RHEED studies of the nucleation, growth, and mobility of Ag atoms on the Si(111)7 x 7 surface

Thesis/Dissertation · Thu Jul 01 04:00:00 EDT 1993

DOI:https://doi.org/10.2172/140415· OSTI ID:140415

Roos, Kelly Ryan ^[1]

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

The low temperature and flux dependent growth of ultrathin Ag films on the Si(111)7x7 surface is studied with Reflection High-Energy Electron Diffraction (RHEED). The grazing incidence geometry of RHEED allows for an incident molecular beam normal to the surface, and makes it an ideal surface probe for studying ultrathin film growth in real time. Short-lived oscillations in the diffracted intensity are observed during Ag deposition at 150 K, indicating quasi-layer-by-layer growth mediated by adatom mobility. When the 150 K growth is performed over a wide range of deposition rates F, the peak intensity is observed to scale, i.e. I(Ft) depends only on the total amount deposited, which implies thermally activated diffusion is absent at 150 K. Scaling is not obeyed at higher temperatures (T≥473 K) for the growth of the √3x√3 R30° (√3) superstructure. Testing for scaling of the diffracted intensity constitutes a new experimental method which can be applied generally to determine if thermal diffusion is active at a particular temperature. Scaling is consistent with a constant diffusion length R₀, independent of substrate temperature and deposition rate. The presence of a non-thermal diffusion mechanism (responsible for the constant diffusion length R₀) is confirmed by monitoring the flux dependence of the √3 superstructure growth during deposition at T≥473 K. At these temperatures the total diffusion length R is given by R=R₀+(4Dt)^1/2, where (4Dt)^1/2 is the thermal component. A non-zero intercept R₀ is found by plotting the peak intensity I_p^1/2 (a measure of the average domain size) vs. deposition rate F^-1/2 (F^-1 is proportional to the available diffusion time.) From the FWHM of a low coverage (0.2 ML) √3 spot, an estimation of 50 Å is made for a lower bound of the magnitude of R₀.

• Research Organization: Ames Lab., IA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 140415
• Report Number(s): IS-T--1664; ON: DE94005551
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
74 ATOMIC AND MOLECULAR PHYSICS
GRAIN GROWTH
NUCLEATION
SILVER
THERMAL DIFFUSION
THIN FILMS