Abnormally large and small adhesion forces between plasma-treated silicon surfaces studied on AFM. Issue 4 (12th March 2021)

• Record Type: Journal Article
• Authors: Lai, Tianmao; Du, Zhengwen; Chen, Yuguo
• Is Part Of: Journal of adhesion. Volume 97:Issue 4(2021)
• Page Start: 305
• Page End: 327
• Publication Date: 2021-03-12
• Subjects: Atomic force microscopy -- contact angles -- adhesion by chemical bonding -- pull-off force -- water bridge; Adhesion -- Periodicals; 541.33
• DOI: 10.1080/00218464.2019.1663732
• Languages: English
• ISSNs: 0021-8464

Abstract

ABSTRACT: Surface hydrophilicity has a crucial effect on adhesion forces in air. However, the influence demands clarification. A spherical tip was used to measure adhesion forces on silicon samples with different treatment methods on an atomic force microscope at high relative humidity. The treatment methods were plasma treatment with storage for a time and ultrasonic cleaning in alcohol and water. Both abnormally large and small adhesion forces were observed, and the adhesion force behavior is closely related to surface hydrophilicity. With plasma treatment, the maximum force can be as large as ~4.8 μN, which was attributed to the formation of siloxane bonds (Si-O-Si) between opposing surfaces and the capillary force due to a water bridge. However, the abnormally large adhesion force can only last for a few hours, and then either decreases gradually or decreases suddenly to an abnormally small value. The decrease was attributed to the displacement of hydroxyl groups by organic molecules and the adsorption of some other airborne contaminants on the surface. The possible reasons for abnormally small forces were also presented. However, the abnormal values were not observed on samples with ultrasonic cleaning. These results may help facilitate the anti-adhesion design for silicon-based small-scale systems.