Silver nanocubes enriched with {100} facets have been extensively used for surface-enhanced Raman scattering. Herein, we report a new water-phase synthesis method for weU-defined Ag nanocubes with tunable sizes via a ...Silver nanocubes enriched with {100} facets have been extensively used for surface-enhanced Raman scattering. Herein, we report a new water-phase synthesis method for weU-defined Ag nanocubes with tunable sizes via a two-step procedure at room temperature. First, irregularly shaped Ag nanoparticles （INPs） were prepared by reducing silver ammonia solution using ethylal. Second, the agglomerated INPs were selectively etched with HNO3 and C1- to yield {100} facet-rich mesoporous Ag nanocubes. The mechanism of Ag-nanocube formation and growth was investigated in detail by elucidating the involved chemical reactions and physical changes at each step during the synthesis. The addition of C1- anions was responsible for facilitating Ag nanoparticle growth by removing surface-adsorbed Ag＋ species, thereby eliminating inter-particle repulsive forces. This agglomeration was found crucial for the subsequent selective oxidation of Ag nanoparticles because the protective agent used, polyvinylpyrrolidone （PVP）, was the most effective one for adsorption on the surfaces of Ag nanoparticles of size greater than approximately 50 nm. Importantly mesopores were found inside the Ag nanocubes; this can be attributed to the unavoidable imperfect packing during the agglomeration of INPs. The newly prepared Ag nanocubes were further used to enhance the Raman signal of rhodamine 6G, which is capable of reducing the detection limitation to 10-16 mol·L-1.展开更多
The diffusion behavior of Cu and Ni atoms undergoing liquidesolid electromigration（L-S EM） was investigated using Cu/Sn/Ni interconnects under a current density of 5.0 103A/cm2 at 250℃. The flowing direction of ele...The diffusion behavior of Cu and Ni atoms undergoing liquidesolid electromigration（L-S EM） was investigated using Cu/Sn/Ni interconnects under a current density of 5.0 103A/cm2 at 250℃. The flowing direction of electrons significantly influences the cross-solder interaction of Cu and Ni atoms, i.e., under downwind diffusion, both Cu and Ni atoms can diffuse to the opposite interfaces; while under upwind diffusion,Cu atoms but not Ni atoms can diffuse to the opposite interface. When electrons flow from the Cu to the Ni, only Cu atoms diffuse to the opposite anode Ni interface, resulting in the transformation of interfacial intermetallic compound（IMC） from Ni3Sn4into（Cu,Ni）6Sn5and further into [（Cu,Ni）6Sn5t Cu6Sn5], while no Ni atoms diffuse to the opposite cathode Cu interface and thus the interfacial Cu6Sn5 remained.When electrons flow from the Ni to the Cu, both Cu and Ni atoms diffuse to the opposite interfaces,resulting in the interfacial IMC transformation from initial Cu6Sn5into（Cu,Ni）6Sn5and further into[（Cu,Ni）6Sn5t（Ni,Cu）3Sn4] at the anode Cu interface while that from initial Ni3Sn4into（Cu,Ni）6Sn5and further into（Ni,Cu）3Sn4at the cathode Ni interface. It is more damaging with electrons flowing from the Cu to the Ni than the other way.展开更多
Solder size effect on early stage interfacial intermetallic compound(IMC) evolution in wetting reaction between Sne3.0Age0.5Cu solder balls and electroless nickel electroless palladium immersion gold(ENEPIG) pads at 2...Solder size effect on early stage interfacial intermetallic compound(IMC) evolution in wetting reaction between Sne3.0Age0.5Cu solder balls and electroless nickel electroless palladium immersion gold(ENEPIG) pads at 250 C was investigated. The interfacial IMCs transformed from initial needle- and rodtype(Cu,Ni)6Sn5to dodecahedron-type(Cu,Ni)6Sn5and then to needle-type(Ni,Cu)3Sn4at the early interfacial reaction stage. Moreover, these IMC transformations occurred earlier in the smaller solder joints, where the decreasing rate of Cu concentration was faster due to the Cu consumption by the formation of interfacial(Cu,Ni)6Sn5. On thermodynamics, the decrease of Cu concentration in liquid solder changed the phase equilibrium at the interface and thus resulted in the evolution of interfacial IMCs; on kinetics, larger solder joints had sufficient Cu flux toward the interface to feed the(Cu,Ni)6Sn5growth in contrast to smaller solder joints, thus resulted in the delayed IMC transformation and the formation of larger dodecahedron-type(Cu,Ni)6Sn5grains. In smaller solders, no spalling but the consumption of(Cu,Ni)6Sn5grains by the formation of(Ni,Cu)3Sn4grains occurred where smaller discrete(Cu,Ni)6Sn5grains formed at the interface.展开更多
This paper provides an analytical approach to determine the optimum pitch by utilizing a thermal resistance network, under the assumption of constant luminous efficiency. This work allows an LED array design which is ...This paper provides an analytical approach to determine the optimum pitch by utilizing a thermal resistance network, under the assumption of constant luminous efficiency. This work allows an LED array design which is mounted on a printed circuit board （PCB） attached with a heat sink subject to the natural convection cooling. Being validated by finite element （FE） models, the current approach can be shown as an effective method for the determination of optimal component spacing in an LED array assembly for SSL.展开更多
文摘Silver nanocubes enriched with {100} facets have been extensively used for surface-enhanced Raman scattering. Herein, we report a new water-phase synthesis method for weU-defined Ag nanocubes with tunable sizes via a two-step procedure at room temperature. First, irregularly shaped Ag nanoparticles （INPs） were prepared by reducing silver ammonia solution using ethylal. Second, the agglomerated INPs were selectively etched with HNO3 and C1- to yield {100} facet-rich mesoporous Ag nanocubes. The mechanism of Ag-nanocube formation and growth was investigated in detail by elucidating the involved chemical reactions and physical changes at each step during the synthesis. The addition of C1- anions was responsible for facilitating Ag nanoparticle growth by removing surface-adsorbed Ag＋ species, thereby eliminating inter-particle repulsive forces. This agglomeration was found crucial for the subsequent selective oxidation of Ag nanoparticles because the protective agent used, polyvinylpyrrolidone （PVP）, was the most effective one for adsorption on the surfaces of Ag nanoparticles of size greater than approximately 50 nm. Importantly mesopores were found inside the Ag nanocubes; this can be attributed to the unavoidable imperfect packing during the agglomeration of INPs. The newly prepared Ag nanocubes were further used to enhance the Raman signal of rhodamine 6G, which is capable of reducing the detection limitation to 10-16 mol·L-1.
基金financial support of the projects from the National Natural Science Foundation of China (Nos. 51475072 and 51171036)
文摘The diffusion behavior of Cu and Ni atoms undergoing liquidesolid electromigration（L-S EM） was investigated using Cu/Sn/Ni interconnects under a current density of 5.0 103A/cm2 at 250℃. The flowing direction of electrons significantly influences the cross-solder interaction of Cu and Ni atoms, i.e., under downwind diffusion, both Cu and Ni atoms can diffuse to the opposite interfaces; while under upwind diffusion,Cu atoms but not Ni atoms can diffuse to the opposite interface. When electrons flow from the Cu to the Ni, only Cu atoms diffuse to the opposite anode Ni interface, resulting in the transformation of interfacial intermetallic compound（IMC） from Ni3Sn4into（Cu,Ni）6Sn5and further into [（Cu,Ni）6Sn5t Cu6Sn5], while no Ni atoms diffuse to the opposite cathode Cu interface and thus the interfacial Cu6Sn5 remained.When electrons flow from the Ni to the Cu, both Cu and Ni atoms diffuse to the opposite interfaces,resulting in the interfacial IMC transformation from initial Cu6Sn5into（Cu,Ni）6Sn5and further into[（Cu,Ni）6Sn5t（Ni,Cu）3Sn4] at the anode Cu interface while that from initial Ni3Sn4into（Cu,Ni）6Sn5and further into（Ni,Cu）3Sn4at the cathode Ni interface. It is more damaging with electrons flowing from the Cu to the Ni than the other way.
基金supported by the National Natural Science Foundation of China under Grant Nos. 51475072 and 51171036
文摘Solder size effect on early stage interfacial intermetallic compound(IMC) evolution in wetting reaction between Sne3.0Age0.5Cu solder balls and electroless nickel electroless palladium immersion gold(ENEPIG) pads at 250 C was investigated. The interfacial IMCs transformed from initial needle- and rodtype(Cu,Ni)6Sn5to dodecahedron-type(Cu,Ni)6Sn5and then to needle-type(Ni,Cu)3Sn4at the early interfacial reaction stage. Moreover, these IMC transformations occurred earlier in the smaller solder joints, where the decreasing rate of Cu concentration was faster due to the Cu consumption by the formation of interfacial(Cu,Ni)6Sn5. On thermodynamics, the decrease of Cu concentration in liquid solder changed the phase equilibrium at the interface and thus resulted in the evolution of interfacial IMCs; on kinetics, larger solder joints had sufficient Cu flux toward the interface to feed the(Cu,Ni)6Sn5growth in contrast to smaller solder joints, thus resulted in the delayed IMC transformation and the formation of larger dodecahedron-type(Cu,Ni)6Sn5grains. In smaller solders, no spalling but the consumption of(Cu,Ni)6Sn5grains by the formation of(Ni,Cu)3Sn4grains occurred where smaller discrete(Cu,Ni)6Sn5grains formed at the interface.
文摘This paper provides an analytical approach to determine the optimum pitch by utilizing a thermal resistance network, under the assumption of constant luminous efficiency. This work allows an LED array design which is mounted on a printed circuit board （PCB） attached with a heat sink subject to the natural convection cooling. Being validated by finite element （FE） models, the current approach can be shown as an effective method for the determination of optimal component spacing in an LED array assembly for SSL.
