Theoretical aspects of vertical and lateral manipulation of atoms

Abstract

Using total energy calculations, based on interaction potentials from the embedded atom method, we show that the presence of the tip not only lowers the barrier for lateral diffusion of the adatom towards it, but also shifts the corresponding saddle point. For a Cu adatom at a (100) microfacetted step on Cu(111) this shift is 0.6 o A . The effect of the tip geometry and shape on the energetics of lateral manipulation was found to be subtle. In the case of vertical manipulation of a Cu adatom on flat, stepped, and kinked Cu surfaces we find an unusual but interesting result. It is found that as the tip approaches the surface, it becomes easier to extract the adatom from the stepped and the kinked surfaces, as compared to the flat surface. This counter intuitive result can be explained in terms of tip induced changes in the bonding of the adatom to its low coordinated surroundings.

Force Field Analysis Suggests a Lowering of Diffusion Barriers in Atomic Manipulation Due to Presence of STM Tip

“…Depending on the tip, manipulation force thresholds reach 38% to 51% of the 150 pN threshold of the classical model. Thus, a linear superposition of the forces acting on the CO is proven to be invalid and the presence of the tip apparently leads to a lowering of the diffusion barrier in agreement with previous work for manipulation on semiconductors and insulators [11,18,[23][24][25] as well as on metal surfaces [13,15].Most data presented here were obtained at a temperature of 7.5 K with a custom-built scanning probe microscope. Force and current were recorded simultaneously by using a qPlus sensor [26].…”

“…Extrapolating this trend to vertical forces of −600 pN yields lateral forces around 150 pN-close to the values reported in [19]. These results suggest the lateral force exerted by the tip on the CO molecule is not the only driver for motion, but the presence of the tip apparently lowers the diffusion barrier, as predicted [13,15]. We confirm this prediction and find that the threshold force to move CO/Cu(111) with ACTs depends on the atomic species: For Cu(100) tips 61 AE 6 pN are needed, compared to 76 AE 2 pN for W(100) and 160 AE 30 pN for the ACT Ir tip in [19].…”

“…While this technique is used widely now [3][4][5][6][7][8][9][10]-even at room temperature [11]-the physics of atomic manipulation is not fully understood. There have been theoretical investigations [12][13][14][15][16][17], but experimental studies are scant [18].…”

A Surface Coordination Network Based on Substrate‐Derived Metal Adatoms with Local Charge Excess

“…[11] Unsurprisingly, integration of the charge density around the copper adatom over the Wigner-Seitz cell [12] surrounding it results in the same amount of charge found surrounding other surface atoms. However, in the case of a Cu adatom coordinated by three DCA molecules, no inward relaxation is found and integration of the charge density leads to an excess of one electron, even after subtracting the charge density of the neighboring nitrogen atoms.…”

Atom-By-Atom Extraction Using the Scanning Tunneling Microscope Tip-Cluster Interaction

“…In recent years, the single atom-molecule manipulation has been a major advance in scanning tunneling microscope (STM) applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The main appeal of STM manipulation is the ability to access, control, and modify the interactions between the tip and the adsorbate, a few angstroms apart [2 -6,9].…”