90 research outputs found
Molecular Spins in the Context of Quantum Technologies
Molecular spins have shown interesting quantum features which make them potential candidates for the implementation of quantum information processing. New challenges related to possible applications in broader class of quantum technologies are currently under discussion. Here, we revisit some key features trying to learn something from experiences in near fields
Observation of different charge transport regimes and large magnetoresistance in graphene oxide layers
We report a systematic study on charge transport properties of thermally reduced graphene
oxide (rGO) layers, from room temperature to 2 K and in presence of magnetic fields up to
7 T. The most conductive rGO sheets follow different transport regimes: at room temperature
they show an Arrhenius-like behavior. At lower temperature they exhibits a thermally
activated behavior with resistance R following a R = R0exp(T0/T)p law with p = 1/3, consistently
with 2D Mott Variable Range Hopping (VRH) transport mechanism. Below a given
temperature Tc, we observe a crossover from VHR to another regime, probably due to a
shortening of the characteristic lengths of the disordered 2D system. The temperature Tc
depends on the reduction grade of the rGO. Magnetoresistance DR/R of our rGO films shows
as well a crossover between positive and negative and below liquid He temperature DR/R
reaches values larger than 60%, surprisingly high for a \u2013 nominally \u2013 non magnetic
material
Modulating the Faradic Operation of All-Printed Organic Electrochemical Transistors by Facile in Situ Modification of the Gate Electrode
Organic electrochemical transistors (OECTs) operated in the faradic regime were shown as outperforming transducers of bioelectric signals in vitro and in vivo. Fabrication by additive manufacturing techniques fosters OECTs as ideal candidates for point-of-care applications, as well as imposes limitations on the choice of materials and their processing conditions. Here, we address the question of how the response of fully printed OECTs depends on gate electrode material. Toward this end, we investigate the redox processes underlying the operation of OECTs under faradic regime, to show OECTs with carbon gate (C-gate) that exhibit no current modulation gate voltages <1.2 V. This is a hallmark that no interference with the faradic operation of the device enabled by redox processes occurs when operating C-gate OECTs in the low-voltage range as label-free biosensors for the detection of electroactive (bio)molecules. To tune the faradic response of the device, we electrodeposited Au on the carbon gate (Au-C-gate), obtaining a device that operates at lower gate voltage values than C-gate OECT. The presence of gold on the gate allowed further modification of the electrical performances by functionalization of the Au-C-gate with different self-assembled monolayers by fast potential-pulse-assisted method. Moreover, we show that the presence in the electrolyte solution of an external redox probe can be used to drive the faradic response of both C- and Au-C-gate OECTs, impacting on the gate potential window that yields effective drain current modulation. The results presented here suggest possible new strategies for controlling the faradic operation regime of OECTs sensors by chemical modification of the gate surface
Structure-dependent electrical properties of graphene nanoribbon devices with graphene electrodes
Graphene nanoribbons (GNRs) are a novel and intriguing class of materials in
the field of nanoelectronics, since their properties, solely defined by their
width and edge type, are controllable with high precision directly from
synthesis. Here we study the correlation between the GNR structure and the
corresponding device electrical properties. We investigated a series of field
effect devices consisting of a film of armchair GNRs with different structures
(namely width and/or length) as the transistor channel, contacted with narrowly
spaced graphene sheets as the source-drain electrodes. By analyzing several
tens of junctions for each individual GNR type, we observe that the values of
the output current display a width-dependent behavior, indicating electronic
bandgaps in good agreement with the predicted theoretical values. These results
provide insights into the link between the ribbon structure and the device
properties, which are fundamental for the development of GNR-based electronics.Comment: Published in Carbon (2019
Single-molecule devices with graphene electrodes
Several technological issues have to be faced to realize devices working at the single molecule level. One of the main challenges consists of defining methods to fabricate electrodes to make contact with single molecules. Here, we report the realization of novel spintronic devices made of a TbPc2 single molecule embedded between two nanometer-separated graphene electrodes, obtained by feedback-controlled electroburning. We demonstrate that this approach allows the realisation of devices working at low temperature. With these, we were able to characterize the magnetic exchange coupling between the electronic spin of the Tb3+ magnetic core and the current passing through the molecular system in the Coulomb blockade regime, thus showing that the use of graphene is a promising way forward in addressing single molecules
Psychological Reactions during and after a Lockdown: Self-Efficacy as a Protective Factor of Mental Health
The aim of the present study was to investigate the effects of home confinement/social isolation (i.e., lockdown), imposed to reduce large-scale spread of a disease in the population, on the mental health of individuals. Through an online survey during the lockdown (DL) related to COVID-19 (1085 respondents, 627 females, agerange: 18-82) (Italy, 23 April-2 May 2020), we revealed that situational factors, i.e., the presence of children at home and female gender, and psychological factors, i.e., a greater sense of isolation, lower perception of safety outside the home and higher trait anxiety, predicted higher levels of state anxiety (R2 = 0.58). The same factors, but with young age instead of the presence of children, predicted higher levels of perceived stress (R2 = 0.63). Then, these data were compared with those collected after the lockdown (AL) (174 respondents, 128 females, agerange: 19-78) (Italy, 1 July-31 October 2021). The results showed that along with a reduced sense of isolation (DL = 2.90 vs. AL = 2.10) and an increased perception of safety outside the home (DL = 2.63 vs. AL = 3.05), a reduction in state anxiety (DL = 45.76 vs. AL= 40.88) and stress appeared (DL = 18.84 vs. AL = 17.63). However, the situation was better for men than for women. Perceived self-efficacy emerged as a protective factor for mental health (R2range: 0.03-0.27). The results are discussed in light of the evidence on the effects of lockdown on individuals worldwide. These results may be used to make more educated decisions on targeted help for individuals who may be most adversely affected by the adoption of lockdowns in the future
Field-regulated switching of the magnetization of Co-porphyrin on graphene
Differentmagnetic couplingmechanisms have been identified for a fewmonolayers of Co-porphyrin molecules
deposited on a graphene-covered Ni(111) single crystal. A relatively strong antiferromagnetic coupling of the
first molecular layer via graphene to the Ni crystal in comparison to a weaker intermolecular coupling gives
rise to a complex field-dependent response of this hybrid system. By continuously increasing the magnetic field
strength, the net magnetization of the molecular system switches from antiparallel to parallel to the field direction
at 2.5 T. Utilizing x-ray absorption spectroscopy and x-ray magnetic circular dichroism, the element-specific
magnetization and field dependence was probed. The nature of the magnetic couplings is identified by means of
density functional theory and orbital-dependent susceptibilities
Magnetic interplay between two different lanthanides in a tris-phthalocyaninato complex: a viable synthetic route and detailed investigation in the bulk and on the surface
Future applications of molecular units in quantum information technologies require a fine control at the
single molecule level. This includes the choice of each functional element, the intramolecular interaction
and the robustness of molecules when dispersed on a substrate. Keeping these goals in mind, we
designed and synthesized a heterometallic phthalocyaninato-complex including two different lanthanides
in each moiety, namely [PcDyPcTbPc*] (Pc being phthalocyanines; and Pc* being 2,3,9,10,16,17,23,24-
octahexyl-substituted phthalocyanines). Full magnetic characterization was performed down to the mK
temperature range on bulk microcrystals by means of AC susceptibility, DC magnetization (including
microSQUID) and specific heat measurements. A weak, yet sizeable, interaction between the two
lanthanides is clearly detected by different techniques, altering the magnetic behavior of the single
lanthanide as observed in the parent [LnPc2] complexes. Isolated [PcDyPcTbPc*] molecules dispersed on
HOPG and the Au surface by liquid phase deposition are proven to maintain their main chemical and
magnetic features by combined XPS, XAS and XMCD analysis and to lie with one Pc ligand flat to the
surface. Opening of a small but sizable hysteresis loop at 1.8 K is directly observed on both Tb and Dy
sites proving the retention of magnetization at the single molecule level
Antiferromagnetic coupling of TbPc2 molecules to ultrathin Ni and Co films
The magnetic and electronic properties of single-molecule magnets are studied by X-ray absorption spectroscopy and X-ray
magnetic circular dichroism. We study the magnetic coupling of ultrathin Co and Ni films that are epitaxially grown onto a Cu(100)
substrate, to an in situ deposited submonolayer of TbPc2
molecules. Because of the element specificity of the X-ray absorption
spectroscopy we are able to individually determine the field dependence of the magnetization of the Tb ions and the Ni or Co film.
On both substrates the TbPc2 moleculescouple antiferromagnetically to the ferromagnetic films, which is possibly due to a superexchange interaction via the phthalocyanine ligand that contacts the magnetic surface
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