Hong-yan Peng

A nanocrystalline CVD diamond film as an x-ray radiation detector

In this work, an x-ray radiation detector was developed from a nanocrystalline diamond (NCD) film. The NCD film, with a grain size of about 20 nm and a thickness of ~5 µm, was deposited on a silicon substrate using a hot-filament chemical vapour deposition (HFCVD) method. The response to radiation and the energy resolution at room temperature of the obtained metal-NCD/Si-metal detector were investigated using 5.9 keV x-rays from a 55Fe source. With an electric field 50 kV cm−1, this detector showed a dark-current of ~5.88 µA, and under x-ray illumination a net response current of ~576 nA and an energy resolution of ~22.7%. It was also shown that the energy resolution deteriorated when the diamond grain size was reduced.

Preparation of free-standing diamond films for high frequency SAW devices

Abstract Free-standing diamond films were prepared by hot filament chemical vapor deposition (HFCVD) method under different conditions. Inter-digital transducers (IDTs) were formed on the nucleation sides of free-standing diamond films by photolithography technique. Then piezoelectric ZnO films were deposited by radio-frequency(RF) reactive magnetron sputtering to obtain the ZnO/diamond film structures. Surface morphologies of the nucleation sides and the IDTs were characterized by means of scanning electron microscopy (SEM), atomic force microscope (AFM) and optical microscopy. The results indicate that the surfaces of nucleation sides are very smooth and the IDTs are of high quality without discontinuity and short circuit phenomenon. Raman spectra show the sharp diamond feature peak at about 1 334 cm −1 and the small amount of non-diamond carbon in the nucleation side. X-ray diffraction (XRD) patterns of the structure of ZnO/diamond films show a strong diffraction peak of ZnO (002), which indicates that as-sputtered ZnO films are highly c -axis oriented.

Characterization of (100)-orientated diamond film grown by HFCVD method with a positive DC bias voltage

The (100)-orientated diamond film was deposited by hot-filament chemical vapor deposition (HFCVD) technology with a positive DC bias voltage. The morphology, X-ray diffraction (XRD), RAMAN spectrum and dark current versus applied voltage characteristics analysis show that the positive dc bias can increase the nucleation density and (100)-orientated growth, making the growth of the high quality diamond film easier and cheaper than using other methods.

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

Abstract 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 1.04×10 8 Ω·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.

Ellipsometric analysis and optical absorption characterization of nano-crystalline diamond film

Abstract A nano-crystalline diamond (NCD) film with a smooth surface was successfully deposited on silicon by a hot filament chemical vapor deposition (HFCVD) method. Scanning electron microscopy (SEM), atomic force microscopy (AFM), RAMAN scattering spectra, as well as spectroscopic ellipsometry were employed to characterize the as-grown film. By fitting the spectroscopic ellipsometric data in the energy range of 0.75–1.50 eV with a three-layer model, Si∣diamond+non-diamond∣diamond+ non-diamond+void∣air, the optical constants are obtained. The refractive index of the NCD film varies little from 2.361 to 2.366 and the extinction coefficient is of the order of 10−2. According to the optical transmittance and absorption coefficient in the wavelength range from 200 to 1 100 nm, the optical gap of the film is estimated to be 4.3 eV by a direct optical transition mechanics.

Influence of nitrogen gas on structure and properties of DLC films prepared by XeCl pulsed laser deposition

Diamond-like carbon (DLC) films were prepared by PLD process using 308 nm(XeCl) laser beam with high power (500 W) and high frequency(300 Hz). The effects of nitrogen pressure on the structure and properties of the DLC films under such extremely high power and repetition rate were studied. The results indicate that the microstructures of the films are varied from amorphous carbon to graphitized carbon in long-order with the increase of N2 pressure, and the optical properties of the films are deteriorated as compared to that of DLC films without nitrogen.

Effects of high magnetic field on the properties of hot-filament CVD diamond films

A hot filament chemical vapor deposition (HFCVD) apparatus, combined with a cyro-cooled superconductor magnet, were recently developed. Nanocrystalline diamond (NCD) films were prepared by above HFCVD apparatus either with or without high magnetic field. Surface morphologies of these films were characterized by means of atomic force microscope (AFM). The results indicated that the mean surface roughness and grain size of these films decreased when the magnetic field varied from 0T to 4T. From Raman scattering measurement, all films prepared either with or without high magnetic field exhibit NCD features. These NCD features of the sample prepared with 4T magnetic field was obviously pronounced. The structure of these films was also investigated by X-ray diffraction (XRD).

Effect of working pressure and temperature on ZnO film deposited on free-standing diamond substrates

Abstract The structure characteristic and electric performance of ZnO film deposited on nucleation side of free-standing diamond substrates under different heating temperatures ( T h ) of substrate and working pressures ( p ) were studied. The structure of the ZnO films tested by X-ray diffraction shows that ZnO film of high c -axis orientation is deposited on the nucleation side of free-standing diamond substrate which is extremely smooth when T h =250 °C and p =0.4 Pa. After annealing at 480 °C in N 2 atmosphere, the SEM and the AFM analyses demonstrate that the c -axis orientation of ZnO film is obviously enhanced. The resistivity of ZnO films also increases up to 8×10 5 Ωcm which is observed by I–V test.

Optical Characteristics of Nano-crystalline Diamond Films as X-ray Lithography Masks for Integrated Circuit Fabrication

In this paper, the structure, morphology and optical properties of nano-crystalline diamond (NCD) films, deposited by hot-filament chemical vapor deposition (HFCVD) method under different carbon concentration, are investigated. With increasing the carbon concentration during the film deposition, the diamond grain size is reduced and thus a smooth diamond film can be obtained. According to the data on the absorption coefficient in the wavelength range from 200 to 1100 nm, the optical gap of the NCD films decreases from 4.3 eV to 3.2eV with increasing the carbon concentration from 2.0% to 3.0%

Studies on coplanar radiation sensor based on diamond film

An X-ray diamond film sensor with coplanar electrode geometry was fabricated and an average charge collection efficiency of 45.8% at an applied electric field of 66.7kV/cm was obtained. Scanning electron microscopy and Raman scattering studies directly demonstrated that the different collection efficiencies of the coplanar and sandwich sensors mainly resulted from the different micro-structural features between the final growth side and the substrate side of the diamond film. The energy resolution of the diamond sensor significantly decreased with the applied electric field. A good energy resolution of 1.55 % was obtained at 66.7kV/cm for the coplanar diamond film sensor