Search

In this study, the local order and the structural evolution of the PdAg binary alloy system during the crystallization process from the amorphous phase under different pressures was investigated using the molecular dynamics simulation method. The structural development and phase transformation of the model alloy system for pressures of 0,1, and 5 GPa are analysed based on variations of the radial distribution function, the bond orientational order parameters, and Honeycutt-Andersen bond-type index method. The simulation results showed that higher pressures favoured amorphous-type atomic clusters and had an important effect on the bond orientational order parameters of the model system of the transformation from amorphous state to stable crystal phase during the isothermal annealing. PACS Nos.: 64.70.Q-, 64.70.kd, 64.70.kj, 64.70.P-. Nous utilisons ici la methode de simulation de dynamique moleculaire pour etudier l'ordre local et revolution structurelle d'alliages binaires PdAg pendant le processus de cristallisation a partir d'une phase amorphe sous differentes pressions. Le developpement structurel et la transformation de phase, a des pressions de 0,1 et 5 GPa, sont analyses sur la base des variations de la distribution radiale, des parametres d'ordre orientationnel de lien et de la methode de lien de HoneycuttAndersen. Les resultats de la simulation montrent que la haute pression favorise la phase amorphe et a un effet important sur les parametres d'ordre orientationnel de lien dans ce modele de la transformation d'une phase amorphe stable a une phase cristalline stable pendant le recuit isotherme. [Traduit par la Redaction], 1. Introduction Amorphous alloys can be prepared through various nonequilibrium processes, such as rapid solidification, physical vapour deposition, and mechanical alloying [1]. Usually, to avoid the nucleation and growth of [...]

Low thermal budget rapid thermal annealing is a promising method of forming highly crystalline silicon thin films on silicon substrates for heterojunction solar cells. In this work, the extent of crystallization was examined by Raman and ultraviolet reflectance spectroscopy, and ellipsometry was used to derive film optical properties. Solar cells were fabricated and analyzed using dark and illuminated current-voltage characteristics, external quantum efficiency, and solar simulator measurements with device efficiency approaching 14%. PACS Nos.: 88.40.jj, 78.66.Db, 78.40.Fy. Le recuit thermique rapide a faible budget thermique est une methode prometteuse pour fabriquer des films minces de silicium hautement cristallin sur des substrats de silicium, pour faire des cellules solaires heterojonctions. Nous examinons ici le niveau de cristallisation par spectroscopie de reflectance Raman et UV et un ellipsometre est utilisee pour determiner les proprietes optiques du film. Nous fabriquons les cellules solaires et nous les analysons en mesurant les caracteristiques courant-voltage en obscurite et sous illumination et le rendement quantique externe et par des mesures solaires simulees avec un rendement approchant 14 %. [Traduit par la Redaction], 1. Introduction Amorphous silicon (a-Si:H) heterojunctions on crystalline silicon (c-Si) substrates have received much interest among the photovoltaic research community. The classic c-Si/a-Si:H structure includes an ultrathin (2-5 nm thick) [...]

Flash lamp annealing (FLA) of micrometre-order thick amorphous silicon (a-Si) films can induce explosive crystallization (EC), high-speed lateral crystallization driven by the release of latent heat. We develop multi-pulse FLA system, which emits a quasi-millisecond pulse consisting of a number of subpulses. The emission frequency of the subpulses can be systematically controlled, and the emission of subpulses leads to the periodic modulation of the temperature of a Si film and the resulting formation of macroscopic stripe patterns. The relationship between a subpulse emission frequency and the width of the macroscopic stripe patterns yields EC velocity. Two kinds of EC modes can be observed, depending on the methods of precursor a-Si deposition and (or) a-Si film thickness. PACS Nos.: 81.10Jt, 81.40.Ef, 88.40.jj. Le recuit par lampe a decharge (FLA) de films de silicium amorphe (a-Si) peut causer une cristallisation spontanee (explosive) (EC) ou une cristallisation laterale induite, soutenue par le rejet de chaleur latente. Nous developpons un systeme de recuit par lampe a decharge multi-pulse qui emet des impulsions presque milliseconde consistant en un nombre de sousimpulsions. La frequence d'emission de ces sous-impulsions peut etre controlee et l'emission de ces sous- impulsions mene aune modulation de la temperature du film de Si, d'oU il resulte la formation d'un patron en bandes macroscopiques. La relation entre la frequence d'emission des sous-impulsions et la largeur de ces bandes donne la vitesse de EC. Nous observons deux types de modes EC, dependant de la methode de deposition du precurseur Si et (ou) de l'epaisseur du film de a-Si. [Traduit par la Redaction], 1. Introduction Thin-film crystalline Si (c-Si) is of great interest as a photovoltaic material because of the possibility of high efficiency and efficient material usage. Of a variety of methods [...]

We deposited amorphous indium gallium nitride (a-[In.sub.x][Ga.sub.1-x]N) films at room temperature by reactive radio frequency sputtering with GaN and InN targets and investigated the change of their properties from thermal annealing at annealing temperatures, [T.sub.a], below 200°C. A large change in the indium and nitrogen composition ratios was not observed by thermal annealing at a [T.sub.a] below 200°C. In the X-ray diffraction patterns of the films annealed at a [T.sub.a] below 200°C, no perceivable peaks assigned to crystalline [In.sub.x][Ga.sub.1-x]N were found. The photoconductivty, [σ.sub.p], increased with an increase in [T.sub.a]. On the other hand, the increase of the dark conductivity, [σ.sub.d], was very small with an increase in [T.sub.a] below 200°C. As a result, the photosensitivity, [σ.sub.p]/[σ.sub.d], increased from 252 to 2500 by thermal annealing at a [T.sub.a] of 200°C. PACS Nos.: 73.61.Ey, 61.43.Dq, 73.61.Jc. Nous deposons des films de nitrure de gallium indium amorphe (a-[In.sub.x][Ga.sub.1-x]N) a temperature de la piece par pulverization cathodique radio-frequence reactive sur des cibles de GaN et de InN et nous analysons le changement de leurs proprietes sous recuit thermique a temperature [T.sub.a] plus basse que 200°C. Nous n'observons pas de changement dans les rapports de composition de l'indium et de l'azote a des temperatures de recuit sous 200°C. Dans les patrons de diffraction X des films recuits sous 200°C, nous ne trouvons aucun pic assignable a du [In.sub.x][Ga.sub.1-x]N cristallin. La photoconductivite [σ.sub.p] augmente avec [T.sub.a]. D'un autre cote, la conductivite en obscurite [σ.sub.d] n'augmente que tres peu lorsque [T.sub.a] augmente sous les 200°C. Le resultat est que le rapport [σ.sub.p]/[σ.sub.d] augmente de 252 a 2500 lorsque [T.sub.a] augmente jusqu'il 200°C. [Traduit par la Redaction], Introduction In multijunction thin film solar cells, photoabsorption layer materials with various band gap energies are required. At present, the band gap energy of the photoabsorption layer materials used in [...]

We have synthesized silicon nanocrystalline structures from thermal annealing of thin film amorphous silicon-based multilayers. The annealing procedure that was carried out in vacuum at temperatures up to 1100°C is integrated in a X-ray diffraction (XRD) setup for real-time monitoring of the formation phases of the nanostructures. The microstructure of the crystallized films is investigated through experimental measurements combined with atomistic simulations of realistic nanocrystalline silicon (nc-Si) models. The multilayers consisting of uniformly alternating thicknesses of hydrogenated amorphous silicon and silicon oxide (Si[O.sub.2]) were deposited by plasma enhanced chemical vapor deposition on crystalline silicon and Corning glass substrates. The crystallized structure consisting of nc-Si structures embedded in an amorphous matrix were further characterized through XRD, Raman spectroscopy, and Fourier transform infrared measurements. We are able to show the different stages of nanostructure formation and how the sizes and the crystallized mass fraction can be controlled in our experimental synthesis. The crystallized silicon structures with large crystalline filling fractions exceeding 50% have been simulated with a robust classical molecular dynamics technique. The crystalline filling fractions and structural order of nc-Si obtained from this simulation are compared with our Raman and XRD measurements. PACS Nos.: 81.10Jt, 81.07.-b, 61.05.cp. Nous fabriquons des structures nanocristallines de silicium par recuit thermique de films minces multicouches de silicium amorphe. La procedure de recuit se fait dans une chambre a vide a temperature jusqu'a 1100°C, avec un appareillage in situ de diffraction X (XRD) pour surveiller en temps reel la formation des phases nanocristallines. Nous etudions la microstructure des films cristallises a l'aide de mesures experimentales et de simulations atomiques de modeles realistes de silicium nanocristallin (nc-Si). Les multicouches sont constitues de couches uniformes alternees de silicium amorphe hydrogene et d'oxyde de silicium Si[O.sub.2] et sont obtenus par depot chimique en phase vapeur avec traitement au plasma sur des substrats de silicium cristallin et de verre Corning. Les structures cristallisees sont des structures nc-Si incrustees dans une matrice amorphe et sont caracterisees par XRD, spectroscopie Raman et par mesures infra-rouge a transformee de Fourier. Nous sommes capables de montrer les differentes etapes de la formation de nanostructure et comment les grosseurs et les fractions massiques cristallisees peuvent etre controlees dans notre montage. Nous avons simule les structures cristallisees de silicium, avec des coefficients de remplissage de plus de 50%, a l'aide une solide technique de dynamique moleculaire classique. Nous comparons les fractions de remplissage et l'ordre structural de nc-Si obtenus dans cette simulation avec nos mesures Raman et XRD. [Traduit par la Redaction], 1. Introduction Silicon quantum dots (QDs) have great potential to be an absorber in solar cells, where the band gap can be tuned by the QD size. QDs have been [...]

In-situ scanning electron microscopy (SEM) enables microstructure evolution to be studied under various loading conditions. Modern SEMs incorporate heating assemblies so they can be tilted to the optimum angle for [...]

In this study, a water-soluble crystallizable polymer, poly(ethylene glycol) (PEG), was compounded with isotactic polypropylene (iPP), and a subsequent thermo-annealing process was added to improve the toughness of iPP/PEG blend. By adding a small amount of PEG (5 wt%) into iPP, only a mild increment of 40% in toughness was achieved. However, the toughness of iPP/PEG (95/5) blend could be improved remarkably when the postprocessing procedure, thermal annealing, was utilized. For example, the notched impact strength of iPP/PEG blend annealed under 120°C for 12 h was five times of that of neat iPP. In addition, the tensile strength of annealed blend was slightly changed, compared with neat iPP. To ascertain the origin of toughening, various crystallographic and mor-phological/structural characterizations, including X-ray diffraction, electron microscopy, and calorimeter were employed. A specific structural change, in which more and more amounts of micrometer/sub-micrometer voids, yielded within the amorphous iPP region during the annealing process, was responsible for the prominent toughening behavior. POLYM. ENG. SCI., 53:2053-2060, 2013. © 2013 Society of Plastics Engineers, INTRODUCTION Isotactic polypropylene (iPP) is a semicrystalline polymer with excellent comprehensive performances. It has been extensively used in automobile parts, household appliances, furniture, and packages, etc. However, its poor impact [...]

The effects of annealing time and temperature on the crystallinity of injection-molded poly(lactic acid) (PLA) were investigated using differential scanning calorimetry and wide-angle x-ray diffraction. Differential scanning calorimetry, tensile test, and dynamic mechanical analysis showed that an increase in crystallinity in the PLA parts from the annealing treatment offers several benefits such as a higher glass transition temperature, better heat resistance, and greater storage modulus and tensile strength. Based on the experimental data, the degree of crystallinity, annealing time, and annealing temperature were found to closely follow the time-temperature superposition relationship. Namely, a master curve could be constructed based on either the Wil-liams-Landel-Ferry equation or the Arrhenius relationship by shifting the crystallinity isotherms in the logarithmic scale horizontally along the log-time axis. This relationship provides a quantitative guideline for annealing postinjection-molded PLA parts to improve the heat resistance and mechanical properties. An increase of over 17% and 26% in tensile strength was achieved at an annealing temperature of 80 °C for 30 min and 65°C for 31 h, respectively. POLYM. ENG. SCI., 53:580-588, 2013. © 2012 Society of Plastics Engineers, INTRODUCTION Poly(lactic acid) or polylactide (PLA) is a biodegradable thermoplastic polyester obtained by synthesis of lactic acid (or lactide), which can be produced from renewable resources such as corn or [...]