IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Friday Sessions
       Session SS3-FrM

Paper SS3-FrM2
Linking Stress to Surface Structure Using STM

Friday, November 2, 2001, 8:40 am, Room 122

Session: Clean and Adsorbed Surfaces
Presenter: G.E. Thayer, UC Davis and Sandia National Labs
Authors: G.E. Thayer, UC Davis and Sandia National Labs
N.C. Bartelt, Sandia National Laboratories
V. Ozolins, Sandia National Laboratories
A.K. Schmid, Lawrence Berkeley National Lab
S. Chiang, University of California, Davis
R.Q. Hwang, Sandia National Laboratories
Correspondent: Click to Email
Understanding the role of stress at solid surfaces is necessary to determine why surfaces have particular structures. While significant progress has been achieved in considering how local elastic interactions might contribute to the total surface energy a nd structure, it had not been possible to explicitly confirm this experimentally. The main reason for this is the difficulty in measuring stress fields on surfaces. Here, our approach has been to directly measure strain fields on a surface arising from l attice mismatch. Studying the phase diagram of CoAg/Ru(0001) single-monolayer films using STM, we found that annealed Co-rich films form an alloy with a structure that is not atomically mixed but instead consists of Ag droplets (15-30 atoms in si ze) with in a Co matrix. To quantitatively answer the question of how surface stress contributes to the formation of this structure, we have directly probed the stress fields on the surface. Analysis of atomically resolved images of the CoAg alloy has allowed us t o perform strain measurements over the surface. In our analysis we have compared strain measurements of about 800 Co atoms in a wide variety of Co-Ag neighborhoods with calculations of strain resulting from the Frenkel-Kontorova (FK) model and first-princ iples local spin density approximation (LSDA) calculations. The close agreement between the measurements and the calculations explicitly shows how stress due to lattice mismatch contributes to the formation of the droplet structure of the alloy. Within th e framework of the FK model we determine the relative forces acting on the surface by the measurement of strain fields and we are able to provide a direct link between surface stress and surface structure. We find the agreement even allows for the determination of details such as elastic spring constants from experimental measurements. Our success firmly demonstrates the possibility of using atomically resolved STM data to investigate surface stress.