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.

Effect of Argon Addition on Morphology and Structure of Diamond Films(from Microcrystalline to Nanocrystalline)

Micro-/nanocrystalline diamond films deposited in Ar/H2/CH4 microwave plasmas have been studied, with argon flow rates in the range of 70-100 sccm. The effects of argon addition on morphology, surface roughness, quality and structure were investigated by scanning electron microscopy, surface profiler, Raman spectrometer and X-ray diffraction （XRD）. It is demonstrated that when the argon flow rate is 70 sccm or 75 sccm, well-faceted polycrystalline diamond films can be grown at a low substrate temperature less than 610 ~C. With the increase in the argon flow rate, the smooth crystallographic planes disappear gradually. Instead, rough crystallographic planes made up of small aggregates begin to take shape, resulting from the increase in the secondary nucleation rate. Nanocrystalline diamond films were obtained at a flow rate of 100 sccm, and all of the prepared diamond films were smooth, with a surface roughness （Ra） less than 20 nm. Raman analyses reveal that the amount of amorphous carbon increases significantly with the increase in argon flow. The results of XRD show that crystalline size and preferential orientation of diamond films depend on the argon content in the plasmas.

Cytotoxicity of Boron-Doped Nanocrystalline Diamond Films Prepared by Microwave Plasma Chemical Vapor Deposition

Boron-doped nanocrystalline diamond（NCD） exhibits extraordinary mechanical properties and chemical stability,making it highly suitable for biomedical applications.For implant materials,the impact of boron-doped NCD films on the character of cell growth（i.e.,adhesion,proliferation） is very important.Boron-doped NCD films with resistivity of 10-2Ω·cm were grown on Si substrates by the microwave plasma chemical vapor deposition（MPCVD） process with H2 bubbled B2O3.The crystal structure,diamond character,surface morphology,and surface roughness of the boron-doped NCD films were analyzed using different characterization methods,such as X-ray diffraction（XRD）,Raman spectroscopy,scanning electron microscopy（SEM） and atomic force microscopy（AFM）.The contact potential difference and possible boron distribution within the film were studied with a scanning kelvin force microscope（SKFM）.The cytotoxicity of films was studied by in vitro tests,including fluorescence microscopy,SEM and MTT assay.Results indicated that the surface roughness value of NCD films was 56.6 nm and boron was probably accumulated at the boundaries between diamond agglomerates.MG-63 cells adhered well and exhibited a significant growth on the surface of films,suggesting that the boron-doped NCD films were non-toxic to cells.

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.

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.

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.

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.

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.

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.

Theoretical Analysis of Solidly Mounted Film Bulk Acoustic Resonator with Nanocrystalline Diamond as High Impedance Material of Bragg Reflector

In this paper,a solidly mounted resonator(SMR)was designed with nanocrystalline diamond(NCD)as the high acoustic impedance material of Bragg reflector to improve the quality.We used Mathcad to investigate the effect of the Bragg reflector on the performance of the SMR,as well as the influence of different materials and the number of layers of Bragg reflector on the quality factor Q.Results show that the Bragg reflector could reduce energy loss effectively,and the higher the impedance of the high acoustic impedance layer,the better the SMR.The parasitic factors of the SMR using two high acoustic impedance materials,tungsten(W)and NCD,were also simulated by an Advanced Design System(ADS)using the Mason model.It was found that the parasitic effect caused by metal would significantly decrease the Q factor of the SMR.In the frequency range below 6 GHz,within which the SMR works normally,NCD performed better than W.Therefore,NCD is a better choice of high acoustic impedance material in the design of the SMR,with improved quality at high frequency and low loss.The optimum number of layers of Bragg reflector is 6.

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＂.

Microstructure and performance of electrodeposited nanocrystalline Ni-W alloys

The electro-deposition method was used for preparation of nanocrystalline Ni-W alloys coating. The formation, microstructure and performance of the nanocrystalline were investigated. X-ray diffraction results show that Ni-W alloys are crystallized in scale of 1730nm. Changing with the depositional time, the coating varies with different surface morphology. The observation on the formation of the coating implies that, the alloys preferentially deposit and grow on the scratch and corrosion pit edges. The hardness of the alloy coatings is related to the solution composition, pH value and current density, and the pH value and current density are mainly concerned. The corrosion resistance of Ni-W alloy coating is excellent compared with that of Cr and Ni coatings.

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.

Micro/nano Indentation and Single Grit Diamond Grinding Mechanism on Ultra Pure Fused Silica

The existing research about ductile grinding of fused silica glass was mainly focused on how to carry out ductile regime material removal for generating very ＂smoothed＂ surface and investigate the machining-induced damage in the grinding in order to reduce or eliminate the subsurface damage.The brittle/ductile transition behavior of optical glass materials and the wear of diamond wheel are the most important factors for ductile grinding of optical glass.In this paper,the critical brittle/ductile depth,the influence factors on brittle/ductile transition behavior,the wear of diamond grits in diamond grinding of ultra pure fused silica（UPFS） are investigated by means of micro/nano indentation technique,as well as single grit diamond grinding on an ultra-stiff machine tool,Tetraform ＂C＂.The single grit grinding processes are in-process monitored using acoustic emission（AE） and force dynamometer simultaneously.The wear of diamond grits,morphology and subsurface integrity of the machined groves are examined with atomic force microscope（AFM） and scanning electron microscope（SEM）.The critical brittle/ductile depth of more than 0.5 μm is achieved.When compared to the using roof-like grits,by using pyramidal diamonds leads to higher critical depths of scratch with identical grinding parameters.However,the influence of grit shapes on the critical depth is not significant as supposed.The grinding force increased linearly with depth of cut in the ductile removal regime,but in brittle removal regime,there are large fluctuations instead of forces increase.The SEM photographs of the cross-section profile show that the median cracks dominate the crack patterns beneath the single grooves.Furthermore,The SEM photographs show multi worn patterns of diamond grits,indicating an inhomogeneous wear mechanism of diamond grits in grinding of fused silica with diamond grinding wheels.The proposed research provides the basal technical theory for improving the ultra-precision grinding of UPFS.

Wear characteristics of Ⅴ shape diamond tool for micro prism pattern with Al alloys

The ultra-precision machining process using a single crystal diamond tool has been mainly used for machining molds of optical components.Since the micro patterns of various shapes having excellent surface roughness can be machined by using ultra-precision machine tools,the micro pattern on a large light guide plate (LGP) is mainly machined using a diamond tool.The tool wear occurs due to long machining distances and time while machining a large-area LGP mold.The deformation and dimensional error of micro pattern are caused by tool wear,as a result,the light efficiency of LGP declines.The characteristics of tool wear should be analyzed in order to precisely machine large-area LGP mold from all sorts of materials.The experiments were performed in order to compare wear characteristics of a V90° diamond tool using Al3003,5052,6061 and 7075.The prism pattern of depth 10 μm was machined in order to analyze characteristics of tool wear according to machining distances (0.5,1 and 1.5 km).The effects of tool wear on pattern shape were analyzed by applying overlapped cutting depths (Rough machining is (10+8+7) μm and Finish machining is (5+3+2+1) μm) by continuously machining a prism pattern of W shape of 25 μm in depth.

Deformation Analysis of Micro/Nano Indentation and Diamond Grinding on Optical Glasses

The previous research of precision grinding optical glasses with electrolytic in process dressing （ELID） technology mainly concentrated on the action of ELID and machining parameters when grinding, which aim at generating very ＂smoothed＂ surfaces and reducing the subsurface damage. However, when grinding spectrosil 2000 and BK7 glass assisted with ELID technology, a deeply comparative study on material removal mechanism and the wheel wear behaviors have not been given yet. In this paper, the micro/nano indentation technique is initially applied for investigating the mechanical properties of optical glasses, whose results are then refereed to evaluate the machinability. In single grit diamond scratching on glasses, the scratching traces display four kinds of scratch characteristics according to different material removal modes. In normal grinding experiments, the result shows BK7 glass has a better machinability than that of spectrosil 2000, corresponding to what the micro/nano indentation vent revealed. Under the same grinding depth parameters, the smaller amplitude of acoustic emission （AE） raw signals, grinding force and grinding force ratio correspond to a better surface quality. While for these two kinds of glasses, with the increasing of grinding depth, the variation trends of the surface roughness, the force ratio, and the AE raw signals are contrary, which should be attributed to different material removal modes. Moreover, the SEM micrographs of used wheels surface indicate that diamond grains on the wheel surface after grinding BK7 glass are worn more severely than that of spectrosil 2000. The proposed research analyzes what happened in the grinding process with different material removal patterns, which can provide a basis for producing high-quality optical glasses and comprehensively evaluate the surface and subsurface integrity of optical glasses.

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.

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.

Generating micro/nanostructures on magnesium alloy surface using ultraprecision diamond surface texturing process

The lightness and high strength-to-weight ratio of the magnesium alloy have attracted more interest in various applications.However,micro/nanostructure generation on their surfaces remains a challenge due to the flammability and ignition.Motivated by this,this study proposed a machining process,named the ultraprecision diamond surface texturing process,to machine the micro/nanostructures on magnesium alloy surfaces.Experimental results showed the various microstructures and sawtooth-shaped nanostructures were successfully generated on the AZ31B magnesium alloy surfaces,demonstrating the effectiveness of this proposed machining process.Furthermore,sawtooth-shaped nanostructures had the function of inducing the optical effect and generating different colors on workpiece surfaces.The colorful letter and colorful flower image were clearly viewed on magnesium alloy surfaces.The corresponding cutting force,chip morphology,and tool wear were systematically investigated to understand the machining mechanism of micro/nanostructures on magnesium alloy surfaces.The proposed machining process can further improve the performances of the magnesium alloy and extend its functions to other fields,such as optics.