We present a theoretical study on the nature and origin of charge carriers, charge transfer, and currents at the interface of an organic field-effect transistor (OFET) structure composed of the ...N,N′-1H,1H′-perfluorobutil dicyanoperylene diimide (PDIF-CN2) organic crystal adsorbed on the (001)-oriented, clean, silicon surface. Starting from the knowledge of the structural and electronic bulk properties of the organic crystal and of the surface of the dielectric substrate, we have evaluated the band structure, density of states, charge transfer, and surface currents in a model crystal made of a reconstructed silicon surface on which a single layer of PDIF-CN2 molecules was deposited in the same packing arrangement as in the bulk PDIF-CN2 organic crystal. In this way alignment of energy bands of the separate PDIF-CN2 and silicon crystals are naturally considered in the model crystal and information on the states involved in charge transport is evidenced. In particular, the analysis of the charge transfer between the dielectric substrate and the adsorbed PDIF-CN2 molecules, of the interface densities of states, and of the currents at the interface allows us to confirm existing experimental results on the distribution and origin of the currents in the FET structure. Namely, that these are essentially determined by the conducting channel made of the π orbitals of the perylene cores of the face-to-face packed PDIF-CN2 molecules on the dielectric substrate. Our results support the description of coherent bandlike transport in OFETs based on the n-type PDIF-CN2 organic crystal.
We study quantum transport through two-terminal nanoscale devices in contact with two particle reservoirs at different temperatures and chemical potentials. We discuss the general expressions ...controlling the electric charge current, heat currents, and the efficiency of energy transmutation in steady conditions in the linear regime. With focus in the parameter domain where the electron system acts as a power generator, we elaborate workable expressions for optimal efficiency and thermoelectric parameters of nanoscale devices. The general concepts are set at work in the paradigmatic cases of Lorentzian resonances and antiresonances, and the encompassing Fano transmission function: the treatments are fully analytic, in terms of the trigamma functions and Bernoulli numbers. From the general curves here reported describing transport through the above model transmission functions, useful guidelines for optimal efficiency and thermopower can be inferred for engineering nanoscale devices in energy regions where they show similar transmission functions.
Aims The implementation of 12-lead ECG in the pre-participation screening of young athletes is still controversial and number of issues are largely debated, including the prevalence and spectrum of ...ECG abnormalities found in individuals undergoing pre-participation screening. Methods and results We assessed a large, unselected population of 32 652 subjects 26 050 (80%) males, prospectively examined in 19 clinics associated to Italian Sports Medicine Federation. Most were young amateur athletes, aged 8–78 years (median 17), predominantly students (68%), engaged predominantly in soccer (39%), volleyball or basketball (8% each), athletics (6%), cycling (5%), swimming (4%). The ECG patterns were evaluated according to commonly used clinical criteria. The 12-lead ECG patterns were considered normal in 28 799 of the 32 652 athletes (88.2%) and abnormal in 3853 (11.8%). The most frequent abnormalities included prolonged PR interval, incomplete right bundle branch block (RBBB) and early repolarization pattern (total 2280, 7.0%). Distinct ECG abnormalities included deeply inverted T-waves in > 2 precordial and/or standard leads (751, 2.3%), increased R/S wave voltages suggestive of LV hypertrophy (247, 0.8%), conduction disorders, i.e. RBBB (351, 1.0%), left anterior fascicular block (162, 0.5%), and left bundle branch block (19, 0.1%). Rarely, cardiac pre-excitation pattern (42, 0.1%) and prolonged QTc interval (1, 0.03%) were found. Conclusion In a large, unselected population of young athletes undergoing pre-participation screening, the prevalence of markedly abnormal ECG patterns, suggestive for structural cardiac disease, is low (<5% of the overall population) and should not represent obstacle for implementation of 12-lead ECG in the pre-participation screening program.
Coupled double quantum dots (c-2QD) connected to leads have been widely adopted as prototype model systems to verify interference effects on quantum transport at the nanoscale. We provide here an ...analytic study of the thermoelectric properties of c-2QD systems pierced by a uniform magnetic field. Fully analytic and easy-to-use expressions are derived for all the kinetic functionals of interest. Within the Green's function formalism, our results allow a simple inexpensive procedure for the theoretical description of the thermoelectric phenomena for different chemical potentials and temperatures of the reservoirs, different threading magnetic fluxes, dot energies and interdot interactions; moreover they provide an intuitive guide to parametrize the system Hamiltonian for the design of best performing realistic devices. We have found that the thermopower S can be enhanced by more than ten times and the figure of merit ZT by more than hundred times by the presence of a threading magnetic field. Most important, we show that the magnetic flux increases also the performance of the device under maximum power output conditions.
By means of DFT calculations, we have individuated a minimum‐energy path connecting two energy minima of clean graphene on clean and relaxed oxygen‐terminated (0001)’SiO2 substrate in the α‐quartz ...configuration: one characterized by mutual graphene–SiO2 substrate distance of ∼2.8 Å and weak (van der Waals) bonds between them, the other by mutual distance of ∼1.4 Å, and presence of strong covalent C–O bonds. Our calculations show that the pathway connecting the two minima goes through a transition state and that the two minima are separated by a barrier of ∼2.25 eV. The covalent C–O bonds, which characterize the lower‐energy configuration, induce significant corrugation of the graphene overlayer with consequent important modification of its electronic band structure and transport properties. In particular, we show that a small gap (EG∼0.16eV) opens in the electronic band structure of the graphene/SiO2 system, and the conical features around the Dirac points are lost. Correspondingly, at the graphene/SiO2 interface, the diffuse π−π conjugation of the isolated graphene layer is modified by the appearance of near’sp3 carbon atoms bound to the top oxygens of the SiO2. This fact also affects conductances and I–V characteristics which become different along different cell directions of the graphene overlayer. Our analysis suggests that the energy barrier between the van der Waals and the covalent minima could be overcome by applying a uniform pressure on the graphene overlayer due to the formation of chemical bonds which are important for the experimental integration of graphene on Si‐compatible technology.
By means of DFT calculations, we have individuated a minimum-energy path connecting two energy minima of clean graphene on clean and relaxed oxygen-terminated (0001)'SiOFormulaomitted substrate in ...the Formulaomitted-quartz configuration: one characterized by mutual graphene-SiOFormulaomitted substrate distance of Formulaomitted2.8Sand weak (van der Waals) bonds between them, the other by mutual distance of Formulaomitted1.4Aa, and presence of strong covalent C-O bonds. Our calculations show that the pathway connecting the two minima goes through a transition state and that the two minima are separated by a barrier of Formulaomitted2.25eV. The covalent C-O bonds, which characterize the lower-energy configuration, induce significant corrugation of the graphene overlayer with consequent important modification of its electronic band structure and transport properties. In particular, we show that a small gap (FormulaomittedeV) opens in the electronic band structure of the graphene/SiOFormulaomitted system, and the conical features around the Dirac points are lost. Correspondingly, at the graphene/SiOFormulaomitted interface, the diffuse Formulaomitted conjugation of the isolated graphene layer is modified by the appearance of near'Formulaomitted carbon atoms bound to the top oxygens of the SiOFormulaomitted. This fact also affects conductances and I-V characteristics which become different along different cell directions of the graphene overlayer. Our analysis suggests that the energy barrier between the van der Waals and the covalent minima could be overcome by applying a uniform pressure on the graphene overlayer due to the formation of chemical bonds which are important for the experimental integration of graphene on Si-compatible technology.
We discuss the consequences of the quantum uncertainty on the spectrum of the electron emitted by the beta-processes of a tritium atom bound to a graphene sheet. We analyze quantitatively the issue ...recently raised by Cheipesh, Cheianov, and Boyarsky Phys. Rev. D 104, 116004 (2021), and discuss the relevant timescales and the degrees of freedom that can contribute to the intrinsic spread in the electron energy. We perform careful calculations of the potential between tritium and graphene with different coverages and geometries. With this at hand, we propose possible avenues to mitigate the effect of the quantum uncertainty.
The outstanding properties of graphene (unique electronic features, exceptional resistance to tension and flexibility, and huge surface-to-mass ratio) stem from a peculiar combination of structure, ...electronic configuration and symmetry, and already manifest at the nano-scale, making it an interesting material for a number of advanced applications 1.In the green economy field for instance, disordered nanoporous graphene based materials of different porosity can be used to store hydrogen 2 or sort CO 2 , and are considered as electrodes for supercaps and batteries 3 and in devices for advanced nano-tronics 4, 5, 6. Very recently, allotropes of graphene such as carbon nanotubes and fullerenes were considered as substrates for advanced applications, namely quantum computing and neutrinos detection 7 exploiting the encapsulation and isolation of single atoms and isotopes.By means of multi-scale molecular dynamics simulation combining ab initio techniques with reactive empirical force flelds 8, we explored the properties of the different allotropic forms of graphene 9, in order to derive quantitative relationship between structure and property of interest (e.g. adsorption capability, fluid diffusivity, electronic conductivity), and aid the material optimization for the given application 10, 11.
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