1,457 Matching Results

Search Results

Advanced search parameters have been applied.

Optical Properties of Three Uranium Phosphates

Description: Abstract: "Crystal system, crystal habit, and principal refractive indices, of uranyl hydrogen phosphate tetrahydrate, uranyl ammonium phosphate trihydrate, and uranyl phosphate tetrahydrate are reported. A procedure for differentation of these three compounds using this data was developed."
Date: September 30, 1949
Creator: Harris, W. W. & Scott, Reberta H.
Partner: UNT Libraries Government Documents Department

Relation between structural and optical properties of InN andInxGa1-xN thin films

Description: Transmission Electron Microscopy (TEM) and opticalmeasurements obtained from InN and In1-xGaxNfilms (0<x<0.54)grown by Molecular Beam Epitaxy are presented. Energy gaps measuredbyabsorption, PR, and PL for InN films grown on c-plane Al2O3 were in therange of 0.7 eV. No In or otherinclusions were observed in these films,ruling out the possibility of a strong Mie scattering mechanism. IntheIn1-xGaxN films the relationship between the structural properties andthe optical properties, inparticular the presence or absence of a Stokesshift between absorption and PL, is discussed. TEM studiesshow that highquality layers do not have a Stokes shift. Some films had compositionalordering; thesefilms also showed a shift between absorption edge andluminescence peak.
Date: July 20, 2004
Creator: Liliental-Weber, Z.; Zakharov, D. N.; Jasinski, J.; Yu, K. M.; Wu, J. W.; Ager, J. W., III et al.
Partner: UNT Libraries Government Documents Department

LDRD final report on Si nanocrystal as device prototype for spintronics applications.

Description: The silicon microelectronics industry is the technological driver of modern society. The whole industry is built upon one major invention--the solid-state transistor. It has become clear that the conventional transistor technology is approaching its limitations. Recent years have seen the advent of magnetoelectronics and spintronics with combined magnetism and solid state electronics via spin-dependent transport process. In these novel devices, both charge and spin degree freedoms can be manipulated by external means. This leads to novel electronic functionalities that will greatly enhance the speed of information processing and memory storage density. The challenge lying ahead is to understand the new device physics, and control magnetic phenomena at nanometer length scales and in reduced dimensions. To meet this goal, we proposed the silicon nanocrystal system, because: (1) It is compatible with existing silicon fabrication technologies; (2) It has shown strong quantum confinement effects, which can modify the electric and optical properties through directly modifying the band structure; and (3) the spin-orbital coupling in silicon is very small, and for isotopic pure {sup 28}Si, the nuclear spin is zero. These will help to reduce the spin-decoherence channels. In the past fiscal year, we have studied the growth mechanism of silicon-nanocrystals embedded in silicon dioxide, their photoluminescence properties, and the Si-nanocrystal's magnetic properties in the presence of Mn-ion doping. Our results may demonstrate the first evidence of possible ferromagnetic orders in Mn-ion implanted silicon nanocrystals, which can lead to ultra-fast information process and ultra-dense magnetic memory applications.
Date: November 1, 2006
Creator: Carroll, Malcolm S.; Verley, Jason C.; Pan, Wei; Banks, James Clifford; Brewer, Luke N.; Sheng, Josephine Juin-Jye et al.
Partner: UNT Libraries Government Documents Department

Symmetry, Optical Properties and Thermodynamics of Neptunium(V) Complexes

Description: Recent results on the optical absorption and symmetry of the Np(V) complexes with dicarboxylate and diamide ligands are reviewed. The importance of recognizing the 'silent' feature of centrosymmetric Np(V) species in analyzing the absorption spectra and calculating the thermodynamic constants of Np(V) complexes is emphasized.
Date: December 21, 2009
Creator: Rao, Linfeng & Tian, Guoxin
Partner: UNT Libraries Government Documents Department

Effect of Native Defects on Optical Properties of InxGa1-xNAlloys

Description: The energy position of the optical absorption edge and the free carrier populations in In{sub x}Ga{sub 1-x}N ternary alloys can be controlled using high energy {sup 4}He{sup +} irradiation. The blue shift of the absorption edge after irradiation in In-rich material (x &gt; 0.34) is attributed to the band-filling effect (Burstein-Moss shift) due to the native donors introduced by the irradiation. In Ga-rich material, optical absorption measurements show that the irradiation-introduced native defects are inside the bandgap, where they are incorporated as acceptors. The observed irradiation-produced changes in the optical absorption edge and the carrier populations in In{sub x}Ga{sub 1-x}N are in excellent agreement with the predictions of the amphoteric defect model.
Date: May 9, 2005
Creator: Li, S.X.; Haller, E.E.; Yu, K.M.; Walukiewicz, W.; Ager III,J.W.; Wu, J. et al.
Partner: UNT Libraries Government Documents Department

Syntheses, Structure, Magnetism, and Optical Properties of Lutetium-based Interlanthanide Selenides

Description: Ln{sub 3}LuSe{sub 6} (Ln = La, Ce), {beta}-LnLuSe{sub 3} (Ln = Pr, Nd), and Ln{sub x}Lu{sub 4-x}Se{sub 6} (Ln = Sm, Gd; x = 1.82, 1.87) have been synthesized using a Sb{sub 2}Se{sub 3} flux at 1000 C. Ln{sub 3}LuSe{sub 6} (Ln = La, Ce) adopt the U{sub 3}ScS{sub 6}-type three-dimensional structure, which is constructed from two-dimensional {infinity}{sup 2} [Ln{sub 3}Se{sub 6}]{sup 3-} slabs with the gaps between these slabs filled by octahedrally coordinated Lu{sup 3+} ions. The series of {beta}-LnLuSe{sub 3} (Ln = Pr, Nd) are isotypic with UFeS{sub 3}. Their structures include layers formed from LuSe6 octahedra that are separated by eight-coordinate larger Ln{sup 3+} ions in bicapped trigonal prismatic environments. Sm{sub 1.82}Lu{sub 2.18}Se{sub 6} and Gd{sub 1.87}Lu{sub 2.13}Se{sub 6} crystallize in the disordered F-Ln{sub 2}S{sub 3} type structure with the eight-coordinate bicapped trigonal prismatic Ln(1) ions residing in the one-dimensional channels formed by three different double chains via edge and corner sharing. These double chains are constructed from Ln(2)Se{sub 7} monocapped trigonal prisms, Ln(3)Se{sub 6} octahedra, and Ln(4)S{sub 6} octahedra, respectively. The magnetic susceptibilities of {beta}-PrLuSe{sub 3} and {beta}-NdLuSe{sub 3} follow the Curie-Weiss law. Sm{sub 1.82}Lu{sub 2.18}Se{sub 6} shows van Vleck paramagnetism. Magnetic measurements show that Gd{sub 1.87}Lu{sub 2.13}Se{sub 6} undergoes an antiferromagnetic transition around 4 K. Ce{sub 3}LuSe{sub 6} exhibits ferromagnetic ordering below 5 K. The optical band gaps for La{sub 3}LuSe{sub 6}, Ce{sub 3}LuSe{sub 6}, {beta}- PrLuSe{sub 3}, {beta}-NdLuSe{sub 3}, Sm{sub 1.82}Lu{sub 2.18}Se{sub 6}, and Gd{sub 1.87}Lu{sub 2.13}Se{sub 6} are 1.26, 1.10, 1.56, 1.61, 1.51, and 1.56 eV, respectively.
Date: October 1, 2007
Creator: Booth, Corwin H; Jin, Geng Bang; Choi, Eun Sang; Guertin, Robert P.; Brooks, James S.; Booth, Corwin H. et al.
Partner: UNT Libraries Government Documents Department

Assessing the Importance of Using Biomodal Size Distribution for Ice Cloud Optical Property Parameterizations

Description: This report represents the final report for DE-AI02-0 IER63074. This work represented some follow-on work to that completed under DE-AI02-0 1 ER62669. The research reported here is undertaken in collaboration with Dr. David Mitchell of the Desert Research Institute in Reno, Nevada. The progress given here represents my contribution to his approach by providing radiative transfer expertise and calculations.
Date: March 31, 2006
Creator: Stackhouse, P. W.
Partner: UNT Libraries Government Documents Department

A 10-Hz Terawatt Class Ti:Sapphire Laser System: Development and Applications

Description: We developed a two stage Ti:Sapphire laser system to generate 16 mJ/80fs laser pulses at the pulse repetition rate of 10 Hz. The key deriver for the present design is implementing a highly efficient symmetric confocal pre-amplifier and employing a simple, inexpensive synchronization scheme relying only on a commercial digital delay-generator. We characterized the amplified pulses in spatial-, spectral-, and temporal-domains. The laser system was used to investigate various nonlinear optical processes, and to modify the optical properties of metal- and semiconductor-surfaces. We are currently building a third amplifier to boost the laser power to the multi-terawatt range.
Date: January 12, 2010
Creator: Sharma, A. K.; Smedley, J.; Tsang, T. & Rao, T.
Partner: UNT Libraries Government Documents Department

Valence band anticrossing in GaBixAs1-x

Description: The optical properties of GaBixAs1-x (0.04&lt; x&lt; 0.08) grown by molecular beam epitaxy have been studied by photomodulated reflectance spectroscopy. The alloys exhibit a strong reduction in the bandgap as well as an increase in the spin-orbit splitting energy with increasing Bi concentration. These observations are explained by a valence band anticrossing model, which shows that a restructuring of the valence band occurs as the result of an anticrossing interaction between the extended states of the GaAs valence band and the resonant T2 states of the Bi atoms.
Date: July 11, 2007
Creator: Alberi, K.; Dubon, O. D.; Walukiewicz, W.; Yu, K. M.; Bertulis, K. & Krotkus, A.
Partner: UNT Libraries Government Documents Department

Optics of a Proton Driver

Description: In a four month study, a design for a Proton Driver was developed as a possible replacement for Fermilab's Booster. Its optical properties are summarized briefly.
Date: May 22, 2003
Creator: al., Leo Michelotti et
Partner: UNT Libraries Government Documents Department

Functional Materials for Microsystems: Smart Self-Assembled Photochromic Films: Final Report

Description: This project set out to scientifically-tailor ''smart'' interfacial films and 3-D composite nanostructures to exhibit photochromic responses to specific, highly-localized chemical and/or mechanical stimuli, and to integrate them into optical microsystems. The project involved the design of functionalized chromophoric self-assembled materials that possessed intense and environmentally-sensitive optical properties (absorbance, fluorescence) enabling their use as detectors of specific stimuli and transducers when interfaced with optical probes. The conjugated polymer polydiacetylene (PDA) proved to be the most promising material in many respects, although it had some drawbacks concerning reversibility. Throughout his work we used multi-task scanning probes (AFM, NSOM), offering simultaneous optical and interfacial force capabilities, to actuate and characterize the PDA with localized and specific interactions for detailed characterization of physical mechanisms and parameters. In addition to forming high quality mono-, bi-, and tri-layers of PDA via Langmuir-Blodgett deposition, we were successful in using the diacetylene monomer precursor as a surfactant that directed the self-assembly of an ordered, mesostructured inorganic host matrix. Remarkably, the diacetylene was polymerized in the matrix, thus providing a PDA-silica composite. The inorganic matrix serves as a perm-selective barrier to chemical and biological agents and provides structural support for improved material durability in microsystems. Our original goal was to use the composite films as a direct interface with microscale devices as optical elements (e.g., intracavity mirrors, diffraction gratings), taking advantage of the very high sensitivity of device performance to real-time dielectric changes in the films. However, our optical physics colleagues (M. Crawford and S. Kemme) were unsuccessful in these efforts, mainly due to the poor optical quality of the composite films.
Date: November 1, 2001
Partner: UNT Libraries Government Documents Department

Optical properties of colloidal germanium nanocrystals

Description: Highly crystalline germanium (Ge) nanocrystals in the size range 2--10 nm were grown in inverse micelles and purified and size-separated by high pressure liquid chromatography with on-line optical and electrical diagnostics. The nanocrystals retain the diamond structure of bulk Ge down to at least 2.0 nm (containing about 150 Ge atoms). The background- and impurity-free extinction and photoluminescence (PL) spectra of these nanocrystals revealed rich structure which was interpreted in terms of the bandstructure of Ge shifted to higher energies by quantum confinement. The shifts ranged from {minus}0.1 eV to over 1 eV for the various transitions. PL in the range 350--700 nm was observed from nanocrystals 2--5 nm in size. The 2.0 nm nanocrystals yielded the most intense PL (at 420 nm) which is believed to be intrinsic and attributed to direct recombination at {Gamma}. Excitation at high energy (250 nm) populates most of the conduction bands resulting in competing recombination channels and the observed broad PL spectra.
Date: May 1, 2000
Partner: UNT Libraries Government Documents Department