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Fabrication and characterization of ZnO and GaN devices for electronic and photonic applications
Fei Tong, 2014, doktorska disertacija

Opis: The research work presented in this book is based on two direct and wide band gap semiconductors: ZnO and GaN. On the first part of the book, the synthesis of ZnO nanorod array via the low temperature solution growth method was discussed. Due to the high surface-to-volume ratio of ZnO nanorod, to alleviate the some of the drawbacks such as carrier mobility and thickness dilemma of organic solar cells, ZnO nanorod array were integrated into organic solar cells. Power conversion efficiency (η) of 1.8% is achieved in our ZnO nanorods integrated bulk heterojunction organic solar cells on flexible In2O3-PET substrates. On the second part of the book, the fabrication and characterization of Aluminum gallium nitride/gallium nitride high electron mobility transistors (AlGaN/GaN HEMTs) were discussed. Device testing and characterization under both room temperature and high temperature up to 300 °C were performed. The results show that the device can operate even at 300 °C with minimal degradation.
Najdeno v: osebi
Ključne besede: ZnO nanorod array, organic-inorganic solar cells, AlGaN/GaN HEMTs.
Objavljeno: 25.01.2017; Ogledov: 2867; Prenosov: 0
.pdf Polno besedilo (8,57 MB)

Role of transport band edge variation on delocalized charge transport in high-mobility crystalline organic semiconductors
Gvido Bratina, Andrey Kadashchuk, Egon Pavlica, Fei Tong, 2017, izvirni znanstveni članek

Opis: We demonstrate that the degree of charge delocalization has a strong impact on polarization energy and thereby on the position of the transport band edge in organic semiconductors. This gives rise to long-range potential fluctuations, which govern the electronic transport through delocalized states in organic crystalline layers. This concept is employed to formulate an analytic model that explains a negative field dependence coupled with a positive temperature dependence of the charge mobility observed by a lateral time-of-flight technique in a high-mobility crystalline organic layer. This has important implications for the further understanding of the charge transport via delocalized states in organic semiconductors.
Najdeno v: osebi
Ključne besede: organic semiconducotrs, time of flight, transport
Objavljeno: 13.09.2017; Ogledov: 3065; Prenosov: 0
.pdf Polno besedilo (374,71 KB)

Negative field‐dependent charge mobility in crystalline organic semiconductors with delocalized transport
Andrey Kadashchuk, Egon Pavlica, Gvido Bratina, Fei Tong, 2018, izvirni znanstveni članek

Opis: Charge-carrier mobility has been investigated by time-of-flight (TOF) transient photocurrent in a lateral transport con- figuration in highly crystalline thin films of 2,7-dioctyl[1]benzothieno [3,2-b][1] benzothiophene (C8-BTBT) grown by a zone-casting alignment technique. High TOF mobility has been revealed that it is consistent with the delocalized nature of the charge transport in this material, yet it featured a positive temperature dependence at T ≥ 295 K. Moreover, the mobility was surprisingly found to decrease with electric field in the high-temperature region. These observations are not compat- ible with the conventional band-transport mechanism. We have elaborated an analytic model based on effective-medium approximation to rationalize the puzzling findings. The model considers the delocalized charge transport within the energy landscape formed by long-range transport band-edge variations in imperfect organic crystalline materials and accounts for the field-dependent effective dimensionality of charge transport percolative paths. The results of the model calculations are found to be in good agreement with experimental data.
Najdeno v: osebi
Ključne besede: time of flight, organic semiconductors, single crystals
Objavljeno: 07.05.2018; Ogledov: 3210; Prenosov: 0
.pdf Polno besedilo (2,01 MB)

Insight into the interdependence of Ni and Al in bifunctional Ni/ZSM-5 catalysts at the nanoscale
Nataša Novak Tušar, Nataša Zabukovec Logar, Gregor Mali, Janez Volavšek, Simone Pollastri, Goran Dražić, Danilo Oliveira de Souza, Iztok Arčon, Hue-Tong Vu, 2022, izvirni znanstveni članek

Opis: Catalyst design is crucial for improving catalytic activity and product selectivity. In a bifunctional Ni/ZSM-5 zeolite type catalyst, catalytic properties are usually tuned via varying Al and Ni contents. While changes in acid properties associated with Al sites are usually closely investigated, Ni phases, however, receive inadequate attention. Herein, we present a systematic structural study of Ni in the Ni/ZSM-5 materials by using Ni K-edge XANES and EXAFS analyses, complemented by XRD and TEM, to resolve the changes in the local environment of Ni species induced by the different Al contents of the parent ZSM-5 prepared by a “green”, template free technique. Ni species in Ni/ZSM-5 exist as NiO crystals (3–50 nm) and as charge compensating Ni2+ cations. The Ni K-edge XANES and EXAFS results enabled the quantification of Ni-containing species. At a low Al to Si ratio (nAl/nSi # 0.04), the NiO nanoparticles predominate in the samples and account for over 65% of Ni phases. However, NiO is outnumbered by Ni2+ cations attached to the zeolite framework in ZSM-5 with a high Al to Si ratio (nAl/nSi ¼ 0.05) due to a higher number of framework negative charges imparted by Al. The obtained results show that the number of highly reducible and active NiO crystals is strongly correlated with the framework Al sites present in ZSM-5 zeolites, which depend greatly on the synthesis conditions. Therefore, this kind of study is beneficial for any further investigation of the catalytic activities of Ni/ZSM-5 and other metal-modified bifunctional catalysts.
Najdeno v: osebi
Ključne besede: Ni/ZSM-5 catalysts, zeolite, Ni XANES, EXAFS
Objavljeno: 11.05.2022; Ogledov: 106; Prenosov: 2
.pdf Polno besedilo (1,25 MB)
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