UScholar Works
 
Filters: Date: "1997" Department: "Physics" Collection: ir_uspace
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CreatorTitleDescriptionSubjectDate
1 Gondolo, PaoloAGAPE: a search for dark matter in M31 by microlensing effects on unresolved starsM 31 is a very tempting target for a microlensing search of compact objects in galactic haloes. It is the nearest large galaxy, it probably has its own dark halo, and its tilted position with respect to the line of sight provides an unmistakable signature of microlensing. However most stars of M 31...M31; AGAPE; Pixel method; Galaxy; Halo; Cosmology; Gravitational lensing1997
2 Gondolo, PaoloAGAPE: andromeda gravitational amplification pixel experimentThe aim of the AGAPE (Andromeda Gravitational Ampli_x000C_cation Pixel Experiment), experiment which has been _x000C_rst proposed in June 1992 is to examine the distribution of massive astrophysical compact halo objects ((MACHO's) which possibly are in the galactic haloes and which could account for...AGAPE; Andromeda Gravitational Amplification Pixel Experiment; Microlensing; MACHO; Massive compact halo objects1997
3 Stringfellow, Gerald B.;Inglefield, Colin E.;Taylor, P. CraigCharacterization of unicompositional GaInP2 ordering heterostructures grown by variation of V/III ratioPhotoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies are employed to investigate single heterostructures based on two GaInP2 layers that have the same composition but different degrees of order on the cation sublattice. Four sample configurations are studied: two complemen...Heterostructures; Growth parameters; Growth temperature1997
4 Vardeny, Zeev Valentine; Raikh, Mikhail E.Cooperative emission from a disordered system: a classical modelThe effect of disorder on the collective emission from a system of classical oscillators is studied theoretically. Three types of disorder are considered: random orientation of dipole moments, finite spread in frequencies of the individual oscillators (diagonal disorder), and dipole-dipole interacti...Cooperative emission; Disordered system; Dipole-dipole interaction; Oscillators1997
5 Williams, Clayton C.Depth dependent carrier density profile by scanning capacitance microscopyThe depth dependent carrier density was measured on an arsenic implanted silicon sample using scanning capacitance microscopy (SCM). The capacitance versus voltage scan was performed by applying dc biases with a dither ac signal. A strong dc bias dependence was observed at the interface of an abru...Carrier density; Silicon submicrometer technology; Scanning capacitance microscopy1997
6 Williams, Clayton C.Depth dependent carrier density profile by scanning capacitance microscopyThe depth dependent carrier density was measured on an arsenic implanted silicon sample using scanning capacitance microscopy (SCM). The capacitance versus voltage scan was performed by applying dc biases with a dither ac signal. A strong dc bias dependence was observed at the interface of an abru...Carrier density; Silicon submicrometer technology; Scanning capacitance microscopy1997
7 Vardeny, Zeev ValentineElectromodulated photoinduced absorption; a new spectroscopy in ∏-conjugated polymer/C60-blendsWe have applied the electromodulated photoinduced absorption (EPA) technique to a variety of C 6 0 -doped and pristine luminescent conducting polymer films. EPA measures the electric field-related change of the absorption in the sample as a result of above-gap illumination. An electric field leads t...Electromodulated photoinduced absorption; EPA; C60 doping; Electromodulated photoluminescence; EPL; Polaron pair polarizability1997
8 Williams, Clayton C.Evidence of internal electric fields in GaInP2 by scanning capacitance and near-field scanning optical microscopyGaInP2 is studied in cross section with the scanning capacitance and near-field scanning optical microscope. Our study shows significant differences in the electronic and optical properties between ordered single- and two-variant GaInP2. In single-variant samples, spatially uniform capacitance signa...Atomic ordering; transmission electron diffraction; near-field scanning optical microscope1997
9 Williams, Clayton C.Evidence of internal fields in two-variant ordered GaInP2 by near-field scanning optical microscopyGaInP2 is studied in cross section with the scanning capacitance and near-field scanning optical microscope. Our study shows significant differences in the electronic and optical properties between ordered single- and two-variant GaInP2. In single-variant samples, spatially uniform capacitance signa...Photoluminescence; GaInP2; Microscopy; Electrical fields1997
10 Vardeny, Zeev ValentineExciton dynamics in soluble poly(p-phenylene vinylene)We report studies of poly(2,5-dioctyloxy paraphenylene vinylene) thin films and solutions by a variety of transient, steady state, and nonlinear optical techniques. The energy states and optical absorption of the dominant even and odd parity excitons have been determined. Photogenerated singlet exci...Exciton dynamics; Poly(p-phenylene vinylene); PPV; Pi-conjugated polymers1997
11 Kieda, David B.High statistics search for ultrahigh energy gamma-ray emission from Cygnus X-3 and Hercules X-1We have carried out a high statistics (2 X 10 9 events) search for ultrahigh energy g-ray emission from the x-ray binary sources Cygnus X-3 and Hercules X-1. Using data taken with the CASA-MIA detector over a five year period (1990-1995), we find no evidence for steady emission from either source. T...Cygnus X-3; Hercules X-1; Ultrahigh energy; X-rays1997
12 Vardeny, Zeev ValentineLaser action in conducting polymersWe discuss both cooperative radiation and stimulated emission and consider their role in spectral narrowing of luminescent conducting polymers. We argue that cooperative radiation is favored in films with poor optical confinement. On the other hand, directional stimulated emission can be observed in...Laser action; Cooperative radiation; Stimulated emission; PPV; Disubstituted polyacetylene; Excitons; Spectral narrowing; Plastic lasers; Superfluorescence; Microcavity lasers1997
13 Vardeny, Zeev Valentine; Gellermann, WernerLaser properties of luminescent conducting polymers in open resonatorsWe have investigated the lasing properties of several luminescent conducting polymers, i.e. DOO-PPV and the bi-substituted polyacetylenes PDPA-nBu, and PHJPA, dissolved in various polar and non-polar solvents. PP V polymers emit with high quantum efficiencies in broad emission bands centered in the ...Lasing; Amplified spontaneous emission; Spectral narrowing1997
14 Kieda, David B.Limits on the isotropic diffuse flux of ultrahigh energy gamma radiationDiffuse ultrahigh energy g radiation can arise from a variety of astrophysical sources, including the interaction of 1020 eV cosmic rays with the 2.7 K microwave background radiation or the collapse of topological defects created in the early Universe. We describe a sensitive search for diffuse g ...G rays; Ultrahigh energy; Muons; Cosmic rays1997
15 Vardeny, Zeev Valentine; Gellermann, WernerNear-infrared ps transient photoinduced absorption in conjugated systemsWe demonstrate the use of a color center laser in a pump-and-probe correlation technique which enables us to extend the probe spectral range into the infrared. As a result, we find strong photoinduced infrared absorption in several 7t-conjugated polymers and oligomers. We associate this absorption w...Ultrafast spectroscopy; Color center laser; Photoinduced absorption; Singlet excitons; Even parity states; Odd parity states; Infrared absorption1997
16 Vardeny, Zeev ValentineOptical probes of pristine and C60-doped silicon-bridged PT polymer; a novel highly luminescent, low bandgap polymerSilicon bridged PT polymer (PTSi) is a new soluble polymer with a strong luminescence in the infrared band (0-0 transition at 1.6 eV). We have applied various spectroscopies such as absorption, electroabsorption (EA), photo induced absorption (PA), electromodulated PA (EPA), photoluminescence (PL) a...Silicon bridged PT polymer; Low bandgap pi-conjugated polymer; C60 doping; Electric field induced exciton dissociation1997
17 Vardeny, Zeev ValentineOptical studies of ordered and disordered α-sexithiophene filmsWe have studied α-sexithiophene (α-6T) films by photoinduced absorption (PA) and optically-detected magnetic resonance (ODMR). The PA of the disordered film is composed of two polaron PA bands and one bipolaron PA band, each with its own vibronic side bands. Measurements of an ordered film indicat...Optically detected magnetic resonance; Sexithiophene conjugated oligomer1997
18 Vardeny, Zeev Valentine; Ehrenfreund, Eitan A.Phonon spectroscopy in π-conjugated polymers; the role of the excited electronic statesThe Raman active vibrational modes in 7r-conjugated polymers are known to have different frequencies in different types of experiments. The best known examples are the resonant Raman scattering (RRS) and doping or photoinduced absorption infrared active vibrations (IRAV) measurements, in which the s...pi-conjugated polymers; Phonon spectroscopy; Resonant Raman scattering; ir-active phonons1997
19 Vardeny, Zeev ValentinePhotoexcitations in disubstituted acetylene polymersWe have used a variety of optical techniques to study the photoexcitations dynamics in several disubstituted acetylene polymer thin films. We found that although these polymers have a degenerate ground state, as determined by iodine doping and C6Q photodoping, they show strong photoluminescence (PL)...Photoexcitations; Disubstituted acetylene polymers; Trans-Polyacetylene; Electron-electron interactions1997
20 Vardeny, Zeev Valentine; Gellermann, WernerRaman scattering gain in DOO-PPV filmsWe have investigated the optical emission characteristics of poly(2,5-dioctyloxy-p-phenylenevinylene) (DOO-PPV) thin films under high intensity ps pulsed laser excitation (Ipump > 1 MW/ cm2). We observed that the emission spectrum consist of a spectrally narrowed emission (SNE) band (FWHM ~ 10 nm)...DOO-PPV; Raman scattering gain; Stimulated emission; Strongly coupled vibrations1997
21 Vardeny, Zeev ValentineSpin and spectral signatures of polaron pairs in π-conjugated polymersWe have studied polaron pair photoexcitations in a variety of π-conjugated polymer films by photoinduced absorption (PA) and optically-detected magnetic resonance (ODMR). An exchange interaction between polarons broadens the ODMR spectrum, permitting the unambiguous identification of the polaron pa...Polaron pair; ODMR; Photoinduced absorption; Spin signatures; Spectral signatures; pi-conjugated polymers1997
22 Vardeny, Zeev ValentineSpin dependent photoinduced absorption in a-Si:HWe have studied photoexcitation dynamics in undoped a-Si:H from 80 K to 300 K by the techniques of photoluminescence (PL), photoinduced absorption (PA) and their respective versions of optically detected magnetic resonance, namely PLDMR and PADMR. Both PL and PA spectra are composed of low and high ...a-Si:H; Amorphous silicon; Spin dependent; Photoinduced absorption1997
23 Vardeny, Zeev ValentineStudies of Raman scattering in novel disubstituted acetylene polymersWe have studied resonant and non-resonant Raman scattering spectra in thin films of novel disubstituted acetylene polymers such as poly(l-ethyl-2-phenylacetylene) (PEtPA), poly(l-n-hexyl-2-phenylacetylene) (PHxPA) and poly(l-phenyl-2-/wibutylphenylacetylene) (PDPA-nBu), which possess high photolumin...Raman scattering; Disubstituted acetylene polymers1997
24 Vardeny, Zeev Valentine; Gellermann, WernerTwo-photon absorption measured in the presence of strong one-photon saturation in cumulene-containing polymerThe Z-scan technique is used to extract the real and imaginary third order nonlinear susceptibilities, Rex(3) and Imx(3), respectively. A series of Z scans were conducted at 590 nm (near one-photon resonance) on a cumulene-containing polymer, poly(p-phenylene-l,4-diphenyl-l,2,3-butatriene) or PPC3, ...Molecular second hyperpolarizability; One-photon saturation; Polymer solution; Chain length1997
25 Vardeny, Zeev Valentine; Gellermann, WernerTwo-photon absorption spectra of luminescent conducting polymers measured over a wide spectral rangeWe report the two-photon absorption (TPA) spectra of poly(2,5-dibutoxy-p-phenylene acetylene) (PPADBO), poly(2,5-dioctyloxy-p-phenylene vinylene) (PPV-DOO), and poly(3-hexylthiophene) (PAT6) in the spectral range extending from 576 nm to 846 nm. Using the Z-scan technique on the polymers in solutio...Two-photon absorption; Two-photon saturation; Luminescent polymers; Dispersion; Polymer solution; PPA-DBO1997
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