Nanoparticle Engineering for Chemical-Mechanical Planarization

Increasing reliance on electronic devices demands products with high performance and efficiency. Such devices can be realized through the advent of nanoparticle technology. This book explains the physicochemical properties of nanoparticles according to each step in the chemical mechanical planarization (CMP) process, including dielectric CMP, shallow trend isolation CMP, metal CMP, poly isolation CMP, and noble metal CMP. The authors provide a detailed guide to nanoparticle engineering of novel CMP slurry for next-generation nanoscale devices below the 60nm design rule. This comprehensive text also presents design techniques using polymeric additives to improve CMP performance

Crack-Growth Behavior in Thermal Barrier Coatings with Cyclic Thermal Exposure

Crack-growth behavior in yttria-stabilized zirconia-based thermal barrier coatings (TBCs) is investigated through a cyclic thermal fatigue (CTF) test to understand TBCs’ failure mechanisms. Initial cracks were introduced on the coatings’ top surface and cross section using the micro-indentation technique. The results show that crack length in the surface-cracked TBCs grew parabolically with the number of cycles in the CTF test. Failure in the surface-cracked TBC was dependent on the initial crack length formed with different loading levels, suggesting the existence of a threshold surface crack length. For the cross section, the horizontal crack length increased in a similar manner as observed in the surface. By contrast, in the vertical direction, the crack did not grow very much with CTF testing. An analytical model is proposed to explain the experimentally-observed crack-growth behavior

Crack-Resistance Behavior of an Encapsulated, Healing Agent Embedded Buffer Layer on Self-Healing Thermal Barrier Coatings

In this work, a novel thermal barrier coating (TBC) system is proposed that embeds silicon particles in coating as a crack-healing agent. The healing agent is encapsulated to avoid unintended reactions and premature oxidation. Thermal durability of the developed TBCs is evaluated through cyclic thermal fatigue and jet engine thermal shock tests. Moreover, artificial cracks are introduced into the buffer layer’s cross section using a microhardness indentation method. Then, the indented TBC specimens are subject to heat treatment to investigate their crack-resisting behavior in detail. The TBC specimens with the embedded healing agents exhibit a relatively better thermal fatigue resistance than the conventional TBCs. The encapsulated healing agent protects rapid large crack openings under thermal shock conditions. Different crack-resisting behaviors and mechanisms are proposed depending on the embedding healing agents

Germanium coating boosts lithium uptake in Si nanotube battery anodes

Si nanotubes for reversible alloying reaction with lithium are able to accommodate large volume changes and offer improved cycle retention and reliable response when incorporated into battery anodes. However, Si nanotubes electrode exhibits poor rate capability because of its inherently low electron conductivity and Li ion diffusivity. Si/Ge double-layered nanotubes electrode show promise to improve structural stability and electrochemical kinetics, as compared to homogeneous Si nanotube arrays. The mechanism explaining the enhancement in the rate capabilities is here revealed by means of electrochemical impedance methods. Ge shell efficiently provides electrons to the active materials which increase the semiconductor conductivity thereby assisting Li+ ion incorporation. The charge transfer resistance which accounts for the interfacial Li+ ion intake from the electrolyte is reduced by two orders of magnitude, implying the key role of Ge layer as electron supplier. Other resistive processes hindering the electrode charge/discharge process are observed to show comparable values for Si and Si/Ge array electrodes

Thermal durability and fracture behavior of layered Yb-Gd-Y-based thermal barrier coatings in thermal cyclic exposure

The effects of structural design on the thermal durability and fracture behavior of Yb-Gd-Y-based thermal barrier coatings (TBCs) were investigated through thermal cyclic exposure tests, such as furnace cyclic thermal fatigue (FCTF) and jet engine thermal shock (JETS) tests. The effects of composition in the bond coat and feedstock purity for the buffer layer on its lifetime performance were also examined. To overcome the drawbacks of Yb-Gd-Y-based material with inferior thermal durability due to poor mechanical properties and low coefficient of thermal expansion, a buffer layer was introduced in the Yb-Gd-Y-based TBC systems. In FCTF tests, the TBCs with the buffer layer showed a longer lifetime performance than those without the buffer layer, showing the longest thermal durability in the TBC with the Co-Ni-based bond coat and the buffer layer of regular purity. In JETS tests, the TBC with the Ni-based bond coat and the buffer layer of high purity showed a sound condition after 2000 cycles, showing better thermal durability for TBC with the Co-Ni-based bond coat rather than that with the Ni-based bond coat in the single layer coating without the buffer layer. The buffer layer effectively enhanced the thermal durability in slow temperature change (in the FCTF test), while the bond-coat composition and the feedstock purity for the buffer layer were found to be important factor to improve the thermal durability of the TBC in fast temperature change (in the JEET test). Finally, these research findings allow us to control the structure, composition, and feedstock purity in TBC system for improving the thermal durability in cyclic thermal environments

Microstructure design for blended feedstock and its thermal durability in lanthanum zirconate based thermal barrier coatings

The effects of microstructure design on the lifetime performance of lanthanum zirconate (La2Zr2O7; LZO)-based thermal barrier coatings (TBCs) were investigated through various thermal exposure tests, such as furnace cyclic thermal fatigue, thermal shock, and jet engine thermal shock. To improve the thermal durability of LZO-based TBCs, composite top coats using two feedstock powders of LZO and 8 wt.% yttria-doped stabilized zirconia (8YSZ) were prepared by mixing in different volume ratios (50:50 and 25:75, respectively). In addition, buffer layers were introduced in layered LZO-based TBCs deposited using an air-plasma spray method. The TBC with the double buffer layer showed the best thermal cycle performance among all samples in all tests. For applications with relatively slow cooling rates, the thermal durability in single-layer TBCs is more effectively enhanced by controlling a composition ratio in the blended powder, better than introducing a single buffer layer. For applications with relatively fast cooling rates, the thermal durability can be effectively improved by introducing a buffer layer than controlling a composition in the top coat, since the buffer layer provides fast localized stress relief due to its high strain compliance. These research findings allow us to control the TBC structure, and the buffer layer is efficient in improving thermal durability in cyclic thermal environments

WO 3 nanofibrous backbone scaffolds for enhanced optical absorbance and charge transport in metal oxide (Fe 2 O 3 , BiVO 4 ) semiconductor photoanodes towards solar fuel generation

Producing clean fuel (O2 and H2) using semiconductors through solar driven water splitting process has been considered as a promising technology to mitigate the existing environmental issues. Unlike the conventional single photoabsorbers, heterostructured semiconductors exhibit the merits of improved solar light photon harvesting and rapid charge separation, which are anticipated to result in high quantum yield of solar fuel generation in photoelectrochemical (PEC) cells. In this report, we demonstrate the electrospun derived WO3 backbone fibrous channel as heteropartner to the primary photoabsorber (Fe2O3 and BiVO4) for promoting the electron transport from charge injection point to charge collector as well as photoholes to the electrolyte. We examine structure, optical, photoelectrochemical and charge transfer property of Fe2O3/WO3 and BiVO4/WO3 electrodes. These results were compared with directly coated Fe2O3 and BiVO4 photoabsorber onto conducting substrate without WO3 backbone. The optical results showed that the absorbance and visible light activity of Fe2O3 and BiVO4 is significantly improved by WO3 backbone fibers due to high amount of photo absorber loading. In addition, one dimensional (1-D) WO3 fibers beneficially enhance the optical path length to the photoanode through light scattering mechanism. The electrochemical impedance analysis exhibits WO3 nanofiber backbone reduces charge transfer resistance at Fe2O3 and BiVO4 by rapid charge collection and charge separation compare to backbone-free Fe2O3 and BiVO4. As a result, Fe2O3/WO3 and BiVO4/WO3 fibrous hetero interface structures showed fourfold higher photocurrent generation from PEC cell

Soft, curved electrode systems capable of integration on the auricle as a persistent brain–computer interface

Recent advances in electrodes for noninvasive recording of electroencephalograms expand opportunities collecting such data for diagnosis of neurological disorders and brain–computer interfaces. Existing technologies, however, cannot be used effectively in continuous, uninterrupted modes for more than a few days due to irritation and irreversible degradation in the electrical and mechanical properties of the skin interface. Here we introduce a soft, foldable collection of electrodes in open, fractal mesh geometries that can mount directly and chronically on the complex surface topology of the auricle and the mastoid, to provide high-fidelity and long-term capture of electroencephalograms in ways that avoid any significant thermal, electrical, or mechanical loading of the skin. Experimental and computational studies establish the fundamental aspects of the bending and stretching mechanics that enable this type of intimate integration on the highly irregular and textured surfaces of the auricle. Cell level tests and thermal imaging studies establish the biocompatibility and wearability of such systems, with examples of high-quality measurements over periods of 2 wk with devices that remain mounted throughout daily activities including vigorous exercise, swimming, sleeping, and bathing. Demonstrations include a text speller with a steady-state visually evoked potential-based brain–computer interface and elicitation of an event-related potential (P300 wave)