Effect of Substrates and Thermal Treatments on Metalorganic Chemical Vapor Deposition-Grown Sb2Te3 Thin Films

Antimony telluride (Sb2Te3) thin films were obtained by metalorganic chemical vapor deposition (MOCVD). The films were grown on crystalline Si(100) and Al2O3(0001) and amorphous SiO2 and alpha-Al2O3 substrates. Their structural properties were compared with those of the Sb2Te3/Si(111) heterostructure. In addition to the effect of the substrate, the influence of pre- and post-growth thermal annealing is also presented. The quality of the films is discussed by comparing their morphological properties, such as roughness and granularity, and ascertaining their crystallinity and their in-plane and out-of-plane orientation

Determination of the anisotropic elastic properties of rocksalt Ge2Sb2Te5 by XRD, residual stress, and DFT

© 2016 American Chemical Society. The chalcogenide material Ge2Sb2Te5 is the prototype phase-change material, with widespread applications for optical media and random access memory. However, the full set of its independent elastic properties has not yet been published. In this study, we determine the elastic constants of the rocksalt Ge2Sb2Te5, experimentally by X-ray diffraction (XRD) and residual stress and computationally by density functional theory (DFT). The stiffnesses (XRD-stress/DFT) in GPa are C11 = 41/58, C12 = 7/8, and C44 = 8/12, and the Zener ratio is 0.46/0.48. These values are important to understand the effect of elastic distortions and nonmelting processes on the performances of increasingly small phase change data bits

Single-step Au-catalysed synthesis and microstructural characterization of core-shell Ge/In-Te nanowires by MOCVD

We report on the self-assembly of core-shell Ge/In-Te nanowires (NWs) on single crystal Si substrates by Metalorganic Chemical Vapour Deposition (MOCVD), coupled to the Vapour-Liquid-Solid (VLS) mechanism, catalysed by Au nanoparticles (NPs). The NWs are formed by a crystalline Ge core and an InTe (II) shell, have diameters down to 15 nm and show <110> oriented growth direction. The role of the MOCVD process parameters and of the NPs size in determining the NWs core-shell microstructure and their alignment was investigated by high-resolution TEM, EDX, XRD and Raman spectroscopy

Controlling magnetoresistance by oxygen impurities in Mq3-based molecular spin valves

The understanding of magnetoresistance (MR) in organic spin valves (OSVs) based on molecular semiconductors is still incomplete after its demonstration more than a decade ago. While carrier concentration may play an essential role in spin transport in these devices, direct experimental evidence of its importance is lacking. We probed the role of charge carrier concentration by studying the interplay between MR and multilevel resistive switching in OSVs. The present work demonstrates that all salient features of these devices, particularly the intimate correlation between MR and resistance, can be accounted for by the impurity band model, based on oxygen migration. Finally, we highlight the critical importance of carrier concentration in determining spin transport and MR in OSVs and the role of interface-mediated oxygen migration in controlling the OSVs response

High‐Density Sb2Te3 Nanopillars Arrays by Templated, Bottom‐Up MOCVD Growth

n/

Large Spin-to-Charge Conversion at Room Temperature in Extended Epitaxial Sb2Te3 Topological Insulator Chemically Grown on Silicon

Spin-charge interconversion phenomena at the interface between magnetic materials and topological insulators (TIs) are attracting enormous interest in the research effort toward the development of fast and ultra-low power devices for future information and communication technology. A large spin-to-charge (S2C) conversion efficiency in Au/Co/Au/Sb2Te3/Si(111) heterostructures based on Sb2Te3 TIs grown by metal-organic chemical vapor deposition on 4 '' Si(111) substrates is reported. By conducting room temperature spin pumping ferromagnetic resonance, a 250% enhanced charge current due to spin pumping in the Sb2Te3-containing system is measured when compared to the reference Au/Co/Au/Si(111). The corresponding inverse Edelstein effect length lambda(IEE) ranges from 0.28 to 0.61 nm, depending on the adopted methodological analysis, with the upper value being so far the largest observed for the second generation of 3D chalcogenide-based TIs. These results open the path toward the use of chemical methods to produce TIs on large area Si substrates and characterized by highly performing S2C conversion, thus marking a milestone toward future technology-transfer

Oxygen impurities link bistability and magnetoresistance in organic spin valves

Vertical cross-bar devices based on manganite and cobalt injecting electrodes and metal-quinoline molecular transport layer are known to manifest both magnetoresistance and electrical bistability. The two effects are strongly interwoven, inspiring new device applications such as electrical control of the magnetoresistance and magnetic modulation of bistability. To investigate the full device functionality, we first identify the mechanism responsible for electrical switching by associating the electrical conductivity and the impedance behavior with chemical states of buried layers obtained by in operando photoelectron spectroscopy. These measurements revealed that a significant fraction of oxygen ions migrates under voltage polarity, resulting in a modification of the electronic properties of the organic material and of the oxidation of interfacial layer with ferromagnetic contacts. Variable oxygen doping of the organic molecule represents the key element for correlating bistability and magnetoresistance and our measurements provide the first experimental evidence in favor of the impurity band model describing the spin transport in organic semiconductors in similar devices

Electrodeposition of nickel-zinc alloy coatings with high nickel content

The electrodeposition of Ni–Zn alloy coatings with high nickel content from a Watts type bath was studied. The investigation was performed by means of cyclic voltammetry, potentiostatic electrodeposition, X-ray diffraction, energy dispersive X-ray analysis, scanning electron microscopy and transmission electron microscopy. The effect of the experimental parameters (deposition potential, bath temperature, zinc concentration, presence of additives) on the coating composition, morphology and structure was studied. The obtained results show that the addition of Zn2+ to the deposition bath leads to a strong decrease in the cathodic current density indicating a remarkable inhibition of Ni reduction. Even if anomalous codeposition was observed for all the studied experimental conditions, nickel rich alloys were obtained due to the mass transport control of zinc deposition. A strong decrease in the current efficiencies was observed when Zn percentage in the deposit was higher than 7wt.%. The incorporation of Zn in the fcc Ni lattice leads to a remarkable decrease in the grain size. The presence of nanocrystalline Ni–Zn beta-phase was observed in the alloys having Zn content higher than about 8 wt.%

Fabrication of ordered Sb–Te and In–Ge–Te nanostructures by selective MOCVD

The controlled growth of chalcogenide nanoscaled phase change material structures can be important to facilitate integration and to enable complex architectures for phase change memory and other microelectronic applications. Here, the growth of Sb–Te and In–Ge–Te alloys by metal–organic chemical vapour deposition (MOCVD) on patterned substrates featured with an array of recesses (~130 nm features width) was investigated. High selectivity, with preferential growth on a CoSi2 metallic layer at the recess bottom with respect to the surrounding SiO2 masking layer, was obtained, leading to a single-step fabrication of arrays of high-aspect-ratio chalcogenide nanostructures. The growth selectivity, as well as the morphology, composition and microstructure of the grown nanostructures, as a function of the different MOCVD process parameters, were investigated by scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, Raman spectroscopy and Fourier transformed infrared spectroscopy. Thanks to the chosen substrates, the synthesized nanostructures were also directly electrically accessible, as proved by conductive-atomic force microscopy