24 research outputs found

    Selected problems of materials science. Vol. 2. Nano-dielectrics metals in electronics. Mеtamaterials. Multiferroics. Nano-magnetics

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    The textbook examines physical foundations and practical application of current electronics materials. Modern theories are presented, more important experimental data and specifications of basic materials necessary for practical application are given. Contemporary research in the field of microelectronics and nanophysics is taken into account, while special attention is paid to the influence of the internal structure on the physical properties of materials and the prospects for their use. English-language lectures and other classes on the subject of the book are held at Igor Sikorsky Kyiv Polytechnic Institute at the departments of “Applied Physics” and “Microelectronics” on the subject of materials science, which is necessary for students of higher educational institutions when performing scientific works. For master’s degree applicants in specialty 105 “Applied physics and nanomaterials”.Розглянуто фізичні основи та практичне застосування актуальних матеріалів електроніки. Подано сучасні теорії, наведено найважливіші експериментальні дані та специфікації основних матеріалів, які потрібні для практичного застосування. Враховано сучасні дослідження у галузі мікроелектроніки та нанофізики, при цьому особливу увагу приділено впливу внутрішньої структури на фізичні властивості матеріалів і на перспективи їх використання. Англомовні лекції та інші види занять за тематикою книги проводяться в КПІ ім. Ігоря Сікорського на кафедрах «Прикладна фізика» та «Мікро-електроніка» за напрямом матеріалознавство, що необхідно студентам вищих навчальних закладів при виконанні наукових робіт. Для здобувачів магістратури за спеціальністю 105 «Прикладна фізика та наноматеріали»

    Interaction of Ionizing Photons with Atomic and Molecular Ions

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    The interaction of ionising radiation with atomic and/or molecular ions is a fundamental process in nature, with implications for the understanding of many laboratory and astrophysical plasmas. At short wavelengths, the photon–ion interactions lead to inner-shell and multiple electron excitations, leading to demands on appropriate laboratory developments of sources and detectors and requiring advanced theoretical treatments which take into account many-body electron-correlation effects. This book includes a range of papers based on different short wavelength photon sources including recent facility and instrumental developments. Topics include experimental photoabsorption studies with laser-produced plasmas and photoionization of atomic and molecular ions with synchrotron and FEL sources, including modifications of a cylindrical mirror analyzer for high efficiency photoelectron spectroscopy on ion beams. Theoretical investigations include the effects of FEL fluctuations on autoionization line shapes, multiple sequential ionization by intense fs XUV pulses, photoelectron angular distributions for non-resonant two-photon ionization, inner-shell photodetachment of Na- and spin-polarized fluxes from fullerene anions

    Abstracts of the XL QUITEL Congress

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    Abstracts of the XL QUITEL Congres

    Annual report / IFW, Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden

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    Annual report / IFW, Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden

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    Proceedings of the Scientific-Practical Conference "Research and Development - 2016"

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    talent management; sensor arrays; automatic speech recognition; dry separation technology; oil production; oil waste; laser technolog

    第一原理実空間伝導計算手法の開発とその応用

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    筑波大学 (University of Tsukuba)201

    Use of chlorinated carbon materials to make nitrogen doped and un-doped carbon nanomaterials and their use in water treatment

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    A thesis submitted to the Faculty of Science at the University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy in ChemistryCarbon nanomaterials (CNMs) and nitrogen doped CNMs (NCNMs) with different morphologies were obtained by decomposition of various chlorinated organic solvents using a chemical vapor deposition (CVD) bubbling and injection methods over a Fe-Co/CaCO3 catalyst. CNFs, CNTs with secondary CNT or CNF growth, bamboo-compartmented and hollow CNTs were obtained. Increasing the growth time to 90 min resulted in growth of ~ 90 % of secondary CNFs on the surface of the main CNTs, using dichlorobenzene (DCB) as source of chlorine. The secondary CNFs grew at defects sites of the CNT wall. Secondary CNFs were not observed at other studied temperatures, 600, 650. 750 and 800 °C. Using an injection CVD method, horn-, straw- and pencil-shaped closed and open-ended CNTs/CNFs were obtained from CH3CN/DCB solutions of various volume ratios. CNT growth was enhanced after addition of chlorine. Highly graphitic carbon materials were produced from feed solutions containing low and high DCB concentrations. CNTs with defects were obtained from solutions containing 66.7 vol.% DCB. Post-doping of the N-CNTs with chlorine and of the chlorinated CNTs with nitrogen resulted in production of highly graphitic materials. Using a bubbling CVD method, mixtures of CNMs namely, hollow and bamboo-compartmented CNTs with and without intratubular junctions and carbon nano-onions filled with metal nanoparticles were obtained from feed solutions containing TTCE. MWCNT/PVP composite nanofibers were successfully synthesized using an electrospinning technique. Adsorption capacities of 15–20 g/g were obtained in pure oil or in oil-water mixtures. The adsorption capability of the MWCNT/PVP composite depended on the type of oil and its viscosity.GR201

    Unraveling surface enabled phenomena in low-dimensional molecular systems

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    This thesis focuses on the investigation of on-surface molecular architectures which exhibit extraordinary magnetic and quantum properties originating from the reduced dimensionality at surfaces. Many different combinations of spin-bearing square planar molecules and substrates were used and probed by local techniques as well as by spatial averaging techniques. Probing low-dimensional molecular magnetism by combination of several complementary techniques provides a more complete insight into the subtle interplay of the interactions involved at the surfaces. The comprehensive study of magnetism of Cr-phthalocyanine molecules supported on several different ferromagnetic and non-magnetic substrates demonstrated how the spin state of such molecules depends on the interaction with the substrate. Also in my work I have shown that the relative orientation of the molecule’s and the substrate’s easy magnetization axes is of great importance, even for molecules which are paramagnetic in the bulk. This is further supported by the example of interactions of Cr-based adsorbates with the Au(111) substrate where, for example, a very strong anisotropy of the Cr magnetic moment is observed. At the same time, the exchange coupling interactions with bare ferromagnetic substrates, Co and Ni are different in both the intensity and sign. These observations indicate that a refinement of the current models describing interface magnetism is needed to understand the peculiar magnetic coupling in these systems. Study of various phthalocyanine molecules on Pb(111) demonstrate the importance of employment of X-ray based techniques to complement the local probe investigations of these spin systems coupled to a superconductor. Although such experiments can drive a system out of the superconductive phase by the presence of a magnetic field, it was shown that some magnetic properties of these molecules won’t depend greatly on whether the system is or is not in the superconducting state. This fact is making X-ray based investigations even more important. The emergence of interesting magnetic phenomena through intra- and inter-molecular interactions was addressed next. Pilot experiments performed on triply-fused bisporphyrin molecules opened up the field for a new class of molecules containing two spin centers that can be exchanged providing a plethora of possibilities for tuning the molecule’s magnetic properties. Following up on our recent observation of long range 2D ferrimagnetic ordering in heteromolecular checkerboard assemblies of Fe and Mn phthalocyanine molecules supported on Au(111), we performed the experiments with similar binary 2D systems to further glimpse into the role of 3d orbitals, their symmetries and filling in maintaining long range ordering. It was shown that depending on the configuration and filling of their 3d orbitals the metallo-phthalocyanine molecules will interact by the RKKY interaction or not. In addition, I reported on a significant asymmetry in the mixing of hetero molecular layers that is occurring due to the pinning of one of the molecular types to the surface. Surprisingly this process modifies the layer structure of multilayers and therefore needs to be taken into account for on-surface metalation reactions or for the design of spintronic devices. Further on, different ways of modification of magnetic properties have been investigated. We reported on how spin states of various phthalocyanine molecules can be altered upon exposure to molecular and atomic hydrogen. In the former case, this process is completely reversible, while in the latter case it leads to irreversible changes of both the spin state of the metal center and of the molecule. Also, the ability to induce a Co surface functionalization with both N and Cl adlayers is demonstrated. Here, X-ray Photoelectron Diffraction has been employed to precisely determine interatomic distances in the created functionalized surfaces. In the last part the importance of development of new preparation/characterization techniques is demonstrated. It is shown how we successfully implemented the technique of deposition of large non-sublimable molecules into the UHV directly from solution, and how we have adapted a detector that is commonly used in time-of-flight mass spectrometry for acquiring fast, time-resolved XAS signal at SIM beamline of the SLS. In short, this thesis represents a collection of several pieces of a larger scientific puzzle grazing through several aspects of molecular magnetism

    OPTO-electrical characterisation of carbon-based thin film solar cells of excitonic descent in bulk heterojuction architecture

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    A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, September, 2017.Organic photovoltaic cells (OPVCs) continue to be intensively investigated due to their low cost and high utility potential. However, their low power conversion efficiency (PCE) has limited their full commercialization. The efficiency of the OPVCs is dependent on charge injection mechanisms, morphology and their underlying kinetics and energetics. Understanding the mechanisms that influence the efficiency of conjugated polymer solar cells is therefore pivotal to the enhancement of the devices‟ performance and the implementation of low priced fabrication technologies. In this regard, we investigated the dependence of the efficiency of organic solar cells on light intensity (I) using thin films of P3HT:PCBM blends, sandwiched between ITO/PEDOT:PSS and Al electrodes, the assembly of which was subjected to differing illumination intensities. Since charge transport through interfaces of such devices depends on charge carrier injection mechanisms, charge injection mechanisms at metal-organic active layer (here-in referred to as „metal-active layer‟) interfaces in the devices were studied under changing external voltage bias. Use was made of the Richardson-Schottky (R-S) thermionic emission currents and those due to Fowler-Nordheim (FN) tunneling in generating complete J(V) curves which were compared with those obtained through combined graphical representations of the variation of open circuit voltage (Voc) and efficiency (η) with light intensity. This led to the findings that under forward bias, the metal- active layer junction of an organic solar cell becomes ohmic after a certain threshold electrical field (Ethresh tunn) associated with quantum mechanical tunneling of charge carriers through the device‟s respective interfaces. Furthermore, we found that the open circuit voltage at which efficiency starts to decrease (Voc thresh eff. decay) approximates in magnitude the internal threshold open circuit voltage (Voc thresh tunn) at which FN quantum mechanical tunneling starts within the device at the electrode (a metal)- active layer interface. Explanatory findings were that for photoactive P3HT:PCBM composite devices, increasing white light intensity incident on them increases the photogenerated open circuit voltages that increasingly bias them with voltages, which with effect from the thresholds due to opto-electrical mechanisms at the devices‟ metal-active layer interfaces, are sufficient to greatly increase the dark currents. The increased dark current reduces the short circuit current density significantly, which in turn inflicts a likewise decrease in the power conversion efficiency of the devices. The theme of the next set of investigations was on the characteristic changes in the opto-electrical properties of the 1:1 blend of P3HT:PCBM with thickness of the active layer in ITO/PEDOT:PSS/P3HT:PCBM/Al solar cells, with intentions of finding out their effect on the threshold voltage at which efficiency starts to decrease (Vthreshold eff decay) and also for purposes of optimizing the thickness of the active layer. To obtain different active layer thicknesses (ALTs), each sample was cast at different spin-coat speeds. The thicknesses determined by surface profilometer through variation of spin-coating speeds were 61.5, 69.4, 77.1 and 84.5 nm. Whilst this study‟s empirical results demonstrated optimal performance at approximately 77.1 nm active layer thickness, the overall findings have been that the existence of a static universal optimum active layer thickness is not practical. Such an optimum rather exhibits contextual dependence. Annealing investigations revolved around attempts to empirically broaden and deepen the presently scarce understanding of the fundamental mechanisms defining thermal annealing process in conjugated polymers. To achieve this, we studied the opto-electrical effects of post-fabrication thermal annealing of bulk heterojunction ITO/PEDOT:PSS/P3HT:PCBM/AL solar cells at different heat treatment temperatures in the range 65 – 180 °C. The photoactive P3HT:PCBM layer was cast in air. The effect of air exposure has been found to chemically dope the polymer. Dedoping brought in by thermal annealing has been demonstrated to be responsible for the aggravated drop of efficiency. Summary findings lead to the generalisation that annealing of polymers is a two-step process, the first of which causes a decrease in conductivity, followed by its increase. Although impurity dedoping decreases „under dark‟ current density in certain regions of the active P3HT:PCBM composite layer during annealing, it has beneficial aftermaths, some of which surface upon illumination of the P3HT:PCBM-based solar cell. When illuminated, photogenerated current density in the illuminated device immediately increases. This happens so, because of less electron capture and immobilization during illumination of the annealed device. Morphologically, thermal annealing has been found to enhance the formation of the deeply quenched bicontinuous network at the nanoscale between P3HT and PCBM, leading to high efficiency devices. We propose that the beneficial structure formation in P3HT:PCBM blends, is initiated by the crystallization of P3HT as it segregates PCBM, possibly to the amorphous P3HT. Thermal annealing renders significant enhancement in Jsc, Voc and FF of the annealed device. The optical absorbance was found to increase with increase in annealing temperature.MT201
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