Simultaneous ultrafast probing of intramolecular vibrations and photoinduced charge carriers in rubrene using broadband time-domain THz spectroscopy

Koeberg, Mattijs; Hendry, Euan; Schins, Juleon M.; Laarhoven, Hendrik A. van; Flipse, C. F. J.; Reimann, K.; Woerner, M.; Elsaesser, Thomas; Bonn, Mischa

doi:10.1103/physrevb.75.195216

Cited by 17 publications

(29 citation statements)

References 35 publications

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“…This strong coupling suggests that injected charge carriers significantly alter the potential landscape of their host molecules-something that should be visible spectroscopically. Koeberg et al (2007) investigated the ultrafast response of intramolecular vibrations after photoexcitation in rubrene, a small-molecule organic semiconductor that possesses one of the largest mobility values. The static absorption and dispersion spectrum is shown in Fig.…”

Section: Ultrafast Dynamicsmentioning

confidence: 99%

Carrier dynamics in semiconductors studied with time-resolved terahertz spectroscopy

et al. 2011

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Time-resolved, pulsed terahertz spectroscopy has developed into a powerful tool to study charge carrier dynamics in semiconductors and semiconductor structures over the past decades. Covering the energy range from a few to about 100 meV, terahertz radiation is sensitive to the response of charge quasiparticles, e.g., free carriers, polarons, and excitons. The distinct spectral signatures of these different quasiparticles in the THz range allow their discrimination and characterization using pulsed THz radiation. This frequency region is also well suited for the study of phonon resonances and intraband transitions in low-dimensional systems. Moreover, using a pump-probe scheme, it is possible to monitor the nonequilibrium time evolution of carriers and low-energy excitations with sub-ps time resolution. Being an all-optical technique, terahertz time-domain spectroscopy is contact-free and noninvasive and hence suited to probe the conductivity of, particularly, nanostructured materials that are difficult or impossible to access with other methods. The latest developments in the application of terahertz time-domain spectroscopy to bulk and nanostructured semiconductors are reviewed.

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Section: Ultrafast Dynamicsmentioning

confidence: 99%

Carrier dynamics in semiconductors studied with time-resolved terahertz spectroscopy

et al. 2011

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“…This is important for the interpretation of broadband pump-probe terahertz experiments, which probe interferences of the Drude electron gas and vibrational resonances. 29 In this section we show what response may be expected from Drude electrons with finite lifetime c =1/⌫. The electron cloud is created at time t = t e with ͑by definition͒ zero position and zero average velocity.…”

Section: Drude Electron Gasmentioning

confidence: 99%

Retrieving the susceptibility from time-resolved terahertz experiments

Schins¹,

Hendry²,

Bonn³

et al. 2007

The Journal of Chemical Physics

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We present an analytical expression for the observed signal in time-and phase-resolved pump-probe studies, with particular emphasis on terahertz time-domain spectroscopy. Maxwell's equations are solved for the response of damped, harmonic oscillators to a driving probe field in the perturbative regime. Our analytical expressions agree with the one previously reported in the literature ͓Nemec et al., J. Chem. Phys. 122, 104503 ͑2005͔͒ in the Drude limit; however, they differ in the case of a vibrational resonance.

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“…24 In Ref. 25, it has been shown for rubrene that optically active, ground state vibrational modes in the terahertz region can give rise to resonances in the conductivity spectrum. This cannot explain the FIG.…”

Section: ͑1͒mentioning

confidence: 99%

On the mechanism of charge transport in pentacene

Laarhoven

Flipse

Koeberg³

et al. 2008

The Journal of Chemical Physics

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Terahertz transient conductivity measurements are performed on pentacene single crystals, which directly demonstrate a strong coupling of charge carriers to low frequency molecular motions with energies centered around 1.1 THz. We present evidence that the strong coupling to low frequency motions is the factor limiting the conductivity in these organic semiconductors. Our observations explain the apparent paradox of the "bandlike" temperature dependence of the conductivity beyond the validity limit of the band model. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2955462͔Recent years have seen much interest in the conductivity of pentacene and other molecular semiconductors of the oligoacene family, fueled by the unique properties of these materials. Oligoacenes are flexible, cheap, and exhibit relatively high charge carrier mobilities, 1 allowing for novel applications in electronic devices. [2][3][4] Despite this interest, the nature of charge transport in the materials has remained the subject of intense debate.Crystalline organic semiconductors exhibit charge mobilities that decrease with temperature. [5][6][7][8][9] In analogy to inorganic semiconductors, this has been interpreted as an indication of delocalized charge carriers and a "bandlike" transport mechanism. 10-13 Theoretical models based on polaronic band conduction 14 indeed provide a good qualitative description of the bandlike mobility of charge carriers in pentacene, but the factors determining the absolute charge mobility remain unknown. For instance, an analysis of the high temperature mobility has indicated that the mean free path of charge carriers is of the same magnitude as the intermolecular distance. 15 It is not clear as to why the signature of delocalized bandlike transport persists at these temperatures, where the mean free path is smaller than the intermolecular distances. Because of the "softness" of these van der Waals bonded organic crystals, it is possible that the coupling of the carriers with the intermolecular vibrations could play a key role in the description of the charge carrier dynamics. Troisi and Orlandi 16 have recently formulated a model ͑TO model͒ that states that the charge mobility in oligoacenes is limited by large fluctuations of the electronic coupling between adjacent organic molecules due to thermal molecular motions, in particular, the low energetic phonon modes with energies around 1 THz. 17 This model correctly describes the bandlike temperature dependence of the mobility, including its absolute value, outside the validity of delocalized transport models. 16 Direct experimental evidence for the various proposed models has been lacking. In particular, experimental insights into the role of intermolecular low frequency vibrational modes in determining the charge transport mechanism have been missing to date.Terahertz spectroscopy 18 provides the opportunity of studying the response of charge carriers in the frequency range of these modes, and has proven useful for investigating photocarrier dynamics in...

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Simultaneous ultrafast probing of intramolecular vibrations and photoinduced charge carriers in rubrene using broadband time-domain THz spectroscopy

Cited by 17 publications

References 35 publications

Carrier dynamics in semiconductors studied with time-resolved terahertz spectroscopy

Carrier dynamics in semiconductors studied with time-resolved terahertz spectroscopy

Retrieving the susceptibility from time-resolved terahertz experiments

On the mechanism of charge transport in pentacene

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