Daily production and photosynthetic characteristics of Nostoc flagelliforme grown under ambient and elevated CO2 conditions

Diurnal photosynthesis of Nostoc flagelliforme was investigated at varied levels of CO2 concentrations and desiccation in order to estimate the effects of enriched CO2 and watering on its daily production. Photosynthetic activity was closely correlated with the desiccated status of the algal mats, increased immediately after watering, reached a maximum at moderate water loss, and then declined with further desiccation. Increased CO2 concentration enhanced the diurnal photosynthesis and raised the daily production. Watering twice per day enhanced the daily production due to prolonged period of active photosynthesis. The values of daily net production were 1321280 mumol CO2 g (d. wt)(-1) d(-1), corresponding to about 0.6-6.1% daily increase in dry weight. High-CO2-grown mats required higher levels of photon flux density to saturate the alga's photosynthesis in air. Air-grown mats showed higher photosynthetic affinity for CO2 and higher levels of dark respiration compared with high-CO2-grown samples.

Structure and magnetic characteristics of nonpolar a-plane GaN : Mn films

Diluted magnetic nonpolar GaN:Mn films have been fabricated by implanting Mn ions into unintentionally doped nonpolar a-plane (1 1 (2) over bar 0) GaN films with a subsequent rapid thermal annealing (RTA) process. The structure, morphology and magnetic characteristics of the samples were investigated by means of high-resolution x-ray diffraction (XRD), atomic force microscopy (AFM) and a superconducting quantum interference device (SQUID), respectively. The XRD analysis shows that the RTA process can effectively recover the crystal deterioration caused by the implantation process and that there is no obvious change in the lattice parameter for the as-annealed sample. The SQUID result indicates that the as-annealed sample shows ferromagnetic properties and magnetic anisotropy at room temperature.

Stability and photoemission characteristics for GaAs photocathodes in a demountable vacuum system

The stability and photoemission characteristics for reflection-mode GaAs photocathodes in a demountable vacuum system have been investigated by using spectral response and x-ray photoelectron spectroscopy measurements at room temperature. We find that the shape of the spectral response curve for the cathode changes with time in the vacuum system, but after applying fresh cesium to the degraded cathode, the spectral response can almost be restored. The change and restoration of curve shape are mainly attributed to the evolution of the surface barrier. We illustrate the evolution and analyze the influence of the barrier on the spectral response of the cathode. (C) 2008 American Institute of Physics.

Influence of fused interface on the optical and thermal characteristics of vertical cavity lasers

From the effective absorption coefficient of bonded interface and the relationship of interface to reflectivity at cavity mode for double bonded vertical cavity laser, it can be seen that bonded interfaces should be positioned at the null of standing wave distribution, and the thickness of interface should be less than 20 nm. Using the finite elements method, the temperature contour map of laser can be calculated. Results showed that the influence of thin interface to thermal characteristics of VCSELS is slight, while thick interface will lead to temperature increase of active region. SEM images demonstrate that hydrophobic bonding is suitable for the fabrication of the device, while hydrophilic bonding interface is unfavorable to optical and thermal properties of devices with interface thickness larger than 40 nm.

Evolution of surface morphology and photoluminescence characteristics of 1.3-mu m In0.5Ga0.5As/GaAs quantum dots grown by molecular beam epitaxy

Evolution of surface morphology and optical characteristics of 1.3-mu m In0.5Ga0.5As/GaAs quantum dots (QDs) grown by molecular beam epitaxy (MBE) are investigated by atomic force microscopy (AFM) and photoluminescence (PL). After deposition of 16 monolayers (ML) of In0.5Ga0.5As, QDs are formed and elongated along the [110] direction when using sub-ML depositions, while large size InGaAs QDs with better uniformity are formed when using ML or super-ML depositions. It is also found that the larger size QDs show enhanced PL efficiency without optical nonlinearity, which is in contrast to the elongated QDs.

Fabrication and modulation characteristics of 1.3 mu m p-doped InAs quantum dot vertical cavity surface emitting lasers

We present the fabrication of 1.3 mu m waveband p-doped InAs quantum dot (QD) vertical cavity surface emitting lasers (VCSELs) with an extremely simple process. The continuous-wave saturated output power of 1.1 mW with a lasing wavelength of 1280 nm is obtained at room temperature. The high-speed modulation characteristics of p-doped QD VCSELs of two different oxide aperture sizes are investigated and compared. The maximum 3 dB modulation bandwidth of 2.5 GHz can be achieved at a bias current of 7 mA for a p-doped QD VCSEL with an oxide aperture size of 10 mu m in the small signal frequency response measurements. The crucial factors for the 3 dB bandwidth limitation are discussed according to the parameters' extraction from frequency response.

The structural, morphological and magnetic characteristics of Mn-implanted nonpolar a-plane GaN films

Dilute magnetic nonpolar GaN films have been fabricated by implanting Mn into unintentionally doped nonpolar a-plane GaN films at room temperature, and a subsequent rapid thermal annealing. The X-ray diffraction analysis shows that after rapid thermal annealing the peak of the GaN X-ray diffraction curve shifts to a lower angle, indicating a slight expansion of the GaN crystal lattice. Atomic force microscopy analysis shows that the annealing process does not change the morphology of the sample greatly. Magnetic property analysis indicates that the as-annealed sample shows obvious ferromagnetic properties. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Structural, morphological, and magnetic characteristics of Cu-implanted nonpolar GaN films

Diluted magnetic nonpolar GaN:Cu films have been fabricated by implanting Cu ions into unintentionally doped nonpolar a-plane(1 1 (2) over bar 0) GaN films and a subsequent thermal annealing process. The structural, morphological and magnetic characteristics of the samples have been investigated by means of high-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), and superconducting quantum interference device (SQUID). The sample shows a clear ferromagnetism behavior at room temperature. It is significantly shown that with a Cu concentration as low as 0.75% the sample exhibits a saturation magnetization about 0.65 mu(B)/Cu atom. Moreover, the possible origin of the ferromagnetism for the sample was also discussed briefly. (C) 2009 Elsevier B. V. All rights reserved.

Recent advances in synthesis and properties of cubic boron nitride films

Cubic boron nitride (c-BN) attracts widespread interest as a promising material for many potential applications because of its unique physical and chemical properties. Since the 1980's the research in c-BN thin films has been carried out, which reached its summit in the mid of 1990's, then turned into a downward period. In the past few years, however, important progress was achieved in synthesis and properties of cubic boron nitride films, such as obtaining > 1 mu m thick c-BN films, epitaxial growth of single crystalline c-BN films, and advances in mechanics properties and microstructures of the interlayer of c-BN films. The present article reviews the current status of the synthesis and properties of c-BN thin films.

Fabrication process and power and lifetime characteristics of very-small-aperture laser

High output power very-small-aperture laser has been created on 650 nm edge emitting laser diodes. The far-field output power is 0.4 mW at the 25 mA driving current, and the highest output power exceeds 1 mW. The special fabrication process is described and the failure mechanism leading to the short lifetime of the devices is discussed.

Homoepitaxial growth and device characteristics of SiC on Si-face (0001) 6H-SiC

Homoepitaxial growth of SiC on a Si-face (0 0 0 1) GH-SIC substrate has been performed in a modified gas-source molecular beam epitaxy system with Si2H6 and C2H4 at temperatures ranging 1000 1450 degreesC while keeping a constant SiC ratio (0.7) in the gas phase. X-ray diffraction patterns, Raman scattering measurements. and low-temperature photoluminescence spectra showed single-crystalline SiC. Mesa-type SiC p-n junctions were obtained on these epitaxial layers, and their I-V characteristics are presented. (C) 2001 Elsevier Science B.V. All rights reserved.

Structural and optical characteristics of self-organized InAs quantum dots grown on GaAs (3 1 1)A substrates

Structural and optical investigations of InAs QDs grown on GaAs (3 1 1)A by molecular beam epitaxy (MBE) were reported. InAs/GaAs (3 1 1)A QDs with nonconventional, faceted, arrowhead-like shapes aligned in the [ - 2 3 3] direction have been disclosed by AFM image. Low defect and dislocation density on the QDs interfaces were indicated by the linear dependence of photoluminescence (PL) intensity on the excitation power. The fast red shift of PL energy and the monotonic decrease of FWHM with increasing temperature were observed and explained by carriers being thermally activated to the energy barrier produced by the wetting layer and then retrapped and recombined in energetically low-lying QDs states. (C) 1999 Elsevier Science B.V. All rights reserved.

The Deposition and Burning Characteristics During Slagging Co-Firing Coal and Wood: Modeling and Numerical Simulation

Numerical analysis was used to study the deposition and burning characteristics of combining co-combustion with slagging combustion technologies in this paper. The pyrolysis and burning kinetic models of different fuels were implanted into the WBSF-PCC2 (wall burning and slag flow in pulverized co-combustion) computation code, and then the slagging and co-combustion characteristicsespecially the wall burning mechanism of different solid fuels and their effects on the whole burning behavior in the cylindrical combustor at different mixing ratios under the condition of keeping the heat input samewere simulated numerically. The results showed that adding wood powder at 25% mass fraction can increase the temperature at the initial stage of combustion, which is helpful to utilize the front space of the combustor. Adding wood powder at a 25% mass fraction can increase the reaction rate at the initial combustion stage; also, the coal ignitability is improved, and the burnout efficiency is enhanced by about 5% of suspension and deposition particles, which is helpful for coal particles to burn entirely and for combustion devices to minimize their dimensions or sizes. The results also showed that adding wood powder at a proper ratio is helpful to keep the combustion stability, not only because of the enhancement for the burning characteristics, but also because the running slag layer structure can be changed more continuously, which is very important for avoiding the abnormal slag accumulation in the slagging combustor. The theoretic analysis in this paper proves that unification of co-combustion and slagging combustion technologies is feasible, though more comprehensive and rigorous research is needed.

Far-field and beam characteristics of vertical-cavity surface-emitting lasers

We have determined the far-field patterns and beam parameters of vertical-cavity surface-emitting lasers (VCSELs) with different structures. The results show that the window diameter and the active-layer aperture of VCSELs strongly influence laser far-field distributions and beam characteristics; for VCSELs with small window omega=5 mu m, only one dominant lobe has been observed in the far-field profiles, even though injected current was increased up to 2 Ith; and the smaller the ratio of the window diameter to the active-layer aperture, the larger is the far-field divergence. The laser structure dependence of the K factor has also been studied. (C) 1996 American Institute of Physics.

Structure and device characteristics of AlxGa1-xAs/GaAs solar cells

AlGa1-xAs/GaAs heterostructures have been grown by two different liquid phase epitaxy (LPE) modes, i.e. the supercooled and melt-etch methods, for the fabrication of highly efficient solar cells. Typical structural characteristics observed under a transmission electron microscope (TEM), an Auger energy spectrometer (AES) and corresponding device parameters were presented. The results indicated that the P+PNN+ configuration grown by the melt-etch method could be used to produce high performance, large area solar cells with effectively reducing the defects of the substrate and improving the minority carrier collection by forming a compositionally graded region in the window layer.