RESUMO
Scanning tunneling microscope (STM) investigations of the step roughening of Ag(110) have shown that the STM tip extracts atoms from otherwise stable steps even at typical imaging conditions. Detailed analyses of single STM scans reveal that none of the so far known lateral manipulation mechanisms (pushing, pulling, sliding) account for the observed atom extraction. The Ag atoms rather follow the energetically favorable path of a tip induced exchange process, similar to the concerted motion proposed previously for the diffusion on fcc(110) surfaces including a metastable and thus experimentally detectable dumbbell transition state.
RESUMO
All elementary steps of a chemical reaction have been successfully induced on individual molecules with a scanning tunneling microscope (STM) in a controlled step-by-step manner utilizing a variety of manipulation techniques. The reaction steps involve the separation of iodine from iodobenzene by using tunneling electrons, bringing together two resultant phenyls mechanically by lateral manipulation and, finally, their chemical association to form a biphenyl molecule mediated by excitation with tunneling electrons. The procedures presented here constitute an important step towards the assembly of individual molecules out of simple building blocks in situ on the atomic scale.
RESUMO
We report experimental results on an insulator-on-metal system which is inherently unstable against lateral pattern formation on the nanometer scale. NaCl deposition on Cu(211) at substrate temperatures >300 K leads to faceting into (311) and (111) facets and selective NaCl growth on (311) facets only, thereby creating alternating stripes of bare Cu and NaCl-covered areas. The mesoscopic restructuring process is brought about by (1) the tendency to form (100)-terminated NaCl layers, (2) epitaxial matching between NaCl(100) and Cu(311), and (3) sufficient mobility of the Cu substrate surface.