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Since the realization that strong interaction forces exist between scanning tunnelling microscope (STM) tip and sample surface[1], STM has been widely used, for controllable repositioning of atoms and molecules[2-4]. Mechanical manipulation is now relatively well established[5], and, in addition, there have been many examples of electronic excitations of atoms and molecules[6]. Few, however, have discussed the role of tunnel current density.
In this study, manipulation and diffusion experiments are performed using a STM at various temperatures. At room temperature, lateral manipulation is demonstrated on Cu(100) surface. The activation energy barrier for manipulation is identified, and it shown that there is a preferential direction of motion. Significantly however, it is shown that the successful manipulation exhibits a tunnel current dependence and thus the relevant role of tunnel current density in this manipulation process is discussed. We discuss the effects of changing voltage, distance dependence, and thus relative contribution of forces in this manipulation mechanism. Similar to Fischlock et al. [7], it is demonstrated that decreasing the voltage and hence separation does not have a similar effect to increasing the tunnel current in manipulation success.
Additionally, we examine the role of temperature in the manipulation process. We identify and quantify the greater diffusional motion observed at higher temperatures. An Arrhenius model for thermally induced diffusion is plotted and compared with the decrease in threshold current required to perform manipulation. This experimental evidence suggests that the increased tunnel current density, locally heats the surface sufficiently to increase the manipulation success rate.
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2. Eigler, D.M. and E.K. Schweizer, Nature, 1990. 344: p. 524-526.
3. Meyer, G., S. Zophel, and K.H. Rieder, Appl. Phys A, 1996. 63: p. 557-564.
4. Jung, T.A., et al., Science, 1996. 271: p. 181-184.
5. Bartels, L., G. Meyer, and K.H. Rieder, Phys. Rev. Lett., 1997. 79: p. 697-700.
6. Avouris, P. and I.W. Lyo, Applied Surface Science, 1992. 60-1: p. 426-436.
7. Fishlock, T.W., et al., Nature, 2000. 404(6779): p. 743-745.
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