Assessment of hydrous affinity of selected material

Abstract

The deposition of films and coatings is well-known to be affected by the presence of physi-sorbed water, which can adversely influence the nucleation and growth processes. The importance of understanding the affinity of the substrate to water cannot be over-emphasized, especially in the case of semiconductors. Our technique centers on the use of atomic force microscopy (AFM) to measure the adhesion forces, which determine the degree of hydrophobicity or hydrophilicity. Previous results reported in recent literature give contradictory information. Our study shows that the choice of the AFM tip is critical in these measurements. This research conducted a systematic study of the influence of humidity on the adhesion forces between two different AFM tips (silicon and silicon nitride) and a cross-section of materials representing silicates, phylo-silicates, calcites, and carbon. Four sets of about ten each force–distance curves measured with the AFM (Park Scientific M5) have been gathered at a series of different humidity levels and different locations on the samples. From these curves the adhesion forces for hydrophobic and hydrophilic materials vs. humidity were obtained. Many of the previously reported measurements of adhesion force were obtained with silicon tips. This paper shows that silicon tips are not sensitive enough to measure the capillary and adhesion forces. On the other hand silicon nitride tips provide reliable results supported by theoretical calculation. The results also show that the adhesion force on graphite, which has hydrophobic character, is independent of humidity variation. Fused quartz, calcite, and mica were found to be hydrophilic and their adhesion forces and capillary forces showed drastic change with increasing humidity. Calcite shows a somewhat different behavior in that it is less hydrophilic than mica and fused quartz. In general the data are in good agreement with the theoretical calculations.