The structural and optical properties of ZnO nanorod arrays

High quality vertical-aligned ZnO nanorod arrays were synthesized by a simple vapor transport process on Si (111) substrate at a low temperature of 520 °C. Field-emission scanning electron microscopy (FESEM) showed the nanorods have a uniform length of about 1 μm with diameters of 40-120 nm. X-ray diffraction (XRD) analysis confirmed that the nanorods are c-axis orientated. Selected area electron diffraction (SAED) analysis demonstrated the individual nanorod is single crystal. Photoluminescence (PL) measurements were adopted to analyze the optical properties of the nanorods both a strong UV emission and a weak deep-level emission were observed. The optical properties of the samples were also tested after annealing in oxygen atmosphere under different temperatures, deep-level related emission was found disappeared at 600 °C. The dependence of the optical properties on the annealing temperatures was also discussed.     

Photoluminescence and optical characterization of CdS nanoparticles prepared by solid-state method at low temperature

The photoluminescence (PL) and optical properties of CdS nanoparticles prepared by the solid-state method at low temperature have been discussed. The effects of NaCl and anionic surfactant SDBS (sodium dodecylbenzene sulfonate) on the luminescent properties of CdS nanophosphors prepared using this method, without the inert gas or the H₂S environment, were studied separately. The synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM), and energy dispersive X-ray spectroscopy (EDAX). UV–VIS absorption and PL spectra were also studied. XRD studies confirmed the single-phase formation of CdS nanoparticles. TEM micrograph revealed the formation of nearly spherical nanoparticles with a diameter of 2.5 nm. The PL emission for the CdS shows the main peak at 560 nm with a shoulder at 624 nm, with an increase in the PL intensity after the addition of SDBS. The effect of Mn doping on PL intensity has also been investigated. The PL spectra show that the emission intensity decreases as the dopant concentration increases.     

Alignment-controlled hydrothermal growth of well-aligned ZnO nanorod arrays

ZnO nanorod arrays (ZNAs) were prepared via a two-step seeding and solution hydrothermal growth process. Effects of preparing parameters such as seed layer, colloid concentration, substrate and precursor concentration, on the alignment control of ZNAs were systematically investigated. The deviation angle of ZnO nanorods was measured to evaluate the alignment of arrays. Results show that seed layer not only controls the vertical orientation of ZNAs, but also the compactness of ZNAs. Altering colloid concentration and substrate can influence the microstructure of ZnO seed layer and affect the ordered alignment of ZNAs. The precursor concentration has an insignificant effect on the alignment of ZNAs but has great impact on the morphology of ZNAs. Alignment-controlled and well-aligned ZnO nanorods with different diameter and aspect ratio can be obtained by properly controlling the preparing parameters. A growth mechanism was proposed for the growth of ZnO nanorods.     

A study on morphology control and optical properties of ZnO nanorods synthesized by microwave heating

In this study, we present morphology control investigations on zinc oxide (ZnO) nanorods synthesized by microwave heating of a mixture of zinc nitrate hexahydrate and hexamethylenetetramine (HMTA) precursors in deionized water (DI water). To study the morphology and structural variations of the obtained ZnO nanorods in different molar ratio of zinc nitrate hexahydrate to HMTA, X-ray diffraction (XRD), scanning electron microscopy (SEM) images, Raman scattering, and photoluminescence (PL) spectroscopy were measured. XRD and SEM images are utilized to examine the crystalline quality as well as the morphological properties of the ZnO nanorods. It is found that morphology control can be achieved by simply adjusting the reactant concentrations and the molar ratio of zinc nitrate hexahydrate to HMTA. Raman scattering and PL spectroscopy measurements were demonstrated to study the size- and shape-dependent optical response of the ZnO nanorods. The Raman scattering result shows that the intensity of LO mode at around 576 cm^?1 decreases with the increase in the molar ratio of zinc nitrate hexahydrate to HMTA, indicating the reduction of defect concentrations in the synthesized ZnO nanorods. Room temperature PL spectrum of the synthesized ZnO nanorods reveals an ultraviolet (UV) emission peak and a broad visible emission. An enhancement of UV emission appears in the PL spectra as the molar ratio of zinc nitrate hexahydrate to HMTA increases, indicating that the defect concentration of the synthesized ZnO nanorods can be reduced by increasing the molar ratio.     

Effect of annealing temperature and annealing atmosphere on the structure and optical properties of ZnO thin films on sapphire (0 0 0 1) substrates by magnetron sputtering

ZnO thin films were epitaxially grown on sapphire (0 0 0 1) substrates by radio frequency magnetron sputtering. ZnO thin films were then annealed at different temperatures in air and in various atmospheres at 800 °C, respectively. The effect of the annealing temperature and annealing atmosphere on the structure and optical properties of ZnO thin films are investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL). A strong (0 0 2) diffraction peak of all ZnO thin films shows a polycrystalline hexagonal wurtzite structure and high preferential c-axis orientation. XRD and AFM results reveal that the better structural quality, relatively smaller tensile stress, smooth, uniform of ZnO thin films were obtained when annealed at 800 °C in N₂. Room temperature PL spectrum can be divided into the UV emission and the Visible broad band emission. The UV emission can be attributed to the near band edge emission (NBE) and the Visible broad band emission can be ascribed to the deep level emissions (DLE). By analyzing our experimental results, we recommend that the deep-level emission correspond to oxygen vacancy (V_O) and interstitial oxygen (O_i). The biggest ratio of the PL intensity of UV emission to that of visible emission (I_NBE/I_DLE) is observed from ZnO thin films annealed at 800 °C in N₂. Therefore, we suggest that annealing temperature of 800 °C and annealing atmosphere of N₂ are the most suitable annealing conditions for obtaining high quality ZnO thin films with good luminescence performance.     

Characterization and optical property of ZnO nano-, submicro- and microrods synthesized by hydrothermal method on a large-scale

In the present paper, well-dispersed ZnO nano-, submicro- and microrods with hexagonal structure were synthesized by a simple low temperature hydrothermal process from zinc nitrate hexahydrate without using any additional surfactant, organic solvent or catalytic agent. The phase and structural analysis were carried out by X-ray diffraction (XRD), the morphological analysis was carried out by field emission scanning electron microscopy (FESEM) and the optical property was characterized by room-temperature photoluminescence (PL) spectroscopy. The results revealed the high crystal quality of ZnO powder with hexagonal (wurtzite-type) crystal structure and the formation of well-dispersed ZnO nano-, submicro- and microrods with diameters of about 50, 200 and 500 nm, and lengths of 300 nm, 1 μm and 2 μm, respectively, on a large-scale just using the different temperatures. Room-temperature PL spectrum from the ZnO nanorods reveals a strong UV emission peak at about 360 nm and no green emission band at ∼530 nm. The strong UV photoluminescence indicates the good crystallization quality of the ZnO nanorods. Room-temperature PL spectra from the ZnO submicro- and microrods reveal a weak UV emission peak at ∼400 nm and a very strong visible green emission at 530 nm, that is ascribed to the transition between V_oZn_i and valence band.     

Thickness effect on the evolution of morphology and optical properties of ZnO films

N-Al co-doped ZnO films with various thicknesses were deposited on glass substrates by ultrasonic spray pyrolysis (USP). The crystalline microstructure, morphology, distribution of elements and photoluminescence properties of ZnO films were characterized by X-ray diffraction (XRD), field emission scanning microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and photoluminescence (PL) spectroscopy. The XRD and FESEM results show that with the increase of film thickness the grain size increases and the grain shape changes from regular hexagonal sheet-like to wedge-shaped, even pyramidal. The PL spectra illustrate that there is an obvious red-shift for the emission center from ultraviolet to blue region, and the intensities of defects emissions increase with the increase of thickness. In addition, the electrical properties are proved to be strongly affected by film thickness.     

自支撑Ag掺杂ZnO花状纳米线阵列及其光学性质

利用简单、温和的二步水浴法制备一种大面积自支撑、可自由迁移的Ag掺杂ZnO花状纳米线阵列。通过场发射扫描电子显微镜（FESEM）、元素能谱（EDS）、X射线衍射谱（XRD）、室温和变温光致发光谱（PL）等一系列表征手段对所制备的自支撑Ag掺杂ZnO纳米线阵列进行了研究。研究结果显示：这种自支撑纳米材料具有良好的晶体质量和光学性质,在低温（85 K）下显示出A⁰X和FA为主导的受主相关发射峰,通过理论公式计算受主结合能为118 meV。在变温光致发光光谱中,FA发射峰位随温度的变化符合理论模型。     

较高浓度PbSe量子点硅酸盐玻璃的制备及光学表征

采用高温熔融-热处理法,以ZnSe作为PbSe量子点的硒源,成功制备了较高浓度的PbSe量子点硅酸盐玻璃。透射电子显微镜(TEM)测试表明,量子点在玻璃基质中的体积比高达2%～4%,高于采用Se作为硒源时的掺杂体积比。X射线衍射(XRD)测试表明,PbSe量子点呈立方晶体结构。光致发光(PL)光谱测试表明,量子点有强烈的荧光发射,发光波长半峰全宽(FWHM)覆盖1400～2600nm,其PL峰值强度和FWHM均大于以Se为硒源时的情形。以ZnSe代替Se作为PbSe量子点的硒源,可有效避免Se组分的高温挥发,同时,残余Zn形成的ZnO有利于玻璃中PbSe量子点的析晶,从而提高了PbSe量子点在玻璃中的含量。该PbSe量子点玻璃,可用来进一步制备成超带宽、高增益的红外光纤放大器。     

The effect of europium oxide impurity on the optical and physical properties of lithium potassium borate glass

The most hosts that is utilized in scientific application is borate glass. By using melt-quenching technique, five samples of lithium potassium borate (LKB) doped with different concentration of europium oxide (Eu₂O₃) were prepared. To investigate the influence of dopant on the optical and physical characteristics of the proposed glass, two methods have been applied (XRD, PL). The amorphous nature was confirmed by X-ray diffraction (XRD). The physical parameters of the glass matrix doped by different oxidation state have been analyzed, these parameters are density, molar volume, ion concentration, inter-nuclear distance, and polaron radius. The exchange in the concentration of Eu³⁺ indicated the influence of Eu as a dopant on the photoluminescence (PL) emission of LKB glasses. The emission spectrum of LKB:Eu³⁺ show a chain of emission bands, which are attributed to ⁵ D ₀-⁷ F _r (r = 1–4) transition of Eu³⁺. The luminescence studies showed four peaks 590 (yellow), 613 (orange), 650 (red), and 698 nm (red) for all samples except sample 0, the high luminescence efficiency is in emitting orange light at 613 nm.     

Structural and optical properties of nanocrystalline ZnO thin films synthesized by the citrate precursor route

Nanocrystalline zinc oxide (ZnO) thin films have been deposited by spin-coating polymeric precursors synthesized by the citrate precursor route using ethylene glycol and citric acid as chelating agents. The ZnO thin films were annealed in air at different temperatures for 10 min. The films were characterized by different structural and optical techniques, including X-ray diffraction (XRD), atomic force microscopy (AFM), optical transmission spectroscopy, and photoluminescence (PL). The thermal decomposition of polymeric precursor was studied by thermogravimetric analysis (TGA). XRD analysis with grazing incidence and rocking curves indicate that the ZnO films are polycrystalline with preferential orientation along the c-axis direction with a full-width at half-maximum (FWHM) of 0.31° for 600 °C-annealed samples. On annealing, the texturing in films increased along with a decrease in FWHM. AFM micrographs illustrate that the ZnO films are crack-free with well-dispersed homogeneous and uniformly distributed spherical morphology. The synthesized ZnO thin films have transparency >85% in the visible region exhibiting band edge at 375 nm, which becomes sharper with anneal. Room temperature PL spectra of these films show strong ultraviolet (UV) emission around 392 nm with an increase in intensity with annealing temperature, attributed to grain growth. Deconvolution of the PL spectra reveals that there is coupling of free excitons with higher orders of longitudinal optical (LO) phonon replicas leading to a broad asymmetric near-band-edge peak.     

Sol–gel derived zinc oxide films: Effect of deposition parameters on structure, microstructure and photoluminescence properties

ZnO films were prepared by sol–gel method and deposited onto glass substrates with spin coating system. XRD patterns and FESEM analysis were used to investigate the effect of deposition parameters such as spin speed and molar concentration on the crystallinity and surface morphology of the films. XRD patterns show that ZnO films are polycrystalline with type-wurtzite hexagonal structure. The film which is deposited at 4000 rpm and with 0.5 M sol has the best crystallinity. The FESEM micrographs showed that the surface morphology of the films was not significantly affected from the spin speed. FESEM micrographs showed that the crystallite sizes of 1000, 4000 and 5000 rpm are almost same. But 2000 and 3000 rpm have lower crystallite sizes than the others. Also, the amount of voids in the 1 M was found higher. The effect of spin speed and molar concentration on the optical properties of ZnO films was investigated by PL spectroscopy. The electrical properties of the ZnO films were investigated by using two probe methods in dark. The highest conductivity values were obtained for ZnO films prepared by 4000 spin speed and 0.5 M of concentration.     

Quenching of surface traps in Mn doped ZnO thin films for enhanced optical transparency

The structural and photoluminescence analyses were performed on un-doped and Mn doped ZnO thin films grown on Si (1 0 0) substrate by pulsed laser deposition (PLD) and annealed at different post-deposition temperatures (500-800 °C). X-ray diffraction (XRD), employed to study the structural properties, showed an improved crystallinity at elevated temperatures with a consistent decrease in the lattice parameter ‘c’. The peak broadening in XRD spectra and the presence of Mn 2p3/2 peak at ∼640 eV in X-ray Photoelectron Spectroscopic (XPS) spectra of the doped thin films confirmed the successful incorporation of Mn in ZnO host matrix. Extended near band edge emission (NBE) spectra indicated the reduction in the concentration of the intrinsic surface traps in comparison to the doped ones resulting in improved optical transparency. Reduced deep level emission (DLE) spectra in doped thin films with declined PL ratio validated the quenching of the intrinsic surface traps thereby improving the optical transparency and the band gap, essential for optoelectronic and spintronic applications. Furthermore, the formation and uniform distribution of nano-sized grains with improved surface features of Mn-doped ZnO thin films were observed in Field Emission Scanning Electron Microscopy (FESEM) images.     

Influence of Al concentration on electrical, structural and optical properties of Al-As codoped p-ZnO thin films

We report the influence of Al concentration on electrical, structural, optical and morphological properties of Al-As codoped p-ZnO thin films using RF magnetron sputtering. Al-As codoped p-ZnO films with different Al concentrations were fabricated using As back diffusion from the GaAs substrate and sputtering Al₂O₃ mixed ZnO targets (1, 2 and 4 at%). The grown films were investigated by Hall effect measurement, X-ray diffraction (XRD), electron probe microanalysis (EPMA), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and atomic force microscopy (AFM) to study the electrical, structural, optical and morphological properties of the films. From the XRD, it was observed that both full-width at half-maximum (FWHM) and c-axis lattice constant have similar trends with respect to Al concentration. Hall measurements showed that the hole concentration increases as the Al concentration increases from 10¹⁵ to 10²⁰ cm⁻³. The increase in hole concentration upon codoping was supported by the red shift in the near-band-edge (NBE) emission observed from room temperature PL spectra. The proposed p-type mechanism due to As_Zn-2V_Zn complex was confirmed by low temperature PL and XPS analysis. The low FWHM, resistivity and peak-to-valley roughness observed by XRD, Hall measurement and AFM, respectively, suggest that 1 at% Al-doped ZnO:As film is the best codoped film.     

Structural and optical properties of an InxGa1−xN/GaN nanostructure

The structural and optical properties of an In_xGa_1−xN/GaN multi-quantum well (MQW) were investigated by using X-ray diffraction (XRD), atomic force microscopy (AFM), spectroscopic ellipsometry (SE) and photoluminescence (PL). The MQW structure was grown on c-plane (0 0 0 1)-faced sapphire substrates in a low pressure metalorganic chemical vapor deposition (MOCVD) reactor. The room temperature photoluminescence spectrum exhibited a blue emission at 2.84 eV and a much weaker and broader yellow emission band with a maximum at about 2.30 eV. In addition, the optical gaps and the In concentration of the structure were estimated by direct interpretation of the pseudo-dielectric function spectrum. It was found that the crystal quality of the InGaN epilayer is strongly related with the Si doped GaN layer grown at a high temperature of 1090 °C. The experimental results show that the growth MQW on the high-temperature (HT) GaN buffer layer on the GaN nucleation layer (NL) can be designated as a method that provides a high performance InGaN blue light-emitting diode (LED) structure.     

Growth of In0.52Al0.48As on InP substrates by molecular beam epitaxy: some effects of V/III flux ratio variation

Growth of In_0.52Al_0.48As epitaxial layers on InP(100) substrates by molecular beam epitaxy at a wide range of arsenic overpressure (V/III flux ratio from 30 to 300) is carried out. Analysis performed using low-temperature photoluminescence (PL) and double-axis X-ray diffraction (XRD) showed a strong and prominent dependence of the PL and XRD linewidths on the V/III flux ratio. Under our growth conditions, both the PL and XRD linewidths exhibit a minimum point at a V/III flux ratio of 150 which corresponds to a maximum in the PL intensity and XRD intensity ratio. Flux ratios exceeding 150 results in an increase in both the PL and XRD linewidths corresponding to a reduction in their associated intensities. Room-temperature Raman scattering measurements show a narrowing in the InAs-like and AlAs-like longitudinal-optic (LO) phonon linewidths which broaden at high flux ratios, while the LO phonon frequencies exhibit a gradual reduction as the flux ratio is increased. PL spectrum taken at increasing temperature show a quenching of the main emission peak followed by the evolution of a broad lower energy emission which is possibly associated with deep-lying centres. This effect is more prominent in samples grown at lower V/III flux ratios. Hall effect measurements showed a gradual reduction in the mobility in correspondence to an increase in the electron concentration as the flux ratio is increased.     

Zn2 SnO4 立方体的水热合成及其荧光性质

利用水合肼作缓释型碱源和络合剂,采用水热法合成了Zn₂SnO₄立方多面体。XRD物相分析表明,产物为结晶良好的立方反尖晶石结构Zn₂SnO₄。FESEM和TEM形貌分析表明,该Zn₂SnO₄微晶为边长100~400 nm左右的立方体,其光致发光光谱是蓝-绿光发射带(中心590 nm处),在400 ℃空气气氛下退火1 h后,蓝-绿光发射带的强度显著降低。这主要是因为退火处理提高了晶体质量,降低了氧空位浓度,从而降低了可见光发射带的强度。     

Structural and electrical studies of template synthesized copper nanowires

The template strategy combined with electrodeposition technique has been used to produce copper nanowires in the cylindrical pores of track-etched polycarbonate membranes. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and UV–visible spectroscopy have been used to characterize as-prepared copper nanowires. XRD study shows the face centered cubic crystal structure of copper nanowires. Williamson–Hall (WH) analysis has been used to determine the crystallite size and microstrain induced due to lattice deformation. FESEM results reveal that copper nanowires are continuous, well aligned with uniform diameter and having high aspect ratio. The optical absorption spectra exhibit a strong peak at 568 nm attributed to the surface plasmon resonance. The current–voltage (I–V) characteristics show an ohmic behavior of the fabricated copper nanowires. The increase in resistivity of nanowires than that of bulk counterpart has been attributed to the surface and size effects in nanowires and explained in the light of Fuchs–Sondeimer and Mayadas–Shatzkes models.     

石英衬底上Au缓冲层对ZnO薄膜微结构的影响

采用单源化学气相沉积(SSCVD)法,在石英衬底上以Au为缓冲层,Zn4(OH)2(O2CCH3)6.2H2O为固相源制备ZnO薄膜。SEM和XRD测试ZnO薄膜的微结构,结果表明:相对于SiO2衬底上生长的ZnO薄膜,Au/SiO2衬底上生长的ZnO薄膜具有较好的结晶质量和表面平整度;对制备ZnO薄膜的衬底温度进行了工艺优化,结果表明:500℃时制备的ZnO薄膜颗粒大小均匀,结晶质量较好;通过荧光光谱仪对Au/SiO2衬底上的ZnO薄膜进行光致发光(PL)谱测试,ZnO薄膜在400nm出现紫光发射峰,而没有出现与缺陷相关的深能级发射峰,表明ZnO薄膜具有较好的结晶质量。     

Preparation and characterization of Mg-doped ZnO thin films by sol-gel method

Undoped and Mg-doped ZnO thin films were deposited on Si(1 0 0) and quartz substrates by the sol-gel method. The thin films were annealed at 873 K for 60 min. Microstructure, surface topography and optical properties of the thin films have been measured by X-ray diffraction (XRD), atomic force microscope (AFM), UV-vis spectrophotometer, and fluorophotometer (FL), respectively. The XRD results show that the polycrystalline with hexagonal wurtzite structure are observed for the ZnO thin film with Mg:Zn = 0.0, 0.02, and 0.04, while a secondary phase of MgO is evolved for the thin film with Mg:Zn = 0.08. The ZnO:Mg-2% thin film exhibits high c-axis preferred orientation. AFM studies reveal that rms roughness of the thin films changes from 7.89 nm to 16.9 nm with increasing Mg concentrations. PL spectra show that the UV-violet emission band around 386-402 nm and the blue emission peak about 460 nm are observed. The optical band gap calculated from absorption spectra and the resistivity of the ZnO thin films increase with increasing Mg concentration. In addition, the effects of Mg concentrations on microstructure, surface topography, PL spectra and electrical properties are discussed.