Site-controlled Ag nanocrystals grown by molecular beam epitaxy-Towards plasmonic integration technology

We demonstrate site-controlled growth of epitaxial Ag nanocrystals on patterned GaAs substrates by molecular beam epitaxy with high degree of long-range uniformity. The alignment is based on lithographically defined holes in which position controlled InAs quantum dots are grown. The Ag nanocrystals self-align preferentially on top of the InAs quantum dots. No such ordering is observed in the absence of InAs quantum dots, proving that the ordering is strain-driven. The presented technique facilitates the placement of active plasmonic nanostructures at arbitrarily defined positions enabling their integration into complex devices and plasmonic circuits.

Preparation and characterization of stable aqueous suspensions of up-converting Er3+/Yb3+-doped LiNbO3 nanocrystals

The preparation of LiNbO3:Er3+/Yb3+ nanocrystals and their up-conversion properties have been studied. It is demonstrated that polyethyleneimine- (PEI) assisted dispersion procedures allow obtaining stable aqueous LiNbO3:Er3+/Yb3+ powder suspensions, with average size particles well below the micron range (100–200 nm) and the isoelectric point of the suspension reaching values well above pH 7. After excitation of Yb3+ ions at a wavelength of 980 nm, the suspensions exhibit efficient, and stable, IR-to-visible (green and red) up-conversion properties, easily observed by the naked eye, very similar to those of the starting crystalline bulk material.

Epitaxial self-alignment: A new route to hybrid active plasmonic nanostructures

Concepts of lateral ordering of epitaxial semiconductor quantum dots (QDs) are for the first time transferred to hybrid nanostructures for active plasmonics. We review our recent research on the self-alignment of epitaxial nanocrystals of In and Ag on ordered one-dimensional In(Ga)As QD arrays and isolated QDs by molecular beam epitaxy. By changing the growth conditions the size and density of the metal nanocrystals are easily controlled and the surface plasmon resonance wavelength is tuned over a wide range in order to match the emission wavelength of the QDs. Photoluminescence measurements reveal large enhancement of the emitted light intensity due to plasmon enhanced emission and absorption down to the single QD level.

Low-density InAs QDs with subcritical coverage obtained by conversion of In nanocrystals

We report growth of InAs/GaAs quantum dots (QDs) by molecular beam epitaxy with low density of 2 μm−2 by conversion of In nanocrystals deposited at low temperatures. The total amount of InAs used is about one monolayer, which is less than the critical thickness for conventional Stranski–Krastanov QDs. We also demonstrate the importance of the starting surface reconstruction for obtaining uniform QDs. The QD emission wavelength is easily tunable upon post-growth annealing with no wetting layer signal visible for short anneals. Microphotoluminescence measurements reveal well separated and sharp emission lines of individual QDs.

Nanocrystals in the manufacture of target for inertial confinement fusion

Systems inertial confinement fusion (ICF) need of a manufacturing process targets very accurate and efficient (Fig. A). Due to the frequency needed for energy production techniques are necessary to achieve high repetition rates, however it is also necessary to increase or maintain the quality and efficiency of these targets. In order to observe more resolution possible problems in the target manufacture (B), we propose the following theoretical methodology, by means of which analyze different phenomena present in the conditions which are fabrication and handled deuterium tritium target spheres (DT ice). Recent experiments show that addition of instabilities caused by the geometry of the solid layer of DT ice (C), and the cover (ablator), one can relate the loss of power delivery in the implosion due to different conformations of the solid layers with regarding handling conditions.

Mechanical Characterization of Lead-Free Sn-Ag-Cu Solder Joints by High-Temperature Nanoindentation

The reliability of Pb-free solder joints is controlled by their microstructural constituents. Therefore, knowledge of the solder microconstituents’ mechanical properties as a function of temperature is required. Sn-Ag-Cu lead-free solder alloy contains three phases: a Sn-rich phase, and the intermetallic compounds (IMCs) Cu6Sn5 and Ag3Sn. Typically, the Sn-rich phase is surrounded by a eutectic mixture of β-Sn, Cu6Sn5, and Ag3Sn. In this paper, we report on the Young’s modulus and hardness of the Cu6Sn5 and Cu3Sn IMCs, the β-Sn phase, and the eutectic compound, as measured by nanoindentation at elevated temperatures. For both the β-Sn phase and the eutectic compound, the hardness and Young’s modulus exhibited strong temperature dependence. In the case of the intermetallics, this temperature dependence is observed for Cu6Sn5, but the mechanical properties of Cu3Sn are more stable up to 200°C.

Identification and dynamics of polyglycine II nanocrystals in Argiope trifasciata flagelliform silk

Spider silks combine a significant number of desirable characteristics in one material, including large tensile strength and strain at breaking, biocompatibility, and the possibility of tailoring their properties. Major ampullate gland silk (MAS) is the most studied silk and their properties are explained by a double lattice of hydrogen bonds and elastomeric protein chains linked to polyalanine β-nanocrystals. However, many basic details regarding the relationship between composition, microstructure and properties in silks are still lacking. Here we show that this relationship can be traced in flagelliform silk (Flag) spun by Argiope trifasciata spiders after identifying a phase consisting of polyglycine II nanocrystals. The presence of this phase is consistent with the dominant presence of the –GGX– and –GPG– motifs in its sequence. In contrast to the passive role assigned to polyalanine nanocrystals in MAS, polyglycine II nanocrystals can undergo growing/collapse processes that contribute to increase toughness and justify the ability of Flag to supercontract.

Mechanical characterization of GdBCO/Ag and YBCO single grains fabricated by top-seeded melt growth at 77 and 300 K

YBaCuO and GdBaCuO + 15 wt% Ag large, single-grain, bulk superconductors have been fabricated via the top-seeded, melt-growth (TSMG) process using a generic NdBCO seed. The mechanical behavior of both materials has been investigated by means of three-point bending (TPB) and transversal tensile tests at 77 and 300 K. The strength, fracture toughness and hardness of the samples were studied for two directions of applied load to obtain comprehensive information about the effect of microstructural anisotropy on the macroscopic and microscopic mechanical properties of these technologically important materials. Splitting (Brazilian) tests were carried out on as-melt-processed cylindrical samples following a standard oxygenation process and with the load applied parallel to the growth-facet lines characteristic of the TSMG process. In addition, the elastic modulus of each material was measured by three different techniques and related to the microstructure of each sample using optical microscopy. The results show that both the mechanical properties and the elastic modulus of both YBCO and GdBCP/Ag are improved at 77 K. However, the GdBCO/Ag samples are less anisotropic and exhibit better mechanical behavior due to the presence of silver particles in the bulk, superconducting matrix. The splitting tensile strength was determined at 77 K and both materials were found to exhibit similar behavior, independently of their differences in microstructure.

Ti/Pd/Ag Contacts to n-Type GaAs for High Current Density Devices

The metallization stack Ti/Pd/Ag on n-type Si has been readily used in solar cells due to its low metal/semiconductor specific contact resistance, very high sheet conductance, bondability, long-term durability, and cost-effectiveness. In this study, the use of Ti/Pd/Ag metallization on n-type GaAs is examined, targeting electronic devices that need to handle high current densities and with grid-like contacts with limited surface coverage (i.e., solar cells, lasers, or light emitting diodes). Ti/Pd/Ag (50 nm/50 nm/1000 nm) metal layers were deposited on n-type GaAs by electron beam evaporation and the contact quality was assessed for different doping levels (from 1.3 × 1018 cm−3 to 1.6 × 1019 cm−3) and annealing temperatures (from 300°C to 750°C). The metal/semiconductor specific contact resistance, metal resistivity, and the morphology of the contacts were studied. The results show that samples doped in the range of 1018 cm−3 had Schottky-like I–V characteristics and only samples doped 1.6 × 1019 cm−3 exhibited ohmic behavior even before annealing. For the ohmic contacts, increasing annealing temperature causes a decrease in the specific contact resistance (ρ c,Ti/Pd/Ag ~ 5 × 10−4 Ω cm2). In regard to the metal resistivity, Ti/Pd/Ag metallization presents a very good metal conductivity for samples treated below 500°C (ρ M,Ti/Pd/Ag ~ 2.3 × 10−6 Ω cm); however, for samples treated at 750°C, metal resistivity is strongly degraded due to morphological degradation and contamination in the silver overlayer. As compared to the classic AuGe/Ni/Au metal system, the Ti/Pd/Ag system shows higher metal/semiconductor specific contact resistance and one order of magnitude lower metal resistivity.