UScholar Works
 
Filters: Department: "Physics" Collection: "ir_uspace"
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CreatorTitleDescriptionSubjectDate
576 Mattis, Daniel C.Phonons and phase transitions of heliumWe find a new collective shear-wave-like mode above Tλ, merging with the longitudinal acoustic mode at a higher critical temperature. The speed of the new sound wave is predicted to vanish near Tλ as s ∞ (T -Tλ)½ .1973-06
577 Vardeny, Zeev ValentinePhoto induced infrared active phonons in trans polyacetyleneWe measured photogenerated ir active phonons in trans-(CH) by the photoinduced absorption technique. A correlation was found to exist with a photoinduced absorption band in which electronic transitions are involved. Our results show photoproduction of free charged defects with long lifetimes.Photoinduced phonons; Trans polyacetylene1983-06
578 Gerton, JordanPhotoassociative frequency shift in a quantum degenerate gasA light-induced frequency shift is observed in single-photon photoassociative spectra of magnetically trapped, quantum degenerate 7Li. The shift is a manifestation of the coupling between the threshold continuum scattering states and discrete bound levels in the excited-state molecular potential in...2001-10
579 Vardeny, Zeev ValentinePhotocarrier dynamics in compensated hydrogenated amorphous siliconThe photocarrier dynamics in compensated a-Si:H is studied using the time-dependent photomodulation technique in the subpicosecond-to-millisecond time range. We find that photocarriers are quickly trapped in shallow impurity levels for t < 10 psec, similar to the behavior in singly doped materials...Photocarriers; a-Si:H; Amorphous silicon; Fast trapping1986-03
580 Vardeny, Zeev ValentinePhotoconductivity and photoinduced absorption in a-Si:F and a-Si:HThe photoconductivity (PC) and photoinduced absorption (PA) of RF glow discharge a-Si:F and a-Si:H samples is reported. The value of the room temperature PC of a-Si:F is lower by some four orders of magnitude relative to that of a-Si:H, but the PA of a-Si:F is found to be significantly higher than t...Photoinduced absorption; a-Si:F; a-Si:H; RF glow discharge; Spin densities1984
581 Vardeny, Zeev ValentinePhotoexcitation dynamics and laser action in solutions and films of PPE-PPV copolymerWe used a variety of ultrafast and steady-state spectroscopy techniques to study the photoexcitation dynamics and laser action in dilute and concentrated solutions and in thin films of poly(phenylene-ethynylene)/ poly(phenylene-vinylene) [PPE-PPV] copolymer. We found that the primary photoexcitatio...Photoexcitation dynamics; Laser action; PPE-PPV copolymers2004-04
582 Vardeny, Zeev ValentinePhotoexcitation dynamics in C60-doped PPV under bias illuminationWe have studied photoexcitation dynamics in pristine and C60-doped PPV films under bias Olumination by photoinduced absorption (PA), optically-detected magnetic resonance (ODMR), and electromodulated PA (EPA). Intrachain polaron pair species are the dominant excitations under these conditions. The p...Photoexcitation dynamics; C60-doped PPV; Bias illumination; PPV films; Photoinduced absorption; ODMR; Electroabsorption1996
583 Vardeny, Zeev ValentinePhotoexcitation dynamics in polyacetylene probed by transient photoinduced resonant Raman scatteringWe have measured photoexcitation dynamics in the picosecond time domain in fully trans and partially isomerized (CH)X and (CD)X films with different cis/trans content ratios, using the technique of transient photoinduced resonant Raman scattering. Following the distinctively different decay kineti...Photoexcitation dynamics1992-05
584 Vardeny, Zeev ValentinePhotoexcitation dynamics in polythiophene/fullerene blends for photovoltaic applicationsWe used the transient and steady state photomodulation spectroscopies for studying the photoexcitations dynamics in blends of regio-regular poly(3-hexylthiophene) (RR-P3HT) and fullerene in a broad spectral range from 0.15 to 2.25 eV. We found that both localized polarons and singlet excitons are in...2012-01-01
585 Vardeny, Zeev ValentinePhotoexcitation dynamics in regioregular and regiorandom polythiophene filmsUsing a variety of optical probes techniques we studied the photoexcitation dynamics in thin films of poly-3-hexyl thiophene with regioregular order that forms lamellae structures with increased interchain interaction, as well as regiorandom order that keeps a chainlike morphology. In regiorandom fi...Photoexcitation dynamics; Regio-regular; Regio-random; Polythiophene films2001-11
586 Vardeny, Zeev Valentine; Ehrenfreund, Eitan A.Photoexcitation spectroscopy of polythiopheneRadiative recombination in polythiophene is studied by cw photoluminescence and photoinduced absorption spectroscopies and by photoluminescence-detected magnetic resonance. The fast-recombination centers are assigned to intrachain excitons in defect-free chains, while the slow recombination is due t...Radiative recombination; Photoexcitation spectroscopy1987-02
587 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
588 Vardeny, Zeev ValentinePhotoexcitations in polythiophene at high pressureWe report optical-absorption, photoluminescence (PL), and picosecond photoinduced absorption (PA) decay in films of poly-3-hexyl-thiophene at pressures up to 80 kbar. The spectral bands redshift nonlinearly with pressure and the PL intensity decreases markedly. Thermochromic transitions are complete...Photoexcitations1993-01
589 Vardeny, Zeev ValentinePhotogenerated gap states in polyacetyleneWe have measured the optical absorption spectrum of photogenerated gap states in polyacetylene, (CH)X . From a comparison with electroabsorption spectra the charge state of the excitations is determined. In both isomers of (CH)X locally neutral (exciton-like) states are observed. In addition a charg...Gap state; Photoexcitation1983-06
590 Vardeny, Zeev ValentinePhotogeneration action spectroscopy of neutral and charged excitations in films of ladder-type poly(para-phenylene)The photogeneration quantum efficiency action spectra of long-lived neutral and charged excitations in films of a ladder-type poly(para-phenylene) were measured. We found that both triplet and polaron action spectra show, in addition to a step function increase at the optical gap, a monotonic rise a...Photogeneration; Neutral excitations; Charged excitations; pi-conjugated polymers; Transient spectroscopy1999-04
591 Vardeny, Zeev ValentinePhotogeneration and recombination processes of neutral and charged excitations in films of a ladder-type poly(para-phenylene)We introduce a version of the cw photomodulation technique, measured far from the steady state, for obtaining the quantum efficiency, η, of long-lived photoexcitations in p-conjugated polymers. We apply this technique to films of a ladder-type poly(para-phenylene) [mLPPP] for studying the photoge...Photogeneration; Recombination process; Neutral excitations; Charged excitations; Ladder-type poly(para-phenylene)1999-08
592 Vardeny, Zeev Valentine; Ehrenfreund, Eitan A.Photogeneration of confined soliton pairs (bipolarons) in polythiopheneFrom photoinduced absorption and light-induced electron-spin resonance, we demonstrate that the dominant photocarriers generated in polythiophene with excitation above the energy gap (Eg) are charged bipolarons (spin 0). The observation of bipolarons (B2± ) rather than polarons (Pf ) as the dominan...Photoinduced absorption; Photocarriers; Bipolarons; Photoexcitation1986-02
593 Vardeny, Zeev ValentinePhotoinduced absorption spectra in amorphous Si:H and Ge:H and microcrystalline Si:HThe steady state subgap photoinduced absorpotion bands in a-Ge:H and a-Si:H are interpreted in terms of two kinds of optical transitions of photoexcited carriers from traps in the gap into the bands of which one produces absorption and the other produces bleaching. The photoinduced absorption in mic...Photoinduced absorption; Si:H; Ge:H; Amorphous silicon; Amorphous germanium; Microcrystalline silicon1984
594 Vardeny, Zeev ValentinePhotoinduced absorption spectra in α-GeH and α-Si:HMeasurements of steady-state photoinduced absorption in α-Ge:H and α-Si:H were extended to cover the energy range from 0.25 to 1.9 eV. The subgap photoinduced-absorption bands in both materials are interpreted in terms of four kinds of optical transitions of photogenerated carriers from traps in ...Photoinduced absorption; in a-GeH; a-Si:H; Amorphous germanium; Amorphous silicon1984-07
595 Vardeny, Zeev ValentinePhotoinduced infrared activity in polyacetylenePhotoexcitation of trans - but not cis -polyacetylene, results in the appearance of strongly-ir-active local modes at 1370 and 1260 cm-1. This observation demonstrates that the photogeneration of self-localized charge carriers is unique to the trans isomer. In spite of their localization the kineti...Photoinduced infrared activity; Photoexcitation1983-06
596 Vardeny, Zeev ValentinePhotoinduced IR active vibrations in trans-(CD)x: a three-mode systemIn a recent Letter Blanchet et al.? have extended photoinduced absorption measurements of frYms-polyacetylene to lower energy than obtained before 2 for both isotopes, (CH)x and (CD)X. While in (CE)X three strong ir-active vibrations (IRAV) are photoinduced, only two IRAV were observed in (CD)X, at...Photoinduced absorption; IR active vibrations1983
597 Vardeny, Zeev ValentinePhotoinduced quantum interference antiresonances in ∏-conjugated polymersWe observed photoinduced quantum interference antiresonances between several discrete infraredactive vibrations and the lower-polaron continuous absorption band in a series of p-conjugated polymer films having superior planar orders, where the polaron transition energy is relatively small. The phot...pi-conjugated polymers; Antiresonances; Fano-type antiresonances2002-05
598 Vardeny, Zeev Valentine; Ehrenfreund, Eitan A.Photomodulation spectroscopy of iodine-doped polyacetylene; phase transition from soliton lattice to metalUsing the photomodulation technique for iodine I3-)-doped polyacetylene, we have found spectroscopic evidence for an abrupt phase transition at 5% I3-. The transition is from the lightly doped phase best described as soliton lattice to the heavily doped metallic phase. The phase transition is chara...Photomodulation spectroscopy; Iodine-doped polyacetylene1986-10
599 Vardeny, Zeev ValentinePhotophysics of excitons in quasi-one-dimensional organic semiconductors: single-walled carbon nanotubes and ∏-conjugated polymersThe nature of the primary photoexcitations in semiconducting single-walled carbon nanotubes (S-SWCNTs) is of strong current interest. We have studied the emission spectra of S-SWCNTs and two different rr-conjugated polymers in solutions and films, and have also performed ultrafast pump-probe spectro...Photophysics; Excitons; Quasi-one-dimensional; Single-walled carbon nanotubes; pi-conjugated polymers2006-02
600 Vardeny, Zeev ValentinePhotophysics of pristine and C60-doped disubstituted polyacetyleneUsing a variety of steady-state spectroscopies we studied the long-lived photoexcitations and electronic excited states of poly disubstituted acetylene (PDPA-nBu), the backbone structure of which is a disubstituted trans-polyacetylene, as well as PDPA-nBu/C60 blends. The cw spectroscopies include a...Photophysics; Pristine disubstituted polyacetylene; C60-doped disubstituted polyacetylene; pi-conjugated polymers; Photoexcitations; Electronic excited states2002-08
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