Perpendicular magnetic anisotropy of full-Heusler films in Pt/Co2FeAl/MgO trilayers

We report on perpendicular magnetic anisotropy (PMA) in a Pt/Co2FeAl/MgO sandwiched structure with a thick Co2FeAl layer of 2-2.5 nm. The PMA is thermally stable that the anisotropy energy density Ku is 1.3{\times}106 erg/cm3 for the structure with 2 nm Co2FeAl after annealing at 350 oC. The thicknesses of Co2FeAl and MgO layers greatly affect the PMA. Our results provide an effective way to realize relative thick perpendicularly magnetized Heusler alloy films.Comment: 15 pages,6 figure

Hybrid bit-to-symbol mapping for spatial modulation

In spatial modulation (SM), the information bit stream is divided into two different sets: the transmit antenna index-bits (TA-bits) as well as the amplitude and phase modulationbits (APM-bits). However, the conventional bitto- symbol mapping (BTS-MAP) scheme maps the APM-bits and the TA-bits independently. For exploiting their joint benefits, we propose a new BTSMAP rule based on the traditional two-dimensional (2-D) Gray mapping rule, which increases the Hamming distance (HD) between the symbol-pairs detected from the same transmit antenna (TA) and simultaneously reduces the average HD between the symbol-pairs gleaned from different TAs. Based on the analysis of the distribution of minimum Euclidean distance (MED) of SM constellations, we propose a criterion for the construction of a meritorious BTS-MAP for a specific SM setup, without the need for any additional feedback-link or extra computational complexity. Finally, Monte Carlo simulations are conducted for confirming the accuracy of our analysis

Low-Complexity Transmit Antenna Selection in Large-Scale Spatial Modulation Systems

Transmit antenna selection (TAS) is an efficient way for improving the system performance of spatial modulation (SM) systems. However, in the case of large-scale multiple-input multiple-output (MIMO) configuration, the computational complexity of TAS in large-scale SM will be extremely high, which prohibits the application of TAS-SM in a real large-scale MIMO system for future 5G wireless communications. For solving this problem, in this paper, two novel low-complexity TAS schemes, named as norm-angle guided subset division (NAG-SD) and threshold-based NAG-SD ones, are proposed to offer a better tradeoff between computational complexity and system performance. Simulation results show that the proposed schemes can achieve better performance than traditional TAS schemes, while effectively reducing the computational complexity in large-scale spatial modulation systems

Low-Complexity Transmit Antenna Selection in Large-Scale Spatial Modulation Systems

Transmit antenna selection (TAS) is an efficient way for improving the system performance of spatial modulation (SM) systems. However, in the case of large-scale multiple-input multiple-output (MIMO) configuration, the computational complexity of TAS in large-scale SM will be extremely high, which prohibits the application of TAS-SM in a real large-scale MIMO system for future 5G wireless communications. For solving this problem, in this paper, two novel low-complexity TAS schemes, named as norm-angle guided subset division (NAG-SD) and threshold-based NAG-SD ones, are proposed to offer a better tradeoff between computational complexity and system performance. Simulation results show that the proposed schemes can achieve better performance than traditional TAS schemes, while effectively reducing the computational complexity in large-scale spatial modulation systems

A scalable polymer-free method for transferring graphene onto arbitrary surfaces

An efficient and reliable transfer for graphene onto the substrates of interests acts as the crucial bridge between the graphene synthesis and applications. The main reason that this issue has not been fully addressed is the use of a polymer medium to protect the one-atom-thick material during the transfer process. Here we demonstrate a general and scalable method to transfer chemical-vapor-deposited graphene onto arbitrary surfaces without any polymers, which yields the transfer of macroscopically and microscopically clean, continuous and uniform graphene samples onto a wide variety of substrates, as well as the scalable layer-by-layer graphene epitaxial structures. Moreover, the transferred graphene exhibits an overall 100% enhancement in the electrical conductivity compared with the conventional method, so that various high-performance flexible transparent electrodes can be demonstrated. We believe that this new transfer technique will offer the opportunities to the industrialization of next generations of flexible electronics and other graphene-based disruptive technologies. (C) 2020 Elsevier Ltd. All rights reserved

Electrical properties of Ba

The crystal structure, microstructure, dielectric properties and energy storage properties of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics with various TiO2 (0%, 1%, 8%, 40%, 50%, 60%) addition ceramics were discussed. Although the perovskite structure remained in samples with low content of TiO2, the secondary phase Ba2Ti5.5O13 appeared in samples with high TiO2 content. According to SEM results, the addition of TiO2 resulted in a significant decrease in the average grain size. With the addition of TiO2, the phase transition temperature, corresponding to Curie temperature (Tc) of BCZT ceramics shifts to lower temperature. Compared with the pure BCZT ceramic, the higher impedance and slimmer hysteresis loops were realized in ceramics with high TiO2 content. The relatively large energy storage density (Wrec ∼ 0.52 J/cm3) together with energy storage efficiency (η ∼ 74.84%) were achieved in ceramic with 40% TiO2 content. When the concentration of TiO2 further increases, the energy storage efficiency increased, but the energy storage density declined. The present research provides a method to improve the energy storage performance of BCZT ceramics

Chemical vapor deposition growth of scalable monolayer polycrystalline graphene films with millimeter-sized domains

The preparation of scalable graphene films has attracted an enormous attention due to its industrial importance for graphene applications. Here we present a synthesis method of high-quality continuous monolayer graphene films with millimeter-sized domains on ordinary Cu substrates using oxygen-assisted chemical vapor deposition. This method demonstrates a significantly improvement to the resultant graphene such as a largely decreased nucleation density from similar to 10(6) to similar to 10(1) nuclei/cm(2), an increased average domain size from similar to 0.004 to similar to 1.5 mm and a film coverage from 64% to 100%. We attributed the success of this growth to the surface layer formed by bonded oxygen in Cu, which provides a higher priority for catalyzing the nucleation and growth of graphene domains. (C) 2018 Elsevier B.V. All rights reserved

Epitaxial nucleation of CVD bilayer graphene on copper

Bilayer graphene (BLG) has emerged as a promising candidate for next-generation electronic applications, especially when it exists in the Bernal-stacked form, but its large-scale production remains a challenge. Here we present an experimental and first-principles calculation study of the epitaxial chemical vapor deposition (CVD) nucleation process for Bernal-stacked BLG growth on Cu using ethanol as a precursor. Results show that a carefully adjusted flow rate of ethanol can yield a uniform BLG film with a surface coverage of nearly 90% and a Bernal-stacking ratio of nearly 100% on ordinary flat Cu substrates, and its epitaxial nucleation of the second layer is mainly due to the active CH3 radicals with the presence of a monolayer-graphene-covered Cu surface. We believe that this nucleation mechanism will help clarify the formation of BLG by the epitaxial CVD process, and lead to many new strategies for scalable synthesis of graphene with more controllable structures and numbers of layers.ope

Direct Identification of Multilayer Graphene Stacks on Copper by Optical Microscopy

Growing graphene on copper (Cu) by chemical vapor deposition (CVD) has emerged as a most promising approach to satisfy its practical requirements, but the fast and large-scale characterization of its grown adlayers remains a challenge. Here we present a facile and inexpensive method to directly identify the multilayer graphene stacks on Cu by optical microscopy, using simple ultraviolet and heating treatments. The sharp optical contrast, originating from the variation in Cu oxide thickness underneath graphene, reproduces the stacking geometry with high fidelity to scanning electron microscopy observation, demonstrating the correspondence among the optical contrast, the oxide thickness variation, and the stack of adlayers. The close correlation roots in the throttling effect of graphene grain with discrete structural defects in controlling the rate-determined Cu oxidizing agent supply. We believe that this approach can enable large-scale evaluation of CVD-derived graphene quality, which are critical for optimizing CVD processing parameters of graphene growth