Diamond nanorods from nanocrystalline diamond films

Diamond nanorods (DNRs) have been prepared by hydrogen plasma post-treatment of nanocrystalline diamond films in radio-frequency (RF) plasma-assisted hot-filament chemical vapor deposition. Single-crystal diamond nanorods with diameters of 3–5 nm and with lengths up to 200 nm grow under hydrogen plasma irradiation of nanocrystalline diamond thin film on the Si substrate at high temperatures. The DNRs growth occurs from graphite clusters. The graphite clusters arises from the etching of diamond carbon atoms and from the non-diamond phase present in the parent film. The graphite clusters recrystallized to form nanocrystalline diamonds which further grow for diamond nanorods. The negative applied bias and surface stresses are suggested to support one-dimensional growth. The growth direction of diamond nanorods is perpendicular to the (1 1 1) crystallographic planes of diamond. The studies address the structure and growth mechanism of diamond nanorods.     

High rate growth of thick diamond films by high-current hot-cathode PCVD

On the basis of a conventional direct-current glow discharge plasma chemical vapor deposition (DC-PCVD), we succeeded in raising the deposition rate of diamond films to a large extent by increasing its discharge power. The maximum deposition rate reached about 20 μm/h. The quality of diamond films was also much improved. The maximum thermal conductivity of diamond films prepared by our process was 15.1 W/K cm. Diamond films with such high thermal conductivity can meet the need of many thermal management applications. In this paper, the influences of the deposition techniques on the characteristics of diamond films were studied experimentally from the viewpoint of discharge current.     

Structure of anthracene thin films

Structure of anthracene thin films as dependent on the temperature of the substrate, thickness and condensation rate is studied. It was found that at temperatures t_s ≦ 55°C condensation is governed by a vapour crystal mechanism while at temperatures t_s > 55°C it follows as vapour fluid one. Depending on the condensation rate the crystals take pyramidal forms, those of dendrites and spherolites. At temperatures t_s < 55°C the films are mainly oriented with its plane (001) parallel to the substrate.     

Growth and real structure of diamond films synthesized on polycrystalline tungsten substrates

X-ray diffraction studies of diamond films obtained by chemical transport reactions at the concentrations of 2% methane and 98% hydrogen under pressures of 10.7 and 21.3 kPa showed that they are textured. The character of the texture depends on the substrate temperature. The films have {110}, {311}, or double {110} + {311} textures. It is established that the dependence of the growth rate of diamond films on the substrate temperature has maxima. The diamond films are finely dispersed and are characterized by pronounced micro-deformations and high dislocation densities. The temperature dependence of the growth rate correlates with the parameters of the real structure of the films.     

Structure of multicomponent amorphous semiconductor films

Composition of multicomponent amorphous semiconductor films varies with the preparation technique and the chemical nature of component atoms. Inhomogeneous structures due to phase separation of compositional fluctuation have been observed in these films. It seems that there are some regularities governing the film growth and the structure of liquid phase condensation.     

Formation of needlelike crystallites during growth of diamond films by chemical vapor deposition

Diamond polycrystalline films have been grown by chemical vapor deposition from a hydrogenmethane mixture. The phase composition and structure of the films were studied using Raman spectroscopy, electron microscopy, and thermogravimetry. It is found that, upon heating in air, the oxidation of the carbon material forming the films occurs at significantly different temperatures, depending on the degree of its order and the crystallite size. This difference is used for selective oxidation of the least ordered fine-grained component of the films. The material obtained by this selective oxidation of the films consists of diamond crystallites shaped like regular micrometer-sized tetragonal pyramids with a radius of tip curvature of several nanometers.     

Growth feature of layered self-standing diamond films by DC arc plasma jet CVD

Layered self-standing diamond films, two-, three- and four-layered films, were fabricated by varying the ratio of methane to hydrogen in high-power DC arc plasma jet CVD. Results of scanning electronic microscopy (SEM) and Raman spectra showed that the layered films were constructed by the micro-crystalline grains layer/nano-crystalline grains layer. The residual stress within the films were balanced, and even diminished in the certain layer. The grain size was calculated by X-ray diffraction (XRD). The layer containing nanocrystalline grains due to a plenty of secondary nucleation can weakly inherit the columnar growth feature of the overlaid layer containing micro-crystalline grains. The grain size and growth orientation of the layer containing micro-crystalline grains can be adjusted by introduction of a mid-layer containing nano-crystalline grains. Growth rate was over 10 mm/h in layered film fabrication.     

Paramagnetic defects in diamond films synthesized by the hot filament chemical vapour deposition

Defects in nitrogen‐doped diamond films, produced by hot filament chemical vapour deposition have been studied by Electron Spin Resonance (ESR), Raman spectroscopy and Scanning Electron Microscopy (SEM). The peak‐to‐peak ESR line width (ΔH _pp) varies in the range 0.36‐0.52 mT and depends on the nitrogen concentration in the process gas. In the case of nitrogen‐doped diamond films ESR spectrum shows a hyperfine structure typical of N_S⁰ paramagnetic centre. The shape of the central ESR line shows that it is a superposition of two components: a narrower Lorentzian and a broader Gaussian one, characterized by different saturation behaviour. With increasing nitrogen concentration in process gas the ratio of integral intensities A _G/A _L (Gausian to Lorentzian) of ESR spectrum also increases. The Raman spectra show that with increasing doping level the diamond Raman line at 1332.5 cm^‐1 broadens, the broad band at about 1530 cm^‐1 becomes more pronounced what indicate on degradation of diamond crystallinity and it is in agreement with SEM observation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X-ray diffraction characterization of epitaxial CVD diamond films with natural and isotopically modified compositions

Comparative investigations of homoepitaxial diamond films with natural and modified isotopic compositions, grown by chemical vapor deposition (CVD) on type-Ib diamond substrates, are carried out using double-crystal X-ray diffractometry and topography. The lattice mismatch between the substrate and film is precisely measured. A decrease in the lattice constant on the order of (Δa/a)_relax ～ (1.1–1.2) × 10^–4 is recorded in isotopically modified ¹³С (99.96%) films. The critical thicknesses of pseudomorphic diamond films is calculated. A significant increase in the dislocation density due to the elastic stress relaxation is revealed by X-ray topography.     

Electron paramagnetic resonance and raman spectroscopy characterization of diamond films fabricated by HF CVD method

Thin polycrystalline diamond films were synthesized on silicon substrate by Hot Filament Chemical Vapor Deposition (HF CVD) technique from a mixture of hydrogen and different content of methyl alcohol. A comparative study on the Electron Paramagnetic Resonance (EPR), Raman spectroscopy and Scanning Electron Microscopy (SEM) were performed. It was shown that EPR signal, Raman spectra and morphology, studied by SEM, strongly depend on the ratio of CH₃OH/H₂ in the HF CVD reactor. The peak‐to‐peak line‐width in EPR signal varies from 0.09 to 0.8 mT depending on diamond quality. The Raman spectra of our diamond film showed, except well defined diamond Raman lines positioned at 1332 cm^‐1 with different Full Width at Half Maximum (FWHM), a broad band having maximum at around 1530 cm^‐1 which is characteristic for amorphous carbon phase. The obtained results show that EPR, SEM and Raman spectroscopy yield complementary results about the defects present in CVD diamond films. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Smooth diamond films grown by hot filament chemical vapor deposition on positively biased silicon substrates

Smooth diamond films have been grown by hot filament chemical vapor deposition under DC bias on mirror-polished Si(100) substrates. Films of a few micrometers thickness were obtained in 30 min. The films were found to have d-spacing at 2.06 and 2.11 Å by X-ray diffraction. Raman spectra showed very broad peaks at 1329 (1336) and 1591 cm^-1. The films have a high density of planar defects and large internal stresses.     

Structure of copper-doped tungsten oxide films for solid-state memory

Copper-doped WO₃ films, which are an active media for programmable metallization cell memory devices, are studied. The highlights of this study are the intercalation products forming on the interface between the WO₃ and Cu during thermal evaporation and also after thermal or photothermal diffusion of Cu into WO₃ films. The diffusion profile is established using Auger spectroscopy. Further characterization is provided using Raman spectroscopy which gives evidence for formation of products with a lower valence state related to W and oxidation products related to Cu. The composition of the intercalation products containing Cu is confirmed using X-ray diffraction which shows the formation of copper oxides and tungstates.     

Structure formation in Gd–Fe thin films

The structure, thermal stability and kinetics of phase transformations were explored for films of Gd₂Fe₁₇ compounds. The films were obtained by means of thermal evaporation in vacuum. Amorphous films were found to form at room temperature of substrates, amorphous-crystal condensates at T_s = 300–500 K, and polycrystalline films at T_s > 500 K. The crystal structure of condensates was determined at various temperatures and crystallization of amorphous films was found to be heterogeneous in character. Two phases, Gd₆Fe₂₃ and a-Fe, were observed in polycrystalline films, while three phases were found to exist in the films obtained at substrate temperatures >500 K: a hexagonal Gd₂Fe₁₇ phase of the Th₂Ni₁₇ structural type, a rhombohedral Gd₂Fe₁₇ phase of the Th₂Zn₁₇ structural type and a hexagonal GdFe₅ phase of the CaCu₅ structural type.     

Structure and growth morphology of RF-sputtered superthin niobium films

Superthin niobium films of 3 to 35 Å thickness prepared by radio-frequency sputtering have been studied by modern X-ray methods, such as reflectometry, fluorescence analysis and grazing beam structure analysis. It has been shown that the films were polycrystalline and consisted of several layers of niobium oxides and solid solution Nb O. Two simple models were used to describe erly stages of film growth. In the stage of island growth the complete oxidation of Nb to Nb₂O₅ is inevitable. Beginning from effective thickness ∼ 5 Å the deposited film becomes continuous, and further, layer-by-layer growth takes place.     

High-quality diamond films grown at high deposition rates using high-power-density MWPCVD method with conventional quartz-type chamber

Undoped and boron-doped homoepitaxial diamond films with high quality have been successfully grown on high-pressure/high-temperature-synthesized type-Ib single-crystalline diamond (1 0 0) substrates. In the growth process, a conventional microwave-plasma (MWP) chemical-vapor-deposition (CVD) system with an easily-exchangeable 36-mm-inner-diameter quartz-tube growth chamber was employed under a condition of high MW power densities while a rather high methane concentration (4%) and high substrate temperatures (>1000 °C) were used. The growth conditions applied to the undoped and B-doped diamond thin films were separately optimized by controlling the MW plasma density and substrate temperatures. The homoepitaxial films thus grown yielded strong exciton-related luminescence even at room temperature, meaning that their crystalline quality was good and roughly comparable with that of homoepitaxial films deposited using a high-power MWPCVD system with a stainless steel chamber having a rather large diameter. This indicates that by using such a conventional deposition system with inexpensive and easily-exchangeable exclusive-use quartz-tube chambers, various growth experiments can be performed under different process conditions without any severe interference among the different experiments.     

Structure and thermal fluctuations in thin films of smectic liquid crystals

Thermal fluctuations of the smectic layers in freely suspended thin liquid crystalline films have been studied by the methods of X-ray diffraction and reflectometry. The fluctuation dynamics is studied by the methods of photon correlation spectroscopy with the use of a source of coherent synchrotron radiation. In freely suspended smectic films, the typical relaxation times are of the order of several microseconds. In thin liquid crystalline films, the simultaneous damped and oscillatory behavior was observed for the layer undulations.     

Structure and electrical conduction of Sb2O3 thin films

Antimony trioxide (Sb₂O₃) thin films have been deposited onto glass substrates using thermal evaporation technique at room temperature. The structural feature and surface morphology were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Sandwich‐type structures were deposited with films thickness d = 0.55 μm using evaporated electrodes of silver. Current‐voltage (J‐U) characteristics have been measured at various fixed temperatures in the range 293‐473 K. In all cases, at low electric field (E <10⁴ V/cm), ohmic behavior is observed. However, at high electric field (E >10⁴ V/cm), non‐ohmic behavior is observed. An analysis of the experimental data indicates that in the range of high‐applied electric field, the dominant conduction mechanism is space charge limited currents (SCLC). Using the relevant SCLC theory, the carrier concentration, total trap concentration and the ratio of free charge to trapped charge have been calculated and correlated with changes in the structures of antimony trioxide thin films. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and optical properties of amorphous GeSx films prepared by PLD

Amorphous GeS_x (x = 2, 4, 6) films were prepared by the pulsed laser deposition (PLD) technique. The optical band gaps (E_g^opt) and refractive indices of the films were obtained from the optical absorption spectra and transmission spectra, respectively. The short-wave absorption edges of the films were described using the ‘non-direct transition’ model proposed by Tauc. The dispersion of the refractive index was analyzed in terms of the single-oscillator Wemple–Di Domenico model. The structural units of the films were characterized using Raman spectroscopy. In addition to the basic structural units of edge-sharing and corner-sharing [GeS₄] tetrahedra, there are S–S homopolar bonds in S-rich GeS₄ and GeS₆ films while Ge–Ge bonds exist in stoichiometric GeS₂ film. The results show that the index of refraction decreases while E_g^opt increases with the sulphur content in the GeS_x films. The changes of E_g^opt were discussed in relation to the structure of GeS_x films, which were confirmed by the Raman spectra analysis.     

Simulation of temperature and gas density field distribution in diamond films growth on silicon wafer by hot filament CVD

In the present study, the temperature and gas density field inside the hot filament chemical vapor deposition (HFCVD) reactor, which play a determinate role on the growth rate and quality of as-deposited diamond films, are simulated using the finite volume method, and the influence of the size and arrangement of filaments and inlets are investigated. Firstly, the correctness of the simulation model is verified by comparing the temperature data obtained from the simulation with that measured in an actual depositing process, and the results show that the error between them is less than 3%. Thereafter, the deposition parameters are optimized using this model as N(filament number)=6, r(filament radius)=0.4 mm, D(filament separation)=16–18 mm, H(substrate–filament distance)=8–9 mm, and 25 inlets. Finally, diamond films are deposited on silicon (100) wafers using above parameters and the results of characterization by SEM and Raman spectrum exhibit that the deposited diamond films appear homogeneous surface with fine-faceted crystals.