Theoretical study of the noble metals on semiconductor surfaces and Ti-base shape memory alloys

Thesis/Dissertation · Wed Jul 27 04:00:00 EDT 1994

DOI:https://doi.org/10.2172/10189837· OSTI ID:10189837

Ding, Yungui ^[1]

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1. Iowa State Univ., Ames, IA (United States)

The electronic and structural properties of the (√3 x√3) R30° Ag/Si(111) and (√3 x √3) R30° Au/Si(111) surfaces are investigated using first principles total energy calculations. We have tested almost all experimentally proposed structural models for both surfaces and found the energetically most favorable model for each of them. The lowest energy model structure of the (√3 x √3) R30° Ag/Si(111) surface consists of a top layer of Ag atoms arranged as ``honeycomb-chained-trimers`` lying above a distorted ``missing top layer`` Si(111) substrate. The coverage of Ag is 1 monolayer (ML). We find that the honeycomb structure observed in STM images arise from the electronic charge densities of an empty surface band near the Fermi level. The electronic density of states of this model gives a ``pseudo-gap`` around the Fermi level, which is consistent with experimental results. The lowest energy model for the (√3 x √3) R30° Au/Si(111) surface is a conjugate honeycomb-chained-trimer (CHCT-1) configuration which consists of a top layer of trimers formed by 1 ML Au atoms lying above a ``missing top layer`` Si(111) substrate with a honeycomb-chained-trimer structure for its first layer. The structures of Au and Ag are in fact quite similar and belong to the same class of structural models. However, small variation in the structural details gives rise to quite different observed STM images, as revealed in the theoretical calculations. The electronic charge density from bands around the Fermi level for the (√3 x √3) R30°, Au/Si(111) surface also gives a good description of the images observed in STM experiments. First principles calculations are performed to study the electronic and structural properties of a series of Ti-base binary alloys TiFe, TiNi, TiPd, TiMo, and TiAu in the B2 structure.

• Research Organization: Ames Lab., IA (United States)
• Sponsoring Organization: USDOE; National Science Foundation (NSF)
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 10189837
• Report Number(s): IS-T--1689; ON: DE95001654; CNN: Grant DMR-8819379
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104
360606
BINARY ALLOY SYSTEMS
FERMI LEVEL
GOLD
PHYSICAL PROPERTIES
SEMICONDUCTOR MATERIALS
SILICON
SILVER
SURFACE PROPERTIES
TITANIUM BASE ALLOYS