Hexamethyldisiloxane Vapor Research Articles

Structure and chemical composition of thin-film nanocomposites based on silver in organosilicon amorphous matrix prepared by High Target Utilization Sputtering

Thin films based on Ag nanoclusters embedded in an organosilicon polymer matrix were deposited using the High Target Utilization Sputtering technique (HiTUS) by simultaneous sputtering of the Ag target and polymerization of hexamethyldisiloxane (HMDSO) vapors in radiofrequency plasma. The influence of deposition parameters on chemical composition and structure of the deposited nanocomposite films was studied using scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray diffraction analytical techniques. The films under investigation exhibit a dense uniform structure with the metallic nanocrystalline silver present in the form of spherical-shaped nanoclusters with dimensions below 10 nm embedded in an amorphous organosilicon plasma polymer. The average size of Ag nanoclusters is increased from 1.8 to 4.4 nm with Ag content increasing from 16 to 57%at. while concentration of nanoclusters is reduced. Incorporation of the metallic silver into the plasma polymerized HMDSO leads to a decrease of carbon and oxygen content as well as a decrease of organosilicon polymer matrix density.

Characterization of hexamethyldisiloxane plasma polymerization in a DC glow discharge in an argon flow

This work aims to study hexamethyldisiloxane (HMDSO) plasma polymerization in a low-pressure glow discharge in a gas flow. HMDSO was activated in a plasma-chemical reactor with a DC glow discharge in an argon flow. The argon flow (the mass flow rate was 230 mg/min) was injected in the direction of the anode from the cathode. HMDSO vapors were injected into the plasma-chemical reactor either through the hollow cathode or through the inlet located between the cathode and the anode. Polymer coatings were deposited on the substrates located in a vacuum chamber. Plasma polymerization was characterized based on the mass of coatings deposited under varying external conditions: the HMDSO mass flow rate (1–10 mg/min), the average discharge current (6–60 mA), and the discharge power (6–30 W). The operation modes of the plasma-chemical system were determined. The chemical structure of the coatings was analyzed using the infrared spectroscopy. The processes occurring in different regions of the glow discharge and at the interface near the substrate surface are proposed. A DC glow discharge in a gas flow can be used for local deposition of polymer coatings on the surface of dielectric or conductive materials.

Sub-micrometer plasma-enhanced chemical vapor deposition using an atmospheric pressure plasma jet localized by a nanopipette scanning probe microscope

We developed a localized plasma-enhanced chemical vapor deposition (PE-CVD) technique to deposit silicon oxide with a sub-micrometer width on a substrate using an atmospheric pressure plasma jet (APPJ) irradiated from a nanopipette nozzle. To realize fine material deposition, hexamethyldisiloxane (HMDSO) vapor was blown into the localized helium APPJ irradiated from the sub-micrometer aperture of the nanpopipette with the jet length limited to the aperture size of the nanopipette. The irradiation distance was controlled using a shear-force positioning technique using scanning probe microscopy (SPM). The proposed system successfully deposited silicon oxide dots with sub-micrometer width on a substrate. After the deposition, the topography of the deposited surface was observed by scanning the nanopipette, which can be used as an SPM probe. The localized PE-CVD properties were systematically investigated by varying the deposition parameters. The amount of deposited material could be controlled by the flow rate of the carrier gas of the HMDSO vapor, APPJ irradiation time, and nanopipette–substrate surface irradiation distance.

Plasma dust deposition in low-pressure parallel plates reactor

Thin dust layers have been elaborated by plasma enhanced chemical vapor deposition (PECVD) in a parallel plates reactor using hexamethyldisiloxane (HMDSO) vapors. The chemical and physical properties of the obtained coating were discussed using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The performed characterizations show a significant impact of the deposition time on powders (NPs) composition and the organic groups concentration in particles such as Si(CH3)2, Si(CH3)3 and Si(CH3)x increases when increasing the time deposition.

Characterization of the electrical and optical properties of a gliding arc tornado device

Optical emission spectroscopy was used to characterize the gas phase in a gliding arc tornado reactor used for plasma applications. Results concerning the transition between spark and fully developed arc regimes are presented, by comparing with the electrical characteristics of the discharge. An extended analysis of spectra of air and helium discharges mixed with water and hexamethyldisiloxane vapors was performed, with the identification of active radical species involved in the surface functionalization of polymeric nanoparticles.Graphic abstract

TiO2–SiO2 nanocomposite thin films deposited by direct liquid injection of colloidal solution in an O2/HMDSO low-pressure plasma

TiO2 nanoparticles (NPs), 3 nm in size, were injected inside a very-low-pressure O2 plasma reactor using a liquid injector and following an iterative injection sequence. Simultaneously, hexamethyldisiloxane (HMDSO) vapor precursor was added to create a SiO2 matrix and a TiO2–SiO2 nanocomposite (NC) thin film. Both the liquid injection and vapor precursor parameters were established to address the main challenges observed when creating NCs. In contrast to most aerosol-assisted plasma deposition processes, scanning/transmission electron microscopy (S/TEM) indicated isolated (i.e. non-agglomerated) NPs distributed in a rather uniform way in the matrix. The fraction of the TiO2 NPs inside the SiO2 matrix was estimated by SEM, spectroscopic ellipsometry (SE), and x-ray photoelectron spectroscopy. All techniques provided coherent values, with percentages between 12% and 19%. Despite the presence of TiO2 NPs, SE measurements confirmed that the plasma-deposited SiO2 matrix was dense with an optical quality similar to the one of thermal silica. Finally, the percentage of TiO2 NPs inside the SiO2 matrix and the effective refractive index of the NCs can be tuned through judicious control of the injection sequence.

Dual liquid/vapor-fed flame synthesis for the effective preparation of SiO2@YAlO3:Nd3+ nanophosphors

Yttrium aluminum oxide YAlO3 is an attractive laser host material for lanthanide ions like Nd3+. In this paper, a dual liquid/vapor-fed flame synthesis (DLVF) system is developed for investigating the role of SiO2 coating on flame-made YAlO3:Nd3+ nanophosphors. The hexamethyldisiloxane (HDMSO) vapor is flexibly fed into the YAlO3:Nd3+ flame spray flow at different positions and molar ratios. We find that the introduction of SiO2 coating dramatically improves the crystallinity of YAlO3:Nd3+cores because of the heat-insulation effect and nearly doubles the fluorescence intensity. Through a timescale analysis, we demonstrate that the best timing for coating injection is when the small particles have already been formed but not heavily aggregated. An early injection could result in segregated SiO2 particles and some impurities like Al2SiO5, while a delayed injection leads to the coating of SiO2 on the entire aggregates instead of on individual particles. Experiments of different coating ratios show that the coating ratio 1:1 of Si:(Y+Nd) produces the best crystallinity and strongest fluorescence intensity. Further increase of the coating ratio does not show any improvements of the crystallinity, and may even causes the decrease of the relative fraction of Nd3+ ions. Compared with YAG:Nd3+ bulk materials (with a typical optimum doping concentration 1.1mol%) and uncoated YAlO3:Nd3+ nanophosphors (with an optimum doping concentration 2 mol%), the SiO2 coating promotes the optimum Nd3+ doping concentration up to 3 mol%.

Changes in the surface roughness of optical glasses in a humid environment

Long-term testing of silicate and borate optical glasses is performed in a humid environment. Products of water reacting with glass components are shown to form on the borate glass surface, causing an increase in the roughness parameter Rz. Pretreatment in hexamethyldisiloxane vapors reliably protects glasses from aggressive moisture. Silicate optical glasses are more resistant to humidity and do not require pretreatment. Roughness parameter Rz is found to be an inadequate metric of the roughness of the surface with a protective coating, owing to the limitations of its determination. Topographic measurements are more reliable in this instance.

A novel approach for detecting HMDSO poisoning of metal oxide gas sensors and improving their stability by temperature cycled operation

Abstract. In this paper we study the effect of hexamethyldisiloxane (HMDSO) vapor on an SnO2-based gas sensor (GGS 1330, UST Umweltsensortechnik GmbH, Geschwenda, Germany) in a temperature cycled operation (TCO). We show that HMDSO poisoning can be quantified at early stages (85 to 340 ppm × min) with a resolution of ±85 ppm × min using TCO. This novel approach for sensor self-monitoring provides a simple method for early detection of HMDSO poisoning. It is thereby possible to detect poisoning before the sensor function is strongly impaired. In this paper we show that by using an appropriate normalization of the sensor data, the stability of gas discrimination by linear discriminant analysis (LDA) can be improved, which in turn facilitates a more accurate determination of the poisoning state by a hierarchical LDA discrimination. For a specific temperature cycle and feature extraction approach, we show that identification of ethanol and carbon monoxide is still possible after poisoning with 900 ppm × min HMDSO, i.e. a HMDSO poisoning dose more than twice as high as required by DIN EN 50194-1.

Contribution of surface energy and roughness to the wettability of polyamide 6 and polypropylene film in the plasma-induced process

Plasma-induced etching and chemical vapor coating processes are well-known technologies that modify the wetting properties of polymeric surfaces by engineering the surface roughness and surface energy. The contributing effect of plasma treatment for O2 etching and hexamethyldisiloxane (HMDSO) vapor coating on the wetting properties was investigated for polyamide 6 (PA6) and polypropylene (PP) substrates. The surface energy components of PA6 and PP were analyzed by the Owens–Wendt model, and were associated with the wettability of water and diiodomethane. With the introduction of roughness by the O2 etching process without HMDSO coating, the wettability of PA6 substrate was enhanced while that of PP was deteriorated when they were observed after 20 days aging. When the surface was etched for 7 min or longer with the subsequent coating with HMDSO, both PA6 and PP lost hydrophilic property, giving water contact angle of 180°. The wettability was examined for the varied treatment conditions and as a function of average nano-pillar length. This study helps better understand the interactions between the surface energy and roughness of polymeric materials, and their influence on surface wettability.

Scratch resistance and tribological properties of SiOx incorporated diamond-like carbon films deposited by r.f. plasma assisted chemical vapor deposition

SiOx containing diamond-like carbon (DLC) films are deposited on the stainless steel 316 substrates by radio frequency (r.f.) plasma assisted chemical vapor deposition (PACVD) process using plasma of Argon, methane gases and Hexamethyl Disiloxane vapors. The sp3/sp2 ratio of carbon bonding in the films is found to increase with increase in bias. Films deposited at low bias voltage (-25V) show onset of film spallation and critical failure during scratch test at low progressive load and it has high friction coefficient. In contrast, film deposited at −100V bias shows low coefficient of friction <0.05. Such a low friction coefficient is related to optimum fraction of sp2 carbon bonding and a-C contents.

Laser oxidative pyrolysis synthesis and annealing of TiO2 nanoparticles embedded in carbon–silica shells/matrix

Titania nanoparticles containing a mixture of anatase and rutile phases (with mean crystalline sizes up to 24nm) covered with/embedded in carbon/silica thin layers or matrix were obtained in a single step using laser oxidative pyrolysis. Titanium tetrachloride and hexamethyldisiloxane (HMDSO) vapors were separately introduced into the reaction zone – both together with the laser-absorbing agent (sensitizer) ethylene – which acts also as carbon source – and the oxidant (air) – through the inner and the concentric nozzle, respectively. By increasing the air flow through the annular nozzle, while keeping constant the TiC4, inner air, HMDSO and C2H4 flows, the atomic carbon concentration as well as the rutile to anatase ratio in the resulted nanopowders decrease. A much brighter and extended flame was observed for the experiment involving the greatest air flow. The Ti/Si atomic ratio in the resulted nanocomposites was higher than that from the introduced precursors (1.8), indicating a partial siloxane conversion to silica. The annealed powders (at 450°C to further carbon content reducing) exhibit a lower bandgap energy than those of the reference sample without silica (and also lower than the commercial Degussa P25 nano-TiO2).

Optical emission spectroscopy of microwave-plasmas at atmospheric pressure applied to the growth of organosilicon and organotitanium nanopowders

An atmospheric-pressure plasma sustained by an electromagnetic surface wave (SW) in the microwave regime combined with a bubbler/flash evaporator for the injection of liquid precursors was used to produce organosilicon and organotitanium nanopowders. Following the addition of hexamethyldisiloxane (HMDSO) vapors in the nominally pure argon plasma, optical emission spectra revealed the apparition of strong C2 molecular bands along with Si and Balmer H emission lines. Such features were not observed in our atmospheric-pressure Ar/HMDSO discharges controlled by dielectric barriers, indicating that microwave plasmas are characterized by much higher fragmentation levels of the precursors due to much higher electron densities. Emission spectra from the Ar/HMDSO SW plasma further showed a high-intensity continuum, the intensity of which decreased with time as powders started to form on the discharge tube walls. In presence of titanium isopropoxide (TTIP) vapors in the nominally pure Ar plasma, the emission was dominated by Ar and Ti lines, with no trace of carbon and no continuum. Fourier-Transform Infrared (FTIR) Spectroscopy of the powders formed in Ar/HMDSO plasmas showed very strong Si-(CH3)x and O-Si-(CH3)x bands, which is consistent with the formation of silicon oxycarbide. Transmission Electron Microscopy (TEM) further showed tube and sheet-like nanofeatures as well as larger structures consisting of agglomerated primary clusters. On the other hand, introduction of O2 in Ar/HMDSO plasmas produced only round-like nanoparticles with strong Si-O-Si bands and no trace of carbon, consistent with the formation of SiOx. The average size of the silica nanoparticles was 50 nm. FTIR spectra of powders formed in Ar/TTIP plasmas showed strong Ti-O signals, even without the addition of O2 in the gas phase. Corresponding TEM analysis showed nano- and agglomerated features comparable to those obtained in Ar/HMDSO although the average size of the titanate nanoparticles was smaller (10 nm). This set of data indicates that SW plasmas represent a promising parametric tool not only to achieve nanopowders with tailored properties for applications, but also for fundamental studies of nanodusty plasmas at atmospheric-pressure.

Breath figures of two immiscible substances on a repellent surface

The understanding of the competition between different substances while condensing on a cold surface is of high interest in situations in which it is desirable to control their condensation rates and the formed morphologies. We do the experiments for mixtures of water and hexamethyldisiloxane vapors at several concentrations. The dropwise condensation of the vapors forms breath figures on a substrate that is repellant to both substances. We report the average radius of the drops for each specie as a function of time. Also, we pay attention to the evolution of the corresponding morphologies and the appearance of hybrid clusters.

C123 燃焼場を用いたSiO_2ナノ粒子生成に関する研究(OS-5: これからの燃焼研究(2))

The temperature from the tip of the methane premixed flame along the flow direction decreased dramatically at low mass flow rate of the Hexamethyldisiloxane (HMDSO) vapor while the temperature was almost constant along the flow direction at high mass flow rate of the HMDSO vapor. From the SEM images, the size of the agglomerates of silica nanoparticles had a maximum at a certain mass flow rate of the HMDSO vapor due to not only the temperature distribution along the flow direction from the tip of the premixed flame but also the temperature. Furthermore, when the concentration of the oxygen in the premixed flame increased, the size of the agglomerates decreased.

Design of Aerosol Coating Reactors: Precursor Injection

Particles are coated with thin shells to facilitate their processing and incorporation into liquid or solid matrixes without altering core particle properties (coloristic, magnetic, etc.). Here, computational fluid and particle dynamics are combined to investigate the geometry of an aerosol reactor for continuous coating of freshly-made titanium dioxide core nanoparticles with nanothin silica shells by injection of hexamethyldisiloxane (HMDSO) vapor downstream of TiO2 particle formation. The focus is on the influence of HMDSO vapor jet number and direction in terms of azimuth and inclination jet angles on process temperature and coated particle characteristics (shell thickness and fraction of uncoated particles). Rapid and homogeneous mixing of core particle aerosol and coating precursor vapor facilitates synthesis of core-shell nanoparticles with uniform shell thickness and high coating efficiency (minimal uncoated core and free coating particles).

Fluorine‐Free Superhydrophobic Microstructured Films Grown by PECVD

AbstractPlasma‐enhanced (PE)CVD is used to create, in a single step, a superhydrophobic (SH) (water contact angle over 150°) layer starting from hexamethyldisiloxane (HMDSO) vapor (i.e., without fluorine) in a low‐frequency, capacitively coupled plasma reactor under low pressure. Several SH microstructures are obtained, depending on experimental parameters (gas pressures, substrate rotation, pulsed glow discharge, plasma duration) deposited on various substrate types. The presented technique can produce thin SH transparent films (below 1 µm) or thicker ones (above 10 µm) to modify the surface of a macroporous hydrophilic membrane in order to render it SH with a water transmembrane pressure close to 2 bar.

Design of Turbulent Flame Aerosol Reactors by Mixing-Limited Fluid Dynamics

Nanoparticle synthesis in turbulent flame aerosol reactors is elucidated by computational fluid dynamics (CFD). Mixing-limited combustion is modeled, and total particle number, area, and volume concentration are described by transport equations including terms for particle dynamics. The spread of the particle size distribution at a given streamline is neglected as flame-made aerosols rapidly attain their self-preserving distribution. Results are in good agreement with primary particle data of turbulent diffusion flame synthesis of silica nanoparticles by oxidation of hexamethyldisiloxane vapor at different laboratories without adjustable parameters. Measured agglomerate mobility diameters best matched the predicted volume-equivalent soft-agglomerate diameters. The employed fractal-like dimensions (Df = 1.5−3) had no effect on the predicted primary particle and aggregate diameters and a rather small effect on volume-equivalent soft-agglomerate diameters.

Design of aerosol particle coating: Thickness, texture and efficiency

Core–shell particles preserve the performance (e.g. magnetic, plasmonic or opacifying) of a core material, while modifying its surface with a shell that facilitates (e.g. by blocking its reactivity) their incorporation into a host liquid or polymer matrix. Here coating of titania (core) aerosol particles with thin silica shells (films or layers) is investigated at non-isothermal conditions by a trimodal aerosol dynamics model, accounting for SiO 2 generation by gas phase and surface oxidation of hexamethyldisiloxane (HMDSO) vapor, coagulation and sintering. After TiO 2 particles have reached their final primary particle size (e.g. upon completion of sintering during their flame synthesis), coating starts by uniformly mixing them with HMDSO vapor that is oxidized either in the gas phase or on the particles’ surface resulting in SiO 2 aerosols or deposits, respectively. Sintering of SiO 2 deposited onto the core TiO 2 particles takes place transforming rough into smooth coating shells depending on the process conditions. The core–shell characteristics (thickness, texture and efficiency) are calculated for two limiting cases of coating shells: perfectly smooth (e.g. hermetic) and fractal-like. At constant TiO 2 core particle production rate, the influence of coating weight fraction, surface oxidation and core particle size on coating shell characteristics is investigated and compared to pertinent experimental data through coating diagrams. With an optimal temperature profile for complete precursor conversion, the TiO 2 aerosol and SiO 2-precursor (HMDSO) vapor concentrations have the strongest influence on product coating shell characteristics.

Growth and properties of the ion beam deposited SiO x containing DLC films

In the present study SiO x containing diamond-like carbon (DLC) films were synthesized by the closed drift ion source from hexamethyldisiloxane vapor. Kinetics of the growth of DLC films was investigated using optical emission spectroscopy (OES). Structure, chemical composition, electrical and optical properties of the synthesized films were studied. The effects of ion beam energy were investigated. The main atomic hydrogen Balmer series lines and the intense broad CH group related peak were detected in the OES spectra registered in-situ during SiO x containing diamond-like carbon film synthesis. The intensity ratio of H-β/CH peaks increased with the increase of applied ion beam energy. It was explained by activation of the dissociation of the hexamethyldisiloxane molecules. Changes of the structure of the diamond-like carbon films were observed for the films deposited under intense dissociation conditions.