Research For Fabrication And Properties Of Nano-crystalline Diamond Film And Radiation Detector

Diamond film is a kind of competitive material with its outstanding electrical, optical, thermal and mechanical properties as well as high anti-radioactive intensity and high physical and chemical stability. Compared with micro-crystalline diamond, Nano-Crystalline Diamond(NCD) is with more slippery surface, lower friction factor and better performance in field ejection, so that, it becomes the new hotpot in the research of diamond films. This essay focuses on the CVD NCD film. The fabrication and properties of NCD films are studied together with that of NCD film radiation detector. H etched NCD fims are studied to see if they can be used as X ray masks. At the same time, NCD films are successfully fabricated under high magnetic field to broaden their applications.First, NCD films are prepared by Hot Filament Chemical Vapor Deposition (HFCVD), while their surface morphology, optical and detective performances are studied in depth. The best growth parameters are got with the samples'grain size being about 30nm, thickness being 1000nm and near infrared transmittance over 50%. An innovative method is proposed hereof for the growth of thick NCD film in a fast way, where a high growth temperature is introduced in initial stage.Next, NCD film radiation detector is successfully fabricated by photolithography and sputtering. ANSYS ( a software based on finite-element method) is used to simulate the distribution of the electric field of the NCD film radiation detectors. The geometric configuration of interdigital electrodes is determined to be 25nm in width and 50nm for pitch. A special photo mask is designed and made for the photolithography. The electrical performance and spectral response of the MSM photo-conductive NCD detectors are studied with the samples'grain size vary from 20nm to 150nm and roughness from 22nm to 45nm. I-V test results show that with the decrease of the grain size, the resistivity of diamond film decreases and the ratio of the photocurrent to the dark-current (Iph/Id) of the detectors decreases rapidly from 0.45 to 0.099 under the radiation of 5.9 keV 55Fe X-ray. At an electric field of 50 kV/cm, the energy resolution of detectors with large grains (150 nm) is 17.5%, for those with small grains (20 nm), the number is 22.7%. All the test results show that larger grain samples are with better counting rate, higher SNR and charge collection efficiency, and therefore, they are more appropriate for nuclear radiation detectors.Then, Hydrogen etching method is applied to the experiments to optimize the NCD film deposition process. From the test of micro-structure, optical and electrical properties, it shows that, with certain deposit parameters, the increase of etching time will lead to the decrease of the grain size and of surface roughness, the increase of the refractive index and optical transmission rate and the diminish of NCD film's dark current and dielectric loss, while their dielectric constant come closer to that of natural diamond. NCD films are also tested for soft X-ray transmission by synchrotron radiation. It can obviously be seen that hydrogen-etched NCD films do much better in X-ray transmission: the transmission reaches 52.8% at an X-ray photon energy of 258eV, while the number for non-etched NCD is only 24.8%. The etched NCD film has met the requirements for X-ray mask materials.Finally, the deposition of NCD films in high magnetic field is researched. The influence of different magnetic field intensity (0-5T) on the performance of NCD films is studied. With the increase of magnetic intensity, the grain size of NCD films decreases. The principle of nano-crystalline diamond film deposition in high magnetic field is also studied.