Large-scale synthesis of highly pure Cd metal hexagonal nanosheets

Highly pure and large-scale single crystalline cadmium (Cd) metal hexagonal nanosheets with 10-12 nm thickness were obtained by catalyst-free thermal decomposition of cadmium oxide (CdO) powder under nitrogen gas at 1000 °C. The as-prepared product was characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy and selected area electron diffraction. Room temperature photoluminescence (PL) spectrum for Cd nanosheets exhibited three very distinct emission bands at 360 nm, 402 nm and 426 nm. UV emission band at 360 nm is attributed to radiative recombination of electrons in the s, p conduction band near the Fermi surface and the holes in the d bands generated by xenon light excitation whereas visible emission bands at 402 nm and 426 nm may be due to surface oxidation effects or induced defects in the nanosheets. The growth mechanism for the formation of Cd metal hexagonal nanosheets is also proposed and discussed briefly.     

Synthesis of metallic Zn microprisms, their growth mechanism and PL properties

Novel metallic Zn hexagonal hollow microprisms have been synthesized by a simple thermal evaporation technique using NH₃ as a carrier gas under atmospheric pressure. As-prepared hollow microprisms were characterized using X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy and transmission electron microscopy. The hollow microprisms collected on silicon substrate are found to be 3-7 μm long with diameter in the range 900-950 nm. A vapour-solid (VS) process based growth mechanism has been proposed for the formation of hexagonal Zn microprisms grown along (0001) basal plane in [0001] direction. Photoluminescence (PL) emission spectrum of zinc microprisms at room temperature exhibited a very prominent peak at 384 nm owing to the radiative recombination of electrons in s, p conduction band near Fermi surface and the holes in the d bands generated by optical excitation.     

Metallic cobalt microcrystals with flowerlike architectures: Synthesis, growth mechanism and magnetic properties

Well-defined, three-dimensional (3D) flowerlike metallic Co microcrystals with several radiating hexagonal-tapered petals assembled by particles size of 150-250 nm were fabricated via a facile hydrothermal reduction route under a fixed basic condition. The morphology and structure of the products were characterized by scanning electronic microscopy (SEM), energy-dispersive X-ray (EDX), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS) and powder X-ray diffraction (XRD). The probable formation mechanism of the flowerlike Co microcrystals was discussed based on the experimental results. Magnetic properties of Co microcrystals were investigated by a commercial Physical Properties Measurement System (PPMS). The flowerlike products exhibited ferromagnetic characteristics with a saturation magnetization of 128.1 emu/g and a coercivity of 232.5 Oe at room temperature. Compared to the coercivity value of bulk Co, the products displayed a remarkable enhanced value due to their special morphology.     

The growth of heavily Mg-doped GaN thin film on Si substrate by molecular beam epitaxy

This paper reports the growth of p-GaN by molecular beam epitaxy. During growth, reflection high electron energy diffraction displayed streaky pattern. Hall Effect measurement indicated a hole concentration of 3.90 × 10²⁰ cm^− 3. Scanning electron microscopy and X-ray diffraction measurements revealed that p-GaN has high structural quality. Photoluminescence spectrum showed that band edge emission was found at 354.1 nm, significantly shifted from usual reported value, i.e. 364 nm. The shift was attributed to Burstein-Moss effect. In addition, a broad emission peak at 387.5 nm was also observed which was due to the transition from conduction band edge to Mg acceptor level. Moreover, the presence of 657 cm^− 1 Raman peak also confirmed the heavy Mg-doped characteristic in p-GaN.     

Photoluminescence study of PVP capped CdS nanoparticles embedded in PVA matrix

Photoluminescence properties of polyvinyl pyrrolidone (PVP) capped cadmium sulphide (CdS) nanoparticles embedded in polyvinyl alcohol matrix (PVA) are reported. The PVP-CdS nanoparticles are prepared by non-aqueous method wherein cadmium nitrate is used as the cadmium source and hydrogen sulphide as the sulphur source. The synthesized nanoparticles are dispersed in polyvinyl alcohol (PVA) matrix and cast as self-standing flexible (PVP-CdS)-PVA films. The nanocomposites are characterized by optical absorption spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. XRD and TEM studies show the formation of cubic CdS particles with average size ∼3-5 nm. Thermal studies, carried out to observe the changes in PVA matrix due to the incorporation of PVP-CdS nanoparticles show strong interaction between the polymer matrix and nanoparticles. The photoluminescence emission spectra of the nanocomposites show two peaks, at 502 and 636 nm, which are attributed to the band edge and surface defects respectively, of CdS nanoparticles. Effective surface capping with optimum concentration of polyvinyl pyrrolidone leads to the quenching of surface defect-related emission.     

Thermal evaporation and condensation synthesis of metallic Zn layered polyhedral microparticles

Metallic zinc layered polyhedral microparticles have been fabricated by thermal evaporation and condensation technique using zinc as precursor at 750 °C for 120 min and NH₃ as a carrier gas. The zinc polyhedral microparticles with oblate spherical shape are observed to be 2-9 μm in diameter along major axes and 1-7 μm in thickness along minor axes. The structural, compositional and morphological characterizations were performed by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). A vapour-solid (VS) mechanism based growth model has been proposed for the formation of Zn microparticles. Room temperature photoluminescence (PL) emission spectrum of the product exhibited a strong emission band at 369 nm attributed to the radiative recombination of electrons in the s, p conduction band near Fermi surface and the holes in the d bands generated by the optical excitation.     

Green hydrothermal synthesis and photoluminescence property of ZnO2 nanoparticles

ZnO₂ nanoparticles were synthesized via a green hydrothermal method using ZnO powder and 30% H₂O₂ aqueous solution as the starting materials, and characterized by X-ray diffraction (XRD), Raman spectra, energy dispersive X-ray (EDX) spectra, field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and room temperature photoluminescence (RTPL) spectra. It was found that suitable reaction temperature (e.g., 80-140 °C) played an important role in obtaining pure cubic phase ZnO₂ nanoparticles. The RTPL spectra disclosed that the as-synthesized ZnO₂ nanoparticles exhibit one strong emission band centered at around 400 nm and one very weak emission band at around 474 nm, which may have originated from the band edge emission and the oxygen vacancy, respectively.     

Synthesis and optical properties of single-crystalline GaN nanorods

Single-crystalline GaN nanorods were successfully synthesized on Si(1 1 1) substrates through ammoniating Ga₂O₃/Mo films deposited on the Si(1 1 1) substrate by radio frequency magnetron sputtering technique. The as-synthesized nanorods are confirmed as single-crystalline GaN with wurtzite structure by X-ray diffraction (XRD), selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). Scanning electron microscopy (SEM) displays that the GaN nanorods are straight and smooth with diameters in the range of 100-200 nm and lengths typically up to several micrometers. X-ray photoelectron spectroscopy (XPS) confirms the formation of bonding between Ga and N. The representative photoluminescence spectrum at room temperature exhibits a strong and broad emission band centered at 371.1 nm, attributed to GaN band-edge emission. The growth process of GaN nanorod may be dominated by vapor-solid (VS) mechanism.     

Low-temperature synthesis and optical properties of wurtzite ZnS nanowires

Single-crystal wurtzite ZnS nanowires have been synthesized via a facile solution route with polyethylene glycol-400 as inducing template at low temperature (170 °C). The as-prepared products have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive X-ray analysis (EDX). Raman and photoluminescence spectrum (PL) were used to investigate the optical properties of ZnS nanowires. The strong emission peak centered at 322 nm in PL spectrum could be attributed to the band to band transitions.     

Defect induced room temperature ferromagnetism in well-aligned ZnO nanorods grown on Si (100) substrate

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 ~ 1 μm and ~ 100 nm 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 ~ 583 nm 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.     

Epitaxial growth of nonpolar m-plane ZnO (10-10) on large-size LiGaO2 (100) substrates

Nonpolar m-plane ZnO epitaxial film with [10-10] orientation was successfully grown on a large-size (100) LiGaO₂ single crystal substrate by chemical vapor deposition method. The dependence of growth characteristics on the different growth conditions was investigated. Following CVD growth, the surface morphologies and epi-film crystallinity were examined by scanning electron microscopy and X-ray diffraction. Room-temperature photoluminescence spectra exhibit a strong near-band-edge emission peak at 377 nm with a negligible green band. Raman spectroscopy showed that the as-grown (10-10) ZnO epilayer on (100) LiGaO₂ are under compressive stress. Further structural characterization and defect analysis of nonpolar ZnO material was performed using transmission electron microscopy.     

Synthesis, characterization and optical properties of sheet-like ZnO

Sheet-like ZnO with regular hexagon shape and uniform diameter has been successfully synthesized through a two-step method without any metal catalyst. First, the sheet-like ZnO precursor was synthesized in a weak alkaline carbamide environment with stirring in a constant temperature water-bath by the homogeneous precipitation method, then sheet-like ZnO was obtained by calcining at 600 °C for 2 h. The structures and optical properties of sheet-like ZnO have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) and UV-vis-NIR spectrophotometer. The results reveal that the product is highly crystalline with hexagonal wurtzite phase and has appearance of hexagon at (0 0 0 1) plane. The HRTEM images confirm that the individual sheet-like ZnO is single crystal. The PL spectrum exhibits a narrow ultraviolet emission at 397 nm and a broad visible emission centering at 502 nm. The band gap of sheet-like ZnO is about 3.15 eV.     

Bio-template route for facile fabrication of Cd(OH)2@yeast hybrid microspheres and their subsequent conversion to mesoporous CdO hollow microspheres

Cadmium oxide (CdO) microspheres with a porous hollow microstructure were prepared by a facile yeast mediated bio-template route. The yeast provides a solid scaffold for the deposition of cadmium hydroxide (Cd(OH)₂) from cadmium acetate and sodium hydroxide solutions to form the hybrid Cd(OH)₂@yeast precursor. Thermal conversions of this at above 500 °C in air have produced hollow CdO microspheres. The products were characterized by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), thermal gravimetric and differential thermal analysis (TGA-DTA), and Brunauer-Emmett-Teller (BET) surface analysis respectively. The obtained CdO microspheres have uniform size (length = 2.6 ± 0.4 μm; width = 2.0 ± 0.2 μm) and a well defined, continuous, mesoporous hollow microstructure. The shell is about 250-280 nm in thickness. The mechanism of formation of Cd(OH)₂@yeast precursor and its conversion to CdO hollow microspheres is discussed. In comparison with traditional template-directed method, the present strategy represents a general, economical and environmentally benign route for the formation of metal oxide hollow microspheres. These materials have potential applications in different fields such as encapsulation, drug delivery, efficient catalysis, battery materials and photonic crystals. The method presented can be extended to the synthesis of other inorganic hollow microstructures of different sizes and shapes by pre-selecting suitable bio-templates.     

The characteristics of ZnO deposited on PPC plastic substrate

In this paper, we report the deposition of ZnO thin film on poly propylene carbonate (PPC) plastic substrate by sputtering technique. The structural, optical and electrical properties of the ZnO thin film were investigated. The ZnO thin film deposited on PPC plastic has a smooth surface morphology as revealed by scanning electron microscopy (SEM). X-ray diffraction (XRD) measurement shows that the ZnO thin film has preferential orientation along the c-axis with strong peak observed at 2θ? = 34.25^o, while the photoluminescence (PL) spectrum shows strong UV emission peak at 385 nm. Spectrophotometry measurements reveal that transmission values of the film are low at wavelength shorter than 380 nm. Current-voltage measurements show that the dark- and photocurrents were found to be 6.11 and 89.3 μA, respectively, under dark and illuminated conditions at 5 V.     

Structure and optical spectrum of GaN nanorods produced on Si(111) substrates

A novel method is applied to prepare nanorods. In this method, nanorods have been successfully synthesized on Si(111) substrates through annealing sputtered Ga₂O₃/Nb films under flowing ammonia at 950 °C in a quartz tube. The as-synthesized nanorods are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The results show that the nanorod is single-crystalline GaN. It has a diameter of about 200 nm and lengths typically up to several micrometers. Photoluminescence spectrum under excitation at 325 nm only exhibits a UV light emission peak is located at about 368.5 nm. Finally, the growth mechanism of nanorods is also briefly discussed.     

Structural properties and morphology of Zn(1 − x)CdxO solid solution grown on ZnO and C-plane sapphire substrate

Zn_(1 − x)Cd_xO solid solutions with a composition ranging from pure ZnO up to x = 0.062 have been grown on ZnO and c-plane sapphire substrates by using metal organic chemical vapor deposition. The optical transmission spectra were used to estimate the cadmium mole fraction of the solid solutions. The lattice deformation and morphology of these films were examined in detail using high resolution X-ray diffraction and atomic force microscopy as Cd incorporation and used substrate. Our study reveals significant lattice deformation from x ≥ 0.7%. The atomic force microscopy images show facetted grains for films grown on ZnO substrate but rather round for c-plane sapphire substrate. The grain shape is controlled by the presence of the ionic charges on the polar surface of ZnO which is disturbed by cadmium incorporation and also the employed substrate material.     

Galvanic deposition of ZnO using mixed electrolyte and their photoluminescence properties

The effects of Zn(OAc)₂ concentrations and chemical nature of supporting electrolytes on the galvanic deposition of ZnO have been investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) microanalysis. The results show that the taper-like ZnO crystals are apt to be produced at lower Zn(OAc)₂ concentrations, while the rod-like ZnO crystals tend to be grown at higher Zn(OAc)₂ concentrations. The photoluminescence of as-prepared ZnO nanorods shows that there exist a strong UV emission band, a broad blue band at 468 nm, and a very weak green band at 550 nm. The blue-shift of UV emission is attributed to the Cl doping of ZnO in chloride electrolyte.     

Nonpolar a-plane ZnO growth and nucleation mechanism on (1 0 0) (La,Sr)(Al,Ta)O3 substrate

Nonpolar a-plane ZnO epitaxial film with [1 1 −2 0] orientation was successfully grown on a (1 0 0) (La_0.3,Sr_0.7)(Al_0.65,Ta_0.35)O₃ (LSAT) substrate by a chemical vapor deposition method. The dependence of surface morphologies and epi-film crystallinity on the growth temperature was studied by a scanning electron microscopy and X-ray diffraction. Room temperature photoluminescence spectra all exhibit a strong near-band-edge emission peak at 378.6 nm without noticeable green band. From high resolution transmission electron microscopy, we found two distinct growth configurations for our a-plane ZnO on (1 0 0) LSAT. To explain the epitaxial properties, we illustrate four possible nucleation sites on (1 0 0) LSAT for two kinds of orientational relationship, i.e. [1 0 −1 0]_ZnO//[0 1 1]_LSAT and [0 0 0 1]_ZnO//[0 1 1]_LSAT.     

Optical and structural characteristics of ZnO thin films grown by rf magnetron sputtering

Nanostructured ZnO thin films on Pyrex glass substrates were deposited by rf magnetron sputtering at different substrate temperatures. Structural features and surface morphology were studied by X-ray diffraction and atomic force microscopy analyses. Films were found to be transparent in the visible range above 400 nm, having transparency above 90%. Sharp ultraviolet absorption edges around 370 nm were used to extract the optical band gap for samples of different particle sizes. Optical band gap energy for the films varied from 3.24 to 3.32 eV and the electronic transition was of the direct in nature. A correlation of the band gap of nanocrystalline ZnO films with particle size and strain was discussed. Photoluminescence emission in UV range, which is due to near band edge emission is more intense in comparison with the green band emission (due to defect state) was observed in all samples, indicating a good optical quality of the deposited films.     

Low temperature synthesis and optical properties of CaTiO3 nanoparticles from Ca(NO3)2·4H2O and TiO2 nanocrystals

Choosing low-melting-point Ca(NO₃)₂·4H₂O and high-reactive-activity TiO₂ nanocrystals as the raw materials, a simple and cost-effective route was developed for the synthesis of CaTiO₃ nanoparticles at 600 °C, which is much lower than that (about 1350 °C) used in the conventional solid state reaction methods. X-ray diffraction, energy dispersive X-ray spectroscopy and field emission scanning electron microscopy revealed the formation of orthorhombic phase CaTiO₃ nanoparticles with oxygen-deficiency at the surface. UV-vis absorption spectrum of the as-obtained CaTiO₃ nanoparticles displayed an absorption peak centered at around 325 nm (3.8 eV), together with a tail at lower energy side. Room temperature photoluminescence spectrum of the as-obtained CaTiO₃ nanoparticles upon laser excitation at 325 nm demonstrated a strong and broad visible light emission ranging from about 527 to 568 nm, which may be originated from the surface states and defect levels.