Square Lattice Arrangement Research Articles

First principles study of electronic structure of x-form phthalocyanine crystals doped with one-dimensional iodine atomic chains

The x-form phthalocyanine (Pc) crystal is composed of a square-lattice arrangement of one-dimensional and double-period molecular chains with molecular planes normal to the stacking direction, and doped iodine (I) atomic chains between these molecular chains are known to induce the insulator-metal transition. Using the van der Waals density functional method, we investigate the electronic structure of a single x-form silicon Pc (x-SiPc) chain and the x-SiPc crystal undoped and doped with I atomic chains in a comparative manner. Although a SiPc molecule has a Si pz derived orbital just above the LUMO, the aligned Si atoms in x-crystals, each of which is at the center of the molecular plane, dimerize in the stacking direction, which prevents formation of a Si metallic band. In a single SiPc chain, two molecules in each primitive unit cell are stacked face-to-face with a staggering angle of 45°. However, when these molecular chains aggregate to create x-crystals, the staggering angle deviates from 45° to about 40° to form H–H bonding orbitals like H2 molecules between neighboring molecular planes in the lateral direction. Doping of the I atomic chains converts half-filling of the doubly degenerate bands to a lower band occupancy, which corresponds to the insulator-metal transition observed experimentally. The equally spaced I atomic chains create a metallic band due to pz-orbital overlapping with an effective-mass ratio of 0.15. Although the SiPc chains operate to create equally spaced I atomic chains, the effect of I atoms trying to trimerize is larger. This trimerization prevents pz orbitals of I atoms from making a metallic band.

Cross-properties of the effective conductivity of the regular array of ideal conductors

We present an accurate expression for the effective conductivity of a regular square-lattice arrangement of ideally conducting cylinders, valid for arbitrary concentrations. The formula smoothly interpolates between the two asymptotic expressions derived for low and high concentrations of the cylinders. Analogy with critical phenomena is suggested and taken to the extent of calculating the superconductivity critical exponent and the particle-phase threshold from the very long expansions in concentration. The obtained formula is valid for all concentrations including touching cylinders, hence it completely solves with high accuracy the problem of the effective conductivity for the square array.

Utilizing Two-Dimensional Photonic Crystals in Different Arrangement to Investigate the Correlation Between the Air Duty Cycle and the Light Extraction Enhancement of InGaN-Based Light-Emitting Diodes

This paper demonstrates that the optimal light extraction enhancement of the 2-D photonic crystals (PhCs) light-emitting diodes (LEDs) among different air duty cycles (ADADCsCs) is independent of the geometry and the shape of the 2-D PhCs. Moreover, it also discusses that the side-directional emission property of the 2-D PhCs LEDs in hexagonal lattice arrangement (HLA) is better than that in square lattice arrangement (SLA). Finally, the light output power of the 2-D PhCs LEDs in SLA and in HLA with the ADC of 51% are significantly improved by 60.4% and 81.9%, respectively, as compared with the reference LED at an injection current of 350 mA.

Near-field optical response of periodically arrayed plasmonic nanogap antennas

We have studied two-dimensional periodically arrayed plasmonic nanogap antennas that exploit a “resonant coupling effect,” efficiently collecting incident light and enhancing the nanogap field. A theoretical investigation was carried out on an infinite array of gold nanoblock dimers in a square-lattice arrangement. Under resonant conditions, the near-field intensity spectra in the gap region showed a narrow peak (full width at half maximum of 50 nm) with a field enhancement that was a factor of ∼5 stronger than that of an isolated single-nanogap antenna. The influence of the geometrical parameters of the array (period, dimer orientation, nanogap size, and number of periods) is discussed.

Enhancement of the magneto-optical properties in 2-dimensional bilayered magnetic anti-dot lattice

The magneto-optical (MO) properties of two-dimensional bilayered magnetic anti-dot lattice (BMAL) structure, which consists of upper perforated “Co” layer over uniform “Ni” underlayer in square-lattice arrangement, were investigated. Enhancement in the MO activity was found in such structures. Nearly 4 times larger MO-Kerr activity was observed for the first-order diffracted beam as compared with that of the zeroth-order one. To understand the origin of the enhanced MO rotation, the magnetization-domain configuration was also investigated by field-dependent magnetic-force microscopy. Additionally, comparison between MO response and magnetization-domain configuration for the rhomboid BMAL structure was done, which allowed us to understand more clearly the enhancement of MO properties.

Morphology and magnetic properties of sputtered Co80Cr20 thin film antidot patterns obtained by Electron Beam Lithography

Antidot patterns of Co80Cr20 magnetic alloy have been produced using Electron Beam Lithography. CAD masks have been generated with both hexagonal and square-lattice arrangement; then they have been transferred on a SiO2/Ti/Au/PMMA substrate. The CoCr metallization process has been performed using RF sputtering (base vacuum 6 * 10−8 Torr), producing films with thicknesses ranging from 25 to 250 nm. After resist liftoff, the antidot patterns have been wholly characterized at room temperature. FESEM images show a pseudo-hexagonal structure of 1 μm antidot diameter with a border to border distance of 1.5 μm. Magnetic information derived from the MFM images was enhanced by means of a numerical procedure, to compensate possible artefacts like instrumental distortions. The samples were demagnetized before each MFM measurement either in plane or out of plane. Magnetic images of Co80Cr20 antidots reveal the existence of maze-domain spin structures.

Comparative Cellular Morphology Suggesting the Existence of Resident Dendritic Cells Within Immune Organs of Salmonids

This report is the first morphological description of cells that resemble dendritic cells, which appear to form resident populations within the spleen and anterior kidney of fish. Based on examination of three salmonid species, including, rainbow trout, brook trout, and Atlantic salmon, the cells were most abundant in the spleen, although they were always present in the anterior kidney. The cells appeared diffusely distributed, often near blood vessels of the spleen and kidney of healthy fish and within the epithelium, connective tissue, and blood vessels of rainbow trout gills with experimentally induced microsoporidial gill disease. The dendritic-like cells in this study contained granules that resemble Birbeck granules, which are considered to be morphological markers of Langerhans cells in mammals. The cells were approximately 6 mum in diameter and contained Birbeck-like (BL) granules localized near centrioles. Although the dendritic-like cells in the three salmonid species shared many similarities, morphological differences were found in the fine structure of the rod portion of the BL granules. Rainbow trout BL granules contained amorphous material, while the other salmonid species contained particulate material arranged in a square-lattice arrangement. The BL granules in the cells of Atlantic salmon had a narrow diameter and contained four layers of particulate material when sectioned longitudinally; two layers enveloped by the granule membrane and two central layers making up a central lamella, which is common in mammalian Birbeck granules.