Carbon Sputtering Research Articles

Fatigue Crack Nucleation Studies on Sulfuric Acid Anodized 7075-T73 Aluminum

The influence of a sulfuric acid anodic coating process on the fatigue crack nucleation behavior of 7075-T73 aluminum alloy was investigated. Silicone surface replication in combination with carbon sputter coating and scanning electron microscopy (SEM) allowed for in situ monitoring of the number of cycles for crack nucleation. A single edge circular notch (SECN) coupon was designed for the present study to localize fatigue damage thus enhancing fatigue crack detection and capture the effects of multiaxial stress conditions indicative of a majority engineering applications. Linear elastic finite element modeling of the SECN coupon was performed to quantify the von Mises equivalent stress distribution and the stress concentration factor of the notched region. The experimental results indicate that the presence of localized pitting corrosion initiated during the anodic coating pretreatment process had an adverse effect on fatigue performance. Specifically, multiple crack nucleation sites were evident as opposed to a single crack origin for the untreated specimens. Post-cycling SEM surface examinations displayed networks of micro-cracks in the anodic coating emanating from the pits although these were not found to be fatigue crack origin sites during post SEM fractographic exams. Thus, the stress concentration effect of the corrosion pits was found to be predominant. The total cycles to failure on average was reduced by approximately 60% for the anodic coated versus untreated specimens. A strategy is also discussed on how to mitigate accelerated crack nucleation by controlled surface pretreatment and use of a chromated chemical conversion coating in lieu of an anodic coating for selective applications.

Chemical sputtering of graphite by low temperature nitrogen plasmas at various substrate temperatures and ion flux densities

We report measurements of chemical sputtering yields of graphite exposed to low temperature nitrogen plasmas. The influence of surface temperature and incoming ion energy on the sputtering yields has been investigated in two distinct ion flux density regimes. Sputtering yields grow consistently with increasing temperatures in experiments with low flux density (Γi≈1020 m−2s−1−1021 m−2s−1) and high flux density (Γi≈1023 m−2s−1). Moreover, empirical fitting of the data suggests that the temperature of 670 °C is optimal for chemical sputtering at high flux density. Negative biasing of the samples was used to vary the ion energy in the low flux density regime. The sputtering yield in this case increases from 0.07 atoms/ion for Ei = 1.5 eV to 0.19 atoms/ion for Ei = 35 eV. After taking into account the dependence of the yields on temperature and ion energy, we evidenced a flux dependence of sputtering, similar to that found for chemical sputtering of carbon by hydrogen.

Carbon Ion Production Using a High-Power Impulse Magnetron Sputtering Glow Plasma

The ionization rate of sputtered carbon species in magnetron sputtering glow plasmas is low because of a low sputtering yield, a high ionization energy and a low reaction rate between the carbon and electron in the plasma. In this paper, efficient ionization of sputtered carbon species is realized in high-power impulse magnetron sputtering (HiPIMS) glow plasma. The arrangement of the permanent magnet placed at the back of the target can recover the above issues, which enables a power consumption as high as over 100 kW with a pulse duration as short as 5.5 μs at a source voltage as high as 2200 V. The magnet arrangement affects the production zone of the HiPIMS glow plasma on the target; the plasma moves outward to the radial direction of the target with an increased number of the inner magnets. When the plasma has a larger diameter on the target, a glow easily transits to an arc discharge even at a lower voltage compared with the case of the small-diameter plasma production, because the distance between the plasma and the grounded plate becomes short. Both the highest target voltage without an arc transition and the highest glow current are obtained at n=1, the least number of the inner magnet. In this case, a source voltage of 2200 V brings into the highest instantaneous power of about 144 kW. It is confirmed that higher the source voltage, higher the intensity of the optical emission spectrometry spectrum of carbon ions is. The high power consumption contributes to the high-density argon plasma production. Hence, the least number of the inner magnet results in a higher acceleration energy to bombard the target to efficiently sputter carbon species and a high ion flux bombarding to the target. The longer pulse duration such as 30 μs results in an arc transition at the source voltage as low as 1200 V. Thus, the highest emission intensity of the carbon optical emission obtained for n=1 at 2200 V with 5.5- μs pulse duration. It is observed that the intensities of the optical emission from argon and carbon ions are proportional to the power consumed in the plasma.

Influence of plasma surface interactions on tokamak startup

The startup phase of a tokamak is a complex phenomenon involving burnthrough of the low-Z impurities and rampup of Ip, the plasma current. The design considerations of a tokamak are closely connected with the startup modeling. Plasma evolution is analysed using a zero-dimensional model. The particle and energy balance is considered of two subclasses of plasmas which are penetrable by neutral gas, together with another component, neutrals trapped in the wall. The first subclass includes plasmas being penetrated by slow neutrals of (∼few eV) temperature. The second includes plasmas being penetrated only by fast neutrals having a temperature comparable to that of the ions. The impact of impurities on energy balance is considered through their generation by ion induced desorption of adsorbed oxygen on the first wall and physical and chemical sputtering of carbon. The paper demonstrates self-consistently that the evolution of initial phase of the discharge is intimately linked to the condition of the plasma facing components (PFCs) and the resultant plasma surface interactions.

Influence of sputtering carbon top-layer on lithium storage performance of amorphous Ni–P films from ionic liquid

Amorphous Ni–P–C films are fabricated by combining the electrodeposition of Ni–P films from a eutectic-based ionic liquid and the direct current magnetron sputtering of amorphous carbon top-layer. The carbon top-layer with a thickness of about 10nm is homogeneously coated on the surface of the Ni–P films. A comparison study is undertaken between Ni–P and Ni–P–C films to evaluate the microstructure and the electrochemical performances of the composite films as anode materials for lithium ion batteries, which allow the decoupling of the effect of the carbon layer. It is found that at lower discharge–charge current densities, the cyclability of both Ni–P and Ni–P–C films is similar. As the discharge–charge current density increases, the Ni–P–C film exhibits improved capability and reversibility over the Ni–P film. The Ni–P–C film delivers an initial discharge capacity of 1060mAhg−1 at 250mAg−1 and the capacity retention after 50 cycles is 62%, much higher than that of the Ni–P film (51%). The cyclability of Ni–P–C film at different discharge–charge current densities from 200 to 500mAg−1 is also much better than those of Ni–P film. This study indicates that the introduction of a carbon top-layer on Ni–P film could significantly improve the electrochemical performances due to the decreased interface electric resistance and the structure stability.

Diamond-like carbon sputtering by laser produced Xe plasma

The sputtering of diamond-like carbon (DLC) was investigated using Xe ion bombardment from the laser plasma X-ray source (LPX). The LPX we developed uses a solid Xe target and emits UV–X-rays and Xe ions. Using the LPX as an ion source, we measured etching depths of DLC, Ru, and Au films using a quartz crystal microbalance (QCM) to determine their ion sputtering rates at incident angles of 0° and 70°. The calculated results by the SRIM code were able to predict the measured results, except for the case of the DLC film at 0° incident. Our measured result indicated that the DLC sputtering at 0° was ten times larger than previously reported data, in which an ion gun was used. We consider that the difference was a characteristic effect of the laser plasma, and can be explained as a synergistic effect of ion bombardment and UV radiation from the Xe plasma.

Characterisation of plasma breakdown at JET with a carbon and ITER-like wall

The recent installation of a full metal, ITER-like, first wall provided the opportunity to study the impact of the plasma-facing materials on plasma initiation or breakdown. This study for the first time presents a full experimental characterisation of tokamak breakdown at JET, using all discharges since 2008, covering both operations with a main chamber carbon and a beryllium ITER-like main chamber wall. It was found that the avalanche phase was unaffected by the change in wall material. However, changes in out-gassing by the wall and lower carbon levels resulted in better controlled density and significantly lower radiation during the burn-through phase with the ITER-like wall. Breakdown failures, that usually developed with a carbon wall during the burn-through phase (especially after disruptions) were absent with the ITER-like wall. These observations match with the results obtained from a new model of plasma burn-through that includes plasma–surface interactions (Kim et al 2012 Nucl. Fusion 52 103016). This shows that chemical sputtering of carbon is the determining factor for the impurity content, and hence also radiation, during the burn-through phase for operations with a carbon wall. As seen experimentally, with a beryllium main wall, the plasma surface effects predicted by the model do not raise the radiation levels much above those expected for pure deuterium plasmas. With the ITER-like wall, operation with higher pre-fill pressures, and thus higher breakdown densities, was possible, which helped maintaining the density after breakdown.

Enhancing the Sensitivity of Molecular Secondary Ion Mass Spectrometry with C60+-O2+ Cosputtering

In the past decade, the C60-based ion gun has been widely utilized in the secondary ion mass spectrometry (SIMS) analysis of organic and biological materials because molecular secondary-ions of high masses could be generated by cluster-ion bombardment. This technique furthers the development of SIMS in bioanalysis by eliminating the need for either heteroatom or isotope labeling. However, the intensity of high-mass parent ions was usually low and limited the sensitivity of the analysis, thus requiring an enhancement in the intensity of these molecular ions to widen the application of SIMS. In this work, the aim was to preserve samples in their original state while using a low kinetic energy O2(+) beam cosputtered with high-energy C60(+) to enhance the ion intensity through the depth-profile. Although O2(+) is generally used to enhance ion intensities in positive SIMS, it is known to alter the chemical structure and primarily provide elemental information; hence, it is not suitable for profiling organic and biological specimens. Nevertheless, owing to its high sputtering yield, cluster C60(+) ion removes and masks the structural damage, hence O2(+) may be used to enhance the ion intensity. The characteristic molecular ions of polyethylene terephthalate (PET), trehalose, and a peptide (papain inhibitor) are enhanced by 35×, 12×, and 3.5× with the use of the auxiliary O2(+) beam, respectively. This significant enhancement in ionization yield is attributed to the oxidation of molecules and formation of a hydroxyl group that serves as a proton donator. In addition to enhancing molecular SIMS signals, C60(+)-O2(+) cosputtering could also alleviate several problems, including sputtering rate decay, carbon deposition, and surface roughening, that are associated with C60(+) bombardment and produced better depth profiles.

Structure, Optical and Mechanical Properties of Direct Current Magnetron Sputtered Carbon: Vanadium Nanocomposite Thin Films

Structure, Optical and Mechanical Properties of Direct Current Magnetron Sputtered Carbon: Vanadium Nanocomposite Thin Films

Ion mass spectrometry investigations of the discharge during reactive high power pulsed and direct current magnetron sputtering of carbon in Ar and Ar/N2

Ion mass spectrometry was used to investigate discharges formed during high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS) of a graphite target in Ar and Ar/N2 ambient. Ion energy distribution functions (IEDFs) were recorded in time-averaged and time-resolved mode for Ar+, C+, N2+, N+, and CxNy+ ions. An increase of N2 in the sputter gas (keeping the deposition pressure, pulse width, pulse frequency, and pulse energy constant) results for the HiPIMS discharge in a significant increase in C+, N+, and CN+ ion energies. Ar+, N2+, and C2N+ ion energies, in turn, did not considerably vary with the changes in working gas composition. The HiPIMS process showed higher ion energies and fluxes, particularly for C+ ions, compared to DCMS. The time evolution of the plasma species was analyzed for HiPIMS and revealed the sequential arrival of working gas ions, ions ejected from the target, and later during the pulse-on time molecular ions, in particular CN+ and C2N+. The formation of fullerene-like structured CNx thin films for both modes of magnetron sputtering is explained by ion mass-spectrometry results and demonstrated by transmission electron microscopy as well as diffraction.

Temperature and chemical sensitivity of carbon films on quartz

Insulating to conductive carbon films were obtained by controlled vacuum annealing of the disordered carbon films deposited on quartz by sputtering of carbon. The change of conductance of the films has been studied on exposure to the vapors of NH3 and NO2, chosen for their opposite donor–acceptor properties. The chemical sensitivity of conductance along with temperature sensitivity is discussed in terms of atomic ordering of the as-deposited films induced by heating at high temperatures and revealed by Raman scattering measurements. The observed dependence of conductance on temperature is explained by a model based on the charge tunneling through thermal vibrational barriers, the average height and width of which change with atomic ordering. Phenomenological description of chemical sensing by the films is given in terms of the time constant τ and the maximum relative change in conductance β, related to the surface and material properties of the films respectively. The expression σ=β/τ is considered a measure of the chemical sensitivity of the films and changes with modifications in the material structure of the films on annealing.

Micromorphological observation of bacterial biofilms on ciliated epithelia of chronic rhinosinusitis

To observe the micromorphological characteristic of bacterial biofilm on mucosa of chronic rhinosinusitis (CRS). Mucosa samples of middle turbinate were obtained from 4 patients of CRS during ESS. The size of each sample was about 4 mm x 4 mm. The samples were fixed in 4% paraformaldehyde for 24 hours, then fixed in 1% osmium tetroxide for 2 hours, graded dehydration with ethanol, dried with carbon dioxide and sputter coated with gold. The ultrastructure of these samples was observed by scanning electron microscope. Bacterial biofilms were found on samples in all 4 patients. The biofilms were mainly formed on the surface of cilia. The bacterial flagella and cilia were intertwined. The biofilms could be found in a lot kinds of bacterial infections or mixed infections which were caused by multiple bacteria and fungi. Bacterial biofilm could be formed on ciliated epithelia.

MD Study on Carbon Sputtering and Redeposition

MD Study on Carbon Sputtering and Redeposition

Magnetotransport properties of Co-C granular thin films depending on the carbon sputtering power

AbstractCoxC1-x granular films were deposited on Si substrates by a co-sputtering method. A large negative MR of 30.3% was obtained at 2 K for the sample prepared with the sputtering power of 50 W (C) and 4 W (Co). We have studied structural properties of Co-C granular films by Raman spectroscopy. Two peaks (D and G modes) from carbon bonds were clearly observed, and the intensity ratio of two peaks changed with the sputtering power, suggesting that the graphitization was promoted with the sputtering power. It was also revealed that the transport mechanism changed from tunneling to Mott’s variable range hopping and MR decreased with the sputtering power.

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.

Copper Filling of Deep Sub-μm Through-Holes and Trenches by Using High-Vacuum Magnetron Sputtering and Supercritical Carbon Dioxide

Two methods of copper (Cu) filling into through-holes and trenches with various barrier metals were investigated: high-vacuum magnetron sputtering and the supercritical carbon dioxide method. In spite of good Cu-filling by using the supercritical carbon dioxide method, adhesion of the Cu films to the barrier metals worsened with relative resistivity. Examples of Cu-filling by both high-vacuum magnetron sputtering and the supercritical carbon dioxide method for obtaining good adhesion to the barrier metals are shown.

Influence of carbon sputtering power on structure, corrosion resistance, adhesion strength and wear resistance of platinum/ruthenium/nitrogen doped diamond-like carbon thin films

Platinum/ruthenium/nitrogen doped diamond-like carbon (PtRuN-DLC) thin films were deposited on conductive p-Si substrates using a DC magnetron sputtering deposition system by varying carbon sputtering power. The chemical composition, bonding structure, surface morphology and adhesion strength of the PtRuN-DLC films were investigated using X-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy, atomic force microscopy (AFM), and micro-scratch test, respectively. The corrosion behavior of the PtRuN-DLC films in a 0.1 M NaCl solution was investigated using potentiodynamic polarization test. The corrosion results indicated that the corrosion resistance of the PtRuN-DLC films increased with increased carbon sputtering power probably due to decreased porosity level in the films with increased growth rate and film thickness. The wear performance of the PtRuN-DLC films was investigated with a ball-on-disc micro-tribometer. It was found that the increased carbon sputtering power significantly improved the wear performance of the films by enhancing the adhesion strength of the films.

Modelling of dust grain formation in a low-temperature plasma reactor used for simulating parasitic discharges expected under tokamak divertor domes

The presence of nanostructured dust particles has been reported in thermonuclear fusion reactors with carbon plasma-facing components. These particles contribute to tritium retention and pollution of the edge plasma. Understanding the way these particles can grow in the plasma phase is necessary for designing engineering solutions that avoid or at least limit their formation. As a first step towards this goal, this paper presents a numerical study of the formation of dust in a simple model laboratory electrical discharge: a dc discharge generated in argon with a graphite electrode. The aim here is to investigate whether carbon sputtering through ion and fast neutral bombardment of the cathode and subsequent molecular growth of carbon clusters and particle nucleation and development can explain dust formation in this model discharge. Results show that field reversal effects and negative cluster formation and trapping can fully explain dust formation in such a dc discharge.

Chemical sputtering of carbon and graphite materials in oxygen plasma flows

Chemical sputtering of different types of carbon and graphite materials in oxygen plasma flows with particle energies lower than 100 eV is investigated. The dependence of the chemical sputtering coefficient for undoped materials on the structure is weakly expressed. The sputtering coefficient of boron-doped materials decreases with their degree of doping. The surface relief of some carbon materials is studied with the help of a scanning electron microscope.

Electrostatic quadrupole plasma mass spectrometer measurements during thin film depositions using simultaneous matrix assisted pulsed laser evaporation and magnetron sputtering

A hybrid plasma deposition process, combining matrix assisted pulsed laser evaporation (MAPLE) of carbon nanopearls (CNPs) with magnetron sputtering of gold was investigated for growth of composite films, where 100 nm sized CNPs were encapsulated into a gold matrix. Composition and morphology of such composite films was characterized with x-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy (TEM) analysis. Carbon deposits on a gold magnetron sputter target and carbon impurities in the gold matrices of deposited films were observed while codepositing from gold and frozen toluene-CNP MAPLE targets in pure argon. Electrostatic quadrupole plasma analysis was used to determine that a likely mechanism for generation of carbon impurities was a reaction between toluene vapor generated from the MAPLE target and the argon plasma originating from the magnetron sputtering process. Carbon impurities of codeposited films were significantly reduced by introducing argon-oxygen mixtures into the deposition chamber; reactive oxygen species such as O and O+ effectively removed carbon contamination of gold matrix during the codeposition processes. Increasing the oxygen to argon ratio decreased the magnetron target sputter rate, and hence hybrid process optimization to prevent gold matrix contamination and maintain a high sputter yield is needed. High resolution TEM with energy dispersive spectrometry elemental mapping was used to study carbon distribution throughout the gold matrix as well as embedded CNP clusters. This research has demonstrated that a hybrid MAPLE and magnetron sputtering codeposition process is a viable means for synthesis of composite thin films from premanufactured nanoscale constituents, and that cross-process contaminations can be overcome with understanding of hybrid plasma process interaction mechanisms.