Growth Of Amorphous Carbon Research Articles

Time development during growth and relaxation of amorphous carbon films. Tight-binding molecular dynamics study

The growth of amorphous carbon (a-C) thin film on a [1 1 1] diamond surface has been studied by a tight-binding (TB) molecular dynamics (MD) technique. Six different three-dimensional networks were constructed with periodic boundary conditions in two dimensions. Time-dependent non-equilibrium growth was simulated with atom-by-atom deposition and it was described as in real experiments without an artificial model of energy dissipation. An additional seventh structure was constructed by a melt quenching procedure which is widely used in computer generations of amorphous networks. The final structures consist of over 100 atoms. Densities, radial distribution functions (RDFs), coordination numbers, bond angle distributions and ring statistics were analyzed. During relaxation the temperature in the amorphous film decreases with stretched-exponential function. The time dependence of bond length and bond angle deviations were also investigated.

Growth of amorphous carbon: Low-energy molecular dynamics simulation of atomic bombardment

The growth of amorphous carbon thin film on a [111] diamond surface has been studied by a tight-binding molecular dynamics technique. Six different three-dimensional networks were constructed with periodic boundary conditions in two dimensions. Time-dependent nonequilibrium growth was simulated and densities, radial distribution functions, coordination numbers, bond angle distributions, and ring statistics were analyzed.

Control of Plasma Parameters for High-Quality Hydrogenated Amorphous Carbon Growth

The correlation between plasma parameters and film properties is demonstrated in the growth of device-grade hydrogenated amorphous carbon (a-C:H) from pure methane (CH4) by capacitively coupled plasma-enhanced chemical vapor deposition (CCP-CVD). The deposition rate, refractive index, film stress and film hardness are strongly correlated with the self-bias voltage, Vdc. Hard, rigid, and transparent a-C:H films can be fabricated when the self-bias voltage, Vdc, is around 160–200 V. The ion energy, which is determined by the Vdc, is used to rearrange the film structure. The Vdc of around 160–200 V corresponds to 70–80 eV of the C ion flux in the case of C2H5+ ions. According to the calculation using a modified Thomas-Fermi potential as the Coulomb screening potential, the incident C ion energy is estimated to penetrate the carbon film of 1.8 g/cm3 density to the depth of about 0.55 nm, which enables the densification of the a-C:H film.

Atomic-scale modeling of the ion-beam-induced growth of amorphous carbon

The results of a detailed molecular-dynamics study of the growth of amorphous carbon $(a\ensuremath{-}\mathrm{C})$ are reported. Carbon atoms with kinetic energies between 10 and 150 eV are deposited on $a\ensuremath{-}\mathrm{C}$ surface originating from bulk $a\ensuremath{-}\mathrm{C}.$ Earlier simulation results of an optimal energy window at 40--70 eV are confirmed. Additionally, it is found that the growth rate is at maximum at around 40 eV. At low implantation energies ${(E}_{\mathrm{beam}}\ensuremath{\approx}10 \mathrm{eV}),$ the growth of amorphous carbon takes place on the surface. At higher energies, the growth proceeds increasingly in the subsurface region by global film expansion and single atom diffusion towards the surface. Scattering events (e.g., the deposited atom does not adsorb to the surface) at intermediate energies ${E}_{\mathrm{beam}}\ensuremath{\approx}100 \mathrm{eV}$ result in a densification of the growing film. Moreover, at ${E}_{\mathrm{beam}}\ensuremath{\approx}150 \mathrm{eV},$ nonpermanent diamond formation is observed.

Insights on the deposition mechanism of sputtered amorphous carbon films

Low energy Ar + ion bombardment (LEIB) during growth of amorphous carbon (a-C) films deposited with magnetron sputtering (MS), results to dense films, rich in sp 3 C–C bonds, and exhibit high hardness and compressive stress. We present here a preliminary study of the growth mechanism of a-C films deposited with negative bias voltage (LEIB) in terms of their composition, density and mechanical properties. The experimental results showed that stress and hardness are directly related with the sp 3 C–C bonding in the film and described well with the so far proposed models on the formation mechanism of tetrahedral carbon. However, the film density, that is a composite property, was found to depend not only on the sp 2 and sp 3 content but also on a new, denser than graphite, carbon phase when the Ar + ion energy is above ∼130 eV.

A model for the simultaneous growth of amorphous carbon and diamond film

A model is developed which describes the growth of graphitic and amorphous carbon, and diamond. The results of detailed calculation illustrate that diamond and amorphous carbon grow simultaneously in the process of diamond chemical vapour deposition, and that their growth rates depend strongly on the substrate temperature and the flux ratio of hydrogen- and carbon-containing species. In addition, it was found that there are critical values for the substrate temperature and the flux ratio of hydrogen- and carbon-containing species below which only graphitic carbon film can grow.

Effects of electron and atomic hydrogen irradiation on gas-source molecular beam epitaxy of diamond with pure methane

Abstract We investigated the effects of electron and atomic hydrogen irradiation on gas-source molecular beam epitaxy (GSMBE) of diamond with pure methane (CH 4 ). Irradiating the C(001) surface with a 200 eV electron-beam at 800°C enhanced the growth rate (GR) ∼ 2–5 times over the method without irradiation. By using a CH 4 beam decomposed by electron impact in addition to the electron-beam irradiation, the GR was enhanced by > 100 times. However, the grown films contained an appreciable amount of amorphous carbon. By contrast, irradiating the surface with an atomic hydrogen beam enhanced the GR by about five-fold without the concurrent growth of amorphous carbon.

Molecular dynamics simulation of thin film amorphous carbon growth

Abstract Molecular dynamics simulations of amorphous diamond thin film growth were carried out using a Stillinger-Weber potential parameterised to describe both sp2 and sp3 carbon bonding. The effects of the incident beam energy and angle and substrate temperature were investigated. It was found that in very thin films, not deep enough to allow the generation of compressive stress, atomic impacts lead to the formation of a graphitic surface layer. Results also indicate that the optimal conditions for the formation of tetrahedral sp3 structures involve low incident beam energy and low substrate temperatures.

Model of the competitive growth of amorphous carbon and diamond films

Recent experiments by D. S. Olson, M. A. Kelly, S. Kapoor, and S. B. Hagstrom [J. Appl. Phys. 74, 5167 (1993)] have demonstrated that depending on the ratio of the fluxes of carbon and atomic hydrogen onto a substrate in a chemical vapor deposition reactor, either an amorphous carbon deposit, or a crystalline diamond film, may be produced. A simple interpretation of these findings is proposed, based on a set of phenomenological rate equations for various growth and etching processes. The model is simple enough to admit analytical solutions in certain circumstances, which may provide insights into the optimisation of carbon film deposition methods.

Growth of silicon carbide on (100) silicon substrates by molecular beam epitaxy

A plasma activated gas source molecular beam epitaxy process has been developed in which the molecular beam is formed by activating a methane-hydrogen mixture in a plasma source. Amorphous carbon growth on (100) silicon substrates occurs when the substrate temperature exceeds 800°C. The growth of cubic silicon carbide is observed above 880°C. Epitaxial silicon carbide layers are characterised using x-ray photoemission spectroscopy, atomic force microscopy, ellipsometry and Rutherford backscattering.

Diamond and non-diamond carbon synthesis in an oxygen-acetylene flame

diamond and non-diamond carbon deposition in an oxygen-acetylene combustion flame has been analyzed over a range of oxidizer:fuel ratios ( R f) and substrate temperatures ( T s). The effects on diamond deposition of substrate preparation and position in the oxygen-acetylene flame have been examined. Diagrams relating diamond, microcrystalline graphite and amorphous carbon growth to the oxygen:acetylene flow ratio and substrate temperature have been developed. In addition, the dependences of particle morphology and growth rate on T s and R f were examined. Micro-Raman spectroscopy, optical microscopy and scanning electron microscopy were used to analyze the growth.

Synthesis of diamond thin films by hot-filament- assisted chemical vapour deposition

Diamond thin films were prepared by thermal decomposition of methane and hydrogen in the presence of a hot tungsten filament. The crystalline structure of the films was characterized by reflection high energy electron diffraction, scanning electron microscopy (SEM) and Raman spectroscopy. SEM morphologies and Raman spectra depend on experimental conditions. The influence of experimental conditions on the growth process is discussed by consideration of the surface properties of diamond. For particular experimental conditions, growth of amorphous carbon with atoms in sp 2 or sp 3 sites is evidenced.