10 research outputs found
Probing thermal expansion of graphene and modal dispersion at low-temperature using graphene NEMS resonators
We use suspended graphene electromechanical resonators to study the variation
of resonant frequency as a function of temperature. Measuring the change in
frequency resulting from a change in tension, from 300 K to 30 K, allows us to
extract information about the thermal expansion of monolayer graphene as a
function of temperature, which is critical for strain engineering applications.
We find that thermal expansion of graphene is negative for all temperatures
between 300K and 30K. We also study the dispersion, the variation of resonant
frequency with DC gate voltage, of the electromechanical modes and find
considerable tunability of resonant frequency, desirable for applications like
mass sensing and RF signal processing at room temperature. With lowering of
temperature, we find that the positively dispersing electromechanical modes
evolve to negatively dispersing ones. We quantitatively explain this crossover
and discuss optimal electromechanical properties that are desirable for
temperature compensated sensors.Comment: For supplementary information and high resolution figures please go
to http://www.tifr.res.in/~deshmukh/publication.htm
Facile fabrication of lateral nanowire wrap-gate devices with improved performance
We present a simple fabrication technique for lateral nanowire wrap-gate
devices with high capacitive coupling and field-effect mobility. Our process
uses e-beam lithography with a single resist-spinning step, and does not
require chemical etching. We measure, in the temperature range 1.5-250 K, a
subthreshold slope of 5-54 mV/decade and mobility of 2800-2500 --
significantly larger than previously reported lateral wrap-gate devices. At
depletion, the barrier height due to the gated region is proportional to
applied wrap-gate voltage.Comment: 3 pages, 3 figure
Magnetotransport properties of individual InAs nanowires
We probe the magnetotransport properties of individual InAs nanowires in a
field effect transistor geometry. In the low magnetic field regime we observe
magnetoresistance that is well described by the weak localization (WL)
description in diffusive conductors. The weak localization correction is
modified to weak anti-localization (WAL) as the gate voltage is increased. We
show that the gate voltage can be used to tune the phase coherence length
() and spin-orbit length () by a factor of 2. In the
high field and low temperature regime we observe the mobility of devices can be
modified significantly as a function of magnetic field. We argue that the role
of skipping orbits and the nature of surface scattering is essential in
understanding high field magnetotransport in nanowires
High Q electromechanics with InAs nanowire quantum dots
In this report, we study electromechanical properties of a suspended InAs
nanowire (NW) resonator. At low temperatures, the NW acts as the island of a
single electron transistor (SET) and we observe a strong coupling between
electrons and mechanical modes at resonance; the rate of electron tunneling is
approximately 10 times the resonant frequency. Above and below the mechanical
resonance, the magnitude of Coulomb peaks is different and we observe Fano
resonance in conductance due to the interference between two contributions to
potential of the SET. The quality factor () of these devices is observed
at 100 mK.Comment: 4 pages. Supplementary material at http://www.tifr.res.in/~nan