Thin film growth from vapors by effusive ampoule physical vapor transport

Abstract

Although the use of white beam stroboscopic topography at synchrotron stations has allowed a good understanding of the propagation of ultra-acoustic waves [1], section topography remains a powerful tool for a quantitative analysis of the deformation induced by the waves [2]. When the deformation increases one may observe different states: firstly the usual extinction fringes are only slightly enlarged, then new fringes appear and progressively become the only visible fringes. Their number is linked to the mode of the excited ultra-acoustic wave. Then the whole image is changed: the fringes are curved and their shape allows to quantitatively measure the shape of the deformation along the surface of the device. At the same time the number of visible fringes decreases.In the present study we will examine by means of experiments performed at synchrotron stations at LURE and at ESRF the different states of the contrast. We will study the transition from weak to important deformations showing the appearance of the new set of fringes. We will show how the fringes in the most deformed areas are linked to the fringes in the less deformed areas, near the edges of the device, where the deformation becomes negligible. Simulations computed in the case of weak and intermediate amplitudes of vibration are in good agreement with the experiments. In the case of important deformations the contrast may be interpreted by means of the kinematical theory only.These experiments demonstrate the interest of an 'old' technique, section topography, used together with a modern one, synchrotron topography, since the resolution achievable with a conventional setting in the laboratory would not permit such a high resolution study of the fringes. The stable quasicrystalline icosahedral phase has been found in Ga-Mg-Zn by melt spinning technique as well as by slow cooling from the melt [1]. In addition the authors observed icosahedral crystals with pentagonal dodecahedral growth morphology in shrinkage cavities. The aim of our investigations was to analyse solidification process for Ga-Mg-Zn alloy for compositions in the vicinity of quasicrystalline phase existence. Slow solidification from the melt was performed using home made apparatus. The sample composition has been different for prepared alloys with Ga content from 16% up to 56%, Mg from 32% to 38 % and Zn content varied between 52% and 10%. During solidification process of different composition of alloys several types of single crystals has been obtained. Polygonal forms of mgzn2 (Laves phase) single crystals crystallised in the shrinkage cavities, the single crystals of Ga28Mg42Zn30 and faceted forms of Ga14Mg27Zn59 single crystals were for the first time observed in our experiment. Apart from that relatively large (2mm x 2mm) polygonal Mg single crystals crystallised in shrinkage cavities. For some compositions in the whole volume of the sample colonies of Zn whiskers were spread out. Having hexagonal cross section and lateral faces {1120} or {1010} type their growth direction was [000...