Atomic-Resolution Imaging of Close-Packed Metal Surfaces by Scanning Tunneling Microscopy

Abstract

The resolution of individual atoms in scanning-tunneling-microscopy (STM) images of Al(lll) is demonstrated. From results of gap-width and energy-dependent measurements the corrugation observed in the STM images cannot reflect the electronic structure of the Al surface near £>, as usually assumed for such images, but must be due to tip-surface interactions. On the basis of an investigation of the process of tip preparation, an elastic deformation of the frontmost end of the tip mediated by adhesive tipsurface interactions is proposed as the predominant factor for atomic-resolution STM imaging of such metal surfaces.

Asymmetry effects in atomically resolved STM images of Cu(014)-O and W(100)-O surfaces measured with MnNi tips

“…[1][2][3][4][5][6][7] In the meantime, the origin of atomic resolution in each particular case still cannot be easily deduced in a straightforward manner despite substantial experimental and theoretical efforts. [8][9][10][11][12][13][14][15][16][17][18][19][20][21] In the early years of STM, the concept of atomic resolution on metals was understood in terms of a single tip orbital of s-like character being responsible for the surface images. 8,9 However, this concept was unable to explain tip electronic structure effects reported in the literature for the first time by Tromp et al 10 as well as giant atomic corrugations frequently observed in real experiments on various metal surfaces including close-packed surfaces.…”

“…8,9 However, this concept was unable to explain tip electronic structure effects reported in the literature for the first time by Tromp et al 10 as well as giant atomic corrugations frequently observed in real experiments on various metal surfaces including close-packed surfaces. Elastic deformation of the tip apex [11][12][13][14][15] and electronic structure effects [17][18][19][20][21] were mainly considered in the literature as two possible mechanisms of corrugation enhancement in STM experiments. One of the explanations of the experimentally observed atomic features with large corrugation heights was given by Chen [18][19][20] in terms of the actual electronic states on realistic tips.…”

The role of surface elasticity in giant corrugations observed by scanning tunneling microscopes

“…This distance range covers more than seven orders of magnitude in the tunneling current. In addition, the method breaks down completely on close packed metal surfaces, where measured corrugations exceed the values obtained from constant density contours by up to one order of magnitude [8][9][10].…”

“…The tip in the high corrugation experiments was therefore atomically sharp and covered by comparatively few Al atoms. The experimental corrugation amplitudes reported in [10] have remained a puzzle for more than 15 years. Here, we find the solution of this puzzle: as for Al the surface atoms are less strongly bound to the surface than for noble metals, their outward relaxation under tunneling conditions is very large.…”

“…To estimate the effect of Al possibly adsorbed at the STM tip, we have performed three separate simulations, using: (i) a tungsten tip in (1 1 0) orientation with a tungsten pyramid; (ii) a tungsten tip with an Al pyramid; (iii) an aluminum tip in (1 1 0) orientation with an Al pyramid. To compare with experiments [10] the bias voltage was set to À50 and À20 mV, respectively. The increase of dynamic effects on this surface is partly due to the higher current observed on this surface (the maximum current before dynamic adjustments is about 12 nA, while it is only 5 nA on the other surfaces).…”