Electrical properties of ZnO nanorods studied by conductive atomic force microscopy

ZnO nanostructures are promising candidates for the development of novel electronic devices due to their unique electrical and optical properties. Here, we present a complementary electrical characterization of individual upright standing and lying ZnO nanorods using conductive atomic force microscopy (C-AFM). Initially, the electrical properties of the arrays of upright standing ZnO NRs were characterized using two-dimensional current maps. The current maps were recorded simultaneously with the topography acquired by contact mode AFM. Further, C-AFM was utilized to determine the local current-voltage (I-V) characteristics of the top and side facets of individual upright standing NRs. Current-voltage characterization revealed a characteristic similar to that of a Schottky diode. Detailed discussion of the electrical properties is based on local I-V curves, as well as on the 2D current maps recorded from specific areas. © 2011 American Institute of Physics.published_or_final_versio

Influence of indium-tin-oxide thin-film quality on reverse leakage current of indium-tin-oxide/n-GaN Schottky contacts

Indium-tin-oxide (ITO)/n-GaN Schottky contacts were prepared by e-beam evaporation at 200°C under various partial pressures of oxygen. X-ray photoemission spectroscopy and positron beam measurements were employed to obtain chemical and structural information of the deposited ITO films. The results indicated that the observed variation in the reverse leakage current of the Schottky contact and the optical transmittance of the ITO films were strongly dependent on the quality of the ITO film. The high concentration of point defects at the ITO-GaN interface is suggested to be responsible for the large observed leakage current of the ITO/n-GaN Schottky contacts. © 2005 American Institute of Physics.published_or_final_versio

Effect of [OH-] linkages on luminescent properties of ZnO nanoparticles

Optical properties of ZnO nanoparticles prepared from a simple chemical method using sodium zincate bath show strong white light emission. X-ray absorption fine structure studies reveal a completely different local environment around Zn in these ZnO nanoparticles. The observed luminescence properties and local structural changes have been explained on the basis of a linkage between Zn and OH- ions in the surface layers of ZnO nanoparticles.Comment: J. Phys. Chem. C. (2011) (in print

Broadband luminescence in defect-engineered electrochemically produced porous Si/ZnO nanostructures

The fabrication, by an all electrochemical process, of porous Si/ZnO nanostructures with engineered structural defects, leading to strong and broadband deep level emission from ZnO, is presented. Such nanostructures are fabricated by a combination of metal-assisted chemical etching of Si and direct current electrodeposition of ZnO. It makes the whole fabrication process low-cost, compatible with Complementary Metal-Oxide Semiconductor technology, scalable and easily industrialised. The photoluminescence spectra of the porous Si/ZnO nanostructures reveal a correlation between the lineshape, as well as the strength of the emission, with the morphology of the underlying porous Si, that control the induced defects in the ZnO. Appropriate fabrication conditions of the porous Si lead to exceptionally bright Gaussian-type emission that covers almost the entire visible spectrum, indicating that porous Si/ZnO nanostructures could be a cornerstone material towards white-light-emitting devices

Device Optimization of Tris-Aluminum (Alq3) Based Bilayer Organic Light Emitting Diode Structures

In this work we present detailed analysis of the emitted radiation spectrum from tris(8-hydroxyquinoline) aluminum (Alq3) based bilayer OLEDs as a function of: the choice of cathode, the thickness of organic layers, and the position of the hole transport layer/Alq3 interface. The calculations fully take into account dispersion in the glass substrate, the indium tin oxide anode, and in the organic layers, as well as the dispersion in the metal cathode. Influence of the incoherent transparent substrate (1 mm glass substrate) is also fully accounted for. Four cathode structures have been considered: Mg/Ag, Ca/Ag, LiF/Al, and Ag. For the hole transport layer, N,N'-diphenyl-N,N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) and N,N'-di(naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB) were considered. As expected, emitted radiation is strongly dependent on the position of the emissive layer inside the cavity and its distance from the metal cathode. Although our optical model for an OLED does not explicitly include exciton quenching in vicinity of the metal cathode, designs placing the emissive layer near the cathode are excluded to avoid unrealistic results. Guidelines for designing devices with optimum emission efficiency are presented. Finally, several different devices were fabricated and characterized and experimental and calculated emission spectra were compared

Phytotoxic Effects of (±)-Catechin In vitro, in Soil, and in the Field

BACKGROUND: Exploring the residence time of allelochemicals released by plants into different soils, episodic exposure of plants to allelochemicals, and the effects of allelochemicals in the field has the potential to improve our understanding of interactions among plants. METHODOLOGY/PRINCIPAL FINDINGS: We conducted experiments in India and the USA to understand the dynamics of soil concentrations and phytotoxicity of (+/-)-catechin, an allelopathic compound exuded from the roots of Centaurea maculosa, to other plants in vitro and in soil. Experiments with single and pulsed applications into soil were conducted in the field. Experimental application of (+/-)-catechin to soils always resulted in concentrations that were far lower than the amounts added but within the range of reported natural soil concentrations. Pulses replenished (+/-)-catechin levels in soils, but consistently at concentrations much lower than were applied, and even pulsed concentrations declined rapidly. Different natural soils varied substantially in the retention of (+/-)-catechin after application but consistent rapid decreases in concentrations over time suggested that applied experimental concentrations may overestimate concentrations necessary for phytotoxicity by over an order of magnitude. (+/-)-Catechin was not phytotoxic to Bambusa arundinacea in natural Indian soil in a single pulse, but soil concentrations at the time of planting seeds were either undetectable or very low. However, a single dose of (+/-)-catechin suppressed the growth of bamboo in sand, in soil mixed with organic matter, and Koeleria macrantha in soils from Montana and Romania, and in field applications at 40 microg l(-1). Multiple pulses of (+/-)-catechin were inhibitory at very low concentrations in Indian soil. CONCLUSIONS/SIGNIFICANCE: Our results demonstrate that (+/-)-catechin is highly dynamic in natural soils, but is phytotoxic well below natural concentrations measured in some soils and applied at low concentrations in the field. However, there is substantial conditionality in the effects of the allelochemical

Roadmap on commercialization of metal halide perovskite photovoltaics

Perovskite solar cells (PSCs) represent one of the most promising emerging photovoltaic technologies due to their high power conversion efficiency. However, despite the huge progress made not only in terms of the efficiency achieved, but also fundamental understanding of the relevant physics of the devices and issues which affect their efficiency and stability, there are still unresolved problems and obstacles on the path toward commercialization of this promising technology. In this roadmap, we aim to provide a concise and up to date summary of outstanding issues and challenges, and the progress made toward addressing these issues. While the format of this article is not meant to be a comprehensive review of the topic, it provides a collection of the viewpoints of the experts in the field, which covers a broad range of topics related to PSC commercialization, including those relevant for manufacturing (scaling up, different types of devices), operation and stability (various factors), and environmental issues (in particular the use of lead). We hope that the article will provide a useful resource for researchers in the field and that it will facilitate discussions and move forward toward addressing the outstanding challenges in this fast-developing field