Time-Dependent Pinning of Nanoblisters Confined by Two-Dimensional Sheets. Part 1: Scaling Law and Hydrostatic Pressure

Abstract

Understanding the mechanics of blisters is important for studying two-dimensional (2D) materials, where nanoscale blisters appear frequently in their heterostructures. It also benefits the understanding of a novel partial wetting phenomenon known as elastic wetting, where droplets are confined by thin films. In this twopart work, we study the static mechanics of nanoscale blisters confined between a 2D elastic sheet and its substrate (part 1) as well as their pinning/depinning dynamics (part 2). Here, in part 1, we investigate the morphology characteristics and hydrostatic pressures of the blisters by using atomic force microscopy (AFM) measurements and theoretical analysis. The morphology characteristics of the blisters are shown to be the interplay results of the elasticity of the capping sheet, the adhesion between the capping sheet and the substrate, and the interfacial tensions. A universal scaling law is observed for the blisters in the experiments. Our analyses show that the hydrostatic pressures inside the blisters can be estimated from their morphology characteristics. The reliability of such an estimation is verified by AFM indentation measurements of the hydrostatic pressures of a variety of blisters.

Time-Dependent Pinning of Nanoblisters Confined by Two-Dimensional Sheets. Part 2: Contact Line Pinning

“…Such a scaling law is indeed also observed for blisters confined in various interfaces 3,6,7,9 and is well explained by our theorical analysis in part 1. 23 Retention Force Measurement. Next, we investigate the pinning effects of the blisters by manipulating them horizontally with contact mode AFM.…”

“…Here, in our case, the radial stretching tension τ in the capping sheet at the blister's edge is obtained as τ = K(h/a) 2 /4 from our analysis in part 1. 23 The capping sheet and the substrate are both graphite, and we then assume the interfacial tension between them as γ cs = 0 and γ cb = γ sb = γ gb . In addition, since we have tan θ = 2h/a from the blister's deflection profile, we derive γ gb ≈ (h/a) 2 τ from eq 1 with a small-angle approximation for θ.…”

“…The sample was prepared and kept under normal room temperature and humidity conditions. More information on the sample can be found in part 1 …”

“…8,20−22 Here, in this work, we investigate the pinning behaviors of nanoscale blisters confined between a 2D elastic sheet and its substrate by using atomic force microscopy (AFM). Our study on the static mechanics of such blisters can be found in an accompanying paper (part 1), 23 which is essential to the analyses in this part. Sealing of droplets by the 2D sheet makes manipulating them and measuring their pinning forces by an AFM probe possible.…”

“…More information on the sample can be found in part 1. 23 Measurement Methods. All of the AFM measurements and manipulations were carried out on a commercial AFM (Dimension Icon, Bruker, CA).…”