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Improvement on the degradation of microwave sintered ZnO varistors by postannealing
(1998-06-01)
Chen, CS
;
Kuo, CT
;
Lin, IN
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The microwave sintering process not only densified the ZnO materials in a higher rate, but also resulted in significantly better varistor characteristics. Large nonlinear coefficient and low leakage current density were attained by cooling the samples under a rate of 80 degrees C/min after sintering, followed by 600 degrees C postannealing for 60 min under oxygen atmosphere. Inappropriate annealing deteriorated the varistor characteristics that can either be attributed to the insufficient reoxidation along grain boundaries when annealed in N-2 (or air) or loss of Zn species in these regions when annealed at 750 degrees C (900 degrees C). By contrast, the degradation behavior of these materials can be improved by the annealing process regardless of the annealing atmosphere or temperature.
High adhesion and quality diamond films on steel substrate
(1998-06-01)
Lin, CR
;
Kuo, CT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A process to deposit a diamond coating on steel substrates has been successfully developed. It includes the electroplating of nickel by using an electrolyte dispersed with micro-diamonds, and then a diamond deposition through a microwave plasma chemical vapor deposition system. The diamond films were characterized by Raman and CL spectroscopy, XRD, SEM and SEM line scanning. The results show a high diamond crystal quality, low residual stress (about 0.67 GPa) and high nucleation density. The adhesion of the films was evaluated by a cutting test and an interface examination. The results show that the retentivity of the diamond grits in the films after the cutting test is much better than that in the commercial electroformed diamond tools. The advantages of the process are: (1) the formation of nickel-carbon-hydrogen alloys to enhance diamond nucleation and growth, (2) the micro-diamonds acting as the seeds for diamond nucleation and growth, and forming effective mechanical interlocking with the nickel interlayer, and (3) the formation of good diffusion bonding of the nickel interlayer with the steel substrate. (C) 1998 Elsevier Science S.A.
Microstructure and nonlinear properties of microwave-sintered ZnO-V2O5 varistors: II, effect of Mn3O4 doping
(1998-11-01)
Kuo, CT
;
Chen, CS
;
Lin, IN
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The microstructure and nonlinear current-voltage characteristics of Mn3O4-doped ZnO-V2O5 ceramics, microwave-sintered at 800 degrees-1200 degrees C for 10 min, have been investigated. A high density (96% of the theoretical density) has been achieved. The incorporation of Mn3O4 additives does not significantly alter the densification behavior of the ZnO-V2O5 materials, but rather pronouncedly increases the non-linear coefficient (alpha = 23.5) and markedly suppresses their leakage current density (J(L) = 2.4 x 10(-6) A/cm(2)). On the other hand, the intrinsic properties of the materials, including the Schottky barrier height (Phi(b)) and the donor density (N-d), are only moderately modified; that is, Phi(b) = 1.16 eV and N-d = 5.4 x 10(17)/cm(3). X-ray diffractometry analyses and energy-dispersive X-ray microanalyses (via scanning electron microscopy) indicate that the V2O5 species facilitate the densification and the development of microstructure via the formation of a liquid phase (Zn-3(VO4)(2)) along the grain boundaries, whereas the Mn3O4 species markedly enhance the nonohmic behavior of the ZnO-V2O5 materials by forming the surface states along the grain boundaries.
Microstructure and nonlinear properties of microwave-sintered ZnO-V2O5 varistors: I, effect of V2O5 doping
(1998-11-01)
Kuo, CT
;
Chen, CS
;
Lin, IN
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The modification of the densification behavior and the grain-growth characteristics of the microwave-sintered ZnO materials, caused by the incorporation of V2O5 additives, have been systematically studied. Generally, the addition of V2O5 markedly enhances the densification rate, such that a density as high as 97.9% of the theoretical density and a grain size as large as 10 mu m can be attained for a sintering temperature as low as 800 degrees C and a soaking time as short as 10 min. Increasing the sintering temperature or soaking time does not significantly change the sintered density of the ZnO-V2O5 materials but it does monotonously increase their grain size. Varying the proportion of V2O5 in the range of 0.2-1.0 mol% does not pronouncedly modify such behavior. The leakage current density (J(L)) of these high-density and uniform-granular-structure samples is still large, which is amended by the incorporation of 0.3 mol% of Mn3O4 in the ZnO materials, in addition to 0.5 mol% of the V2O5 additives. Samples that are obtained using such a method possess good nonohmic characteristics (alpha = 23.5) and a low leakage current density (J(L) = 2.4 x 10(-6) A/cm(2)).
Improvement of mechanical properties of electroplated diamond tools by microwave plasma CVD diamond process
(1998-11-10)
Lin, CR
;
Kuo, CT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The growth and surface modification of irregular diamond grains of electroplated diamond tools have been developed successfully. Results show that the adherence, cutting ability, and wear resistance of diamond grains are improved by this process. In this study, the crystallization and quality of diamond grains were determined by SEM (SE and BSE), Raman spectroscopy, and XRD determination. Tests using a block-on-ring tribotester were also carried out to examine the adherence, cutting ability, and wearing resistance of the electroplated diamond tools, The adherence of diamond grains was also observed on a SEM microphotograph of the cross-section view of specimens. SEM line scanning was performed to determine whether the alloy elements are effectual in promoting the diffusion bonding strength among diamonds, the interlayer and substrate. (C) 1998 Elsevier Science S.A. All rights reserved.
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.
Improvement in adhesion of diamond films on cemented WC substrate with Ti-Si interlayers
(1998-12-01)
Lin, CR
;
Kuo, CT
;
Chang, RM
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Diamond films were deposited on the cemented WC+(3-5)% Co substrates by a microwave plasma chemical vapor deposition system. The substrates were pretreated with various processing steps before diamond deposition, including: polishing, etching for Co removal, Ti coating by DC sputter, and amorphous Si coating by E-gun. The residual stress of the films was determined by both Raman shift and low incident beam angle X-ray diffraction (LIBAD) methods. The adhesion of the films was evaluated by indentation adhesion testing. The him morphology and film-substrate interface structure were examined by SEM and Auger electron spectroscopy, respectively. The results show that Ti-Si can be a good interlayer to improve film adhesion and inhibit diffusion of Co to the substrate surface on diamond nucleation. This is due to the formation of strong TiC and SiC bonding to enhance film adhesion; Si acts as a promoter for diamond nucleation, and the residual stress with application of interlayer is much lower than that interlayer-free. The results also show the existence of an optimum Ti thickness for the best film adhesion. (C) 1998 Elsevier Science S.A. 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.
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.
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.

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