  Tuning the frequency of a resonant element is of vital importance in both the
macroscopic world, such as when tuning a musical instrument, as well as at the
nanoscale. In particular, precisely controlling the resonance frequency of
isolated nanoelectromechanical resonators (NEMS) has enabled innovations such
as tunable mechanical filtering and mixing as well as commercial technologies
such as robust timing oscillators. Much like their electronic device
counterparts, the potential of NEMS grows when they are built up into
large-scale arrays. Such arrays have enabled neutral-particle mass spectroscopy
and have been proposed for ultralow-power alternatives to traditional analog
electronics as well as nanomechanical information technologies like memory,
logic, and computing. A fundamental challenge to these applications is to
precisely tune the vibrational frequency and coupling of all resonators in the
array, since traditional tuning methods, like patterned electrostatic gating or
dielectric tuning, become intractable when devices are densely packed. Here, we
demonstrate a persistent, rewritable, scalable, and high-speed frequency tuning
method for graphene-based NEMS. Our method uses a focused laser and two shared
electrical contacts to photodope individual resonators by simultaneously
applying optical and electrostatic fields. After the fields are removed, the
trapped charge created by this process persists and applies a local
electrostatic tension to the resonators, tuning their frequencies. By providing
a facile means to locally address the strain of a NEMS resonator, this approach
lays the groundwork for fully programmable large-scale NEMS lattices and
networks.
