Microstructured elastomeric surfaces with reversible adhesion and examples of their use in deterministic assembly by transfer printing

Abstract

Reversible control of adhesion is an important feature of many desired, existing, and potential systems, including climbing robots, medical tapes, and stamps for transfer printing. We present experimental and theoretical studies of pressure modulated adhesion between flat, stiff objects and elastomeric surfaces with sharp features of surface relief in optimized geometries. Here, the strength of nonspecific adhesion can be switched by more than three orders of magnitude, from strong to weak, in a reversible fashion. Implementing these concepts in advanced stamps for transfer printing enables versatile modes for deterministic assembly of solid materials in micro/nanostructured forms. Demonstrations in printed two- and three-dimensional collections of silicon platelets and membranes illustrate some capabilities. An unusual type of transistor that incorporates a printed gate electrode, an air gap dielectric, and an aligned array of single walled carbon nanotubes provides a device example.

Fig. 1.

Implementation of elastomeric, microtip adhesive surface in a stamp for deterministic assembly by transfer printing.

Fig. 2.

SEM and FEM images of representative elastomeric stamps in microtip designs, with and without silicon platelets (3 μm thick; 100 × 100 μm) on their surfaces. (A–C) Four-tipped layout. The right frames provide magnified views of one of the microtips and the bottom frames provide corresponding images of the results of finite element modeling (B, C). (D) Schematic illustration for notation of the stamp dimension. (E, F) Five-tipped layout. In this design, the silicon platelet remains in contact only with the largest, central microtip in the final stages of the transfer printing process.

Fig. 3.

Typical force-time (bottom axis) and force-distance (top axis) curves associated with contact of a microtip surface with the flat surface of a silicon wafer (A, B). The inset illustrations correspond to the steps of retrieval (A) and delivery (B) for use of such a surface in a transfer printing mode. Plots of force required to remove a microtip surface (C) and a corresponding flat surface (D) from the silicon, as a function of retraction speed for three different preload cases, simulating the steps of retrieval (0.2 mN) and delivery (1.5, 3 mN) in a printing process. Modeling results for the microtip surface are indicated as a black line (C).

Fig. 4.

SEM images of representative printing results with thick (3 μm) and thin (260 nm) silicon platelets (100 × 100 μm squares) on different surfaces and in free standing and multilayer stacked geometries. (A) Image of platelets printed on an array of square islands. (B) Image of 3 μm thick silicon platelets printed on the rough surface of a film of ultrananocrystalline diamond on a silicon wafer. Images of 3 μm (C) and 260 nm (D) thick silicon platelets printed onto two silicon bars, to yield freely suspended structures. Images of multilayer configurations of 3 μm thick silicon platelets in a single stack with small incremental rotations and translations (E) and four similar stacks, capped with a pair of platelets in the center (F), both on flat silicon wafer substrates.