Imaging Hydrogen Bond in Real Space

TL;DR

This study directly images hydrogen bonds in real space using room-temperature STM, revealing their hybridization and spatial features, challenging the traditional electrostatic-only view of hydrogen bonding.

Contribution

First direct real-space imaging of hydrogen bonds with STM, showing hybridization effects and detailed spatial features at room temperature.

Findings

Hydrogen bonds appear shuttle-like in STM images.

Significant contrast along the O-H direction indicates hybridization.

Appearance height varies with scanning bias, revealing orbital hybridization.

Abstract

Hydrogen bond is often assumed to be a purely electrostatic interaction between a electron-deficient hydrogen atom and a region of high electron density. Here, for the first time, we directly image hydrogen bond in real space by room-temperature scanning tunneling microscopy (STM) with the assistance of resonant tunneling effect in double barrier mode. STM observations demonstrate that the C=O:HO hydrogen bonds lifted several angstrom meters above metal surfaces appear shuttle-like features with a significant contrast along the direction connected the oxygen and hydrogen atoms of a single hydrogen bond. The off-center location of the summit and the variance of the appearance height for the hydrogen bond with scanning bias reveal that there are certain hybridizations between the electron orbitals of the involved oxygen and hydrogen atoms in the C=O:HO hydrogen bond.