Gas-phase Nucleation Research Articles

Nanophase and nanostructure of tungsten carbide: The electrical explosion of a wire in a solid matrix of naphthalene and carbon nanotube

Tungsten carbides are important materials used in ceramic cements, machining tools, catalysts, sensors, and for hydrogen generation. Bulk W–C structures are highly complex; fundamental fully carburized WC and semi-carburized W2C are accompanied by structural transitions depending on the composition and temperature. The relationship between the structures, compositions, and temperatures is summarized in the W–C phase diagram. However, the high-temperature, stable, and single-crystalline nanoparticles related to the WC1-x and W2C phases formed via energetic reactions accompanied by rapid cooling rates are not easy to determine considering the bulk phase diagram, and lead to fundamental questions regarding the origin of the nanophases. In this study, we propose a draft for the W–C nanophase diagram composed of the surface and gas-phase WC, WC1-x, and W2C nanophases according to the composition and temperature. The model undergoes the process of a vapor–nanoliquid–nanophase starting from the gas-phase nucleation induced by an extremely high-temperature electrical explosion. In addition, the high-temperature reactivity and quenched nanophase, including its unique nanostructure, are related to the post-melt rheology, physical morphology, and steric hindrance of the solid matrix during an electrical explosion.

Assessment of Anharmonicities in Clusters: Developing and Validating a Minimum-Information Partition Function.

Precise thermodynamic calculations are essential for understanding the dynamics of cluster systems and new particle formation. However, the widely employed harmonic statistical mechanical approach often falls short in terms of accuracy. In this study, we present an improved statistical model that incorporates vibrational anharmonicity via a novel partition function that requires only one additional system-specific input parameter. In addition to considering vibrational aspects, we also account for anharmonicity related to the configurational space. The role of anharmonicities is thoroughly examined in the case of general clusters, where the complete sets of conformers, mechanically stable spatial arrangements, are known up to clusters composed of 14 monomers. By performing consistent Monte Carlo simulations on these systems, we benchmark the statistical model's efficacy in reproducing key thermodynamic properties (formation free energy and potential energy) in the classical limit. The model exhibits exceptional alignment with simulations, accurately reproducing free energies within a precision of 2kBT and reliably capturing cluster melting temperatures. Furthermore, we demonstrate the significance and applicability of the model by reproducing thermodynamic barriers in homogeneous gas-phase nucleation of larger clusters. The transferability of our developed approach extends to more complex molecular systems and bears relevance for atmospheric multicomponent clusters, in particular.

Understanding the Formation and Growth of New Atmospheric Particles at the Molecular Level through Laboratory Molecular Beam Experiments.

Atmospheric new particle formation (NPF), which exerts comprehensive implications for climate, air quality and human health, has received extensive attention. From molecule to cluster is the initial and most important stage of the nucleation process of atmospheric new particles. However, due to the complexity of the nucleation process and limitations of experimental characterization techniques, there is still a great uncertainty in understanding the nucleation mechanism at the molecular level. Laboratory-based molecular beam methods can experimentally implement the generation and growth of typical atmospheric gas-phase nucleation precursors to nanoscale clusters, characterize the key physical and chemical properties of clusters such as structure and composition, and obtain a series of their physicochemical parameters, including association rate coefficients, electron binding energy, pickup cross section and pickup probability and so on. These parameters can quantitatively illustrate the physicochemical properties of the cluster, and evaluate the effect of different gas phase nucleation precursors on the formation and growth of atmospheric new particles. We review the present literatures on atmospheric cluster formation and reaction employing the experimental method of laboratory molecular beam. The experimental apparatuses were classified and summarized from three aspects of cluster generation, growth and detection processes. Focus of this review is on the properties of nucleation clusters involving different precursor molecules of water, sulfuric acid, nitric acid and NxOy, respectively. We hope this review will provide a deep insight for effects of cluster physicochemical properties on nucleation, and reveal the formation and growth mechanism of atmospheric new particle at the molecular level.

Evidence of gas phase nucleation of nanodiamond in microwave plasma assisted chemical vapor deposition

The mechanism of ballas-like nanodiamond formation still remains elusive, and this work attempts to analyze its formation in the framework of activation energy (Ea) of nanodiamond films grown from a H2/CH4 plasma in a 2.45 GHz chemical vapor deposition system. The Ea was calculated from the Arrhenius equation corresponding to the thickness growth rate using substrate temperature (∼1000−1300 K) in all the calculations. While the calculated values matched with the Ea for nanodiamond formation throughout the literature, these values of ∼10 kcal/mol were lower compared to ∼15–25 kcal/mol for standard single crystal diamond (SCD) formation, concluding thus far that the energetics and processes involved were different. Further, the substrate preparation and sample collection method were modified while keeping the growth parameters constant. Unseeded Si substrate was physically separated from the plasma discharge by a molybdenum disk with a pinhole drilled in it. Small quantity of a sample substance was collected on the substrate. The sample was characterized by electron microscopy and Raman spectroscopy, confirming it to be nanodiamond, thus suggesting that nanodiamond self-nucleated in the plasma and flowed to the substrate that acted as a mere collection plate. It is hypothesized then, if nanodiamond nucleates in gas phase, gas temperature has to be used in the Arrhenius analysis. The Ea values for all the nanodiamond films were re-calculated using the simulated gas temperature (∼1500−2000 K) obtained from a simple H2/CH4 plasma model, giving new values within the range characteristic to SCD formation. Based on these findings, a unified growth mechanism for nanodiamond and SCD is proposed, concluding that the rate-limiting reactions for nanodiamond and SCD formation are the same.

Mechanistic insights into Criegee intermediates with benzoic acid at gas-phase and air-water interface and nucleation of product

Since the detection of Criegee intermediates (CIs) in the gas phase, there has been a growing recognition of the important role of CIs in atmospheric oxidation. Further mechanistic investigations are required to fully elucidate the bimolecular reactions of CIs with atmospheric species, such as OH, RO2/HO2, and carbonyl compounds. This article primarily focused on the reactions of benzoic acid (BA) with syn- and anti- CH3CHOO (C2 CI) in both gas-phase and gas-liquid interface using density functional theory (DFT) and Born-Oppenheimer molecular dynamics (BOMD). The results reveal that the reactions of BA and anti-CH3CHOO represent the principal pathway in the gaseous phase, whereas the water-involved reactions exhibit higher energy barriers, rendering them less favorable for occurrence. At the air-water interface, the reactions of BA and C2 CI as well as the BA-catalyzed hydration take place on the picosecond scale, conforming to the stepwise mechanism. The direct reaction between BA and anti- CH3CHOO remains the main sink for C2 CI at the gas-liquid interface. Molecular dynamics (MD) simulations were employed to investigate the nucleation capabilities of the reaction products and to examine the influence of temperature and water molecules on the nucleation process. The product molecules of BA and C2 CI can form stable clusters with sulfuric acid, ammonia molecules, and water molecules within 30 ns? The nucleation ability tends to decrease with the elevation of temperature, and the presence of water molecules promotes the new particles formation (NPF). Therefore, BA and its products with CIs affect the budget of secondary organic aerosols (SOAs).

Degradable Plasma-Polymerized Poly(Ethylene Glycol)-Like Coating as a Matrix for Food-Packaging Applications.

Currently, there is considerable interest in seeking an environmentally friendly technique that is neither thermally nor organic solvent-dependent for producing advanced polymer films for food-packaging applications. Among different approaches, plasma polymerization is a promising method that can deposit biodegradable coatings on top of polymer films. In this study, an atmospheric-pressure aerosol-assisted plasma deposition method was employed to develop a poly(ethylene glycol) (PEG)-like coating, which can act as a potential matrix for antimicrobial agents, by envisioning controlled-release food-packaging applications. Different plasma operating parameters, including the input power, monomer flow rate, and gap between the edge of the plasma head and substrate, were optimized to produce a PEG-like coating with a desirable water stability level and that can be biodegradable. The findings revealed that increased distance between the plasma head and substrate intensified gas-phase nucleation and diluted the active plasma species, which in turn led to the formation of a non-conformal rough coating. Conversely, at short plasma-substrate distances, smooth conformal coatings were obtained. Furthermore, at low input powers (<250 W), the chemical structure of the precursor was mostly preserved with a high retention of C-O functional groups due to limited monomer fragmentation. At the same time, these coatings exhibit low stability in water, which could be attributed to their low cross-linking degree. Increasing the power to 350 W resulted in the loss of the PEG-like chemical structure, which is due to the enhanced monomer fragmentation at high power. Nevertheless, owing to the enhanced cross-linking degree, these coatings were more stable in water. Finally, it could be concluded that a moderate input power (250-300 W) should be applied to obtain an acceptable tradeoff between the coating stability and PEG resemblance.

The role of sulfur cycle in new particle formation: Cycloaddition reaction of SO3 to H2S

The chemistry of sulfur cycle contributes significantly to the atmospheric nucleation process, which is the first step of new particle formation (NPF). In the present study, cycloaddition reaction mechanism of sulfur trioxide (SO3) to hydrogen sulfide (H2S) which is a typical air pollutant and toxic gas detrimental to the environment were comprehensively investigate through theoretical calculations and Atmospheric Cluster Dynamic Code simulations. Gas-phase stability and nucleation potential of the product thiosulfuric acid (H2S2O3, TSA) were further analyzed to evaluate its atmospheric impact. Without any catalysts, the H2S + SO3 reaction is infeasible with a barrier of 24.2 kcal/mol. Atmospheric nucleation precursors formic acid (FA), sulfuric acid (SA), and water (H2O) could effectively lower the reaction barriers as catalysts, even to a barrierless reaction with the efficiency of cis-SA > trans-FA > trans-SA > H2O. Subsequently, the gas-phase stability of TSA was investigated. A hydrolysis reaction barrier of up to 61.4 kcal/mol alone with an endothermic isomerization reaction barrier of 5.1 kcal/mol under the catalytic effect of SA demonstrates the sufficient stability of TSA. Furthermore, topological and kinetic analysis were conducted to determine the nucleation potential of TSA. Atmospheric clusters formed by TSA and atmospheric nucleation precursors (SA, ammonia NH3, and dimethylamine DMA) were thermodynamically stable. Moreover, the gradually decreasing evaporation coefficients for TSA-base clusters, particularly for TSA-DMA, suggests that TSA may participate in NPF where the concentration of base molecules are relatively higher. The present new reaction mechanism may contributes to a better understanding of atmospheric sulfur cycle and NPF.

CO2 Aggregation on Monoethanolamine: Observations from Rotational Spectroscopy.

The initial stages of the gas-phase nucleation between CO2 and monoethanolamine were investigated via broadband rotational spectroscopy with the aid of extensive theoretical structure sampling. Sub-nanometer-scale aggregation patterns of monoethanolamine-(CO2 )n , n=1-4, were identified. An interesting competition between the monoethanolamine intramolecular hydrogen bond and the intermolecular interactions between monoethanolamine and CO2 upon cluster growth was discovered, revealing an intriguing CO2 binding priority to the hydroxyl group over the amine group. These findings are in sharp contrast to the general results for aqueous solutions. In the quinary complex, a cap-like CO2 tetramer was observed cooperatively surrounding the monoethanolamine. As the cluster approaches the critical size of new particle formation, the contribution of CO2 self-assembly to the overall stability increases.

Superatom Generation and Deposition of Alkali-like Ta@Si16 and Halogen-like Al13 via Atomic Aggregation

Surface modification with uniform nanostructures is a promising way to fabricate functionalized surface, and the synthetic electrode functionalization can be performed by depositing atomically precise nanoclusters with a specific number of atoms and compositions. During atomic nucleation and growth in gas phase, atomic aggregates exhibit novel electronic properties, mimicking atoms at a specific number of atoms and composition, which is called superatom (SA). Tantalum-encapsulating Si16 cage nanoclusters (Ta@Si16) and aluminum 13-mer (Al13) are promising SAs for designing their assembled materials with tunable properties, where one-electron-excessive Ta@Si16 and one-electron-deficient Al13 exhibit alkali- and halogen-like characteristics, respectively, owing to the electron shell closing. In this study, with an intense nanocluster ion source, Ta@Si16 + and Al13 − were generated during the formation of TaSi n + cations and Al n − anions, where Ta@Si16 + was remarkably generated compared with the neighboring species. SA deposition provided uniformly decorated surfaces exhibiting nanofunctional properties superior to those obtained by conventional atom deposition. With mass spectrometry, Ta@Si16 + and Al13 − SAs were size-selectively soft-landed on the substrate surfaces predeposited with n-type fullerene (C60) and p-type hexa-tert-butyl-hexa-peri-hexabenzocoronene (HB-HBC, C66H66). The electronic states of Ta@Si16 and Al13 SAs immobilized on the organic substrates were characterized by X-ray photoelectron spectroscopy and oxidative reactivities under O2 exposure.

(Invited) Temperature Dependence of Electrochemical Gas-Phase Nucleation

Classical nucleation theory (CNT) suggests that the rate of electrochemical nucleation of a gas phase, and the structure of the nuclei, are complex functions of numerous temperature-dependent system properties, including the dissolved gas diffusivity, saturation concentration, and the surface tension of the liquid-gas interface. For example, the diffusion coefficient of dissolved gases increases with temperature, whereas the surface tension of the gas/water interface decreases. Very few studies of the temperature dependence of gas phase nucleation have been reported. In this report, we describe electrochemical measurements of the nucleation of H2 and N2 nanobubbles as a function of temperature (20-75 oC). The nucleation rates of single bubble nuclei were determined using the galvanostatic technique of induction time (tind). A total of 560 measurements of tind were performed and the effect of temperature on the pre-exponential factor (Jo), activation energy (EA), nucleus contact angle (θ), and the number of molecules (n) in the nuclei were determined.

Growth of Nanostructured Diamond Films on Glass Substrates by Low-Temperature Microwave Plasma-Enhanced Chemical Vapor Deposition for Applications in Nanotribology

Low-temperature fabrication of superior nano-/microcrystalline diamond (NCD/MCD) films is a major thrust in diamond technology. The widely used seeding techniques applied on the substrate surface are usually harsh, lead to defect formation, and suffer from the lack of reproducibility in maintaining homogeneity and uniformity over nano-/microdimensions. Low-temperature growth of a significant diamond phase on purely untreated glass substrates is indeed a challenging task. Using CO2 as the supplementary gas-phase constituent included in the (CH4 + H2)-plasma and a specific shadow-mask assembly to generate the diffuse plasma environment above the growth zone, the present experiment succeeds in the spontaneous growth of nanocrystalline diamond (NCD), including microcrystalline diamond (MCD) of an average crystal size of ∼0.9–1.2 μm at ∼300 °C on glass substrates, without any seeding pretreatment. In the plasma, the shadow mask establishes a virtual remote plasma configuration in setting the diffuse plasma, protects the growth surface from a direct bombardment of energetic ions, generates negative self-bias on the substrate, and, importantly, promotes significant gas-phase nucleation dominant over typical solid-state nucleation. The incubation of diamond embryo clusters onto the untreated glass substrates under the shadow-mask structure and its growth evolution through the efficient transport of the preferential carbonaceous precursors proceed within the diffuse plasma. In the course of network modification under the diffuse plasma, atomic O remains instrumental for efficient etching of the a-C overlayer on a diamond embryo and atomic H, with its small physical dimension, conveniently penetrates within the diamond network and promotes crystallization via transferring its moderate chemical energy to the diamond lattice. The low-temperature-grown nanostructured diamond films are up-and-coming for applications in nanotribology.

Gas-Phase Nucleation of Diamond Clusters upon a Sharp Rise in Temperature under Conditions of CVD Synthesis

It is shown that the predominant nucleation of diamond nuclei (instead of graphite ones) in plasma or hot-filament assisted CVD technology is due to a sharp increase in the temperature of the region of the initial gas mixture’s motion. The nucleation of diamond nuclei then occurs immediately in the gas phase. The reason for such predominant nucleation is high oversaturation by small hydrocarbon fragments in the gas mixture, due to a rapid change in temperature and substantial differences between the desorption of such fragments from the surfaces of nuclei and the oxidation of nuclei. A way is described of synthesizing massive diamonds without the use of high pressures and CVD technology in its traditional form.

Origin analysis and the elimination of the columnar crystal defects in the 3C-SiC/Si (1 0 0) heteroepitaxial layers by the modified two-step carbonization process

New columnar crystal defects were formed on the surface of 3C-SiC epitaxial growth on Si (100) substrates by a modified two-step carbonization process. The density of columnar crystal defects was reduced with the increase in the C/Si mole ratio. However, the defects could not be completely removed, even after increasing the C/Si mole ratio from 0.8 to 2.0. The size of the columnar crystal defects in 3C-SiC epi-layer growth in the SiH4-C3H8-H2 system was around 4 μm, and was unaffected by the C/Si mole ratio. The FIB and TEM investigations showed that the columnar crystal defects originated from the supersaturation of Si vapor. The columnar crystal defect was also present along 〈002〉 orientation and inclined along [111] direction at an angle of about 54.7°. HCl was used to inhibit the homogeneous gas-phase nucleation of Si, which was regarded as the formation introducing a factor of columnar defects. When the Cl/Si mole ratio was increased to 5.0, columnar crystal nucleation was completely suppressed.

Non-Equilibrium Synthesis of Highly Active Nanostructured, Oxygen-Incorporated Amorphous Molybdenum Sulfide HER Electrocatalyst.

Molybdenum sulfide emerged as promising hydrogen evolution reaction (HER) electrocatalyst thanks to its high intrinsic activity, however its limited active sites exposure and low conductivity hamper its performance. To address these drawbacks, the non-equilibrium nature of pulsed laser deposition (PLD) is exploited to synthesize self-supported hierarchical nanoarchitectures by gas phase nucleation and sequential attachment of defective molybdenum sulfide clusters. The physics of the process are studied by in situ diagnostics and correlated to the properties of the resulting electrocatalyst. The as-synthesized architectures have a disordered nanocrystalline structure, with nanodomains of bent, defective S-Mo-S layers embedded in an amorphous matrix, with excess sulfur and segregated molybdenum particles. Oxygen incorporation in this structure fosters the creation of amorphous oxide/oxysulfide nanophases with high electrical conductivity, enabling fast electron transfer to the active sites. The combined effect of the nanocrystalline pristine structure and the surface oxidation enhances the performance leading to small overpotentials, very fast kinetics (35.1 mV dec-1 Tafel slope) and remarkable long-term stability for continuous operation up to -1 A cm-2. This work shows possible new avenues in catalytic design arising from a non-equilibrium technique as PLD and the importance of structural and chemical control to improve the HER performance of MoS-based catalysts.

Secondary aerosol formation in winter haze over the Beijing-Tianjin-Hebei Region, China

Severe haze pollution occurs frequently in the winter over the Beijing-Tianjin-Hebei (BTH) region (China), exerting profound impacts on air quality, visibility, and human health. The Chinese Government has taken strict mitigation actions since 2013 and has achieved a significant reduction in the annual mean PM2.5 concentration over this region. However, the level of secondary aerosols during heavy haze episodes showed little decrease during this period. During heavy haze episodes, the concentrations of secondary aerosol components, including sulfate, nitrate and secondary organics, in aerosol particles increase sharply, acting as the main contributors to aerosol pollution. To achieve effective control of particle pollution in the BTH region, the precise and complete secondary aerosol formation mechanisms have been investigated, and advances have been made about the mechanisms of gas phase reaction, nucleation and heterogeneous reactions in forming secondary aerosols. This paper reviews the research progress in aerosol chemistry during haze pollution episodes in the BTH region, lays out the challenges in haze formation studies, and provides implications and directions for future research.

Fast Organic Vapor Phase Deposition of Thin Films in Light-Emitting Diodes.

Fast deposition of thin films is essential for achieving low-cost, high-throughput phosphorescent organic light-emitting diode (PHOLED) production. In this work, we demonstrate rapid and uniform growth of semiconductor thin films by organic vapor phase deposition (OVPD). A green PHOLED comprising an emission layer (EML) grown at 50 Å/s with bis[2-(2-pyridinyl-N)phenyl-C](acetylacetonato)iridium(III) (Ir(ppy)2(acac)) doped into 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) exhibits a maximum external quantum efficiency of 20 ± 1%. The morphology, charge transport properties, and radiative efficiency under optical and electrical excitation of the PHOLED EML are investigated as functions of the deposition rate via both experimental and theoretical approaches. The EML shows no evidence for gas phase nucleation of the organic molecules at deposition rates as high as 50 Å/s. However, the roll-off in quantum efficiency at high current progressively increases with deposition rate due to enhanced triplet-polaron annihilation. The roll-off results from accumulation of stress within the PHOLED EML that generates a high density of defect states. The defects, in turn, act as recombination sites for triplets and hole polarons, leading to enhanced triplet-polaron annihilation at high current. We introduce a void nucleation model to describe the film morphology evolution that is observed using electron microscopy.

Statistical analysis of homogeneous nucleation of metallic nanoparticles during gas-phase synthesis

In this work, we set out to develop a model of gas-phase nucleation in a mixture of copper and argon atoms, which can be further used for analysing macro-systems. Processes occurring at the atomic level are described using coefficients obtained by statistical analysis of molecular dynamic (MD) data on interactions of metal clusters with metal and argon atoms. The MD simulation results are compared with those obtained using the proposed macroscopic model. It is found that the coefficients obtained by averaging the interaction data suitably represent the integral value of the heat of condensation, although result in the smoothing of the energy distribution functions of the clusters. Analysis of the evolution of the number of clusters has shown that the values of their increase rate were lower than those obtained by MD simulation. The conclusion is made, that in order to improve the precision of the developed gas-phase condensation model, it should be supplemented by cluster coagulation.

Structural and mechanical characterization of carbon fibers grown by laser induced chemical vapor deposition at hyperbaric pressures

Laser induced chemical vapor deposition (LCVD) of freestanding carbon fibers from ethylene at hyperbaric pressures was investigated. Relationships between processing conditions, growth behavior, microstructure, and mechanical properties of the carbon fibers were established. It is found that the fiber growth rates are limited by surface reaction kinetics at low temperatures and limited by gas phase nucleation at high temperatures. At higher pressures and intermediate temperatures, growth becomes mass transport limited whereupon the fibers exhibit drastic changes in morphology and microstructure from a core-shell, smooth appearance to nodular formations. The tensile strengths of the carbon fibers grown by LCVD are generally poor due to the nature of graphitic carbon deposits. However, the Weibull modulus among the LCVD grown carbon fibers was found to be very high. Effects of processing conditions and microstructure on the fiber strengths are observed and discussed.

Modeling Nucleation and Growth of ZnO Nanoparticles in a Low Temperature Plasma by Reactive Dynamics.

The very first stages of nucleation and growth of ZnO nanoparticles in a plasma reactor are studied by means of a multiscale computational paradigm where the DFT-GGA approach is used to evaluate structure and electronic energy of small (ZnO) N clusters ( N ≤ 24) that are employed as a training set (TS) for the optimization of a Reactive Force Field (ReaxFF). Reactive Molecular Dynamics (RMD) simulations based on this tuned ReaxFF are carried out to reproduce nucleation and growth in a realistic environment. Inside the reaction chamber the temperature is around 1200 K, and the zinc atoms are oxidized in an oxygen-rich atmosphere at high pressure (about 20 atm), whereas in the quenching chamber where the temperature is lower (about 800 K) the ZnO embryo-nanoclusters are grown. The main processes ruling gas-phase nucleation and growth of ZnO nanoclusters are identified and discussed together with the dependence of the inception time and average stoichiometry of nanoclusters of different size on the composition of precursor material and physical parameters.

A Benchmark of 300mm RP-CVD Chambers for the Low Temperature Epitaxy of Si and Sige

Dichlorosilane (SiH2Cl2) is essential for the Selective Epitaxial Growth of Si and SiGe in the windows of patterned wafers. However, it is plagued by relatively slow growth rates at low temperatures. Meanwhile, hydrogenated silicon precursors (such as silane (SiH4), disilane (Si2H6) or trisilane (Si3H8)), yield significantly higher Si and SiGe Growth Rates (GR) at low temperatures. Such precursors are intrinsically non selective versus dielectric masking materials, but this difficulty can be overcome with advanced (Cyclic) Deposition / Etch processes. Liquid Si precursors such as trisilane have however several drawbacks: (i) they are expensive to produce with electronic-grade quality; (ii) being liquid, they require dedicated bubblers to be delivered into the growth chamber. Taking full advantage of their decomposition at very low temperatures is also not always possible, as the resulting films might be of lesser crystalline and electronic quality (gas phase nucleation and/or an adatom surface mobility which is too low). By contrast, disilane is gaseous and gives higher GR than silane (the Si-Si bond strength, 33 kcal mol.-1, is indeed weaker that the Si-H bond strength, 47 kcal. mol.-1). With the proper process parameters, it is possible to have reasonable growth rates down to 450°C only for SiGe(:B). It is thus a good choice of silicon precursor for the low temperature growth of Si and SiGe layers. This is illustrated in the following, where we have benchmarked SiH4 and Si2H6 against SiH2Cl2 for the low temperature growth of Si and SiGe in 300mm industrial Reduced Pressure – Chemical Vapour Deposition (RP-CVD) chambers from major Suppliers A and B. Si growth rates are, for T < 575°C, approximately ten times higher with Si2H6 than with SiH4, which are in turn roughly ten times higher than with SiH2Cl2 (see Figure 1). Activation energies, 49-52 kcal. mol.-1 (SiH4), 51-56 kcal. mol.-1 (Si2H6) or 60-61 kcal. mol.-1 (SiH2Cl2), are in-between the Si-H and Si-Cl bond strengths. For given GeH4 and Si precursor mass-flow ratios, lower Ge contents and significantly higher SiGe growth rates are obtained at 550°C, 20 Torr with Si2H6 than with SiH4 and especially SiH2Cl2 (see Figure 2). The dependency of the Ge content x on the F(GeH4) / F(Si precursor), linear for a SiH4 - based chemistry (x / (1-x) = 2.27–2.50 * F(GeH4) / F(SiH4)), is parabolic for Si2H6 and SiH2Cl2 based chemistries (x 2 / (1-x) = 0.51–0.58 * F(GeH4) / 2*F(Si2H6) and x 2 / (1-x) = 2.22-2.37 * F(GeH4) / F(SiH2Cl2), respectively). The associated SiGe GR increase linearly with the GeH4 mass-flow irrespective of the Si precursor used. With SiH4 and SiH2Cl2, growth rates (Ge concentrations) are typically lower (slightly lower) in Supplier A than in Supplier B chamber. The situation is the opposite with Si2H6. Growth rates (and Ge contents) are then higher in the former reactor than in the latter. This is assigned to (i) a ~ 5°C offset between the two and (ii) effective precursor flows which are different (likely due to chamber geometry differences). Growth rate activation energies and relationships linking Ge concentration to precursor mass-flow ratios are nevertheless similar, as shown in Figure 3 for the SiH2Cl2 + GeH4 chemistry and various temperatures. Process transfer between the two should be rather easy, We have otherwise assessed the interest of having an in-situ surface preparation chamber connected to the N2-purged transfer chamber of our cluster tool on interfacial contamination and epitaxial quality. There are indeed two ways of removing native oxide on a Si wafer: (i) thanks to an ex-situ “HF-last” wet cleaning followed by a short queue time loading in the N2-purged load-locks or (ii) thanks to an in-situ exposure of the wafer surface to a remote NH3/NF3 plasma which transforms native oxide into a salt which is sublimated at low temperature. As the oxide-free surface is exposed for minutes up to tens of minutes to the air in the former case, while it stays under N2 in the latter case, we would expect the second to be better. We have therefore compared both processes for Si surface preparation prior to epitaxy. Surfaces are with the in-situ process always under high purity N2. This results in a threshold H2 bake temperature (above which there is no O interfacial contamination anymore) which is shifted downwards by ~ 25°C (from 775°C down to 750°C). Below that temperature, O sheet concentrations are with the in-situ process typically one third those associated with “HF-Last” wet cleanings and epitaxial surfaces are smoother, as shown in Figure 4. Figure 1