37 research outputs found
Quasiparticle spectra and excitons of organic molecules deposited on substrates: G0W0-BSE approach applied to benzene on graphene and metallic substrates
We present an alternative methodology for calculating the quasi-particle
energy, energy loss, and optical spectra of a molecule deposited on graphene or
a metallic substrate. To test the accuracy of the method it is first applied to
the isolated benzene (C6H6) molecule. The quasiparticle energy levels and
especially the energies of the benzene excitons (triplet, singlet, optically
active and inactive) are in very good agreement with available experimental
results. It is shown that the vicinity of the various substrates
(pristine/doped graphene or (jellium) metal surface) reduces the quasiparticle
HOMO-LUMO gap by an amount that slightly depends on the substrate type. This is
consistent with the simple image theory predictions. It is even shown that the
substrate does not change the energy of the excitons in the isolated molecule.
We prove (in terms of simple image theory) that energies of the excitons are
indeed influenced by two mechanisms which cancel each other. We demonstrate
that the benzene singlet optically active (E1u) exciton couples to real
electronic excitations in the substrate. This causes it substantial decay, such
as {\Gamma} = 174 meV for pristine graphene and {\Gamma} = 362 meV for metal
surfaces as the substrate. However, we find that doping graphene does not
influence the E1u exciton decay rate.Comment: 16 pages, 14 figure
Femtosecond laser driven molecular dynamics on surfaces: Photodesorption of molecular oxygen from Ag(110)
We simulate the femtosecond laser induced desorption dynamics of a diatomic
molecule from a metal surface by including the effect of the electron and
phonon excitations created by the laser pulse. Following previous models, the
laser induced surface excitation is treated through the two temperature model,
while the multidimensional dynamics of the molecule is described by a classical
Langevin equation, in which the friction and random forces account for the
action of the heated electrons. In this work, we propose the additional use of
the generalized Langevin oscillator model to also include the effect of the
energy exchange between the molecule and the heated surface lattice in the
desorption dynamics. The model is applied to study the laser induced desorption
of O from the Ag(110) surface, making use of a six-dimensional potential
energy surface calculated within density functional theory. Our results reveal
the importance of the phonon mediated process and show that, depending on the
value of the electronic density in the surroundings of the molecule adsorption
site, its inclusion can significantly enhance or reduce the desorption
probabilities.Comment: 11 pages, 8 figure
Femtosecond-laser induced dynamics of CO on Ru(0001): Deep insights from a hot-electron friction model including surface motion
Theoretical Chemistr
Influence of phenol and sugar interactions on antioxidant activity of pomegranate juice
Nowadays, people are focusing on antioxidant-rich food due to its beneficial effect on health. Thus, the goal of this study was to investigate the interactions between catechin, quercetin, and gallic acid in the presence of sugars (sucrose and trehalose) in complex food matrix such as pomegranate juice. Antioxidant activity (AOA) was measured by three different methods, DPPH and ABTS radical scavenging activity and ferric reducing antioxidant power (FRAP). In this paper, fundamental differences among used AOA measuring methods were confirmed, which can be traced back to interactions occurring between phenols and/or sugars. Even though addition of individual phenols increased AOA of mixtures, in the majority of binary and ternary mixtures antagonistic effects were observed. Positive effect of sugar addition was more pronounced in binary mixtures but the results were highly dependent on used AOA method
Imaging of Optically Active Defects with Nanometer Resolution.
Point defects significantly influence the optical and electrical properties of solid-state materials due to their interactions with charge carriers, which reduce the band-to-band optical transition energy. There has been a demand for developing direct optical imaging methods that would allow in situ characterization of individual defects with nanometer resolution. Here, we demonstrate the localization and quantitative counting of individual optically active defects in monolayer hexagonal boron nitride using single molecule localization microscopy. By exploiting the blinking behavior of defect emitters to temporally isolate multiple emitters within one diffraction limited region, we could resolve two defect emitters with a point-to-point distance down to ten nanometers. The results and conclusion presented in this work add unprecedented dimensions toward future applications of defects in quantum information processing and biological imaging
Scalable Authentication and Optimal Flooding in a Quantum Network
The global interest in quantum networks stems from the security guaranteed by the laws of physics. The deployment of quantum networks means facing the challenges of scaling up the physical hardware and, more importantly, of scaling up all other network layers and optimally utilizing network resources. Here, we consider two related protocols and their experimental demonstrations on an eight-user quantum network test bed, and discuss their usefulness with the aid of example use cases. First, we consider an authentication-transfer protocol to manage a fundamental limitation of quantum communicationāthe need for a preshared key between every pair of users linked together on the quantum network. By temporarily trusting some intermediary nodes for a short period of time (<35 min in our network), we can generate and distribute these initial authentication keys with a very high level of security. Second, when end users quantify their trust in intermediary nodes, our flooding protocol can be used to improve both end-to-end communication speeds and increase security against malicious nodes
Trendovi na tržiŔtu mrkve u Republici Hrvatskoj
Iako je proizvodnja povrÄa jedna je od najdohodovnijih grana poljoprivredne proizvodnje u
Hrvatskoj, povrÄe se uzgaja na svega 1% obradivih povrÅ”ina. Proizvodnja mrkve u sladu je
s negativnim trendovima u proizvodnji povrÄa u Republici Hrvatskoj. Cilj rada bio je na
temelju analiziranih podataka o proizvodnji povrÄa i mrkve prikazati trendove u proizvodnji
i vanjskotrgovinskoj razmjeni mrkve u Republici Hrvatskoj te dati prijedloge za poboljŔanje
stanja. U radu su koriŔteni podaci Food and Agriculture Organization Corporate Statistical
Database (FAOStat) o tržiŔnim pokazateljima u Europskoj uniji i Republici Hrvatskoj.
NajveÄi proizvoÄaÄi mrkve u EU u 2016. godini su Poljska (14,7 %), Velika Britanija (12,09
%), NjemaÄka (11,5 %), Nizozemska (10,7 %), Francuska (10,4 %) i Italija (9,5 %). Zadnjih
desetak godina proizvodnja mrkve u RH stagnira i iznosi u prosjeku 10.588 t, a proizvodi se
u prosjeku na 534 ha. Nepovoljni trend u proizvodnji odražava se i na negativnu
vanjskotrgovinsku razmjenu mrkve, gdje izvoz Äini samo 1,16 % izvoza mrkve. PoveÄanje
proizvodnje mrkve i poboljÅ”anje položaja proizvoÄaÄa moguÄe je postiÄi kroz ulaganje u
razvoj, odnosno apliciranje zahtjeva za fondove Euopske unije namijenjene modernizaciji
proizvodnje, kao i udruživanje malih proizvoÄaÄa u cilju boljeg pozicioniranja na tržiÅ”tu