Structural investigation of caffeine monolayers on Au(111)

Malte Schulte*, Andreas Jeindl, Ismail Baltaci, Peter Roese, Marie Schmitz, Ulf Berges, Oliver Hofmann, Carsten Westphal

*Corresponding author for this work

Research output: Contribution to journalArticle

Abstract

The asymmetric and achiral character of caffeine (C8H10N4O2) leads to two on-surface chiralities which has an impact on its on-surface formation. An analysis of its on-surface behavior reveals new insights of its crystallite growth. In this study the structural formation of caffeine monolayers on a Au(111) surface was analyzed by scanning tunneling microscopy (STM), low energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. The monolayers were prepared by molecular beam epitaxy (MBE) and analyzed at room temperature. Caffeine molecules self-assemble in a quasihexagonal phase on Au(111) similar to the high-temperature α phase. Two mirrored hexagonal domains are present with respect to the surface. Within the XPS measurements, no strong surface interaction was found. Therefore, a theoretical analysis of a hypothetical free-standing caffeine monolayer structure was performed by ab initio simulations. We found that a caffeine monolayer with three molecules per unit cell is preferable to one with just a single molecule, as could be expected from the LEED pattern.

Original languageEnglish
Article number245414
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume101
Issue number24
DOIs
Publication statusPublished - 11 Jun 2020

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

Fields of Expertise

  • Advanced Materials Science

Cooperations

  • NAWI Graz

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