Ce travail a porté sur l'étude de la dynamique électronique et vibrationnelle de nano-objets métalliques en fonction de leur taille, forme et composition, ainsi que sur celle des modes de vibration dans les verres, par des techniques optiques résolues en temps à l'échelle femtoseconde. Dans des agrégats mono-métalliques de cuivre, nous avons confirmé l'accélération des échanges d'énergie électrons-réseau pour des tailles inférieures à 10 nm. Nous avons abordé le régime des faibles tailles, inférieures à 2 nm, et mis en évidence les limites d'une modélisation de type solide confiné. Dans les agrégats bi-métalliques nous avons montré que la cinétique des échanges d'énergie reflète la composition pour les composés or-argent mais est plus complexe pour des nanoparticules ségrégées nickel-argent. L'impact de la forme, de la structure et de l'environnement de nano-objets métalliques sur leurs modes de vibration acoustiques a été étudié dans différentes configurations. Les mesures réalisées sur un ensemble et des paires de nano-prismes ont permis de mettre en évidence les fluctuations locales de leur couplage avec le substrat. L'effet de la nano-structuration a été mis en évidence dans des nanocolonnes et dans des composés ségrégés. Par ailleurs, nous avons étudié par spectroscopie Raman impulsionnelle femtoseconde les modes vibrationnels associés à une structuration locale dans les verres. Nous avons ainsi caractérisé les « modes de défaut » dus aux vibrations de structures en anneau dans la silice, et leur évolution en fonction de sa densité. Dans l'oxyde de germanium, nous avons démontré l'existence et caractérisé un mode de vibration dû à la présence d'une structure en anneau.

Les réponses statiques et dynamiques associées aux phonons et aux phasons sont<br />comparées dans des quasicristaux de symétrie icosaédrique et dans leurs approximants 1/1<br />cubiques. Quasicristaux et approximants partagent un même ordre local caractérisé par des amas<br />atomiques icosaédriques de grande taille (diamètre ~ 1.6 nm). L'ordre à longue portée est<br />quasipériodique dans le quasicristal alors que périodique dans l'approximant. Les phasons sont de<br />nouveaux modes hydrodynamiques induits par la quasipériodicité. Les phonons existent dans le<br />quasicristal et dans l'approximant.<br />Nous avons mesuré la distribution de l'intensité diffuse autour des pics de Bragg dans la<br />phase approximante Zn-Sc et dans les phases quasicristallines i-Zn-X-Sc (X = Mg, Ag, Co). Dans<br />la phase Zn-Sc, la diffusion diffuse thermique due aux phonons est seule observée. Dans les phases<br />i-Zn-X-Sc, il y a un signal diffus supplémentaire dû aux phasons. Les constantes élastiques de<br />phason déterminées varient avec la nature de l'élément X.<br />La dynamique des phasons est étudiée en diffusion cohérente des rayons X dans la phase i-<br />Al-Pd-Mn. Les phasons sont activés au-dessus de 600°C. La dynamique est diffusive avec, à<br />650°C, des temps de relaxation de 100 s une longueur d'onde des modes de 90 nm.<br />La dynamique des phonons est mesurée dans les phases i-Zn-Mg-Sc et 1/1-Zn-Sc puis dans<br />les phases i-Cd-Yb et 1/1-Cd-Yb en diffusions inélastiques des neutrons et des rayons X. Les<br />facteurs de structure dynamiques sont similaires dans le quasicristal et son approximant ce qui<br />révèle l'importance de l'ordre local sur la réponse dynamique des modes de vibration dans ces<br />structures. Des différences sont néanmoins observées.

A new quantum transport simulator -- Schrödinger Equation Monte Carlo in Three Dimensions (SEMC-3D) -- has been developed for simulating the carrier transport in nanoscale 3D MOSFET geometries. SEMC-3D self-consistently solves: (1) the 1D quantum transport equations derived from the SEMC method with open boundary conditions and rigorous treatment of various scattering processes including phonon and surface roughness scattering, (2) the 2D Schrödinger equations of the device cross sections with close boundary conditions to obtain the spatially varying subband structure along the conduction channel, and (3) the 3D Poisson equation of the whole device. Therefore, SEMC-3D can provide a physically accurate and electrostatically selfconsistent approach to the quantum transport in the subbands of 3D nanoscale MOSFETs. SEMC-3D has been used to simulate Si nanowire (NW) nMOSFETs to both demonstrate the capabilities of SEMC-3D, itself, and to provide new insight into transport phenomena in nanoscale MOSFETs, particularly with regards to interplay among scattering, quantum confinement and transport, and strain. / text

This dissertation presents thermal and thermoelectric measurements of nanostructures. Because the characteristic size of these nanostructures is comparable to and even smaller than the mean free paths or wavelengths of electrons and phonons, the classical constitutive laws such as the Fourier’s law cannot be applied. Three types of nanostructures have been investigated, including nanoscale constrictions patterned in a sub-100 nm thick silicon film, monatomic thick graphene ribbons supported on a silicon dioxide (SiO₂) beam, and indium antimonide (InSb) nanowires. A suspended measurement device has been developed to measure the thermal resistance of 48-174 nm wide constrictions etched in 35-65 nm thick suspended silicon membranes. The measured thermal resistance is more than ten times larger than the diffusive thermal resistance calculated from the Fourier’s law. The discrepancy is attributed to the ballistic thermal resistance component as a result of the smaller constriction width than the phonon-phonon scattering mean free path. Because of diffuse phonon scattering by the side walls of the constriction with a finite length, the phonon transmission coefficient is 0.015 and 0.2 for two constrictions of 35 nm x 174 nm x220 nm and 65 nm x 48 nm x 50 nm size. Another suspended device has been developed for measuring the thermal conductivity of single-layer graphene ribbons supported on a suspended SiO₂ beam. The obtained room-temperature thermal conductivity of the supported graphene is about 600 W/m-K, which is about three times smaller than the basal plane values of high-quality pyrolytic graphite because of phonon-substrate scattering, but still considerably higher than for common thin film electronic materials. The measured thermal conductivity is in agreement with a theoretical result based on quantum mechanical calculation of the threephonon scattering processes in graphene, which finds a large contribution to the thermal conductivity from the flexural vibration modes. A device has been developed to measure the Seebeck coefficients (S) and electrical conductivities ([sigma]) of InSb nanowires grown by a vapor-liquid-solid process. The obtained Seebeck coefficient is considerably lower than the literature values for bulk InSb crystals. It was further found that decreasing the base pressure during the VLS growth results in an increase in the Seebeck coefficient and a decrease in the electrical conductivity, except for a nanowire with the smallest diameter of 15 nm. This trend is attributed to preferential oxidation of indium by residual oxygen in the growth environment, which could cause increased n-type Sb doping of the nanowires with increasing base pressure. The deviation in the smallest diameter nanowire from this trend indicates a large contribution from the surface charge states in the nanowire. The results suggest that better control of the chemical composition and surface states is required for improving the power factor of InSb nanowires. On approach is to use Indium-rich source materials for the growth to compensate for the loss of indium due to oxidation by residual oxygen. / text

La transition de phase isostructurale du cérium a été et reste l'objet de nombreuses études pour tester les méthodes permettant de décrire les matériaux fortement corrélés.La Théorie du Champ Moyen Dynamique (DMFT) jointe à la Théorie de la fonctionnelle de la densité à permis de décrire de tels systèmes.Pourtant, le calcul des propriétés de l'état fondamental nécessite une très bonne précision de calcul à la fois de la part de la DFT et de la DMFT.Nous utilisons un résolveur Monte Carlo Quantique en Temps Continu (CT-QMC), rapide et capable de simuler les basses températures, combiné à une implantation ondes planes augmentées par projection de la DMFT pour calculer les énergies internes et libres -- et par conséquent l'entropie -- au cours de la transition de phase du cérium.D'importants calculs, utilisant cette implantation, nous ont permis de reconsidérer les propriétés de l'état fondamental et une grande partie de la thermodynamique de la transition de phase α<->γ du cérium à basses températures.En particulier, le bruit stochastique est suffisamment faible pour interpréter, sans ambiguïté, les courbes énergie en fonction du volume.Sur ces dernières, un double point d'inflexion est clairement visible pour l'énergie interne jusqu'à une température relativement basse.Les courbes d'énergie libre mettent, de plus, en évidence l'importance de l'entropie pour ce système.D'autre part, les spectres de photoemission tout au long de la transition de phase sont analysés.Le schéma DMFT est comparé avec des calculs DFT récents et des données expérimentales récentes.Enfin, nous mettons en avant les approximations utilisées et nous nous interrogeons sur leurs validité.

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The calculation of the thermal conductivity of condensed matter has posed a significant challenge to engineers and scientists for almost a century. Thermal conductivity models have been successfully applied to many materials however many challenges still remain. One serious challenge is the inability of current thermal conductivity models to calculate the thermal conductivity of highly complex materials. Another challenge is managing error introduced by using an effective interatomic potential, for many materials this problem is exacerbated because their effective potentials have not been extensively used or characterized. Recent interest in nanostructures has initiated a new set of challenges and unanswered questions. This work addresses different aspects of the aforementioned challenges by using zeolite MFI and gallium nitride as case studies.

Thesis (Ph.D.); Submitted to the University of California, Berkeley, CA (US); 24 Nov 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--56751" McGuire, John Andrew. USDOE Director. Office of Science. Office of Basic Energy Sciences. Materials Science and Engineering Division (US) 11/24/2004. Report is also available in paper and microfiche from NTIS.

PVD hard ceramic coatings grown via the combined cathodic arc/unbalance magnetron deposition process were studied using Raman microscopy. Characteristic spectra from binary, multicomponent, multilayered and superlattice coatings were acquired to gain knowledge of the solid-state physics associated with Raman scattering from polycrystalline PVD coatings and to compile a comprehensive spectral database. Defect-induced first order scattering mechanisms were observed which gave rise to two pronounced groups of bands related to the acoustical (150-300cm[-1]) and optical (400-750cm[-1]) parts of the phonon spectrum. Evidence was gathered to support the theory that the optic modes were mainly due to the vibrations of the lighter elements and the acoustic modes due to the vibrations of the heavier elements within the lattice. A study into the deformation and disordering on the Raman spectral bands of PVD coatings was performed. TiAIN and TiZrN coatings were intentionally damaged via scratching methods. These scratches were then analysed by Raman mapping, both across and along, and a detailed spectral interpretation performed. Band broadening occurred which was related to "phonon relaxation mechanisms" as a direct result of the breaking up of coating grains resulting in a larger proportion of grain boundaries per-unit-volume. A direct correlation of the amount of damage with band width was observed. Band shifts were also found to occur which were due to the stresses caused by the scratching process. These shifts were found to be the largest at the edges of scratches. The Raman mapping of "droplets", a defect inherent to PVD deposition processes, found that higher compressive stresses and large amounts of disorder occurred for coating growth onto droplets. Strategies designed to evaluate the ability of Raman microscopy to monitor the extent of real wear on cutting tools were evaluated. The removal of a coating layer and subsequent detection of a base layer proved successful. This was then expanded to real wear situations in which tools were monitored after 3,6,12,64,120 and 130 minutes-in-cut. A PCA chemometrics model able to distinguish between component layers and oxides was developed. Raman microscopy was found to provide structural and compositional information on oxide scales formed on the surfaces of heat-treated coatings. Wear debris, generated as a consequence of sliding wear tests on various coatings, was also found to be primarily oxide products. The comparison of the oxide types within the debris to those formed on the surface of the same coating statically oxidised, facilitated a contact temperature during sliding to be estimated. Raman microscopy, owing to the piezo-spectroscopic effect, is sensitive to stress levels. The application of Raman microscopy for the determination of residual compressive stresses within PVD coatings was evaluated. TiAlN/VN superlattice coatings with engineered stresses ranging -3 to -11.3 GPa were deposited onto SS and HSS substrates. Subsequent Raman measurements found a correlation coefficient of 0.996 between Raman band position and stress (determined via XRD methods). In addition, there was also a similar correlation coefficient observed between hardness and Raman shift (cm-1). The application of mechanical stresses on a TiAlCrN coating via a stress rig was investigated and tensile and compressive shifts were observed.

Made available in DSpace on 2014-12-17T15:14:50Z (GMT). No. of bitstreams: 1 PauloDSJ.pdf: 1532738 bytes, checksum: 94763a76a879a203043b73e771013af5 (MD5) Previous issue date: 2005-11-12 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / We study the optical-phonon spectra in periodic and quasiperiodic (Fibonacci type) superlattices made up from III-V nitride materials (GaN and AlN) intercalated by a dielectric material (silica - SiO2). Due to the misalignments between the silica and the GaN, AlN layers that can lead to threading dislocation of densities as high as 1010 cm&#8722;1, and a significant lattice mismatch (_ 14%), the phonon dynamics is described by a coupled elastic and electromagnetic equations beyond the continuum dielectric model, stressing the importance of the piezoelectric polarization field in a strained condition. We use a transfer-matrix treatment to simplify the algebra, which would be otherwise quite complicated, allowing a neat analytical expressions for the phonon dispersion relation. Furthermore, a quantitative analysis of the localization and magnitude of the allowed band widths in the optical phonon s spectra, as well as their scale law are presented and discussed / Neste trabalho estudamos o espectro de f?nons ?pticos em estruturas peri?dicas e quasiperi?dicas (tipo Fibonacci) compostas pelos nitretos da fam?lia dos semicondutores III-V (GaN and AlN) intercalados por um material diel?trico (s?lica-SiO2). Devido ao desalinhamento entre as camadas da s?lica e do GaN, AlN, que pode levar a deslocamentos at?micos com densidade eletr?nica t?o alta quanto 1010 cm&#8722;1, e uma diferen?a de par?metro de rede (_ 14%), a din?mica dos f?nons ser? descrita por meio de um modelo te?rico em que as equa??es eletromagn?ticas e el?sticas est?o acopladas atrav?s do tensor piezoel?trico, ressaltando o campo de polariza??o piezoel?trica presente. Usamos tamb?m um tratamento de matriz transfer?ncia para simplificar a ?lgebra do problema, que seria, caso contr?rio, bastante complicada, permitindo uma express?o anal?tica elegante para a curva de dispers?o dos f?nons. Al?m disso, uma an?lise quantitativa da localiza??o e magnitude das larguras de bandas de energia permitida no espectro dos f?nos ?pticos, assim como a sua lei de escala s?o apresentados e discutidos