Speaker
Description
Organic semiconductor thin films of 2,7-diphenyl-BTBT (DPh-BTBT) are known to exhibit high hole mobility, due to hybridization between the HOMO and HOMO−1 of neighboring molecules. Even the BTBT monolayer on Ag(111) with an asymmetric molecular arrangement can still retain enhanced transfer integrals and form dispersive bands [1]. In this study, we aimed to observe the fingerprint of the hybridization between the HOMO and HOMO−1 in the well-ordered monolayer of BTBT/Ag(110). However, the molecular orientation of each molecule remains unclear due to multiple domains. Puschnig has proposed the Orbital Tomography (OT) method, which reconstructs molecular orbitals from photoelectron momentum maps (PMMs) of molecules adsorbed on surfaces, and has elucidated adsorption structures [2]. We developed a Robust Sparse PhaseLift OT method to estimate molecular orbital coefficients from PMM data [3], which can be applied to reconstruct molecular orbitals from multi-domain monolayers.
In this presentation, PMMs of BTBT/Ag(110) were measured. By applying the Robust Sparse PhaseLift OT to this data, we estimate the molecular orbital coefficients to distinguish the molecular orientation of the multi-domain BTBT monolayer.
The PMM intensity can be expressed based on Fermi’s golden rule as I = Δ² (a · c)², where Δ, a, and "c" denote the electron-photon interaction, atomic orbital Fourier transform, and molecular orbital coefficients. I is a squared quantity, the phase information is lost. In the Robust Sparse PhaseLift OT method, c is lifted to a matrix C to formulate a semidefinite program (SDP) with sparsity constraints. The estimated molecular orbital for configuration A agrees with DFT results, indicating adsorption on Ag(110).
[1] Y. Ono et al., Nanoscale, 17, 21729–21736 (2025).
[2] P. Puschnig et al., Science, 326(5953), 702-706 (2009).
[3] K. Niki et al., J. Phys. Chem. A, 128, 2672−2679 (2024).