Polarized Optical Reflection Spectra of the Highly Anisotropic Organic Semiconductor TEA(TCNQ)₂

Abstract

From polarized reflection spectra of TEA(TCNQ), single crystals at room temperature, quantitative values of the complex dielectric function ~( w ) and the optical conductivity a(w) in the range from the far infrared to the ultraviolet have been derived. The polarization of the vibrational bands almost exclusively parallel to the highly conducting direction suggests strong interaction of conduction electrons with intramolecular TCNQ vibrations.An Eirikristallen des hoch anisotropen organischen Halbleiters TEA(TCNQ), wurden bei Zimmertemperatur die polarisierten Reflexionsspektren vom fernen Infrarot bis ins Ultraviolett gemessen. Daraus wurden die kornplexe Dielektrizitatskonstante E ( W ) sonie die optische Leitfahigkeit a(w) bestimnit. Die beobachteten Vibrationsbanden sind fast ausschlieBlich parallel zur Richtung hoher Leitfahigkeit polarisiert. Das ist ein Hinweis dafiir, daI3 die Leitungselektronen ruit den intramolekularen TCNQ-Schningungen stark gekoppelt sind.

Application of the Dimer and Tetramer Models for Interpretation of the IR Spectra of TEA(TCNQ)2

“…These peaks are shown to have a fine structure if the charge density is not shared equally by the constituent molecules [5]. The fine structure of the activated ag modes was observed experimentally in TEA(TCNQ)2 [6][7][8]1].…”

“…We measured the polarized reflection spectra of TEA(TCNQ) 2 single crystals within the range 5000-400 cm -1 and at temperatures from 300 to 80 K. The frequency dependent conductivity σ (ω) was calculated from the spectra, using the Kramers-Kronig analysis and two ranges of extrapolations, on the basis of Brau et al [6] room temperature measurements, namely 50000-5000 cm -1 and 550-20 cm -1 . A full description of the experiment was published in our previous paper [1].…”

Temperature Study of the Polarized Reflectivity of TEA(TCNQ)2Single Crystal

“…Since reflection spectra were measured in a restricted frequency range only, it was indispensable to make reasonable extrapolations. Between the highest measured frequency (5000 cm -1 ) and 50000 cm -1 the reflectance was extrapolated on the basis of Brau et al [10] measurements; this room temperature spectum was used for analysis of the spectra within the whole T-range. Above 50000 cm -1 it was assumed that reflectivity changes as 1/ω 4 .…”

“…The observation in TEA(TCNQ) 2 of a remarkable series of strong IR bands polarized in the TCNQ chain direction was reported some years ago by Kaplunov et al [9] and, in particular detail by Brau et al [10]. Belousov et al [12] measured the IR spectra of TEA(TCNQ) 2 at two temperatures, 100 and 300 K, and analyzed them in terms of a phenomenological model of interacting oscillators.…”

Infrared Absorption and Reflection Spectra of Crystalline TCNQ Salts

“…The coupling of electronic motion with the phonons associated with intramolecular vibrations from the optical properties was identified long ago (Kondow and Sakata 1971;Kalpunov et al 1972), but only a few studies have substantiated this problem (Kalpunov et al 1972;Brau et al 1974;Rice et al 1975Rice et al , 1977Belousov et al 1976Belousov et al , 1978Petzelt et al 1979;Rice 1976Rice , 1978Gutfreund et al 1974). The evaluation of the macroscopic electron-phonon coupling constant using microscopic electron-vibration coupling constants was then successfully attempted (Rice et al 1975(Rice et al , 1977Rice 1976).…”