Showing papers on "Photoexcitation published in 2008"
TL;DR: Electrochemical studies show that the phenoxyl/phenol couple of the model system is chemically reversible and thermodynamically capable of water oxidation.
Abstract: A bioinspired hybrid system, composed of colloidal TiO2 nanoparticles surface modified with a photochemically active mimic of the PSII chlorophyll-Tyr-His complex, undergoes photoinduced stepwise electron transfer coupled to proton motion at the phenolic site. Low temperature electron paramagnetic resonance studies reveal that injected electrons are localized on TiO2 nanoparticles following photoexcitation. At 80 K, 95% of the resulting holes are localized on the phenol moiety and 5% are localized on the porphyrin. At 4.2 K, 52% of the holes remain trapped on the porphyrin. The anisotropic coupling tensors of the phenoxyl radical are resolved in the photoinduced D-band EPR spectra and are in good agreement with previously reported g-tensors of tyrosine radicals in photosystem II. The observed temperature dependence of the charge shift is attributed to restricted nuclear motion at low temperature and is reminiscent of the observation of a trapped high-energy state in the natural system. Electrochemical stu...
141 citations
TL;DR: In this article, the authors employ time resolved photoelectron spectroscopy to monitor the rich dynamics of electrons and phonons during the relaxation toward equilibrium, and show that 1T-TaS2 is indeed a Mott insulator.
Abstract: Photoexcitation of the Mott insulator 1T-TaS2 by an intense laser pulse leads to an ultrafast transition toward a gapless phase. Besides the collapse of the electronic gap, the sudden excitation of the charge density wave (CDW) mode results in periodic oscillations of the electronic states. We employ time resolved photoelectron spectroscopy to monitor the rich dynamics of electrons and phonons during the relaxation toward equilibrium. The qualitative difference between the oscillatory dynamics of the CDW and the monotonic recovery of the electronic gap proves that 1T-TaS2 is indeed a Mott insulator. Moreover the quasi-instantaneous build-up of mid gap states is in contrast with the retarded response expected from a Peierls insulating phase. Interestingly, the photoinduced electronic states in the midgap spectral region display a weak resonance that is reminiscent of a quasiparticle peak.
140 citations
TL;DR: In this article, the optical excitation induced an ultrafast decrease of the transmittance of the terahertz radiation within 0.7ps, and the authors concluded that the electronic states are metallic.
Abstract: We investigated the ultrafast terahertz response to the photoexcitation for vanadium dioxide single crystals and thin films using the optical-pump terahertz-probe technique at room temperature. The optical excitation induced an ultrafast decrease of the transmittance of the terahertz radiation within 0.7ps. Since we expect only the free carrier response in the terahertz range, the decrease of the transmittance is unambiguously assigned to the appearance of the high electronic conductivity due to free carriers. The conductivity increases more than ten times in the picosecond time range after photoexcitation and it is concluded that the electronic states are metallic.
132 citations
TL;DR: In this article, the phonon frequency of graphite upshifts with photoexcitation, and within a few picoseconds relaxes to the stationary value of the graphite phonon.
Abstract: We report the ultrafast dynamics of the $47.4\phantom{\rule{0.3em}{0ex}}\mathrm{THz}$ coherent phonons of graphite interacting with a photoinduced nonequilibrium electron-hole plasma. Unlike conventional materials, upon photoexcitation the phonon frequency of graphite upshifts, and within a few picoseconds relaxes to the stationary value. Our first-principles density functional calculations demonstrate that the phonon stiffening stems from the light-induced decoupling of the nonadiabatic electron-phonon interaction by creating a nonequilibrium electron-hole plasma. Time-resolved vibrational spectroscopy provides a window on the ultrafast nonquilibrium electron dynamics.
123 citations
TL;DR: In this paper, the photo-induced insulator-metal transition in VO2 was studied, correlating threshold and dynamic evolution with excitation wavelength, and it was shown that switching can only be induced with photon energies above the 670-meV gap.
Abstract: We study the photo-induced insulator-metal transition in VO2, correlating threshold and dynamic evolution with excitation wavelength. In high-quality single crystal samples, we find that switching can only be induced with photon energies above the 670-meV gap. This contrasts with the case of polycrystalline films, where formation of the metallic state can also be triggered with photon energies as low as 180 meV, well below the bandgap. Perfection of this process may be conducive to novel schemes for optical switches, limiters and detectors, operating at room temperature in the mid-IR.
120 citations
TL;DR: The aggregates present in solutions ofPhotofrin I and photofrin II are of a different nature than those present in aqueous solutions of hematoporphyrin, because tryptophan is degraded by a singlet oxygen mechanism.
Abstract: — Aqueous solutions of hematoporphyrin and hematoporphyrin derivatives were exposed to light. When present in such solutions tryptophan is degraded by a singlet oxygen mechanism. This is true for excitation at 396 nm, where porphyrin monomers have their absorption maximum, as well as for excitation at 360 nm, where porphyrin aggregates seem to absorb strongly. The quantum yield of singlet oxygen production is similar within 25% for excitation at 396 and 360 nm while the fluorescence quantum yield is more than a factor 2 lower for excitation at 360 nm than for excitation at 396 nm. Photoexcitation of the clinically used hematopotophyrin derivatives photofrin I and photofrin II produces singlet oxygen with significantly smaller yields than photoexcitation of hematoporphyrin. Thus, the aggregates present in solutions of photofrin I and photofrin II are of a different nature than those present in aqueous solutions of hematoporphyrin.
99 citations
TL;DR: In this article, a combination of the Hartree−Fock approximation and the symmetry adapted cluster theory with configuration interaction (SAC-CI) was used to demonstrate that multiple excitons (ME) in PbSe and CdSe quantum dots can be generated directly upon photoexcitation.
Abstract: We demonstrate for the first time using a combination of the Hartree−Fock approximation and the symmetry adapted cluster theory with configuration interaction (SAC-CI) that multiple excitons (ME) in PbSe and CdSe quantum dots (QD) can be generated directly upon photoexcitation. At energies 2.5−3 times the lowest excitation, almost all optically excited states in Pb4Se4 become MEs, while both single excitons and MEs are seen in Cd6Se6. We analyze the high-level SAC-CI results of the small clusters based on the band structure and then extend our band structure analysis to Pb68Se68, Pb180Se180, Cd33Se33, and Cd111Se111. Our results explain the ultrafast generation of MEs without the need for a phonon relaxation bottleneck and clarify why PbSe is particularly suitable for generation of MEs. Efficient exciton multiplication can be used to considerably increase the efficiency of QD-based solar cells.
94 citations
TL;DR: In this article, the authors investigated the time-resolved conductivity dynamics of photoexcited polymer-fullerene bulk heterojunction blends for two model polymers: poly3-hexylthiopheneP3HT and poly2-methoxy-5-3,7-dimethyloctyloxy-1,4-phenylenevinylene MDMO-PPV blended with 6,6-phenyl-C61 butyric acid methyl ester PCBM.
Abstract: Using optical-pump terahertz-probe spectroscopy, we have investigated the time-resolved conductivity dynamics of photoexcited polymer-fullerene bulk heterojunction blends for two model polymers: poly3-hexylthiopheneP3HT and poly2-methoxy-5-3,7-dimethyloctyloxy-1,4-phenylenevinylene MDMO-PPV blended with 6,6-phenyl-C61 butyric acid methyl ester PCBM. The observed terahertzfrequency conductivity is characteristic of dispersive charge transport for photoexcitation both at the � absorption peak 560 nm for P3HT and significantly below it 800 nm. The photoconductivity at 800 nm is unexpectedly high, which we attribute to the presence of a charge-transfer complex. We report the excitationfluence dependence of the photoconductivity over more than four orders of magnitude, obtained by utilizing a terahertz spectrometer based upon on either a laser oscillator or an amplifier source. The time-averaged photoconductivity of the P3HT:PCBM blend is over 20 times larger than that of P3HT, indicating that longlived hole polarons are responsible for the high photovoltaic efficiency of polymer:fullerene blends. At early times ps the linear dependence of photoconductivity upon fluence indicates that interfacial charge transfer dominates as an exciton decay pathway, generating charges with mobility of at least 0.1 cm 2 V �1 s �1 .A t later times, a sublinear relationship shows that carrier-carrier recombination effects influence the conductivity on a longer time scale 1 s with a bimolecular charge annihilation constant for the blends that is approximately two to three orders of magnitude smaller than that typical for neat polymer films.
92 citations
TL;DR: This study provides important new insights into the use of light to control the structure and function of molecular switches in direct contact with metal electrodes.
Abstract: Two-photon photoemission spectroscopy is employed to elucidate the electronic structure and the excitation mechanism in the photoinduced isomerization of the molecular switch tetra-tert-butyl-azobenzene (TBA) adsorbed on Au(111). Our results demonstrate that the optical excitation and the mechanism of molecular switching at a metal surface is completely different compared to the corresponding process for the free molecule. In contrast to direct (intramolecular) excitation operative in the isomerization in the liquid phase, the conformational change in the surface-bound TBA is driven by a substrate-mediated charge transfer process. We find that photoexcitation above a threshold hν≈2.2 eV leads to hole formation in the Au d-band followed by a hole transfer to the highest occupied molecular orbital of TBA. This transiently formed positive ion resonance subsequently results in a conformational change. The photon energy dependent photoisomerization cross section exhibit an unusual shape for a photochemical rea...
87 citations
TL;DR: In this article, photoexcitation of CdTe (λex = 620 nm), spectral bleaching from the state-filling signals of the band-edge optical transitions was measured using a femtosecond white light pulse (λprobe = 350−750 nm).
Abstract: Photoinduced charge transfer dynamics in type-II CdSe/CdTe donor−acceptor nanorods were studied in real-time using femtosecond broadband pump−probe spectroscopy. Following photoexcitation of CdTe (λex = 620 nm), spectral bleaching from the state-filling signals of the band-edge optical transitions was measured using a femtosecond white light pulse (λprobe = 350−750 nm). Excitation of the lowest energy CdTe transition shows an ultrafast change in the bleaching signals of both the CdTe and CdSe lowest energy 1S transitions as well as the characteristic carrier transfer band. Our results indicate that interfacial interconduction band electron transfer CdTe to CdSe occurs on the 500 fs time scale in these heteromaterials.
84 citations
TL;DR: An experimental study of the bonding geometry and electronic coupling of cis-bis(isothiocyanato)bis(2,2(')-bipyridyl-4,4(')-dicarboxylato)-ruthenium(II) (N3) adsorbed on rutile TiO(2)(110) is presented, along with supporting theoretical calculations of the bonded geometry.
Abstract: An experimental study of the bonding geometry and electronic coupling of cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II) (N3) adsorbed on rutile TiO2(110) is presented, along with supporting theoretical calculations of the bonding geometry. Samples were prepared in situ using ultrahigh vacuum electrospray deposition. Core-level photoemission spectroscopy was used to characterize the system and to deduce the nature of the molecule-surface bonding. Valence band photoemission and N 1s x-ray absorption spectra were aligned in a common binding energy scale to enable a quantitative analysis of the bandgap region. A consideration of the energetics in relation to optical absorption is used to identify the photoexcitation channel between the highest occupied and lowest unoccupied molecular orbitals in this system, and also to quantify the relative binding energies of core and valence excitons. The core-hole clock implementation of resonant photoemission spectroscopy is used to reveal th...
TL;DR: In this paper, a stochastic model of nanocrystal exciton and trap-state dynamics was developed to describe coupled excitonic and charge-transfer photoluminescence from a series of CdSe/CdTe collinear quantum rod heterostructures.
Abstract: Trap states are known to influence the excited-state dynamics in nanocrystalline semiconductors, but the nature and magnitude of the exciton−trap interaction is poorly understood owing to the relative optical inactivity of carrier traps and the heterogeneity of trap-state distributions. Nanocrystal time-resolved fluorescence measurements are typically complex traces that contain information about both radiative and nonradiative processes. The interpretation of these fluorescence transients is nontrivial, and typical multi- or stretched exponential analyses yield little specific photophysical information. Here, we develop a stochastic model of nanocrystal exciton and trap-state dynamics, which is used to describe coupled excitonic and charge-transfer photoluminescence from a series of CdSe/CdTe collinear quantum rod heterostructures. In this way we evaluate the photoexcitation dynamics of core nanocrystal states: the CdTe exciton and CdSe(e-)−CdTe(h+) charge-separated state and states associated with one ...
TL;DR: A luminescent cationic iridium complex with a 2,2'-biimidazole ligand forms hydrogen-bonded 1 : 1 adducts with benzoate anions in presence of 3,5-dinitrobenzoate triggers a proton-coupled electron transfer.
TL;DR: In this article, nonequilibrium carriers (electrons and holes) in intrinsic graphene at low temperatures under far-infrared (IR) and midinfrared radiation in a wide range of its intensities were calculated using a quasiclassical kinetic equation.
Abstract: We study nonequilibrium carriers (electrons and holes) in intrinsic graphene at low temperatures under far-infrared (IR) and midinfrared radiation in a wide range of its intensities. The energy distributions of carriers are calculated using a quasiclassical kinetic equation which accounts for the energy relaxation due to acoustic phonons and the radiative generation-recombination processes associated with thermal radiation and the carrier photoexcitation by incident radiation. It is found that the nonequilibrium distributions are determined by an interplay between weak energy relaxation on acoustic phonons and generation-recombination processes as well as by the effect of pumping saturation. Due to the effect of saturation, the carrier distribution functions can exhibit plateaus around the pumping region at elevated intensities. As shown, at sufficiently strong mid-IR pumping, the population inversion can occur below the pumping energy. The graphene dc conductivity as a function of the pumping intensity exhibits a pronounced nonlinearity with a sublinear region at fairly low intensities and a saturation at a strong pumping. However, an increase in the pumping intensity in very wide range leads only to a modest increase in the carrier concentration and, particularly, the dc conductivity. The graphene conductivity at mid-IR irradiation exhibit strong sensitivity to mechanisms of carrier momentum relaxation.
TL;DR: In this article, the GaInN/GaN multiple quantum well light-emitting diode structures in polar c-axis and non-polar m-axis growth have been compared in terms of luminescence properties.
TL;DR: In this article, a photoexcitation of ground state Cs-Ar collision pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules (excimers) was used for optically pumping atomic alkali lasers on the principal series (resonance) transitions with broad linewidth (≳2 nm) semiconductor diode lasers.
Abstract: Lasing on the 62P1/2→62S1/2 (D1) resonance transition of atomic Cs at 894.3 nm has been realised in mixtures of Ar, ethane, and Cs vapour by the photoexcitation of ground state Cs–Ar collision pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules (excimers). The blue satellites of the alkali D2 lines provide a pathway for optically pumping atomic alkali lasers on the principal series (resonance) transitions with broad linewidth (≳2 nm) semiconductor diode lasers.
TL;DR: In this article, the photoexcitation dynamics of Jaggregate films and strongly coupled J-aggregate microcavities are described as a disordered Frenkel exciton system in which relaxation occurs due to the presence of a thermal bath of molecular vibrations.
Abstract: We have developed a model in order to account for the photoexcitation dynamics of J-aggregate films and strongly coupled J-aggregate microcavities. The J aggregates are described as a disordered Frenkel exciton system in which relaxation occurs due to the presence of a thermal bath of molecular vibrations. The correspondence between the photophysics in J-aggregate films and that in J-aggregate microcavities is obtained by introducing a model polariton wave function mixing cavity photon modes and J-aggregate super-radiant excitons. With the same description of the material properties, we have calculated both absorption and luminescence spectra for the J-aggregate film and the photoluminescence of strongly coupled organic microcavities. The model is able to account for the fast relaxation dynamics in organic microcavities following nonresonant pumping and explains the temperature dependence of the ratio between the upper polariton and the lower polariton luminescence.
TL;DR: It is firmly established that protein flexibility is required to observe slow Stokes shift dynamics in this case and examines the underlying dynamics of protein side groups, backbone, and water dynamics to obtain a full picture of the relaxation process.
Abstract: Molecular dynamics simulations are used to calculate the time-dependent Stokes shift following photoexcitation of Trp-7 (W7) in myoglobin. In agreement with experiment, a long time (∼60 ps) component is observed. Since the long time Stokes shift component is absent when we repeat the calculation with protein frozen at the instant of photoexcitation, we firmly establish that protein flexibility is required to observe slow Stokes shift dynamics in this case. A transition between sub-states near the middle of a 30 ns ground-state trajectory gave us an opportunity to compare solvation dynamics in two different environments. While some of the superficial features are different, we find that the underlying dynamics are shared by the two isomers. It is necessary to look beyond a decomposition of the Stokes shift into protein and water contributions and probe the underlying dynamics of protein side groups, backbone, and water dynamics to obtain a full picture of the relaxation process. We analyze water residence ...
TL;DR: A photoelectrochemical signal chain sensitive to the presence of superoxide radicals was developed on the basis of CdSe/ZnS quantum dots which were immobilized on gold electrodes using a dithiol compound and the electrode was found to be sensitive to higher nanomolar concentrations of the radical.
TL;DR: In this paper, the authors presented an approach for the highly sensitive photon detection based on the quantum dots (QDs) operating at temperature of 77K. The detection structure is based on an AlAs ∕GaAs∕AlAs double barrier resonant tunneling diode combined with a layer of self-assembled InAs QDs (QD-RTD).
Abstract: We present an approach for the highly sensitive photon detection based on the quantum dots (QDs) operating at temperature of 77K. The detection structure is based on an AlAs∕GaAs∕AlAs double barrier resonant tunneling diode combined with a layer of self-assembled InAs QDs (QD-RTD). A photon rate of 115 photons per second had induced 10nA photocurrent in this structure, corresponding to the photoexcited carrier multiplication factor of 107. This high multiplication factor is achieved by the quantum dot induced memory effect and the resonant tunneling tuning effect of QD-RTD structure.
TL;DR: The relaxation dynamics of unsubstituted porphyrin, diprotonated p Morphyrin (H4P2+), and tetraoxaporphyrin dication (TOxP2+) has been investigated in the femtosecond-nanosecond time domain upon photoexcitation in the Soret band with pulses of femTosecond duration.
Abstract: The relaxation dynamics of unsubstituted porphyrin (H2P), diprotonated porphyrin (H4P2+), and tetraoxaporphyrin dication (TOxP2+) has been investigated in the femtosecond−nanosecond time domain upon photoexcitation in the Soret band with pulses of femtosecond duration. By probing with spectrally broad femtosecond pulses, we have observed transient absorption spectra at delay times up to 1.5 ns. The kinetic profiles corresponding with the band maxima due to excited-state absorption have been determined for the three species. Four components of the relaxation process are distinguished for H2P: the unresolvably short B → Qy internal conversion is followed by the Qy → Qx process, vibrational relaxation, and thermalization in the Qx state with time constant ≈150 fs, 1.8 ps, and 24.9 ps, respectively. Going from H2P to TOxP2+, two processes are resolved, i.e., B → Q internal conversion and thermal equilibration in the Q state. The B → Q time constant has been determined to be 25 ps. The large difference with r...
TL;DR: This work presents what they believe to be the first implementation of nonequilibrium two-dimensional IR spectroscopy (2DIR) combining electronic excitation within the Fourier transform (FT) approach, and offers insight into complex condensed-phase reaction dynamics.
Abstract: We present what we believe to be the first implementation of nonequilibrium two-dimensional IR spectroscopy (2DIR) combining electronic excitation within the Fourier transform (FT) approach. Nonequilibrium 2DIR spectra of Mn2(CO)10 and its photoproducts are obtained in two modalities: photoexcitation at 400 nm, either before a 2DIR probe or during the waiting time of the FT 2DIR measurement. Extending FT 2DIR to nonequilibrium systems offers insight into complex condensed-phase reaction dynamics.
TL;DR: In this article, the Pariser-Parr-Pople model was adopted to calculate the pump-probe signal in one-dimensional Mott insulators and showed that when the photoexcitation density is below about 10%, an extremely small portion of the energy eigenstates dominates the optical process and the spin-charge separation holds in these dominant energy states.
Abstract: We theoretically investigate the dynamics of insulator-metal transition induced by light-pulse excitation in one-dimensional Mott insulators. We adopt the Pariser--Parr--Pople model and the pump-probe signal is obtained by numerically calculating the time development of the state excited by light pulse. When the photoexcitation density is below about 10%, an extremely small portion of the energy eigenstates dominates the optical process and the spin-charge separation holds in these dominant energy eigenstates. As a result, the Mott gap and the short-range antiferromagnetic (AF) spin order are preserved and spin relaxation does not occur. When the density is above the value, a metallic state without the Mott gap is photogenerated and the magnitude of the short-range AF spin order is significantly reduced by photoexcitation. This is consistent with the experimentally observed photoinduced Mott transition. Furthermore, spin relaxation occurs in the metallic state. This photoinduced Mott transition is a manifestation of the spin-charge coupling in the intensely photoexcited states.
TL;DR: The potential of the novel coincidence imaging machine to unravel in unprecedented detail the various competing pathways in femtosecond time-resolved multichannel multiphoton dynamics of molecules is presented.
Abstract: ion. Furthermore, Rydberg states are believed to be used as “stepping” states responsible for the rather narrow and well-separated photoelectron spectra in the NO 2 parent ion. Slow statistical and fast direct fragmentation of NO 2 after prompt photoelectron ejection is observed leading to formation of NO + + O. Fragmentation from both the ground state and the electronically excited a 3 B 2 and b 3 A 2 states of NO 2 is observed. At short pump probe delay times, the dominant multiphoton pathway for NO + formation is a 3 400 nm+ 1 266 nm excitation. At long delay times 500 fs two multiphoton pathways are observed. The dominant pathway is a 1 400 nm+ 2 266 nm photon excitation giving rise to very slow electrons and ions. A second pathway is a 3 400 nm photon absorption to NO2 Rydberg states followed by dissociation toward neutral electronically and vibrationally excited NOA 2 ,v =1 fragments, ionized by one 266 nm photon absorption. As is shown in the present study, even though the pump-probe transients are rather featureless the photoelectron-photoion coincidence images show a complex time varying dynamics in NO2 .W e present the potential of our novel coincidence imaging machine to unravel in unprecedented detail the various competing pathways in femtosecond time-resolved multichannel multiphoton dynamics of molecules. © 2008 American Institute of Physics. DOI: 10.1063/1.2924134
TL;DR: Both photoexcited and photoionized mechanisms for water photolysis are complementary, which is elucidated by using excited-state ab initio molecular dynamics simulations based on complete active space self-consistent field approach and unrestricted Møller-Plesset second-order perturbation theory based Born-Oppenheimer molecular dynamics simulation.
Abstract: Despite the importance of water photolysis in atmospheric chemistry, its mechanism is not well understood. Two different mechanisms for water photolysis have been proposed. The first mechanism is driven by water photoexcitation, followed by the reaction of the active hydrogen radical with water clusters. The second mechanism is governed by the ionization process. Both photoexcited and photoionized mechanisms are complementary, which is elucidated by using excited-state ab initio molecular dynamics simulations based on complete active space self-consistent field approach and unrestricted Moller-Plesset second-order perturbation theory based Born-Oppenheimer molecular dynamics simulations.
TL;DR: In this paper, the authors reported the observation of the saturation of interband 3-photon absorption (3PA) in wide-gap semiconductors under intense femtosecond laser excitation.
Abstract: We reported the observation of the saturation of interband three-photon absorption (3PA) in wide-gap semiconductors under intense femtosecond laser excitation. Theoretically, we developed a 3PA saturation model that is in agreement with the Z-scan experimental results. The characteristic saturation intensities were determined to be 44 and 210GW∕cm2 for ZnO and ZnS crystals, respectively. The 3PA saturation model is also consistent with the ultrafast dynamics of 3PA-generated charge carriers in ZnO and ZnS crystals, obtained from the femtosecond transient absorption measurements.
TL;DR: It is shown that dynamics is slower in a protic solvent, which is attributed to hydrogen-bonding of the hydroxy groups with the solvent.
Abstract: Conformational changes following photoexcitation of (R)-(+)-1,1′-bi-2-naphthol are studied with a time-resolved circular dichroism (CD) experiment. Two wavelengths are investigated. For λ = 237 nm, we observe a bleaching of the ground-state absorption and a transient CD structure. Thanks to a coupled-oscillator calculation, we can attribute this effect to a decrease of the dihedral angle. For λ = 245 nm, excited-state absorption and CD are observed. All these effects are solvent-dependent. In particular, it is shown that dynamics is slower in a protic solvent, which is attributed to hydrogen-bonding of the hydroxy groups with the solvent.
TL;DR: Using time-resolved optical-pump terahertz-probe spectroscopy, the ultrafast carrier dynamics in In0.53Ga0.47As:ErAs were studied in this article.
Abstract: Using time-resolved optical-pump terahertz-probe spectroscopy, we study the ultrafast carrier dynamics in In0.53Ga0.47As:ErAs, a potential candidate for 1550 nm based terahertz photoconductive detectors. Material growth is performed by codepositing ErAs nanoislands with Be-compensated InGaAs on an InP:Fe substrate using molecular beam epitaxy. The material shows a rapid photoconductivity response following optical excitation. Photoexcitation with ∼0.5 μJ/cm2 800 nm femtosecond laser pulses yields a 3.2 ps carrier lifetime in optical-pump terahertz-probe experiments. We also measure the carrier lifetime using a 1550 nm femtosecond optical pump-probe system, and it is found to agree well with the terahertz measurements. These short lifetimes demonstrate significant potential for implementing terahertz systems using telecommunication based technologies.
TL;DR: A theory is presented for quantitative prediction of the recoil effect of the carbon 1s photoelectron spectrum and the predictions of this theory are in agreement to the measurements.
Abstract: The carbon 1s photoelectron spectrum of CF4 measured at photon energies from 330 to 1500 eV shows significant contributions from nonsymmetric vibrational modes. These increase linearly as the photon energy increases. The excitation of these modes, which is not predicted in the usual Franck-Condon point of view, arises from the recoil momentum imparted to the carbon atom in the ionization process. A theory is presented for quantitative prediction of the recoil effect; the predictions of this theory are in agreement to the measurements. The experiments also yield the vibrational frequencies of the symmetric and asymmetric stretching modes in core-ionized CF4, the change in CF bond length upon ionization, -0.61 pm, and the Lorentzian linewidth of the carbon 1s hole, 67 meV.
TL;DR: In this paper, a detailed study of transient and continuous wave (cw) photoconductivity in solution-grown thin films of functionalized pentacene (Pc), anthradithiophene (ADT), and dicyanomethylenedihydrofuran (DCDHF) is presented.
Abstract: We present a detailed study, on time scales from picoseconds to seconds, of transient and continuous wave (cw) photoconductivity in solution-grown thin films of functionalized pentacene (Pc), anthradithiophene (ADT), and dicyanomethylenedihydrofuran (DCDHF) In all films, at temperatures of 285–350 K, we observe fast carrier photogeneration and nonthermally activated charge transport on picosecond time scales At ∼30 ps after photoexcitation at room temperature and at applied electric field of 12×104 V/cm, values obtained for the product of mobility and photogeneration efficiency, μη, in ADT-tri-isoproplysilylethynyl-(TIPS)-F, Pc-TIPS, and DCDHF films are ∼0018–0025, ∼001–0022, and ∼0002–0004 cm2/V s, respectively, depending on the film quality, and are weakly electric field dependent In functionalized ADT and Pc films, the power-law decay dynamics of the transient photoconductivity is observed, on time scales of up to ∼1 μs after photoexcitation, in the best samples In contrast, in DCDHF amorpho