郑伟涛
超硬、纳米和功能薄膜材料,材料的计算机模拟
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- 姓名:郑伟涛
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学术头衔:
博士生导师
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学科领域:
材料科学基础学科
- 研究兴趣:超硬、纳米和功能薄膜材料,材料的计算机模拟
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729
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成果数
16
郑伟涛, W.T. Zheng a, *, K.Z. Xing a, N. Hellgren a, M. Logdlund a,
Journal of Electron Spectroscopy and Related Phenomena 87 (1997) 45-49,-0001,():
-1年11月30日
Carbon nitride thin films deposited by dc unbalanced magnetron sputtering have been analyzed by high-resolution X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The XPS data show that N ls binding states depend on substrate temperature (T). By comparison with the Raman spectra, N 1 s binding states are assigned in which nitrogen atoms are mainly bound to sp 2 and sp 3 carbon atoms at T=100℃, whereas at Ta=500℃ nitrogen atoms are mainly bonded to sp 2, sp 3 and sp I carbon atoms.
Carbon nitride film, XPS, Raman spectrum, N ls binding energy
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【期刊论文】Reactive magnetron sputtering of CN. thin films at different substrate bias
郑伟涛, W.T. Zheng*, E. Broitman, N. Hellgren, K.Z. Xing, I. Ivanov, H. Sjostrom, L. Hultman, J.-E. Sundgren
Thin Solid Films 308-309(1997)223-227,-0001,():
-1年11月30日
The chemical binding states of C and N atoms, and optical properties of carbon nitride (CNx) thin films deposited by unbalanced magnetron sputtering, have been investigated as a function of the negative substrate bias (Vs). The film deposition rate increased slightly with increasing Vs, having a weak maximum at floating potential (~50V), and decreased sharply to zero for Vs>150 v, While N/c ratios did not exhibit any significant variation. Raman spectroscopy was used to reveal that the structure of the film is predominantly amorphous Fourier transform infra-red Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) analyses showed that N atoms in the films were bound to C atoms through sp2 and sp3 configurations. Triple C-N bonds were also detected by FTIR. The ratio of sp3 to sp2 bonds increased with increasing Vs. The maximum sp3 concentration in CNx films was estimated to be ~20%. The opticaI band gap of CNx fihns was also found to increase with an increase in Vs.
CNx films, Magnetron sputtering
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【期刊论文】Stress development during deposition of CNx thin films
郑伟涛, E. Broitman, a), W. T. Zheng, b), H. Sjostrom, c), I. Ivanov, J. E. Greene, d), and J.-E. Sundgren
Appl. Phys. Lett., Vol. 72, No.20, 18 May 1998,-0001,():
-1年11月30日
We have investigated the influence of deposition parameters on stress generation in CNx (0.3,x,0.5) thin films deposited onto Si (001) substrates by reactive magnetron sputtering of C in pure N2 discharges. Film stress, s, which in all cases is compressive, decreases with an increase in the N2 pressure, PN2, due to structural changes induced by the pressure-dependent variation in the average energy of particles bombarding the film during deposition. The film stress sis also a function of the film growth temperature, Ts, and exhibits a maximum value of; 5 GPa at 350℃. Under these conditions, the films have a distorted microstructure consisting of a three-dimensional, primarily sp2 bonded, network. In contrast, films deposited at Ts, 200℃ with a low stress are amorphous. At 350℃, Ts,600℃, sgradually decreases as Ts is increased and the microstructure becomes more graphitic and ontains fewer defects. Nanoindentation measurements show that the films grown at 350℃ exhibit the highest hardness and elasticity.
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【期刊论文】Field emission enhancement of amorphous carbon films by nitrogen-implantation
郑伟涛, Junjie Li a, *, Weitao Zheng b, Changzhi Gu a, b, Zengsun Jin b, Yongnian Zhao b, Xianxiu Mei c, Zongxi Mu c, Chuang Dong c, Changqing Sun d
Carbon 42(2004)2309-2314,-0001,():
-1年11月30日
Eect of nitrogen-implantation on electron field emission properties of amorphous carbon films has been examined. Raman and X-ray photoelectron spectroscopy measurements reveal different types of C-N bonds formed upon nitrogen-implantation. The threshold field is lowered from 14 to 4V/lm with increasing the dose of implantation from 0 to 5×1017cm-2 and the corresponding ective work function is estimated to be in the range of 0.01-0.1 eV. From the perspective of tetrahedron bond formation, a mechanism for the nitrogen-lowered work function is proposed, suggesting that both the nitrogen nonbonding (lone pair) and the lone-pair-induced carbon antiboding (dipole) states are responsible for lowering the work function and hence the threshold field.
A., Carbon films, B., Implantation, C., Raman spectroscopy, X-ray photoelectron spectroscopy, D., Field emission
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【期刊论文】Magnetic properties and electron spin resonance of charge ordering manganite Y0.5Ca0.5MnO3
郑伟涛, H.W. Tian, W.T. Zheng *, Z.D. Zhao, T. Ding, S.S. Yu, B. Zheng, X.T. Li, F.L. Meng, Q. Jiang
Chemical Physics Letters 401(2005)585-589,-0001,():
-1年11月30日
We report the magnetization and electron spin resonance study on charge-ordering (CO) manganite Y0.5Ca0.5MnO3 (YCMO) across the charge-ordering transition temperature TCO down to the antiferromagnetic ordering transition temperature TN. The transition temperatures of TCO and TN are observed at 275 and 125K, respectively. The observed large decrease in the linewidth from TN to TCO can be explained in terms of motional narrowing caused by the hopping of the Jahn-Teller (JT) polarons. Below TCO the g-value is almost constant, suggesting the weakening of orbital order in the compound of YCMO.
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【期刊论文】Chemical bonding in carbon nitride films studied by X-ray spectroscopies
郑伟涛, W.T. Zheng a, b, c, d, *, J.H. Guo e, Y. Sakamoto b, M. Takaya b, X.T. Li a, P.J. Chao a, Z.S. Jin a, K.Z. Xing c, J.-E. Sundgren c
Diamond and Related Materials 10(2001)1897-1900,-0001,():
-1年11月30日
Carbon nitride films are deposited using dc magnetron sputtering in a N discharge. The nature of chemical bonding of the 2 films is investigated using X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure, and X-ray emission spectroscopy. X-Ray photoelectron spectroscopy spectra show that N1s binding states depend on substrate temperature, in which two pronounced peaks can be observed. The near edge X-ray absorption fine structure at C1s and N1s exhibits a similar absorption profile in the resonance region, but the resonance is sharper in the N1s spectra. Resonant N K-emission spectra show a strong dependence on excitation photo energies. Compared XPS N1s spectra with recent theoretical calculations by Johansson and Stafstrom, two main nitrogen sites are assigned in which N bound to sp3 hybridized C and sp2 hybridized C, respectively. The correlation of X-ray photoelectron, X-ray absorption, and X-ray emission spectra for N in carbon nitride films is also discussed.
Carbon nitride film, Chemical bonding, Magnetron sputtering, X-Ray spectroscopies
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【期刊论文】Chemical bonding, structure, and hardness of carbon nitride thin films
郑伟涛, W.T. Zheng a, b, d, *, W.X. Yu a, H.B. Li a, Y.M. Wang a, P.J. Cao b, Z.S. Jin b, E. Broitman c, J.-E. Sundgren c
Diamond and Related Materials 9(2000)1790-1794,-0001,():
-1年11月30日
owest for the film grown at T s350℃, having a turbostratic-like structure, high hardness and stress. The correlation between the structure and hardness of carbon nitride films is discussed.
Nitrides, Bonding, Structure, Hardness
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郑伟涛, W. T. Zheng, a) J. J. Li, X. Wang, X. T. Li, and Z. S. Jin, B. K. Tay and Chang Q. Sun
J. Appl. Phys., Vol. 94, No.4, 15 August 2003,-0001,():
-1年11月30日
Carbon nitride films have been deposited by rf reactive magnetron sputtered graphite carbon in an N2 discharge. The process parameters, viz., nitrogen partial pressure (PN2), substrate temperature (Ts), and substrate bias (Vb) were varied in order to investigate their influence on the field emission properties. The effective work function for carbon nitride films determined using the Fowler-Nordheim equation is in the range of 0.01-0.1eV. Insight is presented into the nitrogen-lowered threshold of cold cathode electron emission of carbon from the perspective of nitride tetrahedron bond formation. The involvement of nonbonding (lone pair) and lone-pair-induced antibonding (dipole) states is suggested to be responsible for lowering the work function and hence the electron emission threshold. It is found that the substrate temperature of 200℃, floating potential at the substrate, and nitrogen partial pressure of 0.3Pa are favorable to promote the reaction that lowers the work function.
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【期刊论文】Dynamic Isomer Shift in Charge-Ordering Manganite Y0.5Ca0.5MnO3: Mo1ssbauer Spectroscopy Study
郑伟涛, H. W. Tian, W. T. Zheng, *, B. Zheng, X. Wang, Q. B. Wen, T. Ding, and Z. D. Zhao
J. Phys. Chem. B, Vol. 109, No.5, 2005,-0001,():
-1年11月30日
We report the Mossbauer spectroscopy study on Fe-doped charge-ordering manganite Y0.5Ca0.5MnO3. The dynamic isomer shift is observed for charge-ordering manganite, and its origin may be due to strong Jahn-Teller distortions in Y0.5Ca0.5MnO3, causing electron-phonon coupling. The evolution of Mossbauer spectroscopy as a function of temperature shows two different phases with significantly different quadrupole splitting values below the charge-ordering transition temperature. This confirms that there exist two different Mn sites (i.e., Mn3+ and Mn4+ ions), which can be identified by the microscopic method of Mossbauer spectroscopy.
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郑伟涛, J. J. Li, W. T. Zheng a), Z. S. Jin, X. Wang, H. J. Bian, G. R. Gu, and Y. N. Zhao, S. H. Meng, X. D. He, and J. C. Han
J. Vac. Sci. Technol. B 21 (6), Nov/Dec 2003,-0001,():
-1年11月30日
The carbon nitride films deposited by rf magnetron sputtering in a pure N2 discharge were annealed in vacuum up to 900℃. The chemical composition and bonding structure of the films were studied using x-ray photoelectron spectroscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. It was found that the nitrogen atoms were bound to sp, sp2, and sp3 hybridized carbon atoms in as-deposited films. The effects of the thermal annealing on bonding structure and the electron field emission characteristics of CNx films were investigated. The results showed that thermal annealing treatment caused a great loss of N content and favor formation of sp2 bonds in CNx films, which would significantly influence the field emission properties for the CNx films. The CNx films annealed at temperature of 750℃ showed the optimal electron emission properties. Besides, the correlation between the chemical bonding structures and electron emission properties for the CNx films was discussed.
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