AVS 50th International Symposium
    Applied Surface Science Wednesday Sessions
       Session AS-WeP

Paper AS-WeP7
Distinguishing the Dependence of the Apparent Local Barrier Height on Measurement Conditions

Wednesday, November 5, 2003, 11:00 am, Room Hall A-C

Session: Poster Session
Presenter: S. Yagyu, National Institute for Materials Science, Japan
Authors: S. Yagyu, National Institute for Materials Science, Japan
M. Yoshitake, National Institute for Materials Science, Japan
Y. Mizuno, Stanford Linear Accelerator Center
R.E. Kirby, Stanford Linear Accelerator Center
Correspondent: Click to Email
Work function is an important and fundamental property of materials related to the electron emission and reaction of molecules on the surface. As functional materials of reduced dimension become increase, the measurement of the local work function becomes important. The apparent local barrier height (LBH) related to the local work function has been measured by STM. The LBH is not the local work function of a sample material but multi-parameters value correctly, because the LBH based on the STM technique depends on the tip parameters (material, shape), the measurement parameters (tunnel current (I), bias voltage (V) and tip-sample separation (s)) and certainly the local work function of the sample material. Since each LBH obtained on same material surface with various measurement parameters is extremely different, we should know relation between the measurement parameters and the LBH. In STM/LBH measurement a I is proportional to a V and a s. For example, if we fix a I and change a V, a s is changed automatically. We measured dependence of the LBH on the I, V, and s precisely on the reconstructed Au (111) surface with an Au tip. The results under three different conditions, a constant s, I, and V were compared in the low bias voltage range (-50mV to -5mV) where I-V curve shows linear (ohmic). Under a constant s, the LBH does not change with the V, indicating that the LBH is independent of the V. Under a constant I, the LBH increases with the increased V. Under a constant V, the LBH increases with the increased s. The three results indicate that LBH depends exclusively on the s in our experimental conditions.