634 research outputs found
Growth-induced electron mobility enhancement at the LaAlO/SrTiO interface
We have studied the electronic properties of the 2D electron liquid present
at the LaAlO/SrTiO interface in series of samples prepared at different
growth temperatures. We observe that interfaces fabricated at 650{\deg}C
exhibit the highest low temperature mobility () and the lowest sheet carrier density (). These samples show metallic behavior and
Shubnikov-de Haas oscillations in their magnetoresistance. Samples grown at
higher temperatures (800-900{\deg}C) display carrier densities in the range of
and mobilities of at 4K. Reducing their carrier density by field
effect to lowers their mobilites to
bringing the conductance to the
weak-localization regime
Charge doping and large lattice expansion in oxygen-deficient heteroepitaxial WO3
Tungsten trioxide is a versatile material with widespread applications
ranging from electrochromic and optoelectronic devices to water splitting and
catalysis of chemical reactions. For technological applications, thin films of
WO3 are particularly appealing, taking advantage from high surface-to-volume
ratio and tunable physical properties. However, the growth of stoichiometric,
crystalline thin films is challenging because the deposition conditions are
very sensitive to the formation of oxygen vacancies. In this work, we show how
background oxygen pressure during pulsed laser deposition can be used to tune
the structural and electronic properties of WO3 thin films. By performing X-ray
diffraction and low-temperature transport measurements, we find changes in WO3
lattice volume up to 10%, concomitantly with an insulator-to-metal transition
as a function of increased level of electron doping. We use advanced ab initio
calculations to describe in detail the properties of the oxygen vacancy defect
states, and their evolution in terms of excess charge concentration. Our
results depict an intriguing scenario where structural, electronic, optical,
and transport properties of WO3 single-crystal thin films can all be purposely
tuned by a suited control of oxygen vacancies formation during growth
Nanoscale Electrostatic Control of Oxide Interfaces
We develop a robust and versatile platform to define nanostructures at oxide
interfaces via patterned top gates. Using LaAlO/SrTiO as a model
system, we demonstrate controllable electrostatic confinement of electrons to
nanoscale regions in the conducting interface. The excellent gate response,
ultra-low leakage currents, and long term stability of these gates allow us to
perform a variety of studies in different device geometries from room
temperature down to 50 mK. Using a split-gate device we demonstrate the
formation of a narrow conducting channel whose width can be controllably
reduced via the application of appropriate gate voltages. We also show that a
single narrow gate can be used to induce locally a superconducting to
insulating transition. Furthermore, in the superconducting regime we see
indications of a gate-voltage controlled Josephson effect.Comment: Version after peer review; includes additional data on
superconductivit
Epitaxial growth and thermodynamic stability of SrIrO3/SrTiO3 heterostructures
Obtaining high-quality thin films of 5d transition metal oxides is essential
to explore the exotic semimetallic and topological phases predicted to arise
from the combination of strong electron correlations and spin-orbit coupling.
Here, we show that the transport properties of SrIrO3 thin films, grown by
pulsed laser deposition, can be optimized by considering the effect of
laser-induced modification of the SrIrO3 target surface. We further demonstrate
that bare SrIrO3 thin films are subject to degradation in air and are highly
sensitive to lithographic processing. A crystalline SrTiO3 cap layer deposited
in-situ is effective in preserving the film quality, allowing us to measure
metallic transport behavior in films with thicknesses down to 4 unit cells. In
addition, the SrTiO3 encapsulation enables the fabrication of devices such as
Hall bars without altering the film properties, allowing precise
(magneto)transport measurements on micro- and nanoscale devices.Comment: 5 pages, 3 figure
Superconducting quantum point contact with split gates in the two dimensional LaAlO3/SrTiO3 superfluid
One of the hallmark experiments of quantum transport is the observation of
the quantized resistance in a point contact formed with split gates in
GaAs/AlGaAs heterostructures. Being carried out on a single material, they
represent in an ideal manner equilibrium reservoirs which are connected only
through a few electron mode channel with certain transmission coefficients. It
has been a long standing goal to achieve similar experimental conditions also
in superconductors, only reached in atomic scale mechanically tunable break
junctions of conventional superconducting metals, but here the Fermi wavelength
is so short that it leads to a mixing of quantum transport with atomic orbital
physics. Here we demonstrate for the first time the formation of a
superconducting quantum point contact (SQPC) with split gate technology in a
superconductor, utilizing the unique gate tunability of the two dimensional
superfluid at the LaAlO3/SrTiO3 (LAO/STO) interface. When the constriction is
tuned through the action of metallic split gates we identify three regimes of
transport: (i) SQPC for which the supercurrent is carried only by a few quantum
transport channels. (ii) Superconducting island strongly coupled to the
equilibrium reservoirs. (iii) Charge island with a discrete spectrum weakly
coupled to the reservoirs. Our experiments demonstrate the feasibility of a new
generation of mesoscopic all-superconductor quantum transport devices.Comment: 18 page
Optimización de las osteotomÃas de tibia mediante cálculos matemáticos
El objetivo de este trabajo es aclarar con cálculos matemáticos las dificultades
que existen en cuanto a la relación entre la cuña a resecar con la desviación a corregir y los diferentes
alargamientos según que las osteotomÃas sean cuneiformes o bien arciformes. Asà hemos
llegado a las siguientes conclusiones: 1) Se ha establecido una fórmula matemática que nos permite
obtener una relación exacta entre la cuña a resecar y la desviación a corregir; 2) Se demuestra
el importante rol que juega el ancho de la metáfisis como factor relevante en la cuña a
resecar; 3) Las osteotomÃas cuneiformes producen un acortamiento real del hueso, que se ve
compensado con la corrección del eje del mismo; 4) Las osteotomÃas arciformes no modifican la
longitud real del hueso, pero producen un alargamiento aparente del miembro al corregir el eje.This work was aimed at evaluating, by means of a mathematical approachtint,
the relationship between the resected bone wedge and the deformity to be corrected, and second
the different tibial lengthening induced by close wedge or archiform osteotomy. We drew
the following conclusions: 1) a mathematical equation was defined expresing an exact relationship
between the bone wedge and the angular correction; 2) the metaphysical widening has been
found to be a relevant factor conditioning the angle of the bone wedge; 3) core wedge osteotomies
induce a shortening of the tibia which is compensated by the correction of the axis; 4) Archiform
osteotomies do not modify tibial length but produce an apparent limb lengthening
when correcting the axis of the extremity
A Short-Range FMCW Radar-Based Approach for Multi-Target Human-Vehicle Detection
In this article, a new microwave-radar-based technique for short-range detection and classification of multiple human and vehicle targets crossing a monitored area is proposed. This approach, which can find applications in both security and infrastructure surveillance, relies upon the processing of the scattered-field data acquired by low-cost off-The-shelf components, i.e., a 24 GHz frequency-modulated continuous wave (FMCW) radar module and a Raspberry Pi mini-PC. The developed method is based on an ad hoc processing chain to accomplish the automatic target recognition (ATR) task, which consists of blocks performing clutter and leakage removal with an infinite impulse response (IIR) filter, clustering with a density-based spatial clustering of applications with noise (DBSCAN) approach, tracking using a Benedict-Bordner - filter, features extraction, and finally classification of targets by means of a -nearest neighbor ( -NN) algorithm. The approach is validated in real experimental scenarios, showing its capabilities in correctly detecting multiple targets belonging to different classes (i.e., pedestrians, cars, motorcycles, and trucks)
Towards Smart Sensing Systems: A New Approach to Environmental Monitoring Systems by Using LoRaWAN
The proliferation of monitoring in unpredictable
environments has aided the world in solving challenges that were
previously thought to be insurmountable. Drastic advancement
has been pinpointed in the way we live, work, and play; however,
the data odyssey has yet started. From sensing to monitoring,
the endless possibility enabled by LoRa, the long-range low
power solution has made its mark on the technological world.
With the adoption of the LoRaWAN, the long-range low power
wide area network has appeared in existence to cope with the
constraints associated with the Internet of Things (IoT) infrastructure. This paper presents a practical experiment for sensing
the environmental condition using the LoRaWAN solution. The
proposed work allows the users to check the environmental
effects (temperature, and humidity) online. Furthermore, the
signal behavior has been recorded and cross-verified by using
MATLAB software implementation
Design of Operational Transconductance Amplifiers for voltage to current conversion in gas sensing applications
This paper presents a study of Operational Transconductance Amplifiers (OTAs) for voltage to current conversion circuits. The paper includes a comparative analysis of three OTA architectures implemented in 0.35\u3bcm CMOS AMS Technology under \ub1 1.65V power supply voltage. The impact of the OTA topology has been investigated by simulation. The designed OTAs managed to deliver large current values of 10mA and 1mA to the load with a worst-case error of 0.02% under worst-case power supply and temperature conditions and a worst percentage error of 0.12% under process variation for both Miller Compensated and Capacitor Multiplier Compensated OTA. \ua9 2016 AEIT
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