STM image simulation

The strategy used to reach an accurate interpretation of the STM experimental results is to, whenever possible, perform DFT calculations on appropriate model adsorption systems and then to use the optimized DFT structures as input for subsequent STM image simulations [1]. We now briefly describe the details of both of these types of calculation. 

STM simulations. STM image simulations were performed with the GREEN code [31,32]. The STM current is evaluated within a one-electron... 

Bond valence theory can aid in determining structnres when they cannot be solved experimentally. For example, when a periodicity is known from STM images, it is not trivial to determine an atomic structure. Normally models will be proposed, calculated through DPT, the STM image simulated and compared to experiment. In the end, all that can be said definitively is whether the model is consistent with experiment or not. Recently Becerra-Toledo and coworkers incorporated bond valence sums into this process, greatly aiding in structure determination of a series of structures observed via STM [11]. 

Figure4.4 c(2 x 2)A structure. Left panel structural model. Right top panel corresponding simulated STM image (VB = + 1.30V, / = 0.04nA). The protrusions correspond to oxygen couples, whereas the depressions are the hollow sites surrounded by O—H complexes. Right bottom panel simulated current profiles along [00 1] at decreasing (light blue to red) tip-surface distances. (Reprinted with permission from Ref. [18].)...

Figure 4.10 Simulated STM images (sample bias 1V) at constant density (2.5 x 10-6e/B3) of the (a) hydroxylated and (b) reduced (1 1 0) rutile Ti02 surface (one OH group and one oxygen vacancy, respectively) obtained with B3LYP localized basis set calculation. (Reprinted with permission from Ref. [20].)...

The combination of state-of-the-art first-principles calculations of the electronic structure with the Tersoff-Hamann method [38] to simulate STM images provides a successful approach to interpret the STM images from oxide surfaces at the atomic scale. Typically, the local energy-resolved density of states (DOS) is evaluated and isosurfaces of constant charge density are determined. The comparison between simulated and measured high-resolution STM images at different tunneling... 

Figure6.7 (a) STM image of (5 x /SJ-rectvanadium oxide islands on Rh(l 1 1) (1000A x 1000A, + 1.5 V, 0.1 nA). Inset enlarged section of an (5 x 03)-rect island (70A x 70 A, +0.5 V, 0.1 nA) (b) DFT-derived model of the (5 x. y3)-rect structure, unit cell and structural units are indicated (V green, O red, Rh gray). Inset simulated STM image. (Reproduced with permission from Refs [18, 101].)...

Cerda J, van Hove MA (1997) Efficient method for the simulation of STM images. I. Generalized green-function formalism. Phys Rev B 56 15885... 

Figure 6.18. (Top) STM image of the flfe-plane of TTF-TCNQ taken at 63 K (Ft = 50 mV, /t = 1 nA). The image area is 5.3 nm x 5.3 nm. Reprinted with permission from Z. Z. Wang, J. C. Girard, C. Pasquier, D. Jerome and K. Bechgaard, Physical Review B, 67,121401 (2003). Copyright (2003) by the American Physical Society. (Bottom) Simulation of the STM image of the afe-plane of TTF-TCNQ, obtained with DFT calculations in the GGA performed with the Siesta code (Soler et al, 2002) using the Tersoff-Hamann approximation (see Section 4.2). The value of the charge density is 2 x 10 electrons/a.u., which is about 0.2 nm above the surface. Courtesy of Drs P. Ordejon and E. Canadell.

Figure 2. Simulated STM images of the non-rebonded Sb step edge, (a) the filled-state image and (b) the empty-state image, both under high-current conditions.

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