Effect of Cd precursor on structure and optical properties of spin coated Zn0.9Cd0.1O films for optoelectronics applications

The development of transparent conducting oxide materials has gained an increased interest in the scientific community for developing efficient low cost optoelectronic devices. The effect of Cd precursor on structural and optical properties of sol-gel synthesized Zn0.9Cd0.1O nanostructured films has been studied by using XRD, AFM, optical absorption and emission spectroscopic techniques. X-ray diffraction confirms the hexagonal wurtzite crystal structure of the deposited films and the relative intensity of diffraction peaks has been observed with different cadmium salts. The granular surface morphology of the synthesized films has been observed from AFM measurements. The optical transmission, band gap and luminescence intensity was found to change for different cadmium salts. These results are very important for developing new materials for optoelectronic applications.

Chemically Synthesized Hierarchical Flower like ZnO Microstructures

In the present study, we have deposited hierarchical flower-like microstructured zinc oxide (ZnO) thin films directly on a glass substrate by using the simplistic aqueous chemical route for different concentrations of triethanolamine (TEA) which acted like a complexing agent. The as-synthesized ZnO thin films were subsequently annealed at 300 °C and are characterized with characterization techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), photoluminescence (PL), and electrical resistivity. The hexagonal wurtzite crystal structure of as-synthesized ZnO thin films was confirmed by their XRD patterns and the well-resolved ZnO flowers-like morphology was revealed from the FESEM micrographs. From FESEM images it can be seen that the ZnO flower is composed of dozens of nanorods originating from the same core in a symmetric fashion with an average diameter of around 180-300 nm. The flower-like morphology was obtained at 0.3 M TEA concentration. Due to its hierarchical structure, the deposited ZnO thin films were employed for multiple applications such as gas sensing and anti-microbial activity. The ZnO thin films with micro-flowers like morphology showed the maximum gas sensor sensitivity ∼64.50 at 150 °C for 100 ppm of NO2 gas. Moreover, the bacteria were completely destroyed in the presence of as-deposited ZnO thin films.

CATALYST–FREE GROWTH OF WELL–ALIGNED ZnO NANOWIRES ON GRAPHENE/Si SUBSTRATEBY THERMAL EVAPORATION

Vertically well–aligned ZnO nanowire (NW) arrays with high density were directly synthesized on graphene/Si substrate by thermal evaporation of zinc powder without catalysts or additives. The ZnO NWs were characterized by field emission scanning electron microscopy (FE–SEM), high resolution transmission electron microscopy (HRTEM), X–ray diffraction (XRD), photoluminescence (PL), and Raman spectroscopy. The results showed that the obtained ZnO NWs have diameters in the range of 300–350 nm with lengths of several tens micrometers. The prepared ZnO NWs are of a single crystal, which have a hexagonal wurtzite crystal structure with c–axis (002) orientation growth perpendicular to the substrate surface. The NW arrays had a good crystal quality with excellent optical properties, indicating a sharp and strong ultraviolet emission at 380 nm, and a weak visible emission at around 516 nm.

STUDY THE RESPONSE OF GAS SENSOR USING ZnO NANORODS SYNTHESIZED BY HYDROTHERMAL METHOD

Low-dimensional nano structures ZnO are potential material for optoelectronicand gas-sensing applications. The syntheses of a large quantity of ZnO nanostructures play an important role for practical applications for future. In the paper, we propose hydrothermal reduction method to synthesize large quantities ZnO nanorods under atmospheric pressure and without using any catalysts. As-prepared ZnO nanorods exhibited a hexagonal wurtzite crystal structure. For sensing properties, ZnO nanorods were coated on the Pt interdigitated microelectrodes arrays and examined at operating temperatures of 200 to 350 oC for the detection capacity of NO2 gas. The changes in response resistance revealed that the sensor exhibited a high sensing performance for low concentrations of NO2 gas (0.5 ppm). Additionally, the ZnO nanowires sensors have a good performance to ethanol.

Microstructure and optical properties of ZnO nanorods prepared by anodic arc plasma method

Introduction: A one-dimensional ZnO nanostructure is a versatile and multifunctional n-type semiconductor. In this paper, ZnO nanorods were successfully prepared by the anodic arc plasma method in an oxidizing atmosphere. Methods: The composition, morphology, crystal microstructure, and optical properties of ZnO nanorods were characterized by using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and the corresponding selected-area electron diffraction (SAED), X-ray energy dispersive spectrometry (XEDS), ultraviolet-visible (UV-VIS) spectroscopy, Raman scattering spectrum (Raman), and photoluminescence spectrum (PL). Results: The experiment results show that ZnO nanorods synthesized by this method possess hexagonal wurtzite crystal structure with good crystallization, no other impurity phases are observed, the crystalline size is about 18 nm, and the lattice constant distortion occurs compared to that of bulk ZnO. The morphology of the sample is a rod-like shape, the length ranges from 100 nm to 300 nm, the average diameter is approximately 20 nm, and the aspect ratio is relatively high. The UV-VIS absorption spectrum occurs red shift, The Raman spectrum further demonstrates that the major peaks are assigned to ZnO optical vibrational modes, and the PL spectrum exhibits coexistence properties of ultraviolet (UV) and green emission. Conclusions: The results prove that ZnO nanorods with hexagonal wurtzite crystal structure were successfully prepared by the anodic arc plasma method in an oxidizing atmosphere.

Interface energy barrier tailoring the morphological structure evolution from ZnO nano/micro rod arrays to microcrystalline thin films by Mn doping

Hexagonal wurtzite crystal structure of pure and Mn doped ZnO nano/micro rod arrays (N/MRAs) thin films have been grown on ZnO nuclei layers by a cost effective chemical bath deposition (CBD).

Directed Growth of Branched Nanowire Structures

We describe the production of hierarchical branched nanowire structures by the sequential seeding of multiple wire generations with metal nanoparticles. Such complex structures represent the next step in the study of functional nanowires, as they increase the potential functionality of nanostructures produced in a self-assembled way. It is possible, for example, to fabricate a variety of active heterostructure segments with different compositions and diameters within a single connected structure. The focus of this work is on epitaxial III-V semiconductor branched nanowire structures, with the two materials GaP and In As used as typical examples of branched structures with cubic (zinc blende) and hexagonal (wurtzite) crystal structures. The general morphology of these structures will be described, as well as the relationship between morphology and crystal structure.

Microwave AlxGa1−xN/GaN Power HEMT's

ABSTRACTGaN in its hexagonal Wurtzite crystal has 3.4 eV bandgap and is capable of withstanding over 3 MV/cm electric field intensity. It is grown on either sapphire or SiC and the lattice mismatches cause threading dislocations. If it is grown along the c-axis on its Ga face, a thin pseudomorphic AlxGa1−xN barrier layer grown on top causes a substantial electrical polarization, which induces a substantial 2DEG in the GaN [1]. With x =.3 this 2 DEG is about 1 × 1013/cm2 without any doping impurities. The ∼ 109/cm2 threading dislocations accept electrons from the low density ambient donors, yielding very low net electron densities (< 1014/cm3) in the GaN buffer layer used as the HEMT channel [2]. The 2DEG electron mobility can be 1500-1700 cm2/V-s with ≥ 1 × 1013/cm2 electron sheet density. This 2DEG sheet density charge is less than the electrical polarization charge of 1.7 × 1013/cm2 for Al.3Ga.7N/GaN, due to some surface depletion and due to the fact that each dislocation traps ≥ 2 × 103 electrons. The design, processing, and measured performance of such undoped, polarization-induced HEMT's are presented below.