2,277 research outputs found

    Laser-induced forward transfer: fundamentals and applications

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    Laser-induced forward transfer (LIFT) is a digital printing technique that uses a pulsed laser beam as the driving force to project material from a donor thin film toward the receiving substrate whereon that material will be finally deposited as a voxel. This working principle allows LIFT to operate with both solid and liquid donor films, which provides the technique with an unprecedented broad spectrum of printable materials, and thus makes it very competitive over other digital technologies, like inkjet printing. It is not only that LIFT can access a much wider range of ink viscosities and loading particle sizes; the possibility of printing from solid films allows the single-step printing of multilayers and entire devices, and even makes possible 3D printing. This versatility translates, in turn, into a broad field of applications, from graphics production to printed electronics, from the fabrication of chemical sensors to tissue engineering. This monograph provides an extensive review of the LIFT technique, from its origins to the most recent achievements, focusing on the fundamental aspects of both its working principle and transfer dynamics, as well as on its broad range of applications

    Crystal Structures of Metal Complexes

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    This reprint contains 11 papers published in a Special Issue of Molecules entitled "Crystal Structures of Metal Complexes". I will be very happy if readers will be interested in the crystal structures of metal complexes

    Tailoring Properties of Printed Field-Effect Transistors by Design and Material Changes

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    Due to the increasing digitalization in all areas of life and work, including digital signatures or even electronic feedbacks from single component parts or consumer articles, the question for new possibilities for quick and simple manufacturing of circuits arises. In this respect, also mass production of transistors, the core building units of electronic logics, has to be reconsidered in order to overcome the often complex production of silicon chips. In this scope, printing of electronic components has presented itself as a highly promising method within the recent years. Conductive paths, solar cells, or displays have already been integrated as printed electronics in manyfold industrial production processes. In contrast to this, so far, no reliable processes for printed transistors in an industrial scale have been established. Organic and inorganic semiconducting materials often have properties with diametral differences: while organic materials use to be p-type semiconductors and come up with simple processability and mechanical flexibility, inorganic systems tend to be n-type semiconductors, brittle and in need of high processing temperatures. These disadvantages of inorganic, especially oxidic semiconductors however are compensated by often severely better electronic properties and increased environmental stability. In order to achieve very low operation voltages while maintaining sufficiently high currents, it is recommended to realize channel polarization via electrolytes instead of dielectrics, as the formation of Helmholtz double layers allows for locally very high fields. By this, units can be operated at voltages typical for commercially available batteries. Within the scope of this work new and improved methods for the processing of printed field-effect transistors were successfully implemented, contributing to the development towards large-scale production of devices with predictable properties. Starting form planar field-effect transistors with displaced gates, three possibilities for improvements have been examined: a vertical geometry, doped channels and an alternative electrolyte. By changing from a planar to a vertical device geometry, channel lengths may become independent from the material printers’ resolutions and can be reduced to the thickness of the deposited films. By this lengths may be shrunk from a two-digit micron range to submicron values. As channel lengths are directly correlated with output currents, a severe improvement can be realized. However, in this case the channel must be porous in order to allow a large surface being covered by electrolyte. Within this work, a known system with an SnO2 channel could be improved by developing a simplified production method with quickly available materials, successfully resulting in a fully functional device. For reliably tailoring the central property of the threshold voltage, i.e., the gate voltage at which the channel changes from an insulating to a conducting state, on a per-device level, an In2O3 precursor ink with varying chromium doping has been developed. Through this doping, the threshold voltage could be changed linearly with the dopant concentration, however under severe loss in the output current. In a third experimental series, the usually applied composite solid polymer electrolyte has been replaced with Al2O3 . However, instead of a dielectric gating, a material with low density and many hydroxy functionalities acting as an electrolyte was created due to low temperatures during the atom layer deposition process. Depending on the humidity, the functionality of such transistors can be changed as the electrolytic properties are based on protons generated on the Al2O3 surface. Within this work, three alternatives for the production of inorganic field-effect transistors could be successfully shown and a contribution towards the further development of this technology was made

    Synthesis of Quasi-Freestanding Graphene Films Using Radical Species Formed in Cold Plasmas

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    For over a decade, the Stinespring laboratory has investigated scalable, plasma assisted synthesis (PAS) methods for the growth of graphene films on silicon carbide (SiC). These typically utilized CF4-based inductively coupled plasma (ICP) with reactive ion etching (RIE) to selectively etch silicon from the SiC lattice. This yielded a halogenated carbon-rich surface layer which was then annealed to produce the graphene layers. The thickness of the films was controlled by the plasma parameters, and overall, the process was readily scalable to the diameter of the SiC wafer. The PAS process reproducibly yielded two- to three-layer thick graphene films that were highly tethered to the underlying SiC substrate via an intermediate buffer layer. The buffer layer was compositionally similar to graphene. However, a significant number of graphene carbons were covalently bound to silicon atoms in the underlying substrate. This tethering lead to mixing of the film and substrate energy bands which degraded many of graphene’s most desirable electrical properties. The research described in this dissertation was aimed at improving graphene quality by reducing the extent of tethering using a fundamentally different plasma etching mechanism while maintaining scalability. In the ICP-RIE process, the etchant species include F and CFx (x = 1-3) radicals and their corresponding positive ions. These radicals are classified as “cold plasma species” in the sense that they are nominally in thermal equilibrium with the substrate and walls of the system. In contrast, the electrons exist at extremely high temperature (energy), and the ionic species are accelerated to energies on the order of several hundred electron volts by the plasma bias voltage that exists between the plasma and substrate. As a result, the ionic species create a directional, high rate etch that is dominated by physical etching characterized by energy and momentum transfer. In contrast, the neutral radicals chemically etch the surface at a much lower rate. In this work, the effects of physical etching due to high energy ions were eliminated by shielding the SiC substrate using a mask (e.g., quartz) supported by silicon posts. In this way, a microplasma consisting of chemically reactive cold plasma species was created in the small space between the substrate surface and the backside of the quartz mask. This process, referred to here as microplasma assisted synthesis (MPAS), was used to produce graphene films. A parametric investigation was conducted to determine the influence of MPAS operating parameters on graphene quality. The key parameters investigated included ICP power, RIE power, etch time, various mask materials, microreactor height, substrate cooling, initial surface morphology and SiC polytype. The resulting graphene films were characterized by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy (AFM). Following optimization of the MPAS process, some tethering of the graphene films remained. However, films produced by MPAS consistently exhibited significantly less tethering than those produced using the PAS process. Moreover, both XPS and Raman spectroscopy indicated that these films were quasi-free standing, and, in some cases, they approached free standing graphene. From a wide view, the results of these studies demonstrate the potential of MPAS as a technique for realizing the controlled synthesis of high-quality, lightly tethered mono-, and few-layer graphene films directly on an insulating substrate. On a more fundamental level, the results of these studies provide insight into the surface chemistry of radical species

    Polymeric semiconductor and transition-metal dichalcogenide nanocomposites for inkjet-printed thin-film transistor devices

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    Patterned using subtractive processes, conventional thin-film deposition techniques inevitably require high-vacuum deposition and photolithography to define functional layers to create a device structure. Inkjet printing technology has received considerable attention to realize low-cost and potential mass production of large-area electronics at low temperatures using an additive process approach. However, the materials used in the printing process are based on solution-based electronic inks formulated with organic electronic materials. Among them, conjugated polymers are widely used as a semiconductor for thin-film transistor (TFT) applications, but they possess poor charge transport properties compared to other single or polycrystalline inorganic semiconductors. Moreover, the inkjet printing method has a weakness for depositing polymeric solution that form thin films having a highly ordered molecular structure. To overcome this limitation when using printed polymers, a hybrid organic/inorganic semiconductor ink was explored. The hybrid semiconductor ink was prepared by mixing two different materials, molybdenum disulfide (MoS₂) nanosheets and solution-based poly(3-hexylthiopene-2,5-diyl) (P3HT), the former is a two-dimensional semiconductor and the latter a conjugated polymer. To enhance the level of exfoliation and stability of MoS₂ nanosheets in P3HT, the surfactant trichloro(dodecyl)silane (DDTS), was used to functionalize the MoS₂ surface. Printed TFTs using the nanosheet suspension were found to enhance the field-effect mobility by approximately 3× compared to TFTs without the suspension. The introduced single-crystalline MoS₂ nanosheets in the P3HT matrix improved the electrical and structural properties of the inkjet-printed thin-film polymer. Based on these findings and insights, the observed effects can be extended to second-generation polymeric semiconductors, specifically the donor-acceptor (D-A) co-polymers. These materials are renowned for exhibiting the highest mobilities among printable polymers while maintaining ambipolarity, a desirable trait for configuring complementary metal-oxide-semiconductor (CMOS) circuits. In light of this, novel nanocomposite semiconductor inks were developed to demonstrate the influence of 2D nanoparticles on the electronic properties of D-A copolymers, diketopyrrolopyrrole-thieno[3,2-b]thiophene (DPPT-TT). Printed TFTs using this new hybrid semiconductor showed that the field-effect mobility of the devices increased by 33 % and 140 % in both hole (p-type) and electron (n-type) transports, respectively. Atomic force microscopy (AFM) results of the printed hybrid thin film revealed that strongly aggregated polymer domains were observed in films containing the MoS₂ nanosheets. In ultraviolet–visible–near infrared spectroscopy (UV-vis-NIR) measurement, increased intensity of 0-0 and 0-1 peaks from hybrid film indicates improved charge transport was due to enhanced intermolecular charge transfer in the microstructure of the polymer film. Furthermore, the incorporation of hybrid nanocomposites proved particularly beneficial for inkjet-printed TFTs utilizing metal electrodes, as the latter had a tendency to augment contact resistance and thereby compromise device performance. However, the introduction of hybrid nanocomposites effectively counteracted the performance degradation arising from the printed metal electrodes by enhancing the crystallinity of the polymeric film. Moreover, these findings also highlight the feasibility of employing lower sintering temperatures for inkjet-printed metal electrodes. This is attributed to the fact that the result of increased contact resistance associated with lower sintering temperatures can be effectively mitigated by the nanocomposite semiconductor. Consequently, an overall enhancement in device performance was achieved by applying the hybrid nanocomposite ink. This study elucidated the advantageous influence of solution-processed MoS₂ nanosheets on the crystallinity and electrical properties of polymeric thin films, consequently leading to significant improvements in the performance parameters of inkjet-printed TFTs

    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»

    Spectroscopic investigations of photon-induced reactions in tin-oxo cage photoresists

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    Molecular compounds such as tin-oxo cages are promising photoresists for Extreme UltraViolet (EUV) photolithography, which is the latest nano-patterning technology for high-end computer chips. Solubility switching of the resist is the key for pattern transfer to the semiconductor substrate. In this thesis, different spectroscopic techniques were used to gain insight into the photochemistry upon exposure, which is crucial for optimizing the resist performance. In one research line, we developed a laser-based high harmonic generation setup as the exposure source in the soft-X-ray (XUV) region to perform broadband absorption spectroscopy on tin-oxo cage samples. Resist-coated thin films were exposed to light with energies of 21 – 70 eV, and the induced changes in the transmission as a function of exposure dose were used to quantify the photoconversion of the resist. The results were compared with those obtained with EUV (92 eV). The resist properties were further investigated using X-ray photoelectron spectroscopy and Total Electron Yield techniques. A synchrotron beamline was used as the exposure source (5-150 eV) to study the low-energy emitted electrons from the resist. Outgassing measurements (residual gas analysis) and ellipsometry techniques were used to investigate the resist’s photoconversion under 92 eV exposure. Outgassing species from the resist were determined to be mainly organic carbon-containing products. The outgassing rate was measured for a few selected masses and the induced resist’s thickness change at different exposure doses was related to the outgassing rate of the resist. The fundamental insight obtained in our studies can help to design improved EUV photoresists

    Optimization of niobium oxide-based threshold switches for oscillator-based applications

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    In niobium oxide-based capacitors non-linear switching characteristics can be observed if the oxide properties are adjusted accordingly. Such non-linear threshold switching characteristics can be utilized in various non-linear circuit applications, which have the potential to pave the way for the application of new computing paradigms. Furthermore, the non-linearity also makes them an interesting candidate for the application as selector devices e.g. for non-volatile memory devices. To satisfy the requirements for those two areas of application, the threshold switching characteristics need to be adjusted to either obtain a maximized voltage extension of the negative differential resistance region in the quasi-static I-V characteristics, which enhances the non-linearity of the devices and results in improved robustness to device-to-device variability or to adapt the threshold voltage to a specific non-volatile memory cell. Those adaptations of the threshold switching characteristics were successfully achieved by deliberate modifications of the niobium oxide stack. Furthermore, the impact of the material stack on the dynamic behavior of the threshold switches in non-linear circuits as well as the impact of the electroforming routine on the threshold switching characteristics were analyzed. The optimized device stack was transferred from the micrometer-sized test structures to submicrometer-sized devices, which were packaged to enable easy integration in complex circuits. Based on those packaged threshold switching devices the behavior of single as well as of coupled relaxation oscillators was analyzed. Subsequently, the obtained results in combination with the measurement results for the statistic device-to-device variability were used as a basis to simulate the pattern formation in coupled relaxation oscillator networks as well as their performance in solving graph coloring problems. Furthermore, strategies to adapt the threshold voltage to the switching characteristics of a tantalum oxide-based non-volatile resistive switch and a non-volatile phase change cell, to enable their application as selector devices for the respective cells, were discussed.:Abstract I Zusammenfassung II List of Abbrevations VI List of Symbols VII 1 Motivation 1 2 Basics 5 2.1 Negative differential resistance and local activity in memristor devices 5 2.2 Threshold switches as selector devices 8 2.3 Switching effects observed in NbOx 13 2.3.1 Threshold switching caused by metal-insulator transition 13 2.3.2 Threshold switching caused by Frenkel-Poole conduction 18 2.3.3 Non-volatile resistive switching 32 3 Sample preparation 35 3.1 Deposition techniques 35 3.1.1 Evaporation 35 3.1.2 Sputtering 36 3.2 Micrometer-sized devices 36 3.3 Submicrometer-sized devices 37 3.3.1 Process flow 37 3.3.2 Reduction of the electrode resistance 39 3.3.3 Transfer from structuring via electron beam lithography to structuring via laser lithography 48 3.3.4 Packaging procedure 50 4 Investigation and optimization of the electrical device characteristic 51 4.1 Introduction 51 4.2 Measurement setup 52 4.3 Electroforming 53 4.3.1 Optimization of the electroforming process 53 4.3.2 Characterization of the formed filament 62 4.4 Dynamic device characteristics 67 4.4.1 Emergence and measurement of dynamic behavior 67 4.4.2 Impact of the dynamic device characteristics on quasi-static I-V characteristics 70 5 Optimization of the material stack 81 5.1 Introduction 81 5.2 Adjustment of the oxygen content in the bottom layer 82 5.3 Influence of the thickness of the oxygen-rich niobium oxide layer 92 5.4 Multilayer stacks 96 5.5 Device-to-device and Sample-to-sample variability 110 6 Applications of NbOx-based threshold switching devices 117 6.1 Introduction 117 6.2 Non-linear circuits 117 6.2.1 Coupled relaxation oscillators 117 6.2.2 Memristor Cellular Neural Network 121 6.2.3 Graph Coloring 127 6.3 Selector devices 132 7 Summary and Outlook 138 8 References 141 9 List of publications 154 10 Appendix 155 10.1 Parameter used for the LT Spice simulation of I-V curves for threshold switches with varying oxide thicknesses 155 10.2 Dependence of the oscillation frequency of the relaxation oscillator circuit on the capacitance and the applied source voltage 156 10.3 Calculation of the oscillation frequency of the relaxation oscillator circuit 157 10.4 Characteristics of the memristors and the cells utilized in the simulation of the memristor cellular neural network 164 10.5 Calculation of the impedance of the cell in the memristor cellular network 166 10.6 Example graphs from the 2nd DIMACS series 179 11 List of Figures 182 12 List of Tables 19

    Structure and Phase Transformations in Thin Films

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