Water Adsorption, Solvation, and Deliquescence of Potassium Bromide Thin Films on SiO₂ Studied by Ambient-Pressure X-ray Photoelectron Spectroscopy

Abstract

The adsorption of water on KBr thin films evaporated onto SiO 2 was investigated as a function of relative humidity (RH) by ambient pressure X-ray photoelectron spectroscopy. At 30% RH, adsorbed water reaches a coverage of approximately 1 ML (monolayer). As the humidity continues to increase, the coverage of water remains constant or increases very slowly until 60% RH, followed by a rapid increase. At low RHs, the Br/K ratio on a submonolayer-thick film drops to less than 0.1, as a result of loss of Br atoms in the film due to radiation damage. With increasing humidity, solvation increases ion mobility and gives rise to a partial recovery of the Br/K ratio. Above 60% RH, the increase of the Br/K ratio accelerates. Above the deliquescence point (85% RH), the thickness of the water layer continues to increase and reaches more than three layers near saturation. The enhancement of the Br/K ratio at this stage is roughly a factor of 2.3 on a 0.5 nm KBr film, indicating a strong preferential segregation of Br ions to the air-liquid interface of the thin saline solution on SiO 2 .

Comparative study of GeO2/Ge and SiO2/Si structures on anomalous charging of oxide films upon water adsorption revealed by ambient-pressure X-ray photoelectron spectroscopy

“…Details of this estimation are described elsewhere. 17,27 We found that the estimation of a peak area has a deviation of 5%. This leads to an error of about 610% in the calculated water layer thicknesses.…”

Concentration and chemical-state profiles at heterogeneous interfaces with sub-nm accuracy from standing-wave ambient-pressure photoemission

“…OH À anions are also expected to be less prone to beam damage than, for example, halides 37 , due to the presence of water vapour. The CsOH/NaOH layer was prepared by depositing a droplet of 0.01 M CsOH/0.01 M NaOH solution onto the sample.…”

Defect diffusion assisted formation of cesium metal clusters in cesium halide thin films

“…where h is Planck's constant, E 1/2 is the full-width at half maximum of the absorption peak and v F is the Fermi velocity of the electrons. We believe the cesium nano-rods and free cesium on the grain surfaces are eroded by the reaction 2Cs + 2H 2 O = 2CsOH + H 2 (5) Arima et al [32] have observed that this reaction precedes slowly for atmospheric relative humidity (RH) less than 30% and increases with RH. Also, there is a near exponential increase in the rate of reaction for RH above 80%.…”