Shocks in Ion Sputtering Sharpen Steep Surface Topographic FeaturesMichael J. Aziz, Harvard University, DMR-0306997

predictedsurfaceheight

a cb d

lateral position

Ion sputtering from Focused Ion Beams is used for micromachining tall, steep features. A new regime of ion sputtering has been discovered for sufficiently steep slopes. High slopes propagate over large distances without dissipating the steepest features.

A feature, e.g., a metal line can be fabricated at a large length scale and, through uniform ion irradiation, reduced to a smaller length scale while preserving, or even sharpening, the sharpest features.

H.H. Chen, O.A. Urquidez, S. Ichim, L.H. Rodriguez, M.P. Brenner, and M.J. Aziz, Science, in press (2005).

Nonlinear Theory of Sputtering

full 0 full'' ''''h F S h B h

Our treatment:small curvature, treat other terms exactly

Rewrite in terms of slope b=dh/dx

Erosion Rate(Sigmundsputter integral)

2 2

2 2

' ''exp

2 2n

h x a h x x xv x dx

Previous treatments (Bradley-Harper, Makeev et al.)Small-slope expansions of Sigmund sputter integral:valid for small deviations from average slope and curvature.

0 full' ' ' ''''b Cb S b b B b

“The Advection Diffusion Eqn”

the Advection-Diffusion Equation

full 0 full'' '''' 'h F b S b h B h

advectioncurvature effect,small for our cases

where 0 full' ' ' ''''b Cb S b b B b FC C b

b

traveling wave speed

surfacediffusion

Slope Selection

predicted evolution of h(x)conditions for formation

undercompressive shock:

b*=3.89

Strange Matter Illustratedin Boston Museum of Science Exhibition

Michael J. Aziz, Harvard University, DMR-0306997

In a collaboration with the Boston Museum of Science on the traveling exhibit “Strange Matter” developed by the Materials Research Society, the P.I. and graduate students made interactive presentations to visitors of all ages. Visitors explored the unique properties of everyday materials such as honey, cornstarch and silly putty and were introduced to unheard-of materials such as metallic glass. The exhibit exposed tens of thousands of visitors to the wonderment of materials science and gave them an enhanced appreciation of the value of materials in society.