Structural and Optical Properties of ZnO Nanorods Thin Films Prepared by Hydrothermal Method and Effect of growth time
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This paper describes, Synthesis of zinc oxide nanorods (ZnO NRs) using hydrothermal technique at different growth time. The structural and morphological properties were characterized by X-ray diffraction (XRD), Energy Dispersive X-Ray (EDX) and Field Emission Scanning Electron Microscope (FE-SEM). The ZnO NRs were obvious hexangular wurtzite structure and preferentially oriented along the c-axis (002) and growth vertically to the substrates. The optical properties were studied. From UV-Visible spectrophotometer and Photoluminescence (PL), the optical band gap energy of all ZnO NRs samples (S1, S2 and S3) were calculated to be (3.425 eV, 3.4 eV, 3.425 eV) respectively. Also, the effect of growth time on ZnO nanorods was studied.Keywords:
Wurtzite crystal structure
Nanorod
Field emission microscopy
Hydrothermal Synthesis
1-D Ga2O3-GaN core-shell nanorods were successfully fabricated by two-step synthesis processes. The Ga2O3 nanorods were synthesized by the reaction of Ga with SiO2 at 600{degree sign}C. Subsequently, one dimensional Ga2O3-GaN core-shell nanorods were successfully achieved by nitrifying the as-synthesized Ga2O3 nanorods under ammonia ambient at 700{degree sign}C for 6 hours. The field-emission scanning electron microscope (FESEM, JSM- 6500F), X-ray spectrometer (SHINMADZU), and the field-emission transmission electron microscope (FETEM, JEM-3000F) were utilized to investigate the morphologies, crystal structures, and compositions of nanorods in detail, respectively. Furthermore, optical investigation of Ga2O3-GaN coaxial nanorods heterostructures was carried out by photoluminescence (PL) measurements in present study.
Nanorod
Field emission microscopy
Coaxial
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Using FeSO4 x 7H2O and H2O2 as raw materials, a facile route to selective synthesis of alpha-FeOOH and alpha-Fe2O3 nanorods was developed by adjusting the reaction temperature in hydrothermal synthesis. Without undergoing calcinations, the obtained alpha-FeOOH nanorods (at 150 degrees C) and alpha-Fe2O3 nanorods (at 200 degrees C) possess high morphological yield (> 95%). The influences of synthesis conditions such as H2O2, hydrothermal temperature and hydrothermal time were investigated. The formation process of alpha-FeOOH and alpha-Fe2O3 nanorods was discussed in detail, and a possible temperature-controlled selective synthesis mechanism was proposed.
Nanorod
Hydrothermal Synthesis
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The structural and field emission properties of ZnO nanorod at different growth time by sol-gel method have been successfully prepared. FESEM results illustrated that dense ZnO nanorods with hexagonal wurtzite structure were vertically well-aligned and uniformly distributed on the substrate. X-ray diffraction pattern analysis shows that all the obtained ZnO nanorods can be indexed to the hexagonal ZnO wurtzite structure. Field emission measurement was conducted for ZnO nanorod growth at different time to study emission properties. The turn-on field value decreases while field enhancement value increases as longer growth time was applied which related to the increasing of aspect ratio of ZnO nanorod respectively.
Nanorod
Wurtzite crystal structure
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The self-consistent electronic band structures for zincblende and wurtzite BeO are calculated using first-principles pseudopotentials. The calculated direct band gap for wurtzite BeO is consistent with experimental measurement, and the valence-band width is also in good agreement with experiment; however, the value for the forbidden band gap is underestimated. For the hypothetical zincblende compound, an indirect band gap is found. The authors present the band structure, density of states and the valence charge density in a (110) plane for both crystal structures.
Wurtzite crystal structure
Quasi Fermi level
Density of states
Wide-bandgap semiconductor
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Nanorod
Hydrothermal Synthesis
Titanium Dioxide
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The direct to indirect band gap transition in ultrathin [0001] ZnO nanowires with the structural transformation from the regular wurtzite structure to a more close-packed hexagonal structure during uniaxial compression is studied by using the first-principles calculations. The results show that all ZnO nanowires exhibit direct band gap in wurtzite structure and indirect band gap in hexagonal structure. For the same wire the band gap in hexagonal structure is smaller than that in wurtzite structure. The origin of the band gap transition from direct to indirect one is discussed.
Wurtzite crystal structure
Wide-bandgap semiconductor
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The pressure dependence of the optical absorption edge of InN is investigated. Owing to the strong nonparabolicity of the energy bands, wurtzite InN exhibits enhanced optical absorption well above the absorption edge. The direct band gap of wurtzite InN increases linearly with pressure at 29±1 meV/GPa. The wurtzite-to-rocsksalt phase transition is observed at 15.3±0.5 GPa as a clear change in the absorption edge. We find that rocksalt InN is an indirect semiconductor with a band gap energy of around 1.0 eV. A higher energy direct transition is found at ∼2 eV. These results are discussed in terms of theoretical band-structure calculations.
Wurtzite crystal structure
Absorption edge
Hydrostatic pressure
Wide-bandgap semiconductor
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We have simulated the heating process of gold nanorods, elucidating a mechanism by which nanorods alter their aspect ratio at higher temperatures. We also studied the relative stabilities of nanorods by constructing nanorods with varying ratios of {110} to {100} exposed surfaces along the body of the nanorod. The least stable nanorod was found to be the nanorod with the largest {110} surfaces, followed by the nanorod with the largest {100} surfaces, while the nanorod with approximately equal surface areas of {100} and {110} surface was found to be the most stable. It was also found that the addition of surface disorder increased the stability of nanorods with large {110} surfaces, while paradoxically decreasing the stability of nanorods with large {100} surfaces. The reasons for this are elucidated and compared to experimental laser-induced gold nanorod transformation studies.
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Two-step growth technology to successfully synthesize scallion-root-shaped GaN nanorods was presented in this paper. This growth method is applicable to continuous synthesis a large number of single-crystalline GaN nanorods with a high purity at a low cost. X-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) are employed to characterize the structure, composition and morphology of as-grown GaN nanorods. The results show that the obtained nanorods are single-crystal GaN with hexagonal wurtzite structure and have a relatively high purity. The diameter of the nanorods is about 500nm with length up to several tens of micrometers. The representative photoluminescence spectra (PL) measured at room temperature exhibited a strong and broad emission peak at 388nm corresponding to the strong-band-emission in wurtzite GaN, indicating that the nanorods have a good emission property. The growth mechanism is also briefly discussed.
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Wurtzite crystal structure
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