Wojciech Koczorowski

Interface and nanostructure evolution of cobalt germanides on Ge(001)

Cobalt germanide (CoxGey) is a candidate system for low resistance contact modules in future Ge devices in Si-based micro and nanoelectronics. In this paper, we present a detailed structural, morphological, and compositional study on CoxGey formation on Ge(001) at room temperature metal deposition and subsequent annealing. Scanning tunneling microscopy and low energy electron diffraction clearly demonstrate that room temperature deposition of approximately four monolayers of Co on Ge(001) results in the Volmer Weber growth mode, while subsequent thermal annealing leads to the formation of a Co-germanide continuous wetting layer which evolves gradually towards the growth of elongated CoxGey nanostructures. Two types of CoxGey nanostructures, namely, flattop- and ridge-type, were observed and a systematic study on their evolution as a function of temperature is presented. Additional transmission electron microscopy and x-ray photoemission spectroscopy measurements allowed us to monitor the reaction between ...

Growth and evolution of nickel germanide nanostructures on Ge(001)

Nickel germanide is deemed an excellent material system for low resistance contact formation for future Ge device modules integrated into mainstream, Si-based integrated circuit technologies. In this study, we present a multi-technique experimental study on the formation processes of nickel germanides on Ge(001). We demonstrate that room temperature deposition of ∼1 nm of Ni on Ge(001) is realized in the Volmer-Weber growth mode. Subsequent thermal annealing results first in the formation of a continuous NixGey wetting layer featuring well-defined terrace morphology. Upon increasing the annealing temperature to 300 °C, we observed the onset of a de-wetting process, characterized by the appearance of voids on the NixGey terraces. Annealing above 300 °C enhances this de-wetting process and the surface evolves gradually towards the formation of well-ordered, rectangular NixGey 3D nanostructures. Annealing up to 500 °C induces an Ostwald ripening phenomenon, with smaller nanoislands disappearing and larger ones increasing their size. Subsequent annealing to higher temperatures drives the Ni-germanide diffusion into the bulk and the consequent formation of highly ordered, {111} faceted Ni-Ge nanocrystals featuring an epitaxial relationship with the substrate Ni-Ge (101); (010) || Ge(001); (110).

Graphene-based magnetoresistance device utilizing strip pattern geometry

The idea of a raster pattern magnetoresistor made of thin films of III–V compounds and a metallic layer has been known for over fifty years. Based on this knowledge, we present the construction of a magnetoresistor made of combined graphene and metallic strip patterns. The presented device is implemented using a monolayer of graphene epitaxially grown on a semi-insulating substrate. A graphene strip pattern magnetoresistor gives a promising wide range of practical applications due to its very high sensitivity combined with the mono-atomic thickness of the sensitive layer, the simplicity of realization, and a very convenient principle of sensor operation assuming only the usage of two electrical terminals.

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.

Functionalization of the Si(1 1 1) 7 × 7 substrate with coronene molecules using simple molecular source

Abstract The present paper aims at describing a source designed and constructed to generate an organic molecular beam under ultrahigh vacuum conditions. The presented construction solution of the evaporation source allows for independent deposition of three different kinds of molecules. The probability of molecules fragmentation is minimized by using a thermocouple being in contact with a molecular crucible, which enables precise temperature control. In addition, cleanness and molecular beam density are monitored using a quadrupole mass spectrometer and quartz microbalance, respectively. The operational parameters of the molecular source are optimized and deposition rates are measured for the coronene molecule in the sublimation temperature range between 430 K and 460 K. The analysis of scanning tunneling microscope images of the Si(1 1 1) 7 × 7 substrate covered with the sub-monolayer of coronene molecules and comparison with previously published data has been used for verification of the molecular source operation.