Comparative studies between the growth characteristics of Bi2Te3 thin films deposited on SiO2, Si(100) and Si(111)
Thin films of Bi2Te3 on SiO2, Si(100) and Si(111) were deposited using a hot wall epitaxy (HWE) system. The growth conditions were optimized by the criterion of the highest mobility. XRD and SEM analysis show that the films obtained were stoichiometric and present a good morphology. No difference was observed between layers deposited on Si(100) and on Si(111): the layers were not sensitive to the initial orientation of silicon. The electrical measurements performed at room temperature show that the quality of layers deposited on SiO2 was better than the quality of layers deposited on Si(100) and Si(111). The figure of merit obtained in the case of the SiO2 substrate was Z = 1.9 × 10−3K−1, which is close to those reported for the monocrystal. The study of the first growing stage shows that the difference obtained between the substrates can be explained by the degree of reactivity of their surfaces.
In situ reflection high-energy electron diffraction (RHEED) observation of Bi2Te3/Sb2Te3 multilayer film growth
Abstract The variation of in situ reflection high-energy electron diffraction (RHEED) patterns was observed for the study of crystal quality of Bi2Te3/Sb2Te3 multilayer films on sapphire (0 0 0 1) substrates during molecular beam epitaxy (MBE) growth. At the initial stage of growth, the RHEED pattern shows a superposition of spots and streaks which indicates the existence of three-dimensional island growth. Moreover, weak streaks between fundamental streaks, which indicate rotation around the c-axis, are observed. It is found that a clear streaky pattern (1×1) gradually appears with the growth of larger grains. The existence of heterointerfaces in Bi2Te3/Sb2Te3 multilayer films is confirmed from the X-ray diffraction (XRD) measurements and the depth profile of Auger electron spectroscopy (AES) measurements.
Analysis of molecular interactions in solid dosage forms; challenge to molecular pharmaceutics.
The molecular states of active pharmaceutical ingredients (APIs) in pharmaceutical dosage forms strongly affect the properties and quality of a drug. Various important fundamental physicochemical studies were reviewed from the standpoint of molecular pharmaceutics. Mechanochemical effects were evaluated in mixtures of APIs and pharmaceutical additives. Amorphization, complex formation and nanoparticle formation are observed after grinding process depending on the combination of APIs and pharmaceutical additives. Sealed-heating method and mesoporous materials have been used to investigate drug molecular interactions in dosage forms. Molecular states have been investigated using powder X-ray diffraction, thermal analysis, IR, solid state fluorometry, and NMR.