In this work we show that the addition of a small amount of CF4 to a regular CH4 -H2 gas mixture allows diamond growth at lower temperatures with reasonable growth rates. We used a hot filament assisted reactor and observed diamond growth with a substrate temperature as low as 390 ଌ. We present a comparative study for the growth dependence on substrate temperature with and without CF4 addition in the gas mixture. The growth rate is measured by post growth weighting with a micro balance. Raman spectroscopy, SEM and AFM images show the good quality of the films grown at low temperatures when CF4 is added to the feeding gas.

In situ quantitative studies of the effects of substrate temperature, methane and chlorine flow rates on homoepitaxial diamond growth rates on (110) surfaces in a chlorine-activated diamond CVD reactor have been carried out using a Fizeau interferometer. The temperature dependence of diamond growth rates was found to display three distinct growth activation energies, ranging from 9±2 kcal/mol in the substrate temperature of 750-950°C, to 3.2±0.2 kcal/mol in the temperature range of 300-650°C, followed by 1.2±0.2 kcal/mol in the temperature range of 102-250°C. Atomic hydrogen is believed to be the dominant activating species in the highest temperature range, and atomic chlorine is believed to be the dominant species in the lower temperature regions. Studies of the methane flow effect on diamond growth rates revealed a linearity, indicating that the diamond growth rate was of the first order in methane flows. Diamond growth rates were also found to increase linearly with the chlorine flow. At high chlorine flow rates, however, an accelerated diamond growth rate was observed. Discussion is given to explain the observed results.

An ultra-high vacuum chemical vapor deposition system using pulsed, supersonic jets of halogenated hydrocarbon precursors has been constructed with the intention of growing diamond thin films. Experimental results from this system should determine whether the hyperthermal activation of precursors improves the carbon incorporation efficiency of film growth. The jets, produced by commercially available pulsed valves, were characterized with a fast ionization gauge. Parameters such as valve backing pressure and the pulse width were varied to optimize material flux and avoid the formation of boundary layers above the substrate that could reduce the kinetic energy of the precursors.

This work addresses mechanistic issues in conventional and halogen-assisted diamond growth via ab initio molecular orbital calculations on hydrogenated and halogenated carbon clusters (C9H12Xi, X=H, F, or Cl; i=O, 1, or 2) as models of the dimer-reconstructed diamond (100)2× 1 surface. The dimer bond lengths (XC-CX, XC-C., C=C) and the C-X and C=C π bond energies have been determined along with the effects of lattice constraints. The calculations show that dimer bonds are longer in clusters where only the topmost carbon layer is allowed to relax and the remaining carbon atoms are constrained to lie at diamond lattice positions than in fully relaxed clusters. The calculations also predict that the first C-X bond strength is approximately the same in constrained and fully relaxed clusters and that the second C-X bond is distinctly weaker due to π bond formation, particularly in fully relaxed clusters. These results indicate that the π bond between dimer atoms on the clean (100)-(2× 1) surface is weakened considerably by the constraints imposed by the lattice but is quite important nonetheless.

Samples of diamond crystals produced under various high pressure, high temperature conditions were studied using both micro photoluminescence and Raman spectroscopy. The 0.3 - 0.6 mm sized samples exhibited various levels of inclusion content, impurity content and strain. Photoluminescence studies revealed the presence of nitrogen in three forms. The 1.945 eV, 2.15 eV and 2.46 eV zero phonon lines and their associated sidebands were detected. The ratios between forms of impurities and their integrated intensities varied between samples. Variations in the distribution of the nitrogen forms were seen between regions of high and low strain birefringence patterns.

Amorphous hydrogenated carbon (a-C:H) thin films are of great importance in a number of industrial applications due to their hardness, chemical stability, and optical transparency. In many applications, the thickness of the a-C:H film and/or its optical properties are critical for the performance of the complete structure, and, as a result, a means of measuring these quantities is important. In this work we review the use of spectroscopic ellipsometry and transmission measurements for the estimation of the thickness and optical constants of thin a-C:H films. Spectra are shown for films exhibiting Tauc effective bandgaps ranging from 0 - 2.3 eV. The films were prepared by magnetron sputtering and plasma CVD on both silicon and glass substrates. The general energy dependence of the a-C:H optical constants is discussed in terms of the absorption processes which occur in the film.

Hydrogenated and nonhydrogenated nitrogen containing diamondlike carbon films (NDLC including a-C:N and a-C:N:H) were made in a dual ion beam deposition system. The asdeposited films were characterized by Raman spectroscopy, Rutherford backscattering spectroscopy (RBS) and elastic recoil detection analysis (ERD). The compositional stability of the films at temperatures up to 550°C was examined in situ by both RBS and ERD using a heated sample stage in the scattering chamber. The addition of nitrogen altered the Raman parameters when compared with conventional DLC. At elevated temperatures, the a-C:N films do not suffer nitrogen loss; however, the a-C:N:H films undergo nitrogen and hydrogen loss at 400°C.

Unhydrogenated amorphous carbon films were deposited by KrF pulsed laser ablation of graphite under a laser power density of 8×108 W/cm2. The films were characterized using x-ray reflectivity, optical transmittance, spectroscopic ellipsometry and Raman spectroscopy. The physical, optical and bonding properties of the films have been investigated in detail as functions of substrate temperatures Ts (22-300°C) and post-annealing temperatures. Films deposited at Ts, <200°C possessed diamond-like properties with mass densities p=2.8-3.1 g/cm3 and optical bandgaps Eg,=1.5-2.2 eV. Above Ts,=200°C, the films showed typical graphite characteristics. The diamond-like films annealed at temperatures up to 750°C show excellent thermal stability.

One method used by the industry for the deposition of thin carbon films is the dc cathodic arcion plating process. The evaporation of a graphite cathode by a high energy arc beam results in the production of carbon atoms, ions and macroscopic graphitic fragments. All these particles influence the film growth, the structure and therefore the film properties. The incorporation of the macroscopic graphitic fragments can be avoided by the use of mechanical or magnetic filters in front of the cathode. These filters prevent the direct bombardment of the substrates with particles. This particle separation involves decreased substrate current densities and this means lower deposition temperature (< 200°C) and growth rates. With the addition of inert (argon) and reactive gases (nitrogen and methane) and the use of a bias voltage on the substrate economical deposition rates of 2-4 μm/h and good adhesion on various materials can be reached.

This paper describes the production of amorphous hydrogen and hydrogen-free carbon films by a modified cathodic arc evaporation process using a simple mechanical filter for particle reduction. It shows the influence of some process parameters on the optimization of the process stability and process efficiency. Some characteristic properties of these coatings are shown by an example.

Amorphous carbon networks generated by quenching high-density liquid from hightemperature using a tight-binding molecular dynamics method are found to be dominated by tetrahedral bonding sites. The overall structural and electronic properties of these networks resemble those observed in experimental diamond-like amorphous carbon films produced by the mass-selected ion beam deposition technique. Our study shows that bonding and antibonding of π states associated with pairs and quartets of threefold “defected-atoms” embedded in the fourfold matrix yield a band gap of about 2 eV.

Deuteron magnetic resonance (DMR) and infrared absorption spectra have been measured in amorphous hydrogenated carbon (a-C:H and a-C:D,H) and amorphous hydrogenated carbon nitride (a-CN:D,H) films plasma-deposited onto room-temperature substrates from feedstock mixtures of CH4, N2, and D2. DMR spectra and transient magnetization recoveries were measured between room temperature and 4 K. Recoveries are dominated by magnetization transport under extreme inhomogeneity. Methyl rotors CDx H3-x freeze out below 77 K. From the infrared absorption spectra, NH2, CHx, double bonded C-C, and triple bonded C-N stretching modes are observed. As a function of increasing nitrogen concentrations, the NH2 and C-N intensities dramatically increase while the CHx and C-C intensities decrease. In films where the ratio of nitrogen to carbon plus nitrogen is greater than 25%, the absorption spectra are dominated by NH2 stretching and bending modes; in contrast, the DMR spectra show many CDxHy configurations and a broader NDxHy structure. Proton NMR shows significant hydrogen clustering in a-CN:D,H.

The structure of amorphous, diamond-like carbon films is described by the distribution function, obtained by X-ray scattering experiments. In particular the nearest neighbor distance and the average coordination number are determined. A combination of specular reflectivity of neutrons and X-rays enables us to measure not only the mass density, but also the concentration of hydrogen in the films, which varies in our case between 0 and 30 at. %.

We are studying carbon thin films by using a pulsed excimer laser to ablate pyrolytic graphite targets to form highly tetrahedral coordinated amorphous carbon (at-C) films. These films have been grown on room temperature p-type Si (100) substrates without the intentional incorporation of hydrogen. In order to understand and optimize the growth of at-C films, parametric studies of the growth parameters have been performed. We have also introduced various background gases (H2, N2 and Ar) and varied the background gas pressure during deposition. The residual compressive stress levels in the films have been measured and correlated to changes in the Raman spectra of the at-C band near 1565 cm−1. The residual compressive stress falls with gas pressure, indicating a decreasing atomic sp3-bonded carbon fraction. We find that reactive gases such as hydrogen and nitrogen significantly alter the Raman spectra at higher pressures. These effects are due to a combination of chemical incorporation of nitrogen and hydrogen into the film as well as collisional cooling of the ablation plume. In contrast, films grown in non-reactive Ar background gases show much less dramatic changes in the Raman spectra at similar pressures.

Highly tetrahedral-coordinated-amorphous-carbon (a-tC) films deposited by pulsed-laser deposition (PLD) on silicon substrates are studied. These films are grown at room-temperatures in a high-vacuum ambient. a-tC films grown in this manner have demonstrated stability to temperatures in excess of T = 1000°C, more than sufficient for any post-processing treatment or application. Film surfaces are optically smooth as determined both visually and by atomic-force microscopy. PLD growth parameters can be controlled to produce films with a range of sp2 - sp3 carbon-carbon bond ratios. Films with the highest yield of sp3 C-C bonds have high resistivity, with a dielectric permittivity constant s σ 4, measured capacitively at low frequencies (1 – 100 kHz). These a-tC films are p-type semiconductors as grown. Schottky barrier diode structures have been fabricated.

Thin films of amorphous carbon/hydrogen, also known as diamond-like carbon or DLC, are of interest as an economical alternative to diamond in a variety of coatings applications. We have investigated the thermal stability of DLC films deposited onto tungsten and aluminum substrates via plasma CVD of methane. These films contain approximately 40 atom % hydrogen, and based on Auger spectra the carbon in the films is estimated to be approximately 60 % sp3 hybridized and 40 % sp2 hybridized. Thermal desorption, Auger, and Raman measurements all indicate that the DLC films are stable to 250–300° C. Between 300 and 500° C, thermal evolution of hydrogen from the films is accompanied by the conversion of carbon from sp3 to sp2 hybridization, and Raman spectra indicate the conversion of the overall film structure from DLC to micro-crystalline graphite or so-called “glassy” carbon. These results suggest that DLC of this type is potentially useful for applications in which the temperature does not exceed 250° C.

We have measured the microhardness of various amorphous hydrogenated carbon thin films that were grown on both the anode and the cathode of our plasma deposition system. We observe no difference in microhardness between films with the same optical bandgap, whether grown on the cathode or on the anode. We conclude that the ion bombardment during cathode growth does not contribute to the hardness of the films. In contrast, we observe a large variation in microhardness as a function of optical bandgap. We conclude that it is increasing hydrogen concentration, found primarily in the clusters and not in the crosslinks, that decreases the hardness of our films. Finally, we observe that the addition of nitrogen to our films does not change the microhardness; again, the hardness is primarily determined by the hydrogen concentration.

We report the optical properties of amorphous C:Cu films produced by co-sputtering of graphite and copper targets in an argon plasma. Ellipsometric measurements at 632.8 nm were performed to evaluate dielectric permittivity vs copper content. We have observed a pronounced peculiarity of imaginary and real parts of the dielectric function at a copper content of about 14%. A correlation between the concentration dependence of the DC conductivity and that of the imaginary part of permittivity is clearly demonstrated. This correlation points to the existence of a less-conductive phase with the stoichiometric formula CuC6.

- Results on the properties of silicon incorporated hard a-C:H films deposited on the cathode of a glow discharge decomposition system using methane and silane gaseous mixtures are reported. Obtained samples showed an increased deposition rate, high hardness comparable to that of a-C:H, and a large decrease of the internal stress upon silicon incorporation. The structure of the samples seems to be similar to diamond-like a-C:H, as revealed by the total hydrogen content, infrared absorption and hydrogen effusion experiments. Our results indicate that the observed reduction of residual internal stress may be attributed to a less compact material and/or to a smaller density of voids containing hydrogen in comparison to pure a-C:H.

The electron cyclotron resonance (ECR) etching of diamond-like carbon films in an oxygen plasma has been studied. The input variables were flow rate, pressure, power, and bias, while the output parameters were etch rate, and uniformity. In-situ ellipsometry, performed at 44 wavelengths simultaneously, was employed to monitor the etch process in real time. We will show that DLC films can be etched without an applied bias, but the application of an rf induced dc bias greatly enhances etch uniformity. Further, the etch rate is a strong function of the bandgap of the DLC film.

Dual ion beam assisted deposition (DIBAD) techniques are known to produce high quality diamond-like carbon films. The reported extreme hardness and high thermal conductivity characteristics of these films have stimulated our investigation of their use as one component of multilayer x-ray optical elements. Non-crystalline carbon films were produced and were characterized by means of highly collimated x-ray refiectometry (λ = 0.154 nn), atomic force microscopy, and IR Raman spectroscopy techniques. They exhibit extreme smoothness at the surface and interface, near diamond density, high hardness, and high uniformity over areas of 0.58 x 10-4 m2. Multilayers have been constructed of this non-crystalline carbon interposed with high electron density materials that have exhibited very good x-ray and EUV optical characteristics at λ = 0.154 nm and at λ = 4.0 – 8.0 nm.