Topological insulator thin films of Bi2Te3 with controlled electronic structure can be grown by regulating the molecular beam epitaxy (MBE) growth kinetics without any extrinsic doping. N‐ to p‐type conversion results from the change in the concentrations of TeBi donors and BiTe acceptors. This represents a step toward controlling topological surface states, with potential applications in devices.
The growth and characterization of single-crystalline thin films of topological insulators (TIs) is an important step towards their possible applications. Using in situ scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES), we show that moderately thick Sb 2 Te 3 films grown layer-by-layer by molecular beam epitaxy (MBE) on Si(111) are atomically smooth, single-crystalline, and intrinsically insulating. Furthermore, these films were found to exhibit a robust TI electronic structure with their Fermi energy lying within the energy gap of the bulk that intersects only the Dirac cone of the surface states. Depositing Cs in situ moves the Fermi energy of the Sb 2 Te 3 films without changing the electronic band structure, as predicted by theory. We found that the TI behavior is preserved in Sb 2 Te 3 films down to five quintuple layers (QLs).
It is accepted that the historical routine use of agrochemicals may have resulted in undesirable concentrations of metals in the environment. To investigate and assess the effects of land use on concentrations of heavy metals around the Guanting Reservoir in China, 52 surface soil samples (depth of 2-10 cm) were taken from areas where four types of land use were practiced (including arable land, woodland, bare land, orchard land). The metals and metalloids (As, Cr, Ni, Cu, Zn, Cd, and Pb) were analyzed using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Significant accumulation of As, Cd, and Cr was found in soils of arable land. Based on correlation and cluster analysis, it can be concluded that Cd and Zn originate mainly from phosphate fertilizer, Pb from the use of insecticides, fertilizers, and sewage sludge as well as air deposition, and Cu from copper-based fungicides, while As, Ni and Cr might come from parent soil material. According to an ecological risk analysis of metals based on the ecological index suggested by Hakanson, the four types of land can be ranked by severity of ecological risk as follows: arable land [ woodland [ bare land [ orchard land, with a high ecological risk of Cd for all four types. Management measures for land use planners for avoiding water, soil, and sediment pollution caused by metals around the Guanting Reservoir are presented.
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