Jon Gorecki
Optoelectronics Research Centre, University of Southampton
Jon Gorecki is a post graduate researcher at the Optoelectronics Research Centre, currently investigating novel doping methods for graphene and other 2D materials with a view to developing adaptive THz plasmonic platforms. Previous research includes; liquid crystal display applications, and laser based additive manufacturing of metallic components.
We demonstrate non-volatile control by light of electrical conductivity of graphene deposited on iron doped Lithium Niobate (LN).
Doped LN under non-uniform illumination exhibits photorefractive behaviour with electrons diffusing from areas of higher light intensity towards darker areas becoming trapped resulting in a non-uniform charge distribution in LN [1]. This distribution can be “erased” by a thermal cycle which redistributes charge carriers.
Here we employ photorefractive effects in LN to control the carrier concentration of graphene. Owing to its atomic thickness, the electronic and optical properties of graphene are controlled by injecting small numbers of charge carriers [2]. Single-layer CVD graphene was deposited on iron doped LN substrates. A graphene on SiO2/Si control sample was used owing to the absence of photorefractive effect. To measure sheet resistance an array of metallic (Cr/Au 5nm/100nm) electrodes were defined via a shadow-mask (see inset to Fig. 1) at spacings ranging from 50 µm-750µm. The electrodes also act as an illumination mask creating light and dark regions which lead to non-uniform charge distribution in the LN, and therefore to changes in the graphene carrier concentration. In Fig. 1, we show the variation in the sheet resistance of graphene on LN after white light illumination. After final illumination the device is heated to ‘erase’ the charge distribution, this cycle is performed three times. Graphene on LN experiences substantial increase of resistivity. Variation in the graphene/SiO2/Si control sample was within experimental error. We note during electrical measurements the samples were not illuminated.
In conclusion, we have shown that the electrical properties of graphene can be controlled through light illumination mediated by the presence of a photorefractive LN substrate. Our results provide a route towards local control of charge carrier concentration in graphene and consequently of its electronic and electromagnetic properties. Implications for reconfigurable plasmonics and metamaterials will be discussed at the conference.
[1] K. Buse and E. Kratzig,“Three-valence charge-transport model for explanation of the photorefractive effect”, Appl. Phys B 61, 27-32 (1995).
[2] K. S. Novoselov, A. K. Geim, S. V. Morozov, et al. "Electric field effect in atomically thin carbon films," Science. 306, 666-669 (2004).
Photonic & plasmonic nanomaterials , Optical properties of nanostructures , Metamaterials
