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.

Optical and Electronic Properties of Si Nanoclusters Synthesized in Inverse Micelles

Abstract: Highly crystalline, size-selected silicon (Si) nanocrystals in the size range 2-10 nm were grown in inverse micelles and their optical absorption and photoluminescence (PL) properties were studied. High resolution TEM and electron diffraction results show that these nanocrystals retain their cubic diamond stuctures down to sizes {approximately}4 nm in diameter, and optical absorption data suggest that this structure and bulk-like properties are retained down to the smallest sizes produced ({approximately}1.8 nm diameter containing about 150 Si atoms). High pressure liquid chromatography techniques with on-line optical and electrical diagnostics were developed to purify and separate the clusters into pure, monodisperse populations. The optical absorption revealed features associated with both the indirect and direct bandgap transitions, and these transitions exhibited different quantum confinement effects. The indirect bandgap shifts from 1.1 eV in the bulk to {approximately}2.1 eV for nanocrystals {approximately}2 nm in diameter and the direct transition at r(l_"X - r15) blue shifts by 0.4 eV from its 3.4 eV bulk value over the same size range. Tailorable, visible, room temperature PL in the range 700-350 nm (1.8 - 3.5 eV) was observed from these nanocrystals. The most intense PL was in the violet region of the spectrum ({approximately}400 nm) and is attributed to direct electron-hole recombination. Other less intense PL peaks are attributed to surface state and to indirect bandgap recombination. The results are compared to earlier work on Si clusters grown by other techniques and to the predictions of various model calculations. Currently, the wide variations in the theoretical predictions of the various models along with considerable uncertainties in experimental size determination for clusters less than 3-4 nm, make it difficult to select among competing models.

Laser beam shaping : theory and techniques

Abstract: Preface Editor Contributors Introduction Todd E. Lizotte and Fred M. Dickey Hitachi Via Mechanics (USA), Inc., Londonderry, New Hampshire and FMD Consulting, LLC, Springfield, Missouri, USA The Mathematical and Physical Theory of Lossless Beam Shaping Louis A. Romero and Fred M. Dickey Department of Computational and Applied Mathematics, Sandia National Laboratories, Albuquerque, New Mexico, USA and FMD Consulting, LLC, Springfield, Missouri, USA Laser-Beam-Splitting Gratings Louis A. Romero and Fred M. Dickey Department of Computational and Applied Mathematics, Sandia National Laboratories, Albuquerque, New Mexico, USA and FMD Consulting, LLC, Springfield, Missouri, USA Vortex Beam Shaping Carlos Lopez-Mariscal and Julio C. Gutierrez-Vega US Naval Research Laboratory, Washington, District of Columbia, USA and Photonics and Mathematical Optics Group, Tecnologico de Monterrey, Mexico Gaussian Beam Shaping: Diffraction Theory and Design Fred M. Dickey and Scott C. Holswade FMD Consulting, LLC, Springfield, Missouri, USA and Sandia National Laboratories, Albuquerque, New Mexico, USA Geometrical Methods David L. Shealy and John A. Hoffnagle Department of Physics, University of Alabama at Birmingham, USA and Picarro, Inc., Santa Clara, California, USA Optimization-Based Designs Alexander Laskin, David L. Shealy, and Neal C. Evans AdlOptica GmbH, Berlin, Germany, Department of Physics, University of Alabama at Birmingham, USA, and PointClear Solutions, Inc., Innovation Depot, Birmingham, Alabama, USA Beam Shaping with Diffractive Diffusers Jeremiah D. Brown and David R. Brown JENOPTIK Optical Systems, Inc., Huntsville, Alabama, USA and MEMS Optical, LLC, Huntsville, Alabama, USA Engineered Microlens Diffusers Tasso R. M. Sales RPC Photonics Inc., Rochester, New York, USA Multi-Aperture Beam Integration Systems Daniel M. Brown, Fred M. Dickey, and Louis S. Weichman Optosensors Technology, Inc., Gurley, Alabama, USA, FMD Consulting, LLC, Springfield, Missouri, USA, and Sandia National Laboratories, Albuquerque, New Mexico, USA Axicon Ring Generation Systems Fred M. Dickey, Carlos Lopez-Mariscal, and Daniel M. Brown FMD Consulting, LLC, Springfield, Missouri, USA, US Naval Research Laboratory, Washington, District of Columbia, USA, and Optosensors Technology, Inc., Gurley, Alabama, USA Current Technology of Beam Profile Measurement Kevin D. Kirkham and Carlos B. Roundy Ophir-Spiricon, LLC, North Logan, Utah, USA Classical (Nonlaser) Methods David L. Shealy Department of Physics, University of Alabama at Birmingham, USA Index

Rapid prototyping of patterned functional nanostructures

Abstract: Living systems exhibit form and function on multiple length scales and at multiple locations. In order to mimic such natural structures, it is necessary to develop efficient strategies for assembling hierarchical materials. Conventional photolithography, although ubiquitous in the fabrication of microelectronics and microelectromechanical systems, is impractical for defining feature sizes below 0.1 micrometres and poorly suited to pattern chemical functionality. Recently, so-called ‘soft’ lithographic approaches1 have been combined with surfactant2,3 and particulate4 templating procedures to create materials with multiple levels of structural order. But the materials thus formed have been limited primarily to oxides with no specific functionality, and the associated processing times have ranged from hours to days. Here, using a self-assembling ‘ink’, we combine silica–surfactant self-assembly with three rapid printing procedures—pen lithography, ink-jet printing, and dip-coating of patterned self-assembled monolayers—to form functional, hierarchically organized structures in seconds. The rapid-prototyping procedures we describe are simple, employ readily available equipment, and provide a link between computer-aided design and self-assembled nanostructures. We expect that the ability to form arbitrary functional designs on arbitrary surfaces will be of practical importance for directly writing sensor arrays and fluidic or photonic systems.

Dielectrophoresis in microchips containing arrays of insulating posts: theoretical and experimental results.

Abstract: Dielectrophoresis (DEP), a nonlinear electrokinetic transport mechanism, can be used to concentrate and sort cells, viruses, and particles. To date, microfabricated DEP-based devices have typically used embedded metal electrodes to apply spatially nonuniform, time-varying (AC) electric fields. We have developed an alternative method in which arrays of insulating posts in a channel of a microchip produce the spatially nonuniform fields needed for DEP. Electrodes may be located remotely, allowing operation of the device down to zero frequency (DC) without excessive problems of electrolysis. Applying a sufficiently large electric field across an insulating-post array produces two flow regimes through a competition between electrokinetic flow (combined electrophoresis and electroosmosis) and dielectrophoresis. “Streaming DEP” is observed when DEP dominates diffusion but is overcome by electrokinetic flow. Particles concentrated by DEP forces in areas of electric field extrema travel electrokinetically down th...

Direct Assembly of Large Arrays of Oriented Conducting Polymer Nanowires

Abstract: Although oriented carbon nanotubes, oriented nanowires of metals, semiconductors and oxides have attracted wide attention, there have been few reports on oriented polymer nanostructures such as nanowires. In this paper we report the assembly of large arrays of oriented nanowires through controlled nucleation and growth during a stepwise electrochemical deposition process in which a large number of nuclei were first deposited on the substrate using a large current density. After the initial nucleation, the current density was reduced step by step to grow the oriented nanowires from the nucleation sites created in the first step. A very different morphology was also demonstrated by first depositing a monolayer of close-packed colloidal spheres using a similar step-wise deposition process. As a result, the polymer nanofibers grew from the spheres in a radial fashion and formed the continuous three-dimensional network of nanofibers in the film. The principles of control nucleation and growth in electrochemical deposition investigated in this paper should be applicable to other electrical conducting and electrochemical active materials, including metals and conducting oxides. We also hope the oriented electroactive polymer nanostructure will open the door for new applications, such as miniaturized biosensors.