Session C1: Applied Physics

Order Parameters for Two-Dimensional Networks

We derive methods that explain how to quantify the amount of order in ``ordered'' and ``highly ordered'' porous arrays. Ordered arrays from bee honeycomb and several from the general field of nanoscience are compared. Accurate measures of the order in porous arrays are made using the discrete pair distribution function (PDF) and the Debye-Waller Factor (DWF) from 2-D discrete Fourier transforms calculated from the real-space data using MATLAB routines. An order parameter, OP$_{3}$, is defined from the PDF to evaluate the total order in a given array such that an ideal network has the value of 1. When we compare PDFs of man-made arrays with that of our honeycomb we find OP$_{3}$=0.399 for the honeycomb and OP$_{3}$=0.572 for man's best hexagonal array. The DWF also scales with this order parameter with the least disorder from a computer-generated hexagonal array and the most disorder from a random array. An ideal hexagonal array normalizes a two-dimensional Fourier transform from which a Debye-Waller parameter is derived which describes the disorder in the arrays. An order parameter \textbf{S,} defined by the DWF, takes values from [0, 1] and for the analyzed man-made array is 0.90, while for the honeycomb it is 0.65. This presentation describes methods to quantify the order found in these arrays.   

MgO Growth Conditions for Magnetic Tunnel Junctions

A comprehensive study of MgO growth conditions is essential for making high TMR MTJs. We have carried out a systematic study optimizing the MgO growth via presputter and sputtering conditions and underlayer structures. It was found that to prevent water vapour which is detrimental to MgO (200) growth, the chamber pressure needs to be reduced below 1.3 x 10$^{-6}$ Pa (10$^{-8}$ Torr). Pre-deposition ion milling for cleaning the thermal-oxide substrate before depositing metal films does not improve the subsequent MgO crystal growth. Simple underlayers such as 5 nm CoFeB tend to give better MgO, but we have also succeeded in growing MgO on more complicated underlayers. We found that both presputter and sputtering conditions have important effects on the MgO growth. X-ray diffraction (XRD) analysis was used as the characterization tool for optimizing the MgO growth conditions.   

Optical Thickness Monitoring System for a High Vacuum Deposition Chamber for Thin Film Photovoltaic Solar Cells

Groups at the University of Toledo studying CdTe/CdS based thin film photovoltaic solar cells require precise measurement and variation of film parameters to produce the most efficient cells possible. Controlling film thickness of the CdTe and CdS layers is essential to optimizing cell efficiency and desired cell characteristics. A non-destructive film thickness monitoring system for in-situ, real time chamber depositions in the AJA International Inc High Vacuum RF magnetron sputtering chamber was constructed. The monitoring system visualizes interference fringes of reflected laser light from front and back surfaces of the deposited film. Sample thickness is determined from known optical properties of the film material. Complications due to sample rotation during growth, background noise, and limitations from chamber geometry were overcome to achieve clear signal detection.   

80-Channel Multiplexer-Demultiplexer Module for DWDM Communications using Hybrid AWG -- Interleaver Technology

Aside from the more traditional data, voice and e-mail communications, new bandwidth intensive applications in the larger consumer markets, such as music, digital pictures and movies, have led to an explosive increase in the demand for transmission capacity for optical communications networks. This has resulted in a widespread deployment of Dense Wavelength Division Multiplexing (DWDM) as a means of increasing the communications capacity by multiplexing and transmitting signals of different wavelengths (establishing multiple communication channels) through a single strand of fiber. We report on the design, assembly and characterization of a 50-GHz, 80-channel Mux-Demux module for DWDM systems. The module has been assembled from two commercially available 100 GHz, 40-channel Array Waveguide Grating (AWG) modules and a 50-GHz to 100-GHz interleaver. Relevant performance parameters such as insertion loss, channel uniformity, next-channel isolation (crosstalk) and integrated cross-talk are presented and discussed in contrast with the performance of other competing technologies such as Thin-Film-Filter-based Mux-Demux devices.   

Charmed Meson Reconstruction with STAR's Silicon Detectors

We report on a new effort to reconstruct the charged-decays of D0 mesons via the direct reconstruction of their decay vertex using the central silicon trackers in the STAR experiment at RHIC. The effort includes the alignment and calibration of the Silicon detectors (SSD and SVT) almost to their specifications as well as the deployment of new reconstruction techniques that try to take advantage of the system's high track pointing accuracy and the implementation of momentum dependent cuts in the candidate-track selection criteria.   

Genetic Algorithm Optimization of Inlet Bleed Design for a Hypersonic Jet Engine with Mode Transition

A genetic algorithm coupled with computational fluid dynamic software is used to optimize the configuration of an engine inlet at a supersonic speed. The optimization program is written to calculate the pressure recovery of many varying bleed schedules throughout the inlet walls. The goal is to find the best combination of the bleed holes' locations, diameters, and flow rates such that a high pressure recovery is maintained. Parallel computing, by means of a NASA supercomputer, is used to run the algorithm efficiently. This is the first time a genetic algorithm has been applied to inlet bleed design. A test function is used to evaluate and debug the optimization algorithm. The genetic algorithm and its associated programs show potential for use in developing more efficient bleed schedules in a hypersonic engine.   

Convolution Dynamics

Define $T$ on $L^1$ into $L^1$ by $(Tf)(x)= \int_{-\infty}^{\infty} g(x-y)f(y)dy$. With assumptions on $g(x)$ and its Fourier transform,$\hat{g}(t) $, requiring, among other things, that there be only one point,$t_{0}$, at which $|\hat{g}(t_{0})|= sup_{s\epsilon R}|\hat{g}(s)|$ and that $0 [Preview Abstract]

UV excited long persistent LEDs

The first long persistent LED indicator was made by coating Sr$_{2}$MgSi$_{2}$O$_{7}$:Eu$^{2+}$, Nd$^{3+}$, SrAl$_{2}$O$_{4}$:Eu$^{2+}$, Dy$^{3+}$ and CaS:Eu$^{2+}$, Tm$^{3+}$, Ce$^{3+ }$long persistent nanophosphors to a blue LED.$^{ }$When considering long persistent LEDs there is more emphasis on the persistence than there is on the brightness, therefore trapping efficiency should be the first priority. Following this consideration, a UV excited long persistent LED is developed because UV pumped long persistent phosphors usually has longer persistence. UV light can excite the electrons to the conduction band more efficiently than lower energy photons such as a blue photon. Although, UV LEDs are less efficient than blue LEDs for illumination, UV LEDs will produce the highest trapping rate and longest persistence time.   

Sol-gel glass nanocomposite scintillator

Nanocomposite LaBr$_{3}$:Ce$^{3+}$ and SiO$_{2}$ are prepared by using sol-gel method. Concentration of LaBr$_{3}$:Ce$^{3+}$ embedded in SiO$_{2}$ can be as high as 95{\%}. But the sol-gel glass only is transparent up to a concentration of 50{\%}. Emission and excitation spectra are measured. Ce3+ emission is strong and is found at near UV region. This sol-gel nanocomposite material is good for scintillators application.   

Synthesis green emitting PPV thin film via solvent free chemical vapor deposition

A solvent free chemical vapor deposition (CVD) system was build to prepare PPV thin film. $\alpha $,$\alpha $'-dibromo-p-xylene is used as a precursor. The precursor is heated at the precursor chamber to 90 $^{o}$C to sublimit the materials at a base pressure for about 2-3 mTorr. A N$_{2}$ carrier gas is used to deliver the precursor molecules to the reaction chamber. The reaction chamber pressure is kept at 5-40 mTorr with a temperature for about 800 $^{o}$C. Si and ITO substrates are used in the condensation chamber for deposition. Photoluminescence spectra are measured for the deposited PPV.