oxiang Xia

Room temperature homogeneous flow in a bulk metallic glass with low glass transition temperature

We report a high entropy metallic glass of Zn20Ca20Sr20Yb20(Li0.55Mg0.45)20 via composition design that exhibiting remarkable homogeneous deformation without shear banding under stress at room temperature. The glass also shows properties such as low glass transition temperature (323 K) approaching room temperature, low density and high specific strength, good conductivity, polymerlike thermoplastic manufacturability, and ultralow elastic moduli comparable to that of bones. The alloy is thermally and chemically stable.

Modulated terahertz responses of split ring resonators by nanometer thick liquid layers

The terahertz responses of planar arrays of split ring resonators with 50nm thin liquid layers introduced in the interspaces between the metal structures have been studied using the terahertz-time domain spectroscopy technique. In our experimental configuration, both the circular current driven and linear polarization induced resonances show redshifted and enhanced transmission. The dielectric functions extracted from an effective medium model indicate that the behavior of the surface and interface charge oscillations is highly sensitive to the interface environment changes. The results suggest that this kind of device may be used for sensing applications.

Robust adhesion of flower-like few-layer graphene nanoclusters

Nanostructured surface possessing ultrahigh adhesion like “gecko foot” or “rose petal” can offer more opportunities for bionic application. We grow flower-like few-layer graphene on silicon nanocone arrays to form graphene nanoclusters, showing robust adhesion. Their contact angle (CA) is 164° with a hysteresis CA of 155° and adhesive force for a 5 μL water droplet is about 254 μN that is far larger than present reported results. We bring experimental evidences that this great adhesion depends on large-area plentiful edges of graphene nanosheets tuned by conical nanostructure and intrinsic wetting features of graphene. Such new hierarchical few-layer graphene nanostructure provides a feasible strategy to understand the ultra-adhesive mechanism of the “gecko effect” or “rose effect” and enhance the wettability of graphene for many practical applications.

Understanding of nanoscale periodic stripes on fracture surface of metallic glasses

We report the observation of nanoscale striped periodic pattern with similar distinctive characteristics independent of loading conditions on the fracture surface of various bulk metallic glasses. We demonstrate that the periodic stripes are formed by the orderly assembly of nanoscale regular dimples. The similarities between our observed striped pattern and various unequilibrium systems such as oscillating granular and colloidal suspensions systems are found. By drawing an analogy between glassy and granular materials, we propose a model that can capture and simulate the characteristics of the observed corrugations. Our results would provide insight into the origin of fracture surface roughening in brittle materials.

Visible transmission response of nanoscale complementary metamaterials for sensing applications

Metamaterials (MMs) have shown huge potential in sensing applications by detecting their optical properties, which can be designed to operate at frequencies from visible to mid-IR. Here we constructed complementary split ring resonator (CSRR) based metamaterials in nanoscale with unit length of 100 nm and slit width of 30 nm, and observed obvious responses in the visible waveband from 600 to 900 nm. These visible responses show a good tunability with the structures geometry, and are well suited for dielectric detection. We demonstrated good refractive index sensing of CSRR based metamaterials in the visible region under both 0° and 90° polarized incidence. Our results extend the study of CSRR based metamaterials to the visible region, which is expected to deepen the understanding of the response mechanism of CSRRs and benefit their sensing applications in the visible region.

Floral-clustered few-layer graphene nanosheet array as high performance field emitter

Graphene sheet is expected to be a highly efficient field emitter due to its unique electrical properties and open surface with sharp edges. However, it is still a tremendous technical challenge to grow and align a graphene sheet in one particular direction to protrude its sharp edges for good field emission. Here, we report an ideal graphene field emitter of flower-like graphene nanosheets grown on a silicon nanocone array, wherein nanocone array guides the alignment of vertical nanosheets and produces high-density sharp edge protrusions on the conical tip. We observe high performance and stable field emission with low turn-on fields from floral-clustered graphene nanosheets. Protrusive sharp edges on the nanocone tip and optimized spacing between clusters both appear to locally enhance the electric field and dramatically increase field emission. Our new graphene emitter design provides a robust approach to the prospect for development of practical electron sources and advanced devices based on graphene field emitters.

Sensing self-assembled alkanethiols by differential transmission interrogation with terahertz metamaterials

Surface-enhanced electromagnetic response in the resonant regions of split-ring resonators offers a sensitive way to probe the surface dipoles formed by alkanethiol molecules with a terahertz wave by a differential transmission (DT) interrogation method. The DT signal mainly comes from the interaction between alkanethiols and metamaterials by electron transfer and/or the variation of the dielectric constant. The Lorentz model is used to demonstrate the principle of DT interrogation theoretically, which suggests the variation of both frequency and damping of resonance can be captured cooperatively. This method has been employed to experimentally demonstrate the sensing feasibility for the chain length dependence of the alkanethiol molecules. Numerical simulations confirm that the enhancement is large at the gap and corner regions of this kind of metamaterials.

Large-scale ordered silicon microtube arrays fabricated by Poisson spot lithography

A novel approach based on the Poisson spot effect in a conventional optical lithography system is presented for fabricating large-scale ordered ring patterns at low cost, in which the pattern geometries are tuned by controlling the exposure dose and deliberate design of the mask patterns. Following this by cryogenic deep etching, the ring patterns are transferred into Si substrates, resulting in various vertical tubular Si array structures. Microscopic analysis indicates that the as-fabricated Si microtubes have smooth interior and exterior surfaces that are uniform in size, shape and wall-thickness, which exhibit potential applications as electronic, biological and medical devices.

The influences of substrate and metal properties on the magnetic response of metamaterials at terahertz region

The metamaterials (MMs) with planar metal arrays of split ring resonators were fabricated on quartz and silicon substrates; the influences of substrate permittivity and metal conductance on the magnetic responses of in the terahertz region were investigated. The electromagnetic (EM) responses of the metamaterials were characterized by terahertz time-domain spectroscopy. The experimental result reveals that there is a 0.39 THz redshift in the transmission spectra for the magnetic response when the substrate changes from quartz to silicon, which is in consistence with the finite-difference time-domain (FDTD) simulation. Based on the simulation and experimental results, and taking into account the EM properties of substrate materials, a modified L-C model is presented to understand the MM system in terahertz domain.

Time-resolved broadband analysis of split ring resonators in terahertz region

Split ring resonators (SRRs) in micrometer scale were fabricated by photolithography and lift-off technologies. The transmission and dispersion characteristics of SRR were measured by terahertz spectroscopy in broadband time domain. Significant resonances at about 0.88 and 2.01THz have been observed, where two stop-band gaps are formed in the dispersion spectrum of SRR. It is suggested that these two minimum dips in the transmission spectrum are induced by dipole and magnetodipole resonances. The results show good agreement with the effective medium theory and the numerical calculation of electromagnetic propagation using finite-difference time-domain method.