Diamondlike flakes

A carbon coating was vacuum arc deposited on a smooth surface of a target which was simultaneously ion beam sputtered. The bombarding ions have sufficient energy to create diamond bonds. Spalling occurs as the carbon deposit thickens. The resulting diamond like carbon flakes improve thermal, electrical, mechanical, and tribological properties when used in aerospace structures and components

Studies of mechano-chemical interactions in the tribological behavior of materials

Mechano-chemical interaction studies can contribute to the understanding of wear and friction of materials. Specific examples of experimental results relative to the subject are discussed. There are two parts: one describes the synergistic effect of corrosion and wear of iron sliding on sapphire in sulfuric acid, and the other describes the effect of surface films on the wear and friction of plasma-deposited diamondlike carbon (amorphous hydrogenated carbon) films in sliding contact with silicon nitride. The concentration of acid (pH) is an important factor in controlling the iron loss caused by wear-corrosion processes in sulfuric acid. The mechanical action can cause chemical reactions to proceed much faster than they would otherwise. The diamondlike carbon (DLC) films are shown to behave tribologically much like bulk diamond. In a dry nitrogen environment, a mechano-chemical reaction produces a substance which greatly decreases the coefficient of friction. In a moist air environment, mechano-chemical interactions drastically reduce the wear life of DLC films and water vapor greatly increases friction

Synthesis, structure and properties of nanolayered DLC/DLC films

Diamondlike carbon (DLC) films have been explored extensively in the past due to their highly attractive properties. However, the high level of internal stress developed during growth prevents deposition of thick films. Synthesis of DLC/DLC multilayers (DDM) presents a venue to overcome this drawback. In the present study, DLC films and DDM were deposited on Si substrate using dc plasma of CH4 and Ar gas mixture. FTIR was used to analyze the structure of the DLC films. Mechanical properties of the films were characterized by microhardness testing and nanoindentation. The tribological properties were studied by conducting pin-on-disc experiments in the laboratory environment (relative humidity 40-60%). Optical profilometry was used to analyze Intrinsic stress in the films and the wear profiles. A preliminary study was conducted utilizing different processing parameter (bias voltage, chamber pressure and ratio of Ar to CH4) to select the constituents of the DDM. Subsequently, DDM were synthesized consisting of alternating nanolayers of “soft” (high sp2content) and “hard” (low sp2 content) DLC by varying: (i) individual layer thickness while keeping the thickness ratio of soft/ hard DLC film, λ = 1 and; (ii) λ. The multilayered films found to exhibit low intrinsic stress ranging mostly below the average values of the two individual components. Nanoindentation behavior of DDM was comparable to the parent films and no significant variation was observed in different DDM films. DDM films with λ=1 exhibited better tribological properties compared to the films with λ other than unity. The 50 nm/50 nm DDM film exhibited the best tribological properties. It combined the low friction coefficient of the soft DLC component and low wear rate of the harder DLC component. The stress was found to be the average of the parent DLC films; hence it possesses the promise to be deposited as a thick coating, while maintaining desirable mechanical and tribological properties

Plasma enhanced chemical vapor deposition of diamondlike carbon films using acetylene

This study is focussed on the synthesis and characterization of diamondlike carbon (DLQ films deposited on silicon wafers and glass by plasma enhanced chemical vapor deposition (PECVD), using acetylene (C2H4) as a precursor. The process parameters, such as temperature, pressure, power and reactant gas flow rate have been systematically varied and their effects on the film growth rate and properties were investigated. The optimized deposition condition appeared to be at 150°C, 200mTorr, 200 Watts and flow rate = 25 sccm. For these conditions, the films were hard and found to have good adhesion to the substrate, and resistant to BF etching (49% BY diluted to 10% with distilled water). It was found that the adhesion of the DLC film to the substrate is good if the substrate is first etched with oxygen and CF4 prior to the deposition

Laser deposition of diamondlike carbon films at high intensities

Unhydrogenated diamondlike carbon (DLC) thin films have been deposited by laser ablation of graphite, using a high power Ti: sapphire solid state laser system. DLC films were deposited onto silicon substrates at room temperature with subpicosecond laser pulses, at peak intensities in the 4×1014–5×1015 W/cm2 range. A variety of techniques, including scanning and transmission electron microscopy (SEM and TEM), Raman spectroscopy, spectroscopic ellipsometry (SE), and electron energy loss spectroscopy (EELS) have been used to analyze the film quality. Smooth, partially transparent films were produced, distinct from the graphite target. Sp3 volume fractions were found to be in the 50%–60% range, with Tauc band gaps ranging from 0.6 to 1.2 eV, depending on laser intensity. Kinetic energies carried by the carbon ions in the laser induced plasma were measured through time‐of‐flight (TOF) spectroscopy. Their most probable kinetic energies were found to be in the 700–1000 eV range, increasing with laser intensity. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70135/2/APPLAB-67-21-3120-1.pd

Synthesis, characterization and tribological behavior of nitrogen-doped chromium-diamond-like carbon nanocomposite thin films

Diamond-like carbon (DLC) films have been extensively studied for more than two decades due to their highly attractive properties. These films exhibit unique mechanical, chemical and electronic properties and thus, possess great potential for applications in tribology. However, two drawbacks in the DLC films are high level of internal stress developed during growth preventing deposition of thick films and low thermal stability. Synthesis of Me-DLC (Cr-DLC and N-doped Cr-DLC) presents a way to overcome these drawbacks. In the present study, DLC, Cr-DLC and N-doped Cr-DLC films were deposited on Si substrate using a hybrid Plasma assisted CVD/PVD process. Film characterization in terms of microstructure, structure, composition and chemical state of components was carried out by transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) of the Cr-DLC as well as N-doped Cr-DLC films. Mechanical properties of the films were characterized by microhardness testing. The tribological properties were studied by conducting pin-on-disc experiments. Optical profilometry was used to analyze intrinsic stress in the films and the wear profiles and wear rate. TEM and XPS showed that N-doping results in formation of CrN along with Cr carbide in the film. N-doped Cr-DLC films were found to possess higher hardness than the Cr-DLC and DLC films. N-doped Cr-DLC exhibited lower intrinsic stresses while maintaining a comparable friction coefficient and wear rate as well as higher microhardness. The low intrinsic stresses of N-doped Cr-DLC show promise for the deposition of thicker coatings, while maintaining desirable mechanical and tribological properties

A novel approach to diamondlike carbon based mid-infrared attenuated total reflectance spectroelectrochemistry

Structural changes of electroactive species during electrochemical reactions cannot be determined from the electroanalytical technique alone. By incorporating spectroscopic techniques with electrochemistry, additional information about analyte structure and composition of the double layer can be obtained during electrochemical processes. Several spectroscopic methodologies have been tailored for this purpose including electronic and vibrational spectroscopies. Mid-infrared ATR spectroscopy is especially interesting as it provides in-situ information about adsorbates at the electrode surface. Mass transport limitations present in mid-infrared (mid-IR) external reflection and transmission spectroelectrochemistry are circumvented with attenuated total reflectance (ATR) spectroelectrochemistry. However, limitations of appropriate electrode materials for internal reflection configurations have hindered widespread adoption of the technique. The work described in this thesis focuses on the development and coupling of electrically conducting DLC films with mid-IR transparent multi-reflection waveguides for ATR spectroelectrochemistry. Conducting diamondlike carbon (DLC) thin films were developed utilizing pulsed laser deposition systems in collaboration with Joanneum Research (Leoben, Austria) and at the University of North Carolina (Chapel Hill). Nitrogen doping and incorporation of noble metal nanoclusters were investigated as approaches aimed at improving the electrical conductivity of DLC. Detailed compositional studies of nitrogen-doped DLC layers showed that sp2-hybridized carbon is responsible for the observed electrochemical activity. Optical transparency of thin (~ 40 nm) DLC layers in the mid-IR regime was confirmed by transmission-absorption measurements upon deposition on zinc selenide ATR waveguides. Additionally, the first spectroelectrochemical application of conducting DLC films was demonstrated via the electropolymerization of polyaniline onto coated ATR elements. Metal-DLC nanocomposite layers were investigated with various analytical techniques obtaining detailed compositional information. Improved electrochemical activity of metal-DLC demonstrated their suitability as electrode materials. Sufficient mid-IR transmissivity of metal-DLC coated germanium waveguides was displayed to enable spectroelectrochemical application. Finally, electropolymerization of poly(4-vinylpyridine) in acetonitrile was pursued to produce highly cross-linked ion-exchange membranes for spectroelectrochemical sensing. The composition of the pre-polymerization mixture and deposition conditions were tailored to obtain uniform semipermeable membranes. Diffusion of cations to electrodes is restricted by performing the electropolymerization as established herein. By employing the described electropolymerization procedure at DLC-coated waveguides, spectroelectrochemical sensing strategies can now be extended into the mid-IR regime.Ph.D.Committee Chair: Mizaikoff, Boris; Committee Member: Bottomley, Lawrence; Committee Member: Hunt, William; Committee Member: Janata, Jiri; Committee Member: Josowicz, Miroslaw

Lubrication by Diamond and Diamondlike Carbon Coatings

Regardless of environment (ultrahigh vacuum, humid air, dry nitrogen, or water), ion-beam-deposited diamondlike carbon (DLC) and nitrogen-ion-implanted, chemical-vapor-deposited (CVD) diamond films had low steady-state coefficients of friction (less than 0.1) and low wear rates (less than or equal to 10(exp -6)cu mm/N(dot)m). These films can be used as effective wear-resistant, self-lubricating coatings regardless of environment. On the other hand, as-deposited, fine-grain CVD diamond films; polished, coarse-grain CVD diamond films; and polished and then fluorinated, coarse-grain CVD diamond films can be used as effective wear-resistant, self-lubricating coatings in humid air, in dry nitrogen, and in water, but they had a high coefficient of friction and a high wear rate in ultrahigh vacuum. The polished, coarse-grain CVD diamond film revealed an extremely low wear rate, far less than 10(exp 10) cu mm/N(dot)m, in water

Characterization and tribological behavior of diamond-like carbon and nitrogen-doped diamond-like carbon thin films

Diamond-like carbon (DLC) films have been extensively studied for more than two decades due to their highly attractive properties. These films exhibit unique mechanical, electrical and tribological behavior and thus, possess great potential for applications in tribology. However, the high level of internal stress developed and low thermal stability are the main drawbacks. Synthesis of nitrogen-doped DLC (N-DLC) offers the possibility of overcoming these drawbacks. In the present study, DLC and N-DLC films (with low N content) were deposited on Si substrates using a hybrid plasma-assisted CVD/PVD process. Film characterization in terms of microstructure, composition and chemical state of components was carried out by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Mechanical properties of the films were characterized by microhardness testing. The tribological properties were studied by conducting pin-on-disc experiments. Surface optical profilometry was used to analyze the wear profiles and calculate the Archard wear rates. TEM and XPS analysis showed that low amounts of N-doping results in the formation of an amorphous structure with the presence of short-ranged diamond-like structure (sp3). N-doped DLC films were found to possess comparable hardness with that of DLC films. They exhibited friction coefficients as low as 0.04 compared to 0.2 for DLC, but maintained comparable Archard wear rates with DLC of the order of 10-7 mm3/Nm. The N-DLC film with 0.73 at. % N exhibited the best tribological behavior. The nanosmooth appearance of the surface, ultralow friction coefficients and low Archard wear rates of N-DLC films obtained with low doping of N in the DLC matrix, show promise for applications such as magnetic hard drives and medical implants