High-resolution scanning force microscopy of gold nanoclusters on the KBr (001) surface

Abstract

In this study we use a combination of dynamic scanning force microscopy experiments and first-principles simulations to study the imaging process of gold nanoclusters adsorbed on the ͑001͒ surface of KBr. In previous experiments atomic resolution was readily obtained on the KBr substrate. However, it was not possible to resolve atoms within the clusters themselves. This correlates with imaging simulations we present here using several different probable tip models: measurable contrast was readily achieved on the KBr surface and on the gold ͑001͒ surface, but simulations on the clusters demonstrated poor contrast for all tips. We further consider the role of cluster charging in the tip-surface interaction, and the role that surface defects play in the properties of adsorbed clusters.

Sublattice identification in noncontact atomic force microscopy of the NaCl(001) surface

“…12,29 For KBr, for the negatively terminated tip, density-functional theory ͑DFT͒-based calculations yield forces of about a factor of 2 smaller than atomistic simulations, while for the positively terminated tip forces of a similar magnitude are obtained. 31 This could be due to a better modeling of electronic interactions. However, due to the larger calculation times needed for DFT-based calculations, the tip in Ref.…”

“…However, due to the larger calculation times needed for DFT-based calculations, the tip in Ref. 31 comprised only 12 atoms and thus the relaxation could have been underestimated. Our data shows that the relaxation, in particular on the minimum site, concerns atomic layers that are not represented in the 12-atom tip.…”

Imaging nanoclusters in theconstant height modeof the dynamic SFM

“…Since we are not interested in atomic contrast and we know that van der Waals forces dominate the attractive tip-surface interaction at nearly all tip-surface distances [20], for this study we consider only the van der Waals force between the tip and cluster. We performed numerical simulations in which we consider three tip models imaging a cluster on the surface.…”

Imaging the real shape of nanoclusters in scanning force microscopy

“…This chemical interaction remains below 30% of the total interaction and is based on first-principles calculations of the interaction between ionic tips and metal nanoclusters. 22 Once the three-dimensional tip-surface force field has been calculated, it is included into a set of equations describing the cantilever dynamics 13 in order to calculate the detuning ⌬f of the cantilever oscillation frequency, i.e., a simulated image. In the calculations, the parameters describing the cantilever dynamics were taken from experiment ͑canti-lever resonance frequency f 0 = 67.8 kHz, spring constant k = 2.3 N / m, and peak-to-peak amplitude A p-p =12 nm͒.…”

“…The force microscope in its dynamic mode ͑dynamic SFM͒ offers the possibility to image surfaces with a true atomic resolution, [11][12][13] and indeed, to a greater extent in recent years, the dynamic SFM has been used for the imaging of nanoclusters on many types of surfaces. [14][15][16][17][18][19][20][21][22][23][24] However, also in dynamic SFM, the tip-surface convolution strongly reduces the resolution during imaging of the nanoclusters in the standard topography mode. 19,25,26 Furthermore, the scanning speed is limited and does not exceed speeds much higher than ϳ1 − 2 Hz, which does not permit time-dependent measurements on short time scales--a particular problem for biophysical SPM studies.…”