Search results for "defect"
showing 10 items of 879 documents
Comprehensive defect suppression in perovskite nanocrystals for high-efficiency light-emitting diodes
2021
Electroluminescence efficiencies of metal halide perovskite nanocrystals (PNCs) are limited by a lack of material strategies that can both suppress the formation of defects and enhance the charge carrier confinement. Here we report a one-dopant alloying strategy that generates smaller, monodisperse colloidal particles (confining electrons and holes, and boosting radiative recombination) with fewer surface defects (reducing non-radiative recombination). Doping of guanidinium into formamidinium lead bromide PNCs yields limited bulk solubility while creating an entropy-stabilized phase in the PNCs and leading to smaller PNCs with more carrier confinement. The extra guanidinium segregates to th…
<title>F-type centers in LiBaF<formula><inf><roman>3</roman></inf></formula> crystals</title>
2003
A comparative study of optical properties of thermochemically reduced undoped LiBaF3 crystals is reported. In LiBaF3 crystals obtained or treated in a reducing atmosphere an absorption band at 240 nm and a corresponding luminescence band at 505 nm are observed at 85 K. The main constituent of the center may be an anion vacancy with a trapped electron (an F-type center in LiBaF3 crystals).© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
A microscopic model for long-term laser damage in calcium fluoride
2009
Single crystal calcium fluoride (CaF 2 ) is an important lens material in deep-ultraviolet optics, where it is exposed to high radiation densities. The known rapid damage process in CaF 2 upon ArF laser irradiation cannot account for irreversible damage after long irradiation times. We use density functional methods to calculate the properties of laser-induced point defects and to investigate defect stabilization mechanisms on a microscopic level. The mobility of the point defects plays a major role in the defect stabilization mechanisms. Besides stabilization by impurities, we find that the agglomeration of F-centers plays a significant role in long-term laser damage of CaF 2 . We present …
Phase defect inspection of multilayer masks for 13.5 nm optical lithography using PEEM in a standing wave mode
2007
We report on recent developments of an "at wavelength" full-field imaging technique for defect inspection of multilayer mask blanks for extreme ultraviolet lithography (EUVL). Our approach uses photoemission electron microscopy (PEEM) in a near normal incidence mode at 13.5 nut wavelength to image the photoemission induced by the EUV wave field on the multilayer blank surface. We analyze buried defects on Mo/Si multilayer samples down to a lateral size of 50 nm and report on first, results obtained from a six inches mask blank prototype as prerequisite for industrial usage. (c) 2007 Elsevier B.V. All rights reserved.
Ultrasonic phased array inspection of wire plus arc additive manufacture samples using conventional and total focusing method imaging approaches
2019
In this study, three aluminium samples produced by wire + arc additive manufacture (WAAM) are inspected using ultrasonic phased array technology. Artificial defects are machined using a centre drill, ø 3 mm, and electrical discharge machining (EDM), ø 0.5-1 mm, in a cylindrical through-hole topology. The samples are first inspected using a single-element wheel probe mounted on a KUKA robot in order to investigate the feasibility of using a conventional ultrasonic transducer approach. Unfortunately, the wheel probe is found to be unsuitable for scanning the WAAM specimens and ultrasonic phased arrays are employed next. The set-up includes 5 MHz and 10 MHz arrays (128 elements) in direct cont…
Surface properties of AlInGaN/GaN heterostructure
2016
Abstract Surface structural, electronic and electrical properties of the quaternary alloy AlInGaN/GaN heterostructures are investigated. Surface termination, atomic arrangement, electronic and electrical properties of the (0001) surface and (10–11) V-defect facets have been experimentally analyzed using various surface sensitive techniques including spectroscopy and microscopy. Moreover, the effect of sub-band gap (of the barrier layer) illumination on contact potential difference (VCPD) and the role of oxygen chemisorption have been studied.
Optically detected magnetic resonances of nitrogen-vacancy ensembles inC13-enriched diamond
2016
We present an experimental and theoretical study of the optically detected magnetic resonance signals for ensembles of negatively charged nitrogen-vacancy (NV) centers in a $^{13}\mathrm{C}$ isotopically enriched single-crystal diamond. We observe four broad transition peaks with superimposed sharp features at zero magnetic field and study their dependence on an applied magnetic field. A theoretical model that reproduces all qualitative features of these spectra is developed. Understanding the magnetic-resonance spectra of NV centers in an isotopically enriched diamond is important for emerging applications in nuclear magnetic resonance.
Optically active oxygen-deficiency-related centers in amorphous silicon dioxide
1998
Abstract The spectroscopic properties, structure and interconversions of optically active oxygen-deficiency-related point defects in vitreous silica are reviewed. These defects, the E′-centers (oxygen vacancies with a trapped hole or 3-fold-coordinated silicons), different variants of diamagnetic `ODCs' (oxygen-deficiency centers), and their Ge-related analogs play a key role in the fiber-optic Bragg grating writing processes. The controversy surrounding the structural models for the Si- and Ge-related ODCs is discussed and the similarity between the bulk and surface point defects in silica is emphasized. The possible interconversion mechanisms between 2-fold-coordinated Si, neutral oxygen …
Rippling of two-dimensional materials by line defects
2020
Two-dimensional materials and their mechanical properties are known to be profoundly affected by rippling deformations. However, although ripples are fairly well understood, less is known about their origin and controlled modification. Here, motivated by recent reports of laser-controlled creation of line defects in graphene, we investigate how line defects could be used to control rippling in graphene and other two-dimensional materials. By sequential multi-scale coupling of density-functional tight-binding and continuum elasticity simulations, we quantify the amount of rippling when the number and the cumulative length of the line defects increase. Simulations show that elastic sheets wit…
A new approach for actinic defect inspection of EUVL multilayer mask blanks: Standing wave photoemission electron microscopy
2006
Extreme ultraviolet lithography (EUVL) at 13.5 nm is the next generation lithography technique capable of printing sub-50 nm structures. With decreasing feature sizes to be printed, the requirements for the lithography mask also become more stringent in terms of defect sizes and densities that are still acceptable and the development of lithography optics has to go along with the development of new mask defect inspection techniques that are fast and offer high resolution (preferable in the range of the minimum feature size) at the same time. We report on the development and experimental results of a new 'at wavelength' full-field imaging technique for defect inspection of multilayer mask bl…