title: Shape transition of germanium nanocrystals on a silicon (001) surface from pyramids to domes
abstract: Chemical vapor deposition of germanium onto the silicon (001) surface at atmospheric pressure and 600 degrees Celsius has previously been shown to produce distinct families of smaller (up to 6 nanometers high) and larger (all approximately 15 nanometers high) nanocrystals. Under ultrahigh-vacuum conditions, physical vapor deposition at approximately the same substrate temperature and growth rate produced a similar bimodal size distribution. In situ scanning tunneling microscopy revealed that the smaller square-based pyramids transform abruptly during growth to significantly larger multifaceted domes, and that few structures with intermediate size and shape remain. Both nanocrystal shapes have size-dependent energy minima that result from the interplay between strain relaxation at the facets and stress concentration at the edges. A thermodynamic model similar to a phase transition accounts for this abrupt morphology change.
authors.affiliation: Hewlett-Packard Laboratories, 3500 Deer Creek Road, Mail Stop 26U, Palo Alto, CA 94304-1392, USA.
authors.initials: G
authors.lastname: Medeiros-Ribeiro
authors.initials: AM
authors.lastname: Bratkovski
authors.initials: TI
authors.lastname: Kamins
authors.initials: DAA
authors.lastname: Ohlberg
authors.initials: RS
authors.lastname: Williams