Fabrication and application of nanocrystalline diamond films

Nanocrystalline diamond films were deposited on Co-cemented carbide substrates using acetone/ H2/Ar gas mixture by bias-enhanced hot filament chemical vapor deposition（HFCVD） technique.The evidence of nanocrystallinity,smoothness and purity was obtained by characterizing the sample with scanning electron microscopy（SEM）,X-ray diffraction（XRD）,Raman spectroscopy,atomic force microscopy （AFM ）,and field emission transmission electron microscopy（FE-TEM ）.The results show that nanocrystalline diamond films consists of nanocrystalline diamond grains with sizes range from 20 to 80 nm and contain a large amount of grain boundaries.The surface roughness of the films is measured as Ra【50nm.The Raman spectroscopy,XRD pattern,and FE-TEM image of the films indicate the presence of nanocrystalline diamond.A new process is used to deposit composite diamond coatings by a two-step chemical vapor deposition procedure,including first the deposition of the rough polycrystalline diamond and then the smooth fine-grained nanocrystalline diamond film.Such composite diamond coatings not only display good adhesion and wear resistant properties,but also have smooth surfaces that are liable to polishing.This coating technology can not only meet the requirement of the adhesion of diamond coatings,but also reduce surface roughness of diamond coatings effectively,thus remove the obstacles for the industrialization of CVD diamond coatings.The diamondcoated dies with these composite coatings show obvious effect in the practical application.

Impact of nitrogen doping on growth and hydrogen impurity incorporation of thick nanocrystalline diamond films

A much larger amount of bonded hydrogen was found in thick nanocrystalline diamond （NCD） films produced by only adding 0.24% N2 into 4% CH4/H2 plasma, as compared to the high quality transparent microcrystalline diamond （MCD） films, grown using the same growth parameters except for nitrogen. These experimental results clearly evidence that defect formation and impurity incorporation （for example, N and H） impeding diamond grain growth is the main formation mechanism of NCD upon nitrogen doping and strongly support the model proposed in the literature that nitrogen competes with CHx （x = 1, 2, 3） growth species for adsorption sites.

EFFECT OF GRID BIAS ON DEPOSITION OF NANOCRYSTALLINE DIAMOND FILMS

A positive grid bias and a negative substrate bias voltages are applied to the self-made hot filament chemical vapor deposited （HFCVD） system. The high quality nanocrystalline diamond （NCD） film is successfully deposited by double bias voltage nucleation and grid bias voltage growth. The Micro-Raman XRD SEM and AFM are used to investigate the diamond grain size, microstructure, surface morphology, and nucleation density. Results show that the obtained NCD has grain size of about 20 nm. The effect of grid bias voltage on the nucleation and the diamond growth is studied. Experimental results and theoretical analysis show that the positive grid bias increases the plasma density near the hot filaments, enhances the diamond nucleation, keeps the nanometer size of the diamond grains, and improves the quality of diamond film.

Nanocrystalline Diamond Films Grown by Microwave Plasma Chemical Vapor Deposition and Its Biocompatible Property

Due to its unique properties such as high hardness, light transmittance, thermal conductance, chemical stability and corrosion resistance, diamond has drawn tremendous attention in last two decades. These specific properties made diamond film a promising material for cutting tools, microwave windows, heat sinks for electronic devices and diamond electrodes. However, the diamond film with grain sizes at microscale usually exhibits high surface roughness and hinders its applications in the microelectro mechanical system (MEMS) and biological field because it is difficult to be polished by mechanical and chemical methods. With the development of the chemical vapor deposition, the nanocrystalline diamond (NCD) film has been fabricated and found new applications. The grain size of NCD film is in the range of 10 to 100 nm, which inherits the properties of the diamond and possesses the unique properties of the nanoscale materials, and the morphology of the NCD film is granular or needle-like structure. The microwave plasma chemical vapor deposition (MPCVD) has been regarded as the most promising method to deposit NCD film at low temperature. Compared to the hot filament CVD, MPCVD can grow high quality NCD film avoiding of the contamination from the filament materials. The MPCVD technique has high plasma density to activate carbonaceous compound and grow NCD film in high growth rate and low substrate temperature. The unique properties of NCD film, such as the superior electrical, mechanical and biological properties facilitate their application in various fields. The biological application, especially as a biocompatible coating, mainly includes the joint replacement implants and protective coatings and the ophthalmological prosthesis.

Effects of Surface Pretreatment on Nucleation and Growth of Ultra-Nanocrystalline Diamond Films

The effects of different surface pretreatment nmthods on the nucleation and growth of ultra-nanocrystalline diamond （UNCD） fihns grown from focused microwave Ar/CHa/H2 （argon- rich） plasma were systematically studied. The surface roughness, nucleation density, mierostruc- ture, and crystallinity of the obtained UNCD films were characterized by atomic force microscope （AFM）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）, and Raman spectroscopy. The results indicate that the nucleation enhancement was found to be sensitive to the different sur- face pretreatment methods, and a higher initial nucleation density leads to highly smooth UNCD films. When the silicon substrate was pretreated by a two-step method, i.e., plasma treatment followed by ultrasonic vibration with diamond nanopowder, the grain size of the UNCD films was greatly decreased： about 7.5 nm can be achieved. In addition, the grain size of UNCD films depends on the substrate pretreatment methods and roughness, which indicates that the surface of substrate profile has a ＂genetic characteristic＂.

Field emission from Si tips coated with nanocrystalline diamond films

The electron field emission from Si tips coated with nanocrystalline diamond films was investigated. The Si tips were formed by plasma etching, and nano-diamond films were deposited on the Si tips by hot filament chemical vapor deposition. The radius of curvature for the Si tips was averagely about 50 nm. The microstructure of the diamond films was examined by scanning electron microscopy and Raman spectroscopy. The field emission properties of the samples were measured in an ion-pumped vacuum chamber at a pressure of 106 Pa. The experimental results showed that the nanostructured films on Si tips exhibited a lower value of the turn-on electric field than those on flat Si substrates. It was found that the tip shape and non-diamond phase in the films had a significant effect on the field emission properties of the films.

Si/Nanocrystalline Diamond Film Heterojunction Diodes Preparation

With electron assisted hot filament chemical vapor deposition technology, nanocrystalline diamond films were deposited on polished n-(100)Si wafer surface. The deposited films were characterized and observed by Raman spectrum, X-ray diffraction, semiconductor characterization system and Hall effective measurement system. The results show that with EA-HFCVD, not only an undoped nanocrystalline diamond films with high-conductivity (p-type semiconducting) but also a p-n heterojunction diode between the nanocrystalline diamond films and n-Si substrate is fabricated successfully. The p-n heterojunction has smaller forward resistance and bigger positive resistance. The p-n junction effective is evident.

Nanocrystalline Diamond Films Deposited by Electron Assisted Hot Filament Chemical Vapor Deposition

Nanocrystalline diamond films were deposited on polished Si wafer surface with electron assisted hot filament chemical vapor deposition at 1 kPa gas pressure, the deposited films were characterized and observed by Raman spectrum, X-ray diffraction, atomic force microscopy and semiconductor characterization system. The results show that when 8 A bias current is applied for 5 h, the surface roughness decreases to 28.5 nm. After 6 and 8 A bias current are applied for 1 h, and the nanocrystalline films deposition continue for 4 h with 0 A bias current at 1 kPa gas pressure. The nanocrystalline diamond films with 0.5×109 and 1×1010 Ω·cm resistivity respectively are obtained. It is demonstrated that electron bombardment plays an important role of nucleation to deposit diamond films with smooth surface and high resistivity.

Electrochemical Characteristics and Applications of Boron-Doped Polycrystalline Diamond Film Electrodes

The elcetrochemical characteristics of boron doped polycrystalline diamond thin film (BDF) electrode 4×4 mm 2 in size were studied using cyclic voltammetry and potentiostatic method. The diamond electrode exhibits adequate electrochemical activity and its response current changes linearly with K 3Fe(CN) 6 concentrations. The response current is proportional to the square root of the scan rate, reflecting mass transport controlled by planar diffusion. Stable mass transport can be quickly established within 4s. The BDF electrode provides good resolving power for the determination of lead and cadmium and gives satisfactory results in the analysis of pure water sample.

Fabrication and characteristics of nitrogen-doped nanocrystalline diamond/p-type silicon heterojunction

Nitrogen-doped nanocrystalline diamond films(N-NDFs)have been deposited on p-type silicon(Si)by microwave plasma chemical vapor deposition.The reaction gases are methane,hydrogen,and nitrogen without the conventional argon(Ar).The N-NDFs were characterized by X-ray diffraction,Raman spectroscopy,and scanning electron microscopy.The grain sizes are of 8~10 nm in dimension.The N-NDF shows n-type behavior and the corresponding N-NDF/p-Si heterojunction diodes are realized with a high rectification ratio of 102 at^7.8 V,and the current density reaches to1.35 A/cm2 at forward voltage of 8.5 V.The findings suggest that fabricated by CH_4/H_2/N_2 without Ar,the N-NDFs and the related rectifying diodes are favorable for achieving high performance diamond-based optoelectronic devices.

Growth of mirror-like ultra-nanocrystalline diamond(UNCD)films by a facile hybrid CVD approach

In this study, growth of mirror-like ultra-nanocrystalline diamond（UNCD） films by a facile hybrid CVD approach was presented. The nucleation and deposition of UNCD films were conducted in microwave plasma CVD（MPCVD） and direct current glow discharge CVD（DC GD CVD） on silicon substrates, respectively. A very high nucleation density（about 1×10^11 nuclei cm^-2） was obtained after plasma pretreatment. Furthermore, large area mirrorlike UNCD films of Φ 50 mm were synthesized by DC GD CVD. The thickness and grain size of the UNCD films are 24 μm and 7.1 nm, respectively. In addition, the deposition mechanism of the UNCD films was discussed.

Effect of nitrogen on deposition and field emission properties of boron-doped micro-and nano-crystalline diamond films

In this paper,we report the effect of nitrogen on the deposition and properties of boron doped diamond films synthesized by hot filament chemical vapor deposition.The diamond films consisting of micro-grains(nano-grains) were realized with low(high) boron source flow rate during the growth processes.The transition of micro-grains to nano-grains is speculated to be strongly(weekly) related with the boron(nitrogen) flow rate.The grain size and Raman spectral feature vary insignificantly as a function of the nitrogen introduction at a certain boron flow rate.The variation of electron field emission characteristics dependent on nitrogen is different between microcrystalline and nanocrystalline boron doped diamond samples,which are related to the combined phase composition,boron doping level and texture structure.There is an optimum nitrogen proportion to improve the field emission properties of the boron-doped films.

Fibre Metallurgy Characteristic of Short Cast Iron Fibre and Its Applications for Diamond Wheel

A kind of diamond grinding wheel bonded by short cast iron fibres has been developed. ln comparison with high quality bronze bonded diamond grinding wheel. the new wheel was more suitable to grind hard and brittle materials like ceramics. For Si3N4, the grinding efficiency has been raised two times and the grinding ratio five times

Nanodiamond films deposited at moderate temperature on pure titanium substrate pretreated by ultrasonic scratching in diamond powder suspension

Nanocrystalline diamond （NCD） film deposition on pure titanium and Ti alloys is extraordinarily difficult because of the high diffusion coefficient of carbon in Ti, the large mismatch in their thermal expansion coefficients, the complex nature of the interlayer formed during diamond deposition, and the difficulty to achieve very high nucleation density. In this investigation, NCD films were successfully deposited on pure Ti substrate by using a novel substrate pretreatment of ultrasonic scratching in a diamond powder-ethanol suspension and by a two-step process at moderate temperature. It was shown that by scratching with a 30-μm diamond suspension for 1 h, followed by a 10-h diamond deposition, a continuous NCD film was obtained with an average grain size of about 200 nm. Detailed experimental results on the preparation, characterization, and successful deposition of the NCD films on Ti were discussed.

Fabrication and application of nano/microcrystalline composite diamond coated drawing dies using alternative carbon sources

Nano/microcrystalline composite diamond films were deposited on the holes of WC-6%Co drawing dies by a two-step procedure using alternative carbon sources, i.e., methane for the microcrystalline diamond（MCD） layer and acetone for the nanocrystalline diamond（NCD） layer. Moreover, the monolayer methane-MCD and acetone-NCD coated drawing dies were fabricated as comparisons. The adhesion and wear rates of the diamond coated drawing dies were also tested by an inner hole polishing apparatus. Compared with mono-layer diamond coated drawing die, the composite diamond coated one exhibits better comprehensive performance, including higher adhesive strength and better wear resistance than the NCD one, and smoother surface（Ra=65.3 nm） than the MCD one（Ra=95.6 nm） after polishing at the same time. Compared with the NCD coated drawing die, the working lifetime of the composite diamond coated one is increased by nearly 20 times.

Surface energy-mediated fibronectin adsorption and osteoblast responses on nanostructured diamond

Nanostructured diamond have potential applications in many biomedical related fields and demonstrated extraordinary capacity to influence cellular responses. Studying the surface property of nanodiamond and its influence to protein adsorption and subsequent cellular responses along with the mechanism behind such capacity becomes more important. Here the role of surface energy associated with nanostructured diamond in modulating fibronectin and osteoblast(OB, bone forming cells) responses was investigated. Nanocrystalline diamond(NCD) and submicron crystalline diamond(SMCD) films with controllable surface energy were prepared by microwave-enhanced plasma chemical vapor deposition(MPCVD) techniques. Fibronectin adsorption on the diamond films with varied surface energy values was measured via the enzyme-linked immunosorbent assay(ELISA) and the relationship between the surface energy and fibronectin adsorption was studied. The result indicated that fibronectin adsorption on nanostructured surfaces was closely related to both surface energy and material microstructures. The spreading and migration of OB aggregates(each containing 30–50 cells) on the NCD with varied surface energy values were also studied. The result indicates a correlation between the cell spreading and migration on nanodiamond and the surface energy of nanostructured surface.

Plasma-enhanced Deposition of Nano-Structured Carbon Films

By pre-treating substrate with different methods and patterning the catalyst, selective and patterned growth of diamond and graphitic nano-structured carbon films have been realized through DC Plasma-Enhanced Hot Filament Chemical Vapor Deposition (PE-HFCVD). Through two-step processing in an HFCVD reactor, novel nano-structured composite diamond films containing a nanocrystalline diamond layer on the top of a nanocone diamond layer have been synthesized. Well-aligned carbon nanotubes, diamond and graphitic carbon nanocones with controllable alignment orientations have been synthesized by using PE-HFCVD. The orientation of the nanostructures can be controlled by adjusting the working pressure. In a Microwave Plasma Enhanced Chemical Vapor Deposition (MW-PECVD) reactor, high-quality diamond films have been synthesized at low temperatures (310℃-550℃) without adding oxygen or halogen gas in a newly developed processing technique. In this process, carbon source originates from graphite etching, instead of hydrocarbon. The lowest growth temperature for the growth of nanocrystalline diamond films with a reasonable growth rate without addition of oxygen or halogen is 260℃.

Performance improvement of ZnO film by room-temperature oxygen plasma pretreatment

The room-temperature oxygen plasma treatment before depositing ZnO films on nanocrystalline diamond substrates was studied. The nanocrystalline diamond substrates were pretreated in oxygen plasma at 50 W for 30 min at room temperature and then ZnO films were sputtered on diamond substrates at 400 W. The X-ray diffraction (XRD) patterns show that the c-axis orientation of ZnO film increases evidently after oxygen plasma pretreatment. The AFM and SEM measurements also show that the high c-axis orientation of ZnO film and the average surface roughness is less than 5 nm. The resistivity of ZnO films increases nearly two orders of magnitude to 1.04×108■·cm. As a result, room-temperature oxygen plasma pretreatment is indeed a simple and effective way to improve the performance of ZnO film used in SAW devices by ameliorating the combination between diamond film and ZnO film and also complementing the absence of oxygen atoms in ZnO film.

340 GHz宽带金刚石输能窗的设计优化与试验研究

针对340 GHz行波管用金刚石输能窗的宽带传输要求,基于多晶金刚石膜和微米晶-超纳米晶金刚石复合膜,开展了金刚石输能窗的优化设计与试验验证研究。研究结果表明,多晶金刚石输能窗在320~363 GHz带宽内S_(11)<-15 dB,S_(21)>-3 dB;微米晶-超纳米晶复合金刚石输能窗在313~385 GHz带宽内S_(11)<-15 dB,S_(21)>-2.5 dB,同比工作带宽增加近2倍,有效拓展了金刚石输能窗的工作带宽。

纳米金刚石膜/{100}晶面多晶金刚石膜台阶法快速生长研究

通过高功率微波等离子体化学气相沉积(MPCVD)以及台阶式基底排列方法,可以在一次沉积过程中同时沉积纳米晶粒及<100>取向的{100}面多晶金刚石薄膜。详细比较在同一次沉积中同时制备的多种不同类别的金刚石产物的生长速率。采用台阶法并添加少量空气,微波功率从2.0k W增加至3.2 kW,在下面大硅片上生长的纳米金刚石膜的平均生长速率可从0.3μm/h增大到3.0μm/h;而在上面小硅片上生长的纳米金刚石膜的平均生长速率从3.8μm/h也增加到11.2μm/h,同时产物也转变为{100}晶面的多晶膜。另外,在上面小硅片上生长的金刚石膜的边角效应明显,在边界生长的金刚石产物的生长速率更高,从17.0μm/h增大到27.1μm/h。该结果表明少量氮气和氧气同时添加对金刚石生长的形貌多样性调节作用和对生长速率的提升作用强烈依赖于生长条件。