Filled-state Scanning Tunneling Microscopy Research Articles

Structure of Self-Assembled Mn Atom Chains on Si(001).

Mn has been found to self-assemble into atomic chains running perpendicular to the surface dimer reconstruction on Si(001). They differ from other atomic chains by a striking asymmetric appearance in filled state scanning tunneling microscopy (STM) images. This has prompted complicated structural models involving up to three Mn atoms per chain unit. Combining STM, atomic force microscopy, and density functional theory we find that a simple necklacelike chain of single Mn atoms reproduces all their prominent features, including their asymmetry not captured by current models. The upshot is a remarkably simpler structure for modeling the electronic and magnetic properties of Mn atom chains on Si(001).

Special issue: Advanced optical diagnostics of surfaces, nanostructures and ultrathin films

AbstractThe present special issue of physica status solidi (b) is dedicated to the 65th birthday of Wolfgang Richter, now at University Rome II “Tor Vergata”, and reviews recent achievements in the field of solid state and interface optics on inorganic and organic materials.The cover picture of the issue shows, in the background, a filled state scanning tunneling microscopy (STM) topograph of a GaAs(001)(2 × 4) surface, superimposed by a colour plot of time dependent reflectance anisotropy spectra (RAS). RAS was measured in situ during metal‐organic vapour phase epitaxy (MOVPE) growth of a 6‐fold stack of GaAsN layers on GaAs(001)(2 × 4).

STM characterization of the Si-P heterodimer

We use scanning tunneling microscopy (STM) and Auger electron spectroscopy to study the behavior of adsorbed phosphine (PH$_{3}$) on Si(001), as a function of annealing temperature, paying particular attention to the formation of the Si-P heterodimer. Dosing the Si(001) surface with ${\sim}$0.002 Langmuirs of PH$_{3}$ results in the adsorption of PH$_{x}$ (x=2,3) onto the surface and some etching of Si to form individual Si ad-dimers. Annealing to 350$^{\circ}$C results in the incorporation of P into the surface layer to form Si-P heterodimers and the formation of short 1-dimensional Si dimer chains and monohydrides. In filled state STM images, isolated Si-P heterodimers appear as zig-zag features on the surface due to the static dimer buckling induced by the heterodimer. In the presence of a moderate coverage of monohydrides this static buckling is lifted, rending the Si-P heterodimers invisible in filled state images. However, we find that we can image the heterodimer at all H coverages using empty state imaging. The ability to identify single P atoms incorporated into Si(001) will be invaluable in the development of nanoscale electronic devices based on controlled atomic-scale doping of Si.

Structural evolution of the Si(113) surface: Ab initioand tight-binding molecular dynamics calculations

The structural evolution of the Si(113) surface is investigated by ab initio calculations and by tight-binding molecular dynamics calculations using the environment-dependent tight-binding Si potential. In this study, it is found that $3\ifmmode\times\else\texttimes\fi{}2$ and $3\ifmmode\times\else\texttimes\fi{}1$ phases have interstitial structures and the transition from $3\ifmmode\times\else\texttimes\fi{}2$ to $3\ifmmode\times\else\texttimes\fi{}1$ phase results from the increasing of interstitial atoms. The existence of the interstitial structures is proved by the analysis of scanning tunneling microscopy (STM) images and the calculation of surface core level shifts using final state pseudopotential theory. The study of adsorption energy clarified that the phase transition from the $3\ifmmode\times\else\texttimes\fi{}2$ to $3\ifmmode\times\else\texttimes\fi{}1$ interstitial surface plays an important role in the behavior of the ${113}$ facet in the selective epitaxial growth of Si(001). It is also found that the domain boundary observed frequently in the filled state STM images of Si(113) is formed by the local $3\ifmmode\times\else\texttimes\fi{}1$ interstitial structure on the $3\ifmmode\times\else\texttimes\fi{}2$ interstitial surface.

Energy-filtered scanning tunneling microscopy using a semiconductor tip.

The use of cleaved, [111]-oriented monocrystalline InAs probe tips enables state-specific imaging in constant-current filled-state scanning tunneling microscopy. On Si(111)-(7 x 7), the adatom or rest-atom dangling-bond states can thus be mapped selectively at different tip-sample bias. This state-selective imaging is made possible by energy gaps in the projected bulk band structure of the semiconductor probe. The lack of extended bulk states in these gaps gives rise to efficient energy filtering of the tunneling current, to which only sample states not aligned with a gap contribute significantly.

Scanning Tunneling Microscopy Study of the c(4×4) Structure Formation in the Sub-Monolayer Sb/Si(100) System

Upon Sb desorption from a Sb-saturated Si(100) surface, the c(4×4) structure formed at about 0.25 monolayer Sb coverage. The c(4×4) reconstruction has been found to develop best when the surface is slightly contaminated, plausibly, by carbon. The Si(100)-c(4×4)-Sb surface shows up in the high-resolution filled state scanning tunneling microscopy images as being very similar to that of the recently reported c(4×4)-Si reconstruction. Here the main features of the Si(100)-c(4×4)-Sb structure are identified and the possible atomic arrangement is discussed.

Etching and a disordered overlayer on the Ge(100)-S surface

High resolution core level photoelectron spectroscopy (PES) and scanning tunneling microscopy (STM) have been used to study the adsorption and desorption of S on and off the Ge(100) surface. The previously proposed bridge adsorption site of S is consistent with our results at low coverage. At saturation the substrate contains several GeS x species, with x=0.5 to 4. Both photoemission and STM reveals a non-ideal surface, with a saturation coverage above one monolayer. Furthermore, S is found to etch the substrate. The reaction products forms a disordered overlayer on top of the interface. This overlayer is transparent in the filled state STM images.