Figure 1

Ball-and-stick model of the atomic structure of the isolated silicon tips with $[111]$ and $[001]$ termination: (a) and (b) show the unrelaxed and relaxed structure of a ${\mathrm{Si}}_{13}{\mathrm{H}}_{15}$ cluster [Si(111)-type tip]. (c) and (d) represent the unrelaxed and relaxed structure of a ${\mathrm{Si}}_7{\mathrm{H}}_{12}$ cluster [Si(001)-type tip]. (e) Both types of tips were approached to the relaxed structure of a ${\mathrm{Si}}_{10}{\mathrm{H}}_{15}$ cluster with Si(111) termination.Reuse & Permissions

Figure 2

(a) Charge density plots of the unrelaxed (left) and relaxed (right) structure of the ${\mathrm{Si}}_{13}{\mathrm{H}}_{15}$ tip. The relaxed structure is blunt and the charge density of the four front atoms has a diffusive character over these atoms. (b) Charge density plots of the ${\mathrm{Si}}_{13}{\mathrm{H}}_{15}$ tip sharpened via short-range chemical forces corresponding to (010) and (100) crystallographic planes (left and right, respectively). (c) Charge density plots of the relaxed structure of the ${\mathrm{Si}}_7{\mathrm{H}}_{12}$ tip [see Fig. 1d]. The calculated charge density has an axial symmetry without any “two-dangling bond” feature at its apex atom. All charge density plots have been done using the XCrySDen program [31].Reuse & Permissions

Figure 3

The normal component of the short-range tip-tip chemical force $F_{\mathrm{chem}}$ due to the interaction between silicon tips with $[111]$ and $[001]$ termination. The step used during the approach and retraction paths was set to 0.2 Å. (a) Force curves of the first and second approach/retraction cycle of the Si(111)-type tip [see Fig. 1a] towards the smaller Si(111)-type tip [see Fig. 1e]. There is a significant hysteresis for the first cycle. Because of the short-range chemical interactions the atomic structure of the tip changes after the first scan and the tip is more stable. No hysteresis is observed in the second cycle. (b) The Si(001)-type tip is rather stiff and does not change significantly during the approach and retraction paths. A very small hysteresis can be observed in the repulsive regime due to breaking and formation of a chemical bond during approach and retraction [see the dashed line in Fig. 4b].Reuse & Permissions

Figure 4

Ball-and-stick model of the atomic tip structures during the interaction of silicon tips with $[111]$ and $[001]$ termination. (a) During the first scan, on the retraction path at a distance of 3.8 Å the initially blunt Si(111)-type tip (upper tip) becomes sharp due to the jump of one front atom towards the other bottom tip. (b) The small hysteresis due to interaction between Si(001)-type tip and the smaller cluster is associated with the breaking and formation of a chemical bond of two silicon atoms during the approach and retraction path. The broken chemical bond is indicated as a dashed line. The distance of the two silicon atoms increases from 2.6 Å to 3.6 Å during the bond rupture.Reuse & Permissions