Amorphous Diamond Films Research Articles

Consecutive deposition of amorphous SiO2 interlayer and diamond film on graphite by chemical vapor deposition

Chemical vapor deposition (CVD) diamond films can be used as effective protective coatings on graphite components, while the film-substrate adhesion is poor probably due to the graphite etching caused by the atomic hydrogen. It is supposed as a useful way to pre-deposit an amorphous SiO2 (a-SiO2) layer for solving this problem. In this study, by interposing a-SiO2 interlayers, four types of diamond films are deposited on common commercial graphite substrates, and noteworthy is that such the a-SiO2 layer and CVD diamond film are consecutively synthesized in the same hot filament CVD apparatus. It is proved that as-deposited a-SiO2 layer has typical amorphous features, provides sufficient protections on the substrate, and avoids the natural removal of the diamond film when growing. Micro-crystalline diamond, nano-crystalline diamond, boron-doped micro-crystalline diamond (BDMCD) and boron-doped nano-crystalline diamond films deposited on a-SiO2 coated graphite substrates present typical features in consistent with micro- or nano-sized diamond films on other substrates. Among the four diamond films, mainly facing to some application requirements for the electrical conductivity, the BDMCD film shows relatively better comprehensive performance, including high diamond purity, high nano hardness (74.21 GPa) and elastic modulus (890.93 GPa), favorable adhesion and low electrical resistivity (29 μΩ m).

Morphological and electrical characterization of FIB implanted diamond surfaces

We report on the realization of amorphous diamond films obtained by means of Ga+ focused ion beam at different ion dose. We implemented a novel methodology, which combines a selective removal of amorphous carbon material and atomic force microscopy to collect topographic maps and height data. The procedure allowed for a precise measurement of the resistivity of amorphous carbon film by using actual film thickness values instead of data obtained from simulations or theoretical calculations. Large area Ti contacts overlapping the amorphous carbon layer surface were used for current–voltage measurements. An ohmic behavior characterized by a low contact resistance was found. Conversely, the local probing of the amorphous diamond surface with the conductive tip of a C-AFM evidenced an inhomogeneous conductive behavior, ranging from nearly ohmic to nearly rectifying, and a dose dependent surface conduction.

Modeling of the effects of substrate temperature and C2-containing plasma pressure on the structure of carbon films

This paper examines the role of carbon (C2) molecules in structure formation of crystalline and amorphous diamond films. Analysis of the potential energy of chemisorbed particles and possible interactions between them is used to model the layer assembly process. The modeling results demonstrate how the substrate temperature and C2 partial pressure (the most important process parameters) influence the structure of diamond-like carbon films.

Influence of Additive on Diamond Films Synthesized Using Liquid Phase Electrochemical Method

An attempt was made to deposit nano-crystalline (or amorphous) diamond films on silicon and 316L stainless steel substrates by electrochemical deposition using a high-voltage pulsed generator. Alcoholic organic compounds with various concentrations of deionized water were used as electrolysis solutions. The surface morphology and crystal structure of the films were examined by scanning electron microscopy and Raman spectroscopy. Adding de-ionized water into the reaction solution can enhance the deposition rate of amorphous diamond films. The crystalline structure analysis has confirmed unambiguously the formation of diamond nano- or submicron-crystals in the deposits. It is believed that the ion H of electrochemical production plays quite similar roles to those that take place in chemical vapor deposition methods of diamond growth.

Boron doped amorphous diamond window layer deposited by filtered arc for amorphous silicon alloy p–i–n solar cells

In order to improve the conversion efficiency of amorphous silicon (a-Si:H) alloy p–i–n solar cells, the original p-a-Si:H window layer is substituted by the boron-doped amorphous diamond (a-D:B) films deposited using filtered cathodic vacuum arc technology. The microstructural, optical and electrical properties as functions of the boron concentrations in the films were, respectively, evaluated by an X-ray photoemission spectroscopy, an ultraviolet–visible spectrometer and a semiconductor parameter analyzer. The photovoltaic parameters of the solar cell modules were also detected as functions of boron concentration. It has been shown that the conductive a-D:B films could be obtained and still remained a wide optical gap. The p–i–n structural amorphous silicon solar cell using the a-D:B window layer increased the conversion efficiency by a roughly 10% relative improvement compared to the conventional amorphous silicon solar cell because of the enhancement of short wavelength response.

Using Boron Doped Amorphous Diamond Films as Window Layer of Amorphous Silicon Solar Cells

Boron doped amorphous diamond(a-D:B)films,which possess a wide optical gap and good p-type semi-conductive electroconductibility,were prepared using filtered cathodic vacuum arc system, whose target source was highly pure graphite incorporated with boron element.The intrinsic layer and the n-type layer of amorphous silicon solar ceils in a configuration of p-i-n were deposited using PECVD technology.The optical gap of the boron doped amorphous diamond films was characterized with a Lambda 950 UV-Vis photometer.The parameters of solar cells,such as open-circuit voltage,short- circuit current,fill factor and efficiency,were also measured.It shows that using the a-D:B films as the window layer of p-i-n structural amorphous silicon solar cell can increase the cell conversion efficiency by a roughly 10% relative improvement compared to the conventional amorphous silicon solar cell because of the enhancement of short wavelength response.

The characteristics of inorganic electroluminescent devices with an amorphous diamond film as cathode material

Diamond like carbon (DLC) thin films were used as the cathode layers of inorganic alternating current driven thick dielectric electroluminescent devices. The results indicated that electroluminescent (EL) devices with DLC cathode has superior brightness over the EL with Al or Cr-doped DLC cathodes. Cr-doping in DLC thin film can increase the electrical conductivity, but degrades the EL properties. Also, the EL device with DLC cathode possesses the lowest decay rate among various cathodes, because of the high thermal conductivity and the inert nature of DLC film.

Deposition of Amorphous Diamond Films on Different Substrates by Electrolysis of Methanol Solution

Amorphous diamond films were deposited on both (100) silicon and 316L stainless steel substrates at atmospheric pressure and low temperature (60°C) with a direct current pulsed power supply using methanol/additive solution as electrolyte. The morphology and microstructure of the films were analyzed by scanning electron microscopy (SEM) and Raman spectroscopy. The friction and wear behavior of the films were examined on the CERT test system. The SEM observations showed that the films consisted of fine and compact ball-like grains with about 300nm in diameter. Raman spectroscopy analysis confirmed the diamond structure by the presence of strong peaks at 1333cm-1 for both substrates. The friction coefficient of the films deposited on both substrates against WC ball was about 0.10 at ambient conditions. The active additive could play an important role not only in improving adhesive strength between the films and substrates, but also in increasing relative content of diamond phase in the films.

Interfacial evaluation of filtered arc-deposited amorphous diamond films on germanium

The interface between amorphous diamond films deposited by a filtered arc and germanium substrate was characterized by X-ray photoelectron spectroscopy. The coherent energy shifts of carbon and germanium photoelectron lines with prolonged etching time confirm the existence of an amorphous germanium carbide phase consisting of nonhomogeneous components in the interfacial region. This compound forms a buffer layer with a gradient of composition and microstructure from the substrate to the film and is beneficial to film adhesion.

C 1s photoemission investigation of substrate bias and annealing temperature influencing the microstructure of amorphous diamond films

The hybridization composition of amorphous diamond films deposited using a filtered arc has been investigated as functions of the substrate bias and the annealing temperature by the deconvolution of C 1s photoemission spectra. The chemical shift and the half width of the entire C 1s spectrum have demonstrated the clear regularities to the changing bias and temperature. The XPS C 1s core level spectra can provide a powerful way to follow the evolution of the sp3 bonding configurations.

Use of an amorphous diamond film as dental material

The biocompatibility and surface characteristics of dental materials surface-modified by an amorphous diamond film were investigated. The dental materials are poly(methyl methacrylate) (PMMA) and pure titanium and the amorphous diamond film surface was produced by a plasma assisted cathode arc discharge under vacuum. The biocompatibility was evaluated by cell cultivation and animal implants and the wearability of the PMMA tooth after modification was analyzed by a scratching test. The surface characteristics of the film were characterized by SEM. The corrosion resistance of the surface of pure titanium dental material after the surface modification was investigated by the electrochemical analysis of a simulatee oral cavity filled with artificial saliva. Results show that the toxicity of the amorphous diamond film modified dental materials is zero, and the hemolysis ratio is 3.08%. After polarization pre-treatment, the PMMA artificial tooth coated with an amorphous diamond film has a maximium adhesion force of 10.86±0.79N. The self-corrosive potential and the over-passivation potential of the pure titanium after the surface modification were increased. These results demonstrate that coating the surface of dental materials with a diamond film meets the requirements of biocompatibility, anticorrosion and adhesion strength.

Temperature sensibility of amorphous diamond films prepared by filtered arc

The low temperature sensibility and the thermal stability in air of amorphous diamond (a-D) films deposited by filtered arc have been investigated with visible Raman spectroscopy. The films cooled in a range of room temperature to − 190 °C by a liquid nitrogen pump were in-situ measured on a Linkam stage. The films for thermal stability were heated in a furnace. It has been found that the films are thermally very stable in air. They can hold their hardness up to 400 °C and their structure up to 500 °C. However, complete material loss occurs if the temperature is continuously raised. Raman measurements show a shift of the G-peak frequency to higher values with increasing temperature. The films are not sensitive to low temperature and remain stable as temperature is decreased down to − 190 °C.

Mechanical properties and Raman characterization of amorphous diamond films as a function of film thickness

Amorphous diamond (a-D) films with different thicknesses have been prepared on the c-Si substrate under the same deposition conditions using filtered cathodic vacuum arc (FCVA) technology. The film thickness was measured with a calibrated surface profiler. The mechanical properties were analyzed by a nano-indenter and the microstructure was characterized with visible Raman spectroscopy. It has been shown that the residual compressive stress of a-D films drops continuously down with increasing film thickness. When the films are thinner, the stress falls strikingly. However, the falling rate is less pronounced with the monotonic increase in film thickness. Hardness and Young's modulus also persistently rise with growing film thickness. Whereas the critical scratching load decreases at first and then increases again. The peak position of the asymmetric broad peak in the Raman spectra shifts towards low frequencies with increasing film thickness because of the monotonic fall in the residual compressive stress. However, the magnitude of the shift is smaller. Additionally, the Raman characterization is apt to be taken in the film thickness scope of 50–80 nm.

A comparative Raman study of thermal stability of amorphous diamond films deposited with different substrate bias

This paper describes thermal stability of amorphous diamond films deposited using a filtered arc as a function of the substrate bias using a comparative Raman investigation. The thermal stability decreases with increasing substrate bias. The films with the richest sp3 content might not have the best thermal stability. Annealing results in an upward shift and a narrowing of the G-peak. Visible Raman can provide a powerful way to follow the evolution and ordering of sp2 sites in the films.

Superexcellent infrared protective coatings: Amorphous diamond films deposited by filtered cathodic vacuum arc technology

To develop new infrared antireflective and protective coatings on the infrared band, amorphous diamond (a-D) films deposited by filtered cathodic vacuum arc (FCVA) technology have been investigated. The mechanical properties were characterized with the nano-indenter and the stress was calculated using Stoney's equation. The optical properties were analysed with spectroscopic ellipsometry and the microstructure was investigated with EELS. The maximal hardness and Young's modulus consorting with the highest stress are represented at the negative bias of 80 V. When the bias is increased or decreased, hardness, Young's modulus and stress will descend gradually. However, the high impinging energy benefits the better adhesion and the lower stress. In the wide infrared band, the films are transparent. The optical gap and the refractive index exhibit the same changing regularities like hardness and stress, whereas the extinction coefficient demonstrates the reverse trace. The changing rules can be perfectly explained in light of the ratio of the different hybridization and the growth mechanism of the films. In short, a-D films deposited by the FCVA technology are superexcellent infrared protective coatings.

Thermal transport and grain boundary conductance in ultrananocrystalline diamond thin films

Although diamond has the highest known room temperature thermal conductivity, k∼2200W∕mK, highly sp3 amorphous carbon films have k<15W∕mK. We carry out an integrated experimental and simulation study of thermal transport in ultrananocrystalline diamond (UNCD) films. The experiments show that UNCD films with a grain size of 3–5nm have thermal conductivities as high as k=12W∕mK at room temperature, comparable with that of the most conductive amorphous diamond films. This value corresponds to a grain boundary (Kapitza) conductance greater than 3000MW∕m2K, which is ten times larger than that previously seen in any material. Our simulations of both UNCD and individual diamond grain boundaries yield values for the grain boundary conductance consistent with the experimentally obtained value, leading us to conclude that thermal transport in UNCD is controlled by the intrinsic properties of the grain boundaries.

Optical properties of amorphous diamond films evaluated by non-destructive spectroscopic ellipsometry

Abstract In order to investigate the regularities between the optical properties and the deposition conditions, the optical constants of amorphous diamond films deposited at the different substrate bias with the filtered cathodic vacuum arc technology have been measured by spectroscopic ellipsometry. It has been found that the refractive index and the optical gap of the films firstly increase and then decrease with the enhancing bias and there are respectively the maximal values when the negative bias is 80 V. However, the extinction coefficient of the films firstly minishes and then rises with the adding bias and there is the minimal value when the negative bias is also 80 V. The extinction coefficient gradually drops down with the increasing wavelength of incident light and nearly approaches to zero in the infrared band. Moreover, the adjustable scopes of refractive index and extinction coefficient changed by the substrate bias deflate little by little with the adding wavelength of incident light.

Field emission of micro aluminum cones coated by nano-tips of amorphous diamond

Nano-tips of amorphous diamond films were deposited on Al micro cones to form a metal/diamond interface structure. The amorphous diamond films were deposited by cathodic arc at a temperature less than 150 °C. The turn on applied field was 4.5 V/μm at 10 μA/cm 2 for the Al/diamond structure. The turn on applied field is approximately 10 times lower than that for Al alone. The high emission current was obtained (50 mA/cm 2) due to metal/diamond structure and the presence of defect band within band gap of amorphous diamond that allowed electrons to pass through with little hindrance. Moreover, the stability of electron emission was monitored at electrical field strength of 7 V/μm for 100 h. The fluctuations of long-term emission current were at ±4% during the entire duration of monitoring. The fluctuation may be due to the absorption and desorption of molecules by the dangling bonds of carbon atoms on surface of nano-tips of amorphous diamond in a vacuum chamber during electron emission. The high stability of electron emission form micro Al cones by nano-tips amorphous diamond coatings was observed.

Influence of the optimal etching conditions of silicon substrates on field-electron emission from amorphous-diamond films

The effect of chemical etching of silicon substrates on the field-electron emission (FEE) from amorphous-diamond (a-D) films deposited on silicon has been studied systematically and thoroughly. It is found that the greater the roughness of the silicon substrate, the better the FEE performance of the a-D/silicon emitter. For a sodium hydroxide concentration between 20% and 40%, an etching temperature in the range of 60–80 °C, and an etching time of 15–30 min, etching of the silicon substrate surface was found to be optimal for FEE from the a-D/silicon emitter. To explain the experimental results, qualitative analysis of the enhanced electric field caused by nanoprotrusions was done.

次世代超硬質材料の超高圧合成とナノ組織制御 ナノダイヤモンドセラミックス合成 ＩＩ 動的合成法 極短時間の核生成・粒成長の制御

Shock compaction methods for diamond powder can produce nanocrystalline diamond ceramics consisting of particles a few tens of nanometers in diameter. However, by using these methods, it is difficult to consolidate nanocrystalline diamond powder of only a few nanometers in diameter because heat localization, which is essentially important for the shock compaction process, can not be achieved. On the other hand, the SCARQ (shock compression and rapid quenching) method can produce transparent, nanocrystalline and/or amorphous diamond films 5-μm thick by controlling the nucleation and growth process in the phase transition from fullerene to diamond. The stability of the diamond phase dependent on their size is also discussed.