Surface characterization and surface electronic structure of organic quasi-one-dimensional charge transfer salts

Abstract

We have thoroughly characterized the surfaces of the organic charge-transfer salts TTF-TCNQ and (TMTSF) 2 PF 6 which are generally acknowledged as prototypical examples of one-dimensional conductors. In particular x-ray-induced photoemission spectroscopy turns out to be a valuable nondestructive diagnostic tool. We show that the observation of generic one-dimensional signatures in photoemission spectra of the valence band close to the Fermi level can be strongly affected by surface effects. Especially, great care must be exercised taking evidence for an unusual one-dimensional many-body state exclusively from the observation of a pseudogap.

Magic-angle effects in the interlayer magnetoresistance of quasi-one-dimensional metals due to interchain incoherence

“…If the proposed form for the GF is correct, it could be visible in angle resolved photoemission spectra, which measures the spectral density. 3,37,38 Later we will demonstrate that even a very small incoherent term gives rise to observable MA effects.…”

Structural vs electronic origin of renormalized band widths in TTF-TCNQ: An angular dependent NEXAFS study

“…We followed the approach of Outka and Stöhr 17 and fitted the spectra after a proper background subtraction with a minimal number of Gaussian-and Lorentzian-like peaks. Absorption into the free-electron continuum was accounted for by an error function step where appropriate, whose position and width reflect the binding energy and the relative chemical shift 18 due to the various inequivalent atoms in the structure. No "hidden" peaks were included in the fitting at a certain angle unless there was a definitive indication for them in the spectra at neighboring angles and a remnant still seen in the spectrum to be fitted.…”

Electronic structure of the quasi-one-dimensional organic conductor TTF-TCNQ

“…Unfiltered higher order light or direct use of higher photon energies (տ35 eV) reduces the time scale of the VUV-induced surface damage even down to minutes. 9 All data presented in the remainder of this paper were obtained before noticeable surface decomposition occurred. Figure 5 shows energy distribution curves obtained along the b* axis, i.e., the 1D direction.…”

“…Low energy electron diffraction ͑LEED͒ of TTF-TCNQ is strongly hampered by electron-induced surface damage even faster than that caused by the VUV photons. 9 STM as another important structural surface probe is only capable of determining the surface periodicity 26,27 but cannot give any reliable information on molecular off-plane orientation. Therefore, the suggested surface relaxation has to remain a mere speculation at this point.…”

“…7,8 Photoemission experiments on such materials often find unusual spectral behavior such as the absence of a metallic Fermi edge. 2 However, the lack of information on surface quality, especially with regard to the rapid photon-induced decomposition of organic compounds in the vacuum ultraviolet, 9 casts serious doubts to what extent these observations reflect intrinsic electronic properties or rather a strongly disturbed surface. This is further corroborated by the failure of ARPES to detect spectral energy vs momentum dispersions in most charge transfer salts.…”