81 research outputs found
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
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
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
Power dissipation of an inductively coupled plasma torch under E mode dominated regime
This paper focuses on the power dissipation of a plasma torch used for an optical surface fabrication process. The process utilizes an inductively coupled plasma (ICP) torch that is equipped with a De-Laval nozzle for the delivery of a highly collimated plasma jet. The plasma torch makes use of a self-igniting coil and an intermediate co-axial tube made of alumina. The torch has a distinctive thermal and electrical response compared to regular ICP torches. In this study, the results of the power dissipation investigation reveal the true efficiency of the torch and discern its electrical response. By systematically measuring the coolant parameters (temperature change and flow rate), the power dissipation is extrapolated. The radio frequency power supply is set to 800 W, E mode, throughout the research presented in this study. The analytical results of power dissipation, derived from the experiments, show that 15.4% and 33.3% are dissipated by the nozzle and coil coolant channels, respectively. The experiments also enable the determination of the thermal time constant of the plasma torch for the entire range of RF power
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