Electron Cyclotron Wave Resonance Research Articles

Ultrafast UV Luminescence of ZnO Films: Sub‐30 ps Decay Time with Suppressed Visible Component

AbstractUltrafast sub‐100 picosecond luminescence is vital in many applications involving ultrafast events and time‐of‐flight systems. Materials exhibiting fast luminescence, such as barium fluoride (BaF2) and zinc oxide (ZnO), also suffer from an intrinsically slow nanosecond (ns) to microsecond (µs) luminescence. Here, 2.2 micrometer (µm)‐ to 5.7 µm‐thick undoped ZnO films on soda‐lime glass (SLG) substrates without a buffer layer by a hybrid pulsed reactive magnetron sputtering operating in the medium‐frequency range (MF magnetron) assisted by an electron cyclotron wave resonance (ECWR) plasma is deposited. The undoped ZnO films exhibited superior optical properties characterized by intense ultraviolet (UV) luminescence, unprecedented ultrafast decay times, and for the case of MF+ECWR‐deposited films, suppressed defect‐related visible luminescence. The 2.2 µm‐thick MF‐deposited film exhibited the fastest 9‐ps decay time at room temperature. The impressive properties of the films are attributed to the use of advanced deposition technology with properly tuned plasma parameters, especially a high degree of dissociation of molecular oxygen together with an increased proportion of activated zinc particles, leading to a higher deposition rate, better crystallinity, fewer defects, and a lower proportion of oxygen vacancies. These films will pave the way toward the development of time‐of‐flight detectors, high‐resolution nuclear imaging cameras, and high‐rate ultrafast timing devices.

Deposition of Fe2O3:Sn semiconducting thin films by reactive pulsed HiPIMS + ECWR co-sputtering from Fe and Sn targets

Semiconducting Fe2O3 thin films were deposited on SnO2:F (FTO) and Pt substrates by reactive high-power impulse magnetron sputtering combined with electron cyclotron wave resonance plasma (HiPIMS + ECWR). Fe2O3 films were fabricated either by sputtering from a single Fe target or by co-sputtering from an additional Sn target. Plasma parameters during co-sputtering were measured by an RF probe system enabling the comparison between HiPIMS + ECWR and only HiPIMS conditions used for the film deposition. As deposited Fe2O3 films were post-annealed in air at 450 °C and 650 °C, respectively. It was shown that as deposited Fe2O3 films were amorphous but became crystalline after post-annealing at 450 °C. Further increase of annealing temperature to 650 °C did not improve significantly the crystalline structure of the Fe2O3 film. All post-annealed Fe2O3 films exhibited photocurrents in the anodic region; generally, hematite films annealed at 650 °C exhibited higher photocurrents than those annealed at 450 °C. Films doped by Sn co-sputtering had higher photocurrents than films only doped by Sn diffusion during post-annealing from the FTO substrate. Hematite films on Pt substrate doped by Sn co-sputtering and post-annealed at 650 °C exhibited the highest photocurrents. It was verified by XPS analysis with ion sputtering depth profiling that Pt atoms also diffuse from the Pt substrate into the Fe2O3 film during the post-annealing at 650 °C and can, similar to Sn in the case of an FTO substrate, act as a dopant.

High-quality dense ZnO thin films: work function and photo/electrochemical properties

Compact ZnO (wurtzite) thin films are prepared on four different substrates by (i) spray pyrolysis or (ii) pulsed reactive magnetron sputtering combined with a radio frequency electron cyclotron wave resonance plasma. Films are characterized by AFM, XRD, Kelvin probe, cyclic voltammetry, electrochemical impedance spectroscopy, and UV photoelectrochemistry. Film morphologies, defect concentrations, crystallite size, and orientation provided specific fingerprints for the electronic structure of ZnO close to the conduction band minimum. Fabricated films are referenced, if relevant, to a model system based on a wurtzite single crystal with either Zn-face or O-face termination. Kelvin probe measurements of the ZnO/air interface distinguished effects of annealing and UV excitation, which are attributed to removal of oxygen vacancies close to the surface. In turn, the work function, at the electrochemical interface, specifically addressed the growth protocol of the ZnO electrodes but not the effects of crystallinity and annealing. Finally, high photocurrents of water oxidation are observed exclusively on virgin films. This effect is then discussed in terms of photocorrosion, and work function changes due to UV light.Graphical

Anatase TiO2 deposited at low temperature by pulsing an electron cyclotron wave resonance plasma source

Photocatalytic surfaces have the potentiality to respond to many of nowadays societal concerns such as clean H2 generation, CO2 conversion, organic pollutant removal or virus inactivation. Despite its numerous superior properties, the wide development of TiO2 photocatalytic surfaces suffers from important drawbacks. Hence, the high temperature usually required (> 450 °C) for the synthesis of anatase TiO2 is still a challenge to outreach. In this article, we report the development and optimisation of an ECWR-PECVD process enabling the deposition of anatase TiO2 thin films at low substrate temperature. Scanning of experimental parameters such as RF power and deposition time was achieved in order to maximise photocatalytic activity. The careful selection of the deposition parameters (RF power, deposition time and plasma gas composition) enabled the synthesis of coatings exhibiting photocatalytic activity comparable to industrial references such as P25 Degussa and Pilkington Activ at a substrate temperature below 200 °C. In addition, to further decrease the substrate temperature, the interest of pulsing the plasma RF source was investigated. Using a duty cycle of 50%, it is thus possible to synthesise photocatalytic anatase TiO2 thin films at a substrate temperature below 115 °C with a deposition rate around 10 nm/min.

Electron beam injection from a hollow cathode plasma into a downstream reactive environment: Characterization of secondary plasma production and Si3N4 and Si etching

A material etching system was developed by combining beam electron injection from a direct current hollow cathode (HC) electron source with the downstream reactive environment of a remote CF4/O2 low temperature plasma. The energy of the injected beam electrons is controlled using an acceleration electrode biased positively relative to the HC argon discharge. For an acceleration voltage greater than the ionization potential of Ar, the extracted primary electrons can produce a secondary plasma in the process chamber. The authors characterized the properties of the secondary plasma by performing Langmuir probe measurements of the electron energy probability function (EEPF) 2.5 cm below the extraction ring. The data indicate the existence of two major groups of electrons, including electrons with a primary beam electron energy that varies as the acceleration voltage is varied along with low energy electrons produced by ionization of the Ar gas atoms in the process chamber by the injected beam electrons. When combining the HC Ar beam electron with a remote CF4/O2 electron cyclotron wave resonance plasma, the EEPF of both the low energy plasma electron and beam electron components decreases. Additionally, the authors studied surface etching of Si3N4 and polycrystalline Si (poly-Si) thin films as a function of process parameters, including the acceleration voltage (0–70 V), discharge current of the HC discharge (1–2 A), pressure (2–100 mTorr), source to substrate distance (2.5–5 cm), and feed gas composition (with or without CF4/O2). The direction of the incident beam electrons was perpendicular to the surface. Si3N4 and polycrystalline silicon etching are seen and indicate an electron-neutral synergy effect. Little to no remote plasma spontaneous etching was observed for the conditions used in this study, and the etching is confined to the substrate area irradiated by the injected beam electrons. The electron etched Si3N4 surface etching rate profile distribution is confined within a ∼30 mm diameter circle, which is slightly broader than the area for which poly-Si etching is seen, and coincides closely with the spatial profile of beam electrons as determined by the Langmuir probe measurements. The magnitude of the poly-Si etching rate is by a factor of two times smaller than the Si3N4 etching rate. The authors discuss possible explanations of the data and the role of surface charging.

Semiconducting p-Type Copper Iron Oxide Thin Films Deposited by Hybrid Reactive-HiPIMS + ECWR and Reactive-HiPIMS Magnetron Plasma System

A reactive high-power impulse magnetron sputtering (r-HiPIMS) and a reactive high-power impulse magnetron sputtering combined with electron cyclotron wave resonance plasma source (r-HiPIMS + ECWR) were used for the deposition of p-type CuFexOy thin films on glass with SnO2F conductive layer (FTO). The aim of this work was to deposit CuFexOy films with different atomic ratio of Cu and Fe atoms contained in the films by these two reactive sputtering methods and find deposition conditions that lead to growth of films with maximum amount of delafossite phase CuFeO2. Deposited copper iron oxide films were subjected to photoelectrochemical measurement in cathodic region in order to test the possibility of application of these films as photocathodes in solar hydrogen production. The time stability of the deposited films during photoelectrochemical measurement was evaluated. In the system r-HiPIMS + ECWR, an additional plasma source based on special modification of inductively coupled plasma, which works with an electron cyclotron wave resonance ECWR, was used for further enhancement of plasma density ne and electron temperature Te at the substrate during the reactive sputtering deposition process. A radio frequency (RF) planar probe was used for the determination of time evolution of ion flux density iionflux at the position of the substrate during the discharge pulses. Special modification of this probe to fast sweep the probe system made it possible to determine the time evolution of the tail electron temperature Te at energies around floating potential Vfl and the time evolution of ion concentration ni. This plasma diagnostics was done at particular deposition conditions in pure r-HiPIMS plasma and in r-HiPIMS with additional ECWR plasma. Generally, it was found that the obtained ion flux density iionflux and the tail electron temperature Te were systematically higher in case of r-HiPIMS + ECWR plasma than in pure r-HiPIMS during the active part of discharge pulses. Furthermore, in case of hybrid discharge plasma excitation, r-HiPIMS + ECWR plasma has also constant plasma density all the time between active discharge pulses ni ≈ 7 × 1016 m−3 and electron temperature Te ≈ 4 eV, on the contrary in pure r-HiPIMS ni and Te were negligible during the “OFF” time between active discharge pulses. CuFexOy thin films with different atomic ration of Cu/Fe were deposited at different conditions and various crystal structures were achieved after annealing in air, in argon and in vacuum. Photocurrents in cathodic region for different achieved crystal structures were observed by chopped light linear voltammetry and material stability by chronoamperometry under simulated solar light and X-ray diffraction (XRD). Optimization of depositions conditions results in the desired Cu/Fe ratio in deposited films. Optimized r-HiPIMS and r-HiPIMS + ECWR plasma deposition at 500 °C together with post deposition heat treatment at 650 °C in vacuum is essential for the formation of stable and photoactive CuFeO2 phase.

Properties of an ECWR Discharge at Low Pressures

We report an experimental study of an electron cyclotron wave resonance (ECWR) plasma source. The dimensions of the source are considerably larger than in similar experiments. The excitation frequency is 27.12 MHz, the working gas is argon at very low pressures below 0.13 Pa. Spectroscopic data connected with a global model yield electron temperature $T_{\mathrm{ e}}$ , electron number density $n_{\mathrm{ e}}$ , population of the metastable state $n_{\mathrm{ m}}$ . The pressure dependencies of these quantities are discussed. Starting from $T_{\mathrm{ e}}\sim 5$ eV at pressure $p=0.13$ Pa the temperature grows as the pressure goes down until the discharge extinguishes at ${\sim }0.6\times 10^{-2}$ Pa. It becomes in the meantime so high that the emission spectra feature strong Ar(II) lines in the region 400–500 nm. At $p=0.13$ Pa and power 300 W the electron density on the axis is about $4\times 10^{10}~{\mathrm{ cm}}^{-3}$ and falls down due to the increase in $T_{\mathrm{ e}}$ as the pressure drops. The discharge was also electrically characterized to determine the plasma impedance $Z$ . The impedance and the plasma resistance ${\mathrm{ Re}}(Z)$ are presented as functions of the static magnetic field $B_{\mathrm{ 0}}$ . The distribution of power losses are also shown as $B_{\mathrm{ 0}}$ -dependencies.

Investigation of ionized metal flux in enhanced high power impulse magnetron sputtering discharges

The metal ionized flux fraction and production of double charged metal ions Me2+ of different materials (Al, Cu, Fe, Ti) by High Power Impulse Magnetron Sputtering (HiPIMS) operated with and without a pre-ionization assistance is compared in the paper. The Electron Cyclotron Wave Resonance (ECWR) discharge was employed as the pre-ionization agent providing a seed of charge in the idle time of HiPIMS pulses. A modified grid-free biased quartz crystal microbalance was used to estimate the metal ionized flux fraction ξ. The energy-resolved mass spectrometry served as a complementary method to distinguish particular ion contributions to the total ionized flux onto the substrate. The ratio between densities of doubly Me2+ and singly Me+ charged metal ions was determined. It is shown that ECWR assistance enhances Me2+ production with respect of absorbed rf-power. The ECWR discharge also increases the metal ionized flux fraction of about 30% especially in the region of lower pressures. Further, the suppression of the gas rarefaction effect due to enhanced secondary electron emission of Me2+ was observed.

Ion optical effects in a low pressure rf plasma

Ion optical effects in low pressure gas discharges are introduced as a novel input into low pressure plasma technology. They are based on appropriate geometrical plasma confinements which enable a control of the shape of internal density and potential distributions and, hence, the ion motion in the plasma bulk. Such effects are exemplified for an electron cyclotron wave resonance plasma in Ar at 1–5 × 10−3 millibars. The geometry of the plasma chamber is modified by a conical and a cylindrical insert. Computer simulations display spherical plasma density contours to be formed around the conical confinement. This effects an increase of the ratio of the ion currents into the conical and the cylindrical inserts which depends on the fourth power of the plasma electron temperature. A quantitative understanding of this behavior is presented. As another essential result, the shape of the internal plasma contours is found to be independent of the pressure controlled plasma parameters.

Deposition of rutile (TiO2) with preferred orientation by assisted high power impulse magnetron sputtering

The effect of energetic ion bombardment on TiO2 crystallographic phase formation was studied. Films were deposited using high-power impulse magnetron sputtering (HiPIMS) assisted by an electron cyclotron wave resonance (ECWR) plasma. The ECWR assistance allows a significant reduction of pressure down to 0.075Pa during reactive HiPIMS deposition and subsequently enables control of the energy of the deposited species over a wide range. Films deposited at high ion energies and deposition rates form rutile with (101) a preferred orientation. With decreasing ion energy and deposition rates, rutile is formed with random crystallite orientation, and finally at low ion energies the anatase phase occurs. It is supposed that particles gain high energy during the HiPIMS pulse while the ECWR discharge is mostly responsible for substrate heating due to dissipated power. However, the energetic contribution of the ECWR discharge is not sufficient for annealing and phase transformation.

Plasma diagnostics of low pressure high power impulse magnetron sputtering assisted by electron cyclotron wave resonance plasma

This paper reports on an investigation of the hybrid pulsed sputtering source based on the combination of electron cyclotron wave resonance (ECWR) inductively coupled plasma and high power impulse magnetron sputtering (HiPIMS) of a Ti target. The plasma source, operated in an Ar atmosphere at a very low pressure of 0.03 Pa, provides plasma where the major fraction of sputtered particles is ionized. It was found that ECWR assistance increases the electron temperature during the HiPIMS pulse. The discharge current and electron density can achieve their stable maximum 10 μs after the onset of the HiPIMS pulse. Further, a high concentration of double charged Ti++ with energies of up to 160 eV was detected. All of these facts were verified experimentally by time-resolved emission spectroscopy, retarding field analyzer measurement, Langmuir probe, and energy-resolved mass spectrometry.

Highly ionized physical vapor deposition plasma source working at very low pressure

Highly ionized discharge for physical vapor deposition at very low pressure is presented in the paper. The discharge is generated by electron cyclotron wave resonance (ECWR) which assists with ignition of high power impulse magnetron sputtering (HiPIMS) discharge. The magnetron gun (with Ti target) was built into the single-turn coil RF electrode of the ECWR facility. ECWR assistance provides pre-ionization effect which allows significant reduction of pressure during HiPIMS operation down to p = 0.05 Pa; this is nearly more than an order of magnitude lower than at typical pressure ranges of HiPIMS discharges. We can confirm that nearly all sputtered particles are ionized (only Ti+ and Ti++ peaks are observed in the mass scan spectra). This corresponds well with high plasma density ne ∼ 1018 m−3, measured during the HiPIMS pulse.

Chemical structure and mechanical properties of Si-containing a-C:H and a-C thin films and their Cr- and W-containing derivatives

Si-containing a-C:H and a-C thin films with nitrogen, oxygen and transition metal (Cr and W) additives were deposited on polished single crystalline silicon substrates at room temperature by plasma activated CVD, magnetron-sputtering PVD and also by combined PACVD–PVD techniques.In particular Si–, Si–O– and Si–N-containing a-C:H films (denoted as a-C–Si, a-C–Si–O and a-C–Si–N) were deposited respectively from tetramethylsilane (TMS), hexamethyldisiloxane and hexamethyldisilazane vapourised precursors in He carrier gas by electron cyclotron wave resonance RF plasma. Cr-containing a-C:H films, further denoted as a-C–Si–Cr, were deposited with combined PVD–PACVD by sputtering chromium and carbon targets in argon and introducing TMS vapour. Wcontaining a-C films (denoted as a-C–Si–W) were deposited by PVD with simultaneous sputtering of the constituents in Ar. Detailed characterisation of the composition and chemical state of the elements present in the films were done by X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy. Mechanical properties, hardness (H), reduced modulus (E) and scratch behaviour were studied by depth-sensing nanoindentation and scratch tests.In the a-C:H films, the C/Si ratio varied between 1.5 and 3.5 showing a significant deficiency of C as compared to the composition of the precursors. The Cr and W content in the a-C–Si–Cr and a-C–Si–W films varied in a very broad 2–50at.% range.The chemical state of carbon was primarily of sp2 and partly of sp3 type C–C with XPS chemical shifts for C 1s at 284.3eV and 285.0eV, respectively. The Si in the films is bonded predominantly to carbon (Si 2p at 100.8eV BE) or to nitrogen in N-containing films (Si 2p at 101.3eV BE). In the a-C–Si–Cr films Cr–C bonding states were determined (Cr 2p3/2 at 574.5eV and C 1s at 282.8eV). Si formed predominantly Si–C and also Si–Cr bonds. In the a-C–Si–W, films C–Si and C–W (W 4f7/2 at 32.3eV) chemical bonds could be identified.It was discovered that the modified Auger parameter for silicon, αSi (derived from the Si 2p electron and Si KLL Auger line energy), sensitively reflects the entire chemical structure of these films, including crosslinking and densification. These spectroscopic data, supported further by the increase of the bulk plasmon loss energy of the C 1s peak, were directly connected with the mechanical properties of these films. The amorphous nature of the films was deduced from the chemical state analysis and was verified also by transmission electron microscopy (TEM) and electron diffraction (ED) studies.Hardness and elastic modulus of the a-C–Si–(O,N) films could be adjusted in a wide range of approx. 5–15GPa and 40–140GPa, respectively. Systematic alteration of these values with the composition (C/Si, O/Si and N/Si atomic ratio) and with the chemical structure (αSi) was established and their interrelations are discussed. Whilst incorporation of Cr does not alter the mechanical properties, the addition of W increases H and E up to 19GPa and 210GPa, respectively.

Simulation of cylindrical electron cyclotron wave resonance argon discharges

A fluid model of a cylindrical electron cyclotron wave resonance (ECWR) argon discharge is presented. The results for a 1 mTorr argon discharge were checked against the analytical theory, simulation and experimental data. The basic plasma properties as power dissipation, magnetic field, electric potential, electron density and temperature were very well reproduced using predefined boundary conditions for the magnetic potential. The results of this model were further used as inputs for the simulation of plasma expansion into a diffusion region, allowing thus fast and complete modelling of a typical ECWR plasma reactor.

Wear and corrosion behaviour of HVOF WC–CoCr/CVD DLC hybrid coating systems deposited onto aluminium substrate

Hybrid coating systems consisting of a HVOF-sprayed WC–CoCr interlayer (75 μm or 125 μm thick) and a thin DLC-based top layer (obtained by electron cyclotron wave resonance–chemical vapour deposition: ECWR-CVD) were deposited onto AA6082-T6 substrates; their tribological and anti-corrosion performances were evaluated and compared to those of the DLC film deposited directly onto the Al alloy substrate without interlayer. In scratch adhesion testing, the interlayer delays the onset of cracking and spallation of the film, because it provides better mechanical support than the bare Al substrate. As soon as cracking begins, however, complete delamination of the films deposited on cermet interlayers occurs, revealing limited interface adhesion. Accordingly, in ball-on-disk wear tests, the films deposited on cermet interlayers can stand more severe contact conditions without cracking, but, as the contact pressure increases, most of the film delaminates. If no cracking occurs, the film is very effective at producing low wear and low friction, but it is not as effective at preventing penetration of corrosive agents, as shown by corrosion tests in aqueous environments, because it contains some small defects.

Theoretical background and some applications of ECWR-plasmas

Plasma excitation by Electron Cyclotron Wave Resonance ECWR which makes use of a special branch of the dispersion relations of electromagnetic waves in a weakly anisotropic medium is explained on the basis of tensorial electrodynamics. The technical performance of the production of electrodeless low pressure plasmas by ECWR is described, and applications of such plasmas for postionization purposes in surface mass spectrometry SNMS, broad beam ion sources and plasma reactors for PECVD are briefly discussed.

Ion energy distribution of an inductively coupled radiofrequency discharge in argon and oxygen

We report an experimental investigation of the ion energy distribution in an inductively coupled electron cyclotron wave resonance (ECWR) discharge with a superimposed static magnetic field. The inductively coupled discharge is sustained by applying a 13.56MHz radiofrequency (RF) power to an aluminium single-turn coil located inside the vacuum chamber. The source region was separated by a grid from the diffusion region. Ion energy distribution (IEDF) measurements employing an energy-dispersive mass spectrometer or plasma process monitor (PPM) whose entrance opening was 15cm away from the grid were performed in the diffusion region. The IEDF is composed of two peaks; a low-energy peak due thermalized ions and a high-energy peak due to ions coming directly from the source region without undergoing thermalization. The energetic difference between the groups thus reflects the plasma potential difference between the source region and the diffusion region. The pronounced intensity variation of the high-energy peak with increasing pressure is caused by charge-changing collisions yielding a depletion of the high-energy ions with increasing effective path length.

Fluid Model of an Electron Cyclotron Wave Resonance Discharge

A fluid model of a planar electron cyclotron wave resonance argon discharge is presented. The results for a 15-mtorr argon discharge are checked against the particle in cell/Monte Carlo (PIC/MC) simulation results by R. Krimke <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al</i> . and are also compared to the analytical theory and experimental data by B. Pfeiffer. The application of a specific boundary condition for the magnetic potential, the use of an effective electron collision frequency that includes plasma nonuniformities, and the coupled solution of the electrostatic field were found to be essential parameters leading to the agreement of the fluid code with both experimental and PIC/MC findings.

Composition, structure and nanomechanical properties of C–Si–N thin films deposited by ion implantation assisted plasma beam CVD

Si- and N-containing a-C:H films were deposited from tetramethylsilane (TMS) vapour and nitrogen onto silicon wafers by an electron cyclotron wave resonance (ECWR) RF plasma beam CVD with simultaneous pulsed N 2 + and Ar + ion bombardment in a plasma immersion ion implantation (PIII) apparatus. Chemical composition and bonding states of the constituent elements were characterised by X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (XAES). Mechanical properties were studied by depth-sensing nanoindentation measurements. Compared to the C / Si = 4 ratio of the precursor, significant loss of C occurred during deposition, resulting in C / Si ranging from 2.39 to 2.90. This effect was most pronounced at low (< 200 V) and high (> 1000 V) self-bias values. Incorporation of nitrogen was significant, resulting in typical N / Si values from 0.7 to 0.9. Formation of extended silicon or silicon carbide clusters could not be detected. The hardness and the reduced modulus of the layers, having maximum values up to 14 and 145 GPa, respectively, decreased with increasing N / Si atomic ratio. C–Si–N layers grown with the application of PIII were characterised by decreased hardness and reduced modulus as compared to those of the layers grown without PIII.

Surface and nanomechanical properties of Si:C:H films prepared by RF plasma beam CVD

Si-, SiO x- and SiN x-containing a-C:H films (denoted as DLCSi, DLCSiO and DLCSiN) were deposited respectively from tetramethylsilane, hexamethyldisiloxane and hexamethyldisilazane precursors onto silicon wafer and aluminium substrates, using electron cyclotron wave resonance (ECWR) plasma beam CVD. Surface chemical analysis was performed by X-ray photoelectron spectroscopy and X-ray induced Auger electron spectroscopy. Nanomechanical properties like hardness and reduced modulus were determined by the nanoindentation method. For the DLCSi layers the C/Si ratio increased with the increase of the self-bias. Nanohardness and reduced modulus had a strong tendency to increase with increasing C/Si. The modified Auger parameter for silicon (Si α) and the bulk plasmon loss energy of the C 1s peak ( E p) also increased with C/Si. For the whole set of Si-containing a-C:H film samples a correlation has been established between Si α and E p.