357 research outputs found
Calibration of piezoelectric positioning actuators using a reference voltage-to-displacement transducer based on quartz tuning forks
We use a piezoelectric quartz tuning fork to calibrate the displacement of
ceramic piezoelectric scanners which are widely employed in scanning probe
microscopy. We measure the static piezoelectric response of a quartz tuning
fork and find it to be highly linear, non-hysteretic and with negligible creep.
These performance characteristics, close to those of an ideal transducer, make
quartz transducers superior to ceramic piezoelectric actuators. Furthermore,
quartz actuators in the form of a tuning fork have the advantage of yielding
static displacements comparable to those of local probe microscope scanners. We
use the static displacement of a quartz tuning fork as a reference to calibrate
the three axis displacement of a ceramic piezoelectric scanner. Although this
calibration technique is a non-traceable method, it can be more versatile than
using calibration grids because it enables to characterize the linear and
non-linear response of a piezoelectric scanner in a broad range of
displacements, spanning from a fraction of a nanometer to hundreds of
nanometers. In addition, the creep and the speed dependent piezoelectric
response of ceramic scanners can be studied in detail.Comment: 9 pages, 3 figure
Chemical Bonding and Charge Distribution at Metallic Nanocontacts
We present results of electronic structure calculations for aluminium
contacts of atomic size, based on density functional theory and the local
density approximation. Addressing the atomic orbitals at the neck of the
nanocontact, we find that the local band structure deviates strongly from bulk
fcc aluminium. In particular, hybridization between Al 3s and 3p states is
fully suppressed due to directed bonds at the contact. Moreover, a charge
transfer of 0.6 electrons off the contact aluminium site is found. Both the
suppressed hybridization and the violated charge neutrality are characteristic
features of metallic nanocontacts. This fact has serious consequences for
models aiming at a microscopic description of transport properties.Comment: 6 pages, 3 figures, accepted by Chemical Physics Letter
Conductance oscillation and quantization in monoatomic Al wires
We present first-principles calculations for the transport properties of
monoatomic Al wires sandwiched between Al(100) electrodes. The conductance of
the monoatomic Al wires oscillates with the number of the constituent atoms as
a function of the wire length, either with a period of four-atom for wires with
the typical interatomic spacing or a period of six-atom with the interatomic
spacing of the bulk fcc aluminum, indicating a dependence of the period of
conductance oscillation on the interatomic distance of the monoatomic Al wires
Atomically thin mica flakes and their application as ultrathin insulating substrates for graphene
We show that it is possible to deposit, by mechanical exfoliation on SiO2/Si
wafers, atomically thin mica flakes down to a single monolayer thickness. The
optical contrast of these mica flakes on top of a SiO2/Si substrate, which
depends on their thickness, the illumination wavelength and the SiO2 substrate
thickness, can be quantitatively accounted for by a Fresnel law based model.
The preparation of atomically thin insulating crystalline sheets will enable
the fabrication of ultrathin defect-free insulating substrates, dielectric
barriers or planar electron tunneling junctions. Additionally, we show that
few-layer graphene flakes can be deposited on top of a previously transferred
mica flake. Our transfer method relies on viscoelastic stamps, as those used
for soft lithography. A Raman spectroscopy study shows that such an all-dry
deposition technique yields cleaner and higher quality flakes than conventional
wet-transfer procedures based on lithographic resists.Comment: 11 pages, 5 figures, 1 graphical abstrac
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