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.
Microstructure and Thermoelectric Properties of Thin Foils of Bismuth Telluride Alloys
Ultrarapid quenching processes have been extensively studied during the past few years. particularly for glasses. In the case of polycrystalline materials, the problem is slightly different. In this case, the microstructures obtained by this process are very different from those obtained by normal cooling and they induce new physical properties.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.