Structural and photoluminescence properties of terbium-doped zinc oxide nanoparticles

We present in this paper a study of the structural and photoluminescence （PL） properties of terbium （Tb） doped zinc oxide （ZnO） nanoparticles synthesized by a simple low temperature chemical precipitation method, using zinc acetate and terbium nitrate in an isopropanol medium with diethanolamine （DEA） as the capping agent at 60 ℃. The as-prepared samples were heat treated and the PL of the annealed samples were studied. The prepared nanoparticles were characterized with X-ray diffraction （XRD）. The XRD patterns show the pattern of typical ZnO nanoparticles and correspond with the standard XRD pattern given by JCPDS card No. 36-1451, showing the hexagonal phase structure. The PL intensity was enhanced due to Tb^3＋ doping, and it decreased at higher concentrations of Tb^3＋ doping after reaching a certain optimum concentration. The PL spectra of Tb^3＋ doped samples exhibited blue, bluish green, and green emissions at 460 nm （5^D3 - 7^F3）, 484 nm （5^D4 - 7^F6）, and 530 nm （5^D4 - 7^F5）, respectively, which were more intense than the emissions for the undoped ZnO sample. Based on the results, an energy level schematic diagram was proposed to explain the possible electron transition processes.     

Structural and photoluminescence properties of ZnO nanoparticles on silicon oxide

Isolated, self assembled ZnO nanoparticles are grown in two steps: by the electron beam evaporation of Zn on oxidised silicon wafers, during which isolated Zn nanodots are grown, and a subsequent annealing in oxygen that results in the desired ZnO nanodots. Low temperature PL measurements of the ZnO nanodots show that the near band edge part of the spectra is dominated by a zero phonon line near 3.36 eV which is an overlap of two emitting lines near 3.363 eV and 3.367 eV. Characterization by TEM and EELS shows that the nanoparticles are zinc oxide single crystals grown with their c-axis perpendicular to the substrate; their distribution, size and crystallinity depend on the deposition parameters of zinc and the growth substrate. We discuss the effect of these parameters on the morphology of the resulting material. Our approach demonstrates a simple method for the growth of high purity isolated ZnO nanodots of similar sizes, distributed uniformly on a large surface. PACS 61.46.Df; 81.05.Dz; 81.07.-b     

Structural, morphological and photoluminescence properties of W-doped ZnO nanostructures

W-doped ZnO nanostructures were synthesized at substrate temperature of 600 °C by pulsed laser deposition (PLD), from different wt% of WO₃ and ZnO mixed together. The resulting nanostructures have been characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy and photoluminescence for structural, surface morphology and optical properties as function of W-doping. XRD results show that the films have preferred orientation along a c-axis (0 0 L) plane. We have observed nanorods on all samples, except that W-doped samples show perfectly aligned nanorods. The nanorods exhibit near-band-edge (NBE) ultraviolet (UV) and violet emissions with strong deep-level blue emissions and green emissions at room temperature.     

Photoluminescence and Raman scattering in spatially inhomogeneous heteroepitaxial InGaN layers

Spatial inhomogeneities of the indium distribution in In _x Ga_1–x N epitaxial layers grown on sapphire substrate with a GaN buffer layer were investigated using photoluminescence (PL) in addition to confocal scanning Raman spectroscopy (RS) and PL. Broad emission bands from In-enriched InGaN nanoclusters (700–900 nm) and from the volume outside the clusters (about 460 nm) were observed in PL spectra of an epitaxial InGaN layer with an average In content of 25.7%. It was established that larger micro-PL intensities corresponded to energetically shallower clusters. The observed broadly asymmetric A₁(LO) RS band of InGaN confirmed that the In concentration in the layer was highly variable. Modeling the LO phonon band by two Lorentzian curves gave an average In concentration of 21% in the volume outside the clusters and 37% in the nanoclusters, which was considerably higher than the average concentration in the layer and agreed well with their PL band positions.     

Structural,dielectric and photoluminescence properties of co-precipitated Zn-doped SnO2 nanoparticles

Zn-doped SnO₂ nanoparticles were prepared by the chemical co-precipitation route. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses of these prepared nanoparticles were carried out for structural and morphological studies. All the samples have been found to have tetragonal rutile structure of the polycrystalline SnO₂ having crystallite size in the range 13–25 nm. TEM micrographs show agglomeration of nanoparticles in all the samples. At a particular temperature, the dielectric constant of all the samples has been found to decrease with increasing frequencies which may be due to rapid polarization processes occurring in SnO₂ nanoparticles. The ac conductivity, σ (ω), has been found to vary with frequency according to the relation σ (ω) ∝ ω^S. The value of S has been found to be temperature dependent, decreasing with increasing frequency which suggests that a hopping process is the most likely conduction mechanism in these nanoparticles. The room temperature photoluminescence (PL) spectra of the undoped and Zn-doped SnO₂ nanoparticles consist of the near band-edge ultraviolet (UV) emission and the defect related visible emissions. The origin of emission peaks in the visible region is attributed to oxygen-related defects that are introduced during growth.     

Practical interpretation of X-ray rocking curves from semiconductor heteroepitaxial layers

X-ray rocking curves are widely used to study semiconductor heteroepitaxial structures. Examples are given of the use of rocking curves to investigate crystal growth problems, determine layer growth rates, confirm layer thicknesses and to determine the state of relaxation in layers which are above the critical thickness. The application of dynamic simulation and Fourier transformation to the raw data as tools to interpret data from multilayer structures is discussed.     

Electron probe microanalysis of HgCdTe heteroepitaxial structures with CdTe buffer layers

Some results of electron probe microanalysis of HgCdTe heteroepitaxial structures with wide-gap semiconductor CdTe buffer layers are described. It is shown that these structures may be used for manufacturing high-performance photodetectors for registration of infrared radiation in the ranges of 3–5 and 8–12 μm.     

Structural and optical properties of layers of pentacene formed by PLD method

Organic films fabrication offers the possibility of producing electronic devices of low weight, mechanical flexibility and low cost. One suitable material for organic film fabrigation which is the subject of the great interest is pentacene, because it is characterized by the large carrier mobility (∼1 cm²/Vs). In this work, the growth of pentacene layers using pulse laser deposition (PLD) on different substrates (glass/ITO, Si) is described and various processing parameters are investigated. Two pulsed YAG:Nd³⁺ laser wavelengths were used for the ablation of the PLD target: the first harmonic at 1064 nm aGn:dNdth3+e second at 532 nm. The structure of the layers formed was examined using SEM and RHEED methods. The results were compared with results of optical spectroscopy studies. It will be shown that layers deposed using second harmonics have a higher quality than those for first harmonic. The other PLD parametersalso have a strong influence on the structure quality of layers.      

Structural and optical characterization of GaN heteroepitaxial films on SiC substrates

We have estimated the threading dislocation density and type via X-ray diffraction and Williamson-Hall analysis to elicit qualitative information directly related to the electrical and optical quality of GaN epitaxial layers grown by PAMBE on 4H- and 6H-SiC substrates. The substrate surface preparation and buffer choice, specifically: Ga flashing for SiC oxide removal, controlled nitridation of SiC, and use of AlN buffer layers all impact the resultant screw dislocation density, but do not significantly influence the edge dislocation density. We show that modification of the substrate surface strongly affects the screw dislocation density, presumably due to impact on nucleation during the initial stages of heteroepitaxy.     

Electrophysical properties and energetical spectrum of heteroepitaxial germanium films

An epitaxial growth of Ge films from molecular beam is characterized by thermodynamical nonequilibrium. This leads to formation of numerous structural defects connected with local levels in the band gap (mainly acceptor-type). Depending on the deposition temperature the density of such levels may change in wide range (10¹⁶–10¹⁸ cm^?3). This determines various mechanisms of impurity conduction. The tails of the density of states in the band gap are also connected with the defect structure of the films. Stresses in heteroepitaxial Ge films result in the splitting of the valence band atk = 0 and in a change of the band gap. Thus, these stresses have influence on the electrical and optical properties of the films.     

Structural and photoluminescence properties of silicon nanocrystals embedded in SiC matrix prepared by magnetron sputtering

Si nanocrystals (NCs) embedded in an SiC matrix were prepared by the deposition of Si-rich Si_1?xC_x/SiC nanomultilayer films using magnetron sputtering, subsequently followed by thermal annealing in the range of 800～1200 °C. As the annealing temperature increases to 1000 °C, Si NCs begin to form and SiC NCs also start to emerge at the annealing temperature of 1200 °C. With the increase of annealing temperature, two photoluminescence (PL) peaks have an obvious redshift. The intensity of the low-energy PL peak around 669～742 nm gradually lowers, however the intensity of high-energy PL peak around 601～632 nm enhances. The low-energy PL peak might attribute to dangling bonds in amorphous Si (a-Si) sublayers, and the redshift of this peak might be related to the passivation of Si dangling bonds. Whereas the origin of the high-energy PL peak may be the emergence of Si NCs, the redshift of this peak correlates with the change in the size of Si NCs.     

Structure of the free exciton luminescence band of heteroepitaxial ZnSe/GaAs layers

The exciton reflectance and photoluminescence spectra of epitaxial ZnSe/GaAs layers with a thickness of 2–4 μm are investigated in the temperature range 10–120 K. It is shown that one of the causes of the formation of the doublet structure of the A _n=1 photoluminescence band is interference of the exciton radiation at the boundaries of the near-surface dead layer. Fiz. Tverd. Tela (St. Petersburg) 40, 881–883 (May 1998)     

Microprobe photoluminescence measurement on heteroepitaxial GaAs on Si grown by metalorganic chemical vapor deposition

Microprobe photoluminescence (PL) measurements at 77 K were used to study the effect of the GaAs layer thickness on optical quality and variations in strain in GaAs/Si containing microcracks. PL peak intensities increase with the increase in thickness of GaAs layers and the peak intensity for the 5.5 m GaAs layer was a factor of 20 higher than those for the 1–2 m GaAs layers. Spatial nonuniformities in strain in the vicinity of two microcracks reveal that stress was almost released at the intersection of two microcracks and is maximum half way between two microcracks.On leave from Semiconductor Materials Lab., Korea Institute of Science and Technology (KIST)     

Structural and photoluminescence properties of Dy3+ doped different modifier oxide-based lithium borate glasses

Structural and photoluminescence properties of Dy³⁺ doped lithium fluoro-borate glasses with the compositions Li₂B₄O₇–BaF₂–NaF–MO (where M=Mg, Ca, Cd and Pb), Li₂B₄O₇–BaF₂–NaF–MgO–CaO and Li₂B₄O₇–BaF₂–NaF–CdO–PbO have been investigated through XRD, FTIR, optical absorption, emission and decay measurements. From the optical absorption spectra, Judd–Ofelt intensity parameters (Ω_λ, λ=2, 4 and 6) have been evaluated and are in turn used to predict radiative properties such as radiative transition probabilities (A_T), branching ratios (β_r) and stimulated emission cross sections (σ_p) for all emission levels of Dy³⁺ ion in different lithium fluoro-borate glass matrices. From the emission spectra, chromaticity color coordinates have been calculated and indicated emission color for all glass matrices. The nature of decay profiles of ⁴F_9/2 state of Dy³⁺ in all the glass matrices are analyzed.     

The morphology and electrical properties of heteroepitaxial InAs prepared by MBE

An investigation of the growth of heteroepitaxial InAs by MBE is reported. The surface morphology and electrical properties are shown to be critically dependent on growth parameters and the conditions necessary to obtain good material quality are deduced. Analysis of the thickness dependence of the electrical properties of undoped, and Si- or Te-doped InAs shows that interfacial effects contribute to the measured properties. Material remote from the interfacial region compares favourably with VPE- and bulkgrown InAs.     

Structural and photoluminescence properties of SnO2 obtained by thermal oxidation of evaporated Sn thin films

Tin oxide films have been prepared by oxidation of Sn thin films deposited by thermal evaporation method onto glass substrates. The oxidation of films was done, in air at a temperature of 500 °C, from 20 to 120 min. The oxidized films were characterized by X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), photoluminescence spectroscopy (PL) and surface profilometer. The XRD patterns show that the crystalline structure of the oxidized Sn films improves with the annealing time. The tetragonal SnO₂ phase (cassiterite) was obtained after 120 min of annealing with grains sizes between 15 and 20 nm. The thickness of oxide films, as function of the annealing time, follows a parabolic law. The O/Sn atomic ratio increases with the annealing time indicating an improvement of the films quality. Tin interstitials defects density, calculated from PL spectra using Smakula's formula, was found to decrease with the increasing annealing time. Tin interstitials defects density was found proportional to the increasing oxygen density (deduced from RBS). A fit of this proportionality allowed us to quantify the tin cations and oxygen anions diffused through the oxide films.     

Formation and photoluminescence properties of boron nanocones

This paper reports that a simple chemical vapour deposition method has been adopted to fabricate large scale, high density boron nanocones with thermal evaporation of B/B2O3 powders precursors in an Ar/H2 gas mixture at the synthesis temperature of 1000-1200℃. The lengths of boron nanocones are several micrometres, and the diameters of nanocone tops are in a range of 50-100 nm. transmission electron microscopy and selected area electron diffraction indicate that the nanocones are single crystalline α-tetragonal boron. The vapour liquid solid mechanism is the main formation mechanism of boron nanocones. One broad photolumineseence emission peak at the central wavelength of about 650 nm is observed under the 532 nm light excitation. Boron nanocones with good photoluminescence properties are promising candidates for applications in optical emitting devices.     

Synthesis and photoluminescence properties of silver nanowires

Silver nanowires of 50–190 nm in diameters along with silver nanoparticles in the size range of 60–200 nm in prismatic and hexagonal shapes are synthesized through chemical process. The lengths of the silver nanowires lie between 40 and 1000 μm. The characterizations of the synthesized samples are done by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–visible absorption spectroscopy. The syntheses have been done by using two processes. In the first process, relatively thicker and longer silver nanowires are synthesized by a soft template liquid phase method at a reaction temperature of 70 °C with methanol as solvent. In the second process, thinner silver nanowires along with silver nanoparticles are prepared through a polymer mediated polyol process at a reaction temperature of 210 °C with ethylene glycol as solvent. The variations of photoluminescence (PL) emission from the silver nanocluster dispersed in methanol as well as in ethylene glycol are recorded at room temperature under excitation wavelengths lying in between 300 and 414 nm. The blue–green PL emission is observed from the prepared samples and these emissions are assigned to radiative recombination of Fermi level electrons and sp- or d-band holes.     

蓝宝石衬底SnO2:Sb薄膜的制备及结构和光致发光性质

用射频磁控溅射法在蓝宝石(0001)衬底上制备出锑掺杂的氧化锡(SnO2:sb)薄膜.对制备薄膜的结构和发光性质进行了研究.制备样品为多晶薄膜,具有纯SnO2的四方金红石结构.室温条件下对样品进行光致发光测量,在334 nm附近观测到紫外发射峰,并对SnO2:Sb的光致发光机制进行了研究.