Apparatus for dosing liquid water in ultrahigh vacuum

TL;DR

This paper introduces a novel UHV-compatible apparatus for depositing ultrapure liquid water onto samples, enabling atomic-scale studies of solid-liquid interfaces without air exposure, demonstrated on TiO2(110).

Contribution

The development of a UHV-compatible system for in situ liquid water deposition on samples is a new tool for atomic-scale interface studies.

Findings

Achieved unprecedented purity of water on samples as confirmed by XPS and STM.

Enabled separation of water effects from air impurities in surface studies.

Demonstrated application on TiO2(110) single crystals.

Abstract

The structure of the solid-liquid interface often defines function and performance of materials in applications. To study the interface at the atomic scale, we extended an ultrahigh vacuum (UHV) surface-science chamber with an apparatus that allows to bring a sample in contact with ultrapure liquid water without exposure to air. In this process, a sample, typically a single crystal prepared and characterized in UHV, is transferred into a separate, small chamber. This chamber already contains a volume of ultrapure water ice, whose vapor pressure is reduced to UHV range by cooling it to cryogenic temperatures. Upon warming, the ice melts and forms a liquid droplet, which is deposited on the sample. First experiments carried out on rutile TiO2(110) single crystals using this apparatus exhibit unprecedented purity, as tested by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). These results enabled to separate the effect of pure water from the effect of low-level impurities present in the air. Other possible uses of the setup are discussed.