Probing the shape of atoms in real space

Abstract

The structure of single atoms in real space is investigated by scanning tunneling microscopy. Very high resolution is possible by a dramatic reduction of the tip-sample distance. The instabilities which are normally encountered when using small tip-sample distances are avoided by oscillating the tip of the scanning tunneling microscope vertically with respect to the sample. The surface atoms of Si(111)-(7 x 7) with their well-known electronic configuration are used to image individual samarium, cobalt, iron and silicon atoms. The resulting images resemble the charge density corresponding to 4f, 3d and 3p atomic orbitals.Comment: Submitted to Phys. Rev. B, 17 pages, 7 figure

High resolution STM imaging with oriented single crystalline tips

“…Visualization of the f z 3 orbital (l=3, m=0) associated with Sm atom at the apex was claimed in Ref. [8]; however, one could speculate whether the observed halos and extremely sharp surface atomic features reproduce the shape of the tip electron orbital. Recently, two legs of the MnNi tip d xz orbital (l=2, m=1) were resolved in STM experiments on the Cu(014)-O surface but only in a narrow range of bias voltages and tunneling currents [10,11].…”

“…Sums of these individual orbital contributions can be responsible for usual spherically symmetric atomic features but asymmetry effects can be observed in experiments if electron orbitals with non-zero orbital momentum (l) and momentum projection (m) on the quantization axis dominate at the tip apex. It took approximately two decades after the invention of STM to perform direct measurements of the asymmetric charge distribution related to apex atomic orbitals in atomic force microscopy (AFM) [6,7] and STM [8][9][10][11][12] experiments. Visualization of the f z 3 orbital (l=3, m=0) associated with Sm atom at the apex was claimed in Ref.…”

Simultaneous current-, force-, and work-function measurement with atomic resolution

“…Because the atomically resolved STM image is influenced by the atomic and subatomic structure of the tip and sample wave functions, 3,9,12 these structures also influence the decay constant images. 5 The tunneling current can be calculated with a plane-wave expansion of the surface wave a͒ Electronic address: Franz.Giessibl@physik.uni-augsburg.de FIG.…”

“…Atomic force microscopy ͑AFM͒ has progressed rapidly in the past years, 7,8 and a combination with other techniques like STM 9 or kelvin probe microscopy 10 became feasible. Here, we combine AFM with the Pethica et al method by using a qPlus sensor 11 where the STM tip is mounted on a vibrating cantilever.…”

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

“…[26][27][28] Recent results demonstrate that similar fine effects may play a significant role in dynamic STM experiments on Si͑111͒ where the observed subatomic features could be understood in terms of scattering of electrons into double dangling bonds of the silicon tip atoms. 29 The use of dynamic STM mode for atomic orbital imaging 29,30 was necessary because of the crucial importance of having rather small tip-surface separations ͑3-5 Å͒ which could be achieved reproducibly without tip breaking due to lower lateral forces with an oscillating probe.…”