Zinc Oxide Nanostructures: Synthesis and Characterization

The summary should be ca. 200 words; this text will present the book in all promotional forms (e.g. flyers). Please describe the book in straightforward and consumer-friendly terms. [Zinc oxide (ZnO) is a wide band gap semiconductor with an energy gap of 3.37 eV at room temperature. It has been used considerably for its catalytic, electrical, optoelectronic, and photochemical properties. ZnO nanomaterials, such as quantum dots, nanorods, and nanowires, have been intensively investigated for their important properties. Many methods have been described in the literature for the production of ZnO nanostructures, such as laser ablation, hydrothermal methods, electrochemical deposition, sol-gel methods, chemical vapour deposition, molecular beam epitaxy, the common thermal evaporation method, and the soft chemical solution method. The present Special Issue is devoted to the synthesis and characterization of ZnO nanostructures with novel technological applications.

High Temperature VO2 based Microbolometer with Enhanced Light Absorption

Department of Materials Science and EngineeringMicrobolometer depends on the change in electrical resistance of material as the temperature of the material changes. As element technology of microbolometer, VOx thin films are widely used due to high temperature resistance coefficients (TCR) and low noise . However, due to the metal insulator transition (MIT) property of the VO2 thin film, it is difficult to fabricate a micro bolometer at 68oC which can operate at high temperatures. Also, high light absorption is required . Here, we developed VO2 thin films a nd nanowires. And we developed a light absorber to increase the responsivity of microbolometer through high light absorption and applied it to various application. In order to obtain high quality of thermal sensitive material, we fabricated the resistor in cluded in micro bolometer which has a low resistance and a high temperature resistance coefficient (TCR) by growing the tetragonal VO2 crystal phase on the oxide thin film of the perovskite structure. In addition, infrared absorber has multilayer structure in which Ti metal layer and an MgF2 dielectric layer are alternately deposited with a several repetition cycle. The absorber layer shows about 70 % infrared absorption in the range of 8 14 ??m. In this paper, we used VO2 for the TCR material and the infrar ed absorber, showing the enhanced performance compared to that of the conventional micro bolometer. The micro bolometer operates even at high temperature of 100??C. The micro bolometer has a responsivity and detectivity of 4.90 x 10^3 V/W and 1.45 x 10^8 cmHz 1/2 /W at 100oC.clos

Study on Nano-Engineering of High-Capacity Anode Materials for High-Power Energy Storage System

Department of Energy Engineering(Battery Science and Technology)Nano-engineering and nanotechnology issue in various industry fields such as semiconductor, chemistry, energy solution, material science, and medicine. A definition of nanotechnology includes quantum mechanics, molecular chemistry, biology, and atomic level behaviors. Also, nanostructured materials (e.g., nanoparticle, nanorod, nanotube, nanowire, hollow, and yolk-shell) improve properties of materials for performance enhancement of devices. These nanomaterials have been synthesized using bottom-up and top-down approaches. In the early 2000s, many researchers garnered information and experiences about the nanotechnology that led to innovation and progress in industry and academy of science. As a result, many electronic devices were developed for a convenience of our life. Especially, significant advances of devices lead to the development of another new device with more improved performances including faster processing ability, longer working time, light weight, and easy transportation. In this regard, gradual development of energy storage system must need to satisfy this demand for new electric device (e.g. electric vehicle (EV), energy storage system (ESS), even drone) As one of the powerful energy storage systems, lithium-ion batteries (LIBs) are critically important to operate portable electronic devices. However, they cannot meet requirements for more advanced applications, like electric vehicles and energy storage systems due to limitations of conventional cathode/anode materials in high power and high energy density. To overcome these limitations, several strategies have been developed, including nanostructured design of electrode materials, coating of active materials with electrically conductive layers, and control of electrode architectures. Herein, we study on a simple, cost effective and unique synthesis method of various shaped functional materials by nano-engineering process in an each chapter. Also, we conduct research about a mechanism of reaction, key for synthesizing good materials, change of chemical reaction in experiment. So, the developed materials appear outstanding properties such as structural stability, chemical stability in electrochemical test, and mainly used energy storage system like LIBs. In chapter III, we demonstrate a simple route for fabricating trench-type copper patterns by combining a photo-lithography with a wet etching process. Nanostructured CuO was grown on the patterned Cu current collectors via a simple solution immersion process. And silicon nanoparticles were filled into the patterned Cu current collectors. The strongly immobilized CuO on the patterned Cu exhibited high electrochemical performance, including a high reversible capacity and a high rate capability. In chapter IV, we demonstrate multi-scale patterned electrodes that provide surface-area enhancement and strong adhesion between electrode materials and current collector. The combination of multi-scale structured current collector and active materials (cathode and anode) enables us to make high-performance Li-ion batteries (LIBs). When LiFePO4 (LFP) cathode and Li4Ti5O12 (LTO) anode materials are combined with patterned current collectors, their electrochemical performances are significantly improved, including a high rate capability (LFP : 100 mAhg-1, LTO : 60 mAhg-1 at 100 C rate) and highly stable cycling. Moreover, we successfully fabricate full cell system consisting of patterned LFP cathode and patterned LTO anode, exhibiting high-power battery performances. We extend this idea to Si anode that exhibits a large volume change during lithiation/delithiation process. The patterned Si electrodes show significantly enhanced electrochemical performances, including a high specific capacity (825 mAhg-1) at high rate of 5 C and a stable cycling retention. In chapter V, Chemical reduction of micro-assembled CNT@TiO2@SiO2 leads to the formation of titanium silicide-containing Si nanotubular structures. The Si-based nanotube anodes exhibit a high capacity (>1850 mAh g-1) and an excellent cycling performance (capacity retention of >99% after 80 cycles). In chapter VI, we revisit the metallothermic reduction process to synthesize shape-preserving macro-/nano-porous Si particles via aluminothermic and subsequent magnesiotheric reaction of porous silica particles. This process enables us to control the specific capacity and volume expansion of shape-preserving porous Si-based anodes. Two step metallothermic reactions have several advantages including a successful synthesis of shape-preserving Si particles, tunable specific capacity of as-synthesized Si anode, accommodation of a large volume change of Si by porous nature and alumina layers, and a scalable synthesis (hundreds of gram per batch). An optimized macroporous Si/Al2O3 composite anode exhibits a reversible capacity of ~1500 mAh g-1 after 100 cycles at 0.2 C and a volume expansion of ~34% even after 100 cycles. In chapter VII, we report a redox-transmetalation reaction-based route for the large-scale synthesis of mesoporous germanium particles from germanium oxide at temperatures of 420 ~ 600 oC. We could confirm that a unique redox-transmetalation reaction occurs between Zn0 and Ge4+ at approximately 420 oC using temperature-dependent in situ X-ray absorption fine structure analysis. This reaction has several advantages, which include (i) the successful synthesis of germanium particles at a low temperature (∼450 oC), (ii) the accommodation of large volume changes, owing to the mesoporous structure of the germanium particles, and (iii) the ability to synthesize the particles in a cost-effective and scalable manner, as inexpensive metal oxides are used as the starting materials. The optimized mesoporous germanium anode exhibits a reversible capacity of∼1400 mA h g-1 after 300 cycles at a rate of 0.5 C (corresponding to the capacity retention of 99.5%), as well as stable cycling in a full cell containing a LiCoO2 cathode with a high energy density. In chapter VIII, we report a unique synthesis of redox-responsive assembled carbon-sheathed germanium coaxial nanowire heterostructures without a need of metal catalyst. In our approach, germanium nanowires are grown by reduction of germanium oxide particles and subsequent self-catalytic growth mechanism during thermal decomposition of natural gas, and simultaneously, carbon sheath layers are uniformly coated on the germanium nanowire surface. This process is a simple (one-step process), reproducible, easy size-controllable and cost-effective (mass production) process which total mass of metal oxides can be transformed into nanowires. Furthermore, the germanium nanowires exhibit outstanding electrochemical performance including capacity retention of ~96% after 1000 cycles at 1C rate as lithium-ion battery anode.ope

Fabrication of nanoelectronic devices for applications in flexible and wearable electronics

Conventional electronic devices fabricated on rigid crystalline semiconductors wafers have evolved with the motivation to miniaturize thereby realizing faster, smaller and densely integrated devices. A parallel research that is rapidly evolving for future electronics is to integrate the property of flexibility and stretchablity to develop human friendly devices. There have been number of reports on fabricating sensors and electronic devices on stretchable, bendable and soft materials like polyimide, polyurethane sponge, natural rubber, cellulose paper, tissue paper etc. using various nanomaterials such as 2D materials, metal oxides, carbon nanomaterials and metal nanowires. These nanomaterials possess excellent electronic, thermal, mechanical and optical properties making them suitable for fabrication of broadband photodetectors, temperature, pressure and strain sensors which find applications in the field of optoelectronics, sensors, medical, security and surveillance. While most reports on photodetectors focus on improving the responsivity in one region of electromagnetic spectrum by fabricating materials hybrids, the main issue still remains unaddressed which is the inability to absorb wide range of electromagnetic spectrum. Most photodetectors comprise of p-n heterojunction, where one of the material is responsible for absorbance, having metal contacts on p and n type allows for effective separation of photogenerated carriers. But for a broadband photodetector, both the materials of the heterojunction should participate in the absorbance. In such a case, metal contacts on p and n type will trap either the photogenerated electrons or hole which leads to the failure of the device. The first part of the thesis focus on the development of flexible broadband photodetectors based on MoS2 hybrid. Next chapter of the thesis deals with the improvement of responsivity by fabrication of solution processed heterojunction and piezotronic diode on flexible paper substrate for enhanced broadband photodetector and active analog frequency modulator by application of external mechanical strain. The fabricated MoS2 based heterojunctions was further utilized at circuit level for frequency modulation. The external applied strain not only modulates the transport properties at the junction which not only enhances the broadband photoresponse but also changes the depletion capacitance of junction under reverse bias thereby utilizing it for frequency modulation at circuit level. The next part of thesis deals with fabrication of new type of electronic, skin-like pressure and strain sensor on flexible, bio-degradable pencil eraser substrate that can detect pressure variations and both tensile and compressive strain and has been fabricated by a solvent-free, low-cost and energy efficient process. Eraser, serves as a substrate for strain sensing as well as acts as a dielectric for capacitive pressure sensing, thereby eliminating the steps of dielectric deposition which is crucial in capacitive based pressure sensors. Detailed mechanism studies in terms of tunneling effect is presented to understand the proposed phenomena. As a proof of concept, an array of 6 x 8 devices were fabricated and pressure mapping of alphabets “I”, “T” and “H” were plotted which were highly consistent with the shape and weight distribution of the object

Flexographic printed nanogranular LBZA derived ZnO gas sensors: Synthesis, printing and processing

Within this document, investigations of the processes towards the production of a flexographic printed ZnO gas sensor for breath H2 analysis are presented. Initially, a hexamethylenetetramine (HMTA) based, microwave assisted, synthesis method of layered basic zinc acetate (LBZA) nanomaterials was investigated. Using the synthesised LBZA, a dropcast nanogranular ZnO gas sensor was produced. The testing of the sensor showed high sensitivity towards hydrogen with response (Resistanceair/ Resistancegas) to 200 ppm H2 at 328 °C of 7.27. The sensor is highly competitive with non-catalyst surface decorated sensors and sensitive enough to measure current H2 guideline thresholds for carbohydrate malabsorption (Positive test threshold: 20 ppm H2, Predicted response: 1.34). Secondly, a novel LBZA synthesis method was developed, replacing the HMTA by NaOH. This resulted in a large yield improvement, from a [OH-] conversion of 4.08 at% to 71.2 at%. The effects of [OH-]/[Zn2+] ratio, microwave exposure and transport to nucleation rate ratio on purity, length, aspect ratio and polydispersity were investigated in detail. Using classical nucleation theory, analysis of the basal layer charge symmetries, and oriented attachment theory, a dipole-oriented attachment reaction mechanism is presented. The mechanism is the first theory in literature capable of describing all observed morphological features along length scales. The importance of transport to nucleation rate ratio as the defining property that controls purity and polydispersity is then shown. Using the NaOH derived LBZA, a flexographic printing ink was developed, and proof-of-concept sensors printed. Gas sensing results showed a high response to 200 ppm H2 at 300 °C of 60.2. Through IV measurements and SEM analysis this was shown to be a result of transfer of silver between the electrode and the sensing layer during the printing process. Finally, Investigations into the intense pulsed light treatment of LBZA were conducted. The results show that dehydration at 150 °C prior to exposure is a requirement for successful calcination, producing ZnO quantum dots (QDs) in the process. SEM measurements show mean radii of 1.77-2.02 nm. The QDs show size confinement effects with the exciton blue shifting by 0.105 eV, and exceptionally low defect emission in photoluminescence spectra, indicative of high crystalline quality, and high conductivity. Due to the high crystalline quality and amenity to printing, the IPL ZnO QDs have numerous potential uses ranging from sensing to opto-electronic devices

Functional Nanomaterials and Polymer Nanocomposites: Current Uses and Potential Applications

This book covers a broad range of subjects, from smart nanoparticles and polymer nanocomposite synthesis and the study of their fundamental properties to the fabrication and characterization of devices and emerging technologies with smart nanoparticles and polymer integration

From nanoparticle networks to metal-organic frameworks: synthesis, structural engineering and applications

Nanoparticle networks, self-assembled from flame generated hot aerosols consisting of ceramic nanoparticles with well-controlled particle size, are promising materials for many different applications, especially for photodetectors and VOC sensors. Furthermore, the great structural flexibilities of these self-assembled nanoparticle networks including tuneable thickness and hierarchical porosity, precisely-controlled averaged particle size as well as chemical composition make them as potential platforms for templated materials synthesis via chemical conversion. On the other hand, metal-organic framework (MOF), is a growing family of microporous materials consisting of metal cations connected by organic linkers. Their unique properties, including a narrow pore size distribution (intrinsic porosity), designable topology, high accessible surface area, and chemical mutability, make MOFs promising materials for a variety of applications including gas storage, separation, catalysis, biotechnology, optics, microelectronics and energy production/storage. However, there are still several bottlenecks hindering the structural engineering of metal-organic frameworks, especially for pure crystalline MOF materials, including limited attainable thickness, scalability, poor mechanical stability (i.e. brittle nature of MOFs), hard to realize the morphological control (e.g. tuneable extrinsic hierarchical porosity) and geometric designs on pure crystalline MOF components. Thus, a facile synthetic approach for MOF structuring is highly desirable, which could afford the fabrication of three-dimensional MOF materials with possibly unlimited thickness, free-standing feature, the control over extrinsic hierarchy as well as pre-determined designs of MOFs while maintain their crystalline property and intrinsic extreme accessible surfaces. Firstly, we started with the synthesis of pure ZnO nanoparticle networks and the optimization of their particle size. Later, using the ZnO nanoparticle networks with an optimal particle size, a high-performing UV photodetector has been prepared to show a proof of concept application of such structural engineering. After achieving the first structural control over ZnO nanoparticle networks, a multi-dimensional control has been further investigated associated with its potential use for multi-functional devices including transparent conductive oxides and gas sensors. Given the successful structural control over nanoparticle networks, considering the existing bottlenecks in current MOF fabrication, this multi-dimensional structural control has been successfully replicated to MOF preparation via a means of gas phase conversion. Therefore, in this thesis, a systematic study has been presented from the synthesis and applications of nanoparticle networks to those of metal-organic frameworks in the sequence of: (i) the synthesis of three-dimensional nanoparticle networks (i.e. ZnO-based metal oxide nanoparticle networks), (ii) the realization of a precise particle size control over the synthesized nanoparticle networks (e.g. ZnO) and the use of resulted optimal structure for photodetector application, (iii) the realization of chemical composition manipulation over the synthesized nanoparticle networks (e.g. ZnO nanoparticle networks with varied Al doping concentrations) and the use of the resulted structures as proof of concept applications for both porous conductive electrodes and VOC sensor, (iv) the establishment of a synthetic pathway from nanoparticle networks to metal-organic frameworks based on the replication of the structural control over nanoparticle networks towards metal-organic frameworks, and the proof of concept application of the resulted free-standing metal-organic frameworks monolith for effective molecular sieve in batteries, and (v) the use of the established fabrication approach (i.e. from nanoparticle networks to metal-organic frameworks) for monolithic metal-organic framework patterning

Synthesis and Assembly of Copper and Copper (I, II) Oxides Nanostructures

Ph.DDOCTOR OF PHILOSOPH

Nanocellulose and Nanocarbons Based Hybrid Materials

This highly informative and carefully presented book discusses the preparation, processing, characterization and applications of different types of hybrid nanomaterials based on nanocellulose and/or nanocarbons. It gives an overview of recent advances of outstanding classes of hybrid materials applied in the fields of physics, chemistry, biology, medicine, and materials science, among others. The content of this book is relevant to researchers in academia and industry professionals working on the development of advanced hybrid nanomaterials and their applications

Design and engineering of microreactor and smart-scaled flow processes

This book is a reprint of the special issue that appeared in the online open access journal Processes (ISSN 2227-9717) in 2013 (available at: http://www.mdpi.com/journal/processes/special_issues/smart-scaled_flow_processes)