Diamond turning of soft semiconductors to obtain nanometric mirror surfaces

Diamond cutting is a viable alternative to grinding and polishing in the fabrication of high-quality soft semiconductors. Investigation of indentation provides useful information for understanding the practical diamond cutting process of brittle materials. Cutting forces and temperatures were analysed using a Kistler dynamometer and an infrared technique. A zero rake angle cutting tool was found to be most efficient, partly because the effective rake is really a strong negative rake brought about by the peculiar configuration of very low feeds and depths of cut. This is explained by means of the comparison of the force distribution between conventional turning and ultraprecision machining. Atomic force microscopy and scanning electron microscopy were used to study the surfaces. Zinc sulfide gave subnanometric surfaces (0.88 m) and zinc selenide gave Ra values of 2.91 nm

Nanoindentation-induced phase transformation and structural deformation of monocrystalline germanium: a molecular dynamics simulation investigation

Molecular dynamics simulations were conducted to study the nanoindentation of monocrystalline germanium. The path of phase transformation and distribution of transformed region on different crystallographic orientations were investigated. The results indicate the anisotropic behavior of monocrystalline germanium. The nanoindentation-induced phase transformation from diamond cubic structure to β-tin-Ge was found in the subsurface region beneath the tool when indented on the (010) plane, while direct amorphization was observed in the region right under the indenter when the germanium was loaded along the [101] and [111] directions. The transformed phases extend along the < 110 > slip direction of germanium. The depth and shape of the deformed layers after unloading are quite different according to the crystal orientation of the indentation plane. The study results suggest that phase transformation is the dominant mechanism of deformation of monocrystalline germanium film in nanoindentation

Topological Photonic Phase in Chiral Hyperbolic Metamaterials

Recently the possibility of achieving one-way backscatter immune transportation of light by mimicking the topological order present within certain solid state systems, such as topological insulators, has received much attention. Thus far however, demonstrations of non-trivial topology in photonics have relied on photonic crystals with precisely engineered lattice structures, periodic on the scale of the operational wavelength and composed of finely tuned, complex materials. Here we propose a novel effective medium approach towards achieving topologically protected photonic surface states robust against disorder on all length scales and for a wide range of material parameters. Remarkably, the non-trivial topology of our metamaterial design results from the Berry curvature arising from the transversality of electromagnetic waves in a homogeneous medium. Our investigation therefore acts to bridge the gap between the advancing field of topological band theory and classical optical phenomena such as the Spin Hall effect of light. The effective medium route to topological phases will pave the way for highly compact one-way transportation of electromagnetic waves in integrated photonic circuits.Comment: 11 pages, 3 figures. To appear in PR

Advancements in Optical See-through Near-Eye Display

With the development of optical design and manufacturing, the optical see-through near-eye display becomes a promising research topic in recent decades, which can be applied in medical devices, education, aviation, entertainment et al. Typical products include Head-mounted Displays (HMDs) and Augmented Reality (AR) glasses. The optical display system of AR devices mainly consists of a miniature projecting module and an optical imaging module. In this chapter, the display systems used by AR glasses on the market, including various mini-display screens and optical imaging elements, have been systematically summarized. Therein, the differences in optical combinators are the key part to distinguish various AR display systems. Thus, it is essential to figure out the advantages and disadvantages of each optical imaging technology applied in this area. Besides, the characteristics of the projectors are crucial to the quality of the images

First Principle Simulations of Current Flow in Inorganic Molecules: Polyoxometalates (POMs)

In this work we present a simulation study of current flow in inorganic molecular metal oxide clusters known as polyoxometalates (POMs). The simulations are carried out by using combination of the density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. To investigate the current flow in POMs, we investigate two possible ways to place the POM cluster between two gold (Au) electrodes - vertical and horizontal. Our results show that the position of the POM molecule and the contact between the molecule and the Au electrodes determines the current flow. Overall, the vertical configuration of the molecule between the two Au electrodes shows better current flow in comparison to the horizontal configuration. In this work we also establish a link between the underlying electronic structure and transmission spectra and conductance

Plasmon Weyl Degeneracies in Magnetized Plasma

In this letter, we report the presence of novel type of plasmon Weyl points in a naturally existing material - magnetized plasma. In such a medium, conventional, purely longitudinal bulk plasma oscillations exists only along the direction of applied magnetic field (z direction). With strong enough magnetic field, there exist helical propagating modes along z direction with circular polarizations. The orthogonality between the longitudinal bulk plasmon mode and the transverse helical propagating modes guarantees their crossing at the bulk plasmon frequency. These crossing points, embedded in the bulk plasmon dispersion line, serve as monopoles in the k space - the so called Weyl points. These Weyl points lead to salient observable features. These include the highly intriguing observation that, at a magnetized plasma surface which is parallel to the applied magnetic field, reflection of an electromagnetic wave with in-plane wave-vector close to the Weyl points exhibits chiral behavior only in half of the k plane, which is bounded by the projection of the bulk plasmon dispersion line. We also verify the presence of 'Fermi arcs' connecting the two Weyl points with opposite chiralities when magnetized plasma interfaces with trivial photonic materials. Our study introduces the concept of Weyl photonics into homogeneous strongly dispersive photonic materials, which could pave way for realizing new topological photonic devices.Comment: 13 pages, 5 figure

Density functional theory calculation of the properties of carbon vacancy defects in silicon carbide

As a promisingmaterial for quantumtechnology, silicon carbide (SiC) has attracted great interest inmaterials science. Carbon vacancy is a dominant defect in 4H-SiC. Thus, understanding the properties of this defect is critical to its application, and the atomic and electronic structures of the defects needs to be identified. In this study, density functional theorywas used to characterize the carbon vacancy defects in hexagonal (h) and cubic (k) lattice sites. The zero-phonon line energies, hyperfine tensors, and formation energies of carbon vacancies with different charge states (2-, -, 0,+ and 2+) in different supercells (72, 128, 400 and 576 atoms)were calculated using standard Perdew-Burke-Ernzerhof and Heyd-Scuseria-Ernzerhof methods. Results show that the zero-phonon line energies of carbon vacancy defects are much lower than those of divacancy defects, indicating that the former is more likely to reach the excited state than the latter. The hyperfine tensors of VC+(h) and VC+(k) were calculated. Comparison of the calculated hyperfine tensor with the experimental results indicates the existence of carbon vacancies in SiC lattice. The calculation of formation energy shows that the most stable carbon vacancy defects in the material are VC2+(k), VC+(k), VC(k), VC-(k) and VC2-(k) as the electronic chemical potential increases.Peer reviewe

A generic approach of polishing metals via isotropic electrochemical etching

Isotropic etching polishing (IEP), which is based on the merging of hemispherical holes that are formed by isotropic etching, is proposed in this study as a universal metal finishing approach. Modeling of the surface evolution during IEP is also carried out, and the formation of a metal surface is predicted. The etching anisotropy of titanium is experimentally studied, and the results show that isotropic etching can be realized under optimized conditions. Isotropic etching sites originate from a breakdown of the passivation layer. Both the density and growth rate of the holes are affected by the current, and a large etching current is preferred for the realization of highly efficient polishing. IEP has been shown to be effective and efficient for surface finishing of TA2. The surface Sa roughness is drastically reduced from 64.1 nm to 1.2 nm, and a maximum polishing rate of 15 μm/min is achieved under an etching current of 3 A. IEP has also been successfully applied for surface finishing of other metals, including TC4, stainless steel 304, aluminum alloy 6063 and pure nickel, demonstrating that IEP can be considered a universal approach for finishing metals