12 research outputs found
Structure of quantum disordered wave functions: weak localization, far tails, and mesoscopic transport
We report on the comprehensive numerical study of the fluctuation and
correlation properties of wave functions in three-dimensional mesoscopic
diffusive conductors. Several large sets of nanoscale samples with finite
metallic conductance, modeled by an Anderson model with different strengths of
diagonal box disorder, have been generated in order to investigate both small
and large deviations (as well as the connection between them) of the
distribution function of eigenstate amplitudes from the universal prediction of
random matrix theory. We find that small, weak localization-type, deviations
contain both diffusive contributions (determined by the bulk and boundary
conditions dependent terms) and ballistic ones which are generated by electron
dynamics below the length scale set by the mean free path ell. By relating the
extracted parameters of the functional form of nonperturbative deviations
(``far tails'') to the exactly calculated transport properties of mesoscopic
conductors, we compare our findings based on the full solution of the
Schrodinger equation to different approximative analytical treatments. We find
that statistics in the far tail can be explained by the exp-log-cube
asymptotics (convincingly refuting the log-normal alternative), but with
parameters whose dependence on ell is linear and, therefore, expected to be
dominated by ballistic effects. It is demonstrated that both small deviations
and far tails depend explicitly on the sample size--the remaining puzzle then
is the evolution of the far tail parameters with the size of the conductor
since short-scale physics is supposedly insensitive to the sample boundaries.Comment: 13 pages, 9 embedded EPS figures, expanded discussion (with extra one
figure) on small size effec
Boundary hopping and the mobility edge in the Anderson model in three dimensions
It is shown, using high-precision numerical simulations, that the mobility
edge of the 3d Anderson model depends on the boundary hopping term t in the
infinite size limit. The critical exponent is independent of it. The
renormalized localization length at the critical point is also found to depend
on t but not on the distribution of on-site energies for box and Lorentzian
distributions. Implications of results for the description of the transition in
terms of a local order-parameter are discussed
Mehanizam gašenja fotoluminescencije u tankim filmovima N,N'-bis(3-methylphenyl)-N,N'-bis(phenyl)benzidine osvetljenih UV svetlošću u vazduhu
The mechanism of photoluminescence (PL) quenching of thin amorphous N,N'-bis(3-methylphenyl)- N,N'-bis(phenyl)benzidine (TPD) films exposed to UV light in air is studied. TPD is small organic molecule widely used in production of organic light emmiting devices (OLEDs). Photoluminescence of TPD films decays exponentially with time of irradiation, i.e. with the increase of concentration of impurities (photo-oxidized TPD molecules) generated by UV irradiation in air. Intensity of PL decreases to half of its original value when the concentration of impurities reaches 0.4%. Average distance between impurities (acceptors) is almost an order of magnitude larger than average distance between host TPD molecules (donors). Direct long range Forster energy transfer is ruled out as the mechanism of PL quenching, as the overlap between donor and acceptor is lacking, and exciton self-diffusion in TPD films is postulated for the mechanism. The presence of oxidation products is confirmed by infrared (IR) spectroscopy. Vibrational spectra of TPD molecule and few other possible products of photo-oxidation of TPD molecule, obtained by density functional theory, are compared to experimental IR spectra.U ovom radu je prikazana studija mehanizma gašenja fotoluminescencije (FL) tankih amorfnih filmova N,N'-bis(3-methylphenyl)-N,N'-bis(phenyl)benzidine (TPD) izloženih UV zračenju u vazduhu. TPD je organski molekul koji se često koristi u izradi organskih svetlećih dioda (OLED). Prilikom izlaganja TPD filmova UV zračenju u vazduhu, dolazi do fotooksidacije TPD molekula, te iz tog razloga fotoluminescencija TPD filmova opada eksponencijalno sa vremenom osvetljavanja filmova, odnosno sa povećanjem koncentracije nečistoća nastalih usled fotooksidacije. Intenzitet fotoluminescencije opadne na polovinu svoje početne vrednosti u slučaju kada je 0.4 % nečistoća prisutno u filmu. U tom slučaju je srednje rastojanje između nečistoća (akceptora) šest puta veće od srednjeg rastojanja između TPD molekula (donora). Direktan dugodometni Forsterov transfer energije je odbačen kao mehanizam gašenja fotoluminescencije jer je spektralno preklapanje emisije donora i apsorpcije akceptora zanemarljivo. Iz ovog razloga je postulirana ekscitonska difuzija u TPD filmovima, analogno nalazima u postojećoj literaturi. Prisustvo produkata oksidacije je potvrđeno uz pomoć infracrvene (IR) spektroskopije. Takodje, izračunat je IR spektar koristeći teoriju funkcionala gustine (DFT) i dobijeno je dobro slaganje sa eksperimentalnim rezultatima
Bond-disordered Anderson model on a two dimensional square lattice - chiral symmetry and restoration of one-parameter scaling
Bond-disordered Anderson model in two dimensions on a square lattice is
studied numerically near the band center by calculating density of states
(DoS), multifractal properties of eigenstates and the localization length. DoS
divergence at the band center is studied and compared with Gade's result [Nucl.
Phys. B 398, 499 (1993)] and the powerlaw. Although Gade's form describes
accurately DoS of finite size systems near the band-center, it fails to
describe the calculated part of DoS of the infinite system, and a new
expression is proposed. Study of the level spacing distributions reveals that
the state closest to the band center and the next one have different level
spacing distribution than the pairs of states away from the band center.
Multifractal properties of finite systems furthermore show that scaling of
eigenstates changes discontinuously near the band center. This unusual behavior
suggests the existence of a new divergent length scale, whose existence is
explained as the finite size manifestation of the band center critical point of
the infinite system, and the critical exponent of the correlation length is
calculated by a finite size scaling. Furthermore, study of scaling of Lyapunov
exponents of transfer matrices of long stripes indicates that for a long stripe
of any width there is an energy region around band center within which the
Lyapunov exponents cannot be described by one-parameter scaling. This region,
however, vanishes in the limit of the infinite square lattice when
one-parameter scaling is restored, and the scaling exponent calculated, in
agreement with the result of the finite size scaling analysis.Comment: 23 pages, 11 figures. RevTe
Nanosolvation-induced stabilization of a protonated peptide dimer isolated in the gas phase.
Clef UT : 000321298800048International audienceA dash of water: Nanosolvation of a leucine-enkephalin peptide dimer by only three water molecules has a dramatic impact on its stability to VUV photon irradiation. A drastic reduction of the fragmentation abundance of the hydrated protonated peptide dimer precursor, isolated in the gas phase, was observed. Calculations show that hydration in fact stabilizes the dimer structure
VUV photofragmentation of protonated leucine-enkephalin peptide dimer below ionization energy
The experimental investigation of 5-8 eV photons induced dissociation of the leucine-enkephalin (Leu-Enk) peptide dimer, performed by coupling a linear ion trap with a synchrotron beamline, in combination with the tandem mass spectrometry, has been reported. The present work extends the existing results on Leu-Enk VUV-induced dissociation to lower sub-ionization photon energy range. The measured tandem mass spectra show that even at the photon energies below the ionization threshold, VUV irradiation of the protonated Leu-Enk dimer precursor can lead to a rich fragmentation pattern, including peptide sequence ions and neutral losses. The photodissociation yields of selected ionic fragments reveal the absorption bands at about 6.7-7.1 eV (185-175 nm). The experimental results have been supported by theoretical description of the [2Leu-Enk + H](+) precursors, optimized at B3LYP/6-31+G(d,p) level of DFT
УТИЦАЈ НАНОСОЛВАТАЦИЈЕ НА СТАБИЛНОСТ ПЕПТИДА ИЗОЛОВАНОГ У ГАСНОЈ ФАЗИ
International audienc
VUV photofragmentation of protonated leucine-enkephalin peptide: partial ion yield dependence on type of sequence fragments
International audienc
VUV photodissociation of bare and nanosolvated protonated nucleotide isolated in the gas phase
International audienc