Undoped and Doped Oligothiophenes: an In‐situ XPS‐, UPS‐, and HREELS‐Study

Abstract

A new method for doping organic semiconductors is presented. The most common dopant for the widely used a-sexithiophene (a6T), FeC13, was co-sublimed with the oligothiophene under UHV-conditions. The solid-state doping effects were studied for systematically varied dopant concentrations in-situ with XPS, UPS, and HREELS. Up to a doping level of one effective charge per a6T the results can be interpreted as polaron formation. At higher dopant concentrations polaron bands are most probably formed.

Self-Assembly of α-Functionalized Terthiophenes on Gold

“…The spectrum of the (−S−(CH 2 ) 16 −OH) 2 SAM also displays a S2p 1/2 peak (spin−orbit splitting) shifted 1.19 eV toward higher binding energies. The binding energies and relative intensities of these two peaks in the (−S−(CH 2 ) 16 −OH) 2 spectrum are in line with the well-established picture that disulfides dissociate and chemisorb as thiolates on gold. , The thiophene S2p binding energies near 164.9 and 163.8 eV for both molecules are also in agreement with earlier reported values. , However, the S2p peaks in the (−S−T 3 −H) 2 spectrum are slightly shifted toward lower binding energies and less well-resolved as compared to same peaks in the HS−(CH 2 ) 11 −T 3 −H spectrum. Two obvious effects can contribute to these differences.…”

“…49,50 The thiophene S2p binding energies near 164.9 and 163.8 eV for both molecules are also in agreement with earlier reported values. 46,48 However, the S2p peaks in the (-S-T 3 -H) 2 spectrum are slightly shifted toward lower binding energies and less well-resolved as compared to same peaks in the HS-(CH 2 ) 11 -T 3 -H spectrum. Two obvious effects can contribute to these differences.…”

“…The main C1s peak of (-S-T 3 -H) 2 at 284.50 eV appears at a lower binding energy as compared to the corresponding peak in HS-(CH 2 ) 11 -T 3 -H. It is also 0.3-0.4 eV lower than earlier reported C1s binding energies of R-oligothiophenes. [45][46][47][48] This peak together with a clearly visible shoulder near 283.9 eV on the low binding energy side of the main peak reveal the existence of two unique species in the (-S-T 3 -H) 2 SAM, which to the authors knowledge have not been discussed before. To elucidate if these species are homogeneously distributed along the R-T 3 chain or if they are localized to certain parts (rings), we performed also an experiment where the C1s spectrum was collected at a TOA ) 10°w ith respect to the surface of the sample, i.e., in a geometry where the photoelectrons from the outermost rings in the (-S-T 3 -H) 2 assembly are expected to contribute more to the overall XPS intensity.…”