Gas Phase Reaction of Silane with Water at Different Temperatures and Supported by Plasma.

The interaction of silane and water is discussed controversially in literature: some authors suggest monosilane and water react kinetically and sufficiently fast enough to remove water, while others state the reaction occurs only at elevated temperatures. This question is of technological interest for the removal of unavoidable water residues in Ar gases. Thermodynamic calculations show that virtually complete removal of water is expected with superstoichiometric silane addition. However, mass spectrometric and infrared spectroscopic experiments give evidence that the addition of monosilane to such an Ar gas at room temperature is unable to remove residual water, which disagrees with some current hypotheses in the literature. This holds even for very high SiH4 concentrations up to 2 vol.-%. Silane reacts with water above temperatures of 555 °C, initiated by the thermal decomposition of silane. A cold dielectric barrier discharge-plasma used for silane and water dissociation enhances reactivity similar to elevated temperatures. Fourier-transformed infrared spectroscopy points toward silanol generation at temperatures between 400 and 550 °C, while quadrupole mass spectrometry indicates the creation of SiOH+, SiHOH+, SiH2OH+, and SiH3OH+. Cold plasmas generate smaller amounts of SiOH+, SiHOH+, and SiH2OH+ compared to elevated temperatures. Reaction products are hydrogen and nanoscaled particles of non-stoichiometric silicon oxides. The silicon-oxide particles produced differ in elemental composition and shape depending on the prevailing water content during decomposition: SiO x generated with residual water appears with relatively smooth surfaces, while the addition of water supports the formation of significantly rougher particle surfaces. Higher initial water contents correlate with higher oxygen contents of the particles.

Interaction of Reactive Gases with Platinum Aerosol Particles at Room Temperature: Effects on Morphology and Surface Properties.

Nanoparticles produced in technical aerosol processes exhibit often dendritic structures, composed of primary particles. Surprisingly, a small but consistent discrepancy was observed between the results of common aggregation models and in situ measurements of structural parameters, such as fractal dimension or mass-mobility exponent. A phenomenon which has received little attention so far is the interaction of agglomerates with admixed gases, which might be responsible for this discrepancy. In this work, we present an analytical series, which underlines the agglomerate morphology depending on the reducing or oxidizing nature of a carrier gas for platinum particles. When hydrogen is added to openly structured particles, as investigated by tandem differential mobility analysis (DMA) and transmission electron microscopy (TEM) analysis, Pt particles compact already at room temperature, resulting in an increased fractal dimension. Aerosol Photoemission Spectroscopy (APES) was also able to demonstrate the interaction of a gas with a nanoscaled platinum surface, resulting in a changed sintering behavior for reducing and oxidizing atmospheres in comparison to nitrogen. The main message of this work is about the structural change of particles exposed to a new environment after complete particle formation. We suspect significant implications for the interpretation of agglomerate formation, as many aerosol processes involve reactive gases or slightly contaminated gases in terms of trace amounts of unintended species.

Formation of Titanium Nitride, Titanium Carbide, and Silicon Carbide Surfaces by High Power Femtosecond Laser Treatment.

Invited for this month's cover is the group of Prof. Eike G. Hübner at Fraunhofer Heinrich Hertz Institute HHI, Goslar and Clausthal University of Technology, Clausthal-Zellerfeld, Germany. The cover picture shows a titanium plate, on which the crystal structure (golden circle=Ti, blue circle=O/N/C) of isomorphous TiO, TiN or TiC, respectively, has been engraved by a high-power high pulse repetition rate femtosecond laser process. The process allows for a fast and spatially resolved surface transformation of titanium to golden TiN, blue TiO/TiO2 or black TiC in an atmosphere of nitrogen, air or ethene/argon. The background represents a typical surface microstructure of these interstitial compounds obtained during this transformation. Read the full text of the article at 10.1002/cplu.202100118.

Formation of Titanium Nitride, Titanium Carbide, and Silicon Carbide Surfaces by High Power Femtosecond Laser Treatment.

Coatings based on titanium nitrides, titanium carbides and silicon carbides can optimize the surface properties of titanium or silicon for various applications ranging from biocompatibility to chemical stability and durability. Here, we investigated a high power (100 W) high pulse repetition rate femtosecond laser process (λ=1030 nm, τ=750 fs, f=1 MHz) for the treatment of titanium and silicon in atmospheres of argon, nitrogen, methane, ethene and acetylene. In a nitrogen atmosphere, a homogeneous coating of TiON is formed on titanium. In an ethene/argon atmosphere coatings of TiOC and SiC are formed on Ti and Si, respectively. The process allows a fast surface transformation with a process rate of 0.33 cm2 s-1 and a high spatial resolution below 0.5 mm with a minimal heat affected zone at the same time. In contrast to low repetition rate femtosecond laser processed samples, the surfaces are more robust against mechanical impact. At the same time, the surfaces reveal a distinct microstructure in comparison to coatings obtained by vapor deposition techniques.