DEPARTMENT OF MATHEMATICAL SCIENCES

APPLIED AND COMPUTATIONAL MATHEMATICS SEMINAR

**Speaker:**Patrick Shipman, Colorado State

**Title: ***
Self-Assembled Nanoscale Patterns Produced by Ion Bombardment of Binary Compounds
*

**Abstract:**
When a solid surface is bombarded with a broad ion beam, a plethora of self-assembled nanoscale patterns can emerge, including nanodots arranged in hexagonal arrays of remarkable regularity. We discuss a theory that explains the genesis of the strikingly regular hexagonal arrays of nanodots that can form when binary materials are bombarded at normal incidence. In our theory, the coupling between a surface layer of altered stoichiometry and the topography of the surface is the key to the observed pattern formation. Our theory also that predicts that remarkably defect-free ripples can be produced by oblique-incidence bombardment of a binary material if the ion species, energy and angle of incidence are appropriately chosen. This high degree of order cannot be achieved by bombarding an elemental material.
Ion bombardment has the potential to become a cost-effective method to rapidly fabricate large-area nanostructures at length scales beyond the limits of conventional optical lithography. To realize this potentional, however, ways to limit the number of defects in the patterns must be developed. We analyze how a soft mode related to the mean sputter yield can facilitate defect formation and give rise to less ordered patterns.

**Time:** Friday, October 17, 2014, 1:30-2:30 p.m.

**Place:** Exploratory Hall (formerly S & T II), Room 4106

Department of Mathematical Sciences

George Mason University

4400 University Drive, MS 3F2

Fairfax, VA 22030-4444

http://math.gmu.edu/

Tel. 703-993-1460, Fax. 703-993-1491