Lithography-free fabrication of graphene devices

Abstract

We have developed a lithography-free, all-dry process for fabricating graphene devices using an ultrathin quartz filament as a shadow mask to avoid possible contamination of graphene during lithographic process. This technique was used to prepare devices for electrical transport as well as planar tunnel junction studies of n-layer graphene (nLG), with n = 1, 2, 3 and higher. We observed localization behavior and an apparent reduction of density of states (DOS) near the Fermi energy in nLG.There has been a flurry of recent work 1,2 on films of 1-layer graphene (1LG), motivated by the pioneering work of Geim and coworkers 3 and Kim and coworkers 4 . Surprisingly, 1LG was found to host a two-dimensional electron gas with a band structure featuring zero effective mass 5 . Two types of unconventional integer quantum Hall effects (IQHE) were observed in 1LG 1,2 and in 2-layer graphene (2LG) 6 devices, respectively. Theoretical calculation indicates that n-layer graphene (nLG) with n > 2 are also interesting 5 .The highest mobility reported for 1LG devices is around 10,000 cm 2 /Vs at high gate voltages 2 , which is remarkable. However, it may not be sufficiently high to allow the observation of certain physical phenomena, such as fractional quantum Hall effect (FQHE). So far, all graphene devices reported in the literature were prepared by e-beam lithography. Multiple steps are required to pattern a device, including coating with organic materials, which may subject the graphene to possible contamination and add unwanted disorder to the device. It is therefore desirable to pursue alternative graphene device fabrication. Using ultrathin quartz filaments as shadow masks, we have developed a method to fabricate graphene devices, aiming at raising the mobility of the devices. Our method is lithography-free, all dry, and simple to implement. Devices fabricated were measured using a DC technique with a typical excitation current of 1 µA in a dip probe in which the sample was cooled by direct contact with 4 He liquid or gas.Two methods have been used to create graphene samples -exfoliation either mechanically in air 7 or chemically in solutions 8 , and thermal decomposition of SiC 9 . Our nLG flakes were created by mechanical exfoliation in air from freshly cleaved highly oriented pyrolytic graphite (HOPG) 10 . Heavily N-doped silicon with a 300-nm-thick thermally grown SiO 2 top layer was used as substrates. Thin graphene flakes were

Room temperature dry processing of patterned CVD graphene devices

“…Previous studies were mostly aimed at optimizing the morphology of deposited metal structures by controlling the clogging of apertures and deformation in stencil membranes [28,29]. A few attempts of graphene device interconnects involving metal electrodes evaporation through stencil lithography have been reported on pre-patterned exfoliated graphene strips [30] or flakes of suitable size and shape [31]. To our knowledge, multi-step stencil mask usage that includes the graphene etching process steps to pattern complex devices, are not documented to date.…”

Quantum scattering time and its implications on scattering sources in graphene

“…The role of adsorbates is especially highlighted in the current annealing treatment of suspended graphene. 10,11 In the literature, various approaches, including resist-free processing, 16,29,30 UHV baking, 13,16 and current annealing, 31 have been used to remove contaminants on top of graphene without significant improvement to mobility. These observations collectively suggest that adsorbates on top of graphene cannot be the major culprit in limiting mobility at the current level.…”

Graphenes, One of the Hottest Areas in the Nanotechnology: Attention of Chemists is Needed

“…Nanodevices [119,120] are the most perspective present and future application area for graphenes. Thus, graphenes can be potentially used in digital memory devices [121] or as building blocks for novel optoelectronic devices [122].…”