Influence of disorder on physical properties of monolayer graphene – the first true two-dimensional material .

The phenomenal mechanical, thermal, electrical and optical properties discovered in recent years from the first true two-dimensional material - monolayer graphene have attracted the tremendous enthusiasm because of possible graphene-based device application. In this sense, the influence of disorder is interesting due to possibility of obtaining a high-resistance state, which is important for application in electronics. In the experiment, disorder in graphene is introduced in various ways: by oxidation, hydrogenation, chemical doping, as well as irradiation by different ions with different energies. The advantage of the latter method consists in an accuracy and reproducibility of the process and ability to anneal the radiation damage.

In this talk, I will make an introduction into the subject, followed by presentation of the results of investigation of the properties of monolayer graphene samples gradually disordered by ion bombardment. To probe the evolution of disorder, the Raman spectroscopy (RS) and resistance measurements were used. The main new results of this work consist in (i) observation of the utmost degree of disorder, when graphene, due to high density of defects, is no longer continuous film but split into separate fragments; (ii) observation of the correlation between intensity of RS lines and sample resistance: transition from the low-defect to the high-defect density regime occurs at the resistance equal to reciprocal value of the minimal graphene conductivity. (iii) observation of gradual change in the mechanism of electron transport from metallic conductivity in the initial pristine films to the regime of weak localization-weak antilocalization in the weakly disordered samples and finally to the variable-range hopping conductivity of localized carriers in strongly disordered graphene.