimagnetiques dans lesquelles l'interaction entre un gaz de trous 2d et des spins localises de manganese a permis la mise en evidence de la transition de phase ferromagnetique attendue theoriquement. Par ailleurs, un nouveau dopant de type n pour l'epitaxie par jets moleculaire des tellurures a ete teste avec succes sur des couches epaisses, ainsi que pour des heterostructures. Il s'agit de l'aluminium, dont le domaine d'utilisation est plus etendu que les autres dopants utilises jusqu'a present, puisqu'il permet d'obtenir une bonne efficacite meme sur des couches comportant du magnesium.

Ahmed, Tanvir. "Interdiffusion and thermotransport in engineering materials". Thesis, 2018. http://hdl.handle.net/1959.13/1383545.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

Research Doctorate - Doctor of Philosophy (PhD)
In this research in Part A (Macroscopic Description), (1) the Hall method (HM) (specifically designed for determining the interdiffusion coefficient at the low and high composition limits of the corresponding interdiffusion composition profile) is further developed in order to be applied to the whole composition profile resulting in the Extended Hall method (EHM); (2) A comparative study of the HM, EHM, Boltzmann-Matano (BM) and Sauer and Freise (SF) methods is performed using composition profiles generated by computer simulation. The results clearly indicate that the HM/EHM technique is only applicable when the interdiffusion coefficient is constant (i.e. independent of composition) or almost constant at the low composition regions. In all other cases, the BM and SF methods give the best agreement with the input interdiffusion function even at the ends of the composition profiles. In Part B ((Microscopic Description) of this thesis, the thermodynamic and thermophysical properties of the liquid Ni-Al alloys are studied over a wide temperature and concentration range by using molecular dynamics (MD) simulations. The calculations are performed by using equilibrium molecular dynamics simulation in conjunction with the Green-Kubo formalism and one of the most reliable embedded-atom method potentials for this system developed by Purja and Mishin. For an equi-atomic liquid Ni-Al alloy, the calculations are also executed on another potential. The results permit the description of the temperature and concentration dependence of the thermodynamic factor for interdiffusion. Furthermore, the simulations permit analysis of the heat of transport in thermotransport. It is possible to estimate the contributions of Onsager off-diagonal terms for the temperature and concentration range under consideration. Accordingly, in the presence of a temperature gradient, our simulation results for all the considered models of liquid Ni-Al alloys predict consistently Ni and Al to migrate to the cold and hot ends, respectively. Meanwhile, the highest value, about 1.1 ± 0.1 eV, of the reduced heat of transport is observed for Ni₂Al₂ alloy model and it slightly decreases towards Al-rich and Ni rich compositions. The results agree well with previous published experimental and simulation data where available.

Capitoli di libri sul tema "Molecular interdiffusion":

Goyhenex, Christine, R. V. P. Montsouka, Mirosław Kozłowski e Veronique Pierron-Bohnes. "Interdiffusion of Two L1₀Phases without Long-Range Order Decrease: Experiments and Molecular Dynamics Simulations". In Solid State Phenomena, 59–66. Stafa: Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/3-908451-39-6.59.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

BROCHARD-WYART, F. "Kinetics of Polymer/Polymer Interdiffusion". In Molecular Conformation and Dynamcis of Macromolecules in Condensed Systems, 249–56. Elsevier, 1988. http://dx.doi.org/10.1016/b978-0-444-42993-3.50019-5.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Atti di convegni sul tema "Molecular interdiffusion":

Andrade, R. Ribeiro, F. M. Matinaga, A. Malachias, M. V. B. Moreira, A. G. de Oliveira, J. C. González, Jisoon Ihm e Hyeonsik Cheong. "On the Ga interdiffusion in InAs free-standing nanowires grown by molecular beam epitaxy". In PHYSICS OF SEMICONDUCTORS: 30th International Conference on the Physics of Semiconductors. AIP, 2011. http://dx.doi.org/10.1063/1.3666346.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Nakhle, Wissam, Marie-Claude Heuzey e Paula M. Wood-Adams. "Interdiffusion dynamics at the interface between two polystyrenes with different molecular weight probed by a rheological tool". In NOVEL TRENDS IN RHEOLOGY VIII. Author(s), 2019. http://dx.doi.org/10.1063/1.5109505.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Zheng, Yao-Ting, Zaoxiao Zhang, Guang-xu Cheng, Fu-Zhen Xuan e Zhengdong Wang. "Molecular Dynamics Simulation of Hydrogen-Activated Coalescence and Growth of Nano-Voids". In ASME 2017 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/pvp2017-65577.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

The understanding of hydrogen embrittlement (HE) is of significant importance and fundamental interest owing to its negative effects on industrial metallic materials. The effect of solute H on the void coalescence and growth needs to be clarified. Using molecular dynamics simulation, the evolution of preexisting nano voids is studied in the presence of H atoms. As the per unit area concentration of trapped H atom on void surface reaches 0.45 /Å2, the movement of void is observed. It proceeds along with the interdiffusion of H and Fe atoms around the voids. Strain-mediated diffusion of H atoms from void surface to the zone between nearest voids occurs at first. Then the Fe atoms are affected by migrated H and diffuse in the opposite direction following the principle of energy minimization. Such mechanism can help us understand the formation of high pressure bubble at nano scale. Based on this useful information, some methods could be obtained to prevent the growth of voids further, such as strengthening the stability of metal lattice around voids by dopant etc.

Hirn, U., e R. Schennach. "Fiber-Fiber Bond Formation and Failure: Mechanisms and Analytical Techniques". In Advances in Pulp and Paper Research, Oxford 2017, a cura di W. Batchelor e D. Söderberg. Fundamental Research Committee (FRC), Manchester, 2017. http://dx.doi.org/10.15376/frc.2017.2.839.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

In this paper we give a literature overview on three different aspects of pulp fiber-fiber bonding. First we are reviewing how the adhesion between the pulp fibers is created by the capillary pressure during drying of a sheet. Second we are discussing the individual mechanisms relevant for fiber-fiber bonding. They can be grouped in three different groups: (a) The area in molecular contact, which also includes interdiffusion; (b) the intermolecular bonding mechanisms hydrogen bonding, Van der Waals forces and Coulomb interaction; (c) the mechanical bonding mechanisms which are capillary bridges and mechanical interlocking. The third and last part of the review discusses the failure process of fiber-fiber bonds and related single fiber-fiber bond testing methods. The general emphasis of the paper is set on providing a general understanding of the processes responsible for how bonds between fibers are created, how they work and how they are failing.

Barzyk, D., D. H. Page e A. Ragauskas. "Carboxylic Acid Groups and Fibre Bonding". In The Fundamentals of Papermaking Materials, a cura di C. F. Baker. Fundamental Research Committee (FRC), Manchester, 1997. http://dx.doi.org/10.15376/frc.1997.2.893.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Abstract (sommario):

It has been known for a long time that carboxylic acid groups in cellulosic fibres increase swelling in fibres- and hence this impacts flexibility, bonded area, and strength. In a few recent publications, attention has been drawn to the possibility that carboxyl groups may serve another function. Those located at the fibre surface have an effect on specific fibre-fibre bond strength . The evidence for this possibility is at present indirect . Using a technique developed for this work, pulps were prepared with uniform distribution of carboxyl groups across the fibre cell wall, and with carboxyl groups located primarily at the fibre surface. Using values of light scattering coefficient, tensile strength, and z-bond strength, it was possible to determine the relative importance of increased bonded area caused by swelling, and increased bond strength caused by localized surface effects. It was found that specific bond strength could be enhanced roughly 50% by surface enrichment, and this could exceed the strength increase attributable to enhanced bonded area. Previous work on the effect of carboxyl groups on strength needs reevaluation to determine the extent of the two effects . The mechanism of strength increase by surface carboxylic acid groups is not understood . It may be an ionic effect, but it is possible that the increased localized surface swelling allows more molecular flexibility and more intimate molecular contact and interdiffusion as found in other polymers . In practice, there are opportunities, especially in bleaching or other pulp treatments, for enhancing fibre surface carboxyl group concentration, and these may have practical value. The field looks ripe for exciting developments.