Costas P. Grigoropoulos Cambridge University Press 2009
Lasers are effective material processing tools that offer distinct advantages, including choice of wavelength and pulse width to match the target material properties as well as one-step direct and locally confined structural modification. Understanding the evolution of the energy coupling with the target and the induced phase change transformations is critical for improving the quality of micromachining and microprocessing. As current technology is pushed to ever smaller dimensions, the lasers become a truly enabling solution for reducing thermomechanical damage and facilitating heterogeneous integration of components into functional devices. This is especially important in cases where conventional thermo-chemo-mechanical treatment processes are ineffective. Component microfabrication with basic dimensions in the few-microns range via laser irradiation has been implemented successfully in the industrial environment. Beyond this, there is an increasing need to advance the science and technology of laser processing to the nano-scale regime. The book focuses on examining the transport mechanisms involved in the laser material interactions in the context of microfabrication.
The material was developed in the graduate course of Laser Processing and Diagnostics Professor Grigoropoulos taught in Berkeley over the years and drew from the research done at the Laser Thermal Laboratory. The text aims at providing to scientists, engineers and graduate students a comprehensive review of progress and state of the art in the field by linking fundamental phenomena with modern applications.
Seung-Hwan Ko, and Grigoropoulos, C.P. (Editors) Royal Society of Chemistry Publishing 2014 Energy has been the major global issue in our society. Since the Fukushima nuclear disaster in 2011, future renewable energy development has been viewed through the safety prism. Non-nuclear based, safe and sustainable energy sources have therefore attracted tremendous attention. Research studies on energy devices have traditionally focused on the development of new materials for components such as anode, cathode, dye, electrolyte, catalyst. However, in the last decade, new material development has been sluggish as it is admittedly very hard to overcome constraints posed by the intrinsic material structure. Therefore, researchers have been seeking new ground-breaking approaches by smart design/structuring of known materials through three-dimensional (3D) multi-scale hierarchical nano-architectures comprised of nanoscale building blocks. Recently, research in 3D branched hierarchical nanowire structures is booming among researchers in various energy device fields, including energy conversion, storage and consumption. 3D branched hierarchical nanowire structures that possess high surface area and offer direct transport pathways for charge carriers are especially attractive for energy applications. More specifically, 3D branched hierarchical nanowires improve light absorption due to the increased optical path as well as additional light trapping through reduced reflection and multiple scattering in comparison to 1D nanowire arrays, that are beneficial for solar energy harvesting applications. The high surface area can also increase surface activity and electrolyte infiltration in energy storage devices. The direct charge carrier transport pathway in both the trunks and branches boosts the charge collection efficiency. These fascinating properties of branched hierarchical nanowire structures have indeed many ideal characteristics in energy devices. This book focuses on the recent developments in hierarchical nanostructuring, especially for highly efficient energy device applications. Hierarchical nanostructures usually entail a combination of multi-scale, multi-dimensional nanostructures such as nanowires, nanoparticles, nanosheets and nanopores. Because of the ability to tailor the architecture, synergistically combine functionalities and thereby specifically tune the transport properties, hierarchical nanostructures are expected to overcome the limitations of single scale nanostructures for achieving enhanced performance. Surface characteristics are of primary concern in most energy devices where maximizing efficiency can be achieved by either new material development or functional structuring. In this respect, hierarchical functional nanostructuring is particularly effective for achieving surface area increase and favourable electrical properties. The energy devices covered in this book are: 1) energy generation devices (solar cells (DSSC, OPV), fuel cells, piezoelectric, thermoelectric, water splitting etc.), 2) energy storage devices (secondary batteries, super capacitors etc.), 3) energy efficient electronics (displays, sensors, etc.). The hierarchical nanostructuring routes include construction of highly porous metal organic frameworks, nanoparticle assembly with defined pore size, and synthesis of multiple generation highly branched nanowire trees.
The hierarchical nanostructure research has bright future for solving current limitations of energy devices. The ultimate goal is to push energy devices towards practical applications, which requires the development of devices with high efficiency, low cost and long lifespan. It is hoped that this book will provide an account of state of the art research trends and a perspective on hierarchical nanostructures for energy device applications.