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Hydrogenation of silicon tetrachloride(STC) in the presence ofsilicon was investigated both thermodynamically and experimentally.The thermodynamic results revealed that the reaction is thermodynamicallyconstrained and the STC equilibrium conversion is nearly temperature-independentbut increases with increasing pressure and H2/STC feedratio. Trichlorosilane (TCS) was calculated to be the dominant product,with trace amounts of dichlorosilane (DCS) and HCl as feasible byproducts.Experimental tests were conducted in a fixed-bed reactor loaded withsilicon. The results indicated that the reaction is kinetically restrictedin the absence of a catalyst. Adding CuCl to the silicon mass bedwas found to result in a dramatic increase in the STC conversion,and Cu3Si was determined to be the active species. In allof the tests runs, TCS was determined to be the dominant product,and the STC reaction rate was found to increase markedly as the temperatureand STC partial pressure increased but not to depend on the siliconparticle size. [ABSTRACT FROM AUTHOR]

Stoichiometric Cr 2 Se 3 single crystals are particular layer-structured antiferromagnets, which possess a noncollinear spin configuration, weak ferromagnetic moments, moderate magnetoresistance (MR ∼14.3%), and poor metallic conductivity below the antiferromagnetic phase transition. Here, we report an interesting >16 000% colossal magnetoresistance (CMR) effect in Ti (1.5 atomic percent) lightly doped Cr 2 Se 3 single crystals. Such a CMR is approximately 1143 times larger than that of the stoichiometric Cr 2 Se 3 crystals and is rarely observed in layered antiferromagnets and is attributed to the frustrated spin configuration. Moreover, the Ti doping not only dramatically changes the electronic conductivity of the Cr 2 Se 3 crystal from a bad metal to a semiconductor with a gap of ∼15 meV but also induces a change in the magnetic anisotropy of the Cr 2 Se 3 crystal from strong out-of-plane to weak in-plane. Further, magnetotransport measurements reveal that the low-field MR scales with the square of the reduced magnetization, which is a signature of CMR materials. The layered Ti:Cr 2 Se 3 with the CMR effect could be used as two-dimensional (2D) heterostructure building blocks to provide colossal negative MR in spintronic devices.

A series of Cr-doped In 2- x Cr x O 3 (ICO) semiconductor thin films were epitaxially grown on (111)-oriented 0.71Pb(Mg 1/3 Nb 2/3 )O 3 -0.29PbTiO 3 (PMN-0.29PT) single-crystal substrates by the pulsed laser deposition. Upon the application of an electric field to the PMN-0.29PT substrate along the thickness direction, we realized in situ, reversible, and nonvolatile control of the electronic properties and Fermi level of the films, which are manifested by abundant physical phenomena such as the n-type to p-type transformation, metal-semiconductor transition, metal-insulator transition, crossover of the magnetoresistance (MR) from negative to positive, and a large nonvolatile on-and-off ratio of 5.5 × 10 4 % at room temperature. We also strictly disclose that both the sign and the magnitude of MR are determined by the electron carrier density of ICO films, which could modify the s - d exchange interaction and weak localization effect. Our results demonstrate that the ferroelectric gating approach using PMN-PT can be utilized to gain deeper insight into the carrier-density-related electronic properties of In 2 O 3 -based semiconductors and provide a simple and energy efficient way to construct multifunctional devices which can utilize the unique properties of composite materials.

Single-phase (00 l)-oriented Bi 2 Te 3 topological insulator thin films have been deposited on (111)-oriented ferroelectric 0.71Pb(Mg 1/3 Nb 2/3 )O 3 -0.29PbTiO 3 (PMN-PT) single-crystal substrates. Taking advantage of the nonvolatile polarization charges induced by the polarization direction switching of PMN-PT substrates at room temperature, the carrier density, Fermi level, magnetoconductance, conductance channel, phase coherence length, and quantum corrections to the conductance can be in situ modulated in a reversible and nonvolatile manner. Specifically, upon the polarization switching from the positively poled P r + state (i.e., polarization direction points to the film) to the negatively poled P r - (i.e., polarization direction points to the bottom electrode) state, both the electron carrier density and the Fermi wave vector decrease significantly, reflecting a shift of the Fermi level toward the Dirac point. The polarization switching from P r + to P r - also results in significant increase of the conductance channel α from -0.15 to -0.3 and a decrease of the phase coherence length from 200 to 80 nm at T = 2 K as well as a reduction of the electron-electron interaction. All these results demonstrate that electric-voltage control of physical properties using PMN-PT as both substrates and gating materials provides a simple and a straightforward approach to realize reversible and nonvolatile tuning of electronic properties of topological thin films and may be further extended to study carrier density-related quantum transport properties of other quantum matter.

We report the fabrication of 0.71Pb(Mg 1/3 Nb 2/3 )O 3 -0.29PbTiO 3 (PMN-0.29PT)-based ferroelectric field effect transistors (FeFETs) by the epitaxial growth of cobalt-doped tin dioxide (SnO 2 ) semiconductor thin films on PMN-0.29PT single crystals. Using such FeFETs we realized in situ, reversible, and nonvolatile manipulation of the electron carrier density and achieved a large nonvolatile modulation of the resistance (∼330%) of the SnO 2 :Co films through the polarization switching of PMN-0.29PT at 300 K. Particularly, combining the ferroelectric gating with piezoresponse force microscopy, X-ray diffraction, Hall effect, and magnetoresistance (MR), we rigorously disclose that both sign and magnitude of the MR are intrinsically determined by the electron carrier density, which could modify the s-d exchange interaction of the SnO 2 :Co films. Furthermore, we realized multilevel resistance states of the SnO 2 :Co films by combining the ferroelectric gating with ultraviolet light illumination, demonstrating that the FeFETs have potential applications in multistate resistive memories and electro-optical devices.