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Physical Chemistry

Unconventional crystal growth

September 4, 2006 | A version of this story appeared in Volume 84, Issue 36

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Credit: © Science
Credit: © Science

Crystal-growth experiments indicate that a classic growth mechanism may not always be operative. According to a 50-year-old theory, as vapor- or liquid-phase atoms accumulate on crystal surfaces at the site of lattice imperfections known as screw dislocations, under certain conditions, the buildup forms spiral-staircase patterns. Now, researchers at IBM's T. J. Watson Research Center and coworkers at Brown University report that the well-known mechanism holds for certain crystal faces but not others (Science 2006, 313, 1266). Using low-energy electron microscopy as a real-time imaging probe, the group shows that growth on the (111) crystal face of silicon proceeds according to the classic mechanism. In contrast, the unique structure of silicon's (001) surface leads to a more complex pattern of steps that's characterized by an undulating S-shaped profile (shown) and driven by nonuniform surface stresses (indicated by color).

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