Zhaoqi Sun

Name: 孙兆奇

Organization: Anhui University

Department: School of Physics and Materials Science

Title:

Chemicals
References

Electrodeposition of flake-like Cu2O on vertically aligned two-dimensional TiO2 nanosheet array films for enhanced photoelectrochemical properties

Co-reporter:Lei Yang, Miao Zhang, Kerong Zhu, Jianguo Lv, Gang He, Zhaoqi Sun

Applied Surface Science 2017 Volume 391(Part B) pp:353-359

Publication Date(Web):1 January 2017

DOI:10.1016/j.apsusc.2016.07.001

Highlights

•: Flake-like Cu₂O/TNS with exposed {001} facets constructed p-n heterostructure.
•: The TNS arrays were used as starting substrates for Cu₂O growth.
•: The Cu₂O/TNS prepared at −0.4 V exhibits the best photoelectrochemical property.

Electrodeposited Cu2O on the {101} facets of TiO2 nanosheet arrays and their enhanced photoelectrochemical performance

Co-reporter:Lei Yang, Weihua Wang, Hui Zhang, Shenhao Wang, Miao Zhang, Gang He, Jianguo Lv, Kerong Zhu, Zhaoqi Sun

Solar Energy Materials and Solar Cells 2017 Volume 165(Volume 165) pp:

Publication Date(Web):1 June 2017

DOI:10.1016/j.solmat.2017.02.026

•Cu2O was electrodeposited on the {101} facets of anatase nanosheet array film.•Different band edge positions between {001} and {101} facets.•Cu2O/{101} facets have higher band offset value.A novel Cu2O/{101}TiO2 nanosheet (Cu2O/{101}TNS) array film was prepared by the electrodeposition of Cu2O on the {101} facets of anatase nanosheet arrays by varying electrodeposition potential. The crystal structure, morphology, elemental chemical states, optical properties, photoelectrochemical properties, and stability of Cu2O/{101}TNS array films were investigated in detail. For TNS, due to different band structures and band edge positions between {001} and {101} facets, Cu2O/{101} facets of TiO2 have higher band offset value which supply a larger driving force to increase the transport efficiency of carriers. Besides, owing to the directional flow of photo-generated electrons from {001} to {101} facets, the electrodeposition of Cu2O on the {101} facets of TNS will shorten the route length that the electrons must travel, thus reduce recombination of photo-generated electron-hole pairs. In addition, as the applied negative potential is high enough, a part of Cu+ is reduced to Cu, which is beneficial for the photoexcited electrons transfer from CB of Cu2O to that of TiO2. The enhanced photoelectrochemical properties of Cu2O/{101}TNS array films can be attributed to the cocontributions of different band edge positions between {001} and {101} facets, Cu2O-Cu-TiO2 ternary components and vertically aligned single-crystal TiO2 nanosheet structure.Download high-res image (244KB)Download full-size image

Enhanced visible light response of ZnO porous thin film by post-annealing treatment

Co-reporter:Jianguo Lv;Wenhao Wang;Min Zhao;Weili Zhu

Journal of Materials Science: Materials in Electronics 2017 Volume 28( Issue 5) pp:4051-4057

Publication Date(Web):2017 March

DOI:10.1007/s10854-016-6019-7

ZnO thin films were synthesized by a facile electrodeposition method in the aqueous solution. Porous ZnO thin films with wurtzite structure could be achieved by mean of annealing treatment. The growth mechanism of the porous ZnO thin film was discussed. The intensity of the E2 mode in the ZnO thin film, which represents crystalline quality of the thin film increases with the increasing of annealing temperature. Optical properties indicate that annealing temperature has strong effect on the optical band gap value and defect concentrations. Both the green and yellow emissions corresponding to respective oxygen vacancies and oxygen interstitials can be identified. The results show that ZnO annealed at 400 °C exhibits a significant photocurrent density enhancement which is about 18 times larger than that of the as-deposited ZnO thin films. The mechanism of the enhanced photoresponse for the ZnO thin film has been discussed in detail.

Hydroxide MgSn(OH)6: A promising new photocatalyst for methyl orange degradation

Co-reporter:Jiajia Tao;Miao Zhang;Gang He

Electronic Materials Letters 2017 Volume 13( Issue 4) pp:339-343

Publication Date(Web):20 April 2017

DOI:10.1007/s13391-017-6192-8

Effect of ZnS layers on optical properties of prepared CdS/TiO2 nanotube arrays for photocatalyst

Co-reporter:Miao Zhang;Zezhou Gong;Jiajia Tao;Xingzhi Wang

Journal of Nanoparticle Research 2017 Volume 19( Issue 3) pp:

Publication Date(Web):2017 March

DOI:10.1007/s11051-017-3799-5

The TiO2 nanotube arrays (TiO2 NTAs) prepared by re-oxidation were chosen as basement. The NTAs prepared through re-oxidation show smoother surface and more uniform tube mouth on large scale compared with the first as-grown one. We use successive ionic layer adsorption and reaction method to deposit quantum dots (ZnS and CdS) onto the sample successively. The findings reveal that two kinds of quantum dots (∼10 nm) distribute regularly and the nanotube mouth is open. From the UV–Vis absorption spectrum of samples, the red shift occurs after the sedimentation of the two quantum dots, which proves that the double modification can expand the absorption to 650 nm. Among all specimens, the sample produced by co-deposition has the highest speed of catalytic efficiency of 90.7% compared with bare TiO2 NTAs (52.9%) and just CdS QDs sensitized sample (65.8%). In the test of photocatalysis durability, the decay percentages of CdS/TiO2 NTAs and ZnS/CdS/TiO2 NTAs were 35.8 and 48.4%, respectively, which means that the ZnS passivation layer plays a crucial role in enhancing photocatalytic activities.

Optical properties and UV photoresponse of Na2x Zn1−x O thin film

Co-reporter:Jianguo Lv;Wenhao Wang;Min Zhao

Journal of Materials Science: Materials in Electronics 2017 Volume 28( Issue 1) pp:1022-1027

Publication Date(Web):25 August 2016

DOI:10.1007/s10854-016-5623-x

Na2xZn1−xO thin films were successfully synthesized on quartz glass substrates by sol–gel method. The effect of Na content on the microstructure, optical properties and UV photoresponse of the thin films was investigated using X-ray diffraction, optical absorbance, photoluminescence, and conductivity measurements. The results indicate that the Na0.04Zn0.98O thin film exhibits the strongest preferential c-axis orientation with a polycrystalline hexagonal wurtzite structure and has the largest optical band gap. An obvious decrease in crystal size has been observed with the increasing of Na content. A weak ultraviolet emission band at about 381 nm and a strong visible emission band have been observed in the photoluminescence spectra. The Na0.04Zn0.98O thin film has the shortest growth and decay time (45 and 18 s, respectively) and the largest photoresponse. The results indicate that the photoresponse can be effectively improved by means of moderate Na doping.

Enhanced photoelectronic properties of single crystal TiO2 nanosheet array films by selective deposition of CdS nanoparticles on their {101} facets

Co-reporter:Lei Yang, Haiyan Jiang, Weihua Wang, Delin Chu, Jinhong Yang, Miao Zhang, Jianguo Lv, Baoming Wang, Gang He and Zhaoqi Sun

CrystEngComm 2016 vol. 18(Issue 3) pp:496-503

Publication Date(Web):07 Dec 2015

DOI:10.1039/C5CE01905B

Single crystal TiO2 nanosheet array films with dominant {001} facets were synthesized on FTO by a hydrothermal method. A simple strategy for the selective deposition of CdS nanoparticles on the low energy {101} facets by controlling the F content on the surface of TiO2 nanosheets is developed. For CdS/TiO2, under light irradiation, the photo-generated electrons flow from the {001} to {101} facets; meanwhile, the photo-generated electrons transfer from the CdS nanoparticles to the TiO2 nanosheets. The deposition of CdS nanoparticles on the {101} facets will shorten the pathways that the electrons must travel. Herein, the synergistic effect of the selective deposition of CdS nanoparticles on the {101} facets of TiO2 nanosheets and the different band edge positions of the {001} and {101} facets would facilitate the spatial separation of electrons and holes on different facets, leading to enhanced photoelectronic performance.

Nonlinear optical response and two-photon biological applications of a new family of imidazole-pyrimidine derivatives

Co-reporter:Qiong Zhang, Xiaohe Tian, Zhangjun Hu, Caroline Brommesson, Jieying Wu, Hongping Zhou, Jiaxiang Yang, Zhaoqi Sun, Yupeng Tian, Kajsa Uvdal

Dyes and Pigments 2016 Volume 126() pp:286-295

Publication Date(Web):March 2016

DOI:10.1016/j.dyepig.2015.11.026

•A series of novel imidazole-pyrimidine derivatives (EX-1∼EX-4) were designed and confirmed by crystallography.•The photophysical properties were systematically investigated.•The 2PA cross-section values (σ) were obtained both by Z-Scan and 2PEF measurements.•EX-1 and EX-2 were identified to be the best candidates for living cells (HepG2) imaging.A series of novel D–π–A type two-photon absorption (2PA) imidazole-pyrimidine derivatives (EX-1∼EX-4) have been synthesized and characterized, with EX-1 was crystallography confirmed. Based on systematic photophysical investigations, the structure–property relationships can be drawn as follows: (1) Both theoretical and experimental studies indicated that the different donor groups have large influences on the optical properties. (2) The 2PA cross-section values (σ) were obtained both by Z-Scan and two-photon excited fluorescence (2PEF) measurements. 2PA cross sections show an increasing trend with increasing electron-donating strength and the number of branches. (3) Comprehensively considered the optical performance, molecular volume, cytotoxicity and solubility, EX-1 and EX-2 were identified to be the best candidates for living cells (HepG2) imaging. Moreover, the 2PA excitable features of EX-1 and EX-2 are capable of imaging in fresh mouse's liver tissues with a depth of ca. 70 μm.

Enhanced optical and photocatalytic properties of Ag quantum dots-sensitized nanostructured TiO2/ZnO heterojunctions

Co-reporter:Jiajia Tao, Zezhou Gong, Guang Yao, Yunlang Cheng, Miao Zhang, Jianguo Lv, Shiwei Shi, Gang He, Xishun Jiang, Xiaoshuang Chen, Zhaoqi Sun

Journal of Alloys and Compounds 2016 Volume 688(Part A) pp:605-612

Publication Date(Web):15 December 2016

DOI:10.1016/j.jallcom.2016.07.074

•Novel Ag QDs sensitized nanostructured TiO2/ZnO heterojunctions were successfully synthesized.•The TiO2/ZnO/Ag nanostructure showed dramatic optical and photocatalytic activity than pure TiO2 and TiO2/ZnO.•Improving activity is from a combination of the structural features of TiO2/ZnO and the SPR effect of Ag QDs.•The enhanced performance was associated with electron trap mechanism.Ag quantum dots (Ag QDs) sensitized TiO2 nanorod arrays (NRAs)/ZnO nanoparticles (NPs) heterojunctions were fabricated by a three-step method and investigated as photocatalysts. Experimental results showed that the novel material exhibited enhanced optical properties and a high degradation rate (for methyl orange) under UV light (109% compared to bare TiO2 NRAs). The high rate was attributed to an increase in the separation of electrons-holes induced by the introduction of the ZnO NPs and the localized surface plasmon resonance (SPR) of Ag QDs. The degradation mechanism was elucidated based on the band structure. It is suggested that the TiO2/ZnO/Ag nanostructure developed in our work can provide a new platform for the design of highly efficient photocatalysts.

Hydrothermal growth of nanorod arrays and in situ conversion to nanotube arrays for highly efficient Ag-sensitized photocatalyst

Co-reporter:Jiajia Tao, Zezhou Gong, Guang Yao, Yunlang Cheng, Miao Zhang, Jianguo Lv, Shiwei Shi, Gang He, Xiaoshuang Chen, Zhaoqi Sun

Journal of Alloys and Compounds 2016 Volume 689() pp:451-459

Publication Date(Web):25 December 2016

DOI:10.1016/j.jallcom.2016.08.001

•TiO2 NRAs were hydrothermally grown on FTO substrate, and were in situ converted into NTAs by hydrothermally etching.•Novel Ag-TiO2 NTAs with high specific surface area were successfully synthesized.•The Ag-TiO2 NTAs showed dramatic photocatalytic activity than Ag-TiO2 NRAs, pure TiO2 NTAs, and NRAs.•Improving activity is from a combination of SPR effect and high specific surface area effects.TiO2 nanorod arrays (NRAs) were hydrothermally grown on transparent fluorine-doped tin oxide (FTO) substrates, and were converted into nanotubes (NTAs) by hydrothermally in situ etching. Ag nanoparticles (NPLs) were sensitized on the NRAs and NTAs by a simple photodeposition approach (products were denoted as Ag-TiO2 NRAs and NTAs). The Ag-TiO2 NTAs samples possessed a large specific surface area (116 m2 g-1) with Ag NPLs homogeneously dispersed among the TiO2 NTAs. The Ag-TiO2 NTAs exhibited significantly enhanced photocatalytic activities (98.8%) in degradation of methyl orange (MO) compared to Ag-TiO2 NRAs (92.6%), TiO2 NTAs (86.2%), and NRAs (81.7%). The enhanced photocatalytic activities can be attributed to the large specific surface area of TiO2 NTAs and strong surface plasmon resonance (SPR) of Ag NPLs. In addition, Ag-TiO2 NTAs showed easy recovery feature in the recovery process and high durability in the recycling test, which was expected to be an efficient and practical photocatalyst used for waste water treatment.

Rectifying properties of ZnO thin films deposited on FTO by electrodeposition technique

Co-reporter:Jianguo Lv, Yue Sun, Min Zhao, Li Cao, Jiayuan Xu, Gang He, Miao Zhang, Zhaoqi Sun

Applied Surface Science 2016 Volume 366() pp:348-352

Publication Date(Web):15 March 2016

DOI:10.1016/j.apsusc.2016.01.104

Highlights

•: Rectifying ZnO/FTO heterojunction was successfully synthetized.
•: The sample deposited at −0.8 V has the best rectifying characteristics.
•: P-type conductivity of ZnO may be attributed to hydrogen–oxygen complex defect.

Band gap manipulation of cerium doping TiO2 nanopowders by hydrothermal method

Co-reporter:Yunlang Cheng, Miao Zhang, Guang Yao, Lei Yang, Jiajia Tao, Zezhou Gong, Gang He, Zhaoqi Sun

Journal of Alloys and Compounds 2016 Volume 662() pp:179-184

Publication Date(Web):25 March 2016

DOI:10.1016/j.jallcom.2015.12.034

•Different ratio of cerium oxide doped TiO2 nanopowders are prepared by hydrothermal method.•The crystal of cerium oxide is observed in the nanopowders by HRTEM.•The morphology of TiO2 is influenced by Ce doping.•The cut-off wavelength and band gap are effected by cerium doping.•The lowest band gap appears in the 25% Ce doped nanopowders, which is 2.48eV.Cerium doped TiO2 nanopowders were prepared by hydrothermal method with cerium nitrate. The samples were characterized by high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), ultraviolet–visible light diffuse reflectance spectra. Results show that the crystal of cerium dioxide can be observed in the grains of TiO2. The morphology of TiO2 prepared by hydrothermal methods changed from nanosheets to nanopowders by cerium doping. Meanwhile cerium doping can significantly reinforce the absorption of visible light, and adjust the absorption cut-off wavelength, from 373 nm to 499 nm for the undoped and the 25% doped 499 nm samples respectively. With the increase in doping ratio of cerium, the band gaps also decreased from 3.32 to 2.48 eV. Based on our observations, it can be concluded that cerium oxide can improve the absorptivity of TiO2 and may have potential applications in the areas of solar cells and photocatalysis.Download high-res image (295KB)Download full-size image

Enhanced photocatalytic and photoelectrochemical properties of TiO2 nanorod arrays sensitized with CdS nanoplates

Co-reporter:Jiajia Tao, Zezhou Gong, Guang Yao, Yunlang Cheng, Miao Zhang, Jianguo Lv, Shiwei Shi, Gang He, Xiaoshuang Chen, Zhaoqi Sun

Ceramics International 2016 Volume 42(Issue 10) pp:11716-11723

Publication Date(Web):1 August 2016

DOI:10.1016/j.ceramint.2016.04.090

Abstract

TiO₂ nanorod arrays (NRAs) sensitized with CdS nanoplates (NPLs) were fabricated via a two-step method. Vertically aligned TiO₂ NRAs were synthesized by a hydrothermal method, and followed by depositing CdS NPLs on TiO₂ NRAs via successive ion layer absorption and reaction (SILAR) method. Their surface morphology, structure, photoelectrochemical, and photocatalytic properties were investigated. UV-via absorption spectra suggest that the absorption peaks shift from the ultraviolet region (408 nm) to the visible region (580 nm) when compared to pure TiO₂ nanorod arrays. Additionally, upon irradiation of visible light, the photocurrent response of CdS NPL sensitized TiO₂ NRAs after 8 SILAR cycles significantly improved, displaying an optimal photocurrent density of 168.5 μA $μ A$ /cm², which is much higher than that of the unsensitized samples (48.1 μA $μ A$ /cm²). They also exhibited excellent photocatalytic properties where the degradation rate of methyl orange under visible light showed an enhancement of 92.4% compared to bare TiO₂ NRAs. The mechanisms of the enhanced photocatalytic and photoelectrochemical properties of TiO₂ nanorod arrays sensitized with CdS nanoplates are discussed in detail.

NIR-region two-photon fluorescent probes for Fe3+/Cu2+ ions based on pyrimidine derivatives with different flexible chain

Co-reporter:Qiong Zhang, Xiaohe Tian, Hui Wang, Zhangjun Hu, Jieying Wu, Hongping Zhou, Shengyi Zhang, Jiaxiang Yang, Zhaoqi Sun, Yupeng Tian, Kajsa Uvdal

Sensors and Actuators B: Chemical 2016 Volume 222() pp:574-578

Publication Date(Web):January 2016

DOI:10.1016/j.snb.2015.08.079

•Two new two photon chemosensors CCP and COP were synthesized and fully characterized.•They show strong fluorescence quenching and good ratiometric responses.•The two-photon fluorescence intensity could be effectively enhanced on adding EDTA.•The internalization (CCP → Fe3+, COP → Cu2+) with cells and shows the “light switch” property.Two novel NIR-region two-photon fluorescent probes CCP and COP, show strong fluorescence quenching and good ratiometric responses toward Fe3+ and Cu2+, respectively; and their two-photon fluorescence are reversible by the subsequent addition of EDTA. CCP and COP are valuable candidates for two-photon imaging in the biological transparency window.

A series of Zn(II) terpyridine complexes with enhanced two-photon-excited fluorescence for in vitro and in vivo bioimaging

Co-reporter:Qiong Zhang, Xiaohe Tian, Zhangjun Hu, Caroline Brommesson, Jieying Wu, Hongping Zhou, Shengli Li, Jiaxiang Yang, Zhaoqi Sun, Yupeng Tian and Kajsa Uvdal

Journal of Materials Chemistry A 2015 vol. 3(Issue 36) pp:7213-7221

Publication Date(Web):06 Aug 2015

DOI:10.1039/C5TB01185J

It is still a challenge to obtain two-photon excited fluorescent bioimaging probes with intense emission, high photo-stability and low cytotoxicity. In the present work, four Zn(II)-coordinated complexes (1–4) constructed from two novel D–A and D–π–A ligands (L1 and L2) are investigated both experimentally and theoretically, aiming to explore efficient two-photon probes for bioimaging. Molecular geometry optimization used for theoretical calculations is achieved using the crystallographic data. Notably, the results indicate that complexes 1 and 2 display enhanced two-photon absorption (2PA) cross sections compared to their corresponding D–A ligand (L1). Furthermore, it was found that complex 1 has the advantages of moderate 2PA cross section in the near-infrared region, longer fluorescence lifetime, higher quantum yield, good biocompatibility and enhanced two-photon excited fluorescence. Therefore, complex 1 is evaluated as a bioimaging probe for in vitro imaging of HepG2 cells, in which it is observed under a two-photon scanning microscope that complex 1 exhibits effective co-staining with endoplasmic reticulum (ER) and nuclear membrane; as well as for in vivo imaging of zebrafish larva, in which it is observed that complex 1 exhibits specificity in the intestinal system.

Temperature-dependent differences in wettability and photocatalysis of TiO2 nanotube arrays thin films

Co-reporter:Miao Zhang, Guang Yao, Yunlang Cheng, Yanyan Xu, Lei Yang, Jianguo Lv, Shiwei Shi, Xishun Jiang, Gang He, Peihong Wang, Xueping Song, Zhaoqi Sun

Applied Surface Science 2015 Volume 356() pp:546-552

Publication Date(Web):30 November 2015

DOI:10.1016/j.apsusc.2015.08.117

Highlights

•: The anodization conditions were studied carefully and the uniform surface morphology was obtained under certain conditions.
•: Unique morphology composed by nanowire@nanotube can be seen after calcining treatment.
•: The water contact angle before and after UV light illumination were test repetitively, and the error of water contact angle were measured. Tiny change of contact angle was observed when samples were annealed at 600 °C.
•: The sample annealed at 600 °C exhibits the highest photocatalytical activity among the samples.

Enhanced charge collection and photocatalysis performance of CdS and PbS nanoclusters co-sensitized TiO2 porous film

Co-reporter:Miao Zhang, Yanyan Xu, Zezhou Gong, Jiajia Tao, Zhaoqi Sun, Jianguo Lv, Xiaoshuang Chen, Xishun Jiang, Gang He, Peihong Wang, Fanming Meng

Journal of Alloys and Compounds 2015 Volume 649() pp:190-195

Publication Date(Web):15 November 2015

DOI:10.1016/j.jallcom.2015.07.145

•Ti films were obtained from direct current sputtering method.•TiO2 nanoporous in ITO were obtained by etched method in hydrogen peroxide.•CdS/PbS quantum dots were imbedded on TiO2 porous film by SILAR method.•The optical properties of samples were systematically tested and discussed.A novel translucent TiO2 porous film was prepared through etched method. The CdS, PbS and CdS/PbS nanoclusters were imbedded on TiO2 porous film by successive ionic layer adsorption and reaction method. Microstructure, morphology, optical and photoelectron-chemical properties of the as-synthesized thin films were investigated systematically. XRD and morphology analysis showed that PbS or CdS nanoclusters have been attached to the TiO2 porous films. It was found that the energy band gap of TiO2 porous film decreased from 3.46 to 3.2 eV after sensitized with nanoclusters. The photocurrent density of ITO/TiO2 photoelectrode increased from 0.017 to 0.28 mA/cm2 after co-sensitized with CdS and PbS nanoclusters. Besides, the photoelectrode sensitized with two sorts of nanoclusters showed evident higher photocurrent density than which sensitized just one sort of nanoclusters. The photocurrent density of ITO/TiO2/PbS and TO/TiO2/CdS photoelectrode was 0.11 mA/cm2 and 0.22 mA/cm2 respectively. 0.28 mA/cm2 can be obtained by ITO/TiO2/CdS/PbS photoelectrode. The results showed that the optical and photoelectrochemistry properties and phtotcatalysis performance of TiO2 porous film were greatly improved by co-sensitized with CdS and PbS nanoclusters.When CdS and PbS were brought in the cascade structure, such a Fermi level alignment causes upward and downward shifts of the band edges for PbS and CdS, respectively. Therefore the resulting band edges for the ITO/TiO2/CdS/PbS devices are inferred to have a stepwise structure. The elevated conduction band edge of PbS provides a higher driving force for the injection of photogenerated electrons from PbS to CdS as well as the injection of excited holes from CdS to PbS. Such a structure offers efficient separation and transport of the excited electrons and holes.

Effect of seed layer on optical properties and visible photoresponse of ZnO/Cu2O composite thin films

Co-reporter:Jianguo Lv, Jinhua Xu, Min Zhao, Pengpeng Yan, Sicong Mao, Fengjiao Shang, Gang He, Miao Zhang, Zhaoqi Sun

Ceramics International 2015 Volume 41(Issue 10) pp:13983-13987

Publication Date(Web):December 2015

DOI:10.1016/j.ceramint.2015.07.010

ZnO/Cu2O composite thin films were deposited on Cu foil using a simple solution method with a variety of ZnO seed layers inserted between the Cu2O and ZnO layers. Effects of the ZnO seed layers on the microstructure, optical properties and photoresponse of the thin films were investigated. The intensity of the ZnO (002) diffraction peak increases with increasing thickness of the seed layer. Dissolution of ZnO nanoparticles also occurs during growth of the ZnO thin films. The optical band gap of the Cu2O layer decreases gradually from 1.86 to 1.66 eV as the thickness of the ZnO seed layer increases. Change of the optical band gap could be attributed to Cu2+ impurities in the Cu2O and (or) ZnO layers. A visible emission from sample with a seed layer of four times can be attributed to phonon-assisted exciton recombination in Cu2O. An ultraviolet emission centered at 380 nm and a broad visible emission band is observed in the two samples with a seed layer of six and eight times. The best photoresponse performance has been observed in the sample with a seed layer of eight times. This is likely a result of the stronger visible absorption and better band alignment in samples, which facilitates electron transfer from the conduction band of Cu2O to the conduction band of ZnO.

Microstructure, optical and photoelectron-chemical properties of TiO2 microspheres prepared by hydrothermal method

Co-reporter:Xishun Jiang;Yafang Zhang;Zhongwei Li

Journal of Materials Science: Materials in Electronics 2015 Volume 26( Issue 4) pp:2070-2075

Publication Date(Web):2015 April

DOI:10.1007/s10854-014-2649-9

Anatase TiO2 microspheres have been prepared by hydrothermal method and the reaction concentrations of mix solution containing hydrofluoric acid (HF) and ammonium fluoride (NH4F) are 0.1, 0.2, and 0.4 M, respectively. Microstructure, morphology, chemical composition, optical and photoelectron-chemical properties of the as-deposited thin films were investigated in detail. XRD analysis shows that the grain size of the microspheres increases with increasing the reaction concentration. The films deposited at 0.1 and 0.2 M are formed by wellfaceted, regular microspheres with the size of 2–3 μm. XPS measurement indicates that the atomic ratio of Ti:O is estimated to be 1:2.05 for the sample deposited at 0.2 M. The band gap is close to the standard values of anatase TiO2 3.2 eV as the reaction concentration increases. The photocurrent of TiO2 film deposited for 0.1 M reaction concentration is around three times as strong as those for 0.2 and 0.4 M under the same illumination. Current results will help to synthesise desired TiO2 films and expand its applications.

Effect of methanol ratio in mixed solvents on optical properties and wettability of ZnO films by cathodic electrodeposition

Co-reporter:Miao Zhang, Kai Xu, Xishun Jiang, Lei Yang, Gang He, Xueping Song, Zhaoqi Sun, Jianguo Lv

Journal of Alloys and Compounds 2014 Volume 615() pp:327-332

Publication Date(Web):5 December 2014

DOI:10.1016/j.jallcom.2014.06.178

•Different surface morphologies of ZnO films were prepared by cathodic electrodeposition.•The surface morphologies are controlled through add different ratio methanol to electrolyte.•The morphology changes from nanorods with hexagonal structure to net-like nanostructure.•The wettability of films shows obvious change with increasing methanol ratio.•The maximum light-induced CA change has been observed with the methanol ratio of 0.8.ZnO thin films were prepared in the electrolyte with different methanol ratio by cathodic electrodeposition method. Microstructure, surface morphology, optical properties and wettability of the thin films were investigated by X-ray diffractometer, field-emission scanning electron microscope, ultraviolet–visible spectroscope, fluorescence spectrometer and water contact angle apparatus. Increase of methanol ratio in the solvents may restrain the (0 0 2) plane preferential orientation in some extent. Change of current density curves with the ratio of methanol in the solution play a vital role on electrochemical reaction kinetics, microstructure and/or surface morphology of ZnO thin films. With the methanol ratio increase from 0 to 0.8, the surface morphology changes from nanorods to net-like nanostructure. The adsorbed NO3− ions on the polar planes hinder the crystal growth along the c-axis and redirect the growth direction along the nonpolar planes. The maximum and minimum band gaps have been obtained in the ZnO thin films with the methanol ratio of 0.4 and 0.6, respectively. Change of contact angle before UV irradiation may be related to surface morphology and oxygen vacancies. The maximum light-induced water contact angle change has been observed in the sample with the methanol ratio of 0.8. The results may be attributed to the higher surface roughness and net-like morphology.

Controllable hydrothermal synthesis, optical and photocatalytic properties of TiO2 nanostructures

Co-reporter:Yanyan Xu, Maocui Zhang, Miao Zhang, Jianguo Lv, Xishun Jiang, Gang He, XuePing Song, Zhaoqi Sun

Applied Surface Science 2014 Volume 315() pp:299-306

Publication Date(Web):1 October 2014

DOI:10.1016/j.apsusc.2014.07.110

Highlights

•: Different surface morphologies of TiO₂ films were prepared by hydrothermal synthesis method.
•: The surface morphologies are controlled through changing reaction time.
•: The influences of a shorter hydrothermal reaction time (shorter than 6 h) on TiO₂ films are investigated.
•: The surface morphology shows obvious change with increasing reaction time.
•: The optical properties and photocatalytic properties are influenced by reaction time.
•: The ratio of Ti:O is 1:2.28 and close to the atom ratio of TiO₂.

The effect of charge layer separating absorption and multiplication on the performance of GaN avalanche photodiodes

Co-reporter:Jingjing Wanyan, Zhaoqi Sun, Shiwei Shi, Gang He, Mingzai Wu, Guang Li

Solid State Communications 2014 Volume 189() pp:28-31

Publication Date(Web):July 2014

DOI:10.1016/j.ssc.2014.03.009

•Photo-response characteristics of a back-illuminated APD are studied theoretically.•Gain is simulated as a function of charge layer thickness and doping concentration.•The temperature dependence of avalanche voltage shows a large positive coefficient.•Compare the temperature coefficient of the SAM GaN APDs with that of the conventional one.The photo-response characteristics of a back-illuminated avalanche photodiode are studied theoretically by using a charge layer to separate the absorption and multiplication regions. The results show that the average electric field at the breakdown voltage is approximately 3.0 MV/cm, close to the reported value, in good agreement with that of the experiments. Multiplication gain has been calculated as a function of charge layer thickness and doping concentration. A maximum optimal gain of 7×104 is obtained with the doping concentration of 2×1018 cm−3. The temperature dependence of avalanche voltage shows a large positive coefficient of 0.15 V/K, confirming that the avalanche multiplication is the dominant gain mechanism in the photodiodes.

Enhanced photocatalytic activity of Mg0.05Zn0.95O thin films prepared by sol–gel method through a cycle

Co-reporter:Zhitao Zhou;Fengjiao Shang;Guangcai Pan

Journal of Materials Science: Materials in Electronics 2014 Volume 25( Issue 5) pp:2053-2059

Publication Date(Web):2014 May

DOI:10.1007/s10854-014-1839-9

Mg0.05Zn0.95O thin films were prepared on silicon substrates by a sol–gel dip-coating technique. Microstructure, surface topography and optical properties of the thin films were characterized by X-ray diffraction, atom force microscopy, Fourier transform infrared spectrophotometer and fluorescence spectrometer. The results show that the thin film annealed at 700 °C has the largest average grain size and exhibits the best c-axis preferred orientation. As annealing temperature increases to 800 °C, the grain along c-axis has been suppressed. Roughness factor and average particle size increase with the increase of annealing temperature. The IR absorption peak appearing at about 416 cm−1 is assigned to hexagonal wurtzite ZnO. The thin film annealed at 700 °C has the maximum oxygen vacancy, which can be inferred from the green emission intensity. Photocatalytic results show that the thin film annealed at 700 °C exhibits remarkable photocatalytic activity, which may be attributed to the larger grain size, roughness factor and concentration of oxygen vacancy. Enhanced photocatalytic activity of Mg0.05Zn0.95O thin films after a cycle may be attributed to the increase of surface oxygen vacancy and photocorrosion of amorphous MgO on the surface of thin film under UV irradiation.

Effect of Al components on the properties of CuAlO2 thin films deposited by RF magnetron sputtering

Co-reporter:Zhaoqi Sun, Xishun Jiang, Junlei Li, Gang He, Xueping Song

Journal of Alloys and Compounds 2013 Volume 581() pp:488-493

Publication Date(Web):25 December 2013

DOI:10.1016/j.jallcom.2013.07.143

•CAO films with different Al volume fraction of 1–5% were prepared.•The microstructure, optical and hydrophily properties were studied.•CAO films changes from hydrophobicity to hydrophily after annealing.•The mechanism of the evolution of WCA is discussed.CuAlO2 (CAO) thin films with Al volume fraction of 1–5% were prepared by RF magnetron sputtering and were annealed at 1173 K for 4 h in the air. The microstructures, optical and hydrophily properties of the as-deposited films were studied. XRD measurement shows that all films are polycrystalline and present as Cu–Al–O phase. 3D profilometer measurement shows the minimum of surface roughness is 11.6 nm for 1%Al–CAO film, and the maximum is 38.6 nm for 5%Al–CAO film. The transmittance in the visible range decreases from 60% to 40% after the annealing process as a result of impurity and rough surface. The minimum value of average refractive index and extinction coefficient is about 1.41 and 0.031 for 1%Al–CAO film. The estimated direct band gaps of CAO films are 3.37–3.53 eV. CAO films changes from hydrophobicity to hydrophily after annealing, and water contact angle of the annealed film increases from 31.1° to 70.5°.

Effect of Ag-doping on microstructural, optical and electrical properties of sputtering-derived ZnS films

Co-reporter:Xueping Song, Shiwei Shi, Chunbin Cao, Xiaoshuang Chen, Jingbiao Cui, Gang He, Zhaoqi Sun

Journal of Alloys and Compounds 2013 Volume 551() pp:430-434

Publication Date(Web):25 February 2013

DOI:10.1016/j.jallcom.2012.11.020

The ZnS:Ag nano-composite films with different Ag volume fractions (5, 10, 15 and 2 vol.%) were deposited on glass substrates by sputtering. The microstructures, optical and electrical properties of the as-deposited films were studied. XRD measurement shows that all films are polycrystalline with a microstructure of body-centered cubic phase belonged to ZnS. The samples in which Ag volume concentrations lower than 20 vol.% show a preferential orientation along the (2 2 0) direction. When Ag concentration reaches 20 vol.%, the intensity of the (2 2 0) peak belonged to ZnS decreases dramatically while the Ag (1 1 1) peak emerged. Based on our analysis, it can be noted that Ag can help the ZnS grains grow when Ag concentration is lower than 20 vol.%. However, the ZnS crystal growth is suppressed when Ag concentration is 20 vol.%. The refractive index of the samples decreases with the increase of Ag concentration while the extinction coefficient of the samples increases. The resistivity of the film reaches the minimum when Ag concentration is 20 vol.%, showing the electrical conductivity improvement of the composite film by doped Ag nano-particles.Highlights► Ag concentration significantly influenced the grain growth of ZnS film. ► The refractive index of ZnS:Ag film obviously increases when Ag concentration is 20 vol.%. ► The film with high n implies the potential use for antireflective multilayer coating system. ► The extinction coefficient of the films indicates the plasma resonance at different wavelength. ► The film can be used for tunable emission wavelength in electroluminescent plat display devices.

Effect of annealing temperature and CuO on microstructure and optical band gap of CuxZn1−xO thin films

Co-reporter:Jianguo Lv, Zhitao Zhou, Feng Wang, Changlong Liu, Wanbing Gong, Jielin Dai, Xiaoshuang Chen, Gang He, Shiwei Shi, Xueping Song, Zhaoqi Sun, Feng Liu

Superlattices and Microstructures 2013 Volume 61() pp:115-123

Publication Date(Web):September 2013

DOI:10.1016/j.spmi.2013.06.010

•Cu concentrations enhance preferential c-axis orientation CuxZn1−xO thin films.•The optical band gap and PL spectra of CuxZn1−xO thin films were studied.•Effect of Cu concentrations on optical band gap has been reported.•We report the photoluminescence mechanism of CuxZn1−xO thin films.CuxZn1−xO thin films were prepared by the sol–gel process. Microstructure, surface topography and optical properties were studied by X-ray diffractometry, atom force microscopy, UV–Vis spectrophotometer and fluorescence spectrometer. The monoclinic CuO phase has been observed in CuxZn1−xO (x = 0.05, 0.10, and 0.15) thin films annealed at 800 °C. Preferential c-axis orientation of the CuxZn1−xO thin films annealed at 800 °C increases with the increase of x value. The annealing temperature and CuO component have great effect on the absorption coefficient of CuxZn1−xO thin films in the visible region. The decrease of optical band gap may be attributed to the reduction of the fraction of the amorphous phase and stoichiometry deficiency of ZnO due to CuO doping. The deep level emission in ZnO thin film originates from oxygen vacancy and oxygen interstitial defects. The violet emission peaked at about 400 nm has been assigned to the electron transition from zinc interstitial level and the valence band.

Influence of solution concentrations on surface morphology and wettability of ZnO thin films

Co-reporter:Jianguo Lv;Changlong Liu;Feng Wang;Zhitao Zhou

Electronic Materials Letters 2013 Volume 9( Issue 2) pp:171-176

Publication Date(Web):2013 March

DOI:10.1007/s13391-012-2170-3

ZnO thin films were grown on silicon substrates using a hydrothermal method. The XRD patterns show that all of the peaks can be attributed to the wurtzite structures of ZnO. The TC value of (002) plane and average crystal size increase first and then decrease with the increase of solution concentration. SEM and AFM results show that many dense hexagonal cylinder particles have been observed on the surface of the thin films, which grown at 0.08 and 0.10 mol/L. The surface roughness of the thin films deposited at 0.06, 0.08, 0.10, and 0.12 mol/L are 24.5, 38.3, 32.0, and 39.4 nm, respectively. Surface wettability results show that the preferential orientation along c-axis and surface roughness contribute significantly to the hydrophobicity. The reversible switching between hydrophobicity and hydrophilicity is related to the synergy of the transition of wetting model, surface crystal structure, and surface roughness.

Structure and electrical properties of K0.5Na0.5NbO3–SrTiO3 lead-free piezoelectric ceramics with LiSbO3 doping

Co-reporter:Qiyi Yin;Shiwei Shi

Journal of Materials Science: Materials in Electronics 2013 Volume 24( Issue 11) pp:4258-4262

Publication Date(Web):2013 November

DOI:10.1007/s10854-013-1394-9

Lead-free piezoelectric ceramics (1 − x)K0.5Na0.5NbO3–xSrTiO3 with 6 mol% LiSbO3 doping have been prepared by conventional solid state sintering technique at 1,125 °C for 3 h in air. The effects of the SrTiO3 and LiSbO3 on the phase structure and electrical properties of the ceramics were systematically investigated. All ceramic samples show a single phase perovskite structure with tetragonal symmetry when LiSbO3 content was 6 mol% and SrTiO3 content was 2–10 mol% by X-ray diffraction analysis and highly dense structure by SEM patterns. The ceramic with x = 0.04 exhibits optimum electrical properties at room temperature (d33 = 267 pC/N, kp = 46 %, εr = 1,168, tanδ = 0.021, Pr = 30.3 μC/cm2, EC = 1.98 kV/mm), which suggests that the ceramic is a promising candidate material for lead-free piezoelectric ceramics.

Microstructure and opto-electric properties of Cu/ITO thin films

Co-reporter:Xian Wang, Junlei Li, Shiwei Shi, Xueping Song, Jingbiao Cui, Zhaoqi Sun

Journal of Alloys and Compounds 2012 Volume 536() pp:231-235

Publication Date(Web):25 September 2012

DOI:10.1016/j.jallcom.2012.04.063

Cu/ITO thin films were deposited on glass and silicon substrates by DC and RF magnetron sputtering at room temperature. X-ray diffraction results showed that the films were amorphous. Both of SEM images and 3D Profilometer images indicated that the surface morphology of the ITO films had been affected by the Cu layer. The optical and electric properties of the Cu/ITO films changed significantly with the variation of Cu layer thickness. Cu-5.4 nm/ITO film exhibited the highest optical transmittance of 62.9% at 550 nm and the lowest sheet resistance of 96 Ω/□, whereas Cu-16.1 nm/ITO film showed the highest average reflectance of 24.0% and the lowest resistance of 27.4 Ω/□. Based on our analysis, it was evaluated that Cu layer had an important effect on the electrical and optical properties of ITO thin films.Highlights► We prepared Cu/ITO films with different Cu layer thickness. ► We analyzed the relation between opto-electric properties and roughness of the films. ► The Cu-16.1 nm/ITO film shows excellent optical and electric properties. ► Cu/ITO films have great application prospects in new-type transflective displays.

Temperature-dependent shifts of near band-edge emission and their second-order diffraction for ZnO nanorods

Co-reporter:Jianguo Lv, Changlong Liu, Wanbing Gong, Zhenfa Zi, Xiaoshuang Chen, Kai Huang, Tao Wang, Gang He, Shiwei Shi, Xueping Song, Zhaoqi Sun

Optical Materials 2012 Volume 34(Issue 11) pp:1917-1920

Publication Date(Web):September 2012

DOI:10.1016/j.optmat.2012.05.030

The crystal structure and morphology of ZnO, grown on silicon substrate by two-step method, were measured by X-ray diffraction and field emission scanning electron microscopy. The results reveal that the sample is mainly composed of ZnO nanorods and preferentially oriented in the c-axis direction. The photoluminescence properties of the ZnO nanorods were investigated over the temperatures from 10 K to 297 K. There exist three emission bands in near band-edge, green–yellow–orange–red and near-infrared, respectively. Donor bound exciton (D0X) and its phonon replicas emission peaks were observed in low temperature photoluminescence (PL). The D0X and its phonon replicas peak intensity decreased with the increase of temperature and disappeared when the temperature increased up to 87 K. The decay in the D0X and its phonon replicas emission peak intensity stemmed from the thermal dissociation of D0X to free exciton. Temperature-dependent second-order diffraction of the near band-edge emissions were investigated in detail.Highlights► D0X and its phonon replicas emission peaks were observed in low temperature PL. ► The NIR emissions correspond to the second-order diffraction of the NBE emission. ► NBE and NIR emission mechanism were investigated.

Effect of solution concentrations on crystal structure, surface topographies and photoluminescence properties of ZnO thin films

Co-reporter:Jianguo Lv, Changlong Liu, Wanbing Gong, Zhenfa Zi, Xiaoshuang Chen, Kai Huang, Tao Wang, Gang He, Xueping Song, Zhaoqi Sun

Superlattices and Microstructures 2012 Volume 51(Issue 6) pp:886-892

Publication Date(Web):June 2012

DOI:10.1016/j.spmi.2012.02.014

Zinc oxide thin films were deposited on silicon substrates via hydrothermal method. Microstructures, surface topographies and optical properties of ZnO thin films were systematically investigated by X-ray diffraction, atomic force microscopy and fluorescence spectrophotometer. The mean grain size and surface roughness of the thin films decrease first and then increase with increasing the concentration of zinc nitrate hexahydrate. The photoluminescence spectra of ZnO thin films, excited by the 240, 320, 360, 380 and 400 nm excitation wavelength, were investigated in detail. Based on our analysis, it can be noted that mechanisms of the ultraviolet, violet and blue emissions are attributed to the transitions from the localized levels below the conduction band, zinc vacancy, interstitial zinc and extended interstitial zinc levels to the valance band, respectively. Blue–violet emissions of ZnO have great potential in light emitting and biological fluorescence labeling applications.Highlights► A novel UV-violet-blue emission band was discovered in the ZnO thin films. ► The blue emission peak blue shifted with the excitation wavelength increase from 380 to 400 nm. ► The blue emission band was assigned to the electrons transition from extended zinc levels to the valance band.

Facile synthesis of Zn1−xCuxO nanorods with a very broad visible band

Co-reporter:Jianguo Lv;Changlong Liu;Wanbing Gong;Zhenfa Zi

Electronic Materials Letters 2012 Volume 8( Issue 5) pp:477-480

Publication Date(Web):2012 October

DOI:10.1007/s13391-012-2044-8

Zn1−xCuxO nanorods with different Cu concentrations are prepared by a hydrothermal method. Bent and aggregated nanorods are obtained, which is attributed to centripetal surface tension of the evaporation and coagulation processes of the water film on the ZnO nanorods. The broad visible band consists of one violet, three blue, and one green emission. The violet emission is due to the transition of electrons from zinc interstitial (Zni) levels to the valance band. The three blue emissions may be attributed to the transition from extended Zni levels, which are slightly below the simple Zni level, to the valance band. The change of the green emission may be the result of competition between oxygen vacancies (VO) and zinc vacancies (VZn).

Tunable surface wettability of ZnO nanorods prepared by two-step method

Co-reporter:Jianguo Lv, Jianbo Zhu, Kai Huang, Fanming Meng, Xueping Song, Zhaoqi Sun

Applied Surface Science 2011 Volume 257(Issue 17) pp:7534-7538

Publication Date(Web):15 June 2011

DOI:10.1016/j.apsusc.2011.03.113

Abstract

Zinc oxide (ZnO) nanorods were deposited on silicon substrate by two-step method. The crystal structure, surface morphology and water contact angle (WCA) were measured by X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), and water contact angle apparatus. It is demonstrated that the WCA of the as-grown ZnO nanorods varies between 136° and 43° and the contact angle reduction rate of ZnO nanorods changes rapidly with increasing growth time. The variation of contact angle in the as-grown samples and contact angle reduction rate has been attributed to the combined effects of the proportion of nonpolar planes in the outermost surface, the area fraction of vapor on the surface and the increase of surface energy of ZnO nanorods.

Enhanced photo-induced hydrophilicity of the sol–gel-derived ZnO thin films by Na-doping

Co-reporter:Jianguo Lü, Kai Huang, Xuemei Chen, Jianbo Zhu, Fanming Meng, Xueping Song, Zhaoqi Sun

Applied Surface Science 2011 Volume 257(Issue 6) pp:2086-2090

Publication Date(Web):1 January 2011

DOI:10.1016/j.apsusc.2010.09.054

Abstract

Na-doped ZnO thin films with different Na/Zn ratio were prepared by sol–gel method. The microstructure, chemical composition, surface morphology, and wettability of the thin films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and water contact angle apparatus. The relation of wettability and Na/Zn ratio has been studied in detail. The wetting behavior of the thin films can be reversibly switched from hydrophobic to hydrophilic, through alternation of UV illumination and dark storage (or thermal treatment). Photo-induced hydrophilicity of the thin films increases with increasing Na/Zn ratio up to 0.08 and then decreases. The mechanism can be attributed to surface nanostructure and the concentration of Na doping.

Effect of annealing temperature on photocatalytic activity of ZnO thin films prepared by sol–gel method

Co-reporter:Jianguo Lv, Wanbing Gong, Kai Huang, Jianbo Zhu, Fanming Meng, Xueping Song, Zhaoqi Sun

Superlattices and Microstructures 2011 Volume 50(Issue 2) pp:98-106

Publication Date(Web):August 2011

DOI:10.1016/j.spmi.2011.05.003

Zinc oxide thin films are deposited on Si and quartz substrates using the sol–gel method. The thin films, annealed at 400, 600 and 800 °C respectively, are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), ultraviolet–visible spectrophotometer (UV–Vis), fluorescence spectrometer (FL) and the photocatalytic activity is tested by the decomposition of methyl orange dye under UV illumination. The results show that the mean grain size, surface-to-volume ratio, rms roughness and degradation efficiency of the thin films increases with increasing annealing temperature. In particular, ZnO thin film annealed at 800 °C exhibits the highest photocatalytic activity, degrading methyl orange by almost 88% in 180 min. Photocatalytic reaction mechanism of the ZnO thin films is discussed in detail, and the oxygen defects are proposed to be the active sites of the ZnO photocatalyst.Highlights► The highest degradation efficiency of the thin films reaches 88%. ► The band gap decreases with increasing of annealing temperature. ► Increasing annealing temperature will increase degradation efficiency. ► The oxygen defects are proposed to be the active sites of the ZnO photocatalyst.

Effect of preheating temperatures on microstructure and optical properties of Na-doped ZnO thin films by sol–gel process

Co-reporter:Jianguo Lv, Kai Huang, Xuemei Chen, Jianbo Zhu, Lijun Wang, Xueping Song, Zhaoqi Sun

Superlattices and Microstructures 2011 Volume 49(Issue 4) pp:477-486

Publication Date(Web):April 2011

DOI:10.1016/j.spmi.2011.01.005

The chemical composition, crystalline structure, surface morphology and photoluminescence spectra of Na-doped ZnO thin films with different heat treatment process were investigated by X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy and a fluorescence spectrometer. The results show that preferred orientation, residual stress, average crystal size and surface morphology of the thin films are strongly determined by the preheating temperature. The effects of preheating temperature on microstructure and surface morphology have been discussed in detail. The photoluminescence spectra show that there are strong violet & UV emission, blue emission and green emission bands. The violet & UV emission is ascribed to the electron transition from the localized level below the conduction band to the valence band. The blue emission is attributed to the electron transition from the shallow donor level of oxygen vacancies to the valence band, and the electron transition from the shallow donor level of interstitial zinc to the valence band. The green emission is assigned to the electron transition from the level of ionized oxygen vacancies to the valence band.

Optical constants of Na-doped ZnO thin films by sol–gel method

Co-reporter:Jianguo Lv, Kai Huang, Xuemei Chen, Jianbo Zhu, Chunbin Cao, Xueping Song, Zhaoqi Sun

Optics Communications 2011 Volume 284(Issue 12) pp:2905-2908

Publication Date(Web):1 June 2011

DOI:10.1016/j.optcom.2011.01.075

The structural and optical properties of pure and Na-doped ZnO thin films have been investigated by X-ray diffraction (XRD), atom force microscopy and UV–Vis spectrophotometer. The crystal structure of all the thin films is the hexagonal wurtzite. The average grain size and surface roughness increases with the increase of the Na/Zn ratio. The optical band gap of the thin films decreases from 3.26 to 3.12 eV by increasing the Na/Zn ratio from 0.0 to 0.10. Transmittance spectra were used to determine the optical constants of the thin films, and the effect of Na/Zn ratio on the optical constants was investigated. With the increase of Na/Zn ratio, the refractive index decreases and the extinction coefficient increases in the 380–700 nm spectral range.Research Highlights► Transmittance spectra have been used to determine the optical constants. ► Refractive index decreases with Na/Zn ratio increases. ► Increasing Na/Zn ratio will decrease optical band gap. ► The effect of microstructure on the optical constants has been investigated.

Influence of dopant content on morphology and optical constants of ZnO:Na films by sol-gel method

Co-reporter:Jian-guo Lü 吕建国;Chun-bin Cao 曹春斌

Journal of Central South University 2011 Volume 18( Issue 1) pp:42-47

Publication Date(Web):2011 February

DOI:10.1007/s11771-011-0656-z

Undoped and Na-doped ZnO films were deposited by sol-gel method. The effects of sodium incorporation on structure, surface morphology and optical constants of the films were investigated. X-ray diffraction patterns show the hexagonal wurtzite polycrystalline structure and that the sodium incorporation leads to the change in the structural characteristics of ZnO films. The SEM observations show that the surface morphology of the films is affected by the sodium incorporation. The transmission spectra show that the average transmittance of the films is above 85% in the visible range. The absorption edge initially blue-shifts and then red-shifts with the increase of Na doping content. The optical constants of these films were calculated using transmission spectra. Refractive indices of the films in the visible range decrease at first and then increase with increasing Na doping content.

Effect of Na concentrations on microstructure and optical properties of ZnO films

Co-reporter:Jianguo Lü 吕建国;Jielin Dai;Jianbo Zhu

Journal of Wuhan University of Technology-Mater. Sci. Ed. 2011 Volume 26( Issue 1) pp:23-27

Publication Date(Web):2011 February

DOI:10.1007/s11595-011-0160-1

Na-doped ZnO thin films were deposited on the glass substrates using sol-gel method. The effect of Na concentrations on the structural and optical properties of ZnO films was studied. As Na concentration increases from 0.0 at% to 16.0 at%, preferential c-axis orientation becomes more and more obvious, and the intensity of the diffraction peaks from (103) increases. The optical band gap Eg value increases from 3.261 to 3.286 eV first and then decreases as Na concentration increases from 0.0 to 2.0 at% and then beyond 2.0 at%. The intensity of all the emissions increases with increasing Na concentration and the origins of the violet emission (wavelength in the 400–407 nm) and the blue emission (wavelength at 473 nm) were discussed in detail.

Reversible wettability of nanostructured ZnO thin films by sol–gel method

Co-reporter:Jianguo Lü, Kai Huang, Xuemei Chen, Jianbo Zhu, Fanming Meng, Xueping Song, Zhaoqi Sun

Applied Surface Science 2010 Volume 256(Issue 14) pp:4720-4723

Publication Date(Web):1 May 2010

DOI:10.1016/j.apsusc.2010.02.080

Abstract

Nanostructured ZnO thin films were deposited on Si(1 1 1) and quartz substrate by sol–gel method. The thin films were annealed at 673 K, 873 K, and 1073 K for 60 min. Microstructure, surface topography, and water contact angle of the thin films have been measured by X-ray diffractometer, atomic force microscopy, and water contact angle apparatus. XRD results showed that the ZnO thin films are polycrystalline with hexagonal wurtzite structure. AFM studies revealed that rms roughness changes from 2.3 nm to 7.4 nm and the grain size grow up continuously with increasing annealing temperature. Wettability results indicated that hydrophobicity of the un-irradiated ZnO thin films enhances with annealing temperature increase. The hydrophobic ZnO surfaces could be reversibly switched to hydrophilic by alternation of UV illumination and dark storage (thermal treatment). By studying the magnitude and the contact angle reduction rate of the light-induced process, the contribution of surface roughness is discussed.

Surface morphology and optical properties of magnetron – sputtered ultrathin Al films

Co-reporter:Zhaoqi Sun, Chunbin Cao, Ling Cao, Ping Liang, Xingfa Huang, Xueping Song

Vacuum 2010 Volume 84(Issue 6) pp:828-832

Publication Date(Web):4 February 2010

DOI:10.1016/j.vacuum.2009.11.002

Ultrathin Al films with different thicknesses were deposited on glass substrates by DC magnetron sputtering. The effects of film thickness on morphology and optical properties of the films were investigated in detail. When film thickness increases from 7.0 to 84.0 nm, the average grain size and surface roughness enlarges from 27.6 to 94.2 nm and from 0.25 to 1.87 nm, respectively. Below critical thickness of 28.0 nm, which is the thickness that Al films form continuous film, the optical properties vary significantly with thickness increasing and then tend to be stable. In the absorptance spectra, all films exhibit distinct broad peaks which can be attributed to the absorption due to the interband transition. The possible reasons for the shift in the peak position are due to the quantum size effects and internal stress in the ultrathin Al films.

Microstructure and optical properties of nano Ag-ITO films

Co-reporter:Lei Xiao;ChunBin Cao;XuePing Song;FanMing Meng

Science China Technological Sciences 2010 Volume 53( Issue 5) pp:1266-1270

Publication Date(Web):2010 May

DOI:10.1007/s11431-010-0151-z

Nano Ag-ITO films with Ag volume fraction of 0.3%–1.0% were prepared by radio-frequency magnetron co-sputtering and analyzed by X-ray diffraction, scanning electron microscopy and ultraviolet-visible spectroscopy. Microstructure analysis shows that the films are composed of polycrystalline ITO matrix embedded with Ag nanoparticles with a mean size of 60–100 nm. Transmissivity spectra of Ag-ITO films indicate that the visible light transmissivity of the films decreases with increasing the Ag fraction. The transmissivity of the annealed films is higher than that of the as-deposited films. The volume 0.3% Ag-ITO films have the highest light reflectance. The annealed films exhibit lower light absorptance than as-deposited films. A surface plasmon resonance (SPR) peak of volume 0.3% Ag-ITO films is located around 510 nm. Compared with the annealed ITO film, the annealed volume 0.3% Ag-ITO film shows 10% higher reflectivity, while its transmittance is almost the same as that of the annealed ITO film, indicating its potential application in new-type transflective displays.

Microstructure and electrical conductivity of Au–MgF2 nanoparticle cermet films

Co-reporter:Sun Zhaoqi, Cai Qi, Song Xueping

Thin Solid Films 2008 Volume 516(Issue 8) pp:2280-2285

Publication Date(Web):29 February 2008

DOI:10.1016/j.tsf.2007.07.192

Au–MgF2 nanoparticle cermet films with Au volume fraction of 6–50% were prepared by radio-frequency magnetron co-sputtering and analyzed by X-ray diffraction, X-ray photoelectron spectroscopy and temperature-varying four-wire technique. Microstructure analysis shows that the films are composed of mainly amorphous MgF2 matrix with embedded fcc Au nanoparticles with a mean size of 9.8–21.4 nm. The electrical properties of the films from 54 to 300 K were measured. The results show that the electrical percolation threshold occurs between Au 40 vol.% and 50%, and around the percolation threshold the electrical conductivity of the films changes by four orders.

A unique Cu2O/TiO2 nanocomposite with enhanced photocatalytic performance under visible light irradiation

Co-reporter:Yanfen Wang, Jiajia Tao, Xingzhi Wang, Zhuang Wang, Miao Zhang, Gang He, Zhaoqi Sun

Ceramics International (15 April 2017) Volume 43(Issue 6) pp:

Publication Date(Web):15 April 2017

DOI:10.1016/j.ceramint.2016.12.130

A unique Cu2O/TiO2 nanocomposite with high photocatalytic activity was synthesized via a two-step chemical solution method and used for the photocatalytic degradation of organic dye. The structure, morphology, composition, optical and photocatalytic properties of the as-prepared samples were investigated in detail. The results suggested that the Cu2O/TiO2 nanocomposite is composed of hierarchical TiO2 hollow microstructure coated by a great many Cu2O nanoparticles. The photocatalytic performance of Cu2O/TiO2 nanocomposite was evaluated by the photodegradation of methylene blue (MB) under visible light, and compared with those of the pure TiO2 and Cu2O photocatalysts synthesized by the identical synthetic route. Within 120 min of reaction time, nearly 100% decolorization efficiency of MB was achieved by Cu2O/TiO2 photocatalyst, which is much higher than that of pure TiO2 (26%) or Cu2O (32%). The outstanding photocatalytic efficiency was mainly ascribed to the unique architecture, the extended photoresponse range and efficient separation of the electron-hole pairs in the Cu2O/TiO2 heterojunction. In addition, the Cu2O/TiO2 nanocomposite also retains good cycling stability in the photodegradation of MB.

A series of Zn(II) terpyridine complexes with enhanced two-photon-excited fluorescence for in vitro and in vivo bioimaging

Co-reporter:Qiong Zhang, Xiaohe Tian, Zhangjun Hu, Caroline Brommesson, Jieying Wu, Hongping Zhou, Shengli Li, Jiaxiang Yang, Zhaoqi Sun, Yupeng Tian and Kajsa Uvdal

Journal of Materials Chemistry A 2015 - vol. 3(Issue 36) pp:NaN7221-7221

Publication Date(Web):2015/08/06

DOI:10.1039/C5TB01185J