Graphene is believed to be one of the most promising material candidates for the next generation of photonic and plasmonic devices. Graphene, a perfect two-dimensional (2D) carbon sheet in honeycomb lattice, offers unique electrical and optical properties such as electron-hole symmetry near the charge neutrality point, high mobility, high conductivity and low absorption (?2.3% for a monolayer) over a wide spectral range [1]. Recently it has been demonstrated that graphene supports surface plasmons and, hence, it can be exploited for the realization of graphene-based plasmonic devices from visible to THz regimes [2]. Moreover the combination of graphene and plasmonic nanostructures has attracted a great interest since it is possible to conjugate the graphene tunability and gating with the benefits of the plasmonic nanostructures in terms of field enhancement (hot-spots), sensitivity to environmental changes and the possibility to work beyond the diffraction limit. In this paper we propose two different schemes that exploit graphene in the visible-NIR and THz ranges. In particular, we show and detail the fabrication and the optical response of two-dimensional periodic arrays of rectangular gold nanopatches grown on a monolayer graphene placed on a glass substrate (Figure 1). The 2D periodic patterns have been written using a Raith150 e-beam lithography system operating at 30kV. A bi-layer, composed of PMMA-MA and PMMA, has been adopted as positive resist to allow the fabrication of rectangular metal patches with well-controlled geometrical feature sizes. The rectangular geometry allows exciting two different plasmonic resonances (in the visible and in the NIR range, respectively) addressable with a change of the polarization. The influence of the graphene on such a system has been analyzed by means of reflection spectra and Raman spectroscopy. Then the role and the effect of the primer and the adhesion layer on the graphene monolayer behaviour is highlighted. Finally the patterning of the graphene monolayer with 2D antidot arrays, having different shapes (e.g. circles, squares, rectangles), is reported. The 2D patterns have been fabricated using the Raith150 e-beam lithography system operating at 20 kV with a 400 nm-thick PMMA layer. The patterned PMMA layer has been used as a mask for the oxygen plasma (Figure 2(a) and (d)). Figure 2(b) and (e) prove the graphene removal, after the oxygen plasma, since the charging effect due to the presence of the SiO2 substrate is clearly evident. Raman maps for the graphene 2D peak also confirm that the graphene monolayer has been successfully removed as reported in Figure 2(c) and (f). Therefore these structures can be efficiently exploited for the realization of graphene-based metasurfaces for mid-IR and THz ranges miming the behaviour of similar plasmonic devices already reported and analyzed in the visible and infrared regions.
Graphene plasmonics for visible-NIR and THz applications
G V Bianco;G Bruno;
2013
Abstract
Graphene is believed to be one of the most promising material candidates for the next generation of photonic and plasmonic devices. Graphene, a perfect two-dimensional (2D) carbon sheet in honeycomb lattice, offers unique electrical and optical properties such as electron-hole symmetry near the charge neutrality point, high mobility, high conductivity and low absorption (?2.3% for a monolayer) over a wide spectral range [1]. Recently it has been demonstrated that graphene supports surface plasmons and, hence, it can be exploited for the realization of graphene-based plasmonic devices from visible to THz regimes [2]. Moreover the combination of graphene and plasmonic nanostructures has attracted a great interest since it is possible to conjugate the graphene tunability and gating with the benefits of the plasmonic nanostructures in terms of field enhancement (hot-spots), sensitivity to environmental changes and the possibility to work beyond the diffraction limit. In this paper we propose two different schemes that exploit graphene in the visible-NIR and THz ranges. In particular, we show and detail the fabrication and the optical response of two-dimensional periodic arrays of rectangular gold nanopatches grown on a monolayer graphene placed on a glass substrate (Figure 1). The 2D periodic patterns have been written using a Raith150 e-beam lithography system operating at 30kV. A bi-layer, composed of PMMA-MA and PMMA, has been adopted as positive resist to allow the fabrication of rectangular metal patches with well-controlled geometrical feature sizes. The rectangular geometry allows exciting two different plasmonic resonances (in the visible and in the NIR range, respectively) addressable with a change of the polarization. The influence of the graphene on such a system has been analyzed by means of reflection spectra and Raman spectroscopy. Then the role and the effect of the primer and the adhesion layer on the graphene monolayer behaviour is highlighted. Finally the patterning of the graphene monolayer with 2D antidot arrays, having different shapes (e.g. circles, squares, rectangles), is reported. The 2D patterns have been fabricated using the Raith150 e-beam lithography system operating at 20 kV with a 400 nm-thick PMMA layer. The patterned PMMA layer has been used as a mask for the oxygen plasma (Figure 2(a) and (d)). Figure 2(b) and (e) prove the graphene removal, after the oxygen plasma, since the charging effect due to the presence of the SiO2 substrate is clearly evident. Raman maps for the graphene 2D peak also confirm that the graphene monolayer has been successfully removed as reported in Figure 2(c) and (f). Therefore these structures can be efficiently exploited for the realization of graphene-based metasurfaces for mid-IR and THz ranges miming the behaviour of similar plasmonic devices already reported and analyzed in the visible and infrared regions.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
