[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

This review article aims to provide an updated and comprehensive description of the development of the Electric Current Activated/assisted Sintering technique (ECAS) for the obtainment of dense materials including nanostructured ones. The use of ECAS for pure sintering purposes, when starting from already synthesized powders promoters, and to obtain the desired material by simultaneously performing synthesis and consolidation in one-step is reviewed. Specifically, more than a thousand papers published on this subject during the past decades are taken into account. The experimental procedures, formation mechanisms, characteristics, and functionality of a wide spectrum of dense materials fabricated by ECAS are presented. The influence of the most important operating parameters (i.e. current intensity, temperature, processing time, etc.) on product characteristics and process dynamics is reviewed for a large family of materials including ceramics, intermetallics, metal–ceramic and ceramic–ceramic composites. In this review, systems where synthesis and densification stages occur simultaneously, i.e. a fully dense product is formed immediately after reaction completion, as well as those ones for which a satisfactory densification degree is reached only by maintaining the application of the electric current once the full reaction conversion is obtained, are identified. In addition, emphasis is given to the obtainment of nanostructured dense materials due to their rapid progress and wide applications. Specifically, the effect of mechanical activation by ball milling of starting powders on ECAS process dynamics and product characteristics (i.e. density and microstructure) is analysed. The emerging theme from the large majority of the reviewed investigations is the comparison of ECAS over conventional methods including pressureless sintering, hot pressing, and others. Theoretical analysis pertaining to such technique is also proposed following the last results obtained on this topic.

Consolidation/synthesis of materials by electric current activated/assisted sintering

Damascene copper electroplating for on-chip interconnections, a process that we conceived and developed in the early 1990s, makes it possible to fill submicron trenches and vias with copper without creating a void or a seam and has thus proven superior to other technologies of copper deposition. We discuss here the relationship of additives in the plating bath to superfilling, the phenomenon that results in superconformal coverage, and we present a numerical model which accounts for the experimentally observed profile evolution of the plated metal.

Damascene copper electroplating for chip interconnections

Hydrogen evolution reaction (HER) in alkaline medium is currently a point of focus for sustainable development of hydrogen as an alternative clean fuel for various energy systems, but suffers from sluggish reaction kinetics due to additional water dissociation step. So, the state-of-the-art catalysts performing well in acidic media lose considerable catalytic performance in alkaline media. This review summarizes the recent developments to overcome the kinetics issues of alkaline HER, synthesis of materials with modified morphologies, and electronic structures to tune the active sites and their applications as efficient catalysts for HER. It first explains the fundamentals and electrochemistry of HER and then outlines the requirements for an efficient and stable catalyst in alkaline medium. The challenges with alkaline HER and limitation with the electrocatalysts along with prospective solutions are then highlighted. It further describes the synthesis methods of advanced nanostructures based on carbon, noble, and inexpensive metals and their heterogeneous structures. These heterogeneous structures provide some ideal systems for analyzing the role of structure and synergy on alkaline HER catalysis. At the end, it provides the concluding remarks and future perspectives that can be helpful for tuning the catalysts active-sites with improved electrochemical efficiencies in future.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201700464

Electrocatalysts for Hydrogen Evolution in Alkaline Electrolytes: Mechanisms, Challenges, and Prospective Solutions

Hybrid supercapacitors with their improved performance in energy density without altering their power density have been in trend since recent years. The hybrid supercapacitor delivers higher specific capacitance in comparison to the existing electric double layer capacitor (EDLC) and pseudocapacitors. Generally, the asymmetric behavior of hybrid supercapacitors which is the combination of EDLC and pseudocapacitor acts as an enhancer in its respective capacitance values. This asymmetric approach marks a new beginning towards the much-needed pollution free, long lasting and proficient energy-storing performance. Corresponding to their utilization in hybrid electric vehicles and similar sort of power necessity based devices; the research in developing new advanced storage devices finds an enormous and vast future ahead. The most significant factor for the energy efficient applications demands a considerably higher ratio of surface to the volume by incorporation of new materials. This review article gives an overview of recent advances in the development of hybrid supercapacitors, storage mechanism, criteria of formation, components, different electrode and electrolyte materials, electrochemical profile assessment, design fabrication and their applications.

A review on recent advances in hybrid supercapacitors: Design, fabrication and applications

The effect of polyethylene glycols upon copper electrodeposition in methanesulfonate electrolytes is discussed in this paper. By means of linear sweep voltammetry and electrochemical impedance spectroscopy, it is found that polyethylene glycols in methanesulfonat electrolytes have very different behavior from that in traditional sulfuric electrolytes. PEG can adsorb on electrode surface in absent of chloride ion. The presence of chloride would destroy PEG adsorption to the electrode surface. The impedance shows that PEG can inhibit the reactions Cu2+→Cu+ and Cu+→Cu. The special effect of PEG in methanesulfonate electrolyte is probably related to methanesulfonic radical.

The effect of polyethylene glycols upon copper electrodeposition in methanesulfonate electrolytes

The amorphous Ni(P) layer in traditional Electroless Ni/Electroless Pd/Immersion Au (ENEPIG) surface finish has an adverse effect on its performance in high speed circuits due to the relatively high electrical resistance which will cause impact to the signal integrity. By limiting the thickness of Ni(P)layerless than 1μm in ultrathin ENEPIG, the impedance can be significantly reduced and its solderability and corrosion resistance remain as good as those of traditional ENEPIG. In this article, two kinds of ultrathin ENEPIG with Ni(P) layer thicknesses of 0.112 and 0.185μm respectively were reflowed with commercial Sn-3.0Ag-0.5Cu solder. After that the morphology and growth of interfacial IMC were investigated using SEM and EDS analysis. Solder ball shear test, drop test and thermal cycle test (TCT) were then conducted to evaluate their bonding strength as well as performance in board level reliability tests. Results showed that although Ni(P) layer was depleted soon in ultrathin ENEPIG samples, the Ni-Sn-P layer could still act as a diffusion barrier and hinder the growth of brittle IMC, which contributed a lot to the bonding strength. Ultrathin ENEPIG samples with 0.185μm Ni(P) layer survived both TCT and drop test and showed better reliability than electroplated Ni/Au in drop test and better resistance to thermal fatigue than OSP in TCT, indicating that ultrathin ENEPIG could satisfy the reliability requirement for actual application.

Effect of Ni(P) thickness of ultrathin ENEPIG on the interfacial reaction and board level reliability of solder joints

With the increasing connection density of ICs, the technology of flip chip packaging and stacked-die packaging bounded by bumping are gradually replacing the traditional wire bonding to become one of the main styles of the package. And as one of the critical technology the technology of electroplating copper pillar wins more and more concern. This paper concerns about the influence of the electroplating additives which includes accelerator, leveler and the density of electroplating current to the forming of copper pillar. And by adjusting the quantity of the additives and the density of electroplating current, we got the satisfactory copper pillar with the smooth surface.

The study on the shaping of electroplated copper pillar bumping

Titania nanotubes have been widely used in gas sensing applications such as hydrogen sensors. Doping titania nanotubes with other elements are expected to provide tunable band-gap and thus favorable hydrogen sensing properties. In this work, Nb, Zr-doped titania nanotube arrays in crystallized states were fabricated on alloy substrates through anodization and heat-treatment. And doped nanotube sensors were assembled on PCB. Corresponding anodization and sensor fabrication processes were investigated and hydrogen sensing properties of the nanotube sensors were tested in hydrogen atmosphere. Experimental results indicated that the content of Zr had a great impact on the growth, thermal stability and hydrogen sensing property of regular nanotube arrays. The Nb-doped nanotubes demonstrated a good hydrogen sensing performance.

Ming Li

Papers

The effect of polyethylene glycols upon copper electrodeposition in methanesulfonate electrolytes

Effect of Ni(P) thickness of ultrathin ENEPIG on the interfacial reaction and board level reliability of solder joints

The study on the shaping of electroplated copper pillar bumping

Fabrication and hydrogen sensing properties of doped titania nanotubes

Thermal stability and electrical characteristics of NiSi films with electroplated Ni(W) alloy