A radio-frequency spin-polarized scanning tunneling microscope.

A scanning tunneling microscope for spin-resolved studies of dynamic systems is presented. The cryogenic setup allows the scanning tunneling microscope to achieve a cutoff frequency beyond 26 GHz at the tunnel junction and to be operable at temperatures of 1.1 K-100 K in a magnetic field of up to 3 T. For this purpose, the microscope and its wiring as well as the associated cryostat system were specially designed and manufactured. For sample preparation, an ultrahigh vacuum system was developed, which is equipped with modular preparation platforms. Measurements showing the characteristics of the scanning tunneling microscope in the time and frequency domain are presented. As a proof of concept, experimental data of the Pd/Fe/Ir(111) sample system at 95 K in a magnetic field of 3 T are presented.

A molecular switch based on the manipulation of 1,3-dichlorobenzene on Ge(001) between two adsorption sites by inelastic tunneling electrons.

Meta-dichlorobenzene is adsorbed on Ge(001) and investigated by low temperature scanning tunneling microscopy. The molecule is altered between two adsorption sites by inelastic electron tunneling manipulation. These adsorption sites differ largely in conductivity. The necessary energy for switching the molecule between the sites and its polarity dependence indicate that the manipulation is initiated by the electronic excitation of the molecule.

Self-organisation of inorganic elements on Si(001) mediated by pre-adsorbed organic molecules.

A combined theoretical and experimental study on the adsorption of an isolated benzonitrile molecule on the Si(001) surface, followed by the adsorption of Al (group III), Pb (carbon group) and Ag (transition metal) is presented. It is shown that two new adsorption sites with enhanced reactivity are formed on the surface in the vicinity of the pre-adsorbed molecule. This is evidenced by the increase of the calculated binding energy of the metallic ad-atoms adsorbed at these sites. Experimentally, this enhanced local reactivity of the modified surface is only partially retained when more metallic atoms are adsorbed on the modified surface at room temperature. This is evidenced by the formation of 1-dimensional atomic chains (Pb, Al) attached to one side of the pre-adsorbed molecule.

Local tunnel magnetoresistance of an iron intercalated graphene-based heterostructure.

The lateral variation of the tunnel magnetoresistance (TMR) of a graphene-based vertical heterostructure is studied by spin-polarized scanning tunneling microscopy (SP-STM) using an Fe-coated probe tip. The well-defined heterostructure is obtained by the intercalation of a magnetic Fe monolayer at the graphene/Ir(1 1 1) interface. Its structure is characterized by a moiré pattern with a high corrugation. In contrast to the Fe / Ir(1 1 1) surface, graphene/Fe / Ir(1 1 1) exhibits ferromagnetic order with an out-of-plane easy magnetization axis. At the nanometer scale, our experiments reveal that the moiré pattern induces a lateral variation of the TMR, which reaches 80%. The measured TMR at valleys of the moiré pattern is higher than at hills. We interpret this modulation in terms of a different hybridization between graphene and Fe at valleys and hills due to a different graphene-Fe distance at these sites, which leads to a different transmission of spin-polarized states.