Motivated by recent experiments, we present here a detailed theoretical analysis of the joule heating in current-carrying single-molecule junctions. By combining the Landauer approach for quantum ...transport with ab initio calculations, we show how the heating in the electrodes of a molecular junction is determined by its electronic structure. In particular, we show that in general heat is not equally dissipated in both electrodes of the junction and it depends on the bias polarity (or equivalently on the current direction). These heating asymmetries are intimately related to the thermopower of the junction as both these quantities are governed by very similar principles. We illustrate these ideas by analyzing single-molecule junctions based on benzene derivatives with different anchoring groups. The close relation between heat dissipation and thermopower provides general strategies for exploring fundamental phenomena such as the Peltier effect or the impact of quantum interference effects on the joule heating of molecular transport junctions.
Abstract This paper presents the outcomes of a study conducted by SALTO team in the framework of the Student Aerospace Challenge, focusing on designing structures to optimize passenger protection ...against radiation in a suborbital vehicle. The study delves into space radiation characteristics and their potential impact on human health during suborbital flights. Through comprehensive research and the utilization of CARI-7A software, the team evaluated radiation exposure and explored both passive and active shielding solutions. The passive shielding solution involved the design of a multifunctional sandwich panel and a shielding layout for windows, minimizing weight penalties on the vehicle’s structure. Additionally, an active shielding concept utilizing high-temperature superconductor material and solenoid layouts was investigated. The study underscores the benefits and challenges associated with both passive and active shielding methods, emphasizing the importance of further exploration to enhance suborbital flight safety and pave the way for future human space exploration endeavors.
By employing ab initio electronic-structure calculations combined with the nonequilibrium Green's function technique, we study the dependence of the thermopower Q on the conformation in ...biphenyl-based single-molecule junctions. For the series of experimentally available biphenyl molecules, alkyl side chains allow us to gradually adjust the torsion angle varphi between the two phenyl rings from 0degrees to 90degrees and to control in this way the degree of pi-electron conjugation. Studying different anchoring groups and binding positions, our theory predicts that the absolute values of the thermopower decrease slightly towards larger torsion angles, following an a + b cos super(2) varphi dependence. The anchoring group determines the sign of Q and a, b simultaneously. Sulfur and amine groups give rise to Q, a, b > 0, while for cyano, Q, a, b < 0. The different binding positions can lead to substantial variations of the thermopower mostly due to changes in the alignment of the frontier molecular orbital levels and the Fermi energy. We explain our ab initio results in terms of a pi-orbital tight-binding model and a minimal two-level model, which describes the pair of hybridizing frontier orbital states on the two phenyl rings. The variations of the thermopower with varphi seem to be within experimental resolution.
We modelled the adsorption of tetra-pyridyl-porphyrin (TPyP) and Fe(II)-tetra-pyridyl- porphyrin (Fe-TPyP) molecules on Ag(1
1
1). TPyP adsorbs in a flat geometry at a distance of 5.6
Å from the ...surface. The dihedral angle of the pyridyl rings is found to be 70°. The molecular structure remains largely unaffected by the adsorption. The structure of the molecular adlayer should thus be determined mainly by lateral intermolecular interactions. These conclusions are confirmed by scanning tunnelling microscopy observations. Upon metalation spin-polarized states with strong Fe d-character appear in Fe-TPyP near the centre of the gap between the highest occupied and the lowest unoccupied states of a TPyP molecule. We find also that the gap is widened in the presence of Fe. This implies a shift of 0.3
eV of unoccupied states as identified by scanning tunnelling spectroscopy simulations and confirmed by experimental data.
Azurin proteins are the workhorse of protein electronics. This is a branch of biomolecular electronics, a recent research field which investigates electronics based on biomolecules such as proteins, ...peptides, amino acids, bacterial nanowires or DNA. In general, the possibility of including biosystems in solid-state junctions has opened the way to the development of novel electrical devices, and proteins have attracted enormous attention thanks to their many interesting properties. In the particular case of metal-azurin-metal junctions, experimental measurements have revealed extremely efficient electron transport over large distances, showing conductance values which are higher than certain conjugated molecules of similar lengths. Moreover, the electrical current has often been found to be temperature-independent, which has been used as an evidence of coherent transport or quantum tunneling. Interesting effects have been observed, moreover, upon insertion of single amino-acid mutations. In spite of a huge amount of work, the exact mechanism for the charge flow through these systems is still under debate. In this review, we will revise the recent advances made in the electron-transport measurements of azurin-based junctions as well as the corresponding theoretical modelling. We will discuss the interpretation of the currently-available experimental results as well as the open issues which still remain to be clarified.
The cross sections of e+e-→π+π-hc at center-of-mass energies from 3.896 to 4.600 GeV are measured using data samples collected with the BESIII detector operating at the Beijing Electron Positron ...Collider. The cross sections are found to be of the same order of magnitude as those of e+e-→π+π- J/ψ and e+e-→π+π-ψ (2S), but the line shape is inconsistent with the Y states observed in the latter two modes. Two structures are observed in the e+e- → π+π- hc cross sections around 4.22 and 4.39 GeV / c 2 , which we call Y ( 4220 ) and Y ( 4390 ) , respectively. A fit with a coherent sum of two Breit-Wigner functions results in a mass of (4218.4 $+5.5\atop{-4.5 ± 0.9) MeV/c2 and a width of 66.0$+12.3\atop-8.3$±0.4 MeV for the Y (4220), and a mass of (4391.5 $+6.3\atop-16.8$ ± 1.0) MeV/c2 and a width of (139.5$+16.2\atop-20.6 ± 0.6) MeV for the Y (4390), where the first uncertainties are statistical and the second ones systematic. The statistical significance of Y ( 4220 ) and Y(4390) is 10σ over one structure assumption.
PDF
