Table of Content

15 March 2000, Volume 29 Issue 3

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Study on Heavy Metals Partitioning in Carbonate Calcium Formation (2)--Research Progress and Partitioning Mechanism

CHEN Wan-chun;Kato.K;CHEN Zong-xiao;CHEN Su

2000, 29(3):  205-219. 

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Authors have been summarized the research progress on heavy metals partitioning in carbonate calcium formation. The review is divided two parts. The topic for the part 1 is theoretic background and experimental methods. The topic for the part 2 is research progress and partitioning mechanism. Here is the part 2. In this paper, the advanced experiments related to sorption selectivity of heavy metal ions on calcite surface have been summarized. The results for observation of mono-molecular step distribution on the calcite surface by an atomic force microscope (AFM) were introduced. The theoretic mechanism on heavy metal ions partitioning problem, such as: Two Step Model, Multiple Surface Sites Model, Surface Film Model and Chemisorption Model etc. Has been reviewed. The proposal for future work has been presented.

PECVD Amorphous Diamond-like Carbon Films Deposited at Low Substrate Temperatrure

LIAO Xian-bo;DENG Xun-ming

2000, 29(3):  220-223. 

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This paper reports diamond-like carbon (DLC) films prepared by using RF (13.56 MHz) plasma enhanced chemical vapor deposition (PECVD) at a lower substrate temperature. The effects of hydrogen dilution, gas pressure and RF power on the properties of the films have been investigated. The structural and optical properties of the DLC films are analyzed by utilizing optical transmission, infrared absorption and small angle X-ray diffraction spectroscopy. The results show that the DLC films are in amorphous state, with a certain amount of C-H bonds. The films with a thickness of about 230nm possess a high transparency, which is more than 83; at 480nm and longer wavelengths in the visible and infrared spectral region, and the deduced Tauc optical band gap is in the range of 2.7eV to 3.7eV. The possibility of using these DLC films as secondary electron emission materials have also been explored.

Preparation and Characterization of Crystalline β-C3N4 Films

CHEN Guang-hua;ZHANG Yang;ZHU He-sun;YANG Ning

2000, 29(3):  224-228. 

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A continuous and pure crystalline film of β-C3N4 with {221} textured characteristic has been grown using an ECR CVD (electron cyclotron resonance plasma enhanced chemical vapor deposition) process. The morphology of the deposited films was observed using SEM (scanning electron microscopy). Chemical compositions and chemical states of elements in the deposited films were analyzed using XPS (X-ray photoelectron spectroscopy), XRD (X-ray diffraction) and Raman scattering were used to characterize the film structure.

[100]-Oriented Textured Growth of the Diamond Films and Its Infrared Properties

XIA Yi-ben;JU Jian-hua;DAI Wen-qi;WANG Lin-jun;WANG Hong

2000, 29(3):  229-233. 

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The [100]-oriented texture growth diamond films on (100) mirror polished Si have been achieved by microwave plasma chemical vapor deposition (MPCVD) system. The film morphology, phase composition and IR properties were studied by using SEM, Raman spectroscopy and IR transmission spectroscopy. These film properties were compared with respect to the different nucleation and deposition parameters. Results show that the negative field bias between plasma and substrate assisted oriented nucleation and H+ ions etch processing not only improved diamond film [100] oriented growth but also etched off non-diamond phase which formed during the nucleation period. For this reason, the diamond film has better IR transmission after having two hours H+ ions etching during the film deposition process.

Carbon Nitride Films Deposited by MPCVD

GU You-song;ZHANG Yong-ping;CHANG Xiang-rong;TIAN Zhong-zhuo;SHI Dong-xia;ZHANG Xiu-fang;YUAN Lei

2000, 29(3):  234-239. 

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Carbon nitride films have been deposited on Si and Pt substances by microwave plasma chemical vapor deposition (MPCVD). For films deposited on Si substrates, SEM observations showed that polycrystalline films were formed. The nitrogen to carbon ratio was in the range of 1.0-2.0. XRD experiments with films on both Si and Pt substrate showed that the films consisted of crystal phases of α-and β-C3N4. Detailed XPS peak profile analysis showed that the carbon and nitrogen atoms in the films were mainly bound together in single bond covalent C-N bonds. IR spectra also showed characteristic peaks of β-C3N4. Strong evidence shows that crystalline carbon nitride films have been synthesized.

Raman Spectra and Surface Morphology of Nitrogen-doping Tetrahedral Amorphous Carbon Films

WEI Ai-xiang;CHEN Di-hu;ZHANG Hai-yan;TANG Xin-gui;ZHOU You-guo;YANG Zeng-hong

2000, 29(3):  240-244. 

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Nitrogen-containing tetrahedral amorphous carbon films (ta-C) have been prepared by magnetic field filtered plasma stream deposition method. The plasma stream was first formed by sputtering of a graphite target in nitrogen-argon atmosphere. The microstructure and surface morphology of the films having different nitrogen-doping levels have been studied using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and atomic force microscopy. The results showed that the nitrogen-free ta-C films have a single and nearly symmetric very broad Raman peak range from 1200 cm-1 to 2000 cm-1 with the centerline at about 1580 cm-1. The surface morphology of the films is very smooth and uniform. The Raman spectra of nitrogen-containing ta-C films exhibit two broad peaks centered approximately at 1360 cm-1 (D peak) and 1580 cm-1 (G peak). The ratio of the maximum intensity of D band and G band increases with the amount of nitrogen incorporated into ta-C films. The correlation between microstructure and nitrogen content in these films was discussed.

Role of Hydrogen Gas in the Growth of Carbon Thin Films by Pulsed Laser Deposition

Tsuyoshi Yoshitake;Takashi Nishiyama;Kunihito Nagayama

2000, 29(3):  245-249. 

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Carbon thin films with thickness of 100 nm were deposited on glass and silicon substrates at a substrate temperature of 20℃ by pulsed laser deposition (PLD) using a graphite target. The laser source used was an ArF excimer laser (λ= 193 nm, 24ns). The ambient pressure was changed between 1.33×10-5 Pa and 133Pa by adjusting the amount of hydrogen gas flow. The Raman spectrum measurement showed a broad peak with a center of 1550 cm-1, similar to those of the typical DLC films prepared using other methods. With increasing hydrogen pressure, the absorption coefficient decreased and the optical band gap increased. The films deposited at the hydrogen pressure of 133Pa had an optical band gap of more than 2.5 eV, which is twice as large as that of films deposited with no hydrogen atmosphere.Theseresults indicate that the hydrogen gas is effective for etching the sp2 bonding fractions. In PLD method, the ejected species from the target form the plasma, and the hydrogen molecules are expected to be decomposed into atomic hydrogen. This atomic hydrogen must play the role of etching the sp2 bonding fractions, as it does for the case of CVD method.

Epitaxy of Thin Diamond Film with Large-area Monocrystalline

ZHANG Yang;CHEN Guang-hua;ZHU He-sun;YANG Xin-wu;YANG Ning

2000, 29(3):  250-252. 

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The monocrystalline diamond film about 100μm2 in size has been carried out on Si substrate using an electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR CVD) from the gas mixture of methane and hydrogen. The Si substrate was not pre-treated before growth. The radio frequency (RF) bias was employed in the growth process. The substrate was placed in the electron cyclotron region. Experiment result indicates that the growth of the monocrystalline diamond on Si substrate depends on the pre-formed β-SiC interlayer, and the application of RF negative bias to the substrate relative to the plasma played a crucial role in the formation of the β-SiC interlayer.

Diamond-like Carbon Film as a Passivation Coating of Hg1-xCdxTe Infrared Devices

JU Jian-hua;XIA Yi-ben;WANG Lin-jun;WU Wen-hai;TANG Ding-yuan

2000, 29(3):  253-256. 

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A dense and homogeneous nanograins diamond-like carbon (DLC) film has been deposited on the well-polished HgCdTe wafer by radio frequency plasma enhanced chemical vapor deposition at room temperature. The surface photographs of both DLC and MCT are studied by AFM and LFM respectively. The interface of DLC/HgCdTe is studied by AES. Result shows that DLC film can suppress the dissociation of the weak bonding HgTe, and prevent Hg escapingfrom from MCT surface to some extent, when the thickness of DLC film has reached 25nm.AFM and LFM results show that the compositions of some MCT surface regions have dissolved and formed another phase different from MCT substrate, after 30 minutes annealing at 100℃. However this change has not been observed on the surface of DLC coated MCT. This result is agreement with that given by AES.

Deposition and Etching of Amorphous Carbon Films in ECR Plasma

NING Zhao-yuan;MA Chun-lan;CHENG Shan-hua;KANG Jian;XIN Yi;YE Chao

2000, 29(3):  257-263. 

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Amorphous hydrogenated carbon films have been deposited with benzene in an electron cyclotron resonance (ECR) plasma system. To approach as a resist in dry etching processing, etching properties of the films in oxygen plasma have been investigated. The results show that amorphous carbon films have high etching resistance against oxygen plasma, and etch rates of the films correlated not only with etching processing parameters, also with deposition conditions.

Mechanism of Field Electron Emission from a Planar SiC Film

LI De-Chang;YANG Yin-Tang;LIU Guang-Jun;ZHU Chang-Chun

2000, 29(3):  264-268. 

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Besides the general advantages as diamond films in FEE, SiC film is able to be n-type doped or p-type doped easily. The SiC films have been developed as cold cathodes by APCVD. It is found in the FEE tests that the onset field strength is as low as 0.3 MV/m. According to the theoretical analysis about the emission procedure an exponential increase model is deduced to understand the FEE results. According to the model, the electron injection from substrate to the film plays an important role in the FEE, and the electron transport in the film is vital for the FEE. So the distance between the two adjacent conductive centers can be estimated of 0.6 nm.

Optimizing of Hot Filament Parameters on High Quality Diamond Films Deposition by HFCVD

SONG Xue-mei;WANG Bo;ZHANG Xing-wang;ZHANG Sheng-jun;CHEN Guang-hua;YAN Hui

2000, 29(3):  269-274. 

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A hot filaments and substrate thermal model is used to explain the correlation between the geometry parameters of the hot filaments and the uniform of diamond films. Applying this model, both the irradiance field and the temperature field are calculated for diamond films in large area growth by hot filament assisted chemical vapor deposition (HFCVD). According to the results, the uniform of diamond films is rather determined by the irradiance field than the temperature field, which is in agreement with the experimental data. Moreover, the suitable geometry parameters to deposit diamond films on 100mm×100mm area are given.

C3N4 Films Prepared by Hot Filament Assisted RF Plasma CVD

WU Xian-cheng;HE De-yan;WANG Bo;YAN Hui;CHEN Guang-hua

2000, 29(3):  275-279. 

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Carbon nitride (CN) thin films were prepared on Si (100) substrates by hot filament assisted RF plasma chemical vapor deposition. X-ray diffraction spectra indicate that the obtained CN films contain crystalline β-C3N4 and α-C3N4 as well as an unknown structural phase. Obvious absorption peaks from C-N, C＝N and C≡N bonds were observed in Fourier transform infrared absorption spectra of the films, the respective wavenumbers are centered at 1237, 1625 and 2191 cm-1. Some crystalline grains of 1-2 μm in size with a hexagonal cross section were seen in the films by scanning electron microscopy. The maximum hardness of the film deposited at optimum conditions is as high as 72.66 GPa.

Potential Barriers for CVD Diamond Films on Diamond(111) and Si(111) Substrates

WANG Bo;SONG Xue-mei;ZHANG Sheng-jun;ZHANG Xing-wang;YAN Hui

2000, 29(3):  280-284. 

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A thorough understanding of the mechanism of nucleation and growth particularly at the early stage, is very important for the preparation of high quality diamond films. Using a semi-empirical quantum mechanical method (PM3), we calculated the potential barriers of reactions of chemical vapor deposition (CVD) diamond films on Si(111) substrate. Applying methane and acetylene as precursors, we investigated the abstracting of hydrogen and adding of methyl and acetyl radicals at the growth surfaces of Si(111) and diamond(111). It shows that, for both interfaces, the barriers of abstracting hydrogen are much lower than those of adding growth radicals. However, the barrier when acetyl is the precursor is higher than when methyl for both the diamond(111) and Si(111), respectively. It is suggested that only when the C≡C bond of acetylene molecular breaking can it be added to the growth surfaces.

Study on Adhesion of Ti/Ni/Au Multilayers on Diamond Wafer

PAN Cun-hai;XU Ying-hui;WANG Shao-yan;CUI Wen-xiu;DU Su-mei;CAI Yun-hong;DIAO Xi-gang;HE Qi-yu

2000, 29(3):  285-289. 

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Ti/Ni/Au multilayers have been deposited by electron beam evaporation, to metallize CVD diamond wafers. The effect of pre-treatment and post-treatment on adhesion of the multi-layers to the substrates was investigated, and it was found, introducing a pre-fire at elevated temperatures, the adhesion could be improved significantly. Thermal cycling experiments were accomplished according to the Chinese national standard (GJB 126-86), and the multi-layers were not peeled off from the diamond wafers. Rutherford back-scattering spectroscopy (RBS) had been used to characterize the stability of the Ti/Ni/Au metallization scheme at 400℃, 500℃ for 60 min in vacuum. In conclusion, the good adhesion and the stability of the optimized processing between the diamond and the metal-layers can meet the required of the diamond application as heat sink.

Research on the Three-dimensional Temperature Field Model of Substrate Heating Material in Micowave Plasma CVD Diamond Equipment

ZHOU Jian;YUAN Run-zhang;WANG Nian;FU Wen-bin;AI Yang-bin

2000, 29(3):  290-295. 

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In microwave plasma CVD equipment,the inhomogeneous distribution of microwave electromagnetic field results in the inhomogeneous temperature of the plasma ball and substrate,and lowering quality of CVD diamond,so it is necessary to heat the substrate.Material's absorbability to microwave energy relates with microwave frequency,electric field intensity,material's dielectric constant,dielectric loss and material's volume.It is a function that temperature to material's dielectric constant and loss and thermal conductivity and so on. Based on thermodynamic theory, this paper researched the three-dimensional axialsymmetric temperature field model,in which above parameters were changed with temperature to heating substrate material, obtained analytic expression of temperature distribution, used silicon carbon material which can absorb microwave energy powerfully, and used it as material of heating substrate and laid it down in the substrate in the microwave plasma cavity.The calculated results show that the model can come into homogeneous temperature distribution,which has φ76.2mm diameter and temperature change is only less 10℃,so it is very useful to heat the substrate.

A Method of Estimating Thermal Conductivity

LUO Ting-li;ZHANG Yong-gui;HE Qi-yu;WANG Zhi-na;CAI Yun-hong;GUO Hui;SUN Zhen-lu

2000, 29(3):  296-299. 

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The radial thermal conductivity is important specification of diamond films. This paper reported the method of estimating the radial thermal conductivity of D C arc jet CVD diamond films through analyzing the correlation between the radial thermal conductivity and the peak value of X-ray diffraction spectrum of the crystal face. It is required that the CPS of (220) and (311) in three-orientation films with main crystal direction (111) are 23-33; and 8-15;, or the CPS of (400) in four-orientation films is as low as 5;. The range of error value is from -9.5; to 3.5;. When the CPS of (220) is high or the CPS of (311) is low, the estimating results are easy to be more than measurement, and vice verse.

Deposition of Diamond Film on Silicon Nitride Tools by MPCVD

ZHOU Jian;YUAN Run-zhang;YU Wei-hua;WANG Jian-hua;LIU Gui-zhen

2000, 29(3):  300-304. 

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Diamond film's nucleation and growth affects the quality of diamond film. This paper researched the nucleation quality of diamond coating on silicon nitride ceramic tools in different technology conditions in a new model stainless steel resonant cavity type microwave plasma CVD equipment which was made by our lab. The plasma ball's diameter is about 76 mm and homogeneous temperature distribution can realize homogeneous growth of diamond film.We examined and analyzed with scanning electron microscopy (SEM), laser Raman spectrometer (Raman) and researched a preparation technology of diamond coating on silicon nitride ceramic tool in high speed growth and high quality.And the cutting performance of the coating tools in the technology conditions was tested. The results showed that average applied lifetime of coating tools improved over 10 times to that of silicon nitride ceramic tools in cutting 18wt; Si-Al alloy.