Papers by Keyword: Diamond Thin Film

Abstract: Synthetic diamond has remarkable properties comparable with natural diamond and hence is a very promising material for many various applications (sensors, heat sink, optical mirrors, cold cathode, tissue engineering, etc.). Nowadays, deposition of diamond films is normally employed in chemical vapor deposition (CVD) usually at high temperatures (800900 °C), what limit its application to high melting substrates. Gravimetric (mass) sensors belong to the major categories of chemical sensors and the most common type of mass sensor is the bulk acoustic quartz crystal microbalance (QCM). This contribution deals with a nanocrystalline diamond (NCD) growth from the H₂/CH₄/CO₂ gas mixture at low temperature (400 °C) by pulsed linear antenna microwave plasma system on 10 MHz circular AT-cut quartz resonators substrate. Gas sensor based on the NCD-coated QCM was developed for detection of ammonia (NH₃) at room temperature. Measurements not only confirmed the functionality of this first published NCD-coated QCM sensor, but in addition its sensitivity was twofold to a virgin QCM sensor with a gold active layer.

Abstract: In this paper we introduce fully optically transparent impedance biosensors based on intrinsic nanocrystalline diamond (NCD) films deposited on glass substrate. Prepared sensors have an interdigital electrode (IDE) structures realized by local hydrogen and oxygen termination of diamond surface, which mean in-plane configuration of active sensor area. Sensors were tested by real time monitoring of human osteoblast-like MG 63 cells in wide frequency range from 10 Hz to 100 kHz for several days. Two different measurement setups were used and compared regarding to their advantages and disadvantages. Proof of concept of diamond-based impedance sensor is showed, i.e. time dependence and frequency dependence (Nyquist plots) of absolute impedance.

Abstract: Homo-epitaxial (100) single crystal diamond films of different isotopic (13C) composition were synthesized by micro-wave plasma chemical vapor deposition (MPCVD). Undoped 12C (100) films were also synthesized at different thicknesses. The growth surface of 13C doped showed a sequential morphological change from flat surface to stepped or ledge surface and coarsening of the steps/ledges with the increase of 13C-isotope concentration. As the growth proceeds via surface steps/ledges and coarsening of these steps/ledges, further increase in imperfection of the grown CVD single crystal diamonds observed with the development of non-(100) orientations. In case of undoped 12C samples, as the thickness increased the in-grain misorientation got reduced.

Abstract: Abstract: In contrast to their exceptional mechanical properties, titanium and its alloys possess poor friction and wear characteristics. Nanocrystalline diamond (NCD) films appear to be a promising solution for their tribological problem due to their smooth surfaces and small grain size. However, the synthesis of a well adherent NCD film on titanium and its alloys is always complicated due to the different thermal expansion coefficients of the two materials, the complex nature of the interlayer formed during diamond deposition, and the difficulty in achieving very high nucleation density. In this work NCD thin films have been deposited on pure Ti substrates in a microwave plasma chemical vapor deposition (MWPCVD) reactor under fixed pressure and methane concentration in hydrogen but over a wide temperature range. The effects of depositing temperatures on the adhesion of films are evaluated using Rockwell indentation tests. It is found that by increasing the deposition temperature the films bonding deteriorates. The films synthesized are characterized by field emission scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and X-ray diffraction.

Abstract: Diamond films was deposited on cemented carbide tools with two-step pretreatment method under different distances between the substrates and hot filaments, and the effect of the distance between the substrates and hot filaments on the crystallographic orientation of diamond films and the characteristics of diamond coated tools was investigated in bias-enhanced HFCVD system in this paper. The cutting performance of diamond coated tools was verified by the experiments of cutting particles reinforced aluminum base composite material with 15 vol.% Si as compared with uncoated ones. The quality of diamond film was analyzed by means of Scanning Electron Microscopy(SEM), Raman spectroscopy, and X-ray diffraction. The optimization deposition processing was obtained. The relative intensity ratio of (111) facet and (220) facet in the film tested by XRD was one third. The cutting performance of diamond coated tool was improved significantly when machining the Si particle reinforced aluminum-based metal matrix composite; its lifetime was 30 times longer than that of uncoated one. The work done in this paper was of great practical significance to accelerate the industrialization of diamond films coated WC–Co substrates.

Abstract: Under optimization deposition parameters, such as the acetone concentration, reactive pressure, the bias power, diamond films was deposited on cemented carbide tools with two-step pretreatment method under different distances between the substrates and hot filaments, and the study on the effect of the distance between the substrates and hot filaments on the crystallographic orientation of diamond films and the characteristics of diamond coated tools were investigated in bias-enhanced HFCVD system in this paper. The cutting performance of diamond coated tools was verified by the experiments of cutting particles reinforced aluminum base composite material with 15 vol.% Si as compared with uncoated ones. The quality of diamond film was analyzed by means of SEM, Raman spectrum, and X-ray diffraction. The optimization deposition processing was obtained. The relative intensity ratio of (111) facet and (220) facet in the film tested by XRD was one third. The cutting performance of diamond coated tool was improved significantly when machining the Si particle reinforced aluminum-based metal matrix composite; its lifetime was as 30 times long as that of uncoated one. The work of this paper was of great practical significance to accelerate the industrialization of diamond films coated WC–Co substrates.

Abstract: Diamond thin films doped with various boron concentrations were grown on WC-Co cemented carbide tools by hot-filament-assisted chemical vapor deposition (HFCVD). The trimethyl borate dissolved in acetone solution was used as the boron resource (B/C=0%, 0.1%, 0.3%, 0.5%). The surface morphology of diamond films with different boron contents was investigated by Scanning electron microscopy, the adhesive strength was calculated by means of indentation test under a load of 1500N. A real cutting performance was carried out on Al metal matrix composites material (20vol%SiC, 15μm), and the insert flank wear was examined by measuring the scars that appeared on the cutting edge with tool microscope. The research results shown the surface morphology and structure of the diamond films changed owing to boron doping. As the doping levels increased, the average grain size of the films decreased from 10 to 2μm. A significant improvement in adhesion and cutting performance were observed as the boron contents increased from 0% to 0.5%. The adhesion and cutting performance were best when the boron concentration was 0.3%. Adequate boron can effectively suppress the cobalt diffusion to the substrate surface and avoid the catalytic effect of cobalt at the high temperature. It is of great significance for improvement of the adhesive strength and cutting performance of diamond-coated tools using above method.

Abstract: Large advancements have been achieved in understanding nucleation and growth of CVD diamond, but adhesion of diamond film to substrates is poor and there is no good methods about how to quantitative evaluation of the adhesive strength. The blister test is a method appropriate for measuring the adhesion of CVD diamond. In this test a pressure difference is applied across a thin film and the pressure when the film separates from substrate is measured, and the adhesive strength of diamond thin film was calculated using analytical model. Using the finite element model, the deflection at the center of a free-standing window sample of diamond thin films is calculated as a function of applied pressure and the adhesive strength is obtained using the FEM. The result indicates that finite element method-based prediction of the total energy release rate is in good agreement with that obtained from analytical expressions and experimentally observed values.

Abstract: Due to some inferior performance of Chemical Vapor Deposition (CVD) diamond dosimeters, their applications are somewhat limited. The quality of diamond films was improved using Microwave Plasma CVD (MWPCVD) by the modified processes such as cyclic deposition and in-situ plasma post-treatment. The simple radiation dosimeters were fabricated in a sandwich configuration. Influence of purity and orientation of the diamond films on the sensitivity of the dosimeters was studied. The results indicate that the radiation dosimeters have high sensitivity to X-ray and the response of the devices is linear with the X-ray flux. The higher the purity of films is, the higher the resistivity and sensitivity are. The dosimeter based on [100] film has higher sensitivity than that based on [111] film. The dosimeter based on films prepared by cyclic deposition has higher sensitivity than that based on films prepared by the conventional deposition. The characterization of the response to X-ray also shows that in-situ oxygen plasma post-treatment leads to the higher sensitivity of dosimeters compared with in-situ nitrogen, hydrogen plasma post-treatments.

Abstract: Adhesion properties of diamond thin films are essential to their performance in technical applications. To obtain the adhesive strength precisely and quantitatively has been the frontier issue to the related scientists and engineers. In this paper, a new experimental equipment for blister tests was designed purposely and fabricated considering related influencing facts. A free-standing window of diamond thin film with the support of silicon wafer was obtained by the aid of photolithography and anisotropic wet etching technology so as to improve the precision of quantitative adhesion measures of diamond films. The mechanics for calculating the quantitative driving force of blister-induced delamination of diamond thin film is presented, which is on base of intensive modeling and simulation. The laser interferometer measurement with fine solution was used to pick up dynamic signals of diamond thin film bulge deformation in micrometer scale and the relationship demonstration of stress to strain of the diamond thin film was available, as a consequence, the adhesive strength could be obtained precisely and quantitatively by the valid model. The paper confirms the accessibility to precise quantitative adhesion measures of diamond films and the results will be beneficial to wide application of diamond thin films in the related fields.