Enhanced near-infrared photoluminescence from isoelectronic luminescent centers in sulfur-implanted silicon with copper or silver coimplantation

Enhanced near-infrared photoluminescence (PL) from sulfur-related isoelectronic luminescent centers in silicon was observed from thermally quenched sulfur-implanted silicon in which additional copper or silver ions had been coimplanted. The PL from the sulfur and copper coimplanted silicon peaked between 70 and 100 K and persisted to 260 K. This result strongly supports the original conjecture from the optical detection of magnetic resonance studies that the strong PL from sulfur-doped silicon comes from S-Cu isoelectronic complexes [Frens , Phys. Rev. B 46, 12316 (1992); Mason , ibid. 58, 7007 (1998).]. (c) 2007 American Institute of Physics.

Pressure behaviour of the UV and green emission bands in ZnO micro-rods

The pressure behavior of the ultraviolet (UV) and green emission bands in ZnO tetrapod-like micro-rods has been investigated at 300 and 70 K, respectively. The pressure coefficient of the UV band at 300 K is 24.5 meV/GPa, consistent with that of the band gap of bulk ZnO. However, the pressure coefficient of the green band is 25 meV/GPa, far larger than previous literature reports. The green band in this work originates from Cu-related emission, as confirmed by the fine structure observed in the spectra at 10 K. The pressure coefficients of four phonon replicas of the free exciton emission (FX) at 70 K are 21.0, 20.2, 19.8, and 19.3 meV/GPa, respectively. The energy shift rate of the FX emission and the LO phonon energies is then determined to be 21.4 and 0.55 meV/GPa. The pressure coefficient of the neutral donor bound exciton ((DX)-X-0) transition is 20.5 meV/GPa, only 4% smaller than that of FX. This confirms that the (DX)-X-0 emission corresponds to excitons bound to neutral shallow donors. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis and photoluminescence of ZnS : Cu nanoparticles

The room-temperature photoluminescence (PL) of copper doped zinc sulfide (ZnS:Cu) nanoparticles were investigated. These ZnS:Cu nanoparticles were synthesized by a facile wet chemical method, with the copper concentration varying from 0 to 2 mol%. By Gaussian fitting, the PL spectrum of the undoped ZnS nanoparticles was deconvoluted into two blue luminescence peaks (centered at 411 nm and 455 nm, respectively), which both can be attributed to the recombination of the defect sates of ZnS. But for the doped samples, a third peak at about 500 nm was also identified. This green luminescence originates from the recombination between the shallow donor level (sulfur vacancy) and the t(2) level of Cu2+. With the increase of the CU2+ concentration, the green emission peak is systematically shifted to longer wavelength. In addition, it was found that the overall photoluminescence intensity is decreased at the Cu2+ concentration of 2%. The concentration quenching of the luminescence may be caused by the formation of CuS compound. (c) 2005 Elsevier B.V. All rights reserved.

Temperature and pressure dependences of the copper-related green emission in ZnO microrods

We have investigated the temperature and pressure dependences of the copper-related green emission, which show fine structure at low temperature, from tetrapodlike ZnO microrods. The temperature dependence of the green emission energy follows the changes in the band gap from 10-200 K, but deviates from this behavior above 200 K. The pressure dependence of the copper-related green band (25 +/- 5 meV/GPa) is similar to that of the band gap of ZnO, and is larger than that reported previously for defect-related green emission in ZnO. (c) 2006 American Institute of Physics.

Effects of the sulfur pressure on pyrite FeS2 films prepared by sulfurizing thermally iron films

The effect of sulfur vapor pressure in preparing the FeS2 films has been discussed and some incongruous views about sulfur pressure have been clarified in this paper based on experimental results and theoretical analysis. It is shown that lower sulfur pressures than the saturation value only result in poorer crystallization and worse performances, and in other words the FeS2 films could be optimized through improving the sulfur pressure till the saturation point. However for a certain temperature the sulfur pressure is limited by its saturated vapor pressure, and further increase of the sulfur quantity reacted with Fe films has little influence on the structure and properties of the pyrite films. (C) 2003 Elsevier B.V. All rights reserved.

Electronic properties of sulfur passivated undoped-n(+) type GaAs surface studied by photoreflectance

Photoreflectance (PR) has been used to study surface electronic properties (electric field, Fermi level pinning, and density of surface states) of undoped-n(+) (UN+) GaAs treated in the solution of ammonium sulfide in isopropanol. Complex Fourier transformation (CFT) of PR spectra from passivated surface shows that the sulfur overlay on GaAs surface makes no contribution to Franz-Keldysh oscillations (FKOs). The barrier height measured by PR is derived from surface states directly, rather than the total barrier height, which includes the potentials derived from Ga-S and As-S dipole layers. Comparing with native oxidated surface, the passivation leads to 80 meV movement of surface Fermi level towards the conduction band minimum, and reduction by more than one order in density of surface states. (C) 2003 Elsevier Science B.V. All rights reserved.

Green-light-emitting ZnSe nanowires fabricated via vapor phase growth

Stoichiometric ZnSe nanowires have been synthesized through a vapor phase reaction of zinc and selenium powder on the (100) silicon substrate coated with a gold film of 2 nm in thickness. The microstructures and the chemical compositions of the as-grown nanowires have been investigated by means of electron microscopy, the energy dispersive spectroscopy, and Raman spectroscopy. The results reveal that the as-grown materials consist of ZnSe nanowires with diameters ranging from 5 to 50 nm. Photoluminescence of the sample demonstrates a strong green emission from room temperature down to 10 K. This is attributed to the recombination of electrons from conduction band to the medium deep Au acceptors. (C) 2003 American Institute of Physics.

Landauer-Buttiker formula for time-dependent transport through resonant-tunneling structures: A nonequilibrium Green's function approach

A nonequilibrium Green's-function formalism is employed to study the time-dependent transport through resonant-tunneling structures. With this formalism, we derive a time-dependent Landauer-Buttiker formula that guarantees current conservation and gauge invariance. Furthermore, we apply the formula to calculate the response behaviors of the resonant-tunneling structures in the presence of rectangular-pulse and harmonic-modulation fields. The results show that the displacement current plays the role of retarding the tunneling current.

Spectral properties of a double-quantum-dot structure: A causal Green's function approach

Spectral properties of a double quantum dot (QD) structure are studied by a causal Green's function (GF) approach. The double QD system is modeled by an Anderson-type Hamiltonian in which both the intra- and interdot Coulomb interactions are taken into account. The GF's are derived by an equation-of-motion method and the real-space renormalization-group technique. The numerical results show that the average occupation number of electrons in the QD exhibits staircase features and the local density of states depends appreciably on the electron occupation of the dot.

Comparing the Performance of Biomimetic Pattern Recognition with W8 and SVM on Prediction of Horizontal Gene Transfers in Bacteria Genomes

National Natural Science Foundation of China 60753001

Fatty-acids and their C-13 signatures in seep carbonates from hydrocarbon seeps on the upper (GC 185) and lower (AC 645) continental slope of the Gulf of Mexico

Here we reported the fatty-acids and their δ 13C values in seep carbonates collected from Green Canyon lease block 185 (GC 185; Sample GC-F) at upper continental slope (water depth: ∼540 m), and Alaminos Canyon lease block 645 (GC 645; Sample AC-E) at lower continental slope (water depth: ∼2200 m) of the Gulf of Mexico. More than thirty kinds of fatty acids were detected in both samples. These fatty acids are maximized at C16. There is a clear even-over-odd carbon number predominance in carbon number range. The fatty acids are mainly composed of n-fatty acids, iso-/anteiso-fatty acids and terminally branched odd-numbered fatty acids (iso/anteiso). The low δ 13C values (−39.99‰ to.32.36‰) of n-C12:0, n-C13:0, i-C14:0and n-C14:0 suggest that they may relate to the chemosynthetic communities at seep sites. The unsaturated fatty acids n-C18:2 and C18:1Δ9 have the same δ 13C values, they may originate from theBeggiatoa/Thioploca. Unlike other fatty acids, the terminally branched fatty acids (iso/anteiso) show lowerδ 13C values (as low as −63.95‰) suggesting a possible relationship to sulfate reducing bacteria, which is common during anaerobic oxidation of methane at seep sites.

Establishment and characterization of dual-species biofilms formed between a 3,5-dinitrobenzoic-degrading strain and bacteria with high biofilm-forming capabilities

In this study, the possibility of establishing a dual-species biofilm from a bacterium with a high biofilm-forming capability and a 3,5-dinitrobenzoic acid (3,5-DNBA)-degrading bacterium, Comamonas testosteroni A3, was investigated. Our results showed that the combinations of strain A3 with each of five strains with a high biofilm-forming capability (Pseudomonas sp. M8, Pseudomonas putida M9, Bacillus cereus M19, Pseudomonas plecoglossicida M21 and Aeromonas hydrophila M22) presented different levels of enhancement regarding biofilm-forming capability. Among these culture combinations, the 24-h dual-species biofilms established by C. testosteroni A3 with P. putida M9 and A. hydrophila M22 showed the strongest resistance to 3,5-DNBA shock loading, as demonstrated by six successive replacements with DMM2 synthetic wastewater. The degradation rates of 3,5-DNBA by these two culture combinations reached 63.3-91.6% and 70.7-89.4%, respectively, within 6 h of every replacement. Using the gfp-tagged strain M22 and confocal laser scanning microscopy, the immobilization of A3 cells in the dual-species biofilm was confirmed. We thus demonstrated that, during wastewater treatment processes, it is possible to immobilize degrader bacteria with bacteria with a high biofilm-forming capability and to enable them to develop into the mixed microbial flora. This may be a simple and economical method that represents a novel strategy for effective bioaugmentation.