Direct thermal oxidization evaporation growth, structure, and optical properties of single-crystalline nanobelts of moly
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N. Zhang Department of Physics, Tsinghua University, Beijing 100084, People’s Republic of China; and Tsinghua-Foxconn Nanotechnology Research Center, Beijing 100084, People’s Republic of China
H.F. Wang National Center for Nanoscience and Technology of China, Beijing 100084, People’s Republic of China
Z.H. Han Tsinghua-Foxconn Nanotechnology Research Center, Beijing 100084, People’s Republic of China
D. Han National Center for Nanoscience and Technology of China, Beijing 100084, People’s Republic of China
Q.Q. Li Tsinghua-Foxconn Nanotechnology Research Center, Beijing 100084, People’s Republic of China; and Department of Physics, Tsinghua University, Beijing 100084, People’s Republic of China
S.S. Fan Department of Physics, Tsinghua University, Beijing 100084, People’s Republic of China; and Tsinghua-Foxconn Nanotechnology Research Center, Beijing 100084, People’s Republic of China (Received 27 October 2006; accepted 20 February 2007)
Single-crystalline nanobelts of molybdenum trioxides were grown by direct thermal oxidization evaporation of metal molybdenum foils. Their structures, defects, and optical properties were investigated via x-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), atomic force microscopy, micro-Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and ultraviolet-visible spectroscopy (UV-VIS). Single-crystalline nanobelts were identified as an orthorhombic structure with an average stoichiometry of MoO3.02 analyzed by energy dispersive spectroscopy of x-rays. The length, width, and thickness of a nanobelt were determined to be parallel to the b, c, and a axis of the MoO3 unit cell, respectively. The thickness of the nanobelt increased by integer multiples of 0.5a in a layer-by-layer fashion during growth. A density of dislocations as high as about 1.2 × 1013 cm−2 was formed, which may be attributed to relaxation of large strains during cooling. A special dislocation configuration was observed by HRTEM, which was well reproduced by image simulations based on the proposed model. The resulting morphology of nanobelts was proposed to be governed by growth kinetics. Micro-Raman and FTIR spectra were successfully analyzed on the basis of vibration of MoO6 octahedra. It was found that micro-Raman spectra were quite dependent on the size of the nanobelts. A band gap energy of 3.04 eV derived from UV-VIS measurements was observed to be red shifted relative to the previously reported experimental values, which may be due to the presence of a high density of defects.
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0217 J. Mater. Res., Vol. 22, No. 6, Jun 2007
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W.G. Chu et al.: Direct thermal oxidization evaporation growth, structure, and optical properties of single-crystalline nanobelts of MoO3
I. INTRODUCTION
Molybdenum trioxide (MoO3) receives i
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