18 research outputs found
Growth of thin graphene layers on stacked SiC surface in ultra high vacuum
We demonstrate a technique to produce thin graphene layers on C-face of SiC
under ultra high vacuum conditions. A stack of two SiC substrates comprising a
half open cavity at the interface is used to partially confine the depleted Si
atoms from the sample surface during the growth. We observe that this
configuration significantly slows the graphene growth to easily controllable
rates on C-face SiC in UHV environment. Results of low-energy electron
diffractometry and Raman spectroscopy measurements on the samples grown with
stacking configuration are compared to those of the samples grown by using bare
UHV sublimation process
Tuning of 2D rod-type photonic crystal cavity for optical modulation and impact sensing
We propose a novel way of mechanical perturbation of photonic crystal cavities for on-chip applications. We utilize the equivalence of the 2D photonic crystals with perfect electric conductor (PEC) boundary conditions to the infinite height 3D counterparts for rod type photonic crystals. Designed structures are sandwiched with PEC boundaries above and below and the perturbation of the cavity structures is demonstrated by changing the height of PEC boundary. Once a defect filled with air is introduced, the metallic boundary conditions is disturbed and the effective mode permittivity changes leading to a tuned optical properties of the structures. Devices utilizing this perturbation are designed for telecom wavelengths and PEC boundaries are replaced by gold plates during implementation. For 10 nm gold plate displacement, two different cavity structures showed a 21.5 nm and 26 nm shift in the resonant wavelength. Optical modulation with a 1.3 MHz maximum modulation frequency with a maximum power consumption of 36.81 nW and impact sensing with 20 μs response time (much faster compared to the commercially available ones) are shown to be possible
Strong localization in a suspended monolayer graphene by intervalley scattering
A gate induced insulating behavior at zero magnetic field is observed in a
high mobility suspended monolayer graphene near the charge neutrality point.
The graphene device initially cleaned by a current annealing technique was
undergone a thermo-pressure cycle to allow short range impurities to be
adsorbed directly on the ultra clean graphene surface. The adsorption process
generated a strong temperature and electric field dependent behavior on the
conductance of the graphene device. The conductance around the neutrality point
is observed to be reduced from around at 30 K to at 20
mK. A direct transition from insulator to quantum Hall conductor within
accompanied by broken-symmetry-induced plateaux
confirms the presence of intervalley scatterers.Comment: 4 pages, 4 figure
Atmospheric Pressure Mass Spectrometry by Single-Mode Nanoelectromechanical Systems
Weighing particles above MegaDalton mass range has been a persistent
challenge in commercial mass spectrometry. Recently, nanoelectromechanical
systems-based mass spectrometry (NEMS-MS) has shown remarkable performance in
this mass range, especially with the advance of performing mass spectrometry
under entirely atmospheric conditions. This advance reduces the overall
complexity and cost, while improving the limit of detection. However, this
technique required the tracking of two mechanical modes, and the accurate
knowledge of mode shapes which may deviate from their ideal values especially
due to air damping. Here, we used a NEMS architecture with a central platform,
which enables the calculation of mass by single mode measurements. Experiments
were conducted using polystyrene and gold nanoparticles to demonstrate the
successful acquisition of mass spectra using a single mode, with improved areal
capture efficiency. This advance represents a step forward in NEMS-MS, bringing
it closer to becoming a practical application for mass sensing of
nanoparticles.Comment: 24 pages, 4 figure
Full Electrostatic Control of Nanomechanical Buckling
Buckling at the micro and nanoscale generates distant bistable states which
can be beneficial for sensing, shape-reconfiguration and mechanical computation
applications. Although different approaches have been developed to access
buckling at small scales, such as the use heating or pre-stressing beams, very
little attention has been paid so far to dynamically and precisely control all
the critical bifurcation parameters, the compressive stress and the lateral
force on the beam. Precise and on-demand generation of compressive stress on
individually addressable microstructures is especially critical for
morphologically reconfigurable devices. Here, we develop an all-electrostatic
architecture to control the compressive force, as well as the direction and
amount of buckling, without significant heat generation on micro/nano
structures. With this architecture, we demonstrated fundamental aspects of
device function and dynamics. By applying voltages at any of the digital
electronics standards, we have controlled the direction of buckling. Lateral
deflections as large as 12% of the beam length were achieved. By modulating the
compressive stress and lateral electrostatic force acting on the beam, we tuned
the potential energy barrier between the post-bifurcation stable states and
characterized snap-through transitions between these states. The proposed
architecture opens avenues for further studies that can enable efficient
actuators and multiplexed shape-shifting devices
Optimization of piezoresistive motion detection for ambient NEMS applications
Accepted manuscrip
Atmospheric Pressure Mass Spectrometry of Single Viruses and Nanoparticles by Nanoelectromechanical Systems
Mass spectrometry of intact nanoparticles and viruses can serve as a potent
characterization tool for material science and biophysics. Inaccessible by
widespread commercial techniques, the mass of single nanoparticles and viruses
(>10MDa) can be readily measured by NEMS (Nanoelectromechanical Systems) based
Mass Spectrometry, where charged and isolated analyte particles are generated
by Electrospray Ionization (ESI) in air and transported onto the NEMS resonator
for capture and detection. However, the applicability of NEMS as a practical
solution is hindered by their miniscule surface area, which results in poor
limit-of-detection and low capture efficiency values. Another hindrance is the
necessity to house the NEMS inside complex vacuum systems, which is required in
part to focus analytes towards the miniscule detection surface of the NEMS.
Here, we overcome both limitations by integrating an ion lens onto the NEMS
chip. The ion lens is composed of a polymer layer, which charges up by
receiving part of the ions incoming from the ESI tip and consequently starts to
focus the analytes towards an open window aligned with the active area of the
NEMS electrostatically. With this integrated system, we have detected the mass
of gold and polystyrene nanoparticles under ambient conditions and with two
orders-of-magnitude improvement in capture efficiency compared to the
state-of-the-art. We then applied this technology to obtain the mass spectrum
of SARS-CoV-2 and BoHV-1 virions. With the increase in analytical throughput,
the simplicity of the overall setup and the operation capability under ambient
conditions, the technique demonstrates that NEMS Mass Spectrometry can be
deployed for mass detection of engineered nanoparticles and biological samples
efficiently.Comment: 38 pages, 6 figure