Effects of V/III ratio on the growth of a-plane GaN films

The non-polar a-plane GaN is grown on an r-plane sapphire substrate directly without a buffer layer by metal- organic chemical vapour deposition and the effects of V/III ratio growth conditions are investigated. Atomic force microscopy results show that triangular pits are formed at a relatively high V/III ratio, while a relatively low V/III ratio can enhance the lateral growth rate along the c-axis direction. The higher V/III ratio leads to a high density of pits in comparison with the lower V/III ratio. The surface morphology is improved greatly by using a low V/III ratio of 500 and the roughness mean square of the surface is only 3.9 nm. The high resolution X-ray diffraction characterized crystal structural results show that the rocking curve full width at half maximum along the m axis decreases from 0.757° to 0.720°, while along the c axis increases from 0.220° to 0.251° with the V/III increasing from 500 μmol/min to 2000 μmol/min, which indicates that a relatively low V/III ratio is conducible to the c-axis growth of a-plane GaN.

石煤含氟酸浸液中V(Ⅴ)-Fe(Ⅲ)-F-H_(2)O系钒铁分离热力学研究

针对石煤含氟酸浸液中钒铁分离问题,计算并绘制298.15 K下V(Ⅴ)-Fe(Ⅲ)-F-H_(2)O系热力学平衡图,分析含钒离子、含铁离子随总钒浓度、总铁浓度、总氟浓度的变化规律。研究结果表明,随着pH由0升高至3.00,由于氟离子与VO_(2)^(+)、Fe^(3+)的配位作用,含钒物种由阳离子转变为阴离子,含铁物种由阳离子转变为中性分子,此时可实现钒铁有效分离。定义pH_(50%)为含钒阴离子摩尔分数50%时的pH,溶液中总钒浓度升高、总铁浓度升高,均导致pH50%升高,总氟浓度升高,pH_(50%)则降低。采用N235阴离子萃取剂分离含氟溶液中的钒铁,当溶液中总钒浓度为0.05 mol/L、总铁浓度为0.05 mol/L、总氟浓度为0.50 mol/L时,溶液萃取pH升高,钒铁分离系数βV/Fe增加,当pH为1.97时,钒铁分离系数β_(V/Fe)可达122.86,钒铁达到有效分离,与热力学分析结果一致。

Cell Size versus Taxonomic Composition as Determinants of As (III &V) Sensitivity in the Estuarine Diatom Communities

Despite scarce studies have analyzed the relative growth inhibition of As (III) and As (V) to diatom, clear pattern of interspecies difference have been shown, identifying cell size as a key property determining the sensitivity of diatom to As. Evidence from cultures suggests that cell size is a key factor in determining the extent of arsenic (III) & (V) stress of diatom, with relatively lesser effects of As (V) than As (III) on small cells. Cent percent growth inhibition was observed for large size group (Coscinodiscus radiatus, Surirella, Amphipleura, Thalassiothrix, Cyclotella and Thalassiosira decipiens) relative to smaller size group (Skeletonema cf. costatum, Navicula rhombica, Amphora hyaline, Nitzschia longissima except Thalassisira. Interspecies differences in As tolerance by diatom in the mangrove ecosystem indicates cell size could be only one factor contributing to these differences. The results show that 81.7% of total arsenic was uptaken from culture media originally amended with arsenic. Looking to the extreme tolerance and arsenic removal efficiency, application of the species with smaller cell size relative to the other tested diatom for bioremediation purpose can be envisaged.

Control of Threshold and Gain of Parametric Amplification in Magnetoactive III-V Piezoelectric Semiconductors

The effect of doping concentrations and a transverse external magnetostatic field on operational characteristics of parametric amplification of backward Stokes signal has been studied, using hydrodynamic model of semiconductors, in the far infrared regime. The model suggests three achievable resonance conditions: (i) lattice frequency and plasma frequency (ii) stokes frequency and electron-cyclotron frequency (iii) stokes frequency and hybrid (plasma and electron-cyclotron) frequency and these conditions have been utilised, on one hand, to substantially reduce the value of threshold intensity for onset of the parametric amplification and on the other hand, for switching of parametric large positive and negative gain coefficient (i.e. amplification and absorption). For example a strong transverse magnetostatic field 10.0 T with free carrier concentration 1.5 x 1019m-3 enhances the gain by a factor of 103 as in its absence. Results also suggest that a weakly piezoelectric III–V semiconductor duly illuminated by slightly off-resonant not-too-high-power pulsed lasers with pulse duration sufficiently larger than the acoustic phonon lifetime is one of promising hosts for parametric amplifier/frequency converter.

Silicon and III-V Solar Cells: From Modus Vivendi to Modus Operandi

In the present paper, some novel opportunities for the development of high-efficient Si and III-V-based solar cells are considered: energy-saving environment friendly low-temperature technology of forming p-n junctions in Si (1), elaboration of structurally perfect GaAs/Ge/Si epitaxial substrates (2) and application of protective antireflecting coatings based on cubic zirconia (3). As a result: 1) New technique of forming p-n junctions in silicon has been elaborated. The technique provided easy and comparatively cheap process of production of semiconductor devices such as solar cells. The essence of the technique under the study is comprised in formation p-n junctions in silicon by a change of conductivity in the bulk of the sample occurring as a result of redistribution of the impurities, which already exists in the sample before its processing by ions. It differs from the techniques of diffusion and ion doping where change of conductivity and formation of p-n junction in the sample occur as a result of introduction of atoms of the other dopants from the outside;2) The conditions for synthesis of GaAs/Ge/Si epitaxial substrates with a thin (200 nm) Ge buffer layer featured with (1 - 2) × 105 cm-2 density of the threading dislocation in the GaAs layer. Ge buffer was obtained by chemical vapor deposition with a hot wire and GaAs layer of 1 μm thick was grown by the metal organic chemical vapor deposition. Root mean square surface roughness of GaAs layers of the less than 1 nm and good photoluminescence properties along with their high uniformity were obtained;3) The conditions ensuring the synthesis of uniform functional (buffer, insulating and protective) fianite layers on Si and GaAs substrates by means of magnetron and electron-beam sputtering have been determined. Fianite films have been shown to be suitable for the use as an ideal anti-reflecting material with high protective and anticorrosive properties.

氮化钛纳米线的结构特征及其对V(Ⅱ)/V(Ⅲ)的电极过程

采用水热法在钛片表面直接生长二氧化钛纳米线(TiO_2 NWs),随后通过氨氮还原转化为氮化钛纳米线(TiN NWs)。利用扫描电镜(SEM)、透射电镜(TEM)、X射线光电子能谱(XPS)、循环伏安法(CV)和电化学阻抗谱(EIS)对材料的组成、微观结构和电极过程动力学的特征进行表征。结果表明,TiN NWs纳米线的直径约20-50 nm,长度超过5μm,其表面可能存在Ti-N键、Ti-O键和O-Ti-N键,这种含氮和含氧的化学态使得TiN NWs电极具有更好的电导性和电催化性能。TiN NWs电极对V(Ⅱ)/V(Ⅲ)离子表现出更好的可逆性,其电极反应电阻R_(ct)值比TiO_2 NWs和石墨电极分别小约20倍和10倍。同时,TiN NWs电极上V(Ⅲ)还原反应的速率常数为5.21×10^(-4 )cm·s^(-1),约是石墨电极(速率常数9.63×10^(-5 )cm·s^(-1)的5倍,这可归因于TiN NWs的一维纳米线微结构特征及其较高的电催化性能。

Effects of Ⅴ/Ⅲ ratio on species diffusion anisotropy inthe MOCVD growth of non-polar a-plane GaN films

Non-polar a-plane （1120） GaN films have been grown on r-plane （1102） sapphire substrates by metal organic chemical vapour deposition. The influences of V/III ratio on the species diffusion anisotropy of a-plane GaN films were investigated by scanning electron microscopy, cathodoluminescence and high-resolution x-ray diffraction measurements. The anisotropy of a-plane GaN films may result from the different migration length of adatoms along two in-plane directions. V/III ratio has an effect on the growth rates of different facets and crystal quality. The stripe feature morphology was obviously observed in the film with a high V/III ratio because of the slow growth rate along the [1100] direction. When the V/III ratio increased from 1000 to 6000, the in-plane crystal quality anisotropy was decreased due to the weakened predominance in migration length of gallium adatoms.

Effects of V/Ⅲ ratio on a-plane GaN epilayers with an InGaN interlayer

The effects of V/Ill growth flux ratio on a-plane GaN films grown on r-plane sapphire substrates with an InGaN interlayer are investigated. The surface morphology, crystalline quality, strain states, and density of basal stacking faults were found to depend heavily upon the V/III ratio. With decreasing V/III ratio, the surface morphology and crystal quality first improved and then deteriorated, and the density of the basal-plane stacking faults also first decreased and then increased. The optimal V/III ratio growth condition for the best surface morphology and crystalline quality and the smallest basal-plane stacking fault density of a-GaN films are found. We also found that the formation of basal-plane stacking faults is an effective way to release strain.

原子荧光光度法测定天然水体中的Sb(V)和Sb(Ⅲ)

采用氢化物-原子荧光光度法(HG-AFS),测定天然水体中的总溶解态无机锑(Sb(Ⅴ+Ⅲ))和三价锑(Sb(Ⅲ))。选择的最佳仪器条件为:灯电流60 mA,负高压-260 V,原子化器的温度190℃和氩气的载气流量600 mL/min。Sb(Ⅴ+Ⅲ)在1 mol/L HCl介质中进行测定,检出限为0.024μg/L,线性范围为0～14μg/L。对浓度0.3μg/L和0.03μg/L的样品分析精密度分别为2.0%和1.9%(n=9),方法的回收率93.7%～105%。Sb(Ⅲ)是在柠檬酸和柠檬酸钠缓冲溶液中(pH为4.0～4.5),辅以100 mL/min的氢气进行测定,测得检出限为0.0013μg/L,对浓度0.04μg/L和0.01μg/L的样品分析精密度分别为3.8%和5.5%(n=9),方法的回收率91.1%～104%。二者在不同介质中工作曲线的斜率变动范围均小于5%。Sb(Ⅴ)的含量由总溶解态无机锑与三价锑的含量差减得到。

Solvent extraction of V(Ⅴ) and Cr(Ⅲ) from acidic leach liquors of ilmenite using Aliquat 336

Extraction of V（V） and Cr（III） from acidic sulfate leach liquors of ilmenite using 0.4 mol/L Aliquat 336 chloride in kerosene was carried out. Different parameters affecting the extraction process such as equilibrium time, sulfate concentration, Aliquat 336 concentration, equilibrium p H and the extraction temperature were investigated. Extraction of V（V） and Cr（III） by Aliquat 336 involved anion exchange mechanism, and the extracted species are [（VO2SO4）R4N]org at low equilibrium p H for V（V） and [R4N-Cr（OH）4]org at high equilibrium p H for Cr（III）. Calculated thermodynamic parameters show that the extraction process is endothermic reaction for V（V） and exothermic for Cr（III）. Also, calculated values of ？Gex and ？Sex indicate that the extraction reactions of V（V） and Cr（III） proceed as non-spontaneous reaction is more random. V（V） and Cr（III） were stripped, precipitated, separated and calcined at 500 °C for 2.0 h to produce the corresponding oxide in pure form after rinsing and drying.

Electron Transport Property of CdTe under High Pressure and Moderate Temperature by In-Situ Resistivity Measurement in Diamond Anvil Cell

In situ resistivity measurement has been performed to investigate the electron transport property of powered CdTe under high pressure and moderate temperature in a designed diamond anvil cell. Several abnormal resistivity changes can be found at room temperature when the pressure increases from ambient to 33 GPa. The abnormal resistivity changes at about 3.8 GPa and 10 GPa are caused by the structural phase transitions to the rock-salt phase and to the Cmcm phase, respectively. The other abnormal resistivity changes at about 6.5 GPa, 15.5 GPa, 22.2 GPa and about 30 GPa never observed before are due to the electronic phase transitions of CdTe. The origin of the abnormal change occurred at about 6.5 GPa is discussed. The temperature dependence of the resistivity of CdTe shows its semiconducting behaviour at least before 11.3 GPa.

Comparison of the photoemission behaviour between negative electron affinity GaAs and GaN photocathodes

In view of the important application of GaAs and GaN photocathodes in electron sources, differences in photoe- mission behaviour, namely the activation process and quantum yield decay, between the two typical types of III-V compound photocathodes have been investigated using a multi-information measurement system. The activation exper- iment shows that a surface negative electron affinity state for the GaAs photocathode can be achieved by the necessary Cs-O two-step activation and by Cs activation alone for the GaN photocathode. In addition, a quantum yield decay experiment shows that the GaN photocathode exhibits better stability and a longer lifetime in a demountable vacuum system than the GaAs photocathode. The results mean that GaN photocathodes are more promising candidates for electron source emitter use in comparison with GaAs photocathodes.

Enhanced light extraction of GaN-based light-emitting diodes with periodic textured SiO_2 on Al-doped ZnO transparent conductive layer

We report an effective enhancement in light extraction of Ga N-based light-emitting diodes（LEDs） with an Al-doped Zn O（AZO） transparent conductive layer by incorporating a top regular textured SiO2 layer. The 2 inch transparent throughpore anodic aluminum oxide（AAO） membrane was fabricated and used as the etching mask. The periodic pore with a pitch of about 410 nm was successfully transferred to the surface of the SiO2 layer without any etching damages to the AZO layer and the electrodes. The light output power was enhanced by 19% at 20 m A and 56% at 100 m A compared to that of the planar LEDs without a patterned surface. This approach offers a technique to fabricate a low-cost and large-area regular pattern on the LED chip for achieving enhanced light extraction without an obvious increase of the forward voltage.

Synthesis and Characterization of GaN Rods Prepared by Ammono-Chemical Vapor Deposition

GaN rods were deposited by chemical vapor deposition (CVD) onto sapphire (0 0 0 1) and amorphous quartz. The reactive Ga species in vapor the phase was formed with NH4Cl and gallium. The unidirectional growth was catalyzed with gold nanoparticles formed onto the substrate prior to the CVD reaction in order to induce a vapor-liquid-solid (VLS) mechanism. However, this method of synthesis seems to be influenced by other growth mechanisms which formed additional depositions of GaN with different morphology than the rods catalyzed by gold nanoparticles. The moieties of GaN that grew in the absence of gold formed branches in the rods or increased the lateral growth of rods resulting in larger diameters than the size of the gold particle that guided the growth.

N vacancy, substitutional O, and Al defects in the bandgap of composition-tunable nonstoichiometric AlN powder

AlN powders are prepared by direct nitridation via Al liquid and vapor phases in mixed atmospheres of N2 and NH3 with different NH3/N2 ratios. The reaction analysis reveals that NH3 acts as catalyst for N2 dissociation and the transportations of N, O, and Al in the liquid phase are different from those in the vapor phase. Accordingly, the products are Al-rich and composition-tunable nonstoichiometric AlN in which N, O, and Al content values change with nitridation atmosphere and temperature, leading to the variation of the relevant defect concentration. Therefore, the AlN powders exhibit prominent absorption bands around 5.30, 3.40, and 1.50 eV, which are tentatively assigned to VN, ON donors, and AlN acceptor respectively. Furthermore, a new donor named [VN-ON] complex is predicted at 4.40 eV within the 5.90 eV bandgap. It is demonstrated that the optical spectra of nonstoichiometric AlN are preferable to the nominal stoichimometric one for the identification of the defects energy level.

Aluminum incorporation efficiencies in A- and C-plane AlGaN grown by MOVPE

The aluminum incorporation efficiencies in nonpolar A-plane and polar C-plane A1GaN films grown by metalorganic vapour phase epitaxy （MOVPE） are investigated. It is found that the aluminum content in A-plane A1GaN film is obviously higher than that in the C-plane sample when the growth temperature is above 1070 ℃. The high aluminum incorporation efficiency is beneficial to fabricating deep ultraviolet optoelectronic devices. Moreover, the influences of the gas inlet ratio, the V/Ⅲ ratio, and the chamber pressure on the aluminum content are studied. The results are important for growing the A1GaN films, especially nonpolar A1GaN epilayers.

Distribution of Antimony in a Tropical Estuary Dominated by Mangroves

Seasonal variation of antimony was studied in order to characterize its distribution in estuarine water, pore water, sediment, and digenetic behavior in the Sundarbans mangrove ecosystem. The mean concentration of dissolved inorganic Sb ranged between 230.8 and 303.1 ng L–1 over the period of study with a minimum during the post-monsoon closely associated with spring diatom bloom. Molecular diffusion flux of Sb was found greater than its value advected and deposited on sediment-water interface and there was significant remobilization of Sb in the Sundarbans mangrove ecosystem.

壳聚糖-生物铁锰氧化物去除水体中锑的性能及机理研究

锑作为一种强致畸致癌的重金属元素,广泛存在于自然水体环境之中,对人体健康和生态环境造成了一定程度的威胁。利用壳聚糖包埋生物质铁锰氧化物,制备出一种绿色环保、循环利用率高的生物质吸附材料(CH-BFMO)。采用批量吸附实验研究了该复合材料对水体中三价锑和五价锑的吸附性能。基于动力学和吸附等温线分析,并借助FTIR和XPS等表征方法,探究了CH-BFMO对水体中Sb(III)和Sb(V)的吸附机制。其结果表明:负载壳聚糖后,CH-BFMO的形貌结构并未发生明显改变,仍为无定型结构,但其比表面积由79.2 m^(2)·g^(-1)增加到91.3 m^(2)·g^(-1),更加有利于对物质的吸附。批次实验表明,CH-BFMO对Sb(III)和Sb(V)的最大吸附容量分别为37.6 mg·L^(-1)(pH 4)和24.8 mg·L^(-1)(pH 6),二者的吸附动力学过程更接近准二级动力学方程,说明CH-BFMO对Sb(III)和Sb(V)均以化学吸附为主。Sb(III)和Sb(V)的吸附等温曲线都符合Langmuir等温模型,说明该过程均为单层吸附。FTIR及XPS分析表明:CH-BFMO表面含有的丰富的含氧官能团(C=O、C=C、O–H),有利于CH-BFMO对Sb(III)和Sb(V)的吸附去除。对于Sb(V)来说,主要是依靠与CH-BFMO发生化学吸附而实现去除。而对于Sb(III)的来说,其去除过程则可能涉及化学吸附和氧化的共同作用。SO_(4)^(2-)、CO_(3)^(2-)对CH-BFMO吸附Sb(III)和Sb(V)的影响较小,但PO_(4)^(3-)会抑制材料对Sb(III)和Sb(V)的吸附去除。5次循环后,CH-BFMO对Sb(III)与Sb(V)的吸附量仍能保持在92%以上,说明CH-BFMO循环性能优良,是一种潜在的去除水体中锑污染的吸附材料。

液相色谱-氢化物发生-原子荧光光谱法测定中药样品中的4种砷形态

目的 建立一种液相色谱-氢化物发生-原子荧光光谱测定中药样品中4种砷形态的方法。方法 以0.15 mol/L硝酸溶液为提取溶剂,提取处理后的中药样品,全自动石墨消解仪90℃热浸提,离心,取上清,0.45μm滤膜过滤后注入液相色谱仪,梯度洗脱,4种砷形态可在360 s中内完全分离,分离后的亚砷酸根[As(Ⅲ)]、砷酸根[As(Ⅴ)]、一甲基砷(MMA)、二甲基砷(DMA)4种砷形态进入氢化物发生-原子荧光光谱仪进行检测,根据保留时间定性,峰面积定量。结果 本方法在1.0~50.0μg/L范围内线性良好,相关系数(r)均>0.999,加标回收率为96.7%~101.9%,不同浓度水平的RSD均小于3%。所检测的7种中药材样品中,砷主要以As(Ⅲ)和As(Ⅴ)形态存在。结论 本方法前处理简便、检测速度快、检出限低、准确度和精密度较高,可用于中药材样品中4种砷形态的测定。