共查询到20条相似文献,搜索用时 421 毫秒
1.
Masami NishikawaTomohiko Nakajima Toshiya KumagaiTakeshi Okutani Tetsuo Tsuchiya 《Applied Surface Science》2011,257(7):2643-2646
We examined the correlation between thickness of an epitaxial VO2 phase grown on a TiO2 (0 0 1) substrate by the excimer-laser-assisted metal organic deposition (ELAMOD) process and the metal-insulator transition (MIT) property of it. The abrupt and hysteretic MIT was observed for the epitaxial films (thickness: t ≥ 6 nm), and the epitaxial film (t ≤ 4 nm) showed semiconductor behavior. When an amorphous VOx layer was prepared on the ultrathin epitaxial phase (t ≤ 4 nm) by the ELAMOD, a non-hysteretic MIT was successfully observed. The non-hysteretic MIT was found to be owing to roughened interface between the epitaxial phase and the amorphous phase, where there would be a number of structural defects. 相似文献
2.
We examined the electrical and local structural properties of a VO2 film at different electric fields using electrical resistance and x-ray absorption fine structure (XAFS) measurements at the V K edge in the temperature range of 30–100 °C. The Tc value of the metal-to-insulator transition (MIT) during both heating and cooling decreases with electric field. When the electric field exceeds a certain value, the MIT becomes sharper due to Joule heating. The MIT, the structural phase transition (SPT), and the pre-edge peak transition of the VO2 do not congruently occur at a uniform temperature. A metallic VO2 is observed in only the rutile (or M2) symmetry. An electric field induces a substantial amount of conduction electrons in insulating VO2. Simultaneously measured resistance and XAFS reveal that Joule heating caused by an external electric field significantly affects the MIT and SPT of VO2. 相似文献
3.
《Current Applied Physics》2018,18(6):652-657
The insulator-metal transition (IMT) in vanadium dioxide (VO2) which occurs above room temperature (67 °C) is highly sensitive to atomic defects caused by oxygen stoichiometry. The strained growth and the degree of oxygen deficiency in VO2 epitaxial films result in lowering of transition temperature below room temperature as well as the broadening of transition parameters such as transition width and hysteresis width, which limit its application potential. Here we demonstrate the growth of highly oriented strain-relaxed VO2 thin films on (001)-oriented TiO2 substrates at various oxygen partial pressures, exhibiting the narrow transition and hysteresis width. The cross-sectional transmission electron microscopy and x-ray diffraction analyses of the films reveal the highly oriented growth of insulating monoclinic VO2. The IMT parameters associated with temperature-dependent phase transition vary with the oxygen partial pressure used during the deposition. The presence of multiple and mixed valence states of vanadium in the films was confirmed by Raman and XPS analyses. We have achieved a narrow transition width (2.3 °C) and hysteresis width (1.2 °C) through controlling the oxygen stoichiometry during the growth of VO2/TiO2 films. 相似文献
4.
Xiaofeng Xu Xinfeng HeGang Wang Xiaolong YuanXingxing Liu Haiyan HuangSheng Yao Huaizhong XingXiaoshuang Chen Junhao Chu 《Applied Surface Science》2011,257(21):8824-8827
The high quality Vanadium dioxide (VO2) thin films have been fabricated successfully on sapphire by a simple novel sputtering oxidation coupling (SOC) method. All VO2 thin film samples exhibit a good metal-insulator transition (MIT) at about 340 K. The optimal oxidation time at different temperatures has been experimentally investigated. We report on the relationship between optimal oxidation time and different temperatures of metal vanadium thin film samples of 101 nm thickness by oxidation in air. It is found that the optimal oxidation time ln(t) as a function of temperature 1/T shows a significant linear relationship among 703 K-783 K, in good agreement with the Wagner's high-temperature oxidation model. 相似文献
5.
Bongjin Simon Mun Kai Chen Youngchul Leem Catherine Dejoie Nobumichi Tamura Martin Kunz Zhi Liu Michael E. Grass Changwoo Park Joonseok Yoon Y. Yvette Lee Honglyoul Ju 《固体物理学:研究快报》2011,5(3):107-109
VO2 single crystals with unprecedented quality, exhibiting a first‐order metal–insulator transition (MIT) at 67.8 °C and an insulator –insulator transition (IIT) at ~49 °C, are grown using a self‐flux evaporation method. Using synchrotron‐based X‐ray microdiffraction analysis, it is shown that the IIT is related to a structural phase transition (SPT) from the monoclinic M2 phase to the M1 phase upon heating while the MIT occurs together with a SPT of M1 to the rutile R phase. All previous reports have shown that VO2 exists in the M1 phase at room temperature in contrast to the M2 phase observed in this work. We suggest that internal strain inside single crystal VO2 may generate the previously unobserved IIT and the unusual room temperature structure. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
6.
P. Jin G. Xu M. Tazawa K. Yoshimura 《Applied Physics A: Materials Science & Processing》2003,77(3-4):455-459
A novel multifunctional window was demonstrated using VO2-based thermochromic films with a TiO2 antireflection coating. A strong enhancement in luminous transmittance of VO2 was calculated using either a single layer or a double layer of TiO2 for antireflection, with the double layer giving the better performance. A TiO2 (25 nm)/VO2 (50 nm)/TiO2 (25 nm) structure, of which the film thickness has been optimized to a maximum integrated luminous transmittance (Tlum) by calculation, was formed on SiO2 glass by sputtering in turn a V target in Ar+O2 for VO2 and a TiO2 target in Ar for TiO2. Optical properties were measured with a spectrophotometer, and the integrated solar and luminous properties were calculated based on the measured spectra. A maximum increase in Tlum by 86% (from 30.9% to 57.6%) was obtained for VO2 after double-layer TiO2 antireflection coating. The deposited VO2 film on SiO2 exhibits good thermochromism with a sharp optical transition at 58.5 °C, which decreased slightly to 57.5 °C after TiO2 coating. The proposed window is the most advanced among those similarly reported in being multifunctional with automatic solar/heat control, ultraviolet stopping and possibly a wide range of photocatalytic functions in addition to a high value of the luminous transmittance. PACS 42.79.Wc; 78.20.-e; 71.30.+h 相似文献
7.
Masami Nishikawa Tomohiko Nakajima Toshiya Kumagai Takeshi Okutani Tetsuo Tsuchiya 《Applied Physics A: Materials Science & Processing》2010,100(1):297-303
Epitaxial VO2 films were prepared on the TiO2 (001) substrates by the excimer-laser-assisted metal–organic deposition (ELAMOD). The quality of the epitaxial films obtained
by irradiation with a KrF laser was found to be affected by the film structure obtained after preheating at 500 or 300°C.
When the films containing crystal domains, which were obtained by preheating at 500°C, were irradiated with the laser at room
temperature under a base pressure of 250 Pa, epitaxial and polycrystalline VO2 phases were simultaneously formed. In contrast, when the amorphous films containing organic components, which were obtained
by preheating at 300°C, were irradiated with the laser at room temperature in air, a single phase of epitaxial VO2 was formed. By using thermal simulations, we determined that the formation of the epitaxial phase was affected both by the
temperature distribution within the film during the laser irradiation and by the laser intensity at the interface between
the substrate and the film. The latter factor is considered to play a role in the nucleation of crystallization, causing the
epitaxial phase to form preferentially compared to the polycrystalline phase in the amorphous matrix of the films. These results
indicate that the ELAMOD process is effective for the fabrication of epitaxial VO2 films at low temperature. 相似文献
8.
Xiang‐Bai Chen Jun‐Hwan Shin Hyun‐Tak Kim Yong‐Sik Lim 《Journal of Raman spectroscopy : JRS》2012,43(12):2025-2028
We present the studies of the phase transition behaviors of V2O3 thin film using temperature‐dependent Raman scattering spectroscopy. Our results show that in both the cooling and heating processes of V2O3 thin film, the phase transition occurs gradually but not suddenly, contrary to that in single crystal. The coexistence of both the metal and insulator phases with co‐phasing ΔTc larger than 30 K is observed in both the cooling and heating processes. We discuss that this large co‐phasing ΔTc should be distinguished with the large hysteresis ΔTh reported in nanostructures. In addition, our discussions indicate that co‐phasing ΔTc and hysteresis ΔTh would be mainly correlated with stress and defect states in sample, respectively. Furthermore, our Raman analyses suggest that stress would also induce phase transitions in V2O3, and the stress (pressure)‐induced phase transitions would behave differently comparing with the temperature‐induced transitions under normal pressure. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
9.
Y. X. Guo Y. F. Liu C. W. Zou Z. M. Qi Y. Y. Wang Y. Q. Xu X. L. Wang F. Zhang R. Zhou 《Applied Physics A: Materials Science & Processing》2014,115(4):1245-1250
To investigate the effects of oxygen pressure on the structural and phase transition properties for VO2/c-sapphire, highly orientated VO2 thin films were grown on (0001) sapphire substrates by pulsed laser deposition (PLD) with different oxygen pressures. The crystal structure, morphology and component of the films were systematically investigated. The temperature-dependent resistance (R-T) measurement was conducted, which showed the distinct phase transition characteristic for the prepared films. The results indicate that the oxygen pressure plays an important role for the VO2 film preparation. The film grown at 1.7 Pa has lower phase transition temperature, higher film strain, and smaller grain size than that at 5.4 Pa, while no obvious crystal phase transition is observed. The experiment suggests that even a small change in oxygen pressure can influence the structure, morphology and phase-transition behavior of VO2 films obviously, and its potential causes are mainly attributed to the reduction of the kinetic energy to the substrate for target atoms caused by the oxygen pressure, the resulting grain aggregation and interfacial stress. 相似文献
10.
J. Yuan H.B. Wang I. Iguchi S. Arisawa A. Ishii T. Hatano 《Physica C: Superconductivity and its Applications》2009,469(15-20):1140-1142
We measured the in-plane magnetoresistance of Pr0.9LaCe0.1CuO4 (PLCCO) epitaxial thin films under various magnetic fields H applied parallel to the tetragonal c-axis. The measurements were performed at the superconducting state as well as the normal state. As the magnetic field is between the low critical field Hc1 and upper critical field Hc2, a critical scaling behavior of electrical resistivity is found. We analyze the electrical transport properties and show the magnetic field H dependence of glass transition temperature Tg and the characteristic temperature T* for the PLCCO film, which may shed some light on vortex behavior in electron-doped superconductors. 相似文献
11.
12.
本文以原子层沉积超薄氧化铝(Al2 O3)为过渡层, 采用射频反应磁控溅射法在硅半导体基片上制备了颗粒致密并具有(011)择优取向的二氧化钒(VO2)薄膜. 该薄膜具有显著的绝缘体–金属相变特性, 相变电阻变化超过3 个数量级, 热滞回线宽度约为6℃. 基于VO2薄膜构建了平面二端器件并测试了不同温度下I-V曲线, 观测到超过2个数量级的电流跃迁幅度, 显示了优越的电致相变特性. 室温下电致相变阈值电压为8.6 V, 电致相变弛豫电压宽度约0.1 V. 随着温度升高到60℃, 其电致相变所需要的阈值电压减小到2.7 V. 本实验制备的VO2薄膜在光电存储、开关、太赫兹调控器件中具有广泛的应用价值. 相似文献
13.
VO2 thin films are grown on glass substrates by pulsed laser deposition using vanadium metal as a target. In this study, a ZnO thin film was used as a buffer layer for the growth of VO2 thin films on glass substrates. X-ray diffraction studies showed that the VO2 thin film had b-axis preferential orientation on a c-axis oriented ZnO buffer layer. The thickness of the ZnO buffer layer and the oxygen pressure during VO2 deposition were optimized to grow highly b-axis oriented VO2 thin films. The metal-insulator transition properties of the VO2 film samples were investigated in terms of infrared reflectance and electrical resistance with varying temperatures. 相似文献
14.
Study of depth-dependent tetragonal distortion of quaternary AlInGaN epilayer by Rutherford backscattering/channeling
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A 240-nm thick Al0.4In0.02Ga0.58N layer is grown by metal organic chemical vapour deposition, with an over 1-μ m thick GaN layer used as a buffer layer on a substrate of sapphire (0001). Rutherford backscattering and channeling are used to characterize the microstructure of AlInGaN. The results show a good crystalline quality of AlInGaN (χmin=1.5%) with GaN buffer layer. The channeling angular scan around an off-normal <12-13> axis in the {101-0} plane of the AlInGaN layer is used to determine tetragonal distortion eT, which is caused by the elastic strain in the AlInGaN. The resulting AlInGaN is subjected to an elastic strain at interfacial layer, and the strain decreases gradually towards the near-surface layer. It is expected that an epitaxial AlInGaN thin film with a thickness of 850 nm will be fully relaxed (eT = 0). 相似文献
15.
《Journal of Physics and Chemistry of Solids》2004,65(8-9):1391-1395
We have optimized laser ablation thin film deposition and transfer procedures within synchrotron vault, specifically to perform angle-integrated and angle-resolved photoemission spectroscopy (ARPES) on high-Tc and related films without cleaving the samples. However, the chain-containing phases like YBCO-123 easily loose surface oxygen and do not exhibit stable Fermi edge, hence are not suitable for ARPES studies. Direct in situ ARPES studies on strained LSCO-214 films show striking strain effects on the electronic structure. The Fermi surface (FS) of LSCO evolves with doping, yet changes even more significantly with strain. The strain changes the FS topology from hole-like to electron-like, and causes band dispersion along kx and the Fermi level crossing before the Brillouin zone boundary, in sharp contrast to the ‘usual’ flat band remaining ≈30 meV below EF measured on unstrained samples. The associated reduction of the density of states does not diminish the superconductivity; Tc is enhanced in all our strained samples. Implications for the evolving high-Tc theory and studies of nano-engineered film heterostructures are briefly discussed. 相似文献
16.
Davor Pavuna Daniel Ariosa Dominique Cloetta Claudia Cancellieri Mike Abrecht 《Pramana》2008,70(2):237-243
Since 1997 we systematically perform direct angle resolved photoemission spectroscopy (ARPES) on in-situ grown thin (<30 nm) cuprate films. Specifically, we probe low-energy electronic structure and properties of high-T
c superconductors (HTSC) under different degrees of epitaxial (compressive vs. tensile) strain. In overdoped and underdoped
in-plane compressed (the strain is induced by the choice of substrate) ≈15 nm thin La2 − x
Sr
x
CuO4 (LSCO) films we almost double T
c to 40 K, from 20 K and 24 K, respectively. Yet the Fermi surface (FS) remains essentially two-dimensional. In contrast, ARPES
data under tensile strain exhibit the dispersion that is three-dimensional, yet T
c drastically decreases. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO2 plane, enhances the two-dimensional character of the dispersion and increases T
c, while the tensile strain acts in the opposite direction and the resulting dispersion is three-dimensional. We have established
the shape of the FS for both cases, and all our data are consistent with other ongoing studies, like EXAFS. As the actual
lattice of cuprates is like a ‘Napoleon-cake’, i.e. rigid CuO2 planes alternating with softer ‘reservoir’, that distort differently under strain, our data rule out all oversimplified two-dimensional
(rigid lattice) mean field models. The work is still in progress on optimized La-doped Bi-2201 films with enhanced T
c.
相似文献
17.
《Current Applied Physics》2010,10(2):508-512
In the present study, vanadium dioxide films were grown on quartz glass substrate by reactive KrF laser ablation technique using a vanadium dioxide target. The gold films of various thicknesses were then deposited on the VO2 film by sputtering technique. Films were characterized by X-ray diffraction to determine crystallography, by four-point probe to determine the electrical property and by double-beam spectrophotometry to determine optical reflection and transmission behaviour in the 200–2500 nm spectral region. The resistance per square of VO2 thin film decreases by two orders of magnitude across the metal insulator transition (MIT). The optical transmittance and reflectance exhibits, strong temperature dependence in the infrared region without a significant change in the visible region for VO2 thin films. The presence of gold layer on VO2 films significantly reduces the resistance per square, the critical temperature and percentage transmittance of the materials. 相似文献
18.
Xiaofeng Xu Anyuan Yin Jiqing Wang Jiading Liu Xingxing Liu 《Applied Surface Science》2010,256(9):2750-8827
VO2 thin film synthesized by a novel sputtering oxidation coupling (SOC) method has been successfully fabricated. The experimental results show that the optimum oxidation time is 285 s and the thin film exhibits a good metal-insulator transition (MIT) approximately at 340 K. The corresponding structures and surface compositions of the films have been characterized by X-ray diffractometer and X-ray photoelectron spectroscopy separately. 相似文献
19.
L. M. Xu X. J. Xing M. Yang X. Y. Li S. X. Wu P. Hu J. Q. Lu S. W. Li 《Applied Physics A: Materials Science & Processing》2010,98(2):417-421
Room-T
c ferromagnetic insulating Mn-doped TiO2 thin films were prepared by plasma assisted molecular beam epitaxy (PAMBE). The thin films show obvious decay of ferromagnetism
when aged in air at room temperature for one year without any special treatment. A distinct reactivation of ferromagnetism,
together with a decrease in coercive force is achieved in these samples under laser irradiation treatment. The possible mechanism
for the phenomena is also discussed. It is suggested that the bound magnetic polaron (BMP) forming via photo-generated defect-bound
carriers accounts for the laser reactivation of room-T
c ferromagnetism. 相似文献