Articles you may be interested inQuantum-dot laser with a metal-coated waveguide under continuous-wave operation at room temperature

The interface atomic structure of very thin IrSi(IrGe) films grown on the Ir(001) plane has been studied with the field ion microscope. Two distinctive types of structures have been observed. One shows the C(2×2) structure of the substrate. As the size of the layer is reduced by field evaporation, the surface relaxes into a rhombic structure resembling the (011) Ir layer of the IrSi(IrGe) crystal. The other shows a rectangular unit cell of a larger size, which is not yet successfully correlated to the structure of the IrSi(IrGe) crystal.

Thin single crystal NiSi2 films have been grown epitaxially on the [111] oriented Si tip surface in ultrahigh vacuum (UHV). A 180° change in the axial symmetry is found for the field ion images taken before and after the growth of the silicide layers. From this observation and a computer simulation of the field ion images we conclude that the Si-NiSi2 interface has the B-type structure. The field ion image of the NiSi2 films is good enough to reveal the atomic structure of the (111) Ni layer.

The early stages of formation of thin layers of IrSi and IrGe on Ir surfaces have been studied. Distinctive stages of growth have been observed. In the earliest stage on Ir(001), atomically resolved images show a structure resembling the c(2x2) of the substrate, which we believe to have the (Oil) Ir-layer structure of the IrSi and IrGe crystals. In the second stage, the (2x1) image structure on Ir(Oll) is identified to be the Ir layer of the IrSi(OOl) fundamental plane.PACS numbers: 68.35.Fx, 68.55.Gi, 81.60.Bn Formation of thin layers of metal-semiconductor compounds on either semiconductor or metal surfaces is a subject of great basic and technological interest because of their wide application to Ohmic contacts and Schottky barriers in semiconductor devices and in very large-scale integrated circuits. 1 " 3 It is now well recognized that, among other things, Schottky-barrier height can depend significantly on the atomic structure at the metal semiconductor interfaces. 4 Atomic structures at the interface are of course a subject of general interest to solid-state, surface, and material sciences. A field-ion microscope (FIM), with its capability of imaging surface atoms with atomic resolution and of field evaporating surface layers, has recently been successfully used to study the compositional variation and the atomic structure of WSi 2 -W and NiSi 2 -Si interfaces. 5 ' 6 Epitaxial growth of WSi 2 on the W(001) and NiSi 2 on Si(lll) with 5-type interfaces as discussed by FIG. 1. (a) A 15-K He-ion image of an Ir substrate, (b) Two layers of Ir silicide cover the Ir(001). The field-ion image structure resembles ac(2x2)of the substrate.Tung, Gibson, and Poate 7 were clearly seen also. In these preliminary studies, the interface structures were not yet successfully resolved. We report here some interesting observations of atomic structures of compound layers in the different stages of formation of IrSi and IrGe on field-evaporated, clean Ir tip surfaces. We hope our observations will stimulate further studies of these systems with other techniques.An Ir tip, prepared by electrochemical etching, is first cleaned by being heated in vacuum of 10" 9 to IQ-io T orr? anc j i s then field evaporated in He image gas to develop an atomically clean and perfect, nearly hemispherical surface. Two methods are used to grow thin silicide films on Ir tip surfaces. In the first method silicon atoms are vapor deposited on the tip surface by resistive heating of a narrow strip of highpurity Si cut from a wafer. The deposition source is degassed in the 10~~1 0 -Torr range of vacuum for at least 24 h before being used for an experiment. In the second method, a well-developed Ir tip is heated in 5 FIG. 2. He-ion image of a field-evaporation sequence of an Ir silicide layer on Ir(001). The substrate layer is shown in the upper left corner.