Atomic Contacts characterized by Force and Current

Contacts between atoms present the reduction of an electronic system to the smallest scale accessible at the present. Field ion microscopy (FIM) and simultaneous scanning tunneling microscopy (STM) and atomic force microscopy (AFM) were used to characterize atomic contacts between a tungsten (W(111)) STM-tip and a gold (Au(111)) sample. The STM-tip was imaged with atomic resolution using FIM and reconstructed in a three dimensional ball model. Force and current were measured simultaneously while the tip approached an atomically flat Au(111) sample to form a contact.;Force and current data for different structural modifications of the W(111)-Au(111) SPM tunneling junction are presented and discussed. Findings include that the W-Au junction in geometries which were examined in this thesis do not exhibit the conductive properties of a one-atom contact.;A comparison of different theoretical approaches that treat the correlation of force and current in a STM type tunneling junction is presented and the results of this thesis support a F2∝ It proportionality for a three-atom tungsten tip contacting an atomically flat Au(111) sample.;A detailed description of the tip production and characterization using an etching setup that was developed for this thesis is introduced. These tips are characterized by field ion microscopy (FIM). The adaptation of a well known three dimensional ball model reconstruction to the tungsten bcc(111) crystal is described and utilized to reconstruct FIM micrographs of W(111) STM-tips. Using several of such tips, the long-range forces of the tip-sample system were analyzed using recent theoretical models, concluding that van der Waals and electrostatic force contributions were negligible for tips with a radius smaller than rtip = 15 nm within the precision of the FIM-STM/AFM system that was employed for the experiments.