We determined the electromechanical properties of a suspended graphene layer by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements, as well as computational simulations of the graphene-membrane mechanics and morphology. A graphene membrane was continuously deformed by controlling the competing interactions with a STM probe tip and the electric field from a back-gate electrode. The probe tip-induced deformation created a localized strain field in the graphene lattice. STS measurements on the deformed suspended graphene display an electronic spectrum completely different from that of graphene supported by a substrate. The spectrum indicates the formation of a spatially confined quantum dot, in agreement with recent predictions of confinement by strain-induced pseudomagnetic fields.

Graphene is a unique two-dimensional material with rich new physics and great promise for applications in electronic devices. Physical phenomena such as the half-integer quantum Hall effect and high carrier mobility are critically dependent on interactions with impurities/substrates and localization of Dirac fermions in realistic devices. We microscopically study these interactions using scanning tunneling spectroscopy (STS) of exfoliated graphene on a SiO2 substrate in an applied magnetic field. The magnetic field strongly affects the electronic behavior of the graphene; the states condense into welldefined Landau levels with a dramatic change in the character of localization. In zero magnetic field, we detect weakly localized states created by the substrate induced disorder potential. In strong magnetic field, the two-dimensional electron gas breaks into a network of interacting quantum dots formed at the potential hills and valleys of the disorder potential. Our results demonstrate how graphene properties are perturbed by the disorder potential; a finding that is essential for both the physics and applications of graphene.The exposed and tunable two-dimensional graphene electronic system offers a convenient test bed for an understanding of microscopic transport processes and the physics of localization. * These authors contributed equally to this work † To whom correspondence should be addressed: nikolai.zhitenev@nist.gov, joseph.stroscio@nist.gov 2 Graphene's high transport carrier mobility and broad tunability of electronic properties promise multiple applications [1][2][3] . As in semiconductor devices, these features are ultimately determined by electron interactions and scattering from disorder including the surrounding environment of the device. Direct access to the graphene with scanned probes allows for the measurement of these interactions in greater detail 4-13 than possible in conventional semiconductor devices where the transport layers are buried below the surface. For example, STS with atomic resolution has been used 4,5 to study the local density of states of graphene and the role of disorder at zero magnetic field. Scanning single-electron transistor experiments, sensitive to local electric fields, produced local charge density maps with a spatial resolution of 150 nm 6 and detected singleelectron charging phenomena at high magnetic fields 7 .In this article, we present STS measurements of a gated single-layer exfoliated graphene device in magnetic fields ranging from zero to the quantum Hall regime. With the ability to control the charge density of Dirac fermions with an electrostatic back gate with fine resolution, which was missing in previous STS studies 5,[8][9][10][11][12][13][14] , we can investigate local density of states and localization in graphene at the atomic scale while varying the Fermi energy (E F ) with respect to the Dirac (charge neutrality, E D ) point. At zero magnetic field, we observe density fluctuations arising from the disorder potential variations due to charged imp...