We report a study of direct laser fabrication that produces quantum dots with their density higher than the critical density without appearance of large clumps. Atomic force microscopy is used to image GaAs(001) surfaces that are irradiated by high power laser pulses interferentially. The analysis suggests that high density quantum dots be fabricated directly on semiconductor surfaces during epitaxial growth processes.

Carbon nanotube arrays were grown in the presence of an applied mechanical stress (30 min, 60 mN/mm2 mechanical pressure) and dispersed in aqueous solution (0.08 - 2.3 mm2/mL). Optical (450-950 nm) transmission and right angle scattering measurements were performed on these dispersions and on an analogous set of conventional (non-stressed) carbon nanotubes. Results show similar transmission behavior and different right angle scattering dependence on concentration for stress-grown and conventional carbon nanotubes. This investigation provides the first evidence of differentiation between stress-grown and conventional carbon nanotubes in the optical regime, suggesting a point of departure for future applications.

A method for creating pH maps in microchannels containing liquid/liquid and liquid/gas phases comprised of water and CO2 is demonstrated. It is based on a glass slide coated with nanoparticles exhibiting metal-enhanced fluorescence. The time resolution is better than 500 ms, limited by the fluidic control. This work opens the way for new in situ measurements of physical dissolution and chemical reactions in dynamic CO2 gas-liquid systems.

Working gas pressure during sputter deposition can significantly affect the conformality of a thin film when it is grown on a nanostructured surface. In this study, we fabricated core-shell nanostructured photodetectors, where n-type In2S3 nanorod arrays (core) were coated with p-type CuInS2 (CIS) films (shell) at relatively low and high Ar gas pressures. In2S3 nanorods were prepared by glancing angle deposition (GLAD) technique using a thermal evaporator unit. CIS films were deposited by RF sputtering at Ar pressures of 2.7x10-2 mbar (high pressure sputtering, HIPS) and 7.3x10-3 mbar (low pressure sputtering, LPS). The morphological characterization was carried out by means of SEM. The photocurrent measurement was conducted under 1.5 AM Sun under no bias. Nanostructured photodetectors of HIPS-CIS/GLAD-In2S3 (i.e. HIPS-GLAD) were shown to demonstrate enhanced photoresponse with a photocurrent value of 98 μA, which is about ∼230% higher than that of LPS-GLAD devices. The enhancement originates from the improved core-shell structure achieved by more conformal coating of the CIS shell. In addition, the results were compared to their counterpart thin-film devices incorporating an In2S3 film coated either with HIPS or LPS CIS layer. Nanorod devices with high and low pressure CIS films showed photocurrent values ∼20 times and ∼ 19 times higher compared to those of high and low pressure film devices, respectively. This finding can be explained by the higher light absorption property of nanorods, and the reduced inter-electrode distance as a result of core-shell structure, which allows the effective capture of the photo-generated carriers. Therefore, the results of this work can pave way to the development of high photoresponse core-shell semiconductor devices fabricated by physical vapor deposition techniques.

A wurtzite-strained nitride Quantum Well Laser has been characterized for short distance communication wavelength. InN and In0.25Ga0.75N have been chosen as well material and barrier material respectively with In0.4Al0.6N SCH layers at the end of barrier layers to improve the carrier and photon confinement within the active region. This structure shows less compressive strain (7.33%) with respect to previously proposed structure which makes the structure more suitable for fabrication. To obtain the electronic band structure, self-consistent method with k.p formalism has been performed where valence band mixing effect, strain effect and spontaneous and piezoelectric polarization effect has been included. From the electronic characteristics, the optical properties have been performed with numerical model. From the optical properties, the structure has been found as TE polarized with C1-HH1, C1-LH1, C2-HH1 and C2-LH1 dominating transition elements. From the performance of the numerical model, 4731.98 cm−1 optical gain for TE polarization at 1315.5 nm emission wavelength and 8.017×1027 cm−3s−1eV−1 spontaneous emission rate at 1301.7nm wavelength have been found for 12Å well width, 17Å barrier width and 52Å SCH layer width at 5×1019 cm−3 carrier density. The obtained properties have been shown a good agreement with previously published works.

We describe a simple and inexpensive method to enhance the sensitivity or improve the detection limit of solution-phase localized surface plasmon (LSPR) sensors of metallic nanoparticles. The substrate surface contains metallic nanostructures which are replicated from DVD disks via the standard soft lithography. By mixing BSA molecules with nanoparticle solution, we demonstrate that the wavelength shift due to the absorption of BSA molecules on nanoparticle surfaces is amplified by more than an order of magnitude in comparison to that over a smooth flat surface.

For optoelectronic device applications, quantum wires can be used as active media due to their unique physical properties. However, conventional approaches such as the self-assembly via the Stranski-Krastanov (S-K) growth technique have a limited success in their applications toward optoelectronic devices including photovoltaics and solar cells. A novel fabrication mechanism for quality quantum wires has been discovered. The laser fabricated nanowires semiconductor surfaces can have width and height as small as 30 and 5 nm, respectively while the density is one per 200 nm.

Graphene quantum dots (GQDs) of different sizes were synthesized by the top-down approach, using charcoal as the precursor material. Size and absorption characteristics of synthesized GQDs were analyzed using Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), Photoluminescence Spectroscopy (PL), and UV-vis Spectroscopy. The results showed that GQDs with an average height of 8.5 nm, synthesized at a relatively lower temperature of 85°C, exhibited higher UV and visible light absorption. GQD concentration was varied to form 0.5, 1, 2.5, and 5 wt.% GQD-titania (TiO2) nano composites. Surface morphology of the composite was examined using Scanning Electron Microscopy (SEM). Photocatalytic activity of the samples was assessed from methylene blue dye degradation in UV irradiation at 340nm. A distinguishable trend for pure TiO2 and composites at various concentrations were observed.

The electrophoretic transport of ions through single walled carbon nanotubes (SWCNTs) of diameters between 1.2 and 1.8 nm was studied for different monovalent chloride salts using microfluidic devices incorporating either a single or few SWCNTs in parallel. The ionic conductance was found to be about one order of magnitude higher than would be expected from simple bulk electrophoresis without any surface effect. Importantly, the ionic conductance measured for different cations did not scale with their bulk electrophoretic mobility thus indicating a selective cation transport through these sub-2 nm SWCNTs. The transport of Na+ was notably found to be favored in comparison to that of Li+, K+ and Cs+. These results highlight the influence of steric and surface effects induced by the nano-confinement on the transport of ions through sub-2 nm SWCNTs.

Studying the transport of ions through single-walled carbon nanotubes (SWCNTs) necessitate the fabrication of a fluidic setup integrating carbon nanotubes. In this article, we report on the development of a simple fabrication protocol of SWCNTs fluidic devices. This protocol allows an excellent control of the system features and of the experimental conditions compared with previously published protocols. Our protocol based on the use of the popular SU-8, the preferred photoresist for the fabrication of high-aspect-ratio patterns, allows one to prepare sealed microfluidic devices incorporating one or several tens of individual carbon nanotubes of length between 20 and 80 µm.

Membranes for selective water vapor separation were assembled from graphene oxide suspension using techniques compatible with high volume industrial production. The large-diameter graphene oxide flake suspensions were synthesized from graphite materials via relatively efficient chemical oxidation steps with attention paid to maintaining flake size and achieving high graphene oxide concentrations. Graphene oxide membranes produced using scalable casting methods exhibited water vapor flux and water/nitrogen selectivity performance meeting or exceeding that of membranes produced using vacuum-assisted laboratory techniques. (PNNL-SA-117497)