Ratio In Gas Phase Research Articles

SO2 and OCS toward high-mass protostars

Context. OCS and SO2 are both major carriers of gaseous sulfur and are the only sulfurated molecules detected in interstellar ices to date. They are thus the ideal candidates for exploring the evolution of the volatile sulfur content throughout the different stages of star formation. Aims. We aim to investigate the chemical history of interstellar OCS and SO2 by deriving a statistically significant sample of gas-phase column densities toward massive protostars and comparing them to observations of gas and ices toward other sources, from dark clouds to comets. Methods. We analyzed a subset of 26 line-rich massive protostars observed by ALMA in Band 6 as part of the High Mass Protocluster Formation in the Galaxy (ALMAGAL) survey. Column densities were derived for OCS and SO2 from their rare isotopologs O13CS and 34SO2 toward the compact gas around the hot cores. We compared the abundance ratios of gaseous OCS, SO2, and CH3OH with ice detections toward both high- and low-mass sources as well as dark clouds and comets. Results. We find that gas-phase column density ratios of OCS and SO2 with respect to methanol remain fairly constant as a function of luminosity between low- and high-mass sources, despite their very different physical conditions. In our dataset, OCS and SO2 are weakly correlated. The derived gaseous OCS and SO2 abundances relative to CH3OH are overall similar to protostellar ice values, with a significantly larger scatter for SO2 than for OCS. Cometary and dark-cloud ice values agree well with protostellar gas-phase ratios for OCS, whereas higher abundances of SO2 are generally seen in comets compared to the other sources. Gaseous SO2/OCS ratios are consistent with ices toward dark clouds, protostars, and comets, albeit with some scatter. Conclusions. The constant gas-phase column density ratios throughout low- and high-mass sources indicate an early-stage formation before intense environmental differentiation begins. Icy protostellar values are similar to the gas-phase medians and are compatible with an icy origin for these species followed by thermal sublimation. The larger spread in SO2 compared to OCS ratios with respect to CH3OH is likely due to a more water-rich chemical environment associated with the former, as opposed to a CO-rich origin for the latter. Post-sublimation gas-phase processing of SO2 can also contribute to the large spread. Comparisons to ices in dark clouds and comets point to a significant inheritance of OCS from earlier to later evolutionary stages.

Self-catalyzed GaP nanowire MOVPE growth on Si

Typically, vapour liquid solid (VLS)-grown nanowires via metal–organic vapour phase epitaxy (MOVPE) use gold as a liquid growth catalyst. However, incorporating gold as an impurity during growth is disadvantageous. Therefore, we introduce the self-catalyzed VLS growth of GaP nanowires on Si (111) substrates via MOVPE, utilizing (deposited) Ga droplets as seed particles. To understand and optimize the growth process, the influence of various growth parameters such as Ga precursor preflow, growth temperature, growth time and V/III ratio are studied. As main findings we show that nanowire growth without strong tapering is possible. By varying the V/III gas phase ratio the tapering of nanowires can be manipulated during growth via droplet consumption. In addition, nanowires with lengths up to 10 µm and an aspect ratio of around 20 are demonstrated, showing only slight tapering. High-resolution scanning transmission electron microscopy measurements prove the zincblende crystal structure of the GaP nanowires in horizontal and vertical ultramicrotomy cuts. In vertical cross sections, a high number of microtwin boundaries perpendicular to the growth direction are found.

Investigation of non-equilibrium solvent exsolution dynamics and bubble formation and growth of a CO2/C3H8/heavy-oil system by micro-optical visualizations: Experimental and continuum-scale numerical studies

Non-equilibrium exsolution dynamics of a carbon dioxide/propane solvent mixture in heavy oil phase have been studied through a series of micro-optical visualization tests and continuum numerical simulations. The micro-optical visualization tests include bulk-phase Constant-Composition-Expansion (CCE) pressure depletion tests, and bubble-scale exsolution tests from nucleation sites. The CCE tests are aimed to investigate three main parameters of non-equilibrium exsolution dynamics, namely, the total gas phase volume ratio (Vg%), the relative volume of the solvent/heavy oil system (RV), and the solvent molar ratio in free gas phase (e.g., CO2 mol%). The experimental methodology has successfully validated the deviations of the targeting parameters between non-equilibrium and equilibrium state, providing a feasible way to characterize the definition of non-equilibrium. For bubble-scale exsolution tests, two operating schemes have been applied as continuous and segmental depletion. By capturing the growth of bubbles under different depletion schemes, logarithmic relationships have been found between kinetic reaction rate frequency factors (RRFs) of bubble growth and prevailing system pressure. A larger pressure differential from live oil saturation pressure yielded higher kinetic frequency factors. Through all tests, the pseudo-bubble point pressure (where the first batch of gas bubbles were observed) of the solvent/heavy oil system has been determined at ΔP =450∼550kPa from the live oil saturation pressure, which is consistent in terms of the values among different depletion schemes. This has indicated the experimental feasibility in determining the shifting/delay of the bubble point pressure. Numerically, a continuum numerical simulator has been developed to determine the relationship between RRFs and pressure by segmentally history matching Vg%, RV and CO2 mol% of the depletion tests. Similar to the experimental findings, the segmentally optimized RRFs have found to be in logarithmic relationships with pressure. This logarithmic relationship between RRFs and pressure have both been experimentally and numerically verified, and the feasibility of the logarithmic relationship developed from bubble exsolution to be implemented as numerical inputs in continuum reservoir simulation has been validated.

Chemical vapor deposition of sp2-boron nitride on mechanically polished pyrolytic boron nitride substrates

Nanocrystalline sp2-boron nitride (BN) thin films have been grown for 2 and 4.5 h on mechanically polished polycrystalline pyrolytic boron nitride substrates at 1060 °C via chemical vapor deposition using diborane (B2H6) and ammonia (NH3) as the B- and N sources, respectively. The use of an N/B gas phase ratio of 200 resulted in sp2-BN thin films having a stoichiometric surface chemistry, as determined by x-ray photoelectron spectroscopy. Cross-sectional transmission electron microscopy revealed the initial growth of ∼4 nm thick partially ordered [0001] sp2-BN layers regardless of the crystallographic orientation of the sets of layers in the substrate. A transition zone then formed within the deposited films that contained randomly oriented polycrystalline grains and that culminated in the formation of protrusions. Atomic force microscopy verified an increase in roughening of the surfaces of the films with an increase in growth time and the associated thickness.

Boron Induced Crystallization of Silicon on Glass: an Alternate Way to Crystallize Amorphous Silicon Films for Solar Cells

Demand for efficient window layer in thin film solar cells with high crystallinity is ever increasing that finds important application in multi-junction/tandem silicon solar cells. Doping of diborane (B2H6) in hydrogenated silicon films using plasma discharge decomposition of silane (SiH4) and (B2H6) gases were analyzed. The boron flow (FB) to silane ratio was varied from 0 to 0.30. Variation in film characteristics with B2H6 gas-phase ratio were analyzed, and concluded that doping boron induces crystallization in hydrogenated amorphous silicon (a-Si: H) film structure. The Raman and field emission scanning electron spectroscopy (FESEM) confirmed the boron induced crystallinity effect in silicon films at different diborane flow. The results showed that as boron content increases beyond certain ratio, silicon crystallization suppresses and the crystallite sizes were also reduced. From results, it was observed that crystallinity in FB = 0.05 is 79% and decreases to 77% when films are slightly higher doped (FB = 0.10) and further decreases when the films were heavily doped. These results validate that boron suppresses silicon crystallization due to local deformations caused by the impurities. Infra-red absorption studies and their analysis also confirm the crystallization in boron doped films with additional band appears at ~ 611 cm−1. This band is named as boron induced crystallinity mode of vibrational spectra. The estimated hydrogen content (CH) decreases confirmed crystallinity in the silicon structure with boron doping. Further, the energy dispersive spectroscopy (EDX) indicates the presence of boron and other impurities in deposited silicon films. The effect of boron on crystallinity and crystallite size as well as the mechanism were presented in detailed.

Flow-modulated deposition of sp2-boron nitride using diborane and ammonia on chemomechanically polished (0001) 4H-SiC substrates

Nanocrystalline sp2-BN thin films have been grown on (0001) 4H-SiC substrates at 1030 °C via continuous flow and discontinuous flow-modulated chemical vapor deposition techniques using diborane (B2H6) and ammonia (NH3) as the B and N sources, respectively. The latter technique enabled observations of both the effect of hydrogen purge steps between precursor injections and the length of injection times for B2H6 on the stoichiometry and microstructure of the films. Stoichiometric BN was achieved in all films grown continuously within the N/B gas phase ratio range of 20–200; this was not observed for the discontinuously grown films unless both the B2H6 flow rate and the injection time were minimized. Cross-sectional transmission electron microscopy of films grown both continuously and discontinuously at N/B = 200 and using short B2H6 injection times relative to that of NH3 for the latter process route revealed the initial growth of ∼4 nm thick partially ordered sp2-BN layers. A transition zone then formed containing randomly oriented polycrystalline grains. Excess B incorporated into the discontinuously grown films during long B2H6 injection times resulted in single layer mixtures of amorphous and sp2-BN without any observed ordering.

A FRACTAL MODEL FOR PREDICTING THE EFFECTIVE THERMAL CONDUCTIVITY OF ROUGHENED POROUS MEDIA WITH MICROSCALE EFFECT

The effective thermal conductivity (ETC) of roughened porous media (RPM) is of interest in a number of applications of heat transfer. In this work, a fractal analytical model for the ETC of RPM with microscale effect is proposed. The proposed fractal model is expressed in terms of relative roughness, the molecular mean free path, porosity, fractal dimensions (pore area fractal dimension and tortuosity fractal dimension), maximum pore diameter, capillary straight length, and the thermal conductivity of the solid matrix and gas. It is observed that the dimensionless ETC of RPM decreases with increasing relative roughness, pore area fractal dimension and tortuosity fractal dimension. Besides, it is found that the dimensionless ETC of RPM increases with thermal conductivity ratio of gas phase over solid phase. In addition, it is found that the dimensionless ETC of RPM is slightly dependent on the relative roughness and tortuosity fractal dimension when [Formula: see text]. The determined dimensionless ETC of RPM is in good agreement with experimental data and existing models reported in the literature. With the proposed fractal model, the physical mechanisms of heat transport through RPM with microscale effect are better elucidated. Every parameter in the fractal analytical model has clear physical meaning, with no empirical constant.

Etching of Si3N4 induced by electron beam plasma from hollow cathode plasma in a downstream reactive environment

An etching system based on the interaction of electrons extracted from a direct current hollow cathode (HC) Ar plasma and injected toward an Si3N4 covered silicon substrate located in the downstream reactive environment created by an additional remote CF4/O2 plasma source was developed and evaluated. By controlling the properties of the injected beam electrons, this approach allows to deliver energy to a surface functionalized by exposure to reactive species and initiate surface etching. The energy of the primary beam electrons is controlled by the acceleration voltage relative to the HC discharge. Ar atoms flow from the high-pressure HC discharge into the low pressure downstream reactive environment in the process chamber. For an acceleration voltage greater than the ionization potential of Ar and/or process gas species, the energetic primary beam electrons produce a secondary plasma in the process chamber and can also cause additional dissociation. The authors have characterized the properties of the secondary plasma and also surface etching of Si3N4 as a function of process parameters, including acceleration voltage (0–80 V), discharge current of the HC discharge (1–2 A), pressure (3.5–20 mTorr), source to substrate distance (1.5–5 cm), and feed gas composition (20% and 80% O2 in CF4/O2). The electron energy probability function measured with a Langmuir probe about 2.5 cm below the extraction ring suggests several major groups of electrons for this situation, including high energy primary beam electrons with an energy that varies as the acceleration voltage is changed and low-energy electrons produced by beam electron-induced ionization of the Ar gas in the process chamber. When a remote CF4/O2 plasma is additionally coupled to the process chamber, Si3N4 surfaces can be functionalized, and by varying the energy of the beam electrons, Si3N4 etching can be induced by electron-neutral synergy effect with plasma-surface interaction. For conditions without beam electron injection, the remote plasma etching rate of Si3N4 depends strongly on the O2 concentration in the CF4/O2 processing gas mixture and can be suppressed for O2-rich process conditions by the formation of an SiONF passivation layer on the Si3N4 surface. The combination of the HC electron beam (HCEB) source with the remote plasma source makes it possible to induce Si3N4 etching for O2-rich remote plasma conditions where remote plasma by itself produces negligible Si3N4 etching. The electron enhanced etching of Si3N4 depends strongly on the O2/CF4 mixing ratio reflecting changing arrival rates of O and F species at the surface. Optical emission spectroscopy was used to estimate the ratio of gas phase F and O densities and found to be controlled by the gas mixing ratio and independent of HCEB operating conditions. At this time, the detailed sequence of events operative in the etching mechanism is unclear. While the increase of the electron energy is ultimately responsible for initiating surface etching, presently, the authors cannot rule out a role of ions from the simultaneously produced secondary plasma in plasma-surface interaction mechanisms.

The design of two-stage gas and liquid cylindrical cyclone and numerical simulation of internal flow field characteristics

In underwater gas fields, the ratio of gas phase and liquid phase has become higher and higher. Focusing on the special condition above, the design of a new kind of two-stage gas and liquid cylindrical cyclone (GLCC) has been proposed which is different from the traditional one with rectangle inlet. The equivalent volume transforming method has been used in the design of size. Based on the research of the liquid drops breaking in swirl field, a new test method of GLCC diameter has been proposed, according to Navier-Stokes equations. For the structure of this cyclone separator, the optimised numerical simulation has been used to study the internal flow field, which adopts better turbulence models, meshing schemes and discrete formats after comparison. The effects of parameters such as H and Dc on the asymmetric characteristics and vortex-core boundary have also been obtained and analysed. [Received: February 12, 2018; Accepted: May 21, 2018]

The design of two-stage gas and liquid cylindrical cyclone and numerical simulation of internal flow field characteristics

In underwater gas fields, the ratio of gas phase and liquid phase has become higher and higher. Focusing on the special condition above, the design of a new kind of two-stage gas and liquid cylindrical cyclone (GLCC) has been proposed which is different from the traditional one with rectangle inlet. The equivalent volume transforming method has been used in the design of size. Based on the research of the liquid drops breaking in swirl field, a new test method of GLCC diameter has been proposed, according to Navier-Stokes equations. For the structure of this cyclone separator, the optimised numerical simulation has been used to study the internal flow field, which adopts better turbulence models, meshing schemes and discrete formats after comparison. The effects of parameters such as H and Dc on the asymmetric characteristics and vortex-core boundary have also been obtained and analysed. [Received: February 12, 2018; Accepted: May 21, 2018]

Untwinned semipolar (101̅3) AlxGa1-xN layers grown on m-plane sapphire

Heteroepitaxial growth of untwinned mono-crystalline semipolar (101̅3) Alx layers on (101̅3) AlN template was investigated by metalorganic vapour phase epitaxy. The templates were initially deposited on (101̅0) m-plane sapphire substrates by directional sputtering. Different Al/Ga ratios in gas phase were used to adjust the AlN mole fraction over the entire range of composition. All the layers show a triclinic distortion in the wurtzite unit cell due to anisotropic in-plane strain. The AlN mole fraction of the (101̅3) layers and c-plane co-loaded layers estimated by x-ray diffraction is comparable. This is consistent both with their comparable effective bandgap energy estimated from optical transmission measurements and their near band-edge emission energy obtained from room-temperature photoluminescence. The dependence of the bandgap and near band-edge emission energies on the AlN mole fraction indicates a bowing parameter of 0.9 eV.

Nanostructured boron doped diamond enhancing the photoelectrochemical performance of TiO2/BDD heterojunction anodes

Photoelectrochemical (PEC) water splitting provides a promising way for development of sustainable methods of hydrogen generation and water treatment without chemicals. In this paper, we report on the development of a unique PEC electrode consisting of nanostructured p-type boron doped diamond (BDD) layers covered by n-type TiO2 thin film. The influence of nanostructuring and boron doping level, as well as the thickness of TiO2 film on PEC properties, was investigated. As-grown and plasma-nanostructured BDD thin films with two doping levels (B/C = 1 000 ppm and 10 000 ppm in the gas phase) were utilized as substrates for deposition of 20, 100 and 500 nm TiO2 layers using RF magnetron sputtering. The highest photocurrent (60 μA/cm2 and 3.2 mA/cm2 at 0 and 2 V vs Ag/AgCl respectively) was obtained in the case of structured BDD electrode with B/C ratio in gas phase 1 000 ppm, covered by a 500 nm thick TiO2 layer. The experiment confirmed the favorable impact of both nanostructuring and p-n junction, contributing to the hole injection.

Atomization characteristics of aerosol spray from hair spray vessel with various design parameters

Aerosol sprays are used in many fields because they are easy to use and low in cost. Because flash-boiling has a great influence on atomization performance and spray characteristics such as droplet diameter and spray cone angle of aerosol spray, it is necessary to adjust the flash-boiling by changing the internal design of the aerosol vessel to obtain the desired atomization performance. Therefore, spray structure formed on the outside of nozzle during both transient and steady state. with various nozzle design and internal liquid/propellant composition ratio were observed in this study. The spray development process was visualized using a high-speed camera and Nd:Yag laser was used to form a laser sheet and it illuminates the internal structure of spray at steady state. In addition, the diameter and velocity of spray droplets were measured by PDPA equipment, which uses a noninvasive method. Selected design parameters were the number of stem orifice and the diameter of under-tap of the valve and vapor phase tap, and the mass fraction of propellant inside the aerosol vessel. As the diameter of the under tap increased, the ratio of the high-density area increased. However, as the difference between the area of the under-tap orifice and the total area of the stem orifice became smaller, the spray cross section area became larger and the shape of low-density region became closer to the concentric circle. In addition, finer droplets were generated in case with large stem orifice & smaller under-tap. The Vapor Phase Tap and propellant mass fraction have the greatest influence on the atomization characteristics of all design parameters because they change the gas phase ratio inside the jet. However, higher propellant mass fraction makes more uniform droplet diameter distribution than increased vapor phase tap diameter.

Nonpolar m-plane [formula omitted]N layers grown on m-plane sapphire by MOVPE

Heteroepitaxial growth of single-phase nonpolar (101¯0) m-plane AlxGa1-xN layers on m-plane sapphire substrates was investigated by metalorganic vapour phase epitaxy. Different Al/Ga gas phase ratios were used to adjust the AlN mole fraction over the entire range of composition. All m-plane AlGaN layers show an orthorhombic distortion in the wurtzite unit cell due to anisotropic in-plane strain. This distortion decreases with increasing AlN mole fraction due to a decreased anisotropic biaxial strain. The AlN mole fraction of m-plane layers and c-plane co-loaded layers estimated by X-ray diffraction is comparable. This is consistent with their comparable energy bandgaps, which were estimated from room-temperature dielectric functions. The dependence of the energy bandgap on composition indicates a bowing parameter of about 0.9 eV. The crystal-field splitting energy is found for the m-plane layers with a bowing parameter bcf of about −0.15 eV.

Numerical analysis of gas production from reservoir-scale methane hydrate by depressurization with a horizontal well: The effect of permeability anisotropy

Abstract Methane hydrate (MH) is regarded as one of the potential and substantial energy resources. The permeability of hydrate-bearing layer (HBL) can potentially influence heat and mass transfer during hydrate dissociation by depressurization. In this study, a reservoir-scale MH model was constructed to investigate the effect of permeability anisotropy on gas production behaviors by depressurization with a horizontal well. The numerical results indicate that permeability anisotropy can initially negatively influence the hydrate dissociation and gas production, but later promote the process. Meanwhile, permeability anisotropy can lead to an increase of ratio of gas phase to total production and gas-to-water ratio during long-term gas production. Moreover, permeability anisotropy can enhance the horizontal flow and the dissociation reaction in the top part of the HBL for a long period, but also leads to an increase of accumulated free gas in the reservoir. Furthermore, the comparison of horizontal well production and vertical well production indicates that the horizontal well can increase the gas production by one order of magnitude than that of vertical well during a production period of 360 days, and permeability anisotropy appears to have less effect on gas production in the initial short stage when using the vertical well.

Chemistry in disks

Context. Several sulfur-bearing molecules are observed in the interstellar medium and in comets, in strong contrast to protoplanetary disks where only CS, H2CS, and SO have been detected so far. Aims. We combine observations and chemical models to constrain the sulfur abundances and their sensitivity to physical and chemical conditions in the DM Tau protoplanetary disk. Methods. We obtained 0.5′′ Atacama Large Millimeter Array observations of DM Tau in Bands 4 and 6 in lines of CS, SO, SO2, OCS, CCS, H2CS, and H2S, achieving a ~5 mJy sensitivity. Using the non-Local Thermodynamical Equilibrium radiative transfer code RADEX and the forward-modeling tool DiskFit, disk-averaged CS column densities and upper limits for the other species were derived. Results. Only CS was detected with a derived column density of ~2−6 × 1012 cm−2. We report a first tentative detection of SO2 in DM Tau. The upper limits range between ~1011 and 1014 cm−2 for the other S-bearing species. The best-fit chemical model matching these values requires a gas-phase C/O ratio of ≳1 at r ≳ 50−100 au. With chemical modeling we demonstrate that sulfur-bearing species could be robust tracers of the gas-phase C/O ratio, surface reaction rates, grain size and UV intensities. Conclusions. The lack of detections of a variety of sulfur-bearing molecules in DM Tau other than CS implies a dearth of reactive sulfur in the gas phase, either through efficient freeze-out or because most of the elemental sulfur is in other large species, as found in comets. The inferred high CS/SO and CS/SO2 ratios require a non-solar C/O gas-phase ratio of ≳1, consistent with the recent observations of hydrocarbon rings in DM Tau. The stronger depletion of oxygen-bearing S-species compared to CS is likely linked to the low observed abundances of gaseous water in DM Tau and points to a removal mechanism of oxygen from the gas.

Untrapping Kinetically Trapped Ions: The Role of Water Vapor and Ion-Source Activation Conditions on the Gas-Phase Protomer Ratio of Benzocaine Revealed by Ion-Mobility Mass Spectrometry.

The role of water vapor in transforming the thermodynamically preferred species of protonated benzocaine to the less favored protomer was investigated using helium-plasma ionization (HePI) in conjunction with ion-mobility mass spectrometry (IM-MS). The IM arrival-time distribution (ATD) recorded from a neat benzocaine sample desorbed to the gas phase by a stream of dry nitrogen and ionized by HePI showed essentially one peak for the O-protonated species. However, when water vapor was introduced to the enclosed ion source, within a span of about 150 ms the ATD profile changed completely to one dominated by the N-protonated species. Under spray-based ionization conditions, the nature and composition of the solvents have been postulated to play a decisive role in defining the manifested protomer ratios. In reality, the solvent vapors present in the ion source (particularly the ambient humidity) indirectly dictate the gas-phase ratio of the protomers. Evidently, the gas-phase protomer ratio established at the confinement of the ions is readjusted by the ion-activation that takes place during the transmission of ions to the vacuum. Although it has been repeatedly stated that ions can retain a "memory" of their solution structures because they can be kinetically trapped, and thereby represent their solution-based stabilities, we show that the initial airborne ions can undergo significant transformations in the transit through the intermediate vacuum zones between the ion source and the mass detector. In this context, we demonstrate that the kinetically trapped N-protomer of benzocaine can be untrapped by reducing the humidity of the enclosed ion source. Graphical Abstract ᅟ.

Effect of Stoichiometry on the Lifetime and Doping Concentration of Polycrystalline CdTe

The effect of gas phase Cd/Te deposition ratio on the minority carrier lifetime and doping concentration of polycrystalline cadmium telluride (CdTe) was investigated. CdTe thin films were deposited by the elemental vapor transport (EVT) with various Cd/Te gas phase ratios. The films were fabricated into solar cells, and characterized by current–voltage ( JV ) and spectral response measurements. The minority carrier lifetime was measured using time-resolved photoluminescence measurements. Capacitance–voltage ( CV ) measurements indicated a change in doping concentration as a function of gas phase Cd/Te ratio. Films deposited under Te-rich deposition conditions exhibited superior electrical characteristics. Minority carrier lifetimes up to 7 ns and doping concentrations on the order of 1015 cm–3 were measured for CdCl2 heat-treated Te-rich deposited films. The addition of controlled amounts of Cu increased the doping concentration up to 1016 cm–3, however lowered the carrier lifetimes to less than 1 ns. EVT deposited CdTe solar cells exhibited $V_{{\rm{OC}}}$ of 800 mV without Cu and up to 850 mV with Cu doping.

Heterogeneous uptake of ammonia and dimethylamine into sulfuric and oxalic acid particles

Abstract. Heterogeneous uptake is one of the major mechanisms governing the amounts of short-chain alkylamines and ammonia (NH3) in atmospheric particles. Molar ratios of aminium to ammonium ions detected in ambient aerosols often exceed typical gas phase ratios. The present study investigated the simultaneous uptake of dimethylamine (DMA) and NH3 into sulfuric and oxalic acid particles at gaseous DMA ∕ NH3 molar ratios of 0.1 and 0.5 at 10, 50 and 70 % relative humidity (RH). Single-gas uptake and co-uptake were conducted under identical conditions and compared. Results show that the particulate dimethyl-aminium/ammonium molar ratios (DMAH ∕ NH4) changed substantially during the uptake process, which was severely influenced by the extent of neutralisation and the particle phase state. In general, DMA uptake and NH3 uptake into concentrated H2SO4 droplets were initially similarly efficient, yielding DMAH ∕ NH4 ratios that were similar to DMA ∕ NH3 ratios. As the co-uptake continued, the DMAH ∕ NH4 gradually dropped due to a preferential uptake of NH3 into partially neutralised acidic droplets. At 50 % RH, once the sulfate droplets were neutralised, the stronger base DMA displaced some of the ammonium absorbed earlier, leading to DMAH ∕ NH4 ratios up to four times higher than the corresponding gas phase ratios. However, at 10 % RH, crystallisation of partially neutralised sulfate particles prevented further DMA uptake, while NH3 uptake continued and displaced DMAH+, forming almost pure ammonium sulfate. Displacement of DMAH+ by NH3 has also been observed in neutralised, solid oxalate particles. The results can explain why DMAH ∕ NH4 ratios in ambient liquid aerosols can be larger than DMA ∕ NH3, despite an excess of NH3 in the gas phase. An uptake of DMA to aerosols consisting of crystalline ammonium salts, however, is unlikely, even at comparable DMA and NH3 gas phase concentrations.

Metalorganic chemical vapor deposition-regrown Ga-rich InGaP films on SiGe virtual substrates for Si-based III-V optoelectronic device applications

Ga-rich InGaP materials are attractive applications for yellow-green spectral range optoelectronics such as light-emitting diodes and solar cells on silicon substrate. Bulk, Ga-rich InGaP films grown by metalorganic chemical vapor deposition on SiGe virtual substrates were investigated in the V/III compositional ratio range of 44.3–402 using chamber pressures from 100 to 200 mbar. These films were nominally lattice matched to the SiGe virtual substrate with a bandgap energy of 2.07–2.09 eV at low temperature (10 K). The authors show that the surface morphology of the Ga-rich InGaP films was dependent on the growth conditions, including the V/III gas phase ratio, pressure, and growth rate. By optimizing the growth conditions, the authors achieved improved surface morphologies of the Ga-rich InGaP films. The hillock density of the films produced using a V/III gas phase ratio of 44.3 and 75.4, a growth pressure of 100 mbar, and a growth rate of 0.9 μm/h was about an order of magnitude lower (30.3–50 × 104 cm−2) than that observed using higher V/III gas phase ratios such as 201 and 402. An increase in luminescence efficiency of Ga-rich InGaP materials was observed when the hillock density is lower. The authors discuss the mechanisms of the hillock formation.