Strain can tune desirable electronic behavior in graphene, but there has been limited progress in controlling strain in graphene devices. In this paper, we study the mechanical response of graphene on substrates patterned with arrays of mesoscale pyramids. Using atomic force microscopy, we demonstrate that the morphology of graphene can be controlled from conformal to suspended depending on the arrangement of pyramids and the aspect ratio of the array. Non-uniform strains in graphene suspended across pyramids are revealed by Raman spectroscopy and supported by atomistic modeling, which also indicates strong pseudomagnetic fields in the graphene. Our results suggest that incorporating mesoscale pyramids in graphene devices is a viable route to achieving strain-engineering of graphene.

Graphene's linear dispersion relation and the attendant implications for bipolar electronics applications have motivated a range of experimental efforts aimed at producing p-n junctions in graphene. Here we report electrical transport measurements of graphene p-n junctions formed via simple modifications to a PbZr 0.2 Ti 0.8 O 3 substrate, combined with a self-assembled layer of ambient environmental dopants. We show that the substrate configuration controls the local doping region, and that the p-n junction behavior can be controlled with a single gate. Finally, we show that the ferroelectric substrate induces a hysteresis in the environmental doping which can be utilized to activate and deactivate the doping, yielding an "on-demand" p-n junction in graphene controlled by a single, universal backgate. Published by AIP Publishing.

Engineered substrates offer a promising avenue towards graphene devices having tunable properties. In particular, topographically patterned substrates can expose unique behavior due to their ability to induce local variations in strain and electrostatic doping. However, to explore the range of possible science and applications, it is important to create topographic substrates which both have tunable features and are suitable for transport measurements. In this Letter we describe the fabrication of tunable, topographically patterned substrates suitable for transport measurements. We report both optical and transport measurements of graphene devices fabricated on these substrates, and demonstrate characteristic strain and local doping behavior induced by the topographic features. FIG. 1. Fabrication procedure for creating graphene devices on topographically patterned substrates (see text).Graphene is a material with enormous potential for both scientific research and technical applications [1][2][3][4]. In particular, the ability to tune graphene's properties through the use of engineered substrates offers a practical method to explore graphene's properties and modify them for specific applications [5,6]. Previous work on engineered substrates has employed substrate topography[7-10], electrostatic charge injection [11], substrate lattice mis-match[6], and ferroelectric polarization[12] to achieve a range of modifications to graphene's properties.Of the various substrate engineering techniques, topographic substrate patterning has two distinct advantages: first, topographic substrates can create local strain in * nadya@illinois.edu FIG. 2. SEM micrographs of substrates prepared by this method. (A) Graphene deposited on widely spaced topographic features partially delaminates in the vicinity of the SiO2 cones. The lighter region on the left is an Au electrical lead. The scale bar is 500 nm. (B) After the BOE dip the SiO2 pillars are sharpened into cones with a tip diameter of less than 20 nm. The scale bar is 1 µm. Inset: A single sharpened cone. The scale bar is 100 nm. (C) For tight topographic feature spacings the graphene is suspended on the pointed tips of the substrate features. Here, a slightly ripped region of the graphene is used to show the substrate below. The scale bar is 500 nm. (D) After transfer the graphene is patterned in a Hall bar geometry. The six triangular features are Ti/Au electrical leads. The scale bar is 40 µm.graphene. Strain has large effects on graphene's electrical properties [13], from inducing minigaps [14] to creating large pseudo-magnetic fields [5,15]. To date however the techniques used to produce strain in graphene are either not amenable to performing electrical transport measurements on graphene [7,10,[14][15][16][17] or not compatible with standard lithographic fabrication procedures [9]. Second, topographic substrates can modulate the effect of a single electrostatic gate to produce complex doping profiles in graphene without the need for multiple, distinct gate electrodes. H...

We examine the mechanical properties of graphene devices stretched on flexible elastomer substrates. Using atomic force microscopy, transport measurements, and mechanics simulations, we show that micro-rips form in the graphene during the initial application of tensile strain; however subsequent applications of the same tensile strain elastically open and close the existing rips. Correspondingly, while the initial tensile strain degrades the devices' transport properties, subsequent strain-relaxation cycles affect transport only moderately, and in a largely reversible fashion, yielding robust electrical transport even after partial mechanical failure.