Amorphous carbon films were deposited onto (100) Si crystals and onto ultra-pure Al foils by dc-magnetron sputtering with different Ar plasma pressures, from 0.17 to 1.4 Pa. We investigate the voids structure and the voids density in these films by means of small angle x-ray scattering (SAXS) and mass spectrometry of effused gases. The analysis of the effusion spectra provided clear evidence that films deposited at lower pressures are compact, while the films deposited at higher pressure present a more open structural arrangement, confirming density results obtained by using ion beam techniques. SAXS results reveal that the fraction of open volumes increases with the plasma pressure: a direct correlation between film density and open volume fraction is found. These different film microstructures could be explained by the existence of different bombarding regimes during film growth

Tribochemical studies of the effect of lubricant bonding on the tribology of the head/disk interface (HDI) were conducted using hydrogenated (CHx) carbon disk samples coated with perfluoropolyether ZDOL lubricant. The studies involved drag tests with uncoated and carbon-coated A1203-TiC sliders and also thermal desorption experiments in an ultra-high vacuum (UHV) tribochamber. We observed that a larger mobile lubricant portion significantly enhances the wear durability of the (head/disk interface) HDI by providing a reservoir to constantly replenish the lubricant displaced in the wear track during drag tests. In the thermal desorption tests we observed two distinct temperatures of desorption. The mobile ZDOL layer is desorbed at the lower thermal desorption temperature and the residual bonded ZDOL layer is desorbed at the higher thermal desorption temperature. We also observed that the hydrogen evolution from CHx overcoats initiates lubricant catalytic decomposition with uncoated A1203/TiC sliders, forming CF3 (69) and C2F5(119). The generation of Hydroflouric acid (HF) during thermal desorption experiments provides the formation mechanism of Lewis acid, which is the necessary component for catalytic reaction causing Z-DOL lube degradation

Nitrogen-doped carbon (CNx) overcoats, ranging from I to 6nm in thickness, were deposited on magnetic recording disks by a DC-sputtering process. A critical load, based on the first occurrence of coating damage, was used as a semi-quantitative measure of the mechanical strength of these overcoats. It was found that the critical load decreased in a nearly linear manner with the CNx thickness from 6nm down to ∼2nm regime. However, the lnm thick CNx coating deviated from this trend with a significant decrease in critical load. High-resolution SEM was employed to find the critical loads as well as to reveal the details of the coating wear morphology and the CNx failure mechanism

The role of 02 gas addition on the deposition of Diamond-like Carbon (DLC) film was studied for hard disk drive (HDD) media application. The influence of 02 gas mixing ratio on DLC film quality was investigated using the dc magnetron sputtering method with a solid graphite target and Ar, CH4 and 02 mixing gases. The 02 mixing ratio was varied between 0% and 50%. Film quality was evaluated using Raman spectroscopy and XPS. When 02 gas mixing ratio increased the peak in Raman spectra shifted gradually to higher wavenumbers and its bandwidth became narrower. This indicates graphite component increased in the DLC film. In addition, the lubricant coverage on oxygen-containing DLC was improved. Because adding oxygen increases the terminations of carbonyl group on DLC surface, this result suggests that the polar surface causes higher affinity for the lubricant

Nitrogen containing amorphous carbon (a-CNx) films were prepared on silicon single crystal substrates by heating a carbon filament in low pressure nitrogen atmosphere and the effects of argon addition to nitrogen atmosphere were studied by changing the argon fraction under the total pressure of 100 Pa. The growth rate of the films is found to decrease with increasing the argon fraction. x-ray photoelectron spectroscopy shows that the films are composed of carbon and nitrogen and the optimal fraction of argon addition is observed for increasing the nitrogen concentration. Observations by atomic force microscopy reveal that the film surfaces are covered with particle-like features and the size of the features decreases drastically by argon addition. It is concluded that argon addition to the reactant gas is effective in synthesizing a-CNx films with the smooth surface and high nitrogen concentration

Thin films of hydrogenated amorphous carbon ( a-C:H ) deposited by radio frequency plasma-enhanced chemical vapour deposition (rf-PECVD) have been studied for various applications. An interesting property of these films is their high breakdown strength ( 107 Vcm−1 ). This property of a-C:H can be exploited in high breakdown heterostructure diodes or as passivation layers and insulator layers in MIS devices. Reports on the applications of a-C:H/Si diodes exist in the literature. Diodes in which the a-C:H films have been deposited by rf-PECVD, have been reported only once. In this article the diodes produced reportedly failed to exhibit reproducible I-V characteristics under high voltage stress. We have investigated the process dependence of structural and electrical properties of rf-PECVD a-C:H films deposited at room temperature from a CH4/Ar gas mixture (at a pressure of 100 mTorr) using a capacitively coupled rf-PECVD. We observe a clear correlation between the dc-self bias and the rectification ratio of a-C:H/Si heterojunction diodes. Optimised diodes show rectification ratios upto 104 and a stable reverse breakdown voltage, typically around 850 V. I-V and C-V measurements show no evidence of hystersis. Scanning Electron Microscopy was carried out to determine the quality of the films deposited. Micro-Raman analysis was used to estimate the ID/IG ratio in the films deposited under different dc-self bias.

Diamond like carbon has been deposited as a protective layer for coronary stenting applications. Taking advantage of DLC's resistance to chemical attack, its flexibility, and other properties. our current technical objective is to develop DLC as a coating for radioactive rhenium stents. Radioactive rhenium stents are being investigated to limit smooth muscle cell growth following coronary surgery. The DLC coating is being investigated to reduce the release of radioactive rhenium (released activity) into the blood following the stenting procedure. An inductively coupled RF plasma system was used to deposit the DLC onto rhenium substrates. Foils, wires, and coils were coated and tested for adhesion, cytotoxicity, and release of radioactive rhenium. Our initial results indicate up to a three-fold decrease in released activity relative to uncoated rhenium

Electrochemical impedance in H2SO4 solutions and kinetics of redox reactions in the Fe(CN)63-/4- system were studied on amorphous nitrogenated diamond-like carbon (a-C:N:H) thin-film electrodes. Parameters of point defects (trapping centers) were also measured by the Deep Level Transient Spectroscopy techniques. The films have been fabricated on p- and i-type silicon and quartz substrates, using direct ion beam deposition from an RF inductively coupled N2+ CH4 plasma source. The increase in N2/CH4 ratio in the gas mixture lead to a decrease in the electrical resistivity and optical bandgap of the films from 3×1010to 5×106 Ω cm and from 1.3 to 0.6 eV, respectively. Simultaneously, the concentration of electrically active point defects increased significantly and the charge transfer at the a-C:N:H film/redox electrolyte interface was facilitated

Hard, adherent, 2 μm thick lubricious silicon containing diamond-like carbon coatings (Si-DLC) were synthesized by 40 keV Ar+ ion beam assisted deposition (IBAD) of tetraphenyltetramethyl-trisiloxane oil on two, 5 cm by 5 cm by 0.64 cm thick 4340 steel substrates. Two different substrate surface finishes were examined, I polished and 1 600 grit finish (unpolished). The corrosion resistance of the Si-DLC coating was evaluated by Electrochemical Impedance Spectroscopy (EIS) in a 0.005N concentration sodium chloride (NaCI) solution. Low frequency impedance data from each of the coatings were compared with those of bare steel. The Si-DLC coating deposited on the polished substrate performed slightly better than the one deposited on the unpolished surface. Overall the Si-DLC coating did not appear to offer very much corrosion protection to the steel. This was mainly attributed to the presence of pinholes in the coating. Furthermore, to study the effect of radiation on the electronic structure of the Si-DLC coating, three Si-DLC coatings synthesized under the same deposition conditions on silicon substrates at various oil precursor temperatures were irradiated by a 355 nm wavelength, 0.37 Watts, pulsed YAG Laser at 35 kHz. Corrosion and irradiation results and procedures to minimize the pinhole density in the Si-DLC coating will be discussed in detail

CVD diamond films, ET 100 of Norton Diamond Film, were treateds in ultrahigh purity O2 from 420 to 575°C at 95 kPa. Auger and x-ray photoelectron spectra were collected from CVD and natural diamond surfaces. The Auger KVV line shapes of the CVD diamond with various surface conditions were compared to those of natural diamonds and sp2-bound graphite (HOPG) and glassy carbon. Comparisons were made on the peak shape of A1, which is the major satellite peak of carbon KVV. Auger KVV line shaped of oxidized CVD diamonds were more similar to that of natural diamond than either HOPG or glassy carbon. XPS is more sensitive to the change of surface chemisorbed species. The C Is binding energy of oxygenated and oxidized CVD diamonds (287.3 eV) was higher than that of natural diamond (285.7 eV), graphite (283.0 eV) and glassy carbon (284.2 eV). Auger and XPS findings indicated that when treated in O2 from 420 to 575°C at 95 kPa, direct oxidation of CVD diamond occurred without graphitization

Microcrystalline diamond films have been prepared in a 13.56 MHz low pressure inductively coupled plasma, in which the pressure of CH4/H2and CH4/CO/H2 plasmas was varied from 45 to 50 mTorr. The bonded structures of the obtained deposits were studied by Raman spectroscopy with 514, 325, and 244 nm excitation wavelength. 514 nm excited Raman spectra exhibit two peaks at ∼1355 cm−1 and ∼1580 cm−1 corresponding to sp2 bonding without CO additive (CH4/H2, plasma). New peaks at ∼1150 cm−1 assigned to sp3-bonded carbon network and at ∼1480 cm−1 appear with CO additive (CH4/CO/H2, plasma). 325 nm excited Raman spectra show a shoulder at ∼1150 cm−1, a clear 1332 cm−1 diamond peak, and the peak at ∼1580 cm−1 is remarkably enhanced. In 244 nm excited Raman scattering, the 1332 cm−1 diamond peak is only enhanced whereas the peak at ∼1580 cm−1 is correspondingly diminished. These features of the Raman spectra imply that the vibrational modes of sp2 sites are resonantly enhanced with 514 nm excitation because the 514 nm (2.4 eV) corresponds to the π-π* transition in sp2-bonded carbon, while the 325 nm (3.8 eV) and 244 nm (5.1 eV) excitations are possibly sufficient to excite the σ state of both sp2- and sp3-bonded carbon

Amorphous diamond is a new material for surface micromachined microelectromechanical systems (MEMS) and sensors. Its strength and modulus was tested in uniaxial tension by pulling laterally on a specially designed sample with a flat tipped diamond in a nanoindenter. Several sample designs were attempted. Of those, only the single layer specimen with a 1 by 2 μm gage cross section and a fixed end rigidly attached to the substrate was successful. Tensile load was calculated by resolving the measured lateral and normal forces into the applied tensile force and frictional losses. Displacement was corrected for machine compliance using the differential stiffness method. Post-mortem examination of the samples was performed to document the failure mode. The load-displacement data from those samples that failed in the gage section was converted to stress-strain curves using carefully measured gage cross section dimensions. Mean fracture strength was found to be 8.5 ± 1.4 GPa and the modulus was 831 ± 94 GPa. Tensile results are compared to hardness and modulus measurements made using a nanoindenter

Diamond films were grown over Si substrate at 1253K by the hot filament chemical vapor deposition method using CH4/H2 gas mixture, and intrinsic stresses in the film were deduced from the ex-situ curvature measurements. In order to account for the creep deformation of the Si substrate, an elastic/plastic stress and strain analysis were conducted. Results showed that intrinsic stresses were generally several times larger than the average film stresses and always positive increasing with the film thickness. For the film thickness larger than 10μm, stress relaxation by creep of the substrate became significant, and must be considered for the accurate assessment of the film stress in diamond. Later, an analysis based on the grain growth accounted for the development of intrinsic stresses reasonably well

CVD Diamond films with resistivites comparable to that measured in natural type IIA diamond can be fabricated using a microwave-plasma assisted growth environment. Modification of the resistivity of these films is typically accomplished through the introduction of impurities, or dopants such as boron. Some applications, however, require that the purity of the carbon lattice be maintained, while still altering the resistivity of the film. This is the case for many applications of diamond in space. Here, varying the resistivity of CVD diamond is investigated by controlling the introduction of sp2coordinated bonds, yet maintaining the overall diamond structure and carbon purity. Experimental results will be presented, and the use of these materials in NASA's Genesis Discovery Mission will be discussed

Boron-alloy coatings can be formed by sputtering compound targets, through co-deposition with other elemental targets, by utilizing reactive gas mixtures, and/or by post-deposition implantation. Specific to this study, boron-alloy coatings are assessed with respect to composition as deposited by co-sputtering boron and beryllium. Transmission electron microscope (TEM), bright-field images with selected area diffraction are used to reveal the microstructure and phase. Refinement in grain size to the nanoscale occurs through boron addition as well as transition metal impurities. An increase in coating hardness with boron addition is measured using nanoindentation. Scanning electron microscope (SEM), secondary electron images reveal the surface morphology variations for thick coatings that occur with boron addition as measured using energy dispersive spectrometry (EDS). The phase formed in boron-alloyed beryllium coating is found to be dependent on both coating composition and the sputter deposition conditions. It is concluded that the geometry of the deposition sources with the configuration of the substrate effect the coating composition, microstructure, and properties

Nanocrystalline diamond films grown on Si substrates at 800°C from hydrogen-poorplasmas have a number of highly desirable mechanical and electronic properties. Impurities were found by SIMS measurements to be uniformly distributed throughout the thickness of the films at a level of 1017–1018 cm−3. It is likely that the impurities are located at the grain boundaries, which play a crucial role in controlling important characteristics of the films, such as electrical conductivity and electron emission. Density-functional based tight-binding (DFTB) molecular dynamics simulations were performed for diamond high-energy high-angle (100) twist grain boundaries with impurities such as N, Si and H

Dielectric properties of amorphous carbon nitride films made by the layer-by-layer method, (LLa-CNx) consisting of a cyclic process with (A) the deposition of an amorphous carbon nitride layer by sputtering and with (B) the etching by atomic hydrogen, have been compared with that of amorphous carbon nitride (a-CNx) films prepared without the hydrogen etching process. It is found that the nitrogen in a-CNx and LLa-CNx could decrease the refractive index n and the dielectric constant ε at 1 MHz. The nitrogen could create less dense structure in a-CNx and LLa-CNx compared to diamond-like carbon (DLC). The sp3 bonds between carbon atoms seem to increase by the atomic hydrogen treatment in LLa-CNx. The refractive index of LLa-CNx increases with sp3content. Preliminary experiments adding oxygen in amorphous carbon nitride to create a-CNxOy film are tried and discussed briefly.

Amorphous carbon nitride films a-CNx, which made in our laboratory, show high photosensitivity Ps that is a ratio of photoconductivity σp and dark-electrical conductivity σd Maximum Ps of a-CNx is about 5×106 which is about 50 times larger than that of hydrogenated amorphous silicon a-Si:H.

We have succeeded to observe photoconductivity spectra where photoconductivity starts nearly at 2 eV and saturates at 3 eV. Then σp increase again at 3.7 eV up to 6.2 eV. The dependence of σp on excitation energy and intensity is observed. Photoluminescence spectrum is also obtained which have a spectrum from infrared of 0.8 eV up to ultraviolet of 3.5 eV. Using these data together with photothermal deflection spectra, we have presented a refined model of the electronic density of states for LLa-CNx.

Hydrogenated amorphous carbon nitride (α-CNx:H) films are deposited at 50–300°C by radio-frequency plasma decomposition of CH4-CF4-N2 gas mixtures. Effects of fluorine radicals on the deposition rate, composition, and on chemical bonding are investigated. When CF4 gas is added as partial replacement of CH4 gas, the deposition rate at 200°C steeply increases with increasing flow rate ratio RCF = [CF4]/([CH4]+[CF4]) up to ∼0.3, and then it decreases gradually. It is found that the nitrogen content, x, increases from 0.22 to 0.46 when RCF increases from 0 to 0.75. The inclusion of fluorine atoms into the films is less than 5 at%. The infrared absorption spectra shows strong enhancement of the absorption bands related to various forms of C—N bonding by the CF4 addition. It is found that the addition of CF4enhances the formation of C–N bonds in PECVD α-CNx:H films.

To investigate the role of nitrogen in the structure formation and electrical properties of CNx thin films, several carbon thin films containing variable concentrations of nitrogen were deposited using a magnetron sputtering in a reactive N2/ Ar discharge. The chemical composition of the as-deposited films was investigated by means of Rutherford backscattering (RBS) and a [N]/[C] ratio up to 0.5 was obtained. TEM studies confirmed that the deposits are mainly amorphous and contain nanocrystalline CNx compounds. Additional STM investigations reveal a cluster-like microstructure of the surface showing a maximum cluster size of 10 nm in thin films deposited at a N2 / Ar pressure ratio of 30% in the plasma. The electrical resistivity ρ was studied as a function of temperature between 10 K and 320 K. All deposited films show semiconducting behaviour. The lowest ρ values were observed in films containing no nitrogen, whereas the films deposited with 30% N2in the sputter plasma reveal strongest semiconducting properties. The temperature dependence of the measured resistivity will be discussed according to Mott's law and the activation energy for the electrical transport estimated at room temperature will be given.