Materials Science

Burrowing Fullerenes

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Science  25 Jun 2004:
Vol. 304, Issue 5679, pp. 1877
DOI: 10.1126/science.304.5679.1877b

One way to determine the composition of a heterogeneous surface such as a multilayer thin-film structure is to use an ion beam to ablate material that subsequently can be analyzed by mass spectrometry. The ability to reconstruct the composition depends critically on how the surface is eroded. For many atomic ion sources, the rate at which material is removed is affected by surface crystallinity and orientation; so special precautions, such as using low ion energies and rotating the sample, are needed to produce uniform profiles.

Sun et al. compared the use of C60+ ions with a Ga+ ion source in the analysis of nickel-chromium multilayers, which provides a strong test case for depth resolution. For 15-kiloelectron volt (keV) beams, the erosion rate for the C60+ source was five times greater at one-third the ion current density, and the C60+ beam induced a much lower root-mean-square roughness (2.5 versus 100 nm) and thus reduced the need for sample rotation. The simple explanation for this improvement is that the 15-keV C60+ cluster acts like 60 C atoms, each with a much lower energy of only 250 eV. — PDS

Appl. Phys. Lett. 84, 5177 (2004).

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