We use a hot scanning tunneling microscope to make time lapse movies of the growth of Si on a Si(001) substrate. In the initial stages of molecular beam epitaxial growth at 530 K, many small one dimensional (1D) islands are formed. The explanation of this curious shape anisotropy has been controversial. We analyze movies acquired during deposition and follow changes in individual islands to find that the growth rate of 1D islands is independent of length, supporting a model of anisotropic sticking to explain island shape anisotropy. We find the ratio of sticking at side sites versus end sites is 0.019 6 0.003.
Scanning tunneling microscopy is used to investigate the morphological evolution of GaAs/InAs short period superlattice structures. The layers of the superlattice, either grown in compression or tension, exhibit an island or trench morphology. With increasing film thickness, the islands or trenches grow in size and develop a characteristic spacing along [110] of approximately 150 A. This is the first experimental evidence to suggest that lateral composition modulation arises from both thickness variations of the layers and compositional nonuniformities within the atomic plane.
The atomic structure of In 0.81 Ga 0.19 As/InP alloy layers was examined using in situ scanning tunneling microscopy. The ͑2ϫ3͒ reconstruction observed during growth by reflection high-energy electron diffraction represents a combination of surface structures, including a 2͑2ϫ4͒ commonly observed on GaAs͑001͒ and InAs͑001͒ surfaces, and a disordered ͑4ϫ3͒ that is unique to alloy systems. The proposed ͑4ϫ3͒ structure is comprised of both anion and cation dimers. Empty and filled states images show that the features reverse contrast with sample bias, in agreement with the model.
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