AVS 52nd International Symposium
    Nanometer-Scale Science and Technology Wednesday Sessions
       Session NS-WeM

Paper NS-WeM10
STM and AFM Imaging with In-Situ Tip-Characterization

Wednesday, November 2, 2005, 11:20 am, Room 210

Session: Nanometer Scale Imaging
Presenter: C.J. Chen, Hamburg University, Germany
Authors: C.J. Chen, Hamburg University, Germany
O. Pietzsch, Hamburg University, Germany
D. Haude, Hamburg University, Germany
R. Wiesendanger, Hamburg University, Germany
Correspondent: Click to Email
The biggest unknown factor in STM and non-contact atomic-force microscopy (NC-AFM) experiments is tip electronic states. Experimental observations show that the STM and AFM images vary dramatically with change of tip structure, either intentionally, or spontaneously. Conceptually, tunneling is symmetric to tip and sample, and the STM and AFM images should be determined by a convolution of tip electronic states and sample electronic states. From the beginning of STM, various attempts to characterize the tip have been proposed and tried, most notably using FIM. However, the correlation between the FIM image of the tip and the tip electronic states relevant to STM and AFM imaging is still not clearly identified. For spin-polarized STM, the azimuthal dependence of spin polarization of tip electronic states often determines the images. Currently, there is no well-defined method to determine the azimuth of spin polarization. We present a new method for determining the tip electronic states and the azimuthal dependence of spin polarization of the tip by imaging the tip with well-understood samples. For general tip states, Si(111)7X7 is an ideal standard sample, because the dangling-bond states on the adatoms are well separated in space and the mean energy levels cover more than 1 eV across the Fermi level. For spin-polarized tips, the Fe monolayers on W(001) system provides a perfect standard sample, because of its well-known properties of providing different ferromagnetic orientations.@footnote 1,2@ Using tips characterized by standard samples to image unknown samples, image interpretation is becoming much more certain. Furthermore, through tip reconditioning and tip characterization, tip properties can be optimized to achieve maximum contrast. @FootnoteText@@footnote 1@M Bode, O Pietzsch, A Kubetzka, S Heinze and R Wiesendanger, PRL 86, 2142 (2001).@footnote 2@A Kubetzka, M Bode, O Pietzsch and R Wiesendanger, PRL 88, 057201 (2002).