Recently, the size of solder bump interconnects have been significantly reduced with the advent of highdensity packaging, and thus the evaluation of electromigration in solder bumps has become necessary. The present paper proposes a simple method to test the electromigration resistance of Pb-free solders. One of the key points of the present method is the fabrication of a simple solder sample that can produce sufficient current density to cause electromigration. Moreover, the actual local temperature of a small area subjected to electromigration in the sample was measured by a direct method. A right-angled diamondshaped hole was introduced in a thin film of solder using a focused-ion-beam system. A direct current was supplied to the film far from the hole, perpendicular to the diagonal of the hole. In this way, the current density was concentrated near to the corner of the hole, and the value of this was obtained through a theoretical analysis. It was noted that the steady temperature in the film along a line extending from the diagonal, remained constant, although the current density decreased gradually far from the corner. Therefore, the temperature at a position near the corner, where electromigration takes place, can easily be found by measuring the temperature far from the corner. The temperature was measured directly under current flow conditions by utilizing the chemical reagents with known melting points. Finally, by measuring the ratio of hillock volume to the time for the current supply as a measure of the atomic flux divergence due to electromigration, the corresponding resistances of some Pb-free solders to electromigration were evaluated.
Autophagy is a conserved cellular degradation process in eukaryotes, in which cytoplasmic components and organelles are digested in vacuoles/ lysosomes. Recently, autophagic degradation of nuclear materials, termed "nucleophagy", has been reported. In the multinucleate filamentous fungus Aspergillus oryzae, a whole nucleus is degraded by nucleophagy after prolonged culture. While developing an H2B-EGFP processing assay for the evaluation of nucleophagy in A. oryzae, we found that nucleophagy is efficiently induced by carbon or nitrogen depletion. Microscopic observations in a carbon depletion condition clearly demonstrated that autophagosomes selectively sequester a particular nucleus, despite the presence of multiple nuclei in the same cell. Furthermore, AoNsp1, the A. oryzae homolog of the yeast nucleoporin Nsp1p, mainly localized at the nuclear periphery, but its localization was restricted to the opposite side of the autophagosome being formed around a nucleus. In contrast, the perinuclear ER visualized with the calnexin AoClxA was not morphologically affected by nucleophagy. The findings of nucleophagy-inducing conditions enabled us to characterize the morphological process of autophagic degradation of a whole nucleus in multinucleate cells.
We have used a pulse-injection method to fix multi-walled carbon nanotubes (MWNTs) onto hydrogen-terminated Si(100) surfaces. Using scanning-tunneling-microscopy (STM), we first tested several kinds of solvents for organic molecules which were pulse-injected onto the H-terminated Si(100) surfaces. Most of the solvent molecules of hexane and chloroform were desorbed from the surfaces after annealing the substrates, which indicates that they are suitable for fixing molecules onto the surface. Then, we fixed MWNTs which were dispersed in hexane and pulse-injected onto the H-terminated surface. An isolated MWNT was observed by STM and was investigated by scanning tunneling spectroscopy (STS). The STS spectra revealed a metallic feature of the particular MWNT.
General thermometers pose difficulty in measuring the actual surface temperature of a
micro-area, especially in electronic devices. In the present study, an approach to direct measurement
of surface temperature is described, which utilizes the potential of melting point of different chemical
reagents. The present technique exhibits a temperature resolution of about 5○C and the measurable
maximum temperature of about 200○C. A short comment on the application of the technique to
determine the actual surface temperature of small areas in some engineering applications is also
stated.
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