RESUMO
Exploring new phase-change materials is instrumental in the progression of electronic memory devices. Ag2Te with its reversible structural phase transition, and in the form of nanowires, has become an apt candidate for potential use in nanoscale memory devices. Here, we report a study on the temperature- or electrically-driven phase change properties of crystalline Ag2Te nanowires. We first demonstrate that this structural phase change can be achieved via heating up the nanowires, which results in a sharp drop in conductance. Then we show that a DC voltage (<1 V) induced Joule heating can be used to reach the phase transition, even without any external heating. This work shows the potential of using Ag2Te nanowires as a phase-change material in low voltage and low power nanoscale devices.
RESUMO
Atomically-thin 2D materials have opened up new opportunities in the past decade in realizing novel electronic device concepts, owing to their unusual electronic properties. The recent progress made in the aspect of utilizing additional degrees of freedom of the electrons such as spin and valley suggests that 2D materials have a significant potential in replacing current electronic-charge-based semiconductor technology with spintronics and valleytronics. For spintronics, spin-orbit coupling plays a key role in manipulating the electrons' spin degree of freedom to encode and process information, and there are a host of recent studies exploring this facet of 2D materials. We review the recent advances in tuning spin-orbit coupling of 2D materials which are of notable importance to the progression of spintronics.
RESUMO
Synthesis of large-area hexagonal boron nitride (h-BN) films for two-dimensional (2D) electronic applications typically requires high temperatures (â¼1000 °C) and catalytic metal substrates which necessitate transfer. Here, analogous to plasma-enhanced chemical vapor deposition, a nonthermal plasma is employed to create energetic and chemically reactive states such as atomic hydrogen and convert a molecular precursor film to h-BN at temperatures as low as 500 °C directly on metal-free substrates-a process we term plasma-enhanced chemical film conversion (PECFC). Films containing ammonia borane as a precursor are prepared by a variety of solution processing methods including spray deposition, spin coating, and inkjet printing and reacted in a cold-wall reactor with a planar dielectric barrier discharge operated at atmospheric pressure in a background of argon or a mixture of argon and hydrogen. Systematic characterization of the converted h-BN films by micro-Raman spectroscopy shows that the minimum temperature for nucleation on silicon-based substrates can be decreased from 800 to 500 °C by the addition of a plasma. Furthermore, the crystalline domain size, as reflected by the full width at half-maximum, increased by more than 3 times. To demonstrate the potential of the h-BN films as a gate dielectric in 2D electronic devices, molybdenum disulfide field effect transistors were fabricated, and the field effect mobility was found to be improved by up to 4 times over silicon dioxide. Overall, PECFC allows h-BN films to be grown at lower temperatures and with improved crystallinity than CVD, directly on substrates suitable for electronic device fabrication.
RESUMO
The Drude model is one of the most fundamental models used to understand the electronic carrier transport in materials, including recently discovered topological materials. Here, we present a magneto-transport study revealing the non-Drude transport behavior in a heterostructure of topological crystalline insulator (TCI) SnTe and band insulator PbTe which exhibits a nonsaturating linear magneto-resistance (MR) effect, a novel phenomenon widely observed in topological materials with gapless dispersion. It is shown that in the van der Pauw geometry in which the longitudinal and transverse magneto-resistances are measured to extract the magneto-conductivity, the two-band Drude model is not sufficient to self-consistently describe both the longitudinal and transverse magneto-conductivities. Furthermore, in the Corbino geometry, which directly measures the longitudinal magneto-conductivity σ xx( B) for a straightforward comparison with the Drude model, the MR, 1/σ xx( B), still reveals a large linear MR effect, in direct discrepancy with the Drude model. While shining further light on the multiple-carrier transport in TCI, this study highlights an unusual magneto-transport character of topological materials that challenges the standard Drude picture of electron transport.
RESUMO
Manipulating the electron spin with the aid of spin-orbit coupling (SOC) is an indispensable element of spintronics. Electrostatically gating a material with strong SOC results in an effective magnetic field which can in turn be used to govern the electron spin. In this work, we report the existence and electrostatic tunability of Rashba SOC in multilayer InSe. We observed a gate-voltage-tuned crossover from weak localization (WL) to weak antilocalization (WAL) effect in quantum transport studies of InSe, which suggests an increasing SOC strength. Quantitative analyses of magneto-transport studies and energy band diagram calculations provide strong evidence for the predominance of Rashba SOC in electrostatically gated InSe. Furthermore, we attribute the tendency of the SOC strength to saturate at high gate voltages to the increased electronic density of states-induced saturation of the electric field experienced by the electrons in the InSe layer. This explanation of nonlinear gate voltage control of Rashba SOC can be generalized to other electrostatically gated semiconductor nanomaterials in which a similar tendency of spin-orbit length saturation was observed (e.g., nanowire field effect transistors), and is thus of broad implications in spintronics. Identifying and controlling the Rashba SOC in InSe may serve pivotally in devising III-VI semiconductor-based spintronic devices in the future.
