Micro-spectroscopy on silicon wafers and solar cells

Micro-Raman (μRS) and micro-photoluminescence spectroscopy (μPLS) are demonstrated as valuable characterization techniques for fundamental research on silicon as well as for technological issues in the photovoltaic production. We measure the quantitative carrier recombination lifetime and the doping density with submicron resolution by μPLS and μRS. μPLS utilizes the carrier diffusion from a point excitation source and μRS the hole density-dependent Fano resonances of the first order Raman peak. This is demonstrated on micro defects in multicrystalline silicon. In comparison with the stress measurement by μRS, these measurements reveal the influence of stress on the recombination activity of metal precipitates. This can be attributed to the strong stress dependence of the carrier mobility (piezoresistance) of silicon. With the aim of evaluating technological process steps, Fano resonances in μRS measurements are analyzed for the determination of the doping density and the carrier lifetime in selective emitters, laser fired doping structures, and back surface fields, while μPLS can show the micron-sized damage induced by the respective processes

The Coptic Wizard's Hoard

This is the publisher's version, also available electronically from http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=7824067&fileId=S0017816000030224.Within the large collection of ancient manuscripts at the University of Michigan there is a group of Coptic papyri which appears to have been a hoard or library of ancient magical texts. Produced by five copyists sometime in the fourth through seventh centuries and originating from a now unknown location in Egypt, the collection was brought to the British Museum by Sir E. A. Wallis Budge in February 1921 for restoration by C. T. Lamacraft; in August of that year, it underwent philological examination by the Coptic lexicographer Walter E. Crum, and was later forwarded to the University of Michigan

'Proximal' and 'distal' in language and cognition: Evidence from deictic demonstratives in Dutch

In this paper we examine the differences in use between distal and proximal demonstrative terms (e.g., singular '�this�' and '�that�', and plural '�these�' and '�those�' in English). The proximal–distal distinction appears to be made in all languages and therefore promises to be an important window on the cognitive mechanisms underlying language production and comprehension. We address the problem of accounting for the distinction through a corpus-based quantitative study of the deictic use of demonstratives in Dutch. Our study suggests that the distal–proximal distinction corresponds with use of the proximal for intensive/strong indicating (i.e., directing of attention) and the distal for neutral indicating. We compare our findings with empirical findings on the use of English demonstratives and argue that, despite some apparent differences, Dutch and English demonstratives behave roughly similarly though not identically. Finally, we put our findings into context by pulling together evidence from a number of converging sources on the relationship between indicating and describing as alternative modes of reference in the use of distal and proximal demonstratives. This will also lead us to a new understanding of the folk-view on distals and proximals as distinguishing between nearby and faraway objects

Basic notions of information structure

This article takes stock of the basic notions of Information Structure (IS). It first provides a general characterization of IS — following Chafe (1976) — within a communicative model of Common Ground(CG), which distinguishes between CG content and CG management. IS is concerned with those features of language that concern the local CG. Second, this paper defines and discusses the notions of Focus (as indicating alternatives) and its various uses, Givenness (as indicating that a denotation is already present in the CG), and Topic (as specifying what a statement is about). It also proposes a new notion, Delimitation, which comprises contrastive topics and frame setters, and indicates that the current conversational move does not entirely satisfy the local communicative needs. It also points out that rhetorical structuring partly belongs to IS.Peer Reviewe

Enriching news events with meta-knowledge information

Given the vast amounts of data available in digitised textual form, it is important to provide mechanisms that allow users to extract nuggets of relevant information from the ever growing volumes of potentially important documents. Text mining techniques can help, through their ability to automatically extract relevant event descriptions, which link entities with situations described in the text. However, correct and complete interpretation of these event descriptions is not possible without considering additional contextual information often present within the surrounding text. This information, which we refer to as meta-knowledge, can include (but is not restricted to) the modality, subjectivity, source, polarity and specificity of the event. We have developed a meta-knowledge annotation scheme specifically tailored for news events, which includes six aspects of event interpretation. We have applied this annotation scheme to the ACE 2005 corpus, which contains 599 documents from various written and spoken news sources. We have also identified and annotated the words and phrases evoking the different types of meta-knowledge. Evaluation of the annotated corpus shows high levels of inter-annotator agreement for five meta-knowledge attributes, and moderate level of agreement for the sixth attribute. Detailed analysis of the annotated corpus has revealed further insights into the expression mechanisms of different types of meta-knowledge, their relative frequencies and mutual correlations

Sensors and 'Apps' for Community-Based Atmospheric Monitoring

Recent advances in both sensors and wireless communication provide opportunities for improved exposure assessment and increasing community involvement in reducing levels of human exposure to airborne contaminants. These new technologies can enhance data collection to answer science and policy questions related to the health and environmental effects of air pollution. In recent years, wireless sensor networks (WSNs) have matured and greatly lowered the cost of collecting data by eliminating the wiring that was once necessary. A 2010 U.S. Department of Energy cost-benefit analysis of changing from wired to wireless automation systems indicated a three-fold reduction in the initial investment and a five-fold reduction in annual operating costs. 2 In this article, we describe a particulate matter (PM) monitor made by microfabrication techniques, derived from the manufacture of integrated circuits, 3 and show how sensor data can be accessed by existing cell phone technology. Today, the environmental monitoring community can select from digital applications ("apps") for recording, processing, and sharing sensor data. Integrating air pollution and individual physiological data collected simultaneously from networked sensors and suitable apps will empower individuals and communities with information useful in reducing exposures to air pollutants. Present Sensor Landscape At the heart of all sensor systems lie the elements that respond to nearby changes in physical or chemical characteristics and the transducers that convert the responses to electrical signals. Commercially available gas sensors are based on two main principles: (1) Chemical gas sensors depend on reactions between the target gases and the sensing material as used for ozone (O3), nitrogen dioxide (NO 2), and carbon monoxide (CO), and sometimes for carbon dioxide (CO2) and volatile organic compounds (VOCs); and (2) Optical gas sensors measure absorption of light by species of interest, such as O 3 and CO2 or chemiluminescence for NO2. Infrared absorption is widely used for CO 2. Sensors for respirable particles [below 2.5 µm aerodynamic diameter] typically rely on light scattering, a widely used method to monitor PM in near real-time, although not a direct mass measurement. Table S-1 provides additional details on detection principles, concentration ranges, accuracy, and precision, as well as strengths and weaknesses for each sensor type. New Technologies WSNs incorporate recent advances in several areas of electrical engineering. These include • Microfabrication techniques now make possible smaller, mass-produced sensors that are lightweight and ultimately inexpensive. In addition to micro-electro-mechanical system (MEMS) sensors with tiny (mm-scale or smaller) moving parts, sensors incorporating microfluidic, optical, and nanotube elements are also being developed. • The costs of monitoring over large geographical areas are decreasing because signals from widely dispersed sensors can travel over existing secure WSNs. • Energy efficient radios and sensor circuits now allow for low-maintenance operation without the need for plug-in power or direct operator access. Microfabricated Portable PM Monitor Measuring PM mass based on the rate of change in oscillating frequency is a well-established direct mass measurement method (e.g., in the tapered element oscillating microbalance [TEOM]) that has achieved equivalency as a continuous mass monitor for PM 2.5. 5 Use of transparent materials in the device allows for inclusion of optical approaches, such as particle counting to measure the size distribution and, with the simultaneous mass measurement, to obtain particle effective density (µg/cm 3 ). 6 Measuring light absorption and scattering could provide insight into chemical composition and radiative forcing by the aerosol. Another benefit of the PM monitor' s small size is that it can be packaged with sensors for temperature, relative humidity, and gases and even sensors for human physiological responses such as blood pressure and heart rate. Stationary and Mobile Applications Stationary: Indoors and Outdoors Limited spatial and temporal information constrains our understanding of the spatial variability of pollutants indoors and outdoors, and obscures the relationship between them. However, most monitoring and research networks include only a few monitors in a given area, often limited to specific time periods, due to the high cost to site and operate samplers. 7-10 Indoor sampling is usually limited to a small number of homes, with a small number of samplers in each dwelling and for short time periods, days or weeks, such as the study on the relationships of indoor, outdoor, and personal air (RIOPA), as reported by Meng et al. 12 When sensors are used at stationary monitoring sites, the cost advantages of microfabricated multipollutant sensors (see 13 However, Honicky 14 showed that by colocating N identical sensors that have Gaussian response functions, the standard error decreases by 1/N. Adding transmitters to the stationary sensor packages makes possible two-way communication over a WSN in near real-time, allowing this information to be accessed by community members and used for short-range forecasting of air pollution and alerts. Weather Bug is one example of this approach using standard meteorological sensors. [Editor's Note: An example of installing and powering small stationary sensors appears in the supplemental information that can be found in the online version of this article at www.awma.org.] Mobile and Personal Applications The integration of sensors and cell phones begins to provide a new dimension to air quality monitoring. The sensors may be internal or external to the mobile device and may be worn on the body to measure personal exposure. Coupling multifunctional monitors to cell phones also enables geolocation and data transmission via a cellular network. Dutta' s group at the University of Michigan 15 has shown how mobile devices can power sensors via the iPhone headset plug, as well as transmit information through the wireless network. Energy to power the sensor is provided by a 22 kHz audio tone produced by the mobile device and then efficiently amplified and rectified externally to yield approximately 14 milliwatts of DC power. The effective data rate is 30 bytes/sec. These methods provide an elegant approach to obtaining data of This four day conference offers a variety of technical sessions that address technical and policy issues associated with air, water, and waste in connection with shale oil and gas exploration and production. This 90-minute webinar is designed to help shale gas developers respond to stricter government regulations, permitting policies, best practices and more public participation in the administration process. Hear directly from leading industry consultants and, counsel and pose questions via electronic chat

Novel chemoresistive CH4 sensor with 10 ppm sensitivity based on multiwalled carbon nanotubes functionalized with SnO2 nanocrystals

Chemoresistive sensors based on multiwalled carbon nanotubes (MWCNTs) functionalized with SnO2 nanocrystals (NCs) have great potential for detecting trace gases at low concentrations (single ppm levels) at room temperature, because the SnO2 nanocrystals act as active sites for the chemisorption of gas molecules, and carbon nanotubes (CNTs) act as an excellent current carrying platform, allowing the adsorption of gas on SnO2 to modulate the resistance of the CNTs. However, uniform conjugation of SnO2 NCs with MWCNTs is challenging. An effective atomic layer deposition based approach to functionalize the surface of MWCNTs with SnO2 NCs, resulting in a novel CH4 sensor with 10ppm sensitivity, is presented in this paper. Scanning electron microscopy, transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy, and Raman spectroscopy were implemented to study the morphology, elemental composition, and the crystal quality of SnO2 functionalized MWCNTs. High resolution TEM images showed that the crystal quality of the functionalizing SnO2 NCs was of high quality with clear lattice fringes and the dimension almost three times smaller than shown thus far in literature. A lift-off based photolithography technique comprising bilayer photoresists was optimized to fabricate SnO2 functionalized MWCNTs-based chemoresistor sensor, which at room temperature can reliably sense below 10ppm of CH4 in air. Such low level gas sensitivity, with significant reversible relative resistance change, is believed to be the direct result of the successful functionalization of the MWCNT surface by SnO2 NCs