Characterization of an organic field-effect thin-film transistor in operation using fluorescence-yield x-ray absorption spectroscopy.

In situ element-specific observation of electronic states of organic films beneath metal electrodes is achieved by x-ray absorption spectroscopy (XAS) in the bulk-sensitive fluorescence-yield (FY) mode. The molecular orientation in Au-covered oligo-thiophene films is confirmed by the C K-edge FY-XAS spectra and the applied bias dependence of the spectra is successfully detected for the first time. The present method can give deeper insights into the electronic-state investigation of various real-device systems under operational conditions.