Ladungstransportmessungen an Si(111)-Oberflächen mit einem Multispitzen-Rastertunnelmikroskop

This work concernes with the characterization and further development of a multitip scanning tunneling microscope and charge transport measurements on several silicon (Si)(111) surfaces. Multitip-scanning tunneling microscopes are used among others to determine the electrical conductance of nanostructures. To get rid of the contact resistance, the four-point method is used to measure the resistance of the sample. Therefore four individual tips were used to make up the multitip scanning tunneling microscope. Images of the platin (Pt)(100) surface under ambient conditions show a reconstructed surface, atomic steps and a drift of 1.6 Å/min after 18 hours. The development of a new nanopositioner, the KoalaDrive, to approach the tip to the sample, made the new multitip scanning tunneling microsope ultra compact. However a setup of the KoalaDrive, which works reliably in vacuum, had to be found. After a successful characterization and further development of the multitip scanning tunneling microscope, charge transport measurements on several Si(111) surfaces were realised. The conductance of the bismuthterminated Si(111) surface is comparable with a 3Å thick bismuth layer. The conductivity of the bismuthterminated Si(111) surface is (0.16 ± 0.07) mS/. The conductivity of the Si(111)-7×7 surface is (4.0±0.1) μS/ and therefore only 40 times smaller than the conductivity of the bismuthterminated silicon surface. Additionally it will be shown that the Si(111)-7×7 surface is electrically strong decoupled from the bulk and the main part of the current flows through the surface. Furthermore the Si(111) surface will be hydrogen passivated by using a chemical procedure. In doing this the surface states were removed so that the bulk conductance of the silicon sample could be measured. For a planned development of a multitip scanning tunneling microscope in a multitip atomic force microscopes the functionality of a needle-sensor as a force detector will be varified. In comparison to other sensors, the needle-sensor is very compact and due to its geometry it would be optimal for multitip atomic force microscopes. For positioning of all four tips of the multitip atomic force microscope at one location, the sensors have to be attached at an angle of 45° with respect to the surface. It becomes apparent that the imaging of surfaces is more complicated than using a sensor which is perpendicularly mounted to the surface. ”Snap to contact” and eigenfrequencies of the tip which are close to the eigenfrequency of the sensor could be a possible explanation