| Abstract [eng] |
In this work, graphene - metal contact theory and recent publications in this field are discussed. Short introduction into graphene structure and its monolayer synthesis as well as graphene transfer methods using polymer coatings are presented. The main idea of this research is to form a graphene – metal contact and study its contact resistance when for contact formation we used two different metals. In experimental part first graphene transfer was investigated. Graphene layer transfer from copper foil onto SiO2/Si wafer using polymethyl methacrylate (PMMA) dissolved in chlorobenzene as supporting coating is described. Samples were analyzed using optical microscope and Raman spectroscopy methods. Three coatings with different concentration were prepared and analyzed. The best quality of transferred graphene layer containing smallest amount of cracks and tears were obtained using 156,7 g/l concentration PMMA coating. PMMA removal after transfer with two organic solvents chloroform and acetone were investigated and analyzed. After graphene layer transfer process PMMA is most effectively removed with chloroform. Contaminants observed in graphene layer samples have been identified. Raman spectra showed that those contaminants are graphene from back side of copper. Using optimized method parameters graphene – metal contacts were fabricated. Two metals were used to investigate graphene - metal contact. One was chosen from the group of physisorbed metals on graphene - gold and another from the group of chemisorbed metals on graphene – nickel. Metal structures were fabricated using photolithography and magnetron sputtering. After metal structure was made graphene was transferred on top of metal structure. Samples were analyzed using electrical measurements and Raman spectroscopy method. Both structures were heated in argon gas at 300°C temperature to decrease resistivity of contacts. Graphene nickel contact resistance before annealing was 114,9 kΩµm and after annealing was reduced to 13,3 kΩµm. The largest reduction of contact resistance (85 % of total reduction) was achieved through first 4 minutes. These results are similar to those of graphene gold contact, largest reduction was also after first 4 minutes (80 % of total reduction). Graphene gold contact resistance was smaller than graphene nickel, before annealing its resistance was 20.63 kΩµm and after annealing decrease to 5.8 kΩµm. |
