Sputtered Carbon Films Research Articles

The Effect of Thermal Exposure on Change in the Chemical Composition of the Surface Layers of a Titanium Alloy with a Sputtered Carbon Film after Irradiation with N+ Ions

The Effect of Thermal Exposure on Change in the Chemical Composition of the Surface Layers of a Titanium Alloy with a Sputtered Carbon Film after Irradiation with N+ Ions

Immersion infrared reflection‐absorption spectroscopy studies on diamond‐like carbon surfaces. I. Formation of electrophilic groups on surfaces of amorphous carbon films aging in ambient air

AbstractTo study chemical functional groups on surfaces of diamond‐like carbon (DLC) films, a highly sensitive infrared reflection‐absorption spectroscopic technique, immersion infrared reflection‐absorption spectroscopy (IRRAS), is applied in the present study. The method employs (i) a conventional attenuated total reflection (ATR) accessory with a Ge crystal as an immersion medium and (ii) an aluminum underlayer beneath the 50–70 nm thick DLC film. Sensitivity, selectivity, and quantifiability of the method can be enhanced by chemical derivatization (CD), coupling chemical moieties with strong characteristic vibrational bands to specific functional groups on the DLC surface. The method is applied to amorphous sputtered carbon films (a‐C) to demonstrate that electrophilic groups, most probably epoxy groups, are formed during aging under ambient conditions.

Nanocarbon film electrodes for electro-analysis and electrochemical sensors

Carbon films fabricated by sputtering and a related vacuum technique have unique features as regards electrochemical performance including relatively high electrochemical activity, and a wide potential window with low noise, in addition to low cost and the capacity for fabrication with any shape and size. Various applications for detecting environmental and biochemical molecules have been reported in recent years. This review focuses on the fabrication, structure, and electrochemical properties of carbon film electrodes. The review also introduces applications of carbon, heteroatom doped and surface terminated carbon film electrodes for heavy metal detection, biomolecular sensing, and DNA methylation level quantitative analysis. • Sputtered carbon films are introduced including their structure, electrochemical performance, and application. • The potential window of the carbon films increases by increasing sp 3 concentrations. • The electrochemical activity of carbon films depends on the nanocrystalline structure and surface functional groups. • A variety of the applications are introduced including detection of small biochemicals, DNAs and environmental pollutants.

Model electrocatalysts for the oxidation of rechargeable electrofuels - carbon supported Pt nanoparticles prepared in UHV

Isopropanol (IPA) can be used as a rechargeable electrofuel. In this approach, IPA is oxidized to acetone (ACE) in a direct alcohol fuel cell and the formed ACE is subsequently back-converted to IPA in a heterogeneously catalyzed process. To study the electrochemical reaction mechanisms of the IPA oxidation at the molecular level, appropriate and well-defined model electrocatalysts are necessary. In this work we prepare such model electrocatalysts by surface science methods in ultra-high vacuum (UHV). The catalysts consist of well-defined platinum nanoparticles on carbon supports. As carbon support, we use flat highly ordered pyrolytic graphite (HOPG) and thin (20 nm) magnetron sputtered carbon films on a polycrystalline gold substrate. In a first step, we characterize the model electrocatalysts and investigate their stability in-situ with complementary methods, i.e. by electrochemical scanning tunneling microscopy (EC-STM), electrochemical on-line inductively coupled plasma mass spectrometry (ICP-MS) and CO stripping experiments followed by electrochemical infrared reflection absorption spectroscopy (EC-IRRAS). We determined a stability window ranging from -0.65 VRHE to 1.15 VRHE for both sample types, independent of the presence or absence of IPA in the electrolyte. In the second step, we study the oxidation of IPA on tPt nanoparticles using differential electrochemical mass spectrometry (DEMS) and EC-IRRAS. The onset of IPA oxidation is observed at 0.3 VRHE. ACE is formed with high selectivity, while we identify traces of CO2 as the only side-product formed at higher potentials. However, we do not observe any formation of adsorbed CO. A direct comparison of these results with previous work on Pt(111) suggests that low coordinated Pt sites and size effects play a subordinate role for IPA oxidation on Pt electrocatalysts.

Tailored Hydrogen-Free Carbon Films by Tuning the sp2/sp3 Configuration

Carbon configuration is a critical factor in determining the electrical, tribological, and mechanical properties of carbon films. In this work, we synthesized carbon films on a silicate glass by sputtering a graphite target in an Ar atmosphere while varying the DC sputtering power. Using Raman spectroscopy and photoemission analysis, we found that the carbon films produced at low sputtering power consisted mainly of sp3 bonds, while sp2 carbon ordering became dominant as the sputtering power increased. The sp2/sp3 ratio of the carbon film controlled by the sputtering power is associated with two competing carbon deposition mechanisms: (1) collision between the incoming carbon ions and surface carbon atoms at low power (sub-plantation model) and (2) sp3-to-sp2 rehybridization caused by excessive kinetic energy of the incoming carbon ions at high power (thermal relaxation). As the sputtering power increased, the friction, adhesion, and energy dissipation decreased, despite negligible topographical variations, while the conductivity rapidly increased. We fabricated a triboelectric nanogenerator with high durability by utilizing the low friction properties of the sputtered carbon films. Our results show a straightforward and effective way to control the properties of carbon films, which can be used as promising coating films for frictionless protection.

The Basic Electrochemical Properties and Structure of Direct Current Magnetron Sputtered Carbon Films

The Basic Electrochemical Properties and Structure of Direct Current Magnetron Sputtered Carbon Films

Sputtered carbon as a corrosion barrier for x-ray detector windows

Sputtered amorphous carbon thin films were explored as corrosion resistant coatings on aluminum thin films to be incorporated into x-ray detector windows. The requirements for this application include high corrosion resistance, low intrinsic stress, high strains at failure, and high x-ray transmission. Low temperature sputtering was used because of its compatibility with the rest of the window fabrication process. Corrosion resistance was tested by exposure of carbon coated and uncoated Al thin films to humidity. Substrate curvature and bulge testing measurements were used to determine intrinsic stress and ultimate strain at failure. The composition and bonding of the carbon films were further characterized by electron energy loss spectroscopy, Raman spectroscopy, and carbon, hydrogen, and nitrogen elemental analyses. Samples had low compressive stress (down to.08 GPa), a high strain at failure (3%), and a low fraction of sp3 carbon–carbon bonds (less than 5%). The high breaking strain and excellent x-ray transmission of these sputtered carbon films indicate that they will work well as corrosion barriers in this application.

The electrochemical reaction of lithium with high-capacity dense sputtered carbon

Carbon films were prepared by DC magnetron sputtering at various argon pressures ranging from 1 to 30mTorr. The film sputtered at the lowest pressure (1mTorr) was fully amorphous, showing no evidence of the (002) Bragg diffraction peak, and a density of 1.9±0.3g/cc, indicating little, if any, porosity. The film sputtered at the highest pressure (30mTorr) showed a weak and broad (002) Bragg peak and had a density of 1.35±0.15g/cc, indicating significant porosity. The low pressure sputtered films were almost pure carbon (<1% O by weight) while the high pressure sputtered carbon films contained between 13% and 21% O by weight (depending on the measurement method) which was presumably incorporated when the porous films were exposed to air after sputtering. Electrochemical testing in Li/carbon film cells showed that the low pressure sputtered carbon had a reversible specific capacity of about 800mAh/g between 5mV and 2V, an irreversible capacity of 200mAh/g and an average delithiation potential of about 1V vs. Li/Li+. Heating the low pressure sputtered carbon to 900°C in argon decreased the reversible capacity, the irreversible capacity and the average voltage to 600mAh/g, 100mAh/g and 0.75V, respectively. Since the density of these films is almost as large as graphite, these unheated materials have volumetric capacities near 1600mAh/cm3 while the heated materials are near 1200mAh/cm3.

Improvement of corrosion resistance and electrical conductivity of 304 stainless steel using close field unbalanced magnetron sputtered carbon film

Carbon film has been deposited on 304 stainless steel (SS304) using close field unbalanced magnetron sputter ion plating (CFUBMSIP) to improve the corrosion resistance and electrical conductivity of SS304 acting as bipolar plates for proton exchange membrane fuel cells (PEMFCs). The corrosion resistance, interfacial contact resistance (ICR), surface morphology and contact angle with water of the bare and carbon-coated SS304 are investigated. The carbon-coated SS304 shows good corrosion resistance in the simulated cathode and anode PEMFC environment. The ICR between the carbon-coated SS304 and the carbon paper is 8.28–2.59 mΩ cm 2 under compaction forces between 75 and 360 N cm −2. The contact angle of the carbon-coated SS304 with water is 88.6°, which is beneficial to water management in the fuel cell stack. These results indicate that the carbon-coated SS304 exhibits high corrosion resistance, low ICR and hydrophobicity and is a promising candidate for bipolar plates.

Temperature Dependence on Structural, Tribological, and Electrical Properties of Sputtered Conductive Carbon Thin Films

Conductive carbon films were prepared at room temperature by unbalanced magnetron sputtering (UBMS) on silicon substrates using argon (Ar) gas, and the effects of post-annealing temperature on the structural, tribological, and electrical properties of carbon films were investigated. Films were annealed at temperatures ranging from <TEX>$400^{\circ}C$</TEX> to <TEX>$700^{\circ}C$</TEX> in increments of <TEX>$100^{\circ}C$</TEX> using a rapid thermal annealing method by vacuum furnace in vacuum ambient. The increase of annealing temperature contributed to the increase of the ordering and formation of aromatic rings in the carbon film. Consequently, with increasing annealing temperature the tribological properties of sputtered carbon films are deteriorated while the resistivity of carbon films significantly decreased from <TEX>$4.5{\times}10^{-3}$</TEX> to <TEX>$1.0{\times}10^{-6}\;{\Omega}-cm$</TEX> and carrier concentration as well as mobility increased, respectively. This behavior can be explained by the increase of sp2 bonding fraction and ordering <TEX>$sp^2$</TEX> clusters in the carbon networks caused by increasing annealing temperature.

An investigation into which factors control the nanotribological behaviour of thin sputtered carbon films

Ultra-thin (20–100 nm) films deposited on Si surfaces can improve their mechanical and tribological properties. As a stepping stone towards the optimization of such ultra-thin films, herein we report experimental nanoscratch and nanowear data on a-C films of thickness in the range 200–1000 nm on Si aiming to (1) understand the role of film thickness on the nanoscratch behaviour, (2) determine whether the same factors (substrate bias, H/E ratio, etc) are at play for thick films as for the thin films, (3) determine possible design rules for thinner films enabling their optimization for MEMS applications and (4) evaluate the use of the multi-pass (3-scan) procedure for clarifying the locus of failure. To a first approximation, the critical load for total film failure in the nanoscratch test is proportional to thickness provided the films are not too stressed. a-C films of 1 µm with very high H/E, deposited under high substrate bias, perform well at low load but very poorly in more highly loaded situations. Not only do they exhibit low critical loads but also failure involves extensive delamination outside of the scratch track. This is not observed on thinner films. A suitable strategy for optimizing wear resistance for thin films for MEMS applications is to aim to maximize H/E. For the 200 nm films studied here, the films with the highest H/E showed slightly improved scratch resistance.

Improved detection limit for an electrochemical γ-aminobutyric acid sensor based on stable NADPH detection using an electron cyclotron resonance sputtered carbon film electrode

We report an electrochemical γ-aminobutyric acid (GABA) sensor with an improved detection limit based on stable β-nicotinamide adenine dinucleotide phosphate (NADPH) oxidation with an extremely low background current using an electron cyclotron resonance (ECR)-sputtered carbon film electrode. The sensor comprised an ECR carbon electrode modified with gabase co-immobilized bovine serum albumin. We obtained stable responses for NADPH without any electrode surface fouling by electrochemically pretreating the ECR carbon electrode because ECR carbon has an extremely flat surface even after pretreatment and increasing the surface oxygen made the surface more hydrophilic thus suppressing oxidized NADPH (NADP +) fouling of the surface. As a result, we obtained a very low detection limit of 10 nM for NADPH, which was more than one order of magnitude better than that of a conventional glassy carbon electrode (250 nM). We also achieved a low detection limit of 30 nM GABA within 2 min by modifying the pretreated ECR carbon electrode with gabase. The proposed electrochemical GABA sensor exhibited a lower detection limit than any previously reported GABA sensor.

21716 可視域レーザ光の高吸収、高断熱固体壁創製に関する研究(薄膜・計測,OS.12 機械工学が支援する微細加工技術(半導体・MEMS・NEMS))

Varying some types of substrate structure, we measured temperature difference near the Ar^+ laser spot (Φ1[mm]) between front surface on which sputtered carbon film was fabricated and rear surface by thermocouple to compare thermal insulation properties. The point we measured was about 2mm far from laser spot and the diameter of thermocouple is 1.3[μm]. It was cleared that we can gain remarkable insulation effect by inserting air layer between front and rear substrate. Maximum temperature difference on 3-layer substrate (top layer: Glass, second layer: Air, third layer: Polyimide, total: 0.558[mm]) was about 4 times increased than single-layer substrate (top layer: Glass, total: 0.152[mm]). Especially, we could find that effect in average expansion speed of temperature difference (0-1[s])

Electrochemical Performance of Angstrom Level Flat Sputtered Carbon Film Consisting of sp2 and sp3 Mixed Bonds

We have developed ultra-flat carbon film electrodes with a wide potential window and a low capacitive current by the electron cyclotron resonance (ECR) sputtering method. The film consists of sp2 and sp3 bonds (sp3/sp2 ratio = 0.702) and is sufficiently conductive for electrochemical measurements without doping. The film has average roughness of 0.7 A, which is much flatter than that of nanocrystalline diamond film. The potential limit of ECR sputtered carbon (current limit < +/-500 muA/cm2) in the positive direction is 2.0 V vs Ag/AgCl, which is slightly lower than that of boron-doped diamond (2.1 V) and much wider than that of a glassy carbon (GC) electrode (1.7 V). In contrast, a much wider potential window can be obtained in the negative direction. The capacitive current is also much lower than that of a GC electrode due to the ultra-flat surface and the low number of oxygen-containing groups at the film surface. ECR sputtered carbon film can be used to measure each base of oligonucleotides by electrochemical oxidation without any pretreatment. The ultra-flat surface and low surface oxygen concentration suppress fouling with electroactive species, such as oligonucleotides, NADH, and bisphenol A.

The characterisation of e-beam evaporated and magnetron sputtered carbon films fabricated for atomic oxygen sensors

Carbon coatings, for atomic oxygen sensor applications, have been deposited onto alumina substrates and subjected to atomic oxygen and various heat treatments. The effect of these treatments has been studied. Carbon was fabricated using two methods: electron-beam (e-beam) evaporation and dc-magnetron sputtering. The carbon films were exposed to 5 eV atomic oxygen (AO) fluences ranging from 0.5×10 19 to 7.9×10 20 atoms cm −2 and their resultant characteristics investigated. E-beam evaporated carbon films were found to be graphitic in content and conducting. The sputtered carbon films were insulating and their resistivity remained high even after high-temperature annealing. From Raman spectroscopy it was possible to determine the I D/ I G ratio in the carbon from the intensity of the characteristic D and G peaks. After AO exposure, Raman spectroscopy shows the appearance of a characteristic D peak in the e-beam evaporated carbon films, implying the formation of sp 3 clusters. For the magnetron sputtered films, the D peak broadened, the broadening being proportional to ordering in the films. A plot of the G peak position with temperature shows the trend in graphitisation as temperature is increased. From XPS analysis, there was an increase in the surface concentration of the O1s peak at the expense of the C1s peak, signifying that the carbon reacts with oxygen atoms. The reaction of carbon to oxygen is not a physical process, but involves the removal of carbon by a chemical process of CO or CO 2, which is lost to the surrounding environment.

Humidity dependence of microwear characteristics of amorphous carbon films on silicon substrates

Influences of environmental humidity on various scanning-scratched wear characteristics, such as long-term stability of wear resistance and load dependence, scratch number dependence and scratch velocity dependence of wear depth, are evaluated by using an atomic force microscope and diamond tips. Amorphous carbon (a-C) films are deposited on silicon substrates by the electron cyclotron resonance plasma (ECR) sputtering method and the RF sputtering method combined with CVD using argon gas containing methane (CH4) as a sputtering gas. In carbon samples with a higher hydrogen content, clear influences of the humidity on various wear characteristics are observed and their wear resistances decrease with increase of the humidity. In the ECR sputtered carbon film with low hydrogen content, wear resistance is stable during long-term exposure to an environment of high temperature and high humidity. In this film, the influences of humidity on the wear resistance and adhesion forces between the films and the substrates are not observed, since it is highly wear resistant and the wear depths are shallow in each test. Thus, amorphous carbon films with low hydrogen content are suitable as wear resistant protective overcoats from the point of view of the wear resistance, in particular the influence of the humidity on the wear resistance including its long-term stability.

Nanoscale electric modification and observation of sputtered carbon films by atomic force microscopy with conductive tip

SPM-based techniques have many applications, such as in the area of high-density data storage. This paper describes our use of an SPM-based read/write technique in which AFM is used to electrically modify the surface of a sputtered carbon film, and electric conductivity imaging of the modification marks is performed with a conductive tip.

Carbon structural transitions and ohmic contacts on 4H-SiC

The structural properties of sputtered carbon films on SiC are investigated using X-ray photoelectron spectroscopy (XPS) and Raman scattering. The as-deposited films are amorphous with an sp2/sp3 ratio of 1. The sp2 carbon structures gradually increase with increasing temperatures and consist of amorphous aromatic-like carbon, polyene-like carbon, and nano-size graphite flakes. Schottky contacts on carbon/SiC are converted to ohmic contacts after annealing. The concentration of nano-graphitic flakes relative to the aromatic-like and polyene-like carbon increases nearly linearly with annealing temperature. Stacked graphitic structures are not observed. The specific contact resistivities are at 10−3–10−4Ωcm2 on the carbon/SiC after annealing from 1050°C to 1350°C.

Effect of deposition and anneal temperature on the resistivity of magnetron sputtered carbon films

Amorphous carbon (a-C) films were deposited by d.c. magnetron sputtering of a graphite target in an argon plasma. The dependence of film resistivity on deposition and anneal temperatures has been studied in the range 20–650 °C. The film structure was examined by Raman spectroscopy and reflective high-energy electron diffraction (RHEED). Films revealed prominent resistivity anisotropy, the degree of which depends on temperature. The change in substrate temperature during deposition affects more strongly the degree of resistivity anisotropy in a-C films than in the case of post-deposition annealing. The results obtained suggest that film structure is formed by predominantly sp 2-bonded carbon atoms. In the range of deposition temperatures 20–400 °C, ordered regular aromatic rings and graphite-like clusters form, and the extent of ordering increases with the increase in deposition temperature. In the range 450–650 °C the growth mechanism changes and the nuclei of graphite phase form and grow directly on the substrate. Annealing of a-C films in the range 50–300 °C results in intense transformation of distorted aromatic rings into regular ones, and also in ordering of them in the substrate plane without formation of graphite fragments. Further increase in the anneal temperature up to 650 °C has little influence on the structure of the film.

Investigation of ultra-thin carbon films on magnetic disks with super smooth glass substrate

This paper presents new and improved approaches used in a variety of analytical methods (AFM, TEM, XPS, TOF-SIMS, GIXR, HR-RBS, Raman, and GF-AAS) to study the properties of ultra-thin carbon films. Despite fact that a magnetic layer is covered by the thickness of 1.2 nm carbon films in the case of TEM observation, the sputtered carbon films over 3 nm thick are excellent in view of the coverage and corrosion resistance. This film thickness is suitable for use with 60–100 Gbits/in 2 recording media.