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Highlights • Pressure-dependent electronic properties of polycrystalline β -Ag 0.33 V 2 O 5 is investigated for the first time. • An semiconductor-metallic state transition occurs at 4.5 GPa and room temperature. • High temperature/pressure treatment can markedly reduce S-M transition pressure to 1.5 GPa. Abstract The pressure-dependent electronic properties of polycrystalline β -Ag 0.33 V 2 O 5 were investigated and a discontinuous change of electrical resistance is found at around 4.5 GPa, where semiconductive-like decreasing trend before 4.5 GPa and a metallic-like increasing trend after 4.5 GPa with increasing temperature was observed. Furthermore, high temperature/pressure treatment can markedly reduce the semiconductor-metal (S-M) transition pressure to around 1.5 GPa. The results indicate a promising way for engineering the electronic properties of polycrystalline Ag 0.33 V 2 O 5 , and this pressure/temperature induced semiconductor-metal switch may have potential applications in electronics field. [ABSTRACT FROM AUTHOR]

We demonstrate a room temperature semiconductor-metal transition in thin film MoTe2 engineered by strain. Reduction of the 2H-1T' phase transition temperature of MoTe2 to room temperature was realized by introducing a tensile strain of 0.2%. The observed first-order SM transition improved conductance ~10?000 times and was made possible by an unusually large temperature-stress coefficient, which results from a large volume change and small latent heat. The demonstrated strain-modulation of the phase transition temperature is expected to be compatible with other TMDs enabling the 2D electronics utilizing polymorphism of TMDs along with the established materials. [ABSTRACT FROM AUTHOR]

Abstract: Nanocrystalline vanadium dioxide (VO2) thin films were grown on glass substrates by using reactive direct current magnetron sputtering and in situ thermal treatments at low preparation temperatures (≤350°C). The VO2 thin films were characterized by grazing-incidence X-ray diffraction, field emission scanning electron microscope, transmission electron microscopy and spectroscopic ellipsometry (SE). The semiconductor-metal transition (SMT) characteristics of the films were investigated by four-point probe resistivity measurements and infrared spectrometer equipped with heating pads. The testing results showed that the crystal structure, morphology, grain size and semiconductor-metal transition temperature (T SMT) significantly changed as the film thickness decreased. Multilayer structures were observed in the particles of thinner films whose average particle size is much larger than the film thickness and average VO2 grain size. A competition mechanism between the suppression effect of decreased thickness and coalescence of nanograins was proposed to understand the film growth and the formation of multilayer structure. The value of T SMT was found to decrease as average VO2 grain size became smaller, and SE results showed that small nanograin size significantly affected the electronic structure of VO2 film. [Copyright &y& Elsevier]

Crystalline vanadium dioxide (VO2) thin films were prepared by annealing amorphous VO2 films which were deposited by atomic layer deposition on a SiO2 substrate. A large influence of the oxygen partial pressure in the annealing ambient was observed by means of in-situ X-ray diffraction. In the range between 1 and 10Pa of oxygen the interesting VO2(R) phase crystallized near 450°C. Between 2 and 10Pa of oxygen, metastable VO2(B) was observed as an intermediate crystalline phase before it transformed to VO2(R). Anneals in inert gas did not show any crystallization, while oxygen partial pressures above 10Pa resulted in oxidation into the higher oxide phase V6O13. Film thickness did not have much effect on the crystallization behavior, but thinner films suffered more from agglomeration during the high-temperature crystallization on the SiO2 substrate. Nevertheless, continuous polycrystalline VO2(R) films were obtained with thicknesses down to 11nm. In the case where VO2(R) was formed, the semiconductor–metal transition was observed by three complementary techniques. This transition near 68°C was characterized by X-ray diffraction, showing the transformation of the crystal structure, by spectroscopic ellipsometry, mapping optical changes, and by sheet resistance measurements, showing resistance changes larger than 2 orders of magnitude between the low-temperature semiconducting state and the high-temperature metallic state. [ABSTRACT FROM AUTHOR]

Abstract: We provide a detailed physical discussion of the existence of a quantum critical point (QCP) at the metallization threshold of an almost stoichiometric magnetite, with the critical pressure . A presence of an additional crossover or a critical line separating metallic and semiconducting states is proposed. A connection of the critical behavior to that of a spinless-fermion model with coupling of fermions to the lattice distortion is outlined. [Copyright &y& Elsevier]

Abstract: We demonstrate semiconductor–metal transition through diamagnetic susceptibility of a donor in a GaAs/Al x Ga1− x As quantum well for both infinite and finite barrier models. We have also considered the non-parabolicity of the conduction band in our calculation. Our results agree with the earlier theoretical result and also with the recent experimental result. [Copyright &y& Elsevier]

This study develops a variational approach to calculate the binding energy of a shallow hydrogenic impurity in a n-doped In0.53Ga0.47As/InP single quantum well. Using a proper trial wavefunction, both Schro¨dinger and Poisson equations were solved simultaneously within the effective mass approximation, taking into account finite well barriers, finite temperatures, and different effective masses and dielectric constants along the growth direction. Band bending, screening, and many-body effects were considered and it is found these effects reduce drastically the impurity binding energy and lead to the vanishing of this energy when the 2DEG density reaches a critical value. Our results show that such a vanishing occurs even for very thin quantum wells, contrarily to recent calculations developed for GaAs/AlGaAs quantum wells. [Copyright &y& Elsevier]

Semiconductor-metal transition in BAs/BP/BAs/BP sandwiched heterostructure and BAs/BP double-walled nanotubes. • Semiconductor-metal transition occurred in the BAs/BP sandwiched heterostructures. • Semiconductor-metal transition induced by the rotation between inner and outer tubes. • Negative differential resistance in the BAs60 two-probe devices. Significant endeavors have been made to predict the van der Waals (vdW) heterostructures consisted of boron arsenide (BAs) and boron phosphide (BP) sheets, which are indispensable for next-generation nanoelectronic devices. Theoretical results show that the BP intercalation in the BAs/BP sandwiched heterostructures induce a peculiar semiconductor-metal transition, and further results in a dramatic increase in the electronic current, very different from the pure BAs and BP sheets. More strikingly, when a small BP nanotube is inserted into a larger BAs nanotube, because of the rotation between the inner and outer tubes, also leading to the similar semiconductor-metal transition. The semiconductor-metal transition in the sandwiched heterostructures composed of BAs and BP sheets gives a theoretical support for the fundamental science and device technologies and provides a possible approach to design conducting heterostructures by different monolayer semiconductors. [ABSTRACT FROM AUTHOR]

We have studied the electronic structure and the current-voltage (I-V) characteristics of one-dimensional InSe nanoribbons using the density functional theory combined with the nonequilibrium Green’s function method. Nanoribbons having bare or H-passivated edges of types zigzag (Z), Klein (K), and armchair (A) are taken into account. Edge states are found to play an important role in determining their electronic properties. Edges Z and K are usually metallic in wide nanoribbons as well as their hydrogenated counterparts. Transition from semiconductor to metal is observed in hydrogenated nanoribbons HZZH as their width increases, due to the strong width dependence of energy difference between left and right edge states. Nevertheless, electronic structures of other nanoribbons vary with the width in a very limited scale. The I-V characteristics of bare nanoribbons ZZ and KK show strong negative differential resistance, due to spatial mismatch of wave functions in energy bands around the Fermi energy. Spin polarization in these nanoribbons is also predicted. In contrast, bare nanoribbons AA and their hydrogenated counterparts HAAH are semiconductors. The band gaps of nanoribbons AA (HAAH) are narrower (wider) than that of two-dimensional InSe monolayer and increase (decrease) with the nanoribbon width. [ABSTRACT FROM AUTHOR]