Microwave plasma deposition of polycrystalline diamond is investigated over the pressure range 1 to 100 kPa. The conditions of growth, microstructure, and spectroscopic properties of the resulting materials are compared. A phenomenological description of the dependence of diamond microstructure upon growth conditions is developed.

The gas phase chemistry in microwave plasma assisted chemical vapor deposition of diamond is similar to the chemistry that occurs during the oxidation of hydrocarbons in flames. Rapid interconversion between CH₄ and C₂H₂ occurs via hydrogen abstraction and addition reactions. CO formation occurs in the presence of oxygen. Electrons sufficiently energetic to dissociated H₂ and CH₄ are present in the plasma. As a result, chemistry normally associated with high temperature (~2000 degree(s)C) hydrocarbon combustion occurs at a relatively low temperature (~800 degree(s)C) in the plasma during diamond deposition.

Optical emission spectroscopy, Langmuir probes, and calorimetric techniques have been used to characterize the plasma jet in a DC plasma torch diamond deposition apparatus. The experimental data are compared to calculations based on a thermodynamic equilibrium model. The ion temperature obtained from the atomic hydrogen emission is within 10% of the calorimetrically deduced gas temperature, while the electron temperature is approximately a factor of two higher. For a wide range of process conditions, the plasma temperature is almost independent of the torch input power, but depends strongly on the hydrogen concentration in the feed gas. Calorimetry provides a means of measuring the concentration of atomic hydrogen produced by the torch.

High resolution electron microscopy of plasma-assisted chemical vapor deposition (CVD) diamond films was performed. The film was fine-grained with a grain size of 0.1 micrometers . Several features of the microstructure were studied and their importance to the understanding of the diamond film growth was evaluated. The observations include: (1) Twinning density rises as a function of the distance from the center of the crystal. (2) The twins have an important role in the rapid growth of this kind of film The re-entrant angle between intersecting twins serves as a nucleation site for the growth of new (111) planes. (3) The center point of a twin quintuplet has five re-entrant angles and thus serves as a preferred nucleation site for new planes as the crystal grows. (4) Misfit boundaries, being the locus of intersection points of the growing planes on two adjacent twins, can serve as an indicator for the local crystal growth direction. The central nucleation site for the growing planes can thus, in many cases, be traced back to a quintuplet twin point.

Microlithographic surface patterning has been investigated as a means of improving diamond film adhesion on noncompatible substrates. This technique produces significant improvements in film adhesion beyond identical unpatterned substrates, although sufficient film stresses can develop to induce subsurface substrate fracture. The substrate etching geometry can be chosen to simultaneously produce an antireflective surface relief.

The growth of diamond particles using continuous transmission electron microscope (TEM) observation of a side-view of the sample was studied. Diamonds were synthesized using the DC plasma jet chemical vapor deposition (CVD). Synthesis was followed by TEM observation and this cycle was repeated. The shape of the diamond remained almost the same during growth and there were many small SiC particles on the Si surface. Analysis of this continuous observation suggested there was a thin (about 200 nm) gaseous layer containing CH₄ radicals and SiH₄ radicals. It appeared the SiC particles helped diamond particle growth on the Si substrate.

The infrared transmission of relatively thick polished diamond films has been measured by Fourier transform infrared spectroscopy. Transmission of 70% at 10 micrometers for a 198 micrometers thick film and 69% at 10 micrometers for a 338 micrometers thick film is reported. By analysis of the interference fringes in the transmission spectra, it is estimated that, for a wavelength of 10 micrometers , the index of refraction of the films is comparable to that of a Drukker IIa window. The absorption coefficients of two films at the maximum of the one phonon absorption region are compared with the hydrogen and nitrogen content of the films and the Raman spectra of the films.

A thermochemical polishing technique (using low carbon steel at 700 degree(s)C to 900 degree(s)C) was employed to reduce the roughness on the surface of diamond films from 20,000-40,000 angstroms rms to 30-45 angstroms rms. These polycrystalline films were grown by filament assisted chemical vapor deposition (FACVD) onto (100) oriented silicon substrates. SEM micrographs reveal etch pits in the films, and these limit the final polish which can be achieved. This paper show that the hot iron technique polishes a (111) oriented film, which is the hardest direction for abrasive polishing. Preliminary studies indicate that for chemical polishing there is no large difference between the polishing rates of diamond as a function of orientation.

Mid-infrared transmission and absorption in polycrystalline chemical vapor deposition (CVD) diamond films has been studied. Free-standing films were grown in a DC arc-discharge plasma torch apparatus. The intensity of a band near 3.5 micrometers , which was assigned in previous work to a C-H bond-stretching mode, correlates with the hydrogen concentration. One symmetric and one antisymmetric stretching mode were observed, with frequencies corresponding to an sp³-bonded CH₂ species. In some films, the hydrogen-related absorption was reduced below 1 cm^-1. A broadband at 8 micrometers scales in intensity with the 3.5-micrometers band, suggesting its association with hydrogen as well. A sharp feature at 1,330 to 1,335 cm^-1 tentatively is assigned to defect-activated absorption by O((Gamma) ) phonons.

A methyl radical mechanism is described for the growth of diamond on its (110) surface. The growth of diamond in a hot filament reactor is modeled using a simple first order steady state approximation and calculated methyl radical concentrations are found to agree well with recent measurements. Steady state local equilibrium is assumed and used to estimate the mole fraction of reactive sites at the growth surface, giving a value of ~6 X 10^-4 at 1200 K and 50 Torr (0.066 atm) of 1% CH₄ in H₂. A simple first order thermochemical model of hot filament assisted deposition is described and methyl radical concentration estimates found to be in reasonable agreement with recent experimental results. The rate of methyl radical addition onto diamond (110) is calculated using these estimates and, assuming incorporation is as fast or faster than addition, gives a growth rate of ~0.8 micrometer/hr, in good agreement with the experiment. It is proposed that the cubo- cotahedral habit and <100> texture commonly seen in much CVD diamond is due to the <110> being the preferred low index growth rate axis. The reported rotation of polycrystalline texture toward a <100> axis, seen with changes in temperature and feed gas composition, is ascribed to variations in the relative rates of growth by this mechanism along [110] and [011]. Absolute reaction rate theory is sued to estimate a rate constant for methyl radical addition at sterically unhindered tertiary carbon sites. A 'loose' transition state model predicts a rate constant of 10¹² to 10¹³ cm³ mol^-1 sec^-1. If a much 'tighter' transition state is assumed, the predicted value is reduced to 10¹⁰ to 10¹¹ cm³ mol^-1 sec^-1. A 'loose' transition state model is preferred as this gives a result consistent with empirical rate constants for many radical recombinations and is consistent with a simple calculation based steady state approximation. It is argued that the highest rate of growth commonly occurs along <110> as the (110) surface represents a relatively unhindered tertiary carbon surface to which, at most, only two methyl radicals need be added to propagate the diamond lattice.

Transmittance and reflectance spectra of chemical-vapor-deposited (CVD) diamond windows with thicknesses from 0.4 to 1.9 micrometers were measured in the 0.5-6.5 eV photon energy range. The windows were fabricated by microwave-plasma-assisted CVD on silicon substrates, followed by partial removal of the substrates by etching. Three spectra were measured for each window, the reflectance of the top surface, the reflectance of the bottom surface (the surface exposed by etching), and the transmittance. The optical constants were determined as a function of photon energy by fitting the data to a model that includes the effects of surface optical scatter. Root-mean-squared (rms) surface roughness values were also obtained from the analysis. The values of the refractive index (n) were found to be comparable to or slightly less than the values for single-crystal gem diamonds. The values of n were lowest in the most defective films. The absorption coefficient ((alpha) ) differs from that of single-crystal diamond. In some films, substantial absorption occurs in the visible to near- ultraviolet region (2 to 5 eV) where single-crystal diamond is transparent. The spectrum of this low-energy absorption is well-described by the Taucs function, which is used to fit the absorption spectra of 'diamondlike' amorphous carbon materials. There is a steep increase in (alpha) at photon energies at and above the indirect bandgap of diamond (5.5 eV). The absorption rises more steeply from 5.5 to 6.5 eV in these films than in single-crystal diamond, and the shape of the high-energy absorption edge is approximately exponential.

The phono-dispersion curves derived from neutron-scattering experiments performed on diamond are not accurate enough to yield the exact frequencies of critical-point (CP) phonons and, thus, to provide a satisfactory interpretation of second-order optical spectra. A self- consistent analysis of such spectra proved to be difficult because it is not a straightforward task to assign second-order absorption and scatter features to specific two-phonon summations. A more effective method for obtaining accurate CP-phonon frequencies involves investigating defect-activated one-phonon absorptions; in this paper, the authors take advantage of the availability of chemically vapor-deposited (CVD) diamond for the purpose of locating and assigning infrared (IR) absorption features in the one-phonon region to CP phonons at the Brillouin-zone boundary. Fourier-transform IR absorbance spectra of CVD diamond exhibit a complex structure at wavenumbers below the 1333-cm^-1 band-mode cutoff, which is induced by nitrogen-associated defect centers and yields the precise positions of sixteen zone-edge CP phonons. In conjunction with the triply-degenerate zone-center mode, this set of phonons then provides the basis for predicting the positions of second-order optical features through simple summations. Taking the selection rules into account, the procedure yields excellent results, not only in terms of CVD-diamond IR spectra, but also in regard to earlier measurements of the intrinsic two-phonon absorption coefficient of type-IIa natural diamond and the second-order polarization-dependent Raman-scatter characteristics recorded by Solin and Ramdas.

The purpose of this work is to show that diamond-like carbon (DLC) films of good quality can be deposited by sputtering of a graphite target in an argon-hydrogen atmosphere. The details of the RF diode sputtering system are described. The main features of the deposition process, such as the detection of CH radicals in the plasma, are presented. The advantages of this system are discussed. For example, it joins the easy-to-scale characteristics of the glow discharge process with the independent control of carbon and hydrogen sources found in dual ion beam sputtering. The DLC character of the films are checked measuring the Knupp hardness and the optical energy gap.

The optical properties of hard amorphous carbon layers deposited by different techniques (ECR-microwave plasma deposition, dc-plasma deposition, rf-sputtering, and electron beam evaporation) have been investigated from the middle IR up to the visible spectral regions. Refractive indices and absorption coefficient behavior have been determined by means of spectral transmittance and reflectance measurements. ECR microwave and dc-plasma deposited layers show a transparency wind w in the middle IR in the wavenumber range 1700 cm^-1 < ν < 2800 cm^-1. The refractive indices in the window region are between 1.9 and 2.3 with weak dispersion and show the usual increase of film mass density. However, absorption losses in the window-region are considerably higher than those in the case of diamond. For dc-plasma deposited layers, IR-absorption losses have been discussed in terms of a dispersion model, considering the absorption losses detected to be caused by a superposition of Lorentz lines and an Urbach tail. RF sputtered layers represent some kind of intermediate between graphiticlike layers (deposited by electron beam evaporation) and IR-transparent carbon formations. For rf-sputtered layers, IR-refractive indices show an extraordinary dependence on film mass density, which could be explained in terms of a mixing model, considering these layers to be built from graphiticlike and polymericlike compounds.

Measurements of the first-order Raman spectrum in homoepitaxially grown synthetic diamond for the temperature range of 300 to 1200 K are presented. Similar measurements for natural type IIa diamond for the temperature range of 300 to 2000 K are also given. Both the Stokes and anti-Stokes components are analyzed for their intensity, Raman shift, and width variation with temperature. The depolarization of the Raman signal at elevated temperatures was found to be the same as that at room-temperature. The synthetic diamond Raman shift indicated the presence of internal stress. The experimental first-order Raman shifts for natural diamond, using units of cm^-1 and absolute temperature, are conveniently expressed as (Delta)(nu) = a₁T² + a₂T + a₃ with the coefficients found to be -1.124 X 10^-5 cm^-1 K^-2, -6.71 X 10^-3 cm^-1 K^-1, and 1334.5 cm^-1, respectively.

Laser spectroscopic techniques to foster a fundamental understanding of diamond film growth by hot filament chemical vapor deposition (CVD) are being developed. Several spectroscopic techniques are under investigation to identify intermediate species present in the bulk reactor volume, the thin active volume immediately above the growing film, and the actual growing surface. Such a comprehensive examination of the overall deposition process is necessary because a combination of gas phase and surface chemistry is probably operating. Resonantly enhanced multiphoton ionization (REMPI) techniques have been emphasized. A growth reactor that permits through-the-substrate gas sampling for REMPI/time-of-flight mass spectroscopy has been developed.

In previous work it has been demonstrated that diamond thin films can be grown in a heated quartz flowtube by adding organic molecules to a stream of atomic hydrogen. In this system, the pattern of diamond film growth may be used to obtain information about the growth kinetics. In the present work, a thin, moveable catalytic probe that detects hydrogen atoms has been added. Since the flowtube is at a uniform temperature and has a high flowspeed, the rate of decay of H-atoms down the tube may be converted to a sticking coefficient, after making a small correction for diffusive mass transfer. The data were taken at a tube temperature of 800 Celsius and a pressure of 3.7 torr, with 1 SCCM of methane injected into a flow of 150 SCCM of 90% argon, 10% hydrogen. Calibration of the H-atom probe indicates that all the hydrogen is initially nearly dissociated. The probe measurements give a sticking coefficient at 800 Celsius of about 3 X 10^-4 for the silicon/diamond substrates. During diamond deposition, i.e., when methane is flowing, the apparent sticking coefficient rises to 2.5 X 10^-3, although this includes the effect of gas phase reaction as well as wall loss. We will discuss how these numbers shed light on proposed mechanisms for diamond formation.

Diamond particles were employed to toughen zinc sulfide--an infrared transparent, but mechanically weak material in its pure state. The optical properties of pure ZnS were preserved in a composite when the diamond particles were well dispersed and, when compared to the wavelength, their sizes were sufficiently small. Careful control of the processing parameters was required to maintain a small grain size and to limit the phase transformation of ZnS to a non-cubic phase at high temperatures. Measurement of the reflectivity of this composite in the region of the lattice vibration spectrum was used to compare the measured electrodynamic properties with those predicted by two different theoretical models that assume different microstructural morphology. Good agreement was found with the Bruggemann model that assumes both components in the composite have the same type of interconnectedness.

The activities for diamond film by so-called 'magneto-active low pressure plasma CVD' with film characteristics were started in 1987. The motivation has been to establish the fabrication of high-quality and wide-area diamond films at low deposition temperature. How and why the low pressure (0.1 ~ 0.001Torr) plasma which is 3 or 4 order of magnitude lower than conventional plasma CVD can be used for diamond films with deposition rate of about 1 micrometers /hr are examined. How and why the starting gases have been changed from the conventional CH₄ + H₂ to CH₄ + CO + CO₂ + H₂ and also CH₂ (OH) + H_e (no H₂) are discussed. How successfully the double- probe method has been applied to characterize the low pressure plasma for the first time is presented. How the SENTAXY diamond films composed of very high quality diamond particles have been improved is considered. The paper also discusses how detailed the Cathode Luminescence (CL) method has been applied for the characterization of diamond films and the analysis of the impurity and radiation induced color centers in the films, and how other characterization techniques such as XPS, RBS have been applied for the first time to investigate the CVD diamond films.

The nucleation and growth mechanism of polycrystalline diamond films prepared by chemical vapor deposition (CVD) have received increasing research interest. To verify the existence of the transition layers between CVD diamond films and substrates, and to investigate their composition, structure and properties are very meaningful research topics for understanding the mechanism of diamond film growth and developing the applications of CVD diamond films. In this work, the transition layers of carbides for the substrates of molybdenum (Mo), silicon (Si), tungsten (W), tantalum (Ta), and niobium (Nb) and titanium (Ti) have been systematically studied by x-ray diffraction characterization. The experiment results have provided evidence of the existence of transition layers and have revealed that the transition layers are polycrystalline Mo₂C, SiC, WC and W₂C, TaC and Ta₂C, NbC and Nb₂C, as well as TiC for the substrates of Mo, Si, W, Ta, Nb and Ti, respectively.

Nitrogen ions were implanted into diamond films formed by microwave plasma CVD. A color cathodoluminescence (CL) system were used to investigate the emission centers of as implanted and the subsequent annealed films. A zero-phono-line (ZPL) from the implanted N+ was observed at 3.19 eV. After annealing, a ZPL at 2.16 eV and a strong emission center in the violet region with a ZPL at 3.19 eV and phonon replicas were observed. The color CL images of the annealed films show that an orange-red color emission comes only from the {100} sectors because of the difference in crystal quality between the {100} and {111} sectors.

Recent progress in ion beam polishing has successfully led to the production of smooth diamond films. By means of an oxygen ion beam, a 5 cm diameter, 1 micrometers rough film grown by microwave plasma chemical vapor deposition on silicon has been polished. The polished film root-mean-square and peak-to-valley roughness values averaged over 15 points are respectively 5.5 nm and 55.4 nm. Scattering has been decreased to the point where the polished film is transparent at wavelengths above the silicon absorption edge and shows interference fringes. This suggests that diamond films polished by this process can be used in optical applications. This paper describes the polishing technique and presents the results obtained by surface profilometry of the polished sample. The main advantages of ion beam polishing over other existing methods lie in the fact that it is noncontact and low-temperature technique.

Preparation of diamondlike carbon films (DLC) from various kinds of organic Langmuir- Blodgett (LB) films by laser light irradiation is reported. The properties of DLC films is discussed. Using surface enhanced Raman scattering techniques, DLC films were analyzed during formation. These films are expected to be very promising for various applications.

The morphological evolution on the (1 1 1 } and (100 } faces of CVD diamond proceeded overwhelmingly through a two-dimensional layer mechanism. However, experimental evidence on defect-facilitated renucleation on the {1 1 1} faces and direct atom attachment to the lattice on the {100} faces was also found which resulted in one-dimensional growth. The {100)-oriented films were developed through a typical competitive, evolutionary selection process with sufficient surface diffusion which leaded to the formation of the pronounced <100> textured columnar structure, whereas the {1 1 1}-faceted crystals were produced under conditions of very high adatom mobility with periodical renucleation, the preferential growth direction of which was along the <110>. On the other hand, films produced at high carbon supersaturations possessed a randomly oriented columnar structure with ball shaped clustered surface, the growth process of which was dominated by constant renucleation. While the {1 1 1}-faceted crystals were usually highly defective in their internal structure, the {100}-oriented crystals were generally planar-defect free.