Water Vapor Adsorption Effect on Silica Surface Electrostatic Patterning

Abstract

This work verifies a model for the creation and dissipation of reproducible electric potential patterns on silica surfaces, based on water adsorption, ionization, and ion migration under applied electric potential. Samples were thin silica films grown on silicon wafers and partially covered with sets of parallel gold stripe interdigitated electrodes that are normally used for Kelvin force microscope calibration. Noncontact electric potential measurements with a 20 nm spatial resolution were done using the Kelvin method under controlled atmosphere, in an atomic force microscope (AFM) with a Kelvin force attachment (KFM) mounted within an environmental chamber. Patterns were observed in micrographs acquired while one electrode set was biased and the other was grounded and when both were short-circuited and grounded. Electrostatic charging and discharging are much faster at high relative humidity, showing that the charged or discharged silica states are both changed faster under high humidity, while pattern preservation is effective under low humidity. The results are explained considering surface conductance and the partitioning of water cluster ions both in the solid−gas interfaces and the atmosphere, under the biased electrode potential.

Adhesion Hysteresis from Interdependent Capillary and Electrostatic Forces

“…However, extracting the magnitude of the capillary force from the pull-off force requires assuming that the other intersurface forces, e.g., electrostatic or hydration forces, are either constant or unimportant, which may not always be justified. 22,23 As well, the pull-off force may be governed by multiple hysteretic processes that are not easily distinguished. In ultrahigh vacuum (UHV), adhesion hysteresis can arise from charge transfer from triboelectrification, plastic deformation, material transfer, differences in work function, contact angle hysteresis in solidÀsolid wetting, and induced molecular vibrations (beating) of the solid surfaces.…”

The role of electrostatic charge in the adhesion of spherical particles onto planar surfaces in atmospheric systems

“…This may be attributed to the heterogeneous surface properties of silica. It is reported that the surface potential of dielectric surfaces is heterogeneous [16,17,33]. Surface roughness may be another contributor to the variation because the silica surface also has a surface roughness of about 2 nm in RMS (root mean square), whereas mica is atomically flat [21].…”

“…It is unclear what led to this result, but the heterogeneity of silica including surface roughness and electrostatic charge can be a possible reason it is difficult to reproduce or predict the surface potential of insulating materials [16].…”

“…Since water is a polar molecule, which can be attracted by a charged surface, the presence of surface charge considerably affects water adsorption onto surfaces. It has also been reported that water adsorption contributes to charge build-up [15,16], as well as dissipation of the charge by increasing the conductance of the material [16,17]. Thus, it is essential to consider not only the effects of surface charge and RH upon the adhesive force of micronand submicron-size particles in atmospheric systems, but also the relationship between surface charge and RH.…”

Eletrização de dielétricos: novas propostas para resolver velhos problemas

“…47 Posteriormente 48 foram analisadas superfícies não cristalinas de sílica de Stöber (Figura 3), sendo observado que o seu potencial elé-trico é modificado quando se muda a umidade, dentro de um ambiente completamente isolado eletricamente e aterrado (Figura 4). Esse resultado é particularmente interessante, pois mostra a eletrização de isolantes muito bem protegidos da ação de campos externos, ao mesmo tempo em que vincula a eletrização com adsorção de vapor de água.…”