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Nitrogen ion bombardments in SrTiO₃ for enhanced photocatalysis

Tao Sun

Department of Optical Science and Engineering, Fudan University

Abstract

Strontium titanate (SrTiO₃ or STO) is a prototype of perovskites [1], which has found applications in fields such as oxide electronics as a substrate material [2, 3], and environmental protection [4-6] and hydrogen production [7-9] as a photocatalyst. When used as a photocatalyst, STO absorbs only ultraviolet (UV) lights due to its large bandgap width of 3.2 eV [10]. In order to expand the wavelength range of the available light, efforts have been made, including doping transition metal cations such as Rh [7], Cr [11], Mo [12], and Fe [13] into Ti sites. However, anion doping into O sites for visible-light photocatalysis in STO has been relatively less investigated due to the difficulty of material synthesis [14]. Substitutions of O ions by anions especially nitrogen ions in perovskite oxides have been considered to be a promising approach to modify the bandgap of perovskites [14-17]. Low-energy ion bombardments of solid surfaces have been employed to modify properties of the materials by tuning the composition and microstructure of the surface region [18, 19]. Low-energy Ar⁺ ion bombardments of STO have been reported for observation of blue-light emission at the room temperature [20-22]. Diwald et al. [23] investigated the photochemistry in rutile TiO₂ bombarded by nitrogen ions of 3 keV, and an unexpected blueshift of the photodesorption curve for the nitrogen doped sample as compared to the pure crystalline TiO₂ was reported. However, how nitrogen ion bombardment influences the photocatalytic activity of STO has not been well understood so far. Here, we reported the photocatalytic responses of STO(100) that had been bombarded with 1.5 keV nitrogen ions. It is found that the visible-light photocatalysis as well as the UV one in nitrogen-ion bombarded STO were significantly enhanced as compared to the pure STO. Change in absorptivity of a methylene blue (MB) solution loaded with STO has been used to evaluate the photocatalytic ability of STO. UV-visible absorption spectroscopy, X-ray photoelectron spectroscopy, cross-sectional transmission electron microscopy, and atomic force microscopy measurements were performed to explore the origin of the photocatalysis enhancements. The enhancement of visible-light photocatalysis in nitrogen-ion bombarded STO could be attributed to the nitrogen ion doping that causes the bandgap narrowing; while the enhancement of UV photocatalysis is due to generation of defects at the surface region, which act as additional dissociative absorption sites.

References

1.    P.A. Cox, Transition Metal Oxides (Clarendon Press, Oxford, 1995)

2.    C. Cen, S. Thiel, J. Mannhart, J. Levy, Science 323, 1026 (2009)

3.    A.F. Santander-Syro, O. Copie, T. Kondo, F. Fortuna, S. Pailhes, R. Weht, X.G. Qiu, F. Bertran, A. Nicolaou, A. Taleb-Ibrahimi, P. Le Fevre, G. Herranz, M. Bibes, N. Reyren, Y. Apertet, P. Lecoeur, A. Barthelemy, M.J. Rozenberg, Nature 469, 189 (2011)

4.    T. Sun, M. Lu, Appl. Phys. A 108, 171 (2012)

5.    A. Bhardwaj, N.V. Burbure, A. Gamalski, G.S. Rohrer, Chem. Mater. 22, 3527 (2010)

6.    U. Sulaeman, S. Yin, T. Sato, Appl. Catal. B: Environ. 105, 206 (2011)

7.    K. Iwashina, A. Kudo, J. Am. Chem. Soc. 133, 13272 (2011)

8.    Y. Sasaki, A. Iwase, H. Kato, A. Kudo, J. Catal. 259, 133 (2008)

9.    J. Shi, S. Shen, Y. Chen, L. Guo, S.S. Mao, Opt. Exp. 20, A351 (2012)

10.  A. Kudo, Y. Miseki, Chem. Soc. Rev. 38, 253 (2009)

11.  P. Reunchan, N. Umezawa, S. Ouyang, J. Ye, Phys. Chem. Chem. Phys. 14, 1876 (2012)

12.  X. Qiu, M. Miyauchi, H. Yu, H. Irie, K. Hashimoto, J. Am. Chem. Soc. 132, 15259 (2010)

13.  T.H. Xie, X. Sun, J. Lin, J. Phys. Chem. C 112, 9753 (2008)

14.  A. Fuertes, J. Mater. Chem. 22, 3293 (2012)

15.  A. Mukherji, B. Seger, G.Q. Lu, L. Wang, ACS Nano 5, 3483 (2011)

16.  T. Onishi, Top. Catal. 53, 566 (2010)

17.  J. Wang, S. Yin, M. Komatsu, Q. Zhang, F. Saito, T. Sato, J. Photochem. Photobiol. A: Chem. 165, 149 (2004)

18.  M. Lu, B.N. Makarenko, Y.Z. Hu, J.W. Rabalais, J. Chem. Phys. 118, 2873 (2003)

19.  H. Gnaser, Low-energy Ion Irradiation of Solid Surfaces (Springer-Verlag, Berlin, 1999)

20.  D. Kan, T. Terashima, R. Kanda, A. Masuno, K. Tanaka, S. Chu, H. Kan, A. Ishizumi, Y. Kanemitsu, Y. Shimakawa, M. Takano, Nat. Mater. 4, 816 (2005)

21.  Z.H. Li, H.T. Sun, Z.Q. Xie, Y.Y. Zhao, M. Lu, Nanotechnology 18, 165703 (2007)

22.  H. Yasuda, Y. Yamada, T. Tayagaki, Y. Kanemitsu, Phys. Rev. B 78, 233202 (2008)

23.  O. Diwald, T.L. Thompson, E.G. Goralski, S.D. Walck, J.T. Yates, Jr., J. Phys. Chem. B 108, 52 (2004)

Growth of aligned ZnO nanorod arrays  on different condition by aqueous

                         Yang Qin

Abstract:

     Zinc oxide (ZnO) is a fascinating material with versatile properties which are suitable for high-technology such as light emitting diodes, photodetectors, photodiodes, optical modulator waveguides, chemical and bio sensors,solar cells and so on owing to its wide band gap, chemical and thermal stability, electronic, optoelectronic and piezoelectric properties.ZnO also has a great diversity in structural morphology, probably the richest family of nanostructures among all materials both in structural and properties viewpoints. Therefore, it has received broad attention from scientists, which has led to the publication of thousands of research papers and hundreds of patents. ZnO could be one of the most important materials for future research and applications.

     Morphology controlled ZnO nanorod arrays were prepared on pre-coated substrates by aqueous approach under different conditions. The effect of substrate treatment, precursor concentration, growing temperature and growing time were studied mainly by scanning electron microscopy. It is demonstrated that the morphology of ZnO nanorods were varied with different substrate, different precursor concentration, different growing temperature and different growing time. Annealing, precursor concentration, growing temperature and growing time, all of them can increase the dimension of the rod diameter. They also can increase the length of the rod, especially with respect to the growing time.

Reference:

[1] Yoon.-Bong Hahn. (2011). "Zinc oxide nanostructures and their applications." Review.

[2] Teng Ma, M. G., Mei Zhang, Yanjun Zhang and Xidong Wang (3 January 2007). "Density-controlled hydrothermal grpwth of well-aligned ZnO nanorod arrays." Nanotechnology 18(035605): 7.

[3] Jaejin Song, Sangwoo Lim, "Effect of seed layer on the growth of ZnO nanorods",

J.Phys. Chem. C 2007, 111, 596-600

[4] Dongxu Zhao, Caroline Andreazza, Pascal Andreazza etc. "Buffer layer effect on ZnO nanorods growth alignment", Chemical Physics Letters 408(2005)335-338

[5] Min Guo, Peng Diao, Shengmin Cai, "Hydrothermal growth of well-aligned ZnO nanorod arrays: Dependence of morphology and alignment ordering upon preparing conditions", Journal of Solid State Chemistry 178(2005) 1864-1873

[6] Dong Chan Kim, Bo Hyun Kong, Hyung Koun Cho etc. "Effects of buffer layer thickness on growth and properties of ZnO nanorods grown by metalorganic chemical vapour deposition", Nanotechnology

[7] Yinglei Tao, Ming Fu, Ailun Zhao, Dawei He etc. "The effect of seed layer on morphology of ZnO nanorod arrays grown by hydrothermal method", Journal of Alloys and Compounds 489(2010)99-102

[8] N. Gopalakrishnan, L.Balakrishnan, K. Latha etc. "Influence of substrate and film thickness on structural, optical and electrical properties of ZnO thin films", Cryst. Tes. Technol. 46, No. 4, 361-367(2011)

[9] Teng Ma, Min Guo, Mei Zhang etc. "Density-controlled hydrothermal growth of well-aligned ZnO nanorod arrays", Nanotechnology 18(2007)035605(7pp)

[10] H.Ghayour, H.R. Rezaie, Sh. Mirdamadi, A.A. Nourbakhsh, "The effect of seed layer thickness on alignment and morphology of ZnO nanorods", Vacuum 86(2011)101-105

Er,Yb fiber laser resonantly pumped 1.6 μm

 Er:YAG Ceramic Lasers

Yong Wang

Department of Optical Science and Engineering, Fudan University

Abstract

Lasers operating at ~1.6 μm have numerous applications in remote sensing, free space communication, and mid-infrared radiation generation at 3-5 μm regions. This wavelength region lasers are eye-safe since the laser light is absorbed at the cornea part to prevent it from injuring the retina. Various technologies are adoptted to demontrate the laser radition at ~1.6 μm wavelength region, e.g. 1 μm laser pumped OPOs, 976 nm laser diode pumped Er,Yb glass with bulk or fiber geometry, in-band pumped Er³⁺-doped solid-state lasers, and so on. With the development of laser diode technology and the fiber laser technology, in-band pumped erbium ion singly doped solid-state lasers have exhibited prominent advantages, such as high quantum efficiency, simple laser architecture.

Transparent ceramics doped with rare-earth elements have drawn great attention in recent years as new laser gain media due to a number of important advantages over single crystals, including rapid and large volume fabrication, extreme flexibility in doping concentration, profile and sample structure, etc. With the progress in fabrication technology, Nd- and Yb-doped optical quality YAG ceramics are now routinely available with essentially the same lasing efficiency as that of the sigle crystals. While the majority efforts have been focused on Nd- and Yb-doped ~1 μm ceramic lasers, ceramics with other dopants (Tm, Ho and Er) have begun to draw attentions. Ceramic-based laser operation at this wavelength region was first demonstrated with liquid-nitrogen-cooled polycrystalline Er:Sc₂O₃ and Er:Y₂O₃ ceramics. An by far the most commonly used laser gain host, YAG has many unique properties that favor laser operation. The fabrication and spectra characterization of a YAG ceramic with high Er concentrations were reported and laser oscillation at 2.94 μm was demonstrated. It was not until recent years that efficient laser oscillation at 1.65 μm was demontrated for an Er:YAG ceramic that structured composite, and ~6.8 W of quai-CW output power has been generated with a slope efficiency of 56.9% with respect to the absorbed pump power.

In this presentation, I will firstly give a brief overview about ~1.6 μm wavelength region lasers and the polycrytalline tranparent ceramics. In th body part of this talk, 1532 nm Er, Yb fiber laser resonantly pumped Er:YAG ceramic laser will be discussed, and in-band pumping technology and its advantages will be presented at the same time. Then, Er:YAG ceramic laser operating at 1617 nm will be used as the pump source of Tm:YAG ceramic laser to generate 2 μm radiation. With this ceramic material, the scattering loss of the Tm:YAG ceramic is estimated to be 0.36%cm^-1.

References

[1] A. Ikesue and Y. L. Aung, “Ceramic laser materials,” Nat. Photon. 2, 721 (2008).

[2] J. Wisdom, M. Digonnet, and R. L. Byer, “Ceramic lasers: ready for action,” Photonics Spectra 38, 2 (2004).

[3] T. Taira, “RE³⁺-doped YAG ceramic lasers,” IEEE J. Sel. Top. Quantum Electron. 13, 798 (2007).

[4] A. Pirri, D. Alderighi, G. Toci, and M. Vannini, “High-efficiency, high-power and low threshold Yb³⁺:YAG ceramic laser,” Opt. Express 17, 23344 (2009).

[5] M. Dubinskii, N. Ter-Gabrielyan, L. D. Merkle, G. A. Newburgh, “First laser performance of Er³⁺-doped scandia (Sc₂O₃) ceramic,” Proc. of SPIE 6952, 69520O (2008).

[6] N. Ter-Gabrielyan, L. D. Merkle, G. A. Newburgh, and M. Dubinskii, “Resonantly pumped Er³⁺:Y₂O₃ ceramic laser for remote CO₂ monitoring,” Laser Phys. 19, 867 (2009).

[7] N. Ter-Gabrielyan, L. D. Merkle, E. R. Kupp, G. L. Messing, and M. Dubinskii, “Efficient resonantly pumped tape cast composite ceramic Er:YAG laser at 1645 nm,” Opt. Lett. 35, 922 (2010).

[8] D. Y. Shen, H. Chen, X. P. Qin, J. Zhang, D. Y. Tang, X. F. Yang, and T. Zhao, “Polycrystalline ceramic Er:YAG laser in-band pumped by a high-power Er, Yb fiber laser at 1532 nm,” Appl. Phys. Express 4, 052701 (2011).

[9] X. F. Yang, D. Y. Shen, T. Zhao, H. Chen, J. Zhou, J. Li, H. M. Kou, Y. B. Pan, “In-band pumped Er:YAG ceramic laser with 11 W of output power at 1645 nm,” Laser Phys. 21, 1013 (2011).

[10] C. Zhang, D. Y. Shen, Y. Wang, L. J. Qian, J. Zhang, X. P. Qin, D. Y. Tang, X. F. Yang, T. Zhao, “High-power polycrystalline Er:YAG ceramic laser at 1617 nm,” Opt. Lett. 36, 4767 (2011).

[11] S. D. Setzler, M. P. Francis, Y. E. Young, J. R. Konves, and E. P. Chicklis, “Resonantly pumped eyesafe Erbium lasers,” IEEE J. Sel. Top. Quantum Electron. 11, 645 (2005).

[12] Y. Wang, D. Y. Shen, H. Chen, J. Zhang, X. P. Qin, D. Y. Tang, X. F. Yang, T. Zhao, “Highly efficient Tm:YAG ceramic laser resonantly pumped at 1617 nm,” Opt. Lett., 36, 4485(2011).