Ratio In Gas Phase Research Articles

Experimental investigation on nitrogen related complex acceptors in nitrogen-doped ZnO films

In this article, experiments have been designed to investigate the nature, introduction, and control of the shallow acceptor states in nitrogen-doped ZnO material. With the help of a batch of characterizing experiments, we have confirmed shallow acceptor states in the form of (NH4)Zn and (N2)Zn. The content of the acceptor-like nitrogen complexes could be tuned by varying the VI/II ratio in gas phase during growth. The formation mechanism of the complexes has also been discussed. The formation energy of the (NH4)Zn complex could be lower than that of VZn at O-rich condition, making its formation at zinc site energetically favorable. However, although the formation energy of the (N2)Zn complex is slightly higher than that of VZn, the complex could be stabilized by binding to adjacent lattice oxygen or additional hydrogen, which could lower the total energy through transferring electrons to the high energy states. Furthermore, direct introduction of (N2)Zn via growth has been suggested to be more efficient as compared to that via post-growth process demonstrated previously. All these mechanisms lead to a reasonable co-existence of the (NH4)Zn and (N2)Zn acceptor-like complexes in ZnO lattice, which is responsible for the experimentally observed shallow acceptor state in nitrogen-doped ZnO material.

MOVPE growth of (GaIn)As/Ga(AsSb)/(GaIn)As type-II heterostructures on GaAs substrate for near infrared laser applications

The growth of high quality (GaIn)As/Ga(AsSb)/(GaIn)As “W”-quantum well heterostructures is discussed with respect to their application in 1300nm laser devices. The structures are grown using metal organic vapor phase epitaxy and characterized using high-resolution X-ray diffraction, scanning transmission electron microscopy and photoluminescence measurements. The agreement between experimental high-resolution X-ray diffraction patterns and full dynamical simulations is verified for these structurally challenging heterostructures. Scanning transmission electron microscopy is used to demonstrate that the structure consists of well-defined quantum wells and forms the basis for future improvements of the optoelectronic quality of this materials system. By altering the group-V gas phase ratio, it is possible to cover a large spectral range between 1200nm and 1470nm using a growth temperature of 550°C and a V/III ratio of 7.5. A comparison of a sample with a photoluminescence emission wavelength at 1360nm with single quantum well material reference samples proves the type-II character of the emission. A further optimization of these structures for application in 1300nm lasers by applying different V/III ratios yields a stable behavior of the photoluminescence intensity using a growth temperature of 550°C.

GaAsP Nanowires Grown by Aerotaxy.

We have grown GaAsP nanowires with high optical and structural quality by Aerotaxy, a new continuous gas phase mass production process to grow III-V semiconductor based nanowires. By varying the PH3/AsH3 ratio and growth temperature, size selected GaAs1-xPx nanowires (80 nm diameter) with pure zinc-blende structure and with direct band gap energies ranging from 1.42 to 1.90 eV (at 300 K), (i.e., 0 ≤ x ≤ 0.43) were grown, which is the energy range needed for creating tandem III-V solar cells on silicon. The phosphorus content in the NWs is shown to be controlled by both growth temperature and input gas phase ratio. The distribution of P in the wires is uniform over the length of the wires and among the wires. This proves the feasibility of growing GaAsP nanowires by Aerotaxy and results indicate that it is a generic process that can be applied to the growth of other III-V semiconductor based ternary nanowires.

Investigation of CO2 separation from synthesis CO2/CH4 mixture utilizing tetra‐n‐butyl ammonium bromide semi‐hydrate

Semi‐clathrate hydrates of tetra‐n‐butyl ammonium bromide (TBAB) offer a potential solution for separation of CO2 from biogas. In this work, gas hydrate formation from a CO2/CH4 mixture in distilled water with 0.05 g/g (5 wt%) TBAB was examined at 275, 277, and 279 K with pressures of 4000, 5000, and 6000 kPa. The compositional changes of the gas phase were analyzed continuously during the hydrate formation process. The results indicated that no significant induction occurred during hydrate formation. The CO2 separation factor increased with decreasing temperature and increasing pressure. The maximum amount of CO2 gas molar ratio in the residual gas phase was 79.81 mol% at 4000 kPa and 275 K with a gas/liquid volume ratio (Vg/Vl) of 1. TBAB promoted hydrate formation and CO2 separation; however, the CO2 separation factor decreased in a decomposed solution compared with fresh TBAB solution. The experimental results provide a theoretical basis for the use of hydrate‐based gas separation (HBGS) technology in biogas purification.

MOVPE growth studies of Ga(NAsP)/(BGa)(AsP) multi quantum well heterostructures (MQWH) for the monolithic integration of laser structures on (001) Si-substrates

High-quality, pseudomorphically strained Ga(NAsP)/(BGa)(AsP)-multiple quantum well heterostructures (MQWH) have been deposited on exactly oriented (001) Si-substrate by metal organic vapour phase epitaxy (MOVPE) in a wide temperature range between 525°C and 700°C. The individual atomic incorporation efficiencies, growth rates as well as nanoscale material properties have been clarified by applying detailed high-resolution X-ray diffraction (HR-XRD), photoluminescence (PL) spectroscopy and high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) studies. An almost constant N-incorporation efficiency is obtained for a wide growth temperature range from 550°C up to 650°C. The P-incorporation is steadily increasing with increasing growth temperature reaching values at high temperatures in excess of the applied gas phase ratio. While the lower interface from the binary GaP- to the quaternary Ga(NAsP)-material system is very sharp, the upper interface is significantly rougher with a roughness scale of ±0.43nm in quantum well thickness variation at a growth temperature of 525°C. This roughness scale increases steadily with increasing growth temperature. No indication of any phase separation effects is detected in the Ga(NAsP)-material system even at the highest growth temperature of 700°C. The obtained experimental results are briefly discussed with respect to the anticipated metastable character of the novel dilute-nitride Ga(NAsP)-material system grown lattice-matched to (001) Si-substrate.

Redox reaction of nitric oxide and carbon monoxide over Fe2O3 and Co3O4 phases

Fe2O3 and Co3O4 phases are synthesized by the thermal treatment in an air-flow of hydrated salts based on Fe and Co. The materials are characterized by X-ray diffraction, energy dispersive spectroscopy, scanning electron microscopy, thermogravimetric analysis and surface area measurements. Fe2O3 and Co3O4 were tested for nitric oxide reduction with carbon monoxide in a 1:5 gas phase ratio and showed reaction rates in a range from 8.7 × 10−11 to 5.9 × 10−10 mol s−1 g−1 with an activation energy interval from 50.2 to 54.4 kJ mol−1. Fe2O3 and Co3O4 achieved (100 and 98) % NO conversion with (96 and 80) % selectivity to N2 at (275 and 350) °C. Fe2O3 and Co3O4 have the advantages such as facile synthesis, low-cost, good thermal stability, high activity and selective to N2. These results regarding activity and selectivity are better or similar to some catalysts based on noble metals (Rh, Pt and Pd) currently used for air pollutants control.

Effect of culture conditions on hydrogen production by Thermoanaerobacter strain AK68

Thermoanaerobacter strain AK68, isolated from a hot spring in Iceland, was investigated for hydrogen production from sugars. Strain AK68 is most closely related to Thermoanaerobacter thermohydrosulfuricus (99.9% similarity). The strain has a temperature optimum between 65 °C and 70 °C and a pH optimum between pH 7.0 and 8.0. The strain degraded the majority of substrates examined including common hexoses and disaccharides as well as xylose but not arabinose or starch. Various environmental variables were investigated to gain a deeper understanding of the factors that are of importance for hydrogen production since the strain shows inhibition at relatively low initial glucose concentrations. Factors investigated included initial glucose concentration, phosphate buffer concentration, liquid–gas phase ratio, effect of various external electron acceptors, and different initial pH values. Substrate utilization was shown to be inhibited by increased partial pressure of hydrogen, as evidenced by increased utilization of glucose using electron scavenging systems and manipulation of the liquid–gas phase ratio, rather than substrate or end product inhibition.

Co-adsorption and mutual interaction of nCO + mH2 on the Fe(1 1 0) and Fe(1 1 1) surfaces

Spin-polarized density functional theory computations have been performed to investigate nCO+mH2 co-adsorption and mutual interaction on the Fe(110) and Fe(111) surfaces. It is found that CO pre-coverage affects hydrogen adsorption strongly, while H pre-coverage hardly affects CO adsorption. It is possible to have CO+H2 co-adsorption on Fe(110), while very strong preference of CO pre-coverage on Fe(111) has been found. On Fe(111), it is also found that each CO molecule blocks on average 2H adsorption sites at all CO pre-coverage. All these findings are consistent with available experimental results. Compared with CO/H2 ratios in gas phase, CO/H2 surface ratios are very different and much more sensitive to temperature than pressure. Our results provide the basis for exploring the mechanisms of iron-catalyzed conversion of synthesis gas.

Branched-chain alcohol formation from branched-chain amino acids by Thermoanaerobacter brockii and Thermoanaerobacter yonseiensis

Thermoanaerobacter species degrade branched-chain amino acids to a mixture of their corresponding branched-chain fatty acids and alcohols in the presence of thiosulfate; only acid formation occurred when Thermoanaerobacter strains were cultivated in co-culture with a hydrogenotrophic methanogen. Increased pH2 at high liquid–gas phase ratios increases the relative concentration of branched-chain alcohol.

Boron Elimination Filter from SiH4 and B2H6 Gas Mixture for Purification of Metallurgical Si

We have proposed the solar-grade Si film formation method from metallurgical-grade (MG) Si source by using a chemical transport induced by high-pressure hydrogen plasma1). In this method, selectivity of hydrogen induced chemical reaction was utilized to eliminate the metal impurities from MG-Si source. However, MG-Si also contains B and P which are electrically active element in Si matrix. These are difficult to remove by using above method, because they can form volatile hydrides. So, the simple process to eliminate these elements is necessary. Fortunately, it can be expected that elimination of PH3 would be easily achieved by using a molecular sieve due to the polarity of PH3 2). However, B2H6 molecule has no dipole moment in common with SiH4, hence molecular sieve is not expected to remove B2H6 efficiently from SiH4 and B2H6gas mixture.Then, in this study, we have attempted to eliminate B2H6 from the gas mixtures by using difference of the pyrolytic behavior of both gases and demonstrated that the developed filter can operate effectively as B2H6filter. EXPERIMENTAL The porous carbon plate with its thickness of 5mm was used as filter element to the benefit of its chemical inertness, electrical conductivity (162μΩcm), relatively wide specific surface area, and its porosity (30%). The plate was settled in the filter vessel and connected to the heater power source to control its temperature by electrical heating. To investigate the elimination property of the pyloritic filter precisely, the SiH4 and B2H6 gases supplying from gas cylinder were used in this study. The gas mixture ratio of SiH4 and B2H6 was controlled through mass flow controller. Moreover, H2 and He are used as carrier gas. The transmission property of SiH4 and B2H6for porous carbon filter at various temperatures was evaluated by gas phase FTIR. To ensure the Boron elimination from Si material by using the filter, Si film was formed on Si substrate by thermal CVD at 800°C through the use of gas mixture after passing through the filter and B concentration in the film was evaluated by SIMS. RESULTS AND DISCUSSION Figure 1 shows the filter temperature (Tfilter) dependence of transmission properties of SiH4 and B2H6. He carrier gas flow rate was 10 slm. During the experiment, the filter vessel pressure was kept at 200 Torr. As shown in Fig.1, B2H6 transmittance begins to decrease at 200°C and is reduced to almost zero at 350°C. On the other hand, SiH4 begins to decrease at 450°C and shows the transmittance of 10% even at 550°C. From this result, it is found that B2H6 can be eliminated efficiently without sacrifice of SiH4, if the Tfilteris kept at 400°C.Figure 2 shows the B removal performance of the porous carbon filter at various temperatures. The carrier gas flow rate was 10slm. The removal performance (RPgas/film) was defined by dividing the concentration ratio in the gas phase(([B]/[Si])gas) by that in the Si film(([B]/[Si])film). The supplying concentration ratio in gas phase was 10-3 in this study. RPgas/film exponentially increases from 60 to 3200 with increasing the Tfilter from 300°C to 500°C. This temperature dependence of RPgas/film assures that the filter operates on the basis of difference of thermochemical decomposition between SiH4 and B2H6. CONCLUSION We have proposed and developed the B eliminating filter operating on the basis of difference of pyrolitic behavior between B2H6 and SiH4. B concentration in both gas phase and Si film could be decreased by filtering the gas mixture at the Tfilterof more than 300°C.REFERENCES1) H. Ohmi et al., Appl. Phys. Lett. 95(2009) 181506-1-3.2) A. Yusa et al., J. Electrochem. Soc. 122 (1975) 1700.

Influence of the C/O ratio on titanium and vanadium oxides in protoplanetary disks

Context. The observation of carbon-rich disks have motivated several studies questioning the influence of the C/O ratio on their gas phase composition in order to establish the connection between the metallicity of hot-Jupiters and that of their parent stars. Aims. We to propose a method that allows the characterization of the adopted C/O ratio in protoplanetary disks independently from the determination of the host star composition. Titanium and vanadium chemistries are investigated because they are strong optical absorbers and also because their oxides are known to be sensitive to the C/O ratio in some exoplanet atmospheres. Methods. We use a commercial package based on the Gibbs energy minimization technique to compute the titanium and vanadium equilibrium chemistries in protoplanetary disks for C/O ratios ranging from 0.05 to 10. Our calculations are performed for pressures ranging from 1e-6 to 1e-2 bar, and for temperatures ranging from 50 to 2000 K. Results. We find that the vanadium nitride/vanadium oxide and titanium hydride/titanium oxide gas phase ratios strongly depend on the C/O ratio in the hot parts of disks (T > 1000 K). Our calculations suggest that, in these regions, these ratios can be used as tracers of the C/O value in protoplanetary disks.

Deposition model of the Si3N4 coating on hard alloys

The influence of the process temperature, the SiCl4/NH3 gas-phase ratio, and the gas-phase pressure on the equilibrium degree of transformation is investigated. A mathematical model of the dependence under study is selected to describe the experimental results and coefficients of equations are calculated.

Evolution of microstructure and opto-electrical properties in boron doped nc-Si:H films deposited by HW-CVD method

Demand for an efficient window layer for a-Si:H based solar cells in terms of electrical conductivity and optical band gap is ever increasing since the inception of single junction and tandem solar cells. In this paper, we report synthesis of highly conducting boron doped p-type nc-Si:H films by HW-CVD using the mixture of silane (SiH4) and diborane (B2H6) without hydrogen (H2) dilution. Variation in film characteristics with B2H6 gas-phase ratio was studied, and revealed that the boron doping induces amorphization in nc-Si:H film structure. The AFM analysis show increase in rms surface roughness and micro-void density while FTIR spectroscopy analysis show shift of hydrogen bonding from Si–H2 and (Si–H2)n complexes to Si–H configuration on boron doping. The hydrogen content was found <2.66 at.% while the band gap remain as high as 1.8 eV or more. At optimized B2H6 gas-phase ratio, we have obtained p-type nc-Si:H films having high band gap (∼2.0 eV), high dark conductivity (∼1.2 S/cm) with low hydrogen content (∼1.78 at.%) at reasonably high deposition rate (∼9.2 A/s). The obtained films can be used as a window layer in a-Si:H based p–i–n and tandem solar cells and color light detectors.

EXPLORING IO'S ATMOSPHERIC COMPOSITION WITH APEX: FIRST MEASUREMENT OF34SO2AND TENTATIVE DETECTION OF KCl

The composition of Io's tenuous atmosphere is poorly constrained. Only the major species SO2 and a handful of minor species have been positively identified, but a variety of other molecular species should be present, based on thermochemical equilibrium models of volcanic gas chemistry and the composition of Io's environment. This paper focuses on the spectral search for expected yet undetected molecular species (KCl, SiO, S2O) and isotopes (34SO2). We analyze a disk-averaged spectrum of a potentially line-rich spectral window around 345 GHz, obtained in 2010 at the APEX-12m antenna (Atacama Pathfinder EXperiment). Using different models assuming either extended atmospheric distributions or a purely volcanically-sustained atmosphere, we tentatively measure the KCl relative abundance with respect to SO2 and derive a range of 4x10^{-4}-8x10^{-3}. We do not detect SiO or S2O and present new upper limits on their abundances. We also present the first measurement of the 34S/32S isotopic ratio in gas phase on Io, which appears to be twice as high as the Earth and ISM reference values. Strong lines of SO2 and SO are also analyzed to check for longitudinal variations of column density and relative abundance. Our models show that, based on their predicted relative abundance with respect to SO2 in volcanic plumes, both the tentative KCl detection and SiO upper limit are compatible with a purely volcanic origin for these species.

Highly Conducting Phosphorous Doped nc-Si:H Thin Films Deposited at High Deposition Rate by Hot-Wire Chemical Vapor Deposition Method

In this paper, we report the synthesis of highly conducting phosphorous doped hydrogenated nanocrystalline silicon (nc-Si:H) films at substantially low substrate temperature (200 degrees C) by hot-wire chemical vapor deposition (HW-CVD) method using pure silane (SiH4) and phosphine (PH3) gas mixture without hydrogen dilution. Structural, optical and electrical properties of these films were investigated as a function of PH3 gas-phase ratio. The characterization of these films by low-angle X-ray diffraction, Raman spectroscopy and atomic force microscopy revealed that, the incorporation of phosphorous in nc-Si:H induces an amorphization in the nc-Si:H film structure. Fourier transform infrared spectroscopy analysis indicates that hydrogen predominately incorporated in phosphorous doped n-type nc-Si:H films mainly in di-hydrogen species (Si-H2) and poly-hydrogen (Si-H2)n bonded species signifying that the films become porous, and micro-void rich. We have observed high band gap (1.97-2.37 eV) in the films, though the hydrogen content is low (< 1.4 at.%) over the entire range of PH3 gas-phase ratio studied. Under the optimum deposition conditions, phosphorous doped nc-Si:H films with high dark conductivity (sigma Dark -5.3 S/cm), low charge-carrier activation energy (E(act) - 132 meV) and high band gap (- 2.01 eV), low hydrogen content (- 0.74 at.%) were obtained at high deposition rate (12.9 angstroms/s).

Rapid determination of benzene series in seawater by gas chromatography-mass spectrometry with static headspace extraction

A method for the simultaneous determination of 13 benzene series (BTEX) in seawater using gas chromatography-mass spectrometry with static headspace extraction (HS-GC/MS) was developed. To carefully characterize the performance of this method, several factors affecting parameters were studied in detail, such as the type of column, heating procedure, equilibrium temperature, equilibrium time and the volume ratio of gas phase to liquid phase. The optimized conditions were as follows: the polar column of DB-WAX; heating procedure, 40 degrees C kept for 4 min, then raised to 120 degrees C at 10 degrees C/min, to 180 degrees C at 25 degrees C/min; equilibrium temperature, 80 degrees C; equilibrium time, 10 min; and the volume ratio of gas phase to liquid phase, 1:1. Under the optimized conditions, the linear equations were obtained in the concentration range of 0.16-320 microg/L with correlation coefficients greater than 0.999. The limits of detection (S/N = 3) were 0.019-0.033 microg/L. The recoveries at the three spiked levels of 1.6, 16 and 160 microg/L ranged from 81. 25% to 103.73% with the relative standard deviations (RSD, n=6) from 0.3% to 4.4%. The analytical results of the practical seawater samples from Shanghai Huangpu District were satisfactory. The determination of the 13 benzene series can be finished in 12 min. The method is simple, accurate, reliable, efficient and environmental-friendly.

BORON DOPED nc-Si:H WINDOW LAYER PREPARED BY HW-CVD FOR SOLAR CELL APPLICATIONS

In this work, we report on synthesis of boron doped hydrogenated nanocrystalline silicon ( p - nc - Si : H ) films by HW-CVD method. Films were prepared at low substrate temperature (165 °C) and low process pressure (20 mTorr) by varying diborane gas phase ratio [defined as R B 2 H 6 = ( F B 2 H 6/ F SiH 4)×100%]. The material properties of these films are studied using micro-Raman spectroscopy, low angle X-ray diffraction, X-ray photoelectron spectroscopy (XPS), UV-visible spectroscopy, dark conductivity measurements etc. The correlation between R B 2 H 6 and resulting material properties such as crystalline volume fraction, crystallite size, band gap and hydrogen content has been established. We have obtained high band gap (~ 2.48 eV) p - nc - Si : H films having dark conductivity (~ 0.6 S/cm) with low hydrogen content (~ 1.8 at. %) at high deposition rate (~19.2 Å/s). The employment of these films in a - Si : H based p - i - n solar cell as a p -type window layer could have low absorption losses thereby enhancing the current density which in turn would enhance the conversion efficiency of solar cell.

Highly conducting phosphorous doped n-type nc-Si:H films by HW-CVD for c-Si heterojunction solar cells

Phosphorous doped hydrogenated nanocrystalline silicon (nc-Si:H) films were prepared using the hot wire chemical vapor deposition (HW-CVD) method at a low substrate temperature of 200 °C. The microstructure and opto-electrical properties of these films were systematically studied using Raman spectroscopy, low angle XRD, high resolution transmission electron microscopy (HR-TEM), UV-Visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, dark conductivity and its activation energy measurements and Hall measurement as a function of PH3 gas-phase ratio. It has been found that with an increase in the PH3 gas-phase ratio, both the volume fraction of the crystallites and its size decrease, signifying that the phosphorous atom favors the growth of amorphization in the nanocrystalline Si network. At the optimized PH3 gas-phase ratio we have obtained n-type nc-Si:H films with a band gap of ∼1.84 eV, high dark conductivity (∼6.78 S cm−1) with low hydrogen content (∼1.72 at. %), at a reasonably high deposition rate (∼10 A s−1). Finally, Al/ZnO:Al/n-nc-Si:H/buffer a-Si:H/p-c-Si/Al heterojunction solar cells were fabricated using the optimized n-layer, showing excellent photovoltaic performance with Voc = 719 mV, Jsc = 9.94 mA cm−2, FF = 53.8%, and an energy conversion efficiency of 5.2%. These are very encouraging results for the future fabrication of high efficiency silicon heterojunction solar cells and thin film tandem solar cells.

Iodide sorption and partitioning in solid, liquid and gas phases in soil samples collected from Japanese paddy fields

Sorption kinetics of iodide (I(-)), which is one of the major inorganic chemical forms of iodine in soil environments, were studied under four sets of experimental conditions characterised by temperature or biological activity. We compared partitioning ratios in solid, liquid and gas phases in soils as well as soil-soil solution distribution coefficients (K(d)s) at two different temperatures 4 and 23 °C, for 63 paddy soil samples collected throughout Japan. Interestingly, (125)I emission from soil was observed; the partitioning ratios in gas phase ranged from 0 to 27 % at 4 °C and from 0 to 42 % at 23 °C. In addition, the authors found that K(d) values at 23 °C had good correlation with pH though there was no correlation between K(d) values at 4 °C and pH because of the difference in biological activity.

Design and selection of sparger for bubble column reactor. Part II: Optimum sparger type and design

The ease with which residence time could be adjusted, the absence of moving parts, higher values of heat and mass transfer coefficient are the attractive features of bubble columns, hence are widely used for conducting several mass transfer operations/chemical reactions. However selection of sparger design and type is crucial and it affects performance of the reactor implicitly and explicitly. The Part I of this work addressed the roles of various parameters to be considered while designing the sparger for bubble column reactors. The second part, deals with the selection of optimum design and type of the sparger for several designs of bubble column, i.e., effect of column diameter, aspect ratio, operating pressure and volumetric flow rate of gas phase.