Electronic structure of PTCDA adsorbed on the In/Si(1 1 1)-4 × 1 surface studied by photoelectron spectroscopy

초록

The adsorption of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on the In/Si(1 1 1)-4 × 1 surface has been studied using photoelectron spectroscopy. A strongly element-selective substrate response is observed: the Si 2p core levels remain essentially unchanged, whereas the In 4d spectra show clear adsorption-induced modifications. This behavior demonstrates that the interaction is mediated primarily by the indium nanowires. The outer-In-derived In 4d component exhibits an anomalous shift toward lower binding energy, indicating that a simple local chemical shift alone cannot account for the spectral evolution. Adsorption-induced structural relaxation of the In chains is proposed to contribute significantly to this behavior. Despite the expected involvement of the carbonyl O atoms inferred from the adsorption geometry, the O 1s core levels exhibit only minimal changes, while the anhydride-derived C 1s components shift toward lower binding energy in the monolayer regime. These trends indicate that charge transferred from the indium nanowires is redistributed into the π-conjugated molecular framework rather than localized at the O–In bond. The spectroscopic results provide an electronic-structure perspective that complements STM observations and clarifies the weak, site-selective interactions governing the one-dimensional self-assembly of PTCDA on the In/Si(1 1 1)-4 × 1 surface. © 2026 Elsevier B.V.

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