Eutectic solidification in near-eutectic Al-13 wt pct Si casting alloys and the effect of trace addition of boron or strontium on it have been investigated using thermal analysis and microstructural characterization.I...Eutectic solidification in near-eutectic Al-13 wt pct Si casting alloys and the effect of trace addition of boron or strontium on it have been investigated using thermal analysis and microstructural characterization.In unmodified alloy,dual eutectic structure has been observed.The coarse eutectic(dendrite-like Al+coarse Si flakes)is formed above the equilibrium temperature of eutectic(Al+Si)reaction(577℃).The coarse eutectic(CE)grains nucleate from the primary silicon particles formed earlier due to local enrichment of silicon solute and grow in a divorced mode between the dendritic Al phase and large silicon flakes.The fine eutectic(FE)grains nucleate later on other potential sites activated by melt undercooling and grow in coupled-growing mode with the silicon crystals as fine flakes.The formation of the FE grains is favored in the alloys containing boron because of a great number of potential nucleation sites being added from boron-containing particles.Addition of strontium to the alloys restrains completely the formation of primary silicon particles and hence limits the nucleation of the CE.This is because the eutectic point has moved far enough to make the alloy,at this composition(Al-13 wt pct Si),hypo-eutectic.Local cooling rate during solidification has an important influence on competition formation of these two eutectics.展开更多
Miniaturization has been an everlasting theme in the development of semiconductor lasers.One important breakthrough in this process in recent years is the use of metal-dielectric composite structures that made truly s...Miniaturization has been an everlasting theme in the development of semiconductor lasers.One important breakthrough in this process in recent years is the use of metal-dielectric composite structures that made truly subwavelength lasers possible.Many different designs of metallic cavity semiconductor nanolasers have been proposed and demonstrated.In this article,we will review some of the most exciting progresses in this newly emerging field.In particular,we will focus on metallic-cavity nanolasers with volume smaller than wavelength cubed under electrical injection with emphasis on high-temperature operation.Such devices will serve as an important component in the future integrated nanophotonic systems due to its ultra-small size.展开更多
基金supported by the National Natural Science Foundation of China under Grant No.50771031the Research Foundation of Southeast University under Grant No.XJ0612238
文摘Eutectic solidification in near-eutectic Al-13 wt pct Si casting alloys and the effect of trace addition of boron or strontium on it have been investigated using thermal analysis and microstructural characterization.In unmodified alloy,dual eutectic structure has been observed.The coarse eutectic(dendrite-like Al+coarse Si flakes)is formed above the equilibrium temperature of eutectic(Al+Si)reaction(577℃).The coarse eutectic(CE)grains nucleate from the primary silicon particles formed earlier due to local enrichment of silicon solute and grow in a divorced mode between the dendritic Al phase and large silicon flakes.The fine eutectic(FE)grains nucleate later on other potential sites activated by melt undercooling and grow in coupled-growing mode with the silicon crystals as fine flakes.The formation of the FE grains is favored in the alloys containing boron because of a great number of potential nucleation sites being added from boron-containing particles.Addition of strontium to the alloys restrains completely the formation of primary silicon particles and hence limits the nucleation of the CE.This is because the eutectic point has moved far enough to make the alloy,at this composition(Al-13 wt pct Si),hypo-eutectic.Local cooling rate during solidification has an important influence on competition formation of these two eutectics.
基金Research reported in this article in the authors group was supported by the Defense Advanced Research Project Agency program Nanoscale Architectures of Coherent Hyper-Optical Sources(grant no.W911-NF07-1-0314)by the Air Force Office of Scientific Research(grant no.FA9550-10-1-0444,Gernot Pomrenke)We thank Martin Hill for his collaboration over the last few years.
文摘Miniaturization has been an everlasting theme in the development of semiconductor lasers.One important breakthrough in this process in recent years is the use of metal-dielectric composite structures that made truly subwavelength lasers possible.Many different designs of metallic cavity semiconductor nanolasers have been proposed and demonstrated.In this article,we will review some of the most exciting progresses in this newly emerging field.In particular,we will focus on metallic-cavity nanolasers with volume smaller than wavelength cubed under electrical injection with emphasis on high-temperature operation.Such devices will serve as an important component in the future integrated nanophotonic systems due to its ultra-small size.
