Lenka Zajíčková

Deposition of thin organosilicon polymer films in atmospheric pressure glow discharge

The atmospheric pressure glow discharge burning in nitrogen with small admixture of organosilicon compounds such as hexamethyldisilazane or hexamethyldisiloxane was used for the deposition of thin organosilicon polymer films. The properties of the discharge were studied by means of optical emission spectroscopy and electrical measurements. The deposited films were characterized by atomic force microscopy, x-ray photoelectron spectroscopy, infrared transmission measurements, ellipsometry, depth sensing indentation technique and contact angle measurements. The films were polymer-like, transparent in the visible range, with uniform thickness and without pinholes. The film hardness varied from 0.3 to 0.6 GPa depending on deposition conditions, the elastic modulus was in the range 15-28 GPa and the surface free energy was in the range 26-45 mJ m-2. The studied films exhibited good adhesion to the substrate.

Deposition Process Based on Organosilicon Precursors in Dielectric Barrier Discharges at Atmospheric Pressure—A Comparison

Dielectric barrier discharges (DBD) at atmospheric pressure are presented as a tool to create organosilicon deposits on technical planar aluminium substrates (up to 15 × 8 cm2) by admixing small amounts of hexamethyldisiloxane (HMDSO) and tetraethoxysilane (TEOS) to the carrier gas of the discharges. Using barrier materials of different specific capacities (2.6 × 104 and 3.2 pF/cm2) in two electrode arrangements operated at less than 1 W, the influence of the filament properties on the deposition is studied. In comparison to these arrangements, a third electrode setup with a barrier of the specific capacity of 2.9 pF/cm2 is operated at approximately 50 W to study the influence of the specific energy of the plasma (energy per molecule) on the deposition process. The plasma chemical process was studied qualitatively by Gas Chromatography, and properties of the plasma-treated substrates were examined by means of X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared (FTIR) spectroscopy, as well as visually.

Plasma modification of polycarbonates

Abstract We deposited protective coatings on polycarbonates from hexamethyldisiloxane (HMDSO) and HMDSO/O2 mixtures by the plasma enhanced CVD method. In particular, we studied deposition rate, optical constants in UV/VIS, film composition and mechanical properties dependent on rf power and oxygen to HMDSO flow rate ratio. Plasma polymer HMDSO films (PP-HMDSO) showed good transparency in the visible and increased absorption in UV region. The optical constants of HMDSO/O2 films were similar to the tabulated SiO2. In general, the films were characterised by a relatively high content of hydrogen (22–66%) and a carbon content below 20%. The films deposited at an oxygen-to-HMDSO flow rate ratio higher than 15 exhibited higher tensile stress and higher hardness than those prepared at ratios of 5–10. The nature of the internal stress changed to compressive for PP-HMDSO. Plasma pre-treatment of polycarbonate in argon significantly improved the film adherence, especially when low powers and short treatment times were used.

Temperature dependence of mechanical properties of DLC/Si protective coatings prepared by PECVD

One of the main problems of amorphous diamond-like carbon (a-C:H or DLC) films deposited by plasma-enhanced chemical vapor deposition (PECVD) is their poor thermomechanical stability. The thickness of the films is limited to a few hundreds of nanometers in order to guarantee stable coatings. It is shown that major improvements in the mechanical properties of DLC films can be obtained if hexamethyldisiloxane is added in the gas mixture used for DLC deposition. The mechanical properties of hard protective DLC/Si films deposited by PECVD from an argon-methane-hexamethyldisiloxane mixture have been analyzed using microindentation techniques as the main experimental characterization tool. The formation and development of crack lines and patterns have been studied in order to determine the fracture toughness of the film and of the interface as a function of temperature.

Models of dielectric response in disordered solids

Two dispersion models of disordered solids, one parameterizing density of states (PDOS) and the other parameterizing joint density of states (PJDOS), are presented. Using these models, not only the complex dielectric function of the materials, but also some information about their electronic structure can be obtained. The numerical integration is necessary in the PDOS model. If analytical expressions are required the presented PJDOS model is, for some materials, a suitable option still providing information about the electronic structure of the material. It is demonstrated that the PDOS model can be successfully applied to a wide variety of materials. In this paper, its application to diamond-like carbon (DLC), a-Si and SiO2-like materials are discussed in detail. Unlike the PDOS model, the presented PJDOS model represents a special case of parameterization that can be applied to limited types of materials, for example DLC, ultrananocrystalline diamond (UNCD) and SiO2-like.

Deposition of protective coatings in rf organosilicon discharges

The paper discusses the deposition of protective coatings ranging from organosilicon plasma polymers to SiO2-like films and hard diamond-like carbon/silicon oxide (DLC?:?SiOx) coatings in radio frequency capacitively coupled discharges using hexamethyldisiloxane (HMDSO). As a result of the optimization of the deposition conditions it was possible to obtain high performance protective coatings. In the HMDSO/O2 mixture, it was shown that rather than the SiO2-like film a hard cross-linked SiOxCyHz polymer film can be used as a protective coating for polycarbonate. The optimum conditions for the deposition of an almost stress-free film were 17% of HMDSO and dc bias voltage of ?240?V. The film hardness and elastic modulus were 10?GPa and 75?GPa, respectively. The refractive index at 600?nm was 1.5 and the extinction coefficient decreased from 0.02 at 240?nm down to zero at 600?nm.The films deposited from HMDSO/CH4 and HMDSO/CH4/H2 mixtures exhibited the attractive properties of DLC films with the partial elimination of some of their drawbacks, such as absorption in the visible and a high intrinsic stress. The optimum concentration of the HMDSO was approximately 21%. Under these conditions the concentration of SiOx in the films was approximately 9?at.%. The film hardness and elastic modulus were above 22?GPa and 120?GPa, respectively.

Deposition of hard thin films from HMDSO in atmospheric pressure dielectric barrier discharge

An atmospheric pressure dielectric barrier discharge burning in nitrogen with a small admixture of hexamethyldisiloxane (HMDSO) was used for the deposition of thin organosilicon films. The thin films were deposited on glass, silicon and polycarbonate substrates, and the substrate temperature during the deposition process was increased up to values within the range 25 - 150 C in order to obtain hard SiOx-like thin films.

Characterization of silicon oxide thin films deposited by plasma enhanced chemical vapour deposition from octamethylcyclotetrasiloxane/oxygen feeds

Abstract Plasma enhanced chemical vapour deposition (PECVD) of thin oxide films was investigated, changing electrical potential conditions at the substrate electrode (dc, rf coupled or positive biased). Rf discharge at the frequency of 13.56 MHz was generated in a planar reactor with two internal electrodes. Silicon substrates were placed on the powered electrode. The octamethylcyclotetrasiloxane (OMTS) was chosen as a source of OSiO groups in order to test new possibilities in the silicon oxide depositions. The reflectance in the visible, the transmittance in the infrared region, X-ray photoelectron spectra (XPS) and Rutherford backscattering method (RBS) analyses were applied to describe the deposition rate, the optical properties, the composition and the structure of the deposited films. The comparison among these four methods concerning the film composition and structure is discussed. The pronounced changes in the deposition rate with rf power or dc bias typical of every electrical potential condition were observed. However, other film characteristics seemed to be very similar. The film optical parameters and the atomic composition were close to those of amorphous silicon dioxide.

Rf sputtering of composite SiOx/plasma polymer films and their basic properties

Abstract Composite SiOx/PTFE films were deposited by rf sputtering in argon using balanced magnetron equipped with a PTFE/SiO2 target. The composition of deposited films, found by XPS and FTIR, ranged from fluorocarbon plasma polymers with very small SiOx content up to coatings with a greater incorporation of SiOx. The hardness of fluorocarbon polymer films with increased concentration of SiOx was 2400 N/mm2. This is between two to three times higher than in the case of fluorocarbon plasma polymers with very low SiOx content. The static contact angle of water ranges from 112 to 95° and the refractive index from 1.49 to 1.43, when incorporation of SiOx into fluorocarbon plasma polymer matrix decreases.

Atmospheric pressure microwave torch for synthesis of carbon nanotubes

The microwave (mw) plasma torch at atmospheric pressure has been studied for carbon nanotube (CNT) synthesis. The depositions were carried out on silicon substrates with 515 nm thin iron catalytic overlayers from the mixture of argon, hydrogen and methane. The optical emission spectroscopy of the torch showed the presence of C2 and CH radicals as well as carbon and hydrogen excited atoms. The vicinity of the substrate influenced the relative intensities and increased the emission of C2. For fixed mw power, the temperature of the substrate strongly depended on its position with respect to the nozzle electrode and on the gas mixture, particularly the amount of H2. The speed of the substrate heating during an early deposition phase had a significant effect on the CNT synthesis. An abrupt increase of the temperature at the beginning increased the efficiency of theCNTsynthesis. Areas of dense straight standing CNTs, 30 nm in average diameter, with approximately the same sized iron nanoparticles on their tops were found in accordance with the model of growth by plasma enhanced chemical vapour deposition. However, the deposit was not uniform and a place with only several nanometres thick CNTs grown on much larger iron particles was also found. Here, taking into account the gas temperature in the torch, 31003900 K, we can see similarities with the dissolutionprecipitation model of the CNT growth by high temperature methods, arc or laser ablation.