[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

Co-Ni films are widely used in electronics industry for their excellent magnetic, mechanical and electrical properties. In this work, the influence of substrate type and deposition parameters on the morphologies of electroplating Co-Ni nanostructures was investigated. It was found that scallop shell-like Co-Ni depositions could be fabricated on copper wafers. The tendency to form the scallop shell-like depositions increased with increase of deposition time and current density. While on silicon wafers, scallop shell-like Co-Ni depositions could not form. Only acupuncture-like nanostructures could be fabricated on silicon wafers at a high current density.

Electrodeposition of Co-Ni nanostructures

The formation and growth of intermetallic compounds of Sn-2.0Ag-2.5Zn solder on Cu and Ni substrates after soldering and subsequent aging process have been investigated in this study. Ni films were electrodeposited on copper substrates. The interfacial micrographs of solder joints prepared at 250°C for 15s and aged for 24h, 96h and 216 h respectively. Double-layer IMC composed with Cu5Zn8 and Ag3Sn was observed at the interface of Sn-2Ag-2.5Zn and Cu couple, which was compact and acted as a barrier layer to confine the further growth of Cu-Sn IMC. On Ni barrier layer, a thin Ni3Sn4 film appeared between the solder and Ni-W layer, which is thin and smooth. After aging process, the thickness increased slowly and steadily, which revealed that Ni barrier layer acts as a promising barrier layer.

Formation and growth of intermetallic compounds of Sn-2Ag-2.5Zn on Cu and Ni substrates

A novel low-temperature solid-state bonding method that Cu microcones coated with Ag and Ag buffer has been proposed. Thin Ag layer was used to prevent the oxidation of Cu microcones and Ag layer of several micrometers was used as a buffer layer between Cu microcones and Cu bumps. No brittle IMCs formed in the interfaces.

A low-temperature solid-state bonding method using Ag-modified Cu microcones and Ag buffer

In this paper, the effect of reflow time on shear property of Sn-9Zn solder bumps was studied. The Sn-9Zn solder bumps were prepared by two step electroplating method. With the increase of reflow time, the shear strength decreased first and then increased. The change of shear strength was closely related to the formation of intermetallic compounds (IMCs). Scanning electron microscope (SEM) and Energy dispersive spectrometer (EDS) were used to analyze the composition and morphology of IMCs. The results indicated that IMCs were thickening with increasing reflow time and the morphology was flat, while IMCs thickness decreased and the morphology became fluctuant and unconsolidated when the reflow time extended to 20 min. The change trend of the shear strength was consistent with that of IMCs thickness. In addition, bumps fracture occurred inside the solders and dimples were observed on the fracture surface, which indicated that the solder bumps still had good ductility after reflow.

Effect of reflow time on shear property of Sn-9Zn solder bumps

Three different Cu films using three commercial levelers (leveler A, leveler B and leveler C) were obtained by electrodeposition, and the films were heat treated at different temperatures. The effects of three different levelers on the electrical properties of Cu films during annealing were compared from the aspects of microstructure and impurities. After heat treatment at 200°C for 10 min, the sheet resistances of the three Cu films obtained by leveler A, leveler B and leveler C dropped to 84.55%, 82.2% and 83.53% of the initial values respectively. The impurity content of these films after heat treatment varies greatly. The impurity distribution along the depth direction is not uniform with an oscillation phenomenon. In addition, this work will provide a basis for obtaining Cu films with excellent electrical properties in electronic industry applications.

Ming Li

Papers

Electrodeposition of Co-Ni nanostructures

Formation and growth of intermetallic compounds of Sn-2Ag-2.5Zn on Cu and Ni substrates

A low-temperature solid-state bonding method using Ag-modified Cu microcones and Ag buffer

Effect of reflow time on shear property of Sn-9Zn solder bumps

Effect of leveler on electrical resistance and microstructural of electroplated copper after heat treatment