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.

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.

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.

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.

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.

Body Building on Diamonds

Whereas conservative therapies aim to stall the advance of disease,regenerative medicine strives to reverse it.The capacity of most tissues to regenerate derives from stem cells,but there are a number of barriers which have to be circumvented before it will be possible to use stem-cell-based therapies.Such therapies,however,are expected to improve human health enormously, and knowledge gained from studying stem cells in culture and in model organisms is now laying the groundwork for a new era of regenerative medicine.One of the most prominent methods to study stem cell differentiation is to let them to form embryoid bodies.Under favourable conditions any stem cell line will form embryoid bodies.However,the mechanism of the formation of embryoid bodies is not very well understood,and to produce them in the laboratory is in no way trivial-an important technical barrier in stem cell research.Recently,the embryoid body cultivation step has been successfully circumvented for the derivation of osteogenic cultures of embryonic stem cells.Here we report on a simple and reusable system to cultivate embryoid bodies in extremely short times.The method is inspired by the principles that lead to the establishment of the biomimetic triangle.

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.