15 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
Nondestructive imaging of atomically thin nanostructures buried in silicon
It is now possible to create atomically thin regions of dopant atoms in silicon patterned with lateral dimensions ranging from the atomic scale (angstroms) to micrometers. These structures are building blocks of quantum devices for physics research and they are likely also to serve as key components of devices for next-generation classical and quantum information processing. Until now, the characteristics of buried dopant nanostructures could only be inferred from destructive techniques and/or the performance of the final electronic device; this severely limits engineering and manufacture of real-world devices based on atomic-scale lithography. Here, we use scanning microwave microscopy (SMM) to image and electronically characterize three-dimensional phosphorus nanostructures fabricated via scanning tunneling microscope–based lithography. The SMM measurements, which are completely nondestructive and sensitive to as few as 1900 to 4200 densely packed P atoms 4 to 15 nm below a silicon surface, yield electrical and geometric properties in agreement with those obtained from electrical transport and secondary ion mass spectroscopy for unpatterned phosphorus δ layers containing ~1013 P atoms. The imaging resolution was 37 ± 1 nm in lateral and 4 ± 1 nm in vertical directions, both values depending on SMM tip size and depth of dopant layers. In addition, finite element modeling indicates that resolution can be substantially improved using further optimized tips and microwave gradient detection. Our results on three-dimensional dopant structures reveal reduced carrier mobility for shallow dopant layers and suggest that SMM could aid the development of fabrication processes for surface code quantum computers.ISSN:2375-254
2D-3D crossover in a dense electron liquid in silicon
Doping of silicon via phosphene exposures alternating with molecular beam
epitaxy overgrowth is a path to Si:P substrates for conventional
microelectronics and quantum information technologies. The technique also
provides a new and well-controlled material for systematic studies of
two-dimensional lattices with a half-filled band. We show here that for a dense
(\,cm) disordered two-dimensional array of P
atoms, the full field angle-dependent magnetostransport is remarkably well
described by classic weak localization theory with no corrections due to
interaction effects. The two- to three-dimensional cross-over seen upon warming
can also be interpreted using scaling concepts, developed for anistropic
three-dimensional materials, which work remarkably except when the applied
fields are nearly parallel to the conducting planes.Comment: 9 pages, 4 figures, supplementary informatio
Tunable thermal conductivity in defect engineered nanowires at low temperatures
We measure the thermal conductivity (κ) of individual InAs nanowires (NWs), and find that it is three orders of magnitude smaller than the bulk value in the temperature range of 10–50 K. We argue that the low κ arises from the scattering of phonons in the random superlattice of twin defects oriented perpendicular to the axis of the NW. We observe a significant electronic contribution arising from the surface accumulation layer, which gives rise to the tunability of κ with the application of an electrostatic gate and a magnetic field. Our devices and measurements of κ at different carrier concentrations and magnetic field offer a means to study unique aspects of nanoscale thermal transport
Non-destructive imaging of atomically-thin nanostructures buried in silicon
Original data in support of our publication, "Non-destructive imaging of atomically-thin nanostructures buried in silicon"