Co-reporter:Yongbo Chen, Xiaomin Li, Zhijie Bi, Xiaoli He, Xiaoke Xu, Xiangdong Gao
Electrochimica Acta 2017 Volume 251(Volume 251) pp:
Publication Date(Web):10 October 2017
DOI:10.1016/j.electacta.2017.08.170
In this paper, core-shell nanorod arrays of crystalline/amorphous TiO2 (c/a-TiO2) are demonstrated for the comprehensive enhancement of electrochromic performance. The amorphous TiO2 (a-TiO2) shell was conformally deposited on the surface of single-crystalline TiO2 nanorod arrays (c-TiO2) core via a facile layer-by-layer method, which ensures the high-quality contact between the core and shell. The optimal c/a-TiO2 core-shell structure with 13 nm a-TiO2 layer combines the assets of distinct porous morphology in c-TiO2 and high charge density in a-TiO2, possessing notably larger optical contrast (43%) and higher coloration efficiency (16.2 cm2C−1) than c-TiO2 (18%, 8.8 cm2C−1) at 800 nm. Compared to the pristine c-TiO2, c/a-TiO2 shows lower threshold voltage and faster response speed due to the low energy barrier and rapid ion migration in the a-TiO2 shell during lithium insertion/extraction. Moreover, the c/a-TiO2 nanostructures can offer outstanding cycling stability in different potential windows upon extensive electrochemical cycling.Download high-res image (182KB)Download full-size image
Co-reporter:Yongbo Chen, Zhijie Bi, Xiaomin Li, Xiaoke Xu, Shude Zhang, Xuemei Hu
Electrochimica Acta 2017 Volume 224(Volume 224) pp:
Publication Date(Web):10 January 2017
DOI:10.1016/j.electacta.2016.12.044
In this paper, we report an electrochromic device (ECD) using novel porous TiO2@prussian blue core-shell nanostructures as electrodes. The core-shell nanostructures were formed by coating prussion blue (PB) on TiO2 nanorod templates through two-step soft chemical methods. The surface area of PB is remarkably enlarged and the diffusion length of ions is notably shortened due to the distinct porous morphology of the nanostructures, resulting in highly increased storage capacity of K+ ions in electrochromic process. Compared with the ECD based on dense PB film, higher optical contrast (48%) and faster response speed (tc = 6.2 s, tb = 2.2 s) are realized in the TiO2@PB core-shell structures. In particular, the coloration efficiency of the ECD based on the core-shell nanostructures is significantly improved to 131.5 cm2 C−1 at 700 nm. Moreover, a model of insertion/extraction of K+ ions was proposed to interpret the enhanced electrochromic performance of core-shell nanostructures.Download high-res image (112KB)Download full-size image
Co-reporter:Zhijie Bi, Xiaomin Li, Yongbo Chen, Xiaoke Xu, Shude Zhang, Qiuxiang Zhu
Electrochimica Acta 2017 Volume 227(Volume 227) pp:
Publication Date(Web):10 February 2017
DOI:10.1016/j.electacta.2017.01.003
In this paper, the tungsten trioxide/zinc oxide (WO3/ZnO) nanocomposites were formed on flexible substrates by combining facile hydrothermal process and pulsed laser deposition (PLD) method. As bi-functional electrodes, the WO3/ZnO nanocomposites possess large specific surface area and a great number of micro channels, significantly increasing the area of WO3 active layer and facilitating the diffusion of Li+ ions during the electrochemical process. Compared with dense WO3 film, WO3/ZnO nanocomposites exhibit enhanced electrochromic and capacitive performance of wider optical contrast (68.2%), greater coloration efficiency (80.6 cm2C−1) and higher areal capacitance (15.24 mF cm−2). Furthermore, based on the WO3/ZnO nanocomposites structure, a novel flexible electrochromic-supercapacitor was demonstrated, which functions as a smart energy storage device able to visually monitor the level of stored energy by rapid and reversible color variation. The results present great potential of WO3/ZnO nanocomposites for electrochromic and energy storage applications.Download high-res image (177KB)Download full-size image
Co-reporter:Qiu-Xiang Zhu;Ming-Min Yang;Ming Zheng;Ren-Kui Zheng;Li-Jie Guo;Yu Wang;Jin-Xing Zhang;Xiao-Min Li;Hao-Su Luo;Xiao-Guang Li
Advanced Functional Materials 2015 Volume 25( Issue 7) pp:1111-1119
Publication Date(Web):
DOI:10.1002/adfm.201403763
Multiferroic heterostructures composed of complex oxide thin films and ferroelectric single crystals have aroused considerable interest due to the electrically switchable strain and charge elements of oxide films by the polarization reversal of ferroelectrics. Previous studies have demonstrated that the electric-field-control of physical properties of such heterostructures is exclusively due to the ferroelectric domain switching-induced lattice strain effects. Here, the first successful integration of the hexagonal ZnO:Mn dilute magnetic semiconductor thin films with high performance (111)-oriented perovskite Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) single crystals is reported, and unprecedented charge-mediated electric-field control of both electronic transport and ferromagnetism at room temperature for PMN-PT single crystal-based oxide heterostructures is realized. A significant carrier concentration-tunability of resistance and magnetization by ≈400% and ≈257% is achieved at room temperature. The electric-field controlled bistable resistance and ferromagnetism switching at room temperature via interfacial electric charge presents a potential strategy for designing prototype devices for information storage. The results also disclose that the relative importance of the strain effect and interfacial charge effect in oxide film/ferroelectric crystal heterostructures can be tuned by appropriately adjusting the charge carrier density of oxide films.
Co-reporter:Q.X. Zhu, M.M. Yang, M. Zheng, W. Wang, Y. Wang, X.M. Li, H.S. Luo, X.G. Li, H.L.W. Chan, R.K. Zheng
Journal of Alloys and Compounds 2013 Volume 581() pp:530-533
Publication Date(Web):25 December 2013
DOI:10.1016/j.jallcom.2013.07.061
•Ferroelectric polarization switching induces strain and electric charge.•Strain effect competes with charge effect.•Magnetoelectric coupling is strain-mediated at high temperature but charge-mediated at low temperature.The evolution of the competition and coaction between the ferroelectric field effect and the strain effect with temperature has been studied for the LaMnO3+δ film/Pb(Mg1/3Nb2/3)O3–PbTiO3 crystal heterostructure. The polarization-rotation-induced strain has a dramatic impact on the electronic transport properties at room temperature. Upon cooling, the polarization-rotation-induced interfacial charge effect competes with and finally overwhelms the strain effect, and modulates the transport and magnetic properties of the LaMnO3+δ film reversibly via the depletion or accumulation of hole carriers at interface. The identification of charge carrier-mediated electric-field-control of the electronic transport and magnetic properties would help researchers better understand the magnetoelectric coupling mechanism in manganite film/ferroelectric crystal heterostructures.
Co-reporter:Jijun Qiu, Xiaomin Li, Xiangdong Gao, Xiaoyan Gan, Binbin Weng, Lin Li, Zijian Yuan, Zhisheng Shi and Yoon-Hwae Hwang
Journal of Materials Chemistry A 2012 vol. 22(Issue 44) pp:23411-23417
Publication Date(Web):20 Sep 2012
DOI:10.1039/C2JM34574A
A novel three-dimensional branched double-shelled TiO2 nanotube network (3DNTNs) structure was constructed on transparent conducting oxide substrates (TCO) by using a ZnO-nanorod array template-assisted method. Various morphological features, such as branch length and population density, could be easily tailored by simply modifying the growth time. The performances of dye-sensitized solar cells (DSCs) fabricated with TiO2 3DNTNs are higher than those assembled with 1-dimensional nanotube arrays. The hollow branches filling in the spaces between the double-shelled stem nanotubes increase the amount of dye-loading, resulting in an enhanced light-harvesting ability.
Co-reporter:Jijun Qiu, Fuwei Zhuge, Xiaomin Li, Xiangdong Gao, Xiaoyan Gan, Lin Li, Binbin Weng, Zhisheng Shi and Yoon-Hwae Hwang
Journal of Materials Chemistry A 2012 vol. 22(Issue 8) pp:3549-3554
Publication Date(Web):19 Jan 2012
DOI:10.1039/C2JM15354H
The performance of one-dimensional (1D) TiO2 nanotube based dye-sensitized solar cells (DSCs) was limited by the insufficient surface area of TiO2 nanotubes. To solve this issue, coaxial multiple-shelled TiO2 nanotube arrays were successfully synthesized on the transparent conductive oxide (TCO) substrates by using improved ZnO nanorod template assisted layer by layer absorption and reaction (LbL-AR) technique. To fabricate tube-in-tube nanostructures, LbL-AR TiO2 coatings were successively deposited on the exterior walls of the ZnO nanowires and the sacrificial sol–gel ZnO spacers, which were removed together by selective etching to form the hollow tubal structures. The performance of dye-sensitized solar cells (DSCs) increases with increasing the shell number of multi-shelled TiO2 nanotube photoanodes, attributed to the increase of the surface area, which was confirmed by N2 adsorption-desorption isotherms and the dye-loading capacities. A maximum efficiency of 6.2% was achieved for a quintuple shelled TiO2 nanotube photoanode with a short-circuit current density (Jsc) = 15 mA cm2, open-circuit voltage (Voc) = 0.73 V and fill factor (FF) = 0.57.
Co-reporter:Feng Zhang, Xiaomin Li, Xiangdong Gao, Liang Wu, Fuwei Zhuge, Qun Wang, Xinjun Liu, Rui Yang, Yong He
Solid State Communications 2012 Volume 152(Issue 17) pp:1630-1634
Publication Date(Web):September 2012
DOI:10.1016/j.ssc.2012.04.073
In this study, unipolar resistive switching (URS) characteristics in ZnO thin film memory devices were systematically investigated with variable defect content. ZnO films displayed typically URS behavior while oxygen-deficient ZnO1−x films did not show resistive switching effects. The devices with two intentional Ohmic interfaces still show URS. These results show that appearance of URS behavior can be dominated by initial oxygen vacancy content in ZnO thin films. Modest increase in oxygen vacancy content in ZnO films will lead to forming-free and narrower distributions of switching parameters (set and reset voltage, high and low resistance states). It indicates that controlling the initial oxygen vacancy content was an effective method to enhance the URS performance.Highlights► ZnO films displayed typically unipolar resistive switching (URS) behavior. ► Oxygen-deficient ZnO1−x films do not show resistive switching effects. ► The devices with two intentional Ohmic interfaces still show URS. ► URS behavior can be dominated by initial oxygen vacancy content in ZnO thin films. ► Modest increase in oxygen vacancy content in ZnO films leads to better performance
Co-reporter:Liang Wu, Xiaomin Li, Xiangdong Gao, Renkui Zheng, Feng Zhang, Xinjun Liu, Qun Wang
Solid-State Electronics 2012 Volume 73() pp:11-14
Publication Date(Web):July 2012
DOI:10.1016/j.sse.2012.01.008
Co-reporter:Jijun Qiu, Fuwei Zhuge, Kun Lou, Xiaomin Li, Xiangdong Gao, Xiaoyan Gan, Weidong Yu, Hyung-Kook Kim and Yoon-Hwae Hwang
Journal of Materials Chemistry A 2011 vol. 21(Issue 13) pp:5062-5068
Publication Date(Web):21 Feb 2011
DOI:10.1039/C0JM03689G
TiO2
nanotube arrays (NTAs) on transparent conducting oxides (TCO) have attracted great attention due to the potential application in dye-sensitized solar cells (DSCs). Here, we introduce the template-assisted process for direct fabrication of aligned TiO2 NTAs on TCO substrates, involving layer-by-layer adsorption and reaction (LBL-AR) assembled TiO2 coating on ZnO nanorods (NR). Key factors of the fabrication process on the microstructures of TiO2 NTAs are analyzed, and the geometry effects of TiO2 NTAs on the performance and electron transport properties of DSCs are investigated by using electrochemical impedance spectra (EIS). An efficiency of 4.25% (under AM1.5 irradiation, 100 mW cm−2) is obtained from N719 sensitized 20 μm thick TiO2 NTAs with a wall thickness of 20 nm, with Jsc = 8.2 mA cm−2, Voc = 0.81 V and FF = 63%.
Co-reporter:Y.Z. Li, X.M. Li, X.D. Gao
Journal of Alloys and Compounds 2011 Volume 509(Issue 26) pp:7193-7197
Publication Date(Web):30 June 2011
DOI:10.1016/j.jallcom.2011.04.039
The Schottky contact of Pt/ZnO was formed by depositing ZnO films oriented along c-axis by pulsed-laser deposition on Pt/Ti buffer layer supported by SiO2/Si substrate. Effects of the post-annealing on the crystallinity, uniformity and native defects of ZnO film as well as Schottky contacts of Pt/ZnO films were investigated. Results show that the annealing can improve the crystallinity of ZnO film, suppress the native defects, and enhance the performance of Pt/ZnO Schottky contacts dramatically. The best Schottky diode shows the largest barrier height of 0.8 eV with reverse leakage current of 1.5 × 10−5 A/cm2. The zero-biased photodetector based on the best Schottky diode possesses responsivity of 0.265 A/W at 378 nm, fast photo-response component with rise time of 10 ns and fall time of 17 ns. This report demonstrates possibility of ZnO films/Pt hetero-junction with large area Schottky contact, and establishes the potential of this material for use in UV photodetector devices.Highlights► The novelty of proposed structure of Schottky diode. ► First systematic research on effects of post-annealing on Pt/ZnO Schottky contact. ► First the zero-biased Schottky photodetector was obtained. ► The performance of photodetector is comparable with the previous report.
Co-reporter:C. Yang, X.M. Li, X.D. Gao, X. Cao, R. Yang, Y.Z. Li
Solid State Communications 2011 Volume 151(Issue 3) pp:264-267
Publication Date(Web):February 2011
DOI:10.1016/j.ssc.2010.11.008
ZnMgAlO films with a broad spectral range of optical transmission and high conductivity were prepared by pulsed laser deposition. The optical and electrical properties of ZnMgAlO films could be controlled by adjusting Al and Mg contents. As the Mg content increased from 10 to 30 at.%, the bandgap value could be modulated from 3.78 to 4.66 eV, and the transparent wavelength range was widened within near-UV, visible and near-IR regions. The optimized ZnMgAlO film possesses a wide bandgap of 4.5 eV and a low resistivity of 1.6×10−3Ω cm. The broad spectral range of optical transmission and high conductivity maked ZnMgAlO films are of interest as TCO window materials for optoelectronic devices.Research highlights► ZnMgAlO films provide a new way of bandgap modulation for TCOs. ► High conductivity can be achieved by optimizing the Al content. ► The energy bandgap mainly depends on the Mg content.
Co-reporter:Xiaoyan Gan, Xiaomin Li, Xiangdong Gao, Fuwei Zhuge, Weidong Yu
Thin Solid Films 2010 Volume 518(Issue 17) pp:4809-4812
Publication Date(Web):30 June 2010
DOI:10.1016/j.tsf.2010.01.043
Hybrid ZnO/TiO2 photoanodes for dye-sensitized solar cells were prepared by combining ZnO nanowire (NW) arrays and TiO2 nanoparticles (NPs) with the assistance of the ultrasonic irradiation assisted dip-coating method. Results show that the ultrasonic irradiation was an efficient way to promote the gap filling of TiO2 NPs in the interstices of ZnO NWs. Hybrid ZnO NW/TiO2 NP electrodes prepared with ultrasonic treatment exhibited better gap filling efficiency and higher visible absorptance. The overall conversion efficiency of the hybrid electrode was 0.79%, representing 35% improvement compared with that of the traditional one (0.58%). The enlarged surface area and improved attachments of TiO2 NPs onto the walls of ZnO NWs induced by the application of ultrasonic irradiation may be the underlying reason. Electrochemical impedance spectroscopy measurements indicated that hybrid electrodes combined the advantages of improved electron transport along the ZnO NWs and increased surface area provided by infiltrated TiO2 NPs, both of which are responsible for the improved cell efficiency.
Co-reporter:Xun Cao, Xiaomin Li, Weidong Yu, Yiwen Zhang, Rui Yang, Xinjun Liu, Jingfang Kong, Wenzhong Shen
Journal of Alloys and Compounds 2009 Volume 486(1–2) pp:458-461
Publication Date(Web):3 November 2009
DOI:10.1016/j.jallcom.2009.06.175
Polycrystalline TiO2 thin films were formed on Pt(1 1 1)/Ti/SiO2/Si by thermal oxidation of Ti films with temperatures ranging from 600 °C to 800 °C. Results of Raman spectra testing indicate that the structure of the oxidized TiO2 films is rutile phase. The resistance switching behaviors (RSB) have been confirmed in Pt/TiO2/Pt structures. A stable RSB with a narrow dispersion of the resistance states and switching voltages was observed in the sample fabricated with the oxidation temperature of 600 °C. The resistance ratios of high resistance states to low resistance states are larger than 103 with the set and reset voltage as low as 2.5 V and 0.6 V, respectively.
Co-reporter:Xiliang He, Jiehua Wu, Xiaomin Li, Xiangdong Gao, Xiaoyan Gan, Lili Zhao
Journal of Alloys and Compounds 2009 Volume 478(1–2) pp:453-457
Publication Date(Web):10 June 2009
DOI:10.1016/j.jallcom.2008.11.077
Tantalum oxide films were synthesized by pulsed laser deposition (PLD). The influences of annealing temperatures and oxygen pressures on the crystalline, morphological and optical properties were investigated. Experimental results indicate that annealed film became crystallized in orthorhombic structure at 700 °C. The root-mean-square (RMS) roughness of the film became higher with the increase of annealing temperature. The transmittance and the optical band gap of the film increased with the increase of annealing temperature and the increase of annealing oxygen pressure. In addition and interestingly, crystallinity led to a decrease of transparency due to the increase of scattering losses, which resulted from the polycrystalline structure and the increase of RMS roughness. At the optimized ambience of 600 °C and 20 Pa, the transmittance of the annealed film achieved about 93% (the transmittance of bare substrate) at its peak values. And its optical band gap was 4.18 eV, which was close to the theoretical value of 4.2 eV.
Co-reporter:Xiliang He, Jiehua Wu, Xiaomin Li, Xiangdong Gao, Lili Zhao, Lingnan Wu
Applied Surface Science 2009 Volume 256(Issue 1) pp:231-234
Publication Date(Web):15 October 2009
DOI:10.1016/j.apsusc.2009.08.005
Abstract
Silicon dioxide (SiO2) thin films were deposited on BK7 substrates by pulsed laser deposition (PLD) method using ceramic SiO2 targets (C-SiO2-Ts), which was sintered by solid state sintering. The reason for using C-SiO2-T instead of the silicon target is to reduce the oxygen-deficiency phenomenon in deposited SiO2 thin films. The influence of substrate-temperatures, oxygen-pressures and oxygen-plasma-assistance on the properties of synthesized films was studied. X-ray diffraction, atomic force microscopy, ultraviolet–visible–near-infrared scanning spectrophotometry were used to characterize the crystallinity, morphology and optical properties of deposited films. Results show that the root-mean-square roughness of films increased with the increase of oxygen-pressure, substrate-temperature and with the employment of oxygen-plasma. The transmittance of films increased with the increase of oxygen-pressure and decreased with the increase of substrate-temperature and with the employment of oxygen-plasma. Stoichiometric SiO2 thin film with high optical quality was synthesized at room-temperature and 20 Pa oxygen-pressure using C-SiO2-T.
Co-reporter:Xiaoyan Gan, Xiaomin Li, Xiangdong Gao, Weidong Yu
Journal of Alloys and Compounds 2009 Volume 481(1–2) pp:397-401
Publication Date(Web):29 July 2009
DOI:10.1016/j.jallcom.2009.03.013
High-density vertically aligned ZnO nanotube arrays were prepared on ITO-coated glass substrates by a simple and facile chemical etching process from electrodeposited ZnO nanorods. The as-prepared nanotubes are single crystal, with hexagonal cross-section, a diameter of about 400 nm and a uniform central pore. Such ZnO nanotube arrays exhibited strong ultraviolet emissions at 372 nm at room temperature but negligibly defect-related visible emissions, indicating their high crystallinity and excellent optical quality. The nanotube formation was rationalized in terms of selective dissolution of the metastable Zn-rich (0 0 1) polar face. It was proposed that the diameters of the ZnO nanorods played a key role in the nanotube formation.
Co-reporter:Fuwei Zhuge, Xiaomin Li, Xiangdong Gao, Xiaoyan Gan, Fengling Zhou
Materials Letters 2009 Volume 63(Issue 8) pp:652-654
Publication Date(Web):31 March 2009
DOI:10.1016/j.matlet.2008.12.010
Co-reporter:Xiaoyan Gan, Xiaomin Li, Xiangdong Gao, Xiliang He, Fuwei Zhuge
Materials Chemistry and Physics 2009 Volume 114(2–3) pp:920-925
Publication Date(Web):15 April 2009
DOI:10.1016/j.matchemphys.2008.10.073
Well crystallined ZnO–eosin Y hybrid thin films were deposited on ITO substrate by two-step cathodic electrodeposition from aqueous mixture of zinc nitrate and esoin Y sodium salt. Effects of the deposition potential on the crystal structure, morphology, and optical properties of the hybrid films were investigated. Results showed that the deposition potential had significant influences on the preferred orientation and the dye loading efficiency of the hybrid film. The nanoporous film with high dye concentration (0.79 mol L−1) was obtained at −0.8 V, while compact films with entrapping eosin Y molecules of relatively lower dye loading (0.28–0.10 mol L−1) were deposited at more negative potentials. The prototype of dye sensitized solar cells utilizing these hybrid films were fabricated, and their photoelectrochemical properties were characterized. It revealed that the hybrid film with porous nature had better photoelectrochemical property, exhibiting the conversion efficiency of 0.21%, open circuit photovoltage of 0.64 V, and short-circuit photocurrent density of 0.67 mA cm−2 under AM 1.5 illumination.
Co-reporter:Xiliang He, Jiehua Wu, Xiaomin Li, Xiangdong Gao, Lingnan Wu, Lili Zhao, Xiaoyan Gan, Fuwei Zhuge
Thin Solid Films 2009 Volume 518(Issue 1) pp:94-98
Publication Date(Web):2 November 2009
DOI:10.1016/j.tsf.2009.06.041
Tantalum pentoxide films were deposited on BK7 glass substrates using oxygen plasma enhanced pulsed laser deposition (OPE-PLD). X-ray diffraction, atomic force microscopy, ultraviolet–visible–near infrared scanning spectrophotometry, and spectroscopic ellipsometry were used to characterize the crystallinity, microscopic morphology and optical properties of films. Results show that the film roughness increased with the increase of oxygen pressure, and decreased with the application of OPE. Meanwhile the use of oxygen plasma in a 2 Pa O2 pressure resulted in the transmittance of the thin film of 91.8% at its peak position (the transmittance of bare substrate). Moreover, the root-mean-square roughness as low as 0.736 nm, and refractive index of 2.18 at 633 nm wavelength, close to the refractive index of bulk Ta2O5 (~ 2.20 at 633 nm wavelength), were obtained.
Co-reporter:Xun Cao, Xiaomin Li, Weidong Yu, Xinjun Liu, Xiliang He
Materials Science and Engineering: B 2009 Volume 157(1–3) pp:36-39
Publication Date(Web):15 February 2009
DOI:10.1016/j.mseb.2008.12.005
TiO2 thin films were deposited on ITO (indium–tin-oxide)-buffered glass by pulsed laser deposition. Bipolar resistive switching behaviors of Ag/microcrystalline TiO2/ITO stacked structures were systematically investigated. Dependence of switching voltage and band gap energy on deposition temperature were also analyzed. Results indicate that the reset voltages and band gap energy (Eg) vary from −0.9 V to −6.8 V and 3.26 eV to 3.18 eV respectively, while the TiO2 films were formed from 300 °C to 600 °C. These bipolar switching phenomena have been also discussed based on the Schottky barrier at the Ag/TiO2 interface structure.
Co-reporter:Xiliang He, Jiehua Wu, Lingnan Wu, Lili Zhao, Xiangdong Gao, Xiaomin Li
Applied Surface Science 2008 Volume 254(Issue 6) pp:1730-1735
Publication Date(Web):15 January 2008
DOI:10.1016/j.apsusc.2007.07.127
Abstract
The amorphous silicon oxide SiO2−x thin films were prepared by the plasma-assisted pulsed laser deposition (PLD) method. X-ray diffraction spectrometry (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-VIS-NIR scanning spectrophotometry and ellipsometry were used to characterize the crystallinity, microscopic morphology and optical properties of obtained thin films. The influences of substrate temperatures, oxygen partial pressures and oxygen plasma assistance on the compositions of silicon oxide (SiO2−x) thin films were investigated. Results show that the deposited thin films are amorphous and have high surface quality. Stoichiometric silicon dioxide (SiO2) thin film can be obtained at elevated temperature of 200 °C in an oxygen plasma-assisted atmosphere. Using normal incidence transmittance, a novel and simple method has been proposed to evaluate the value of x in transparent SiO2−x thin films on a non-absorbing flat substrate.
Co-reporter:Xiaoyan Gan, Xiangdong Gao, Jijun Qiu, Xiaomin Li
Applied Surface Science 2008 Volume 254(Issue 13) pp:3839-3844
Publication Date(Web):30 April 2008
DOI:10.1016/j.apsusc.2007.12.005
Abstract
ZnO-SDS hybrid thin films were grown on ITO glass using the potentiostatic electrodeposition route from aqueous zinc nitrate solution containing surfactant sodium dodecyle sulfanate (SDS). The electrochemical process of the hybrid films was analyzed by comparing the cyclic voltammetric curve and current–time curve with those of pure ZnO film. Results showed that the addition of a small amount of SDS could decrease the deposition current density, and inhibit the growth of ZnO crystals significantly. The hybrid films electrodeposited at −0.9 V for 30 min exhibited smooth and platelet-like morphology, with the film thickness of about 110 nm. The well-defined ZnO-SDS lamellar structures could be clearly observed, with two interlayer spaces of 35.1 and 30.9 Å, respectively. Optical analysis showed that the hybrid films had good optical quality, and exhibited the fundamental absorption edge of ZnO at 380 nm.
Co-reporter:Xiliang He, Jiehua Wu, Lili Zhao, Jia Meng, Xiangdong Gao, Xiaomin Li
Solid State Communications 2008 Volume 147(3–4) pp:90-93
Publication Date(Web):July 2008
DOI:10.1016/j.ssc.2008.05.007
Co-reporter:Feng Wu, Xiaomin Li, Weidong Yu, Xiangdong Gao, Xun Cao
Solid State Communications 2008 Volume 145(Issue 4) pp:178-181
Publication Date(Web):January 2008
DOI:10.1016/j.ssc.2007.10.029
Co-reporter:Y.F. Gu, X.M. Li, J.L. Zhao, W.D. Yu, X.D. Gao, C. Yang
Solid State Communications 2007 Volume 143(8–9) pp:421-424
Publication Date(Web):August 2007
DOI:10.1016/j.ssc.2007.06.014
The n-Zn/p-Si heterostructure detector for ultra-violet was fabricated by pulsed laser deposition. Plasma oxygen was used for the deposition of n-ZnO thin films to decrease the concentration of deep-level defects such as oxygen vacancies and zinc interstitials. The electron concentration of n-ZnO thin film was reduced to a low level of 1014 cm−3, resulting in the depletion width in p-Si decreasing significantly. The spectral response of the detector shows that the responsivity to visible light has been eliminated effectively by using plasma oxygen in the ZnO film growth. The visible–blind mechanism for the n-Zn/p-Si heterostructure detector has been discussed.
Co-reporter:Jun-Liang Zhao, Xiao-Min Li, Ji-Ming Bian, Wei-Dong Yu, Can-Yun Zhang
Thin Solid Films 2006 Volume 515(Issue 4) pp:1763-1766
Publication Date(Web):5 December 2006
DOI:10.1016/j.tsf.2006.06.032
ZnO thin films have been deposited by pulsed laser deposition (PLD) and ultrasonic spray pyrolysis (USP) method, respectively. X-ray diffraction and transmission electron microscopy characterizations indicate that ZnO film grown by PLD exhibits better crystallinity than that grown by USP. Photoluminescence spectra show that the near-band edge ultraviolet emission of film grown by PLD is narrower and shifts to higher energy, compared with that of film grown by USP. In the visible range, ZnO film grown by PLD exhibits four local level emission centered at 470 nm, 486 nm, 544 nm, and 613 nm, respectively, while the film grown by USP only presents a weak broad band emission centered at 502 nm. Hall measurement shows higher carrier density and lower hall mobility in ZnO film grown by PLD than that in film grown by USP. The higher density of intrinsic defects as well as higher crystallintiy is considered to account for the difference of photoluminescence in ZnO film grown by PLD with that in film grown by USP.
Co-reporter:Xia Zhang, Xiao Min Li, Tong Lai Chen, Ji Ming Bian, Can Yun Zhang
Thin Solid Films 2005 Volume 492(1–2) pp:248-252
Publication Date(Web):1 December 2005
DOI:10.1016/j.tsf.2005.06.088
The structural and optical properties of Zn1−xMgxO films deposited by ultrasonic spray pyrolysis were studied. All the Zn1−xMgxO thin films maintained the ZnO wurtzite structure and had no impurity phase, even for the Mg content up to x = 0.27. The optical properties were characterized by transmittance, absorption spectroscopy and photoluminescence measurements. For all the films, the average transmission in the visible wavelength region (λ = 400–800 nm) was over 85%, and the absorption edge shifted to a shorter wavelength as the Mg content increased. The optical energy band gap of Zn1−xMgxO thin films, measured from transmittance spectra, could be controlled between 3.29 and 3.58 eV by adjusting Mg contents. The photoluminescence emission peaks of Zn0.94Mg0.06O and Zn0.73Mg0.27O thin films were located at 369 and 349 nm, showing an evident blue-shift with Mg content increase. The room temperature absorption and photoluminescence properties of the films were also discussed.
Co-reporter:Tong Lai Chen, Xiao Min Li, Rui Dong, Qun Wang, Li Dong Chen
Thin Solid Films 2005 Volume 488(1–2) pp:98-102
Publication Date(Web):22 September 2005
DOI:10.1016/j.tsf.2005.04.115
Investigated was the epitaxial growth of La0.7Ca0.3MnO3 (LCMO)/Ir/MgO multilayer on silicon substrate, which was prepared by pulsed-laser deposition. The whole growth process of multilayer was in situ monitored by using reflection high-energy electron diffraction (RHEED). The reflection high-energy electron diffraction observations and X-ray diffraction analysis show that the LCMO film can be epitaxially grown on silicon substrate with an out-of-plane alignment of LCMO(001)//Ir(001)//MgO(001)//Si (001). The field-induced polarity-dependent reversible resistance-switching was observed in the Ag–LCMO–Ir sandwich structure with a newly discovered accumulation-like phenomenon. Further characterization through I–V measurements for “ON”-/”OFF”-State shows that the resistance-switching phenomenon occurred in our Ag–LCMO–Ir sandwich structure should be attributed to a carrier-injection-ordering process.
Co-reporter:Canyun Zhang, Xiaomin Li, Jiming Bian, Weidong Yu, Xiangdong Gao
Surface and Coatings Technology 2005 Volume 198(1–3) pp:253-256
Publication Date(Web):1 August 2005
DOI:10.1016/j.surfcoat.2004.10.088
The most significant impediment to the widespread exploitation of ZnO-related materials in electronic and photonic applications is the difficulty in p-type doping and synthesizing ZnO p–n homojunctions. To resolve the problem of p-type doping in ZnO, nitrogen and aluminum (N–Al) codoped ZnO films were prepared by ultrasonic spray pyrolysis technique. The structural, optical and electrical properties of the as-grown ZnO films were investigated by X-ray diffraction (XRD), photoluminescence (PL) spectra, Hall-effect and Seebeck-effect measurements. The results demonstrate that the N–Al codoped ZnO films show extremely excellent p-type conduction and good ultraviolet emission characteristics. Furthermore, ZnO homojunctions were synthesized by depositing the undoped ZnO layers on the N–Al codoped ZnO layers, and the current–voltage (I–V) characteristics measured from the two-layer structure show a typical rectifying characteristics of p–n junctions with a low turn-on voltage of about 2.5 V.
Co-reporter:Canyun Zhang, Xiaomin Li, Jiming Bian, Weidong Yu, Xiangdong Gao
Solid State Communications 2004 Volume 132(Issue 2) pp:75-78
Publication Date(Web):October 2004
DOI:10.1016/j.ssc.2004.07.033
To resolve the problem of p-type doping in ZnO, nitrogen and aluminum (N–Al) codoped ZnO films were prepared by the ultrasonic spray pyrolysis (USP) technique. The structural and electrical properties of N–Al codoped ZnO films were investigated. The results demonstrate that the undoped ZnO films exhibit the preferential orientation of (002) plane, while ZnO films show high orientation of (101) plane after codoping with N and Al. The N–Al codoped ZnO films under optimum conditions show p-type conduction, with a low resistivity of 1.7×10−2Ω cm, carrier concentration of 5.09×1018 cm−3 and high Hall mobility of 73.6 cm2 V−1 s−1. A conversion from p-type conduction to n-type was observed during the increase of measurement temperature.
Co-reporter:Xiliang He, Jiehua Wu, Lili Zhao, Jia Meng, Xiangdong Gao, Xiaomin Li
Solid State Communications (July 2008) Volume 147(3–4) pp:90-93
Publication Date(Web):1 July 2008
DOI:10.1016/j.ssc.2008.05.007
In this work, tantalum oxide (TaOx) films were deposited on quartz glass substrates by pulsed laser deposition (PLD) and ionized plasma-assisted pulsed laser deposition (IPA-PLD). The effects of oxygen pressures and ionized oxygen plasma-assistance (IOPA) on the optical properties of deposited films have been studied. Ultraviolet–visible–near infrared (UV–VIS–NIR) scanning spectrophotometry was used to measure the transmittance of deposited films and to determine the optical band gap and absorption coefficient. Results show that the transmittance, absorption coefficient, band gap and chemical composition of deposited films reveal a strong dependence on the oxygen pressures and IOPA. Under optimum condition of IOPA, the refractive index of the synthesized film was 2.22 (at 633 nm wavelength), while an optical band gap of 4.18 eV was obtained. These two values compare very favorably with films produced by other methods.
Co-reporter:C. Yang, X.M. Li, X.D. Gao, X. Cao, R. Yang, Y.Z. Li
Journal of Crystal Growth (15 March 2010) Volume 312(Issue 7) pp:978-981
Publication Date(Web):15 March 2010
DOI:10.1016/j.jcrysgro.2009.12.068
Wurtzite ZnBeMgO films with high magnesium content were deposited by the pulsed laser deposition method at various oxygen partial pressures. Results show that the crystallinity and the band gap of ZnBeMgO films were strongly influenced by the oxygen partial pressure. With the increase of the oxygen pressure, the crystalline structure of ZnBeMgO films changed from cubic rock-salt to hexagonal wurtzite. The steady decrease in the bandgap of ZnBeMgO films from 4.71 to 4.50 eV was observed when the oxygen partial pressure increased from 2×10−4 to 2 Pa.
Co-reporter:Leilei Xu, Xiaomin Li, Qiuxiang Zhu, Xiaoke Xu, Meng Qin
Materials Letters (15 April 2017) Volume 193() pp:
Publication Date(Web):15 April 2017
DOI:10.1016/j.matlet.2017.01.125
•The BFMO films epitaxially grown on LSMO/TiO2 buffered GaN substrates.•We first employ LSMO/TiO2 double-layer as the buffer layer.•The BFMO films are of single phase and highly (1 1 1)-oriented.•The BFMO (1 1 1) films show excellent ferroelectric performance and large Pr.•The LSMO/TiO2 buffer layer enhanced the ferroelectric property of BFMO film.The highly (1 1 1)-oriented BiFe0.95Mn0.05O3 (BFMO) films owning excellent ferroelectric performance have been epitaxially grown on (0 0 0 2) GaN substrates with La0.7Sr0.3MnO3 (LSMO)/TiO2 bi-layer buffer by pulsed laser deposition. By means of the LSMO/TiO2 bi-layer buffer, the lattice mismatch between perovskite (1 1 1) BFMO and wurtzite (0 0 0 2) GaN was miraculously decreased from 12.4% to 1.4%. The remnant ferroelectric polarization and coercive field of the BFMO (1 1 1) film were determined to be 115 μC/cm2 and 450 kV/cm, respectively. Compared with the BFMO film deposited on the bare GaN substrate, the remnant ferroelectric polarization was enhanced by 92%. The piezoresponse force microscopy (PFM) image further confirmed that the BFMO (1 1 1) film owned perfect ferroelectric switching properties.
Co-reporter:Jijun Qiu, Fuwei Zhuge, Xiaomin Li, Xiangdong Gao, Xiaoyan Gan, Lin Li, Binbin Weng, Zhisheng Shi and Yoon-Hwae Hwang
Journal of Materials Chemistry A 2012 - vol. 22(Issue 8) pp:
Publication Date(Web):
DOI:10.1039/C2JM15354H
Co-reporter:Jijun Qiu, Fuwei Zhuge, Kun Lou, Xiaomin Li, Xiangdong Gao, Xiaoyan Gan, Weidong Yu, Hyung-Kook Kim and Yoon-Hwae Hwang
Journal of Materials Chemistry A 2011 - vol. 21(Issue 13) pp:NaN5068-5068
Publication Date(Web):2011/02/21
DOI:10.1039/C0JM03689G
TiO2
nanotube arrays (NTAs) on transparent conducting oxides (TCO) have attracted great attention due to the potential application in dye-sensitized solar cells (DSCs). Here, we introduce the template-assisted process for direct fabrication of aligned TiO2 NTAs on TCO substrates, involving layer-by-layer adsorption and reaction (LBL-AR) assembled TiO2 coating on ZnO nanorods (NR). Key factors of the fabrication process on the microstructures of TiO2 NTAs are analyzed, and the geometry effects of TiO2 NTAs on the performance and electron transport properties of DSCs are investigated by using electrochemical impedance spectra (EIS). An efficiency of 4.25% (under AM1.5 irradiation, 100 mW cm−2) is obtained from N719 sensitized 20 μm thick TiO2 NTAs with a wall thickness of 20 nm, with Jsc = 8.2 mA cm−2, Voc = 0.81 V and FF = 63%.
Co-reporter:Jijun Qiu, Xiaomin Li, Xiangdong Gao, Xiaoyan Gan, Binbin Weng, Lin Li, Zijian Yuan, Zhisheng Shi and Yoon-Hwae Hwang
Journal of Materials Chemistry A 2012 - vol. 22(Issue 44) pp:NaN23417-23417
Publication Date(Web):2012/09/20
DOI:10.1039/C2JM34574A
A novel three-dimensional branched double-shelled TiO2 nanotube network (3DNTNs) structure was constructed on transparent conducting oxide substrates (TCO) by using a ZnO-nanorod array template-assisted method. Various morphological features, such as branch length and population density, could be easily tailored by simply modifying the growth time. The performances of dye-sensitized solar cells (DSCs) fabricated with TiO2 3DNTNs are higher than those assembled with 1-dimensional nanotube arrays. The hollow branches filling in the spaces between the double-shelled stem nanotubes increase the amount of dye-loading, resulting in an enhanced light-harvesting ability.
