Controlling The Growth Of Nanoparticles Produced In A High Power Pulsed Plasma

Nanotechnology can profoundly benefit our health, environment and everyday life. In order to make this a reality, both technological and theoretical advancements of the nanomaterial synthesis methods are needed. A nanoparticle is one of the fundamental building blocks in nanotechnology and this thesis describes the control of the nucleation, growth and oxidation of titanium particles produced in a pulsed plasma. It will be shown that by controlling the process conditions both the composition (oxidationstate) and size of the particles can be varied. The experimental results are supported by theoretical modeling. If processing conditions are chosen which give a high temperature in the nanoparticle growth environment, oxygen was found to be necessary in order to nucleate the nanoparticles. The two reasons for this are 1: the lower vapor pressure of a titanium oxide cluster compared to a titanium cluster, meaning a lower probability of evaporation, and 2: the ability of a cluster to cool down by ejecting an oxygen atom when an oxygen molecule condenses on its surface. When the oxygen gas flow was slightly increased, the nanoparticle yield and oxidation state increased. A further increase caused a decrease in particle yield which is attributed to a slight oxidation ofthe cathode. By varying the oxygen flow, it was possible to control the oxidation state of the nanoparticles without fully oxidizing the cathode. Pure titanium nanoparticles could not be produced in a high vacuum system because oxygen containing gases such as residual water vapour have a profound influence on nanoparticle yield and composition. In an ultrahigh vacuum system titanium nanoparticles without significantoxygen contamination were produced by reducing the temperature of the growth environment and increasing the pressure of an argon-helium gas mixture within whichthe nanoparticles grew. The dimer formation rate necessary for this is only achievable at higher pressures. After a dimer has formed, it needs to grow by colliding with a titanium atom followed by cooling by collisions with multiple buffer gas atoms. The condensation event heats up the cluster to a temperature much higher than the gas temperature, where it is during a short time susceptible to evaporation. When the clusters’ internal energy has decreased by collisions with the gas to less than the energy required to evaporate a titanium atom, it is temporarily stable until the next condensation event occurs. The temperature difference by which the cluster has to cool down before it is temporarily stable is exactly as many kelvins as the gas temperature.The addition of helium was found to decrease the temperature of the gas, making it possible for nanoparticles of pure titanium to grow. The process window where this is possible was determined and the results presented opens up new possibilities to synthesize particles with a controlled contamination level and deposition rate.The size of the nanoparticles has been controlled by three means. The first is to change the electrical potential around the growth zone, which allows for size (diameter) control in the order of 25 to 75 nm without influencing the oxygen content of the particles. The second means is by increasing the pressure which decreases the ambipolar diffusion rate of the ions resulting in a higher growth material density. By doing this, the particle size can be increased from 50 to 250 nm, however the oxygen content also increases with increasing pressure when this is done in a high vacuum system. The last means of size control was by adding a helium flow to the process where higher flows resulted in smaller nanoparticle sizes. When changing the pressure in high vacuum, the morphology of the nanoparticles could be controlled. At low pressures, highly faceted near spherical particles were produced. Increasing the pressure caused the formation of cubic particles which appear to ‘fracture’ at higher pressures. At the highest pressure investigated, the particles became poly-crystalline with a cauliflower shape and this morphology was attributed to a lowad atom mobility. The ability to control the size, morphology and composition of the nanoparticles determines the success of applying the process to manufacture devices. In related work presented in this thesis it is shown that 150-200 nm molybdenum particles with cauliflower morphology were found to scatter light in which made them useful in photovoltaic applications, and the size of titanium dioxide nanoparticles were found to influence the selectivity of graphene based gas sensors.

The first overview of this topic begins with some historical aspects and a survey of the principles of the gas aggregation method. The second part covers modifications of this method resulting in different specialized techniques, while the third discusses the post-growth treatment that can be applied to the nanoparticles. The whole is rounded off by a review of future perspectives and the challenges facing the scientific and industrial communities. An excellent resource for anyone working with the synthesis of nanoparticles, both in academia and industry.

Nanomaterials in Biomass Conversion: Advances and Applications for Bioenergy, Biofuels and Bio-based Products critically reviews the basic principles through to the latest advances in the emerging field of nanotechnology for the production of biofuels and bioenergy. Divided into 3 parts, the first five chapters explain the fundamentals of nanomaterials, their properties, characterization, and basic processes for synthesis. Part 2, which constitutes the majority of the book, reviews the various methods and technologies for the conversion of biomass to bioenergy, biofuels, and value-added products using nanomaterials. This includes homogeneous and heterogeneous nano-catalytic systems, nano-photocatalytic conversion, nanomaterial-assisted anaerobic digestion, nanoparticles-immobilized enzymes conversion, the production of biogas, volatile fatty acids, and value-added products, and in carbon capture and conversion to sustainable energy products, as well as the potential of nano-biochar, nano-cellulose, and other nanomaterials in microbial fuel cells, bioelectrochemical systems, and batteries. Finally, Part 3 addresses the techno-economics and financial viability in the context of the circular economy, risk related to toxicology, stability, and environmental impacts, and considers the various challenges and future opportunities of biomass conversion through nanomaterials. Nanomaterials in Biomass Conversion is an invaluable resource for researchers and engineers involved in the production of bioenergy, biofuel, and bioproducts, and will also be of benefit to those interested in environmental remediation, pollution management, and cleaner energy production. Critically examines the role of nanomaterials in the management of waste biomass as applied to bioenergy and biofuels Explains various nanotechnological methods for the conversion of waste biomass into value-added products Discusses the basic principles, operational aspects, ongoing developments, and future perspectives related to the applications of nanotechnologies and nanomaterials in biomass conversion Provides solutions to the key challenges of nanotechnologies and nanomaterials in the conversion of biomass, along with future challenges and risks

This book focuses on the prospects of fresh market waste management in developing countries. It characterizes fresh market wastewater and solid wastes, and highlights the human health impact of corresponding waste management practices. With regard to treatment technologies, the book discusses the anaerobic digestion of fresh solid wastes; the application of natural coagulants for wastewater treatment; the remediation of xenobiotics in wastewater using nanotechnology; and biofilter aquaponic systems for nutrient removal. All of these technologies are recent innovations, offer several concrete advantages, and can be applied in developing countries as non-central treatment systems. In addition, the book covers electricity production from fresh solid wastes using microbial fuel cells, demonstrating the potential held by recycling fresh market wastewater and solid wastes.

The first overview of this topic begins with some historical aspects and a survey of the principles of the gas aggregation method. The second part covers modifications of this method resulting in different specialized techniques, while the third discusses the post-growth treatment that can be applied to the nanoparticles. The whole is rounded off by a review of future perspectives and the challenges facing the scientific and industrial communities. An excellent resource for anyone working with the synthesis of nanoparticles, both in academia and industry.

Technical plasmas have a wide range of industrial applications. The Encyclopedia of Plasma Technology covers all aspects of plasma technology from the fundamentals to a range of applications across a large number of industries and disciplines. Topics covered include nanotechnology, solar cell technology, biomedical and clinical applications, electronic materials, sustainability, and clean technologies. The book bridges materials science, industrial chemistry, physics, and engineering, making it a must have for researchers in industry and academia, as well as those working on application-oriented plasma technologies. Also Available Online This Taylor & Francis encyclopedia is also available through online subscription, offering a variety of extra benefits for researchers, students, and librarians, including: Citation tracking and alerts Active reference linking Saved searches and marked lists HTML and PDF format options Contact Taylor and Francis for more information or to inquire about subscription options and print/online combination packages. US: (Tel) 1.888.318.2367; (E-mail) e-reference@taylorandfrancis.com International: (Tel) +44 (0) 20 7017 6062; (E-mail) online.sales@tandf.co.uk

Nanomaterials are important tools for enabling technological progress as they can provide dramatically different properties as compared to the bulk counterparts. The field of nanoparticles is one of the most investigated within nanomaterials, thanks to the existing, relatively simple, means of manufacturing. In this thesis, high-power pulsed hollow cathode sputtering is used to nucleate and grow magnetic nanoparticles in a plasma. This sputtering technique provides a high degree of ionization of the sputtered material, which has previously been shown to aid in the growth of the nanoparticles. The magnetic properties of the particles are utilized and makes it possible for the grown particles to act as building blocks for self-assembly into more sophisticated nano structures, particularly when an external magnetic field is applied. These structures created are termed “nanowires” or “nanotrusses”, depending on the level of branching and inter-linking that occurs. Several different elements have been investigated in this thesis. In a novel approach, it is shown how nanoparticles with more advanced structures, and containing material from two hollow cathodes, can be fabricated using high-power pulses. The dual-element particles are achieved by using two distinct and individual elemental cathodes, and a pulse process that allows tuning of individual pulses separately to them. Nanoparticles grown and investigated are Fe, Ni, Pt, Fe-Ni and Ni-Pt. Alternatively, the addition of oxygen to the process allows the formation of oxide or hybrid metal oxide – metal particles. For all nanoparticles containing several elements, it is demonstrated that the stoichiometry can be easily varied, either by the amount of reactive gas let into the process or by tuning the amount of sputtered material through adjusting the electric power supplied to the different cathodes. One aim of the presented work is to find a suitable material for the use as a catalyst in the production of H2 gas through the process of water splitting. H2 is a good candidate to replace fossil fuels as an energy carrier. However, rare elements (such as Ir or Pt) needs to be used as the catalyst, otherwise a high overpotential is required for the splitting to occur, leading to a low efficiency. This work demonstrates a possible route to avoid this, by using nanomaterials to increase the surface-to-volume ratio, as well as optimizing the elemental ratio between different materials to lower the amount of noble elements required.

Plasma technology can facilitate the fabrication of nanomaterials and nanoscale structures. On the other hand, nanotechnology could be possibly used in plasma science. Several advanced nanomaterials and nanodevices could be used to fabricate nanoplasma (nanoscale plasma), such as nanoelectrodes, nanoantennae, nanolasers, nanoreactors, nanomagnets, nanosensors, nanobatteries, nanogenerator and supercapacitors. This book provides information on fundamental design concepts and promising applications of nanoplasma. It explains how, for the next generation of electronic devices with high data rate communications, a high-speed operation of electronic switches could be attained using nanoplasma. Similarly, in the field of heath and aesthetics, nanoplasma can be used as a non-surgical localized treatments for the face and neck, such as eyelid correction. In addition, various kinds of advanced nanostructures can be fabricated using the plasma technology Outlines the main properties of nanotechnology-enhanced plasma Discusses major applications of plasma technology Assesses the major challenges of manufacturing nanoplasma on an industrial scale