Browsing by Author "Lu, TR"

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Crystalline SiCN: a hard material rivals to cubic BN
(1999-11-01)
Chen, LC
;
Chen, KH
;
Wei, SL
;
Kichambare, PD
;
Wu, JJ
Growth and mechanical properties of SiCN materials prepared by microwave plasma enhanced chemical vapor deposition (CVD) as well as electron cyclotron resonance plasma CVD are reported. Large (several tens of microns), well-faceted ternary SiCN crystals were grown by microwave plasma-enhanced chemical vapor deposition. whereas amorphous SiCN films were deposited by ECR-CVD. The ternary crystalline compound (C; Si)(x)N-y exhibits a hexagonal structure and consists of a network wherein the Si and C are substitutional elements. While the N content of the crystalline compound is about 50 at.%, the extent of Si substitution varies and can be as low as 10 at.%. The amorphous SIGN films contain only about 30 at.% N. Nano-indentation studies were employed to investigate the mechanical properties of the SiCN materials. From the load versus displacement curves. we estimated the hardness and the effective modulus of the SIGN crystals to be around 30 and 321.7 GPa, respectively. The corresponding values for the amorphous SiCN were around 22 and 164.4 GPa, respectively. These values are well above most reported values for CN films. (C) 1999 Elsevier Science S.A. All rights reserved.
Deposition of silicon carbon nitride films by ion beam sputtering
(1999-11-01)
Wu, JJ
;
Wu, CT
;
Liao, YC
;
Lu, TR
;
Chen, LC
Silicon carbon nitride films have been successfully synthesized at a temperature below 100 degrees C from an adenine(C5N5H5)-silicon-mixed target sputtered by Ar ion beam. The effects of Ar ion sputtering voltage, area ratio of Si to adenine in the mixed target and nitrogen atom addition during deposition on the film growth are investigated. XPS, XRD, and ellipsometry were employed to characterize the composition, chemical bonding, structure, and optical property of the films. The growth characteristic and film properties of the silicon carbon nitride films are also compared with those of the carbon nitride films deposited from an adenine target to elucidate the effect of silicon incorporation. The silicon content of the resultant films increased significantly as the area ratio of Si to adenine increased, whereas a higher Ar ion voltage led to a lower level of silicon incorporation, presumably due to differential sputtering yield of Si and adenine. XPS chemical stare analysis revealed multiple bonding structures for every element in the SiCN films, of which possible implications are given. XRD studies showed that only amorphous films for Si-rich SiCN were obtained, while the films with low Si incorporation and deposited at high Ar ion beam voltage contained nanocrystallites. Furthermore, the: refractive index of the SiCN films increased with increasing silicon content. The appearance of the nanocrystalline structure in the films led to a reduction in the refractive index. (C) 1999 Elsevier Science S.A. All rights reserved.
Effect of target materials on crystalline carbon nitride film preparation by ion beam sputtering
(1999-08-01)
Kuo, CT
;
Chen, LC
;
Chen, KH
;
Chen, TM
;
Lu, TR
In order to provide abundant chemical information, two novel bio-molecular target materials, instead of the conventional graphite target, were successfully developed to determine the possible formation mechanisms of carbon nitride during ion beam deposition. The azaadenine and adenine targets consist of carbonitro bonding, high N/C ratio as well as a six-fold carbonitro ring structure similar to that in hypothetical C3N4. Mass spectroscopy was used to determine the possible mechanisms of these two target materials. A lower electron beam energy at 75 eV was adopted to generate as abundant fragmental ions during the decomposition of these targets. Mass spectroscopy study on these two different targets indicates that the adenine target exhibits a more complex decomposition mechanism than the azaadenine target. However, the seven common hydrogenated carbonitro-species may suggest the same predominant mechanism during the decomposition of these two targets under the present deposition condition. The good correlation is one reason why two different targets can make almost the same quality crystalline carbon nitride films, including bonding, composition and structure. (C) 1999 Elsevier Science S.A. All rights reserved.
High purity nano-crystalline carbon nitride films prepared at ambient temperature by ion beam sputtering
(1999-07-18)
Lu, TR
;
Kuo, CT
;
Yang, JR
;
Chen, LC
;
Chen, KH
High purity nano-crystalline carbon nitride films have been successfully deposited by ion beam sputtering. A novel biomolecular C-N compound, 6-aminopurine, of which the characteristic features include covalent C-N bonding, high N/C ratio and a six-membered ring structure similar to that in the hypothetical C3N4 crystal, has been employed as the target material. The films can be deposited onto a variety of substrate, such as copper, silver, stainless steel, nickel and silicon wafer at ambient temperature. SAM examination indicates a high nitrogen-to-carbon ratio at about 0.51. XPS, IR and Raman studies reveal that the chemical bonding structures consist mainly of sp(3)-hybridized carbon as well as sp(2)-hybridized nitrogen and carbon. Both TEM and SAM mapping investigations indicate that the film contains a very dense and homogenous distribution of nanocrystalline grains. However, the structures of these crystals are yet to be determined since their TEM diffraction patterns only matched partially with the calculated pattern for beta-C3N4. (C) 1999 Elsevier Science S.A. All rights reserved.
Internal stresses and microstructures of commercial thick diamond films deposited by different deposition methods
(2001-11-01)
Kuo, CT
;
Wu, JY
;
Lin, CH
;
Lu, TR
;
Sung, CM
Structures and stress state of six commercial freestanding thick diamond films (> 300 mum) were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and Raman spectroscopy. These films represent the typical samples synthesized by three different chemical vapor deposition (CVD) methods, including DC are, microwave plasma, and hot filament. It was found that the higher diamond deposition rate it reaches, the more non-diamond carbons it contains, and the larger the residual compressive stress it possesses. Moreover, the samples with the highest degree of optical transparency are under the lowest compressive stress. These crystal characteristics can be manipulated by selecting different deposition methods and parameters that affect nucleation rate and growth rate of diamond. The present results show that the DC are method gives poorly developed crystals, and its residual compressive stress of the films is the highest due to the fastest diamond nucleation and crystal growth rates. (C) 2001 Elsevier Science B.V. All rights reserved.
Nano-carbon nitride synthesis from a bio-molecular target for ion beam sputtering at low temperature
(1999-03-01)
Wu, JJ
;
Lu, TR
;
Wu, CT
;
Wang, TY
;
Chen, LC
Nano-crystalline carbon nitride has been successfully synthesized at a temperature below 100 degrees C from an adenine(C5N5H5) target sputtered by an Ar ion beam. Because adenine possesses a ring structure similar to the hypothetical beta-C3N4 phase, the use of this bio-molecular compound as the target is believed to reduce the energy barrier of carbon-nitride growth. The effect of Ar ion-sputtering voltage on the film growth and the effect of extra-N-atom incorporation on the carbon-nitride film growth are examined in this study. Only a carbon film is formed with an ion energy of 500 V. For the ion-beam energy above 750 V, carbon nitride films are deposited, and there is some hydrogen incorporation in the films. The N/C composition ratio in the films could reach 1:1 and is independent on the ion beam voltage. The nitrogen is bonded with carbon within the films, as determined by the IR and XPS measurements. However, the films deposited at a higher ion voltage could possess some original functional groups of adenine. A strong and broad peak at a d-spacing of 0.32 nm, comparable to the calculated d-spacing of the beta-C3N4(110), is observed in the XRD spectra of the carbon nitride films. The TEM results indicated that the film contained nano-crystalline grains. Several d values are also in good agreement with those of adenine and the calculated values of beta-C3N4. The C/N ratios of the films are still kept at almost 1:1 with N atoms added during deposition. The XRD spectra and IR spectra of these films are all similar to the film deposited without nitrogen source. (C) 1999 Elsevier Science S.A. All rights reserved.
Preparation of a novel target material for carbon nitride film deposition
(1997-10-31)
Lu, TR
;
Kuo, CT
;
Chen, TM
;
材料科學與工程學系
;
應用化學系
To increase the nitrogen content and the degree of crystallinity in carbon nitride films by film deposition techniques (i.e. sputtering, laser ablation etc.), a novel target material composed of carbon nitride has been prepared by UV photo-assisted synthesis. The intention is to replace the traditional graphite target with this material. This synthesis involves photo-chemical reaction of sodium amide and chloroform as carbon and nitrogen sources, respectively, followed by high temperature sintering under flowing nitrogen. Elemental analyses indicate the presence of C, N and H in the target material with a nitrogen to carbon ratio of 0.23. Infrared spectroscopy shows a mixture of sp(3) and sp(2) carbon and sp(2) nitrogen in the sintered powder. Six diffraction peaks attributable to alpha-C3N4 were observed in XRD pattern. Grains of similar to 0.3 pm in diameter in an extended network were also observed in the SEM micrographs. The sintered carbon nitride powder is stable up to 800 degrees C. (C) 1997 Elsevier Science S.A.
Sputtering process of carbon nitride films by using a novel bio-molecular C-N containing target
(1998-11-02)
Lu, TR
;
Chen, LC
;
Chen, KH
;
Bhusari, DM
;
Chen, TM
In order to reduce the activation energy barrier for the formation of carbon nitride during ion beam sputtering, a novel bio-molecular target material, instead of the conventional graphite target, is successfully developed to deposit the crystalline carbon nitride films. The adenine target consists of a high N/C ratio as well as a 6-fold carbonitro-ring structure similar to that in the hypothetical C3N4. The mass spectrum of adenine indicates the existence of 11 main carbonitro-hydrogen containing species. Thus, the adenine target is anticipated to enhance the nucleation and growth of carbon nitride films by providing abundant carbonitro-hydrogen containing species as intermediate states. X-ray photoelectron spectrum analyses of these films indicated the presence of C and N in the films, with high nitrogen to carbon ratio at about 0.48. Both infrared and Raman spectroscopies confirm the chemical bonding between the carbon and nitrogen. X-ray and electron diffraction indicates the presence of crystalline carbon nitride in the film. (C) 1998 Elsevier Science S.A. All rights reserved.
Structural and superconducting properties of phases in the underdoped Y-2(Ba1-xSrx)(4)Cu7O14+delta system: The evidence for a chemical pressure effect
(1997-03-01)
Lu, TR
;
Chen, TM
;
應用化學系
;
Department of Applied Chemistry
An attempt was made to investigate the chemical pressure effect (i.e., smaller isovalent cation substitution) on the superconductivity of phases in the Y-2(Ba1-xSrx)(4)Cu7O14+delta (Sr-doped 247) system. A series of Sr-doped 247 phases with x = 0, 0.05, 0.10, 0.15, 0.175, 0.20 and 0.30 were prepared under 20 bar of oxygen at 900 degrees C, followed by thermal annealing under 100 bar of oxygen at 300 degrees C and slowly cooled down to ambient temperature. The solubility limit of Sr in the 247 phase was found to be ca. 0.10 to 0.15 and the orthorhombic lattice distortion for the Sr-doped 247 phases increased with increasing Sr content, as determined from X-ray diffraction (XRD). Rietveld refinement based on the XRD data obtained for Y-2(Ba0.9Sr0.1)(4)Cu7O14.74 indicated that 92.5% of Sr atoms substituted for the Ba sites in the YBa2Cu4O8 subcell. The T-c of the Sr-doped 247 phases increased from 72 K(x = 0) to 75 K(x = 0.10) monotonically upon Sr substitution, as indicated by both dc resistivity and magnetic susceptibility data. The dopant composition coefficient of T-c, dT(c)/dx, for the series of Sr-doped 247 phases with 0 less than or equal to x less than or equal to 0.10 was also determined to be +7.5 K per Sr atom per formula unit based on magnetic susceptibility data. We have demonstrated that the principle of chemical pressure effect can be applied to enhance T-c in a series of Sr-doped 247 phases without applying high physical pressure.
Structural and superconducting properties of phases in the underdoped Y-2(Ba1-xSrx)(4)Cu7O14+delta system: The evidence for a chemical pressure effect
(1997-03-01)
Lu, TR
;
Chen, TM
;
應用化學系
;
Department of Applied Chemistry
An attempt was made to investigate the chemical pressure effect (i.e., smaller isovalent cation substitution) on the superconductivity of phases in the Y-2(Ba1-xSrx)(4)Cu7O14+delta (Sr-doped 247) system. A series of Sr-doped 247 phases with x = 0, 0.05, 0.10, 0.15, 0.175, 0.20 and 0.30 were prepared under 20 bar of oxygen at 900 degrees C, followed by thermal annealing under 100 bar of oxygen at 300 degrees C and slowly cooled down to ambient temperature. The solubility limit of Sr in the 247 phase was found to be ca. 0.10 to 0.15 and the orthorhombic lattice distortion for the Sr-doped 247 phases increased with increasing Sr content, as determined from X-ray diffraction (XRD). Rietveld refinement based on the XRD data obtained for Y-2(Ba0.9Sr0.1)(4)Cu7O14.74 indicated that 92.5% of Sr atoms substituted for the Ba sites in the YBa2Cu4O8 subcell. The T-c of the Sr-doped 247 phases increased from 72 K(x = 0) to 75 K(x = 0.10) monotonically upon Sr substitution, as indicated by both dc resistivity and magnetic susceptibility data. The dopant composition coefficient of T-c, dT(c)/dx, for the series of Sr-doped 247 phases with 0 less than or equal to x less than or equal to 0.10 was also determined to be +7.5 K per Sr atom per formula unit based on magnetic susceptibility data. We have demonstrated that the principle of chemical pressure effect can be applied to enhance T-c in a series of Sr-doped 247 phases without applying high physical pressure.
Synthesizing crystalline carbon nitrides by using two different bio-molecular materials
(2001-11-01)
Kuo, CT
;
Wu, JY
;
Lu, TR
;
材料科學與工程學系
;
Department of Materials Science and Engineering
It is important to examine the deposition mechanism of crystalline carbon nitrides and to investigate the linkage between bio-molecular and superhard materials. Two different CN compound bio-molecular targets with the sixfold ring structure similar to that in the hypothetical beta -C3N4 were proposed to be used for synthesizing carbon nitride films on different substrates by reactive ion beam sputtering. Effect of the substrate material and the correlation between the bonding characters of the different target materials and the deposited films were examined. The deposited films exhibit no significant differences in the atomic NIC ratio and film properties at the condition of 1000 eV Ar-ion beam, no matter which one of the two target materials and which one of the seven substrate materials are. The XPS and AES analyses reveal that the atomic NIC ratio of the films can go up to 0.50, which is much higher than most of the reported values (0.2-0.35). The FTIR, XPS and Raman spectra clearly indicate the co-existence of chemical bondings of C-N single bond and C=N double bond; and no detectable C dropN triple bonding is observed, which forms a favor basis for further processing of the films to improve the film quality. The XRD, electron diffraction, TEM and AFM analyses indicate that the deposited films may consist of the nano-sized beta -C3N4 crystaflites embedded in matrix of graphite form of C3N4 Structure, and the volume concentrations of the crystalline phases are high enough to be detected by XRD. The implication of the results is that one highly probable way to explore the deposition mechanisms of crystalline carbon nitrides is to manipulate chemical bonding information using different target materials. (C) 2001 Elsevier Science B.V. All rights reserved.
The use of a biomolecular target for crystalline carbon nitride film deposition by Ar ion-beam sputtering without any other source of nitrogen
(1998-06-29)
Chen, LC
;
Lu, TR
;
Kuo, CT
;
Bhusari, DM
;
Wu, JJ
Carbon nitride films have been synthesized by argon ion-beam sputtering from a biomolecular compound target, 8-aza-6-aminopurine (C4N6H4) The compound has a six-membered ring structure similar to that existing in the hypothetical beta-C3N4. Except fur the target material, no other source of nitrogen was used during sputtering deposition. It was found that crystalline carbon nitride with high N/C atomic composition ratios of 0.43-0.56 can be formed even at room temperature. The infrared spectra of the film exhibit two peaks at 1383 and 1643 cm(-1), corresponding to C-N and C=N stretching modes, respectively. No detectable peak at 2200 cm(-1) (C=N stretching mode) is observed. Both x-ray diffraction and transmission electron microscopy show a very strong broad peak at 3.2 Angstrom, comparable to the d spacing of the (110) orientation in the beta-C3N4 structure. However, it is suggested that the film contains a nanocrystalline phase with a crystal structure yet to be determined. (C) 1998 American Institute of Physics.