Multiphonon emission model of spin-dependent exciton formation in organic semiconductors

The maximum efficiency in organic light-emitting diodes (OLEDs) depends on the ratio, $r=k_S/k_T$, where $k_S$ ($k_T$) is the singlet (triplet) exciton formation rate. Several recent experiments found that r increases with increasing oligomer length from a value $r \approx 1$ in monomers and short oligomers. Here, we model exciton formation as a multi-phonon emission process. Our model is based on two assertions: (i) More phonons are emitted in triplet formation than in singlet formation. (ii) The Huang-Rhys parameter for this phonon emission is smaller in long oligomers than in short ones. We justify these assertions based on recent experimental and theoretical data.Comment: 8 pages, 7 figure

Gas sensing properties of carbon nanotubes modified with calixarene molecules measured by QCM techniques

1st International Congress on Advances in Applied Physics and Materials Science (APMAS), Antalya, Turkey, 12-15 May, 2011This study focuses on the characterization and optimization of calixarene modified carbon nanotube thin films for gas detection. Calixarene molecules were synthesized individually by considering their functional groups to attract the gas. Calixarene modified carbon nanotube based sensors were fabricated using drop-casting method on a quartz crystal microbalance gold electrode. Carbon monoxide, carbondioxide, oxygen and dry air were used as active gases for adsorption process, while high-purity nitrogen gas was used for desorption process. The selectivity and sensitivity of calixarene modified carbon nanotube are investigated in detail. Our experimental results show that functional calixarene modified carbon nanotube coated quartz crystal microbalance sensors are very sensitive and selective to gas of CO 2 at room temperature operation.This research was supported by TÜBİTAK under project numbers TBAG 109 T240 and 110 M349 and IYTE research project number 2010IYTE2

Hyperfine interaction and magnetoresistance in organic semiconductors

We explore the possibility that hyperfine interaction causes the recently discovered organic magnetoresistance (OMAR) effect. Our study employs both experiment and theoretical modelling. An excitonic pair mechanism model based on hyperfine interaction, previously suggested by others to explain magnetic field effects in organics, is examined. Whereas this model can explain a few key aspects of the experimental data, we, however, uncover several fundamental contradictions as well. By varying the injection efficiency for minority carriers in the devices, we show experimentally that OMAR is only weakly dependent on the ratio between excitons formed and carriers injected, likely excluding any excitonic effect as the origin of OMAR.Comment: 10 pages, 7 figures, 1 tabl

Some harvesting system transforming energy wastes of compressed air to electricity

Energy harvesting devices are self-powered systems which are associated with input ambient energy and convert such energy to electrical one. In this study, we focus on input ambient energy deriving from compressed air. Using arbitrary pneumatic machine, the compressed air after work - with its typical parameters as overpressure 6 bar or higher and variable volume flow - is exhausted to atmosphere. This generates energy losses. We have constructed some device which transforms the loss of compressed air energy to electricity. It illustrates the principle of action very well and does not perturb operation of pneumatic machines being source of energy losses

Strategy revision opportunities and collusion

This paper studies whether and how strategy revision opportunities affect levels of collusion in indefinitely repeated two-player games. Consistent with standard theory, we find that such opportunities do not affect strategy choices, or collusion levels, if the game is of strategic substitutes. In games of strategic complements, by contrast, revision opportunities lead to more collusion. We discuss alternative explanations for this result

Gas Sensing Properties of Carbon Nanotubes Modified with Calixarene Molecules Measured by QCM Techniques

1st International Congress on Advances in Applied Physics and Materials Science (APMAS) -- MAY 12-15, 2011 -- Antalya, TURKEYWOS: 000299603000075This study focuses on the characterization and optimization of calixarene modified carbon nanotube thin films for gas detection. Calixarene molecules were synthesized individually by considering their functional groups to attract the gas. Calixarene modified carbon nanotube based sensors were fabricated using drop-casting method on a quartz crystal microbalance gold electrode. Carbon monoxide, carbondioxide, oxygen and dry air were used as active gases for adsorption process, while high-purity nitrogen gas was used for desorption process. The selectivity and sensitivity of calixarene modified carbon nanotube are investigated in detail. Our experimental results show that functional calixarene modified carbon nanotube coated quartz crystal microbalance sensors are very sensitive and selective to gas of CO2 at room temperature operation.Istanbul Kultur Univ, Gebze Inst Technol, Doga Nanobiotech Inc, Terra Lab Inc, LOT Oriel Grp, PHYWE, Delta Elekt In

Effect of Fe doping on the CO gas sensing of functional calixarene molecules measured with quartz crystal microbalance technique

This article presents comprehensive studies of carbon monoxide (CO) responses of bare and iron doped six calix[4]arene derivatives substituted with various functional groups based on quartz crystal microbalance (QCM) technique. The functional groups in calixarene molecules were chosen to increase the affinity towards CO. The sensitive films were prepared by using drop casting method on a QCM gold electrode with resonance frequency of 7.995 MHz. The responses of bare and Fe doped calixarene molecules were investigated in details. Our QCM results showed that although both bare and Fe doped calixarene molecules are very sensitive to CO gas and Fe doped calixarene molecules have higher affinity to CO about 27.88 times greater than bare are. Therefore, these results open an approach to create new materials for the gas sensing applications. © 2015 Elsevier B.V.TBAG 109T240This research was supported by TUBITAK (Turkish Scientific Association) under project number TBAG 109T240 . We are grateful to Dr. Mustafa Can for help with fruitful discussions about the results of organic molecules. Cebrail Özbek was born in 1987, in Izmir, Turkey. He received his bachelor degree in Department of Physics at the Akdeniz University, Turkey, and master degree in Department of Physics from Izmir Institute of Technology, Turkey, in 2008 and 2013, respectively. In 2010, he started working at Izmir Institute of Technology as project assistant. He is presently a Research Assistant at Material Science and Engineering Department, Izmir Katip Celebi University, Turkey. His main field of interest includes gas sensors and devices, electrical and structural characterization of thin films. Salih Okur received his bachelor's degree in physics from Hacettepe University in Ankara, Turkey in 1989, his master's degree in physics from Ankara University in Ankara, Turkey in 1992, and his Ph.D. in physics from IIT in 1998. He worked in Department of Physics at Izmir Institute of Technology in Izmir, Turkey between 1993 and 2011. He is currently a Professor in the Department of Material Science and Engineering in İzmir Katip Çelebi University. His current research interests include organic semiconducting thin film interfaces and their application to electronic devices such as organic photovoltaics, OLEDs, OTFTs and organic gas sensors. Ömer Mermer received his bachelor's degree and his master's degree in electrical and electronics engineering from Ege University (Turkey) in 1998 and 2001, respectively, and his PhD in physics from Iowa University (USA) in 2006. He is currently Associate Professor in Electrical and Electronics Engineering Department at Ege University (Turkey). His current research interests include magnetic effect in organic semi-conductor devices such as OMARs, OLEDs, OTFTs; organic spintronics and sensor applications. Mustafa Kurt received his bachelor's degree in physics from Hacettepe University in Ankara, Turkey in 1993, his master's degree in physics from Sakarya University in Sakarya, Turkey in 1996, and his Ph.D. in physics from Gazi University in 2003. He worked in Department of Physics at Sakarya University in Sakarya, Turkey between 1993 and 2003. He is currently a Professor in the Department of Physics Department in Ahi Evran University. His current research interests include experimental and theoretical (by using DFT) vibrational spectroscopy of organic molecules, such as IR, Raman, etc. Serkan Sayin received his bachelor's degree in Science Education from Ataturk University (Turkey) in 2005, his master's degree in organic chemistry from Afyon Kocatepe University Institute of Science in 2008 and also his Ph.D. in organic chemistry from Selcuk University Institute of Science in 2013. He is currently a Post Doc researcher on organic chemistry in Department of Chemistry. His research interests have been the synthesis and functionalization of isoalloxazine, alloxazine, cyclodextrin and calixarene-based materials, and their applications in enzyme immobilization, Lewis-acidcatalysis, sensors, ion carrying studies, enantioselective studies, and delivery of therapeutic gold nanoparticles etc. In addition, his research interests focus on the preparation of iron-oxide magnetite nanoparticles in order to use as supporting materials for the immobilization of calixarene derivatives, and on the design and development of biosensor using nanomaterials for a broad range of analytes: proteins and cancer cells. Mustafa Yilmaz received his bachelor's degree in chemistry from Ataturk University (Turkey) in 1978, his Ph.D. in organic chemistry from Selcuk University Institute of Science in 1987. He is currently a Professor of organic chemistry in Department of Chemistry. His research interests have been the synthesis of calixarene-based materials and their applications in enzyme immobilization, chiral catalysis, sensors, ion carrying studies. -