Search

A general and flexible synthetic route, which leads to the synthesisof brazilin-like compounds, was developed. The aza--brazilinderivatives show strong anticancer activities in MTT assay towardsa number of human cancer cell lines including HT29, A549, HL60,and K562.

Highly purified polycrystalline wafers of Zr and Hf were chosen as substrates for diamond deposition by means of the d.c. arc discharge plasma CVD method. Polycrystalline diamond films were formed on both substrates. Scanning electron microscopy and high resolution X-ray diffraction were used to investigate the surface morphology of the diamond films and the composition of the interface layers between the diamond films and substrates. The experiments showed that the transition layer between the diamond films and Zr substrates was ZrC, ZrH and ZrC0.32H1.2. For Hf substrates, in addition to HfC, it is supposed that there were also some hydrides or carbohydrides in the transition layer, because several X-ray reflections appeared which could not be assigned to Hf, HfC or diamond.

Boron-doped (B-doped) polycrystalline diamond films (PDFs) were synthesized by thermal filament chemical vapour deposition, and the Hall effect, together with the resistivity of samples with different dosages, was measured by Van der Pauw's method. The Hall mobility and the hole concentration in the samples were also calculated. The experimental results show that B-doped PDFs are p-type semiconductors in which the resistivity has decreased by 11 orders of magnitude compared with the intrinsic samples (from 10 9 Ω cm to 10 −2 Ω cm). The activation energy of the B-doped PDFs was reduced through 0.307 eV (for lightly doped PDFs) to 0.075 eV (for heavily doped PDFs). However, the Hall mobility of the samples was only about 7 cm 2 V −1 s −1 and was almost independent of the impurity concentration. A preliminary discussion of the experimental results is also given in this paper.

Studies of current-voltage I–V characteristics of diamond films synthesized by d.c. arc discharge chemical vapour deposition are reported in this paper. Experimental results demonstrated ohmic-type I–V characteristics for as-deposited diamond films with a typical resistivity of the order of 106 ohm; cm. However, the resistivity increased by 6 orders of magnitude, being of the order of 1012 ohm; cm after the diamond films were annealed in a nitrogen atmosphere for 90 min at 600°C, and the I–V characteristics revealed a space-charge-limited current behaviour in the presence of traps at times. When the annealed samples were rehydrogenated in the hydrogen plasma, the resistivity returned to the value of the asdeposited films. An exponential energy distribution of traps and the order of its peak value were also estimated in our work.

The depth profile of the structure of synthetic diamond thin films prepared by the d.c. arc discharge plasma chemical vapour deposition (CVD) method has been investigated by sample-tilting X-ray diffraction. The results show that, at first, a layer of carbide is deposited which saturates the substrate surface. For a single-crystal silicon (c-Si) substrate, the compound is silicon carbide (SiC); for a molybdenum wafer substrate, the compound is molybdenum carbide (Mo2C). A diamond film grows on the carbide layer. The orientation of the crystal grains with depth in the polycrystalline diamond thin films is irregular. The main contaminant in diamond thin films prepared by the d.c. arc discharge plasma CVD method is tungsten carbide (WC).

Diamond polycrystal powder has been produced directly from gas phase in an arc discharge plasma jet system. Acetylene diluted in argon was used as hydrocarbon source gas. The product was the mixture of diamond polycrystal powders and soot. The 3C cubic phase diamond which is dominant, and the mixture phases of cubic and 6H hexagonal diamond are identified in the produced diamond polycrystal powders by electron diffraction patterns.

In order to investigate the growth mechanism of diamond thin films, the in situ optical emission spectra of direct current (dc) arc discharge plasma, including the spatial distributions and different CH4/H2 ratios, have been measured during the growth processes of diamond thin films prepared by the dc arc discharge plasma chemical vapor deposition method. The results show that there are a great number of atomic hydrogens in the arc discharge plasma. This is the key factor for the growth of diamond films with a high rate and high quality. In addition, the effects of the CH4/H2 ratio on the quality of diamond films are discussed in detail in this letter.

Among the strong carbide forming elements, ten of them have melting points above 1400 degrees Centigrade. The observed transition layers between CVD diamond films and the substrates of Mo, Si, W, Ta, Nb, and Ti have been reported previously. In this paper, further research results on transition layers for the substrate elements of V, Cr, Zr, and Hf are presented. The specimens are prepared in an arc discharge plasma CVD system with the substrate temperature of 900 - 1000 degrees Centigrade and characterized by a high resolution X-ray diffusion diffraction instrument. the experimental results show that the transition layers are polycrystalline VC and V2C, Cr7C3 and HfC for the substrates of V, Cr, and Hf respectively. For the transition layers between CVD diamond films and Zr substrates, the composition of polycrystalline ZrH, ZrC, and their complex compound are verified and the content of hydride is comparable to the content of carbide in this case.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The nucleation and growth mechanism of polycrystalline diamond films prepared by chemical vapor deposition (CVD) have received increasing research interest. To verify the existence of the transition layers between CVD diamond films and substrates, and to investigate their composition, structure and properties are very meaningful research topics for understanding the mechanism of diamond film growth and developing the applications of CVD diamond films. In this work, the transition layers of carbides for the substrates of molybdenum (Mo), silicon (Si), tungsten (W), tantalum (Ta), and niobium (Nb) and titanium (Ti) have been systematically studied by x-ray diffraction characterization. The experiment results have provided evidence of the existence of transition layers and have revealed that the transition layers are polycrystalline Mo2C, SiC, WC and W2C, TaC and Ta2C, NbC and Nb2C, as well as TiC for the substrates of Mo, Si, W, Ta, Nb and Ti, respectively.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In order to investigate the nucleation and growth mechanisms of diamond thin film, the in situ optical emission spectra (OES) of direct-current (DC) arc plasma chemical vapor deposition (CVD) have been measured during the growth processes of diamond thin films under the case of various CH4/H2 and C2H2/H2 ratios. We compared the results of OES with that of Raman spectra. The results show that there are a great numbers of atomic H in the arc discharge plasma, this is the key factor of the growth of diamond thin films with a high rate and high quality, furthermore, the carbon sources and the H2 dilution ratios have strong effects on the quality of the films. When the ratios of CH4/(CH4+H2) and C2H2/(C2H2+H2) increase, the non-diamond carbon phase in the films increase due to the increasing of C2 radical and the decreasing of atomic H, moreover, when the carbon source is C2H2, and when C2H2/H2=2%, the IG/ID derived from Raman spectra is 33%, but when CH4 is served as carbon source and CH4/H2=2%, the IG/ID=10%, obviously as a carbon source, CH4 is better than C2H2.