We have developed and characterized ultrafast and highly sensitive photodetectors based on GaAs nanowhiskers fabricated with an improved top-down etching method. We evaluated the material properties of the etched nano...
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We have developed and characterized ultrafast and highly sensitive photodetectors based on GaAs nanowhiskers fabricated with an improved top-down etching method. We evaluated the material properties of the etched nanowhiskers by micro photoluminescence measurements and studied the effect of post annealing on nanowhiskers' luminescence. The nanowhiskers were integrated into the coplanar striplines for device testing using DC and time-resolved electro-optic characterization techniques. Our photodetectors exhibit a very low dark current below 500 pA at 10 V bias as well as a high responsivity of 0.19 A/W at 30 V, and a cut-off frequency of 1.3 THz. These characteristics make the GaAs nanowhisker photodetectors very promising candidates for high-speed optoelectronics and efficient THz emitters.
RNA interference (RNAi) has shown immense potential for treating diseases by selectively silencing an abnormal/pathological pathway through the degradation of target messenger RNA (mRNA). However, exploitation of RNAi...
Laser-induced breakdown of an optically trapped nanoparticle is a unique system for studying cavitation dynamics. It offers additional degrees of freedom, namely the nanoparticle material, its size, and the relative p...
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Laser-induced breakdown of an optically trapped nanoparticle is a unique system for studying cavitation dynamics. It offers additional degrees of freedom, namely the nanoparticle material, its size, and the relative position between the laser focus and the center of the optically trapped nanoparticle. We quantify the spatial and temporal dynamics of the cavitation and secondary bubbles created in this system and use hydrodynamic modeling to quantify the observed dynamic shear stress of the expanding bubble. In the final stage of bubble collapse, we visualize the formation of multiple submicrometer secondary bubbles around the toroidal bubble on the substrate. We show that the pattern of the secondary bubbles typically has its circular symmetry broken along an axis whose unique angle rotates over time. This is a result of vorticity along the jet towards the boundary upon bubble collapse near solid boundaries.
Erbium additions of 0.25, 0.5, 1.0 and 2.0 atomic percent were incorporated into base alloys of 40 at.% titanium - 60 at.% aluminum by arc melting. Samples of 0.30g were electromagnetically levitated and melted and th...
Erbium additions of 0.25, 0.5, 1.0 and 2.0 atomic percent were incorporated into base alloys of 40 at.% titanium - 60 at.% aluminum by arc melting. Samples of 0.30g were electromagnetically levitated and melted and then rapidly solidified by double anvil splat quenching with liquid temperatures ranging from the liquidus temperature to near the maximum undercooling temperature for each alloy. Microstructures of TiAl with 0.25 and 0.5 at.% Er showed the presence of small erbium rich particles within ψ grains as well as antiphase domain boundaries, while TiAl with 1.0 and 2.0 at.% Er showed no evidence of these features. These observations were correlated with solidification velocity measurements on levitated samples. Evidence for disordered primary solidification and a solid state disorder/order reaction is presented.
Sapphire wafers are widely used as the substrates for fabricating GaN light-emitting diodes (LEDs). The quality of LEDs depends directly on the quality of the sapphire wafers. A series of machining processes is requir...
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Sapphire wafers are widely used as the substrates for fabricating GaN light-emitting diodes (LEDs). The quality of LEDs depends directly on the quality of the sapphire wafers. A series of machining processes is required to turn sapphire barstock into wafers with the desired geometry and surface quality. This paper reviews the literature on various machining processes for sapphire wafers: slicing (including outer diameter cut-off grinding, inner diameter cut-off grinding, loose abrasive multi-wire sawing, fixed abrasive slicing, and fixed abrasive multi-wire sawing), flattening (including lapping and grinding), and surface finishing (including mechanical polishing and chemical mechanical polishing). New machining technologies are also introduced.
The morphology of nanocrystalline (nc)-Si/amorphous (a)-SiO2 superlattices (SLs) is studied using Raman spectroscopy in the acoustic and optical phonon ranges, transmission electron microscopy (TEM), and atomic force ...
The morphology of nanocrystalline (nc)-Si/amorphous (a)-SiO2 superlattices (SLs) is studied using Raman spectroscopy in the acoustic and optical phonon ranges, transmission electron microscopy (TEM), and atomic force microscopy (AFM). It is demonstrated that high temperature annealing (up to 1100°C) and oxidation in O2/H2O ambient do not destroy the SL structure, which retains its original periodicity and nc-Si/a-SiO2 interface abruptness. It is found that oxidation at high temperatures reduces the defect density in nc-Si/a-SiO2 SLs and induces the lateral coalescence of Si nanocrystals (NCs). The size, shape, packing density, and crystallographic orientation of the Si nanocrystals are studied as a function of the oxidation time.
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