J.E. Klemberg-Sapieha

Mechanical and optical properties of hard SiCN coatings prepared by PECVD

Novel amorphous SiCN coatings are becoming increasingly attractive because of their mechanical, optical and electronic properties. In the present work, SiCN films were fabricated by PECVD from SiH4/CH4/N2/Ar gas mixtures at a temperature of 400 °C. Mechanical properties such as hardness, Youngs modulus, friction coefficient and stress were evaluated, respectively, by depth-sensing indentation, pin-on-disk, micro-scratch and curvature methods. Films deposited under optimized conditions exhibited a hardness >30 GPa, Youngs modulus >190 GPa, elastic rebound of 85% and a compressive stress of approximately 1 GPa. A friction coefficient against Al2O3, ranging from 0.75 to 0.25 and a low surface roughness of approximately 1 nm were found to be accompanied by a refractive index ranging from 1.85 to 2.10 (at 550 nm) and an extinction coefficient between 1.0×10−4 and 4.5×10−2. The film behavior is correlated with the microstructure and composition determined by SEM, XPS, AFM and broad-range UV–VIS–NIR–IR spectroscopic ellipsometry.

Advances in basic and applied aspects of microwave plasma polymerization

Abstract Microwave plasma polymerization of organosilicone compounds has several features of basic as well as applied importance. One of these is the attainment of high deposition rates, in the range of several hundred angstroms per second. Another is the ability to “tailor” (that is, to vary predictably and reproducibly) film structure and properties by controlled variation of substrate temperature T s or power density P in the plasma or both: it is shown that the composition of films can be controllably shifted from primarily “organic” characteristics, obtained at low T s or P , to predominantly “inorganic” character at high T s or P . Together with chemical composition, morphological and physicochemical properties also undergo substantial changes: films deposited at high T s or P are free of defects and adhere strongly to their substrate; they are dense, have low permeability to gases or vapours and display a high optical refractive index. The potential applied value of organosilicone plasma polymers is illustrated by two examples: the inhibition of corrosion on coated metal surfaces exposed to aggressive media and the surface modification of aromatic polyamide fibres, used to reinforce polymer-based composites. Apparatus is being developed for pilot- or industrial-scale implementation of microwave plasma processes.

Dual‐frequency N2 and NH3 plasma modification of polyethylene and polyimide

Surfaces of polyethylene and polyimide films were treated in NH3 and N2 plasma using ‘‘dual‐frequency’’ excitation: The samples were exposed to a microwave (2.45 GHz) glow discharge, while variable radio frequency (13.56 MHz)—induced negative direct current bias voltage values were simultaneously applied. The surface chemical structure was determined by high‐resolution x‐ray photoelectron spectroscopy. Up to 40 at. % of nitrogen was incorporated onto the sample surface by exposure to a microwave discharge in N2, while systematically lower N uptake was found in NH3 plasma. Nitrogen was found to be bonded predominantly in amine (C–N) groups by NH3 ‐type plasma, and in imine groups (C=N) by N2 plasma. Surface ‘‘damage’’ of polyimide, including opening of benzene rings and breaking of carbonyl groups, accompanied by the formation of increasing concentrations of chemically reactive receptor sites, has been demonstrated with increasing the energy of bombarding species.

Relationship between the mechanical properties and the microstructure of nanocomposite TiN/SiN1.3 coatings prepared by low temperature plasma enhanced chemical vapor deposition

Abstract Nanocomposite hard coatings were fabricated by PECVD from TiCl4/SiH4/N2/H2/Ar gas mixtures at substrate temperatures of 300 and 500 °C. The mechanical characteristics such as micro- and nanohardness, Youngs modulus, toughness and stress were evaluated, respectively, by depth-sensing and classical indentations and by curvature method. The mechanical and tribological properties are systematically correlated with the film microstructure and composition determined by XRD, SEM, ERD-TOF, XPS and AFM. For optimized nanocomposite films consisting of approximately 8 nm size TiN grains incorporated in an amorphous SiN1.3 matrix, we found Youngs modulus >270 and >350 GPa, hardness >25 and >40 GPa and compressive stresses ∼1.0 GPa and ∼2.5 GPa for low and high deposition temperatures, respectively. The effect of microstructure on the mechanical characteristics is discussed and the methodology of hardness measurements, in particular, the correlation between the depth-sensing indentation and the indentation size effect are addressed in detail.

Vacuum Ultraviolet Irradiation of Polymers

The interest in incoherent sources for wavelength-selective photochemistry has increased lately, but little is still known about the behavior of polymers when exposed to far UV and vacuum UV (VUV) radiation. The same dearth of information exists regarding UV (VUV) radiation emitted by low-pressure plasmas during polymer treatment. In order to study VUV-UV effects on several polymers (polyethylene - PE, polystyrene - PS, hexatriacontane - HTC, and poly(methyl methacrylate) - PMMA), we have used the well-characterized emissions from hydrogen (broad-band emission) and hydrogen/argon mixture (near-monochromatic radiation) plasmas as light sources. During irradiation, samples were kept under vacuum or in a flow of pure oxygen at low pressure; in both cases the radiation fluxes at the sample position have been precisely determined by careful spectroscopic calibration experiments. We have employed a quartz crystal microbalance (QCM) to measure in-situ any possible mass change of the various polymers. Following irradiation, samples were analysed by ellipsometry (for thickness and refractive index), X-ray photoelectron spectroscopy (XPS, to evaluate the near-surface composition and content of various functional groups), and atomic force microscopy (AFM, for surface topography and roughness measurements).

Oxidation and ablation of polymers by vacuum-UV radiation from low pressure plasmas

Low-pressure glow discharge plasmas are increasingly used as an effective method for the surface modification of polymers; they can also serve in the laboratory to simulate low Earth orbital environment (LEO). Although Vacuum-Ultraviolet (VUV, λ < 200 nm) is an important component of plasma environment, only few studies have focused on its effects so far. The emission from low-pressure microwave plasma in the VUV-UV regions was investigated in order to use this plasma as light sources for the study of the VUV/UV effects on various polymers (polyethylene, polymethylmethacrylate, etc.) or high molecular weight oligomers (hexatriacontane). We have employed a quartz crystal microbalance (QCM) in order to measure in situ the net mass change of the polymeric films exposed to VUV/UV radiation originating from hydrogen plasmas. Measurements were made with the specimens in vacuum, or immersed in low-pressure oxygen, directly exposed to the VUV/UV (perpendicular to the radiation flux), or only to the VUV-generated atomic oxygen, AO (parallel to the radiation flux). Following irradiation, samples were analysed by X-ray Photoelectron Spectroscopy (XPS), in order to study the evolution of the oxygen content and of the various functional groups.

Hard carbon films deposited under high ion flux

Abstract Hydrogenated amorphous carbon (a-C:H) films were deposited from methane or methane-argon mixtures in a “dual” microwave (MW)-r.f. plasma: the substrates were placed on a negatively biased, capacitively coupled r.f. (13.56 MHz) electrode and simultaneously exposed to an MW (2.45 GHz) discharge. Application of the MW power and/or addition of argon is found to enhance substantially gas phase processes such as dissociation of CH 4 , formation of atomic hydrogen and of C 2 , C 3 and CH species (revealed by optical emission spectroscopy) and the concentration of sp 3 component in the layers (IR spectroscopy). This approach is shown to enable deposition of thick (about 10 μm), hard (30–50 GPa), low stress (0.5 GPa) a-C:H films at a lower ion bombardment energy (less than 100 eV) than in a simple r.f. plasma.

Plasma-deposited silicon oxide and silicon nitride films on poly(ethylene terephthalate): A multitechnique study of the interphase regions

The “interphase” region between the deposited layer [e.g., plasma-enhanced chemically vapor deposited (PECVD) SiO2 or SiN] and the poly(ethylene terephthalate) (PET) substrate has been investigated and compared to physical vapor deposited (PVD) (electron beam evaporated) SiO2. Composition profiles determined by time-of-flight elastic recoil detection, electron microprobe analysis, and x-ray photoelectron spectroscopy all show an extended interphase region more than 50 nm in width, while the profile of the PVD SiO2 is narrower. However, since these analytical techniques are invasive and prone to artifacts, we have also examined ultrathin (about 10 and 20 nm) SiO2 and SiN PECVD layers on 50 nm spin-coated PET substrates by nondestructive infrared (IR) techniques. The IR spectra confirm that the thin PECVD deposits also comprise an organosilicon phase with Si–CHx bonds. We explain these observations in terms of a fragmentation/redeposition mechanism: During the earliest stage of PECVD, interaction between th...

Dual microwave-r.f. plasma deposition of functional coatings

Abstract Plasma silicon nitride (P-SiN) and amorphous hydrogenated silicon (a-Si:H) films were deposited in a dual-frequency plasma, consisting of a microwave discharge with r.f. power simultaneously superimposed on the substrate holder. It is shown that the r.f.-induced negative substrate bias voltage Vb substantially affects the deposition rate (between 15 and 30 A s−1), the film composition and electrical properties. Ion fluxes bombarding the growing layers have been measured and found to be several times greater in the dual-frequency mode than in the “pure” r.f. mode. It is estimated that ionic species contribute about 30%–40% to the film growth rate. The increasing ion flux and energy with increasing Vb enhance the formation of densely packed coatings which, in turn, reduces the dielectric loss tan δ of P-SiN, and the resistivity of a-Si:H by several orders of magnitude, when |Vb| is raised from 0 to −800 V.

Dynamics of reactive high-power impulse magnetron sputtering discharge studied by time- and space-resolved optical emission spectroscopy and fast imaging

Time- and space-resolved optical emission spectroscopy and fast imaging were used for the investigation of the plasma dynamics of high-power impulse magnetron sputtering discharges. 200 μs pulses with a 50 Hz repetition frequency were applied to a Cr target in Ar, N2, and N2/Ar mixtures and in a pressure range from 0.7 to 2.66 Pa. The power density peaked at 2.2–6 kW cm−2. Evidence of dominating self-sputtering was found for all investigated conditions. Up to four different discharge phases within each pulse were identified: (i) the ignition phase, (ii) the high-current metal-dominated phase, (iii) the transient phase, and (iv) the low-current gas-dominated phase. The emission of working gas excited by fast electrons penetrating the space in-between the electrodes during the ignition phase spread far outwards from the target at a speed of 24 km s−1 in 1.3 Pa of Ar and at 7.5 km s−1 in 1.3 Pa of N2. The dense metal plasma created next to the target propagated in the reactor at a speed ranging from 0.7 to 3...