3,708 research outputs found
A versatile scanning photocurrent mapping system to characterize optoelectronic devices based on 2D materials
The investigation of optoelectronic devices based on two-dimensional
materials and their heterostructures is a very active area of investigation
with both fundamental and applied aspects involved. We present a description of
a home-built scanning photocurrent microscope that we have designed and
developed to perform electronic transport and optical measurements of
two-dimensional materials based devices. The complete system is rather
inexpensive (<10000 EUR) and it can be easily replicated in any laboratory. To
illustrate the setup we measure current-voltage characteristics, in dark and
under global illumination, of an ultra-thin PN junction formed by the stacking
of an n-doped few-layer MoS2 flake onto a p-type MoS2 flake. We then acquire
scanning photocurrent maps and by mapping the short circuit current generated
in the device under local illumination we find that at zero bias the
photocurrent is generated mostly in the region of overlap between the n-type
and p-type flakes.Comment: 9 pages, 3 figures, 1 table, supporting informatio
Vortex ratchet reversal: The role of interstitial vortices
Triangular arrays of Ni nanotriangles embedded in superconducting Nb films
exhibit unexpected dynamical vortex effects. Collective pinning with a vortex
lattice configuration different from the expected fundamental triangular
"Abrikosov state" is found. The vortex motion which prevails against the
triangular periodic potential is produced by channelling effects between
triangles. Interstitial vortices coexisting with pinned vortices in this
asymmetric potential, lead to ratchet reversal, i.e. a DC output voltage which
changes sign with the amplitude of an applied alternating drive current. In
this landscape, ratchet reversal is always observed at all magnetic fields (all
numbers of vortices) and at different temperatures. The ratchet reversal is
unambiguously connected to the presence of two locations for the vortices:
interstitial and above the artificial pinning sites.Comment: 21 pages, 4 figures, 1 Tabl
A Comparison of Two-Level and Multi-level Modelling for Cloud-Based Applications
The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-319-21151-0_2The Cloud Modelling Framework (CloudMF) is an approach to apply model-driven engineering principles to the specification and execution of cloud-based applications. It comprises a domain-specific language to model the deployment topology of multi-cloud applications, along with a models@run-time environment to facilitate reasoning and adaptation of these applications at run-time. This paper reports on some challenges encountered during the design of CloudMF, related to the adoption of the two-level modelling approach and especially the type-instance pattern. Moreover, it proposes the adoption of an alternative, multi-level modelling approach to tackle these challenges, and provides a set of criteria to compare both approaches.The research leading to these results has received funding from the European Commission’s Seventh Framework Programme (FP7/2007-2013) under grant agreement numbers 317715 (PaaSage), 318392 (Broker@Cloud), and 611125 (MONDO), the Spanish Ministry under project Go Lite (TIN2011-24139), and the Madrid Region under project SICOMORO (S2013/ICE-3006)
Enhanced Visibility of MoS2, MoSe2, WSe2 and Black Phosphorus: Making Optical Identification of 2D Semiconductors Easier
We explore the use of Si3N4/Si substrates as a substitute of the standard
SiO2/Si substrates employed nowadays to fabricate nanodevices based on 2D
materials. We systematically study the visibility of several 2D semiconducting
materials that are attracting a great deal of interest in nanoelectronics and
optoelectronics: MoS2, MoSe2, WSe2 and black phosphorus. We find that the use
of Si3N4/Si substrates provides an increase of the optical contrast up to a
50%-100% and also the maximum contrast shifts towards wavelength values optimal
for human eye detection, making optical identification of 2D semiconductors
easier.Comment: 4 figures + 3 supp.info. figure
Ferromagnetic proximity effect in a-Co_xSi_(1-x)/Nb bilayers: Role of magnetic disorder and interface transparency
The superconducting and magnetic properties of a-Co_(x)Si_(1−x) /Nb bilayers have been studied as a function of Co content in order to analyze the superconducting/ferromagnetic proximity effect in a system with strong disorder in the magnetic layers. As Co atoms become more diluted, the magnetization of the amorphous a-CoxSi1−x alloy decreases gradually, whereas their resistivity increases and enters in a weak localization regime. The superconducting transition temperatures of the a-Co_(x)Si_(1−x) /Nb bilayers follow a decreasing trend as Co content is reduced, reaching the lowest value at the boundary between the ferromagnetic-nonmagnetic amorphous phases. These results can be understood in terms of the increase in interface transparency together with the changes in the spin-flip scatterin
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