51. Search for Anisotropy in the Ultra High Energy Cosmic Ray Spectrum using the Telescope Array Surface DetectorR.U. Abbasi, Jon Paul Lundquist, 2017, other component parts Abstract: The Telescope Array (TA) experiment is located in the western desert of Utah, USA, and observes ultra high energy cosmic rays (UHECRs) in the Northern hemisphere. At the highest energies, E>10~EeV, the shape of cosmic ray energy spectrum may carry an imprint of the source density distribution along the line of sight different in different directions of the sky. In this study, we search for such directional variations in the shape of the energy spectrum using events observed with the Telescope Array's surface detector. We divide the TA field of view into two nearly equal-exposure regions: the "on-source" region which we define as ±30∘ of the supergalactic plane containing mostly nearby structures, and the complementary "off-source" region where the sources are further away on average. We compare the UHECR spectra in these regions by fitting them to the broken power law and comparing the resulting parameters. We find that the off-source spectrum has an earlier break at highest energies. The chance probability to obtain such or larger difference in statistically equivalent distributions is estimated as 6.2±1.1×10−4 (3.2σ) by a Monte-Carlo simulation. The observed difference in spectra is in a reasonable quantitative agreement with a simplified model that assumes that the UHECR sources trace the galaxy distribution from the 2MRS catalogue, primary particles are protons and the magnetic deflections can be neglected. Keywords: cosmic radiation: UHE, detector: surface, cosmic radiation: spectrum, cosmic radiation: energy spectrum, deflection: magnetic, numerical calculations: Monte Carlo, anisotropy Published in RUNG: 27.04.2020; Views: 2818; Downloads: 98 Full text (169,05 KB) |
52. A novel functionalization strategy for the dispersion of permanently magnetic barium-hexaferrite nanoplatelets in biological mediaTanja Goršak, Darko Makovec, Uroš Javornik, Blaž Belec, Slavko Kralj, Darja Lisjak, 2019, published scientific conference contribution abstract Keywords: colloidal stability, magnetic, nanoplatelet, biological media, dextran Published in RUNG: 30.09.2019; Views: 3935; Downloads: 0 This document has many files! More... |
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54. Magnetic anisotropy of strontium ferrite nanoparticlesCesar de Julian Fernandez, D. Mishra, M. Cabassi, M. Petrecca, M. Albino, M. Suara-Muzquiz, Petra Jenuš, A. Quesada, T. Schliesch, Blaž Belec, C. Sangregorio, F. Albertini, 2019, published scientific conference contribution abstract Keywords: hexaferrite, nanoparticles, magnetic anisotropy, SPD Published in RUNG: 04.06.2019; Views: 3534; Downloads: 0 This document has many files! More... |
55. Incorporation of Sc into the structure of barium-hexaferrite nanoplatelets and its ex-traordinary finite-size effect on the magnetic propertiesDarko Makovec, Matej Komelj, Goran Dražić, Blaž Belec, Tanja Goršak, Sašo Gyergyek, Darja lisjak, 2019, original scientific article Keywords: Nanoparticles, Magnetic properties, Size effect, Structure properties relationship, Ferrite. Published in RUNG: 06.05.2019; Views: 3184; Downloads: 0 This document has many files! More... |
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60. PHOTO-EXCITATION ENERGY INFLUENCE ON THE PHOTOCONDUCTIVITY OF ORGANIC SEMICONDUCTORSNadiia Pastukhova, 2018, doctoral dissertation Abstract: In this work, we experimentally studied the influence of photoexcitation energy
influence on the charge transport in organic semiconductors. Organic semiconductors
were small molecules like corannulene, perylene and pentacene derivatives, polymers
such as polythiophene and benzothiophene derivatives, and graphene, along with
combinations of these materials in heterojunctions or composites.
The first part of this study is focused on the photoexcitation energy influence on
the transient photoconductivity of non-crystalline curved π-conjugated corannulene
layers. The enhanced photoconductivity, in the energy range where optical absorption
is absent, is deduced from theoretical predictions of corannulene gas-phase excited
state spectra. Theoretical analysis reveals a consistent contribution involving
transitions to Super Atomic Molecular Orbitals (SAMOs), a unique set of diffuse
orbitals typical of curved π-conjugated molecules. More, the photoconductivity of the
curved corannulene was compared to the π-conjugated planar N,N′-1H,1H-
perfluorobutyldicyanoperylene-carboxydi-imide
(PDIF-CN2),
where
the
photoexcitation energy dependence of photocurrent closely follows the optical
absorption spectrum.
We next characterized charge transport in poly(3-hexylthiophene) (P3HT) layers
deposited from solution. Our results indicate that time-of-flight (TOF) mobility
depends on the photoexcitation energy. It is 0.4× 10 −3 cm 2 /Vs at 2.3 eV (530 nm) and
doubles at 4.8 eV (260 nm). TOF mobility was compared to field-effect (FET) mobility
of P3HT field-effect transistors (OFETs). The FET mobility was similar to the 2.3 eV
excitation TOF mobility. In order to improve charge mobility, graphene nanoparticles
were blended within a P3HT solution before the deposition. We found that the mobility
significantly improves upon the addition of graphene nanoparticles of a weight ratio
as low as 0.2 %. FET mobility increases with graphene concentration up to a value of
2.3× 10 −2 cm 2 /Vs at 3.2 %. The results demonstrate that phase segregation starts to
influence charge transport at graphene concentration of 0.8 % and above. Hence, the
graphene cannot form a bridged conduction channel between electrodes, which would
cancel the semiconducting effect of the polymer composite.
An alternative approach to enhance mobility is to optimize the molecular ordering
of organic semiconductors. For that purpose, we studied an innovative nanomesh
device. Free-standing nanomesh devices were used to form nanojunctions of N,N′-
iiDioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) nanowires and crystalline
bis(triisopropylsilylethinyl)pentacene (TIPS-PEN). We characterized the photocurrent
response time of this novel nanomesh scaffold device. The photoresponse time
depends on the photon energy. It is between 4.5 − 5.6 ns at 500 nm excitation
wavelength and between 6.7 − 7.7 ns at 700 nm excitation wavelength. In addition, we
found that thermal annealing reduces charge carrier trapping in crystalline nanowires.
This confirms that the structural defects are crucial to obtaining high photon-to-charge
conversion efficiency and subsequent transport from pn junction in heterostructured
materials.
Structural defects also influence the power conversion efficiency of organic
heterostructured photovoltaics (OPVs). Anticipating that polymers with different
backbone lengths produce different level of structural defects, we examined charge
transport
dependence
on
the
molecular
weight
of
poly[4,8-bis(5-(2-
ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-
ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl]
(PTB7-Th)
from 50 kDa to 300 kDa. We found p-type hopping transport in PTB7-Th,
characterized by 0.1 – 3× 10 −2 cm 2 /Vs mobility, which increases with temperature and
electric field. The polymer molecular weight exhibits a non-trivial influence on charge
transport. FET mobility in the saturation regime increases with molecular weight. A
similar trend is observed in TOF mobility and FET mobility in the linear regime,
except for the 100kDa polymer, which manifests in the highest mobility due to reduced
charge trapping. The lowest trapping at the dielectric interface of OFET is observed at
200 kDa. In addition, the 200 kDa polymer exhibits the lowest activation energy of the
charge transport. Although the 100 kDa polymer indicates the highest mobility, OPVs
using the 200 kDa polymer exhibit the best performance in terms of power conversion
efficiency. Keywords: organic
semiconductors, optical
absorption
spectroscopy, time-of-flight
photoconductivity, transient photocurrent spectroscopy, organic thin film transistors, atomic force microscopy, superatomic molecular orbitals, pn heterojunction, organic
nanowires, graphene, composites, charge mobility, charge trapping, temperature
dependence, photodetector, photovoltaic, solar cell, organic electronics Published in RUNG: 08.10.2018; Views: 5462; Downloads: 164 Full text (4,56 MB) |