연사: Johannes Seibel from Institute of Physical Chemistry, Karlsruhe Institute of Technology

일시: 2026년 10월 20일, 1:30 – 2:30pm

장소: 연구협력관 B1 Jupiter 세미나룸

세미나 명: “Beyond Sublimation: Electrospray and Electron Impact Ion Beam Deposition for STM and TDS Investigations of Molecular Interfaces"

초록: 

Preparative mass spectrometry has recently emerged as a versatile approach for preparing molecular samples for scanning probe microscopy (SPM) and other surface-science techniques. By enabling mass-selective deposition of molecular ions onto surfaces under ultra-high-vacuum (UHV) conditions, it overcomes key limitations of conventional sublimation-based preparation and expands the range of molecules accessible to surface characterization.[1]

Here, two complementary ionization-based deposition strategies are explored: soft ionization by electrospray (ESI) and hard ionization by electron impact (EII). ESI enables the deposition of fragile and non-volatile (bio)molecules that are otherwise inaccessible to UHV-based surface studies. As an example, mass-selective deposition of glycan molecules followed by scanning tunneling microscopy (STM) provides real-space information down to the single-molecule level, including the differentiation of D- and L-cellohexaose enantiomers and the visualization of intermolecular interactions and chiral self-assembly.[2,3] Deposition of enantiopure and racemic cellohexaose further reveals mirror-symmetric assemblies and conglomerate formation, demonstrating the potential of STM to investigate chirality and molecular organization at the single-molecule level.

In contrast, EII provides access to molecular fragments and reaction products generated through ionization-induced fragmentation. We demonstrate mass-selective deposition of tetraphenylporphyrins (TPPs) and halogenated polycyclic aromatic hydrocarbons together with their respective fragments. STM and temperature-programmed desorption (TDS) measurements demonstrate that the parent molecular ions can be deposited intact, while the deposition of selected fragments reveals stable species formed through intramolecular reactions. In the case of TPP and coronene fragments, small amounts of dimers further indicate the potential for intermolecular reactions. Thus, EII-based deposition provides access to both intact molecules and selected molecular fragments, opening a route toward the controlled deposition of species that are difficult or impossible to access by conventional preparation methods and providing new opportunities for studying molecular structure, reactivity and assembly at surfaces.