Sandia National Laboratories

About: Sandia National Laboratories is a facility organization based out in Livermore, California, United States. It is known for research contribution in the topics: Laser & Thin film. The organization has 21501 authors who have published 46724 publications receiving 1484388 citations. The organization is also known as: SNL & Sandia National Labs.

Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact†

Abstract: tion (AR) coatings, [7–10] and optical resonators. [11] In many cases, however, the unavailability of materials with desired refractive indices, particularly materials with very low refractive indices, prevents the implementation of optical components with very high performance. In addition, the choice of a material with desired refractive index often forces a compromise in other materials properties such as optical transmittance and electrical conductivity that are also important for most optoelectronic applications. Here, we show that oblique-angle deposition can be used to tailor the refractive index of a thinfilm material that is chosen for its desired material properties other than refractive index. The unique ability to control the refractive index of thin film materials allows one to eliminate Fresnel reflection, one of the fundamental limitations in lightextraction efficiency of light-emitting diodes (LEDs), by fabricating coatings whose refractive index gradually decreases from the refractive index of the active semiconductor layer to the refractive index of the surrounding medium. As an example of this concept, we present a six-layer graded-refractiveindex (GRIN) AR coating made entirely of a single material, indium tin oxide (ITO), chosen for its high conductivity, high optical transmittance, and low contact resistance with GaN. Each layer has a refractive index that is individually tuned to form a stack with refractive index graded from its dense ITO value down to the value close to that of air for an optimum AR performance. It is shown that GaInN LEDs with a GRIN ITOAR contact achieve a light-extraction efficiency enhancement of 24.3 % compared to the LEDs with dense ITO coating due to a strongly reduced Fresnel reflection at the ITO– air interface. Oblique-angle deposition is a method of growing porous thin films, and hence thin films with low-refractive index (lown), enabled by surface diffusion and self-shadowing effects during the deposition process. [12–16] In oblique-angle deposition, a random growth fluctuation on the substrate produces a shadow region that the incident vapor flux cannot reach, and a non-shadow region where incident flux deposits preferentially, thereby creating an oriented rodlike structure with high porosity. Figure 1 shows the cross-sectional scanning-electron microscopy (SEM) image of low-n ITO, which is electrically conductive and optically transparent in visible wavelengths, COMMUNICATION

Wavelet Transform for Structural Health Monitoring: A Compendium of Uses and Features:

Abstract: The strategic and monetary value of the civil infrastructure worldwide necessitates the development of structural health monitoring (SHM) systems that can accurately monitor structural response due to real-time loading conditions, detect damage in the structure, and report the location and nature of this damage. In the last decade, extensive research has been carried out for developing vibration-based damage detection algorithms that can relate structural dynamics changes to damage occurrence in a structure. In the mean time, the wavelet transform (WT), a signal processing technique based on a windowing approach of dilated ‘scaled’ and shifted wavelets, is being applied to a broad range of engineering applications. Wavelet transform has proven its ability to overcome many of the limitations of the widely used Fourier transform (FT); hence, it has gained popularity as an efficient means of signal processing in SHM systems. This increasing interest in WT for SHM in diverse applications motivates the authors...

Fundamentals of technology roadmapping

Abstract: Technology planning is important for many reasons. Globally, companies are facing many competitive problems. Technology roadmapping, a form of technology planning can help deal with this increasingly competitive environment. While it has been used by some companies and industries, the focus has always been on the technology roadmap as a product, not on the process. This report focuses on formalizing the process so that it can be more broadly and easily used. As a DOE national security laboratory with R&D as a major product, Sandia must do effective technology planning to identify and develop the technologies required to meet its national security mission. Once identified, technology enhancements or new technologies may be developed internally or collaboratively with external partners. For either approach, technology roadmapping, as described in this report, is an effective tool for technology planning and coordination, which fits within a broader set of planning activities. This report, the second in a series on technology roadmapping, develops and documents this technology roadmapping process, which can be used by Sandia, other national labs, universities, and industry. The main benefit of technology roadmapping is that it provides information to make better technology investment decisions by identifying critical technologies and technology gaps and identifying ways to leverage R&D investments. It can also be used as a marketing tool. Technology roadmapping is critical when the technology investment decision is not straight forward. This occurs when it is not clear which alternative to pursue, how quickly the technology is needed, or when there is a need to coordinate the development of multiple technologies. The technology roadmapping process consists of three phases - preliminary activity, development of the technology roadmap, and follow-up activity.

Sensor Placement in Municipal Water Networks

Abstract: We present a model for optimizing the placement of sensors in municipal water networks to detect maliciously injected contaminants. An optimal sensor configuration minimizes the expected fraction of the population at risk. We formulate this problem as a mixed-integer program, which can be solved with generally available solvers. We find optimal sensor placements for three test networks with synthetic risk and population data. Our experiments illustrate that this formulation can be solved relatively quickly and that the predicted sensor configuration is relatively insensitive to uncertainties in the data used for prediction.