We achieve robust bonding of Cu wires to Cu pads on polyimide with silver nanopaste cured at 373 K. The paste is prepared by simply condensing Ag nanoparticle (NP) solution via centrifuging. The bonding is formed by solid state sintering of Ag NPs through neck growth and direct metallic bonding between clean Ag–Cu interfaces. Both experiment and Monte Carlo simulation confirm that the melting point of joint clusters increases during sintering. This creates improved bonds for use at an elevated operating temperature using Ag NPs.
We consider the problem of synchronizing a general complex network by means of the on-off coupling strategy; in this case, the on-off time scale is varied from a very small to a very large value. In particular, we find that when the time scale is comparable to that of node dynamics, synchronization can also be achieved and greatly optimized for the upper bound of the stability region which nearly disappears, and the synchronization speed is accelerated a lot, independent of network topologies. Our study indicates that the time scale for network variation is of crucial importance for network dynamics and synchronization under the comparable time scale which is much more advantageous over other time scales. Both analysis and experiments confirm the conclusions.
Dodecagonal ZnO microrods were fabricated by vapor transport method. A dodecagonal ZnO microrod with diameter of 6.35 μm was employed as a whispering gallery mode microcavity, the low threshold exciton lasing was stimulated. In another smaller microrod, the electron-hole plasma lasing was observed under intense excitation as the carrier density was larger than the Mott transition density. The interference condition in the dodecagonal cavity was deduced, and the mode structures were investigated. Compared to the hexagonal microcavity with same diameter, the dodecagonal microcavity has higher lasing performance.
Nanojoining, a burgeoning research area, becomes a key manufacturing of complicated nanodevices with functional prefabricated components. In this work, various nanojoining methods are first reviewed. For nanojoining of Ag/Au nanoparticles, three methods are investigated comparatively. Thermal annealing shows a two-step solid state diffusion mechanism. Laser annealing by millisecond pulses displays the thermal activated solid state diffusion. Meanwhile, two effects have been identified in femtosecond laser irradiation with different laser intensities: photofragmentation at rather high intensity (∼1014 W/cm2) and nanojoining at low intensity (∼1010 W/cm2). The photofragmentation forms a large number of tiny nanoparticles with an average size of 10 nm. Control over irradiation conditions at intensities near 1010 W/cm2 results in nanojoining of most of the nanoparticles. This nanojoining is obtained through a nonthermal melting and a surface fusion welding. Joined Au nanoparticles are expected to have numerous applications, such as probes for surface enhance Raman spectroscopy.
An Ag/ZnO microrod/Ag ultraviolet photodetector is fabricated, the ZnO microrod shows a hexagonal whispering gallery cavity structure. Upon a 325 nm ultraviolet illumination, the device shows a high sensitivity of 4 × 10(4) A/W and a high photocurrent gain of 1.5 × 10(5) at 5 V bias. Under different illumination power P, the photocurrent Ilight obeys a power law relation Ilight ∝ P(0.69). The high performance is probably attributed to a Schottky barrier at Ag/ZnO interface and optical whispering gallery mode effect in the ZnO microrod.
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