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.
Preparation and Thermoelectric Properties of Doped 
Bi2Te3-Bi2Se3 Solid Solutions
Since Bi2Te3 and Bi2Se3 have the same crystal structure, they form a homogeneous solid solution. Therefore, the thermal conductivity of the solid solution can be reduced by phonon scattering. The thermoelectric figure of merit can be improved by controlling the carrier concentration through doping. In this study, Bi2Te2.85Se0.15:Dm (D: dopants such as I, Cu, Ag, Ni, Zn) solid solutions were prepared by encapsulated melting and hot pressing. All specimens exhibited n-type conduction in the measured temperature range (323 K to 523 K), and their electrical conductivities decreased slightly with increasing temperature. The undoped solid solution showed a carrier concentration of 7.37 × 1019 cm−3, power factor of 2.1 mW m−1 K−1, and figure of merit of 0.56 at 323 K. The figure of merit (ZT) was improved due to the increased power factor by I, Cu, and Ag dopings, and maximum ZT values were obtained as 0.76 at 323 K for Bi2Te2.85Se0.15:Cu0.01 and 0.90 at 423 K for Bi2Te2.85Se0.15:I0.005. However, the thermoelectric properties of Ni- and Zn-doped solid solutions were not enhanced.
Adsorption and dissociation of Si2H6 on Ge(001)2 × 1
Adsorption and thermally-induced dissociation of disilane (Si2H6) on clean Ge(001)2 × 1 surfaces have been investigated using a combination of Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), reflection high-energy electron diffraction (RHEED), and scanning tunneling microscopy (STM). With initial Si2H6 exposure at room temperature, the Si surface coverage increased monotonically, the EELS surface dangling bond peak intensities continuously decreased, and the intensity of half-order RHEED diffraction rods decreased. The low-coverage Si2H6 sticking probability at 300 K on Ge(001) was found to be ∼ 0.5 while the saturation coverage was ∼ 0.5 ML. A new EELS feature, GSH, involving Si-H and Ge-H bond states was observed at Si2H6 exposures φ ≳ 3.4 × 1013 cm−2. In contrast to Si2H6 -saturated Si(001), the saturated Ge(001) surface significant fraction of dimerized bonds. Adsorbed overlayers were highly disordered with the primary species on saturated surfaces being SiH2, GeH, and undissociated SiH3· Si2H6-saturated Ge(001)2 × 1 substrates were annealed for l min at temperatures Ta between 425 and 825 K. Admolecules were mobile at Ta = 545 K giving rise to significant ordering in one-dimensional chains. By Ta = 605 K, essentially all of the admolecules were captured into coarsened islands. Dangling-bond EELS peaks reappeared by 625 K and the intensities of the half-order RHEED diffraction rods increased. Ge segregation to the surface, which began at Ta ≳ 625 K, occurred rapidly at Ta ⩾ 675 K. All H was desorbed by 725 K.