1. Designing new renewable nano-structured electrode and membrane materials for direct alkaline ethanol fuel cellDe Chen, Jia Yang, Jørgen Svendby, Qingjun Chen, Gvido Bratina, Egon Pavlica, Ji-Song Huang, Jessie Lue Shingjiang, 2020, končno poročilo o rezultatih raziskav Najdeno v: ključnih besedah Povzetek najdenega: ...fuel cell, ethanol oxidation, graphene, oxygen reduction, catalyst, pt-free, electrochemical impedance spectroscopy... Ključne besede: fuel cell, ethanol oxidation, graphene, oxygen reduction, catalyst, pt-free, electrochemical impedance spectroscopy Objavljeno: 03.12.2020; Ogledov: 2056; Prenosov: 0
Polno besedilo (5,31 MB) |
2. Designing new renewable nano-structured electrode and membrane materials for direct alkaline ethanol fuel cellEgon Pavlica, Ahmed Kreta, Gvido Bratina, končno poročilo o rezultatih raziskav Najdeno v: ključnih besedah Povzetek najdenega: ... graphene, membrane, chitosan, polysaccharide, fuel cell, alkaline, ethanol,... Ključne besede: graphene, membrane, chitosan, polysaccharide, fuel cell, alkaline, ethanol, morphology, elemental analysis Objavljeno: 03.12.2020; Ogledov: 1994; Prenosov: 0
Polno besedilo (19,13 MB) |
3. Designing new renewable nano-structured electrode and membrane materials for direct alkaline ethanol fuel cellEgon Pavlica, Ahmed Kreta, Gvido Bratina, končno poročilo o rezultatih raziskav Najdeno v: ključnih besedah Povzetek najdenega: ... graphene, chitosan, polysaccharide, fuel cell, alkaline, ethanol, photoconductivity,... Ključne besede: graphene, chitosan, polysaccharide, fuel cell, alkaline, ethanol, photoconductivity, ionic conductivity, mixed-conductor model Objavljeno: 03.12.2020; Ogledov: 1855; Prenosov: 0
Polno besedilo (10,55 MB) |
4. THE MORPHOLOGY DEPENDENCE ON GROWTH PARAMETERS IN NANOSTRUCTURED SEMICONDUCTORSMiha Gunde, 2014, diplomsko delo Opis: Poly(3-hexylthiophene) (P3HT) is an organic semiconductor material that is widely studied in the photovoltaics and transistor fields of research. The polymer exhibits a relatively high charge carrier mobility when the molecules are ordered in a crystalline way. In this
case the material exhibits a fibril-like morphology, which is usually studied by atomic force microscopy (AFM). Previous studies show that blending P3HT with graphene can further improve the charge carrier transport properties of the film. In this experiment, the scanning electron microscope (SEM) has been chosen, due to its practical aspects such as speed of operation and ease of use. Three sets of samples have been analyzed, containing films made of P3HT+graphene blends at different concentrations. The aims of the experiment are:
i) to find good conditions for the observation of the morphology features of the film
ii) to perform a morphological analysis of the surface of three sets of samples containing both pure P3HT, and P3HT+graphene blend, and possibly to highlight correlation between morpholgy and the charge transport properties.
Surface analysis is done by detecting the secondary electron (SE) emission, which is sensitive to topographical features of the surface. Good observation conditions were established by coating the specimen with a thin layer of conductive coating, using a high energy beam (30 keV), and tilting the sample to an angle (30 ◦ ). In two out of three of the analyzed pure P3HT films, the presence of fibrilles indicated a possibly good charge mobility, which has
been confirmed by electrical measurements using time-of-flight photoconductivity method (TOF). The presence of graphene has only slightly modified morphology of the film. Features of graphene flakes, which lie flat in the film, have been observed such as flake edges and folds. The flakes are homogeneously dispersed in the film without forming any connected network. TOF measurements have shown an increase in mobility of the charge carriers in the P3HT+graphene film. Najdeno v: ključnih besedah Povzetek najdenega: ...Previous studies show that blending P3HT with graphene can further improve the charge carrier transport... Ključne besede: scanning electron microscope, organic semiconductor thin film, P3HT, graphene, morphology Objavljeno: 01.12.2016; Ogledov: 5646; Prenosov: 163
Polno besedilo (30,93 MB) |
5. HETEROGENEOUS PHOTOCATALYTIC OXIDATION FOR THE REMOVAL OF BISPHENOL A FROM AQUEOUS SOLUTION OVER TiO2/GRAPHENE OXIDE (GO) BASED NANOCOMPOSITESAna Veternik, 2017, magistrsko delo Opis: Since water is an essential substance for all life on earth, it is therefore vital to prevent its pollution and to improve wastewater purification processes. There is a vast number of pollutants which can contaminate water, of which bisphenol A (known as an endocrine disruptor) is the pollutant studied herein. In this study, several TiO2/GO based nanocomposites with various GO loadings (2, 4, 10, 20 and 40%) and differently shaped nanocrystalline TiO2 phases (titanate nanotubes (TNTs) and calcined titanate nanotubes (TNTs_500)) were synthesised. All of the nanocomposites were characterised through SEM, UV-vis-DR, TGA, BET, FT-IR and CHNS analyses and were used in the heterogeneous photocatalytic degradation of bisphenol A and compared to the activity of pure TNTs and TNT_500 photocatalysts. All TiO2/GO nanocomposites exhibit much better activity than pure TNTs and TNTs_500 catalysts. The conversion of the BPA was analysed using HPLC and the mineralisation was analysed using a TOC analysis. The best experiment was performed with TNTs_500 + 10% GO composite, which can be attributed to the TiO2 crystalline structure obtained. According to the results obtained, TiO2 + 10% GO was found to exhibit the best degradation ratio, which can be ascribed to the fact that excessive GO can act as a charge carrier recombination centre and promotes the recombination of electron-hole pairs in reduced GO. Najdeno v: ključnih besedah Ključne besede: heterogeneous photocatalysis, titanium dioxide, graphene oxide, bisphenol A Objavljeno: 23.02.2017; Ogledov: 4991; Prenosov: 284
Polno besedilo (2,96 MB) |
6. Interface-controlled growth of organic semiconductors on grapheneJinta Mathews, Saim Emin, Egon Pavlica, Matjaž Valant, Gvido Bratina, 2017, izvirni znanstveni članek Opis: We have studied submonolayer coverages of N,N-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDIF-CN2) on mechanically exfoliated graphene transferred onto SiO2 substrates. Our atomic force microscopy (AFM) data show that PDIF-CN2 forms irregularly-shaped 1.4 nm-high islands. From the selected area diffraction performed with transmission electron microscope (TEM) we conclude that this height corresponds to π−π
stacks of molecules, which are inclined for 43° relative to the graphene surface. AFM also showed complete absence of PDIF-CN2 on single-layer graphene (SLG). Electric force microscopy revealed a marked difference in surface charge density between a single-layer graphene and bilayer graphene, with a higher surface charge on SLG than on the bilayer graphene. We associate this behavior with p−
type doping of graphene due to the electrostatic dipole induced by the molecular water layer present at the graphene/SiO2 interface. The crucial role of the graphene/SiO2 interface in determining growth of PDIF-CN2 was further confirmed by TEM examination of PDIF-CN2 deposited onto unsupported SLG. Najdeno v: ključnih besedah Ključne besede: afm, organic semiconductors, graphene Objavljeno: 18.05.2017; Ogledov: 4123; Prenosov: 0
Polno besedilo (2,02 MB) |
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8. PHOTO-EXCITATION ENERGY INFLUENCE ON THE PHOTOCONDUCTIVITY OF ORGANIC SEMICONDUCTORSNadiia Pastukhova, 2018, doktorska disertacija Opis: 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. Najdeno v: ključnih besedah Povzetek najdenega: ...polymers
such as polythiophene and benzothiophene derivatives, and graphene, along with
combinations of these materials in heterojunctions... Ključne besede: 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 Objavljeno: 08.10.2018; Ogledov: 4495; Prenosov: 158
Polno besedilo (4,56 MB) |
9. Scanning Photoelectron Spectro‐Microscopy: A Modern Tool for the Study of Materials at the NanoscalePatrick Zeller, Matteo Amati, Hikmet Sezen, Mattia Scardamaglia, Claudia Struzzi, Carla Bittencourt, Gabriel Lantz, Mahdi Hajlaoui, Evangelos Papalazarou, Marino Marsi, Mattia Fanetti, Stefano Ambrosini, Silvia Rubini, Luca Gregoratti, 2018, pregledni znanstveni članek Najdeno v: ključnih besedah Povzetek najdenega: ...Scanning photoemission microscopy, graphene, GaAs, nanowires, Fermi Level, Mott-Hubbard transition... Ključne besede: Scanning photoemission microscopy, graphene, GaAs, nanowires, Fermi Level, Mott-Hubbard transition Objavljeno: 07.12.2018; Ogledov: 2876; Prenosov: 0
Polno besedilo (1,12 MB) |
10. The role of charge transfer at reduced graphene oxide/organic semiconductor interface on the charge transport propertiesGvido Bratina, Egon Pavlica, 2019, izvirni znanstveni članek Opis: The effect of 1-pyrenesulfonicacid sodium salt (1-PSA), tetracyanoethylene (TCNE) and tetrafluoro- tetracyanoquinodimethane (F4-TCNQ) on charge transport properties of reduced graphene oxide (RGO) is examined by measuring the transfer characteristics of field-effect transistors and co-planar time-of-flight photocurrent technique. Evidence of p-type doping and a reduction of mobility of electrons in RGO upon deposition of these materials is observed. Time-resolved photocurrent measurements show a reduction in elec- tron mobility even at submonolayer coverage of these materials. The variation of transit time with different coverages reveals that electron mobility decreases with increasing the surface coverage of 1-PSA, TCNE and F4- TCNQ to a certain extent, while at higher coverage the electron mobility is slightly recovered. All three molecules show the same trend in charge carrier mobility variation with coverage, but with different magnitude. Among all three molecules, 1-PSA acts as weak electron acceptor compared to TCNE and F4-TCNQ. The additional fluorine moieties in F4-TCNQ provides excellent electron withdrawing capability compared to TCNE. The experimental results are consistent with the density functional theory calculations. Najdeno v: ključnih besedah Ključne besede: organic semiconductors, reduced graphene oxide, time-resolved photocurrent measurements, organic thin film transistors Objavljeno: 28.10.2019; Ogledov: 2711; Prenosov: 1
Polno besedilo (2,22 MB) |