Surface structure of low-coveraged Cs on Si(0 0 1)-() system

Alkali metals (AM) on semiconductors have been investigated as a simple model system for the metal-semiconductor interfaces due to their simple electronic structures. Especially, cesium (Cs) on Si(0 0 1) surface has been studied with various experimental techniques. In this study, we investigated the atomic structure of initial Cs adsorption on Si(0 0 1)-(2×1) surface using coaxial impact collision ion scattering spectroscopy. When Cs atoms are adsorbed on Si(0 0 1)-(2×1) up to 0.2 ML at room temperature, the initial adsorption site is on-top T3 site with poor periodicity and the length of Si dimer is reserved as in the clean Si(0 0 1) surface. It is also found that Cs atoms adsorbed on Si(0 0 1) surface with a height of 2.83±0.05 Å from the second layer of Si(0 0 1) surface.     

Measurement of the muonic branching fractions of the narrow upsilon resonances

The decay branching fractions of the three narrow Upsilon resonances to mu(+)mu(-) have been measured by analyzing about 4.3 fb(-1) e(+)e(-) data collected with the CLEO III detector. The branching fraction B(Upsilon(1S)-->mu(+)mu(-))=(2.49+/-0.02+/-0.07)% is consistent with the current world average, but B(Upsilon(2S)-->mu(+)mu(-))=(2.03+/-0.03+/-0.08)% and B(Upsilon(3S)-->mu(+)mu(-))=(2.39+/-0.07+/-0.10)% are significantly larger than prior results. These new muonic branching fractions imply a narrower total decay width for the Upsilon(2S) and Upsilon(3S) resonances and lower other branching fractions that rely on these decays in their determination.     

Velocity renormalization and carrier lifetime in graphene from the electron-phonon interaction

We present a first-principles investigation of the phonon-induced electron self-energy in graphene. The energy dependence of the self-energy reflects the peculiar linear band structure of graphene and deviates substantially from the usual metallic behavior. The effective band velocity of the Dirac fermions is found to be reduced by 4%-8%, depending on doping, by the interaction with lattice vibrations. Our results are consistent with the observed linear dependence of the electronic linewidth on the binding energy in photoemission spectra.     

Comment on “An enhanced polarization mechanism for the metal cations modified amorphous TiO2 based electrorheological materials” by Qing Wu, Bin Yuan Zhao, Chen Fang and Ke Ao Hu

Comments on a recent article on an enhanced polarization mechanism for the metal cations modified amorphous TiO₂ based electrorheological materials are presented, based upon an examination of the yield stress, which is a function of electric-field strength, of the materials. Using the deduced critical electric-field strengths, we find that the universal yield stress equation proposed collapses the data given by Qing Wu, Bin Yuan Zhao, Chen Fang, Ke Ao Hu, Eur. Phys. J. E 17, 63 (2005), onto a single curve.     

Native oxide buried InAlAs ridge waveguide laser diode

InAlAs wet thermal oxidation process was adopted to fabricate ridge waveguide laser diodes. First, applying the oxidation process on the whole etched surface of an InAlAs upper cladding layer, we formed a current blocking and optical confining layer of ridge waveguide laser diode. This is a self-aligned structure, which makes the laser diode fabrication steps much simpler and etching-depth control less important. Assessment of the fabricated laser diode revealed that current-voltage characteristics and slope efficiency did not worsen, and threshold current was reduced by the oxidation process. PACS 85.35.Be; 42.55.Px     

Effects of the Various Cooling Conditions on 1,064-nm nd:Yag Laser Treatment for Selective Photothermolysis

The purpose of this study was to find optimum treatment conditions for selective photothermolysis by evaluating internal–external heat distributions according to different cooling methods. The 1,064-nm Nd:YAG laser was transmitted into a skin-mimicking phantom with different cooling conditions, and its minimum temperatures and sub-zero times were measured. The cooling methods were classified into a total of eight conditions composed of five cryogen spray cooling conditions and three air cooling conditions. Based on the experimental results, condition 2 was selected as the optimum cooling condition for selective photothermolysis obtained from the cryogen spray cooling method.     

Multiferroic characteristics of the strained epitaxial Bi0.9Ho0.1FeO3 thin film

We fabricated high quality epitaxial Bi_0.9Ho_0.1FeO₃ thin films which exhibited the tetragonally stained structure with a c/a ratio of about 1.04. The Bi_0.9Ho_0.1FeO₃ thin film showed a good ferroelectric property with the high remanent polarization (P_r) of about 80 μC/cm². The ferromagnetic hysteresis loop with a clear remanent magnetization was shown. The coercive field and the remanent magnetization of the Bi_0.9Ho_0.1FeO₃ film are 6200 Oe and 1.7 emu/g, respectively. The abrupt conduction due to space charge limited (SCL) was revealed in leakage current density versus electric field.     

Supercapacitive electrochemical performance of graphene-containing carbon aerogel prepared using polyethyleneimine-modified graphene oxide

Graphene-containing carbon aerogel was prepared by a sol–gel polymerization of resorcinol-formaldehyde (RF) method using polyethyleneimine (PEI)-modified chemically exfoliated grapheme oxide, and its electrochemical performance as an electrode for supercapacitor was examined. The effect of PEI in the preparation of RFGO (resorcinol-formaldehyde and graphene oxide) solution on the physicochemical and electrochemical properties of graphene-containing carbon aerogel (CAPG) was investigated. For comparison, graphene-containing carbon aerogel was prepared using PEI-free graphene oxide (CAG). Graphene-free carbon aerogel (CA) was also prepared. CAPG showed the highest BET surface area (792 m²/g) and the largest pore volume (1.64 cm³/g) with well-developed porous structure. Various electrochemical measurements revealed that CAPG showed high specific capacitance (205 F/g), low equivalent series resistance (0.55 Ω), and superior capacitive behavior. The PEI-modified graphene oxide played an important role in enhancing physicochemical properties and supercapacitive electrochemical performance of CAPG.     

Photovoltaic performance of flexible Cu(In,Ga)Se2 thin-film solar cells with varying Cr impurity barrier thickness

We report the effect of Cr impurity barrier on Cu(In,Ga)Se₂ (CIGS) thin-film solar cells prepared on flexible substrates. The Cr films with varying the thickness (t_Cr) were deposited on stainless steel substrates using direct-current magnetron sputtering. The solar cell performance was improved by increasing t_Cr since the diffusion of Fe impurities from the substrate to CIGS was suppressed. Although the elemental composition, grain size, and strain of CIGS film showed little change with varying Fe content, the fill factor and the short-circuit current density increased as decreasing Fe. The Fe increased the series resistance, shunt paths, and saturation current density. The reduction of Fe caused a steeper bandgap grading in CIGS which enhances current collection due to higher electric fields in bulk CIGS. CIGS solar cells with 1000 nm-thick Cr barrier showed the best conversion efficiency of 9.05%.