Characterization of hydrogen plasma defined graphene edges

Abstract

We investigate the quality of hydrogen plasma defined graphene edges by Raman spectroscopy, atomic resolution AFM and low temperature electronic transport measurements. The exposure of graphite samples to a remote hydrogen plasma leads to the formation of hexagonal shaped etch pits, reflecting the anisotropy of the etch. Atomic resolution AFM reveals that the sides of these hexagons are oriented along the zigzag direction of the graphite crystal lattice and the absence of the D-peak in the Raman spectrum indicates that the edges are high quality zigzag edges. In a second step of the experiment, we investigate hexagon edges created in single layer graphene on hexagonal boron nitride and find a substantial D-peak intensity. Polarization dependent Raman measurements reveal that hydrogen plasma defined edges consist of a mixture of zigzag and armchair segments. Furthermore, electronic transport measurements were performed on hydrogen plasma defined graphene nanoribbons which indicate a high quality of the bulk but a relatively low edge quality, in agreement with the Raman data. These findings are supported by tight-binding transport simulations.

Electron wave and quantum optics in graphene

“…A controlled approach to achieve Mach-Zehnder interferences was demonstrated in a recent study [324] where electronic beam splitters were utilized, leveraging the valley degree of freedom in graphene. The concept of valley beam splitters builds upon theoretical work by [325,326] and earlier experimental work of [323,327], where the crystalline structure at the corner of a graphene p-n junction enables electron scattering between p-n interface channels with opposite valley polarizations of quantum Hall edge channels. In the experiment, the researchers employed small electrostatic side gates to tune the mixing point of the edge channels along the edge of the graphene flake, thereby controlling the scattering process.…”

Dirac fermion optics and directed emission from single- and bilayer graphene cavities

“…As a result, the combination of these various special properties, i.e., that charge carriers in graphene partly behave like photons, are deflected by magnetic fields, are reflected or diffracted at p-n junctions and propagate dispersionless, * martina.hentschel@physik.tu-chemnitz.de has opened up the swiftly expanding field of Dirac electron optics based on ultraclean ballistic graphene devices. Correspondingly, optics analogues comprise Klein tunneling in single-layer graphene p-n-p junctions [1][2][3][4][5][6][7], p-n junctions [8][9][10], or Fabry-Pérot type settings [7,11,12] as well as anti-Klein tunneling in bilayer graphene [1,[13][14][15][16][17] where in particular circular p-n junctions were considered [18]. Collimation [8,19], various electron lensing [20][21][22][23], and guiding [24][25][26][27][28][29][30] phenomena were investigated in this context.…”

Dirac fermion optics and directed emission from single- and bilayer graphene cavities

“…that charge carriers in graphene partly behave like photons, are deflected by magnetic fields, are reflected or diffracted at p-n junctions and propagate dispersionless, has opened up the swiftly expanding field of Dirac electron optics based on ultraclean ballistic graphene devices. Correspondingly, optics analogues comprise Klein tunneling in singlelayer graphene p-n-p junctions [1][2][3][4][5][6][7] , p-n junctions [8][9][10] , or Fabry-Pérot type settings 7,11,12 as well as anti-Klein tunneling in bilayer graphene 1,[13][14][15][16][17] where in particular circular p-n junktions were considered 18 . Collimation 8,19 , various electron lensing [20][21][22][23] and guiding [24][25][26][27][28][29][30] phenomena were investigated in this context.…”