460 research outputs found
Black phosphorus: narrow gap, wide applications
The recent isolation of atomically thin black phosphorus by mechanical
exfoliation of bulk layered crystals has triggered an unprecedented interest,
even higher than that raised by the first works on graphene and other
two-dimensional, in the nanoscience and nanotechnology community. In this
Perspective we critically analyze the reasons behind the surge of experimental
and theoretical works on this novel two-dimensional material. We believe that
the fact that black phosphorus band gap value spans over a wide range of the
electromagnetic spectrum that was not covered by any other two-dimensional
material isolated to date (with remarkable industrial interest such as thermal
imaging, thermoelectrics, fiber optics communication, photovoltaics, etc), its
high carrier mobility, its ambipolar field-effect and its rather unusual
in-plane anisotropy drew the attention of the scientific community towards this
two-dimensional material. Here we also review the current advances, the future
directions and the challenges in this young research field.Comment: Updated version of the perspective article about black phosphorus,
including all the feedback received from arXiv users + reviewer
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
Superlattices based on van der Waals 2D materials
Two-dimensional (2D) materials exhibit a number of improved mechanical,
optical, electronic properties compared to their bulk counterparts. The absence
of dangling bonds in the cleaved surfaces of these materials allows combining
different 2D materials into van der Waals heterostructures to fabricate p-n
junctions, photodetectors, 2D-2D ohmic contacts that show unexpected
performances. These intriguing results are regularly summarized in
comprehensive reviews. A strategy to tailor their properties even further and
to observe novel quantum phenomena consists in the fabrication of superlattices
whose unit cell is formed either by two dissimilar 2D materials or by a 2D
material subjected to a periodical perturbation, each component contributing
with different characteristics. Furthermore, in a 2D materials-based
superlattice, the interlayer interaction between the layers mediated by van der
Waals forces constitutes a key parameter to tune the global properties of the
superlattice. The above-mentioned factors reflect the potential to devise
countless combinations of van der Waals 2D materials based superlattices. In
the present feature article, we explain in detail the state-of-the-art of 2D
materials-based superlattices and we describe the different methods to
fabricate them, classified as vertical stacking, intercalation with atoms or
molecules, moir\'e patterning, strain engineering and lithographic design. We
also aim to highlight some of the specific applications for each type of
superlattices.Comment: Perspective article. 6 Figures. 133 reference
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