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ZnO nanoparticles doped with Co at different concentration (Zn1−xCoxO) were synthesized by sol–gel auto combustion method and are characterized by using various characterization tools. Structural study using X-ray diffraction technique (XRD) analysis showed the crystalline nature with hexagonal wurtzite geometry and the composition analysis using energy dispersive X-ray spectroscopy (EDX) confirmed the incorporation of Co in the ZnO lattice in the case of doped nanoparticles. Scanning electron-microscopy (SEM) and transmission electron microscopy (TEM) analysis showed the prepared nanoparticles as spherical, loosely agglomerated and having dimension of nanoscale. UV–vis DRS studies indicated a red shift in optical band gap with Co doping. PL spectra exhibits emission in the UV and visible region and the analysis revealed information about the presence of various types of defects in the ZnO lattice. An increase in the excitation wavelength gives intense emission in the high wavelength region for doped nanoparticles confirming the presence of divalent and monovalent oxygen as main defects. The Zn0.93Co0.07O nanoparticles records CIE coordinates lying in the white region of CIE color space at 350 nm with CCT of 5561.4 K suggesting their suitability in fabrication of white light emitting diodes. [ABSTRACT FROM AUTHOR]

The work aims to evaluate the impact of zinc oxide nanoparticles (ZnO-NPs) in the electroluminescence enhancement of organic light-emitting diodes (OLEDs). ZnO-NP was synthesized by using the sol-gel method. XRD, optical, and photoluminescence analysis indicate the average crystallite size of the ZnO-NP is 8.19 nm, exhibits a high energy band gap of 4.15 eV, and high luminescence at 530 nm. OLED performance analysis revealed that the ZnO-NP significantly improves the luminescence brightness and device efficiency by acting as an electron transport and hole-blocking layer, which promotes a high number of electron-hole accumulation in the emissive layer. [ABSTRACT FROM AUTHOR]

In the present work, dysprosium doped ZnO (DZO). nanoluminophores with different Dy concentrations are prepared by simple, one-step and mass-scale productive solid state reaction method. The structural, morphological and optical properties of synthesized Dy doped ZnO nanoluminophores have been characterized using X-ray diffraction (XRD) patterns, field emission scanning microscopy (FE-SEM), Fourier transfer infrared spectroscopy (FT-IR) and photoluminescence (PL) spectroscopy respectively. The XRD patterns of Dy-doped ZnO samples show hexagonal wurtzite structure having broadening in peaks indicates the formation of nano-sized structures. The estimated particle sizes of prepared samples are found to be in the range of ∼17–85 nm. The SEM micrographs indicate that the synthesized samples are spherical in natures and observed a change in their morphologies with Dy concentrations. FTIR results exhibit several absorption bands of ZnO:Dy nanoluminophores at room temperature. Photoluminescence spectra illustrate enhanced PL emission intensity of peaks at ∼391–397 nm in UV region and defects related green emissions ranging from ∼505–510 nm in visible region. The obtained results reveal the suitability of synthesized rare-earth (RE) doped ZnO nanoluminophores for optoelectronic devices.

Pure zinc oxide (ZnO) and Co and Mn co-doped ZnO nanoparticles were synthesized via a solution combustion technique. Structural, compositional, morphological, functional, optical, magnetization, and photoluminescence properties were examined. X-ray diffraction studies confirmed the hexagonal structure, and the average crystallite size of the synthesized samples was found to be around 20 to 30 nm. From the SEM analysis, all synthesized samples were spherical. Energy dispersion spectra confirm the presence of all selective elements in the synthesized samples. From UV-Vis spectra, we observed that there is decrease in band gap with increase in Co/Mn concentration. From photoluminescence (PL) studies, a decrease in the rate of recombination of electron-hole pair generation is observed. Experiments carried out using vibrating sample magnetometer studies revealed magnetic properties that indicate ferromagnetism in synthesized samples at room temperature. This material offers enormous potential to develop spintronics and optoelectronic materials due to its low cost and good yield. [ABSTRACT FROM AUTHOR]

Nano crystalline zinc sulfide thin films were deposited onto glass substrates by chemical bath deposition method. One of the samples was annealed at 300 °C for 2 h in air using a muffle furnace. The prepared thin films were investigated by X-ray diffraction (XRD), UV–visible spectroscopy (UV–vis), photoluminescence spectroscopy (PL), scanning electron microscopy (SEM) and Raman spectroscopy (FT-R) studies before and after annealing. The analysis confirmed the thermal-induced anion substitution and conversion of ZnS crystal to ZnO wurtzite crystal. XRD pattern showed that these films were phase pure and polycrystalline in nature. Optical band gap was found to be 3.86 eV for ZnS and 3.21 eV for ZnO. The films prepared by this simple, low-cost technique are suitable for photovoltaic and optoelectronic applications. [ABSTRACT FROM AUTHOR]

Abstract Impurities and surface hydroxyl groups play vital roles in tailoring the physicochemical properties of metal oxides. Herein, commercial ZnO nanocrystals (Sigma-Aldrich) were selected to trace the impurity and hydroxyl group evolution by temperature dependent photoluminescence spectrum, infrared spectrum and electron spin resonance spectrum. It is found that the structured Cu impurity emission in ZnO appeared when the temperature is down to 100 K. As thermal annealing reduced the donors significantly, the corresponding 5780 cm−1 and 5820 cm−1 IR peaks can be observed when the annealing temperature is above 600 °C. Further annealing at 800 °C increases the Cu2+ concentration as well as activates the diffusion of lithium impurity, both of which contribute to the visible luminescence. Besides, a group of IR peaks in the range of 3400–3700 cm−1 were found to be vanished after 800 °C thermal annealing, demonstrating their hydroxyl features rather than the previously proposed defect origin. [ABSTRACT FROM AUTHOR]

In this article, ZnO thin-film deposition on a glass substrate was done using microwave induced oxygen plasma based CVD system. The prepared thin-films were tested in terms of crystallinity and optical properties by varying the microwave power. The effect of power variation on the morphology and size of final products was carefully investigated. The crystal structure, chemical composition and morphology of the final products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy, Raman spectroscopy and photoluminescence (PL). This technique confirmed the presence of hexagonal ZnO nanocrystals in all the thin-films. The minimum crystallite grain size as obtained from the XRD measurements was ~9.7 nm and the average diameter was ~18 nm. [ABSTRACT FROM AUTHOR]

ZnO defect luminescence is a fascinating but still highly controversial issue. Herein, the role of interstitial oxygen played on the photoluminescence (PL) property of ZnO nanostructures is investigated through oxygen plasma exposure and low temperature O 2 annealing. In contrast to previous reports, no interstitial oxygen related deep level emission was observed in PL spectra from room temperature (RT) to 7 K after oxygen-rich treatments, except apparent suppression of the exciton emission due to the upward band bending effect. This work illustrates that the isolated interstitial oxygen seems not to cause the widely reported yellow/orange emission regardless of the ZnO growth method. [ABSTRACT FROM AUTHOR]

Research is described here that is directed toward obtaining p -type ZnO crystals either by doping or by creating native defects. Theoretically, zinc vacancies are shallow acceptors that should allow for p -type conduction. Bulk ZnO crystals can be grown by chemical vapor transport (CVT), melt solidification, and hydrothermal methods. Here we have explored annealing processes with the goal of creating zinc vacancies in bulk ZnO crystals. Positron annihilation spectra reveal the reproducible formation of high concentrations (>10 20 cm −3 ) of isolated zinc vacancies ( V Zn ) in oxygen-annealed, CVT-grown ZnO crystals in the ∼100–150 nm near-surface. Melt- and hydrothermally grown samples, in contrast, show insignificant levels of zinc vacancy creation. Photoluminescence (PL) emission spectra indicate a V Zn (0/-1) acceptor level at ∼ 155–165 meV; red PL (∼1.7 eV) emission, related to the V Zn (-1/-2) level, was also observed. Infrared absorption spectroscopy reveals the presence of a zinc vacancy complex with a hole binding energy range of 420–450 meV – and with a continuum suggesting a p -type region. XPS measurements support the deficiency of Zn after oxygen annealing the CVT-grown ZnO single crystal. [ABSTRACT FROM AUTHOR]

The effects of Al and Ti seed layers were studied for undoped and Fe-doped ZnO thin films deposited on n-type Si substrates by electron beam (e-beam) evaporation. The films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The films grown on seed layers showed wurtzite hexagonal crystal nanorod and nanowire structures. A higher angle phase shift was observed in the doped thin films compared to the pristine ZnO films. Microstructural studies confirmed the growth of nanorods and nanowires with average widths of ~32 nm and ~8–29 nm, respectively. The nanostructures were denser and more crystalline on the Al seed layer than on the Ti seed layer for the doped thin films. However, in the undoped thin films, a more crystalline nature was observed on the Ti seeded layer than the Al seeded layer. [ABSTRACT FROM AUTHOR]

Wurtzite ZnO films were grown on MgO(111) substrates by plasma-assisted molecular beam epitaxy (MBE). Different initial growth conditions were designed to monitor the film quality. All the grown ZnO films show highly (0001)-oriented textures without in-plane rotation, as illustrated by in situ reflection high-energy electron diffraction (RHEED) and ex situ X-ray diffraction (XRD). As demonstrated by atomic force microscopy (AFM) images, 'ridge-like' and 'particle-like' surface morphologies are observed for the ZnO films grown in a molecular O atmosphere with and without an initial deposition of Zn adatoms, respectively, before ZnO growth with oxygen plasma. This artificially designed interfacial layer deeply influences the final surface morphology and optical properties of the ZnO film. From room-temperature photoluminescence (PL) measurements, a strong defect-related green luminescence band appears for the ZnO film with a 'particle-like' morphology but was hardly observed in the films with flat 'ridge-like' surface morphologies. Our work suggests that the ZnO crystallinity can be improved and defect luminescence can be reduced by designing interfacial layers between substrates and epilayers. [ABSTRACT FROM AUTHOR]

ZnO nanoneedle clustered thin film with individual needles of length of 1000-1500 nm and diameter of around 100-200 nm were deposited on top of ZnO buffer layer coated indium doped tin oxide (ITO) glass substrate and quartz substrate by a facile solution process which is both cheap and has a low thermal budget. The microstructure of the as deposited thin films were characterized by scanning electron microscopy (SEM), whereas the x-ray diffraction (XRD) was used to determine the crystal structure in these nanoneedles. The optical characteristics of the thin films were obtained by determining the optical transmittance of the films at room temperature. The ZnO nanoneedle thin films had a bandgap of about 3.21 eV. The photoluminescence (PL) spectra obtained at room temperature confirmed the presence of defects related luminescence characterized by the broad PL peak centered at 2.1 eV. [ABSTRACT FROM AUTHOR]

This paper demonstrated the synthesis of p-type ZnO by high temperature annealing of zinc phosphate powder. Zinc phosphate pellets were annealed in programmable furnace with 140 sccm oxygen flow rate atvarious temperatures (500 to 1000 0C) for one hour. XRD data confirmed that Zinc Phosphate orthorhombic phase completely converted into Zinc Oxide hexagonal phase at annealing temperature 800C. It is argued that P-Zn bond was broken due to high temperature thermal annealing and oxygen atom gained enough thermal energy to replace the P atom in the lattice. Arrhenius plot (1000/T verses log resistivity) was drawn to calculate the dissociation energy of P-Zn bond which was found to greater than energy required to break P-Zn bond. PL data consists of neutral-acceptor emission of ZnO at 3.35 eV when annealed over 600C but un-annealed sample has not showed any PL peak. Hall measurements were demonstrated the hole carriers in the samples annealed at 800, 900 and 1000C. A representative Raman data measured at 8000C also verified the E2 (high) mode of ZnO along with p-related LVM at 342 cm-1. [ABSTRACT FROM AUTHOR]

In this work, we fabricate the p-type ZnO/AlN/ZnO core-shell nanowire arrays on Al2O3 substrate. The SEM images show the core-shell structure and the connection phenomenon appeared during the deposition process. The XRD results show a better crystal quality after annealing. The sample exhibits some unique properties after annealing treatment. Including the improvement of crystal quality and the shift of the PL emission peak. The low temperture PL spectra show a neutral acceptor bound exciton (A0X) emission (at 3.355 eV), and the emission at 3.325 eV is ascribe to the free electron to the acceptor transition (FA). The calculated result is found in good coincidence with the experiment. [ABSTRACT FROM AUTHOR]

In this study the effect of annealing environment on both low temperature and room temperature photoluminescence (PL) characteristics of ZnO nanorods, grown in solution, is presented. Particular attention is given to the effect of hydrogen defect passivation and its PL related line. It is shown that, irrespective of annealing ambient, an optimum annealing temperature of 300 °C suppresses the defect related emission and significantly improves the UV emission. By considering the stability of hydrogen impurities, the observed results in the PL spectra are analyzed. There is an observed asymmetric broadening on the low energy side of the bound exciton luminescence in the low temperature annealed samples which is explained by a high concentration of ionized impurities related to hydrogen. This has been attributed primarily to the conversion of hydrogen molecule to substitutional hydrogen on the oxygen site (H O ) as a result of annealing. [ABSTRACT FROM AUTHOR]

Un-doped and Neodymium (Nd)-doped zinc oxide (ZnO) thin films were deposited on glass substrates by spray pyrolysis experimental setup at 400 °C. The doping concentration of Nd is varied between 0.05 at.% and 0.25 at.%, in the spray solution. XRD studies confirmed the hexagonal wurtzite crystal structure of the deposited films irrespective of the variation in the Nd doping concentration. The SEM microstructures reveal that the average diameter of the Nd ring on the ZnO surface is ranging between 1.87 μm and 11.45 μm depending on the Nd doping concentration. EDS analysis confirmed the presence of Nd in the doped samples. Further, it is understood that Nd/Zn ratio in the deposited films is varied between 0.05 at.% and 0.25 at.%. The optical band gap is found to be ranging between 3.20 eV and 3.22 eV for the variation in Nd/Zn ratio from 0.05 at.% to 0.25 at.%. The PL of films is more intensive in UV region. Concentration of oxygen vacancy related defects and excitation wavelength in ZnO film were observed by PL studies. The green emission has been interpreted as the transition between singly charged oxygen vacancy and a photoexcited hole from PL studies. [ABSTRACT FROM AUTHOR]

ZnO is a wide band gap semiconductor and is very attractive because of its fundamental and technological importance. It is extensively used in research due to its properties viz. excellent chemical & thermal stability, large exciton binding energy, anti-corrosion and heat resistance. It is a promising material for optoelectronic devices in both UV and Visible regions. In the present investigation, ZnO nano powder was synthesized by single step Sol-gel technique using zinc acetate dihydrate as a precursor and ethanol as a medium. The synthesized ZnO nano powder was characterized using UV–Vis, FTIR, XRD, RAMAN, Photoluminescence (PL), Nano-particle size analyzer, SEM and EDX techniques. UV–Vis spectra gives intense peak at 372 nm wavelength showing the presence of absorption band due to ZnO nano powder. The chemical bonding among Zn and O can be clearly observed from FTIR spectrum. XRD spectra displays sharp peaks which indicates the crystalline nature of ZnO. It also shows homogeneity and size consistency of prepared nanoparticles. The crystallite size of ZnO nano powder were calculated using Scherrer's formula. The morphology and elemental analysis have been studied via SEM and EDX techniques. All the characterization results have been correlated with each other. [Display omitted] • The band gap energy for ZnO is approximately 3.3 eV (using UV–Visible) and 3.18 eV (using PL). • Raman peaks at 335 and 582 cm−1 confirms the structural defects present in ZnO nanopowders. • The average size of synthesized nanorods is 70.9 nm and of nanoflowers is 458.6 nm. • The average crystallite size of nano powder is 18.22 nm and bond length is 1.9798 Å (calculated from XRD data). • The atomic percentage of Zn and O in ZnO is 41.18% and 58.82% respectively. [ABSTRACT FROM AUTHOR]

Radial-like ZnO structures were prepared using zinc sulfate (ZnSO4·7H2O) and zinc acetate [Zn(CH3COO)2·2H2O] as zinc sources by a facile template-free hydrothermal method in this paper. Structural and optical properties of radial-like ZnO structures are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV-vis spectrophotometer and photoluminescence measurement (PL). It has been found that the distinct surface morphologies of radial-like ZnO structures grown by different zinc sources. Slim radial-like ZnO with a hexagonal wurtzite structure is grown by using ZnSO4·7H2O as zinc sources, whereas coarse radial-like ZnO with zincite structure is achieved by zinc acetate. The UV-vis absorption spectra of them both display an obvious and significant absorption in the ultraviolet region. The room temperature PL spectra of ZnO structures grown by two different zinc sources possess a common feature that consists of a strong ultraviolet (UV) peak and visible emission band. [ABSTRACT FROM AUTHOR]

Thin films of Zn 1− x Nd x O were deposited by spray pyrolysis on Si(111) substrates preheated at 400 °C temperature and were studied as a function of neodymium (Nd)-doping concentration. X-ray diffraction (XRD) patterns confirmed that the deposited films possess hexagonal wurtzite ZnO structure. Further, it is observed that the doped films show a preferential orientation along the c -axis (0 0 2), which is perpendicular to the substrate. The un-doped films seem to be having a bit low-crystallinity, which is corroborated by the scanning electron microscope (SEM) analysis that showed nano-crystalline like features. Further, SEM analysis showed that the Nd doping triggers the formation bubble-like structure on top of the nano-crystalline structure. The SEM microstructures are interpreted with the Micro-Raman studies. Photoluminescence (PL) and XRD characterizations indicate that above 5 at.% doping concentrations, the Nd atoms preferentially agglomerate in the large islands. [ABSTRACT FROM AUTHOR]

We have investigated the influence of in situ annealing on the optical, electrical, structural and morphological properties of ZnO thin films prepared on p-type Si(100) substrates by dual ion beam sputtering deposition (DIBSD) system. X-ray diffraction (XRD) measurements showed that all ZnO films have (002) preferred orientation. Full-width at half-maximum (FWHM) of XRD from the (002) crystal plane was observed to reach to a minimum value of 0.139° from ZnO film, annealed at 600 °C. Photoluminescence (PL) measurements demonstrated sharp near-band-edge emission (NBE) at ~ 380 nm along with broad deep level emissions (DLEs) at room temperature. Moreover, when the annealing temperature was increased from 400 to 600 °C, the ratio of NBE peak intensity to DLE peak intensity initially increased, however, it reduced at further increase in annealing temperature. In electrical characterization as well, when annealing temperature was increased from 400 to 600 °C, room temperature electron mobility enhanced from 6.534 to 13.326 cm/V s, and then reduced with subsequent increase in temperature. Therefore, 600 °C annealing temperature produced good-quality ZnO film, suitable for optoelectronic devices fabrication. X-ray photoelectron spectroscopy (XPS) study revealed the presence of oxygen interstitials and vacancies point defects in ZnO film annealed at 400 °C. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) thin films were deposited on Si (100) substrate through sputtering of zinc by DC magnetron, followed by thermal oxidation. Different deposition rates were used in coating films with 100 nm thickness (0·6-4·5 nm/s). Photoluminescence spectra of the produced samples were obtained and it was found that the violet emission peak intensity increases with deposition rate. Scanning electron microscopy (SEM) micrograph and atomic force microscopy (AFM) images for the zinc oxide films were obtained. Morphological changes due to various deposition rate are discussed in the light of changes observed in the ZnO crystals. Low coating rates produced smooth surface with small grains while higher deposition rates increased the surface roughness and larger grain size. AFM and SEM results are in good agreement and support the PL results. [ABSTRACT FROM AUTHOR]

A green synthesis route using starch as a capping agent was effectively employed to synthesize ZnO nanostructures through chemical bath deposition. Sodium borohydride was used in one of the approaches in synthesis. Broadening of X-ray diffraction peaks suggested formation of nanosize ZnO in agreement with the high resolution transmission electron microscopy images. As-synthesized ZnO nanostructures were polycrystalline having wurtzite type structure. Average size of the particles was about 8 nm which was in close agreement with measurements from optical studies. Starch was found to play a key role in bringing the strong quantum confinement in ZnO particles. Optical absorption edge was found to be around 240-275 nm which exhibited a clear large blue shift and thereby enhancement of band gap energy. A strong green photoluminescence emission at 604.5 nm was observed in ZnO nanoparticles synthesized using sodium borohydride and may be attributed to the defect controlled recombination mechanism. [ABSTRACT FROM AUTHOR]

Highlights: [•] Here, a colloid of ZnO nanoparticles is sprayed on PS layers. [•] PS stability attributed to the strong absorption/adsorption of ZnO. [•] Vast surface area & strong absorbality of PS with ZnO would lead to sensors. [Copyright &y& Elsevier]

Abstract: Zinc oxide (ZnO) thin films were produced by thermal oxidation of Zn layers (200nm thickness) which were coated on Si (100) substrate by DC magnetron sputtering. In order to study the effect of annealing temperature on photoluminescence (PL) properties and the surface morphology of the ZnO samples, the annealing temperature range of 500–700°C was employed. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) for investigation of surface morphology of the ZnO samples were carried out. The surface statistical characteristics of these ZnO thin films are then evaluated against data which outcome from AFM. SEM and AFM results indicated that the annealing temperature produces larger grains and rough surfaces at higher temperatures. The results of PL spectra represent an increase in interstitial zinc with increasing annealing temperature. [Copyright &y& Elsevier]

Numerous zinc oxide (ZnO) nanomaterials, with unique physical and chemical properties, have recently been synthesised by various methods. In this study, a hydrothermal method was developed to synthesise ZnO nanomaterials with different morphologies on indium doped tin oxide (ITO), and the growth mechanism was discussed. The structure and morphologies of the synthesised samples were characterised by X-ray diffraction and SEM. The photoluminescence (PL) and field emission characteristics of ZnO nanomaterials with different morphologies were measured. X-ray diffraction and SEM images indicate that ZnO with morphologies of nanocones, nanorods and nanotubes is grown along c axis to the ITO substrates. The room temperature PL spectra reveal a strong and sharp ultraviolet emission band at 386 nm and a weak blue emission band at 470 nm. The field emission measurements show that the turn-on field of ZnO nanocones, nanorods and nanotubes at emission current density of 10 μA cm-2 is approximately 2·62, 4·31 and 3·92 V μm-1. Moreover, the emission image of ZnO nanocones is more homogeneous than that of ZnO nanorods and nanotubes at the electric field of 4·5 V μm-1. The experimental results indicate that ZnO nanomaterials with different morphologies have good photoelectric properties. As cold cathode materials, ZnO has a great number of potential applications for the field emission display in the future. [ABSTRACT FROM AUTHOR]

Abstract: ZnO nanoparticles and ZnO encapsulated with polyethylene glycol (PEG) was synthesized using zinc acetate as a precursor at low temperature and characterized by different techniques. The influence of the types of solvent, synthesis parameters, and PEG encapsulation on the crystallization, the surface morphology, and the luminescent properties of ZnO nanoparticles prepared by the sol–gel process were investigated. The influence of different addition molar masses of the PEG during the synthesis on the ZnO emission peaks was systematically monitored. The crystallinity, the surface morphology, and the photoluminescence (PL) properties of ZnO depended highly on the synthesis process and PEG encapsulation. X-ray diffraction (XRD) spectra of ZnO nanoparticles show that all the peaks corresponding to the various planes of wurtzite ZnO indicate the formation of a single phase. The absorption edges of these ZnO nanoparticles are shifted by additions of the PEG polymer. The photoluminescence (PL) characterization of the ZnO nanostructures exhibited a broad emission in the visible range with maximum peak at 450 and/or 560nm. [Copyright &y& Elsevier]

Abstract: The photoluminescence study of self-assembled ZnO nanorods grown on a pre-treated Si substrate by a simple chemical bath deposition method at a temperature of 80°C is hereby reported. By annealing in O2 environment the UV emission is enhanced with diminishing deep level emission suggesting that most of the deep level emission is due to oxygen vacancies. The photoluminescence was investigated from 10K to room temperature. The low temperature photoluminescence spectrum is dominated by donor-bound exciton. The activation energy and binding energy of shallow donors giving rise to bound exciton emission were calculated to be around 13.2meV, 46meV, respectively. Depending on these energy values and nature of growth environment, hydrogen is suggested to be the possible contaminating element acting as a donor. [Copyright &y& Elsevier]

In the current work, tetraleg zinc oxide (ZnO) nanostructure has been fabricated using evaporation method, the structural and optical properties investigated using high resolution X-ray diffraction (HRXRD) which confirmed that ZnO film is successfully deposited on silicon (Si) substrate. This result is line with scanning electron microscopy (SEM) and atomic force microscopy (AFM) result which used to imaging the morphology of the film and it indicate that the roughly surface film was obtained. Photoluminescence (PL) emission employed to study the optical properties of ZnO film that showed two PL peaks have been observed; one in UV region at 371 nm (3.34 eV) and the other in visible region at 530 nm (2.34 eV). The visible emission of PL spectrum which attributed to the yellow defects inside the films has high intensity. This is expected to provide a suitable antireflection coating (ARC) for enhancing the efficiency of the photovoltaic devices such as solar cells and photodetectors. [ABSTRACT FROM AUTHOR]

Abstract: ZnO thin films were firstly deposited on glass substrates by the sol-gel process, and then Zn ions with energy of 56 keV were implanted into the ZnO films to a dose of 1×1017cm-2. The effects of ion implantation on the structural and optical properties of the ZnO films were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL) and optical transmittance measurements. The results showed that the as-deposited films had hexagonal wurtzite structure with high c-axis preferred orientation and (002) peak disappeared after ion implantation. Both the near band edge (NBE) excitonic UV emission at 390nm and the defect related deep level emission (DLE) centered at 470nm in the visible region were greatly decreased after Zn ion implantation. The optical band gap redshifted from 3.10 to 3.04eV after ion implantation. [Copyright &y& Elsevier]

Abstract: Highly transparent and conducting Chromium doped ZnO (Cr:ZnO) thin films with preferential c-axis orientation were grown on (0001) sapphire substrates using buffer assisted pulsed laser deposition. The resistivity of Cr:ZnO thin films was found to decrease to a minimum value of ∼1.13×10−3Ωcm with the increasing Cr concentration up to ∼1.9at.% and then increase with further increase of Cr concentration. On the contrary, the band gap and carrier concentration of Cr:ZnO thin films increased up to ∼3.37eV and ∼2×1020 cm−3, respectively, with the increase of Cr concentration up to ∼1.9at.%, then decreased with further increase of Cr concentration. The increase of carrier concentration and conductivity with Cr doping at low Cr concentrations (<1.9at.%) could be attributed to the presence of Cr in +3 valence state in ZnO thus acting as donor while decrease of carrier concentration beyond ∼1.9at.% of Cr concentration could be attributed to the charge compensating effect due to the presence of acceptor like point defects such as oxygen interstitials. This was experimentally confirmed using x-ray photoelectron spectroscopy. The observed variation in the band gap of Cr:ZnO thin films with increasing Cr doping was attributed to the competing effects of the high free carrier concentration induced Burstein-Moss blue shift and band gap narrowing. [Copyright &y& Elsevier]

Porous tin oxide was prepared on silicon(111) substrate by the sol-gel route. Then, the samples were dried in air at 600°C for 30 min in an electric furnace. Scanning electron microscope (SEM) images indicated the high density of the pores. Circular microvoids formed by the rigid shaped microarray network of 200-300 nm sizes are clearly seen in the plan view SEM image. The high homogeneity and uniformity of the porous region could also be visualized by this easy method. Nanocrystalline zinc oxide (ZnO) thin films have been deposited onto porous SnO2 substrates at high growth rates by radio frequency (RF) sputtering using a ZnO target. The surface morphology of the nanocrystalline ZnO films was characterized by scanning electron microscope (SEM). Photoluminescence (PL) spectroscopy is a powerful, contactless and excellent nondestructive optical tool to study the acceptor binding energy of ZnO nanostructures. The PL measurements were also operated at room temperature. The peak luminescence energy in nanocrystalline ZnO on porous SnO2 is blue-shifted with regard to that in bulk ZnO (381 nm). PL spectra peaks are distinctly apparent at 375 nm for ZnO film grown on porous SnO2/Si(111) substrates. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we report the fabrication of high quality single-crystalline ZnO nanorod arrays which were grown on the silicon (Si) substrate using a microwave assisted solution method. The as grown nanorods were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photo-luminescence (PL) and magnetization measurements. The XRD results indicated that the ZnO nanorods are well oriented with the c-axis perpendicular to the substrate and have single phase nature with the wurtzite structure. FE-SEM results showed that the length and diameter of the well aligned rods is about ~1μm and ~100nm respectively, having aspect ratio of 20–30. Room-temperature PL spectrum of the as-grown ZnO nanorods reveals a near-band-edge (NBE) emission peak and defect induced green light emission. The green light emission band at ~583nm might be attributed to surface oxygen vacancies or defects. Magnetization measurements show that the ZnO nanorods exhibit room temperature ferromagnetism which may result due to the presence of defects in the ZnO nanorods. [Copyright &y& Elsevier]

In this paper, a template free method has been employed to fabricate porous ZnO. Brick shaped precursor was first synthesized by a mild hydrothermal process. Accompanied with the decomposition of the precursor during the subsequent annealing treatment, porous ZnO with the inherited morphology of the precursor was obtained. The as-prepared products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It exhibited that the porous hierarchical frame consists of nano-sheets with wurtzite-type. The size of the pores as well as the size of the particles varied with the annealing temperature. Mechanism speculation showed that the crystal-aggregation in the growth process of the precursor is the key to the establishment of pore structure. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The current interest in materials consisting of more than one component, has increased in recent years due to the properties they present. In this work, we carried out a study of photoluminescent properties of ZnO: a-SiOx composites. To obtain the material, hot filament chemical vapor deposition (HFCVD) technique was employed in a temperature range of 900-1100 °C. We include a solid source of quarts (SiO2) in the growth environment, to study its effect on deposited films properties. Structural characterization by X-ray diffraction (XRD) and infrared spectroscopy (FTIR), indicated that the phases ZnO and a-SiOx coexist regardless of the deposit temperature, although this parameter is decisive in the dominant photoluminescent emission phase. [ABSTRACT FROM AUTHOR]

Abstract: There is a considerable interest in studying organic/inorganic hybrid structures for various applications in optoelectronic devices. We have recently demonstrated fabrication of 3,4,9,10-perylenetetracarboxylicdiimide (PTCDI) nanostructures and hybrid PTCDI/ZnO nanorod structures and studied their optical properties, and we found that PTCDI nanoclusters exhibit significantly different light emission compared to PTCDI films. Since the emission spectrum of PTCDI nanoclusters exhibited dependence on the deposition substrate, we have studied the influence of ZnO nanorod growth method and post-growth annealing in oxygen atmosphere at different temperatures on the energy transfer to PTCDI nanostructures by photoluminescence measurements. Fabricated structures have been investigated using scanning electron microscopy and photoluminescence measurements, and the obtained results are discussed. [ABSTRACT FROM AUTHOR]

Zinc thin films were deposited onto porous silicon (PSi) substrates by dc sputtering using a Zn target. These films were then annealed under flowing (6 l/min) oxygen gas environment in the furnace at 600°C for 2 h. Porous silicon is used as an intermediate layer between silicon and ZnO films and it provides a large area composed of an array of voids. The PSi samples were prepared using photoelectrochemical method on n-type silicon wafer with (111) and (100) orientation. To prepare porous structures, the samples were dipped into a mixture of HF:ethanol (1:1) for 5 min with current densities of 50 mA/cm2, and subjected to external illumination with a 500 W UV lamp. The surface morphology and the nanorod structure of the ZnO films were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). We synthesized the ZnO nanorods with diameter of 80-100 nm without any catalysts or templates. The XRD pattern confirmed that the ZnO nanorods were of polycrystalline structure. The surface-related optical properties have been investigated by photoluminescence (PL) and Raman measurements at room temperature. Micro-Raman results showed that A1(LO) of hexagonal ZnO/Si(111) and ZnO/Si(100) have been observed at 522 cm-1 and 530 cm-1, respectively. PL spectra peaks are clearly visible at 366 cm-1 and 368 cm-1 for ZnO film grown on porous Si(111) and Si(100) substrates, respectively. The PL spectral peak position in ZnO nanorods on porous silicon is blue-shifted with respect to that in unstrained ZnO (381 nm). [ABSTRACT FROM AUTHOR]

The evolution of ZnO nanowires has been studied under supersaturation of Zn metal species with and without a ZnO thin-film buffer layer on α-Al2O3 deposited by the pulsed laser ablation technique. The nanowires had diameters in the range of 30 nm to 50 nm and lengths in the range of 5 μm to 10 μm with clear hexagonal shape and $$ [000\bar{1}] $$, $$ [10\bar{1}1] $$, and $$ [10\bar{1}0] $$ facets. X-ray diffraction (XRD) measurements indicated crystalline properties for the ZnO nanostructures grown on pulsed laser deposition (PLD) ZnO nucleation layers. The optical properties were analyzed by photoluminescence (PL) and cathodoluminescence (CL) measurements. The ZnO nanowires were found to emit strong ultraviolet (UV) light at 386 nm and weak green emission as observed by PL measurements. The stoichiometry of Zn and O was found to be close to 1 by x-ray photoelectron spectroscopy (XPS) measurements. The process-dependent growth properties of ZnO nanostructures can be harnessed for future development of nanoelectronic components including optically pumped lasers, optical modulators, detectors, electron emitters, and gas sensors. [ABSTRACT FROM AUTHOR]

In this work, we report the morphology and optical properties of zinc oxide (ZnO) layers prepared by dry thermal oxidation at different annealing conditions. Morphology studies using scanning electron microscope (SEM) show that the amount of nanowires and nanosheets increases with the introduction of a flow of O2 gas. High-resolution X-ray diffraction (HR-XRD) data show that typical polycrystalline ZnO nanostructure layers have been deposited. Near-perfect stoichiometry of Zn and O atom vacancies has been observed from energy dispersion spectroscopy (EDS) spectrum. Photoluminescence (PL) spectra show strong peaks at UV and green regions. An increase in the stoichiometry of ZnO has been achieved with the oxygen gas flow during annealing indicating that deep-level defects represented by interstitial oxygen and antisite oxygen are gas pressure dependent. A single exciton peak with binding energy 60 meV has been observed at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: ZnO has attracted a great deal of attention in recent years because of its potential applications for fabricating optoelectronic devices. Using a multi-spectroscopic approach including positron annihilation spectroscopy (PAS), deep level transient spectroscopy (DLTS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), we have studied the two observed phenomena from ZnO related structures. They namely included the H2O2 pre-treatment induced ohmic to rectifying contact conversion on Au/n-ZnO contact and the p-type doping by nitrogen ion implantation. The aim of the studies was to offering comprehensive views as to how the defects influenced the structures electrical and optical properties of the structures. It was also shown that PAS measurement using the monoenergetic positron beam could offer valuable information of vacancy type defects in the vertical ZnO nanorod array structure. [Copyright &y& Elsevier]

Abstract: High energy electron irradiation (HEEI) effects on the as-grown and annealed ZnO thin films grown by electrochemical deposition were investigated. Both samples were exposed to the sequential electron irradiations of 6, 12 and 15MeV energies at a fluence of 1×1012 e−/cm2. The results of X-ray diffraction suggest that a highly strong crystallographic structure can be produced by annealing process. Photoluminescence (PL) studies show that the EI produces violet emission which results from the zinc interstitial. Recombination lifetime (RL) values of the both films reveal that the high quality crystals are obtained. The decreasing trends of RL values with increasing electron energy have been explained by the formation of crystal defects due to the HEEI. [Copyright &y& Elsevier]

Abstract: ZnO nanorods were grown by a simple near room temperature, chemical solution method on ZnO-seeded silicon substrates. Study of the ZnO nanorods over different growth times by electron microscopy methods revealed that the resulting ZnO nanorods were single crystalline with a highly preferential growth perpendicular to the substrate and a very good -axis alignment. The size of the nanorods increased with increasing growth time. The growth mechanism is briefly discussed. Post-annealing in oxygen slightly improved the surface roughness of the ZnO nanorods. Photoluminescence experiments at 1.6 K revealed a major emission peak of the nanorods at around 3.36 eV which is attributed to the band edge transition of ZnO, while defect-related emission is relatively weak. [Copyright &y& Elsevier]

Abstract: We have studied the structural and optical properties of ZnO thin films prepared by thermal oxidation of ZnS films deposited by plasma assisted electron-beam evaporation on Si(100) substrates. The transformation from zinc blende ZnS to hexagonal wurtzite ZnO is confirmed by Raman and X-ray diffraction (XRD) measurement. For the sample thermally oxidized at 600°C for 2h, a novel UV emission peak Ix located at 3.22eV (385nm) has been observed. The temperature-dependent photoluminescence spectra show that the integrated intensity of Ix increases exponentially with increasing temperatures within the measuring temperature range, from 80 to 300K, but the peak position remains nearly constant. We explain this behavior in terms of electron tunneling into the radiative recombination centers. [Copyright &y& Elsevier]

Abstract: ZnO thin films have been deposited on Sapphire (0001) substrate at 500°C by the pulsed laser deposition (PLD). The grown samples have been treated under the high pressure oxygen (5atm) for 24, 72, 240 and 480h, respectively. The prepared thin films have been characterized by X-ray diffractometer (XRD), photoluminescence (PL) and Hall systems. From PL studies, it is observed that the intensities of defect peaks at 2.1 and 2.5eV have increased slightly, while the near band edge (NBE) emission has no change in its intensity. From XRD, the FWHM has rapidly decreased until 24h and after that it has been stabilized. From the Hall measurement, we have found that the carrier concentration has decreased, while the mobility has increased by the oxygen treatment. [Copyright &y& Elsevier]