Electrical properties and emission mechanisms of Zn-doped β-Ga2O3 films

We study the electrical properties and emission mechanisms of Zn-doped β-Ga₂O₃ film grown by pulsed laser deposition through Hall effect and cathodoluminescence which consist of ultraviolet luminescence (UV), blue luminescence (BL) and green luminescence (GL) bands. The Hall effect measurements indicate that the carrier concentration increases from 7.16×10¹¹ to 6.35×10¹² cm⁻³ with increasing a nominal Zn content from 3 to 7 at%. The UV band at 272 nm is not attributed to Zn dopants and ascribed as radiative electron transition from conduction band to a self-trapped hole while the BL band is attributable to defect level related to Zn dopant. The BL band has two emission peaks at 415 and 455 nm, which are ascribed to the radiative electron transition from oxygen vacancy (V_O) to valence band and recombination of a donor–acceptor pair (DAP) between V_O donor and Zn on Ga site (Zn_Ga) acceptor, respectively. The GL band is attributed to the phonon replicas’ emission of the DAP. The acceptor level of Zn_Ga is estimated to be 0.26 eV above the valence band maximum. The transmittance and absorption spectra prove that the Zn-doped β-Ga₂O₃ film is a dominantly direct bandgap material. The results of Hall and cathodoluminescence measurements imply that the Zn dopant in β-Ga₂O₃ film will form an acceptor Zn_Ga to produce p-type conductivity.     

Single generator problem

Using the Stone-\v{C}ech compactification of integers, we introduce a free extension of an almost periodic flow. Together with some properties of outer functions, we see that, in a certain class of ergodic Hardy spaces , , the corresponding subspaces are all singly generated. This shows the existence of maximal weak- Dirichlet algebras, different from of the disc, for which the single generator problem is settled.

     

Measurement of Optical Constants of CVD-Diamond for Short-Wavelength Far-Infrared Lasers

A diagnostic system using short-wavelength far-infrared (FIR) lasers (40–70 m in wavelength) is now being developed for high density and large volume plasmas. In the wavelength region, a CVD-diamond is the excellent materials for optical windows of the laser and the plasma vessel and beam splitters of a multichannel interferometer. To design these optical elements, the optical constants (refractive index n, absorption coefficient and transmissivity T) of the CVD-diamond have been measured precisely by using FIR lasers of 48-, 57- and 71-m in wavelength. As an example, the result for 57.1511 m light is n = 2.383(1) ± 0.002, = 0.19 ± 0.05 cm^-1 and T = 97.5 ± 1.5% at 1.023 mm in thickness.     

On the pagenumber of trivalent Cayley graphs

Book embedding of graphs is one of the graph layout problem. It is useful for the multiprocessor network layout or the fault-tolerant processor arrays. We show that the trivalent Cayley graphs proposed by Vadapalli and Srimani can be embedded in five pages, and show some additional results on cube-connected cycles.     

Topological structure of the inter-band phase difference soliton in two-band superconductivity

Two-component superconductivity based on the two-band superconductor has a functional topology such as an inter-band phase difference soliton (i-soliton) to realize topological electronics (topolonics). Many gauge field theories are applied to investigate the topology of two-band superconductivity. To ease experimental and electronics applications, these theories should be refined. Weinberg–Salam theory and SU(2) (two-dimensional special unitary symmetry) gauge field theory are proper starting points. An effective extra force field because of the crystal structure and inter-band Josephson interaction, rather than spontaneous symmetry breaking, simplifies the conventional gauge field theory.     

Size-selected copper oxide nanoparticles synthesized by laser ablation

Size-tuned copper oxide nanoparticles with sizes of 9, 12, and 15 nm were fabricated by laser ablation and on-line size selection using a differential mobility analyzer at a gas pressure of 666 Pa. The dependence of the particle properties on the in situ annealing temperatures and selection sizes was investigated. The crystalline phases of the nanoparticles fabricated at temperatures below 973 K were assigned to monoclinic cupric oxide (CuO) which converted into cubic cuprous oxide (Cu₂O) when the annealing temperature was above 1,173 K. This indicates that the crystalline phases can be easily controlled by changing the annealing temperature. TEM images confirmed that well-crystallized and well-dispersed CuO and Cu₂O nanoparticles with narrow size distributions were obtained using this method. This fabrication process is useful and promising for the future investigation of the intrinsic size-dependent properties of CuO and Cu₂O.     

High-speed wavelength-division multiplexing quantum key distribution system

A high-speed quantum key distribution system was developed with the wavelength-division multiplexing (WDM) technique and dedicated key distillation hardware engines. Two interferometers for encoding and decoding are shared over eight wavelengths to reduce the system's size, cost, and control complexity. The key distillation engines can process a huge amount of data from the WDM channels by using a 1 Mbit block in real time. We demonstrated a three-channel WDM system that simultaneously uses avalanche photodiodes and superconducting single-photon detectors. We achieved 12 h continuous key generation with a secure key rate of 208 kilobits per second through a 45 km field fiber with 14.5 dB loss.     

Determination of inorganic anions in biological fluids with direct sample injection by electrostatic ion chromatography using zwitterionic micelles in both stationary and mobile phases

A new ion chromatographic (IC) system, which uses zwitterionic (e.g., Zwittergent 3-14) micelles as both stationary and mobile phases, highly useful for the analysis of inorganic anions in biological samples, was developed. The zwitterionic micellar stationary phase (which is obtained by immobilizing the zwitterionic surfactant on surfaces of the reversed-phase ODS) showed high ability to confine the elution bands of the large amount of SO4(2-) and Cl- to narrow zones. As a result, a base-line separation of NO2-, Br- and NO3- from SO4(2-) and Cl- is always achieved. The zwitterionic micellar mobile phase, (which is obtained by dissolving the zwitterionic surfactant with a suppressive electrolytic solution, e.g., aqueous NaHCO3 solution), on the other hand, showed high ability for rapid elution of proteins. The separation column is therefore always being cleaned up even after the protein-containing sample is directly injected. The zwitterionic micelles are also insensitive to conductivity detection, therefore either the suppressed or the non-suppressed conductivity detection method is applicable for detection of the analyte ions. Urine and serum were chosen as the model real samples and were analysed with direct sample injection; the results of successful determination of a number of inorganic anions (SO4(2-), Cl-, NO2-, Br- and NO3-) in both samples have demonstrated the usefulness of this new IC system.     

Sorption and pervaporation properties of crosslinked membranes of poly(ethylene oxide imide) segmented copolymer to aromatic/nonaromatic hydrocarbon mixtures

Poly(ethylene oxide imide) segmented copolymer (PEO‐PI) membranes were crosslinked by the chemical reaction between ethylene glycol diglycidyl ether and benzylalcohol groups of diamine moieties in polyimide segments at high temperatures. Sorption and diffusion of penetrants took place in poly(ethylene oxide) segment microdomains. Sorption and desorption behavior of pure vapors such as benzene (Bz), cyclohexane (Cx) and n‐hexane (Hx) was classified as the Fickian diffusion. Sorption isotherms of binary liquid mixtures could be represented by the Flory–Rehner model, but the model overpredicted the sorption amounts of Cx and Hx, leading to small predictions of sorption selectivity α_S for Bz/Cx and Bz/Hx systems. UNIFAC‐FV model fairly well predicted the sorption amounts of aromatic hydrocarbons, but significantly overestimated those of nonaromatic ones, leading to too small predictions of α_S. Pervaporation (PV) behavior of PEO‐PI membranes was governed by sorption behavior followed by membrane swelling. Diffusion coefficient weakly depended on the minimum cross section of a penetrant. The diffusivity selectivity α_D hardly depended on the feed composition and was about 1.4 and 0.75 for Bz/Cx and Bz/Hx, respectively. PV selectivity α_PV was larger for Bz/Hx than for Bz/Cx because of larger α_S. PEO‐PI membranes displayed high specific permeation flux Ql and reasonably high α_PV for aromatic/nonaromatic hydrocarbons; for example, Ql = 60 Kg μm/(m² h) and α_PV = 8 for a feed mixture containing Bz, Tol, Hx, n‐Ot and i‐Ot of 20 wt % at 353 K. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1800–1811, 2000     

Solubilization of n-alkylbenzenes into decanoyl-N-methylglucamide (Mega-10) solution

Solubilization of benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, n-pentylbenzene, and n-hexylbenzene into micelles of decanoyl-N-methylglucamide (Mega-10) was studied, where equilibrium concentrations of the above solubilizates were determined spectrophotometrically at 303.2 K. The concentration of the above solubilizates remained constant below the critical micelle concentration (cmc) and increased linearly with an increase in Mega-10 concentration above the cmc. The Gibbs free energy change of the solubilizates from the aqueous bulk to the liquid solubilizate phase was evaluated from the dependence of their aqueous solubility on the alkyl chain length of the solubilizates, which leads to -3.46 kJ mol-1 for DeltaG(0)(CH), the energy change per CH2 group of the alkyl chain. The first stepwise solubilization constant (K(overline)1 ) was evaluated from the slope of the change of solubilizate concentration versus Mega-10 concentration. The Gibbs free energy change (DeltaG(0,s)) for the solubilization decreased linearly with the carbon number of the alkyl chain of the solubilizates, from which DeltaG(0,s)(CH2) as evaluated to be -2.71 kJ mol-1. The similar values above clearly indicate that the location of the alkyl chain is a hydrophobic micellar core, which is also supported by the absorption spectrum of the solubilized molecules.