AVS 49th International Symposium
    Surface Science Wednesday Sessions
       Session SS-WeP

Paper SS-WeP23
Bias Voltage Dependence of Apparent Local Barrier Height at Constant Tip-Sample Separation

Wednesday, November 6, 2002, 11:00 am, Room Exhibit Hall B2

Session: Surface Science 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
Correspondent: Click to Email
The bias voltage dependence of apparent local barrier height (LBH) corresponding to "work function" at nanometer-scale has been measured by STM on Au (111) surface with Au tip at constant tip-sample separation (CS). The obtained main result is that in the bias voltage range of I-V curve showing nearly straight (ohmic), the LBH does not depend on the bias voltage and beyond this range the LBH decrease with increasing the bias voltage. The bias voltage dependence has been reported at relatively high bias voltage above 1.5 V. However, these reports had been measured at constant current (CC) conditions generally used in STM / LBH measurements. To measure its dependence under CC, the bias voltage is varied, which causes change in separations. In this situation, the measured results contain both effects (bias voltage and separation). Therefore, to measure the effect of bias voltage on LBH truly, the separation effects have to be eliminated. We have measured bias voltage dependence of LBH at CS using the current on I-V curve, and have compared results at CS with CC. At CS measurements, in the ohmic range (below 0.1V), LBH does not depend on bias voltage within the experimental error. Beyond this range, that is off ohmic, LBH decrease with increasing the bias voltage. On the other hand, at CC measurements, the range of I-V curve showing the ohmic and a slightly off the ohmic, the LBH increase with increasing the bias voltage, because of the increasing in separation. Beyond this range, LBH decreases with increasing the bias voltage as CS case, indicating that separation does not affect any more.