Low-pressure Reactor Research Articles

Growth of 3C–SiC on 150-mm Si(100) substrates by alternating supply epitaxy at 1000 °C

To lower deposition temperature and reduce thermal mismatch induced stress, heteroepitaxial growth of single-crystalline 3C–SiC on 150 mm Si wafers was investigated at 1000 °C using alternating supply epitaxy. The growth was performed in a hot-wall low-pressure chemical vapor deposition reactor, with silane and acetylene being employed as precursors. To avoid contamination of Si substrate, the reactor was filled in with oxygen to grow silicon dioxide, and then this thin oxide layer was etched away by silane, followed by a carbonization step performed at 750 °C before the temperature was ramped up to 1000 °C to start the growth of SiC. Microstructure analyses demonstrated that single-crystalline 3C–SiC is epitaxially grown on Si substrate and the film quality is improved as thickness increases. The growth rate varied from 0.44 to 0.76 ± 0.02 nm/cycle by adjusting the supply volume of SiH 4 and C 2H 2. The thickness nonuniformity across wafer was controlled with ± 1%. For a prime grade 150 mm virgin Si(100) wafer, the bow increased from 2.1 to 3.1 μm after 960 nm SiC film was deposited. The SiC films are naturally n type conductivity as characterized by the hot-probe technique.

Heterogeneous Reactions of Alkylamines with Ammonium Sulfate and Ammonium Bisulfate

The heterogeneous reactions between alkylamines and ammonium salts (ammonium sulfate and ammonium bisulfate) have been studied using a low-pressure fast flow reactor coupled to an ion drift-chemical ionization mass spectrometer (ID-CIMS) at 293 ± 2 K. The uptake of three alkylamines, i.e., monomethylamine, dimethylamine, and trimethylamine, on ammonium sulfate shows a displacement reaction of ammonium by aminium, evidenced by the release of ammonia monitored using protonated acetone dimer as the reagent ion. For the three alkylamines, the initial uptake coefficients (γ(0)) range from 2.6 × 10(-2) to 3.4 × 10(-2) and the steady-state uptake coefficients (γ(ss)) range from 6.0 × 10(-3) to 2.3 × 10(-4) and decrease as the number of methyl groups on the alkylamine increases. A different reaction mechanism is observed for the uptake of the three alkylamines on ammonium bisulfate, which is featured by an acid-base reaction (neutralization) with irreversible alkylamine loss and no ammonia generation and occurs at a rate limited by diffusion of gaseous alkylamines to the ammonium bisulfate surface. Our results reveal that the reactions between alkylamines and ammonium salts contribute to particle growth and alter the composition of ammonium sulfate and bisulfate aerosols in the atmosphere.

Surface modification by glow discharge gasplasma treatment improves vascularization of allogenic bone implants

Sufficient induction of blood vessel ingrowth decisively influence transplant functionality. In this study, microvascular response to transplants of surface modified bone substitutes were assessed in vivo. The surface modification of allogenic bone substitutes (dehydrated human femoral head) was achieved in a double-conductive low-pressure gasplasma reactor (Ar(2) /O(2) , 13.65 MHz, 1,000 W, 5 Pa). The modified bone substitutes (n = 10) as well as untreated bone substitutes serving as controls (n = 10) were placed into the dorsal skinfold chamber of female balb/c mice (n = 10). Dynamic assessment of microcirculatory parameters was performed using intravital fluorescence microscopy during an implantation period of 10 days. The angiogenic response was found markedly accelerated in gasplasma-treated bone. Compared to untreated implants, the gasplasma-activated bone substitutes showed significantly higher microvascular density on days 5 and 10. The quantification of the microvascular diameters, red blood cell velocity, and microvascular permeability displayed stable perfusion and vascular integrity of the newly developed blood vessels throughout the 10-day observation period. The surface activation via cold low-pressure glow discharge gasplasma supports the vascular integration of allogenic bone by earlier induction of the angiogenesis.

Modelling of NO destruction in a low-pressure reactor by an Ar plasma jet: species abundances in the reactor

The destruction of NO molecules by an Ar plasma jet in a low-pressure (0.2 Torr) reactor is investigated by means of a 3D hydrodynamic model. The density distribution of species created through molecular kinetics triggered by the collision of Ar+ with NO is calculated, showing that in the case of the most abundant species a quasi-homogeneous density distribution builds up in a large part of the reactor. The conversion of NO into stable O2 and N2 molecules is followed under different plasma jet conditions and NO gas flows, and the effect of N2 addition on NO destruction is studied. It is shown that in the present system the reproduction of NO molecules on the surface through surface-assisted recombination of N and O atoms becomes impossible due to the fast disappearance of N atoms in the jet's inlet vicinity.

Dependence of chemical composition and bonding of amorphous SiC on deposition temperature and the choice of substrate

Amorphous SiC has superior mechanical, chemical, electrical, and optical properties which are process dependent. In this study, the impact of deposition temperature and substrate choice on the chemical composition and bonding of deposited amorphous SiC is investigated, both 6 in. single-crystalline Si and oxide covered Si wafers were used as substrates. The deposition was performed in a standard low-pressure chemical vapour deposition reactor, methylsilane was used as the single precursor, and deposition temperature was set at 600 and 650 °C. XPS analyses were employed to investigate the chemical composition, Si/C ratio, and chemical bonding of deposited amorphous SiC. The results demonstrate that these properties varied with deposition temperature, and the impact of substrate on them became minor when deposition temperature was raised up from 600 °C to 650 °C. Nearly stoichiometric amorphous SiC with higher impurity concentration was deposited on crystalline Si substrate at 600 °C. Slightly carbon rich amorphous SiC films with much lower impurity concentration were prepared at 650 °C on both kinds of substrates. Tetrahedral Si–C bonds were found to be the dominant bonds in all deposited amorphous SiC. No contribution from Si–H/Si–Si but from sp 2 and sp 3 C–C/C–H bonds was identified.

Temperature‐dependent rate coefficients and mechanism for the gas‐phase reaction of chlorine atoms with acetone

AbstractThe rate coefficient for the gas‐phase reaction of chlorine atoms with acetone was determined as a function of temperature (273–363 K) and pressure (0.002–700 Torr) using complementary absolute and relative rate methods. Absolute rate measurements were performed at the low‐pressure regime (∼2 mTorr), employing the very low pressure reactor coupled with quadrupole mass spectrometry (VLPR/QMS) technique. The absolute rate coefficient was given by the Arrhenius expression k(T) = (1.68 ± 0.27) × 10−11 exp[−(608 ± 16)/T] cm3 molecule−1 s−1 and k(298 K) = (2.17 ± 0.19) × 10−12 cm3 molecule−1 s−1. The quoted uncertainties are the 2σ (95% level of confidence), including estimated systematic uncertainties. The hydrogen abstraction pathway leading to HCl was the predominant pathway, whereas the reaction channel of acetyl chloride formation (CH3C(O)Cl) was determined to be less than 0.1%. In addition, relative rate measurements were performed by employing a static thermostated photochemical reactor coupled with FTIR spectroscopy (TPCR/FTIR) technique. The reactions of Cl atoms with CHF2CH2OH (3) and ClCH2CH2Cl (4) were used as reference reactions with k3(T) = (2.61 ± 0.49) × 10−11 exp[−(662 ± 60)/T] and k4(T) = (4.93 ± 0.96) × 10−11 exp[−(1087 ± 68)/T] cm3 molecule−1 s−1, respectively. The relative rate coefficients were independent of pressure over the range 30–700 Torr, and the temperature dependence was given by the expression k(T) = (3.43 ± 0.75) × 10−11 exp[−(830 ± 68)/T] cm3 molecule−1 s−1 and k(298 K) = (2.18 ± 0.03) × 10−12 cm3 molecule−1 s−1. The quoted errors limits (2σ) are at the 95% level of confidence and do not include systematic uncertainties. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 724–734, 2010

Multifractal Spectra of INGaN/GaN Self-Assembled Quantum Dots Films

The surface shape and microstructure of semiconductor thin films, especially nanometer thin films, have important influence to construct physical characteristics, such as electricity, magnetic, and optics nature to the thin films. In this work, we use the multifractal spectra to study the surface morphology of InGaN/GaN self-assembled quantum dot films after the annealed process. Samples used in this study were grown on the (0001)-oriented sapphire (Al2O3) substrates in a vertical low-pressure metal-organic chemical vapor deposition reactor with a high-speed rotation disk. The fractal dimension and multifractal spectra can be used to describe the influence of different annealed conditions on surface characterization. Fractal analysis reveals that both the average surface roughness and root-mean-square roughness of nanostructure surfaces are decreased after the thermal annealing process. It can be seen that a smoother surface was obtained under an annealing temperature at 800°C, and it implies that the surface roughness of this case is minimum in all tests. The results of this paper also described a mathematical modeling method for the observation of the fractal and multifractal characteristics in a semiconductor nanostructure films.

Heterogeneous Reaction of NO2 on Fresh and Coated Soot Surfaces

The heterogeneous reaction of nitrogen dioxide (NO(2)) on fresh and coated soot surfaces has been investigated to assess its role in night-time formation of nitrous acid (HONO) in the atmosphere. Soot surfaces were prepared by incomplete combustion of propane and kerosene fuels under lean and rich flame conditions and then processed by heating to evaporate semivolatile species or by coating with pyrene, sulfuric acid, or glutaric acid. Uptake kinetics and HONO yield measurements were performed in a low-pressure fast-flow reactor coupled to a chemical ionization mass spectrometer (CIMS), using atmospheric-level NO(2) concentrations. The uptake coefficient and the HONO yield upon interaction of NO(2) with nascent soot depend on the type of fuel and combustion regime and are the highest for samples prepared using fuel rich flame. Heating the nascent soot samples before exposure to NO(2) removes the organic material from the soot backbone, leading to a significant increase in NO(2) uptake coefficient and HONO yield. Continuous exposure to NO(2) reduces the reactivity of soot because of irreversible deactivation of the surface sites. Our results support the oxidation-reduction mechanism involving adsorptive and reactive centers on soot surface where NO(2) is converted to HONO and other products. Coating of the soot surface by different materials to simulate atmospheric aging has a strong impact on its reactivity toward NO(2) and the resulting HONO production. Coating of pyrene has little effect on either reaction rate or HONO yield. Sulfuric acid coating does not alter the uptake coefficient, but significantly reduces the amount of HONO formed. Coating of glutaric acid significantly increases NO(2) uptake coefficient and HONO yield. The results of our study indicate that the reactivity and HONO generating capacity of internally mixed soot aerosol will depend on the chemical composition of the coating material and hence will vary considerably in different polluted environments.

Heterogeneous Chemistry of Alkylamines with Sulfuric Acid: Implications for Atmospheric Formation of Alkylaminium Sulfates

The heterogeneous interaction of alkylamines with sulfuric acid has been investigated to assess the role of amines in aerosol growth through the formation of alkylaminium sulfates. The kinetic experiments were conducted in a low-pressure fast flow reactor coupled to an ion drift-chemical ionization mass spectrometer (ID-CIMS). The measurements of heterogeneous uptake of methylamine, dimethylamine, and trimethylamine were performed in the acidity range of 59-82 wt % H(2)SO(4) and between 243 and 283 K. Irreversible reactive uptakes were observed for all three alkylamines, with comparable uptake coefficients (gamma) in the range of 2.0 x 10(-2) to 4.4 x 10(-2). The measured gamma value was slightly higher in more concentrated sulfuric acid and at lower temperatures. The results imply that the heterogeneous reactions of alkylamines contribute effectively to the growth of atmospheric acidic particles and, hence, secondary organic aerosol formation.

Composition of a plasma generated from N2–O2 by an Ar ion jet in a low pressure reactor

The expansion of a supersonic Ar+ ion jet in a low pressure (0.2 Torr) reactor filled with N2 and O2 has been investigated by means of hydrodynamic modelling. The gas velocity fields and the gas temperature distribution in the three-dimensional reactor have been determined. The formation of different species through the molecular kinetics triggered by the collision of Ar+ ions with N2 and O2 molecules has been studied. We have investigated the effect of the ions velocity and molecular gas flow rates on the gas temperature and species density distributions. We have shown that the main difference between this system and an N2–O2 post-discharge lies in the dissociation degrees of N2 and O2. While in an N2–O2 post-discharge the N2 dissociation degree is low and that of O2 is high, in the present system this can be varied through the gas flow rate of the molecular gases. We have also shown that the NO(X) molecules formation is governed by the surface processes, which is strongly influenced by the state of the surface.

Low pressure–temperature–gas flow HVPE growth of GaP for nonlinear optical frequency conversion devices

This paper describes advances in the development of quasi-phase-matched (QPM) gallium phosphide (GaP) crystals for agile laser sources in the mid-infrared regions between 3–5 and 8–12 μm. In the quest for a nonlinear optical material with the potential to efficiently convert near infrared energy (wavelength ∼1 μm) to a powerful mid-infrared source, we have investigated the growth of GaP by hydride vapor phase epitaxy (HVPE). The process is shown to produce high quality thick layers at rapid growth rates in a low-pressure horizontal reactor. This process was used to grow thick layers on orientation-patterned (OP) templates. The OP-GaP templates were fabricated by lithographic patterning of inverted wafer-fused GaP. HVPE growth on both OP-GaP and OP-GaAs templates was performed, showing that HVPE can successfully replicate the initial template pattern. However, for longer growth duration at given conditions the patterned structure can be lost, with annihilation of every other domain.

Desorption of Polycyclic Aromatic Hydrocarbons from a Soot Surface: Three- to Five-Ring PAHs

The kinetics of the thermal desorption of a set of three- to five-ring polycyclic aromatic hydrocarbons (PAHs) from a laboratory-generated kerosene soot surface was studied over the temperature range 250-355 K in a low-pressure flow reactor combined with an electron-impact mass spectrometer. Two methods were used to measure the desorption rate constants: monitoring of the surface-bound PAH decays due to desorption using off-line HPLC measurements of their concentrations in soot samples and monitoring of the desorbed molecules (anthracene and phenanthtrene) in the gas phase using in situ mass spectrometric detection. The Arrhenius parameters (A factors and activation energies) for the desorption rate constants of 10 soot-bound PAHs were determined. The PAH-soot binding energies were found to be similar for PAHs with the same number of carbon atoms and to increase with increasing number of PAH carbon atoms. The experimental data are discussed in the frame of the existing theoretical gas to particle partitioning model.

Analytic model of nanoparticle formation and growth in a SiH4-Ar plasma

A kinetic model of formation and growth of nanoparticles in a low-pressure plasma-chemical reactor with an rf capacitive discharge in a SiH4-Ar mixture is presented. Analytic formulas are derived for calculating the concentration of monomers, as well as the concentration and average size of nanoparticles. The results are compared with the results of numerical calculations and experimental data for nanoparticles in a SiH4-Ar plasma.

Rate constants and the H atom branching ratio of the reactions of the methylidyne CH(X2Π) radical with C2H2, C2H4, C3H4(methylacetylene and allene), C3H6(propene) and C4H8(trans-butene)

The reactions of the CH radical with several unsaturated hydrocarbons C2H2 (acetylene), C2H4 (ethylene), C3H4 (methyl-acetylene and allene), C3H6 (propene) and C4H8 (trans-butene) were studied at room temperature, in a low-pressure fast-flow reactor. CH(X2pi, v = 0) radicals were obtained from the reaction of CHBr3 with potassium atoms. The overall rate constants at 300 K are CH + C2H2: (3.6 +/- 0.6) x 10(-10), CH + C2H4: (3.1 +/- 0.6) x 10(-10), CH + C3H4 (methyl-acetylene): (3.4 +/- 0.6) x 10(-10), CH + C3H4 (allene): (3.6 +/- 0.6) x 10(-10), CH + C3H6 (propene): (4.2 +/- 0.8) x 10(-10) and CH + C4H8 (trans-butene): (4.0 +/- 0.80) x 10(-10) cm3 molecule(-1) s(-1) (errors are cited at the level of +/- 1 sigma). Absolute atomic hydrogen production was determined by vacuum ultra-violet (VUV) resonance fluorescence, H production from the CH + CH4 reaction being used as a reference. Observed H branching ratios for these CH reactions were: C2H2: 0.90 +/- 0.08, C2H4: 0.94 +/- 0.08, C3H4 (methyl-acetylene): 0.98 +/- 0.08, C3H4 (allene): 0.97 +/- 0.08, C3H6 (propene): 0.78 +/- 0.10, C4H8 (trans-butene): 0.69 +/- 0.12 (errors are cited at the level of +/- 1 sigma). A compilation of the available kinetic data on these reactions has been made in order to propose rate coefficients for each possible channel of the different reactions for astrochemical models.

Desorption of Polycyclic Aromatic Hydrocarbons from Soot Surface: Pyrene and Fluoranthene

The kinetics of thermal desorption of two four-ring polycyclic aromatic hydrocarbons, fluoranthene, and pyrene from well-characterized laboratory-generated kerosene soot surface was studied over the temperature range 260-320 K in a low-pressure flow reactor combined with an electron-impact mass spectrometer. Two methods were used to measure the desorption rate constants: monitoring of the surface-bound fluoranthene and pyrene decays due to desorption using off-line HPLC measurements of their concentrations in soot samples, and monitoring of the desorbed molecules in the gas phase using in situ mass spectrometric detection. Results obtained with the two methods were in good agreement and yielded the following Arrhenius expressions for the desorption rate constants: k(des) (fluoranthene) = 4 x 10(14) exp[-(93900 +/- 1700)/RT] and k(des) (pyrene) = 6 x 10(14) exp[-(95200 +/- 1800)/RT] (k(des) are in units of s(-1), and activation energies are in J mol(-1)). In addition, the combined uptake coefficient of fluoranthene and pyrene on soot (calculated using specific surface area) was estimated to be near 5 x 10(-3) at T = 310 K.

Low-Pressure Microwave Plasma Sterilization of Polyethylene Terephthalate Bottles

A low-pressure microwave plasma reactor was developed for sterilization of polyethylene terephthalate (PET) bottles. In contrast to the established method using aseptic filling machines based on toxic sterilants, here a microwave plasma is ignited inside a bottle by using a gas mixture of nitrogen, oxygen, and hydrogen. To that effect, a reactor setup was developed based on a Plasmaline antenna allowing for plasma ignition inside three-dimensional packages. A treatment time below 5 s is provided for a reduction of 105 and 104 CFU of Bacillus atrophaeus and Aspergillus niger, respectively, verified by means of a count reduction test. The sterilization results obtained by means of this challenge test are in accordance with requirements for aseptic packaging machines as defined by the U.S. Food and Drug Administration and the German Engineering Federation. The plasma sterilization process developed here for aseptic filling of beverages is a dry process that avoids residues and the use of maximum allowable concentrations of established sterilants, e.g., hydrogen peroxide.

Low-Pressure Metallorganic Chemical Vapor Deposition of Fe2O3 Thin Films on Si(100) Using n-Butylferrocene and Oxygen

thin films have been deposited on Si(100) substrates using n-butylferrocene and oxygen in a low-pressure metallorganic chemical vapor deposition reactor. The iron precursor is liquid at room temperature having a high enough vapor pressure; its thermogravimetric analysis shows that it undergoes clean evaporation without decomposition. The growth rates were studied in the temperature range of . The resulting thin films were characterized for structure and morphology using X-ray diffraction and scanning electron microscopy. Their composition was analyzed using energy-dispersive X-ray spectroscopy, and chemical bonding states were probed using X-ray photoelectron spectroscopy. Films deposited at were mostly noncrystalline and had carbon contamination. Films deposited at higher temperatures were crystalline .

Evaporative cooling of binary drops in a low-pressure flow reactor

A mathematical model of the evaporative cooling of binary drops in a flow reactor, accounting for the latent-heat liberation as a result of the phase transformation of the binary-drop components in the process of their condensation, the inverse processes of evaporation of these components, and the latent-heat liberation in the process of dissolution of one of the binary-drop components, has been developed. The numerical calculations were carried out for diluted ammonia spirits. It is shown that the evaporative cooling of binary drops in a flow reactor can be controlled by varying the compositions of the gas mixture and the solution and the ratio between their flow rates, and that the rate of cooling of drops can reach 2·105 K/sec.

Absolute Rate Coefficient Determination and Reaction Mechanism Investigation for the Reaction of Cl Atoms with CH2I2 and the Oxidation Mechanism of CH2I Radicals

The gas-phase reaction of atomic chlorine with diiodomethane was studied over the temperature range 273-363 K with the very low-pressure reactor (VLPR) technique. The reaction takes place in a Knudsen reactor at pressures below 3 mTorr, where the steady-state concentration of both reactants and stable products is continuously measured by electron-impact mass spectrometry. The absolute rate coefficient as a function of temperature was given by k = (4.70 +/- 0.65) x 10-11 exp[-(241 +/- 33)/T] cm3molecule-1s-1, in the low-pressure regime. The quoted uncertainties are given at a 95% level of confidence (2sigma) and include systematic errors. The reaction occurs via two pathways: the abstraction of a hydrogen atom leading to HCl and the abstraction of an iodine atom leading to ICl. The HCl yield was measured to be ca. 55 +/- 10%. The results suggest that the reaction proceeds via the intermediate CH2I2-Cl adduct formation, with a I-Cl bond strength of 51.9 +/- 15 kJ mol-1, calculated at the B3P86/aug-cc-pVTZ-PP level of theory. Furthermore, the oxidation reactions of CHI2 and CH2I radicals were studied by introducing an excess of molecular oxygen in the Knudsen reactor. HCHO and HCOOH were the primary oxidation products indicating that the reactions with O2 proceed via the intermediate peroxy radical formation and the subsequent elimination of either IO radical or I atom. HCHO and HCOOH were also detected by FT-IR, as the reaction products of photolytically generated CH2I radicals with O2 in a static cell, which supports the proposed oxidation mechanism. Since the photolysis of CH2I2 is about 3 orders of magnitude faster than its reactive loss by Cl atoms, the title reaction does not constitute an important tropospheric sink for CH2I2.

Core and grain boundary sensitivity of tungsten-oxide sensor devices by molecular beam assisted particle deposition

In this study, we investigate the synthesis of WO3 and WOx (2.6≥x≤2.8) by adding different concentrations of tungsten hexafluoride (WF6) into a H2/O2/Ar premixed flame within a low-pressure reactor equipped with a particle-mass spectrometer (PMS). The PMS results show that mean particle diameters dp between 5 and 9 nm of the as-synthesized metal-oxides can be obtained by varying the residence time and precursor concentration in the reactor. This result is further validated by N2 adsorption measurements on the particle surface, which yielded a 91 m2/g surface area, corresponding to a spherical particle diameter of 9 nm (Brunauer-Emmett-Teller technique). H2/O2 ratios of 1.6 and 0.63 are selected to influence the stoichiometry of the powders, resulting in blue-colored WOx and white WO3 respectively. X-ray diffraction (XRD) analysis of the as-synthesized materials indicates that the powders are mostly amorphous, and the observed broad reflexes can be attributed to the orthorhombic structure of β-WO3. Thermal annealing at 973 K for 3 h in air resulted in crystalline WO3 comprised of both monoclinic and orthorhombic phases. The transmission electron microscope micrograph analysis shows that the particles exhibit spherical morphology with some degree of agglomeration. Impedance spectroscopy is used for the electrical characterization of tungsten-oxide thin films with a thickness of 50 nm. Furthermore, the temperature-dependent gas-sensing properties of the material deposited on interdigital capacitors are investigated. Sensitivity experiments reveal two contributions to the overall sensitivity, which result from the surface and the core of each particle.