Stamp Deformation During Microcontact Printing
- PDF / 1,731,560 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 62 Downloads / 249 Views
STAMP DEFORMATION DURING MICROCONTACT PRINTING ANAND JAGOTA, KENNETH G. SHARP, DAVID F. KRISTUNAS E.I. du Pont de Nemours and Co., Inc., Central Research Department, Wilmington, DE 198800323 ABSTRACT Stamp deformation often produces undesirable effects that limit the practice and precision of micro-contact printing. We have experimentally studied one of the most pervasive consequences of undesired deformation: roof collapse of low-aspect-ratio recesses. Stamp behavior under increasing loads can readily be assessed by mounting stamps on flat glass and viewing stamps from below through an inverted microscope. Dynamic as well as limiting equilibrium behavior can be determined. Features with aspect ratios varying by a factor of ten were examined. We find that roof collapse initiates with the formation of a contact between the roof of the stamp and the substrate. This is followed by rapid growth of the contact region, driven by attractive interfacial forces. Contact growth usually terminates leaving a noncontacting ”moat” region. Experimental measurements of the critical stress for roof collapse are in very good agreement with theory. INTRODUCTION In the widely practiced mode of soft lithography known as micro-contact printing (µCP) [1,2], the same elastomeric silicone stamp material – Sylgard 184 [3]– has been nearly universally employed. Such polydimethylsiloxane (PDMS) materials possess several properties which render them highly useful for µCP: the precursor fluids can be cured under mild conditions with minimal shrinkage; low interfacial adhesion allows the stamps to be peeled from the master surface; and the flexibility of the stamp enables patterning of and conformal contact with both planar and curved surfaces. In some instances, the transparency of Sylgard 184 is also beneficial. Under ideal conditions, the peeled elastomer stamp is an exact negative replica of the master. There are, however, limitations to both the size and fidelity of features which can be reproduced by µCP. Many of these limitations relate to the material properties of PDMS, especially its low modulus (typical shear modulus, G, of ≈ 1 MPa). Several modes of stamp deformation can occur when the aspect ratio h/2w or h/2a (see Figure 1) of the features in the stamp differs substantially from one. Delamarche, et al., and others [4-6] have discussed several aspects of mechanical failure of elastomeric stamps.
Figure 1. Stamp with rectangular cross section “roof” recesses. S8.41.1 Downloaded from https://www.cambridge.org/core. Access paid by the UCSB Libraries, on 28 Jun 2020 at 07:07:19, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-728-S8.41
We have recently described and modeled [7,8] a number of stamp deformation behaviors. We have obtained results for critical combinations of geometrical parameters in terms of materials properties such as modulus, surface tension, interfacial tension, and the applied stamping stress. Figure 2 shows some of the modes of stamp fail
Data Loading...
