Showing papers by "Guangcun Shan published in 2018"

Two-dimensional materials: Emerging toolkit for construction of ultrathin high-efficiency microwave shield and absorber

Abstract: Two-dimensional (2D) materials generally have unusual physical and chemical properties owing to the confined electro-strong interaction in a plane and can exhibit obvious anisotropy and a significant quantum-confinement effect, thus showing great promise in many fields. Some 2D materials, such as graphene and MXenes, have recently exhibited extraordinary electromagnetic-wave shielding and absorbing performance, which is attributed to their special electrical behavior, large specific surface area, and low mass density. Compared with traditional microwave attenuating materials, 2D materials have several obvious inherent advantages. First, similar to other nanomaterials, 2D materials have a very large specific surface area and can provide numerous interfaces for the enhanced interfacial polarization as well as the reflection and scattering of electromagnetic waves. Second, 2D materials have a particular 2D morphology with ultrasmall thickness, which is not only beneficial for the penetration and dissipation of electromagnetic waves through the 2D nanosheets, giving rise to multiple reflections and the dissipation of electromagnetic energy, but is also conducive to the design and fabrication of various well-defined structures, such as layer-by-layer assemblies, core–shell particles, and porous foam, for broadband attenuation of electromagnetic waves. Third, owing to their good processability, 2D materials can be integrated into various multifunctional composites for multimode attenuation of electromagnetic energy. In addition to behaving as microwave reflectors and absorbers, 2D materials can act as impedance regulators and provide structural support for good impedance matching and setup of the optimal structure. Numerous studies indicate that 2D materials are among the most promising microwave attenuation materials. In view of the rapid development and enormous advancement of 2D materials in shielding and absorbing electromagnetic wave, there is a strong need to summarize the recent research results in this field for presenting a comprehensive view and providing helpful suggestions for future development.

A Low-Loss Design of Bandpass Filter at the Terahertz Band

Abstract: This letter demonstrates a terahertz (THz) bandpass filter with a center frequency of ~340 GHz, low insertion loss of ~ −0.6 dB, and bandwidth of ~5.3%. The diaphragm thickness is quantitatively analyzed to obtain accurate filter parameters based on equivalent circuit and diaphragm coupling in THz band for the first time, and the simulation results based on calculated filter parameters show that diaphragm thickness has great influence on the filter performance. The test results show a good agreement with the theoretical analysis and simulation results. Meanwhile, the relationship between fabrication error and insertion loss was discussed and a quantitative mathematical model is given. The filter also shows an excellent performance when compared with the performance of other filters from the current literature reports.

Evolution of 3D nanoporosity and morphology in selectively dealloying ternary Au55Cu25Si20 metallic glass ribbon with enhanced alcohol electro-oxidation performance.

Abstract: Current fabrication methods of nanoporous gold (NPG) mainly rely on dealloying Ag–Au binary crystalline precursors, typically Ag65Au35, with the “dealloying threshold” or “parting limit” above 55 at%. Here we report a simple chemical dealloying process, through selective dissolution of one element from a Au55Cu25Si20 metallic glass ribbon with low ‘parting limit’, and a novel peculiar three-dimensional ‘cone shaped protrusion’ nanoporous structure which has never been reported before. In this structure, a metastable gold silicide formed in the initial dealloying stage was decomposed into gold nanoparticles and amorphous SiOx in the later coarsening stage. Our finding provides insights into the underlying relationship between ‘parting limit’ and atomic level structure of metallic glass. Comprehensive discussions on the porosity evolution stages as well as the correlation between the porous ‘cone shaped protrusion’ development and potential energy landscape are made in this report. The fabricated 3D NPG also exhibited excellent electro-oxidation catalytic ability attributed to the high density of low-coordinated atomic sites provided by the gold particle inside of ‘cone shaped protrusion’.

3D Nanoporous Gold with Very Low Parting Limit Derived from Au-Based Metallic Glass and Enhanced Methanol Electro-oxidation Catalytic Performance Induced by Metal Migration

Abstract: Nanoporous gold (NPG) with bi-continuous ligaments and pores structure has promising potential in functional applications, among which one prominent example is fuel cell electrocatalysts. However, current application of NPG is mostly limited to methanol electro-oxidation (MOR) due to its weak catalytic performance. Here we report a simple chemical dealloying process for generating peculiar three-dimensional (3D) free-standing NPG with ‘parting limit’ as low as 25 % (lower than theoretical ‘paring limit’ 55 %) and high specific surface area (maximum ≈31 m2 g−1) associated with a novel porous ‘cone shaped protrusion’ morphology. This NPG structure possesses the highest specific activity of MOR catalytic performance reported NPG catalysts so far. In addition, taking advantage of this excellent structural feature of the NPG, a nanoporous Pd catalyst (NPG@Pd) thin film was fabricated on the NPG substrate. The NPG@Pd catalyst exhibited greatly enhanced MOR performance (maximum MOR specific activity 2.14 mA cm−2). We attribute the enhancement of MOR activity to the increase of active sites as well as the modification of surface composition and electronic structure due to migration of Au to the Pd thin film layer.

Face Centered Cubic Co81.8Si9.1B9.1 With High Magnetocrystalline Anisotropy

Abstract: Despite the composition close to glassy forming alloys, face centered cubic (FCC) Co81.8Si9.1B9.1, designed based on Co9B atomic cluster (polyhedral), are synthesized as singlephase ribbons successfully. These ribbons, with grain sizes of ca. 92 nm, show supreme ductility and strong orientation along (111), which couples with shape anisotropy leading to high magnetocrystalline anisotropy comparable to Co rich Co-Pt nanoscale thin films, with a coercivity of 430 Oe and squareness of 0.82 at room temperature. The stability and magnetic behaviors of the phase are discussed based on experimental electronic structure. This work not only develops low cost Co-based materials for hard magnetic applications, but also extends the atomic cluster model developed for amorphous alloys into the design of new crystalline materials.