SEARCH · Engineering Papers
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ZnO–Ag x Au 1−x oxide–nanoalloy vertically aligned nanocomposite thin films have been grown via pulsed laser deposition and the film morphology and optical properties were tuned through oxygen partial pressure.
The photothermal energy conversion in hanging and floating polyaniline (PANi)-cotton fabrics is investigated using a model based on the heat diffusion equation.
The nanocavity construction of the 3D-graphene combines with the optical cavity system of the SOI to improve the interaction between the incident light and 3D-graphene. These properties enhance electronic interactions, thereon improving chemical/charge transfer effects in heterojunctions.
The formation of clusters in non-aromatic molecules can give rise to unconventional luminescence or clusteroluminescence.
We use multi-photon photoemission electron microscopy (PEEM) to image the enhanced electric fields of silver nanoparticles supported on a silver thin film substrate. Electromagnetic field enhancement is measured by comparing the photoelectron yield of the nanoparticles with respect to the photoelectron yield of the surrounding silver thin film. We investigate the dependence of the photoelectron yield of the nanoparticle as a function of size and shape. Multi-photon PEEM results are presented for three average nanoparticle diameters: 122 ± 6, 75 ± 6, and 34 ± 2 nm. The enhancement in photoelectron yield of single nanoparticles illuminated with femtosecond laser pulses (400 nm, ~3.1 eV) is found to be a factor of 102 to 103 times greater than that produced by the flat silver thin film. High-resolution, multi-photon PEEM images of single silver nanoparticles reveal that the greatest enhancement in photoelectron yield is localized at distinct regions on the surface of the nanoparticle whose magnitude and spatial extent is dependent on the incident electric field polarization. In conjunction with correlated scanning electron microscopy (SEM), nanoparticles that deviate from nominally spherical shapes are found to exhibit irregular spatial distributions in the multi-photon PEEM images that are correlated with the unique shape and topology of the nanoparticle.
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No abstract prepared.
Two types of Au nanorods (NRs) possessing longitudinal/transverse axes of 55/11 (NR{sub 11}) and 90/18 nm (NR{sub 18}) are, respectively, incorporated into the hole extraction layer to improve optical-to-electrical conversion performances in polymer photovoltaic cells. Totally different improvement factors in short-circuit current and power conversion efficiency occur in the NR{sub 11}- and NR{sub 18}-doped cells. Optical simulations, electrical analysis, and morphology alteration accompanying with the incorporation of NRs were proceeded to investigate the reason, and analysis demonstrates that a slower damping of field around NRs{sub 18} (results in a field and absorption enhancement around the active layer) and one order higher scattering cross section in the NR{sub 18}-incorporated cell are key factors contributed to the improvement of cell performances.
Metal oxidation at high temperatures has long been a challenge in cermet solar thermal absorbers, which impedes the development of atmospherically stable, high-temperature, high-performance concentrated solar power (CSP) systems. In this work, we demonstrate solution-processed Ni nanochain-SiO{sub x} (x < 2) and Ni nanochain-SiO{sub 2} selective solar thermal absorbers that exhibit a strong anti-oxidation behavior up to 600 °C in air. The thermal stability is far superior to previously reported Ni nanoparticle-Al{sub 2}O{sub 3} selective solar thermal absorbers, which readily oxidize at 450 °C. The SiO{sub x} (x < 2) and SiO{sub 2} matrices are derived from hydrogen silsesquioxane and tetraethyl orthosilicate precursors, respectively, which comprise Si-O cage-like structures and Si-O networks. Fourier transform infrared spectroscopy shows that the dissociation of Si-O cage-like structures and Si-O networks at high temperatures have enabled the formation of new bonds at the Ni/SiO{sub x} interface to passivate the surface of Ni nanoparticles and prevent oxidation. X-ray photoelectron spectroscopy and Raman spectroscopy demonstrate that the excess Si in the SiO{sub x} (x < 2) matrices reacts with Ni nanostructures to form silicides at the interfaces, which further improves the anti-oxidation properties. As a result, Ni-SiO{sub x} (x < 2) systems demonstrate better anti-oxidation performance than Ni-SiO{sub 2} systems. This oxidation-resistant Ni nanochain-SiO{sub x} (x < 2) cermet coating also exhibits excellent high-temperature optical performance, with a high solar absorptance of ∼90% and a low emittance ∼18% measured at 300 °C. These results open the door towards atmospheric stable, high temperature, high-performance solar selective absorber coatings processed by low-cost solution-chemical methods for future generations of CSP systems.
Rapid and strong joining of clear glass to glass containing randomly distributed embedded spherical silver nanoparticles upon nanosecond pulsed laser irradiation (∼40 ns and repetition rate of 100 kHz) at 532 nm is demonstrated. The embedded silver nanoparticles were ∼30–40 nm in diameter, contained in a thin surface layer of ∼10 μm. A joint strength of 12.5 MPa was achieved for a laser fluence of only ∼0.13 J/cm{sup 2} and scanning speed of 10 mm/s. The bonding mechanism is discussed in terms of absorption of the laser energy by nanoparticles and the transfer of the accumulated localised heat to the surrounding glass leading to the local melting and formation of a strong bond. The presented technique is scalable and overcomes a number of serious challenges for a widespread adoption of laser-assisted rapid joining of glass substrates, enabling applications in the manufacture of microelectronic devices, sensors, micro-fluidic, and medical devices.
Single nanoantenna spectroscopy was carried out on realistic dipole nanoantennas with various arm lengths and gap sizes fabricated by electron-beam lithography. A significant difference in resonance wavelength between realistic and ideal nanoantennas was found by comparing their spectral response. Consequently, the spectral tunability (96 nm) of the structures was significantly lower than that of simulated ideal nanoantennas. These observations, attributed to the nanofabrication process, are related to imperfections in the geometry, added metal adhesion layer, and shape modifications, which are analyzed in this work. Our results provide important information for the design of dipole nanoantennas clarifying the role of the structural modifications on the resonance spectra, as supported by calculations.
We report on the direct experimental determination of the temperature increment caused by laser irradiation in a optical recording media constituted by a polymeric film in which gold nanorods have been incorporated. The incorporation of CdSe quantum dots in the recording media allowed for single beam thermal reading of the on-focus temperature from a simple analysis of the two-photon excited fluorescence of quantum dots. Experimental results have been compared with numerical simulations revealing an excellent agreement and opening a promising avenue for further understanding and optimization of optical writing processes and media.
A film-coupled metamaterial structure is numerically investigated for enhancing the light absorption in an ultrathin photovoltaic layer of crystalline gallium arsenide (GaAs). The top subwavelength concave grating and the bottom metallic film could not only effectively trap light with the help of wave interference and magnetic resonance effects excited above the bandgap, but also practically serve as electrical contacts for photon-generated charge collection. The energy absorbed by the active layer is greatly enhanced with the help of the film-coupled metamaterial structure, resulting in significant improvement on the short-circuit current density by three times over a free-standing GaAs layer at the same thickness. The performance of the proposed light trapping structure is demonstrated to be little affected by the grating ridge width considering the geometric tolerance during fabrication. The optical absorption at oblique incidences also shows direction-insensitive behavior, which is highly desired for efficiently converting off-normal sunlight to electricity. The results would facilitate the development of next-generation ultrathin solar cells with lower cost and higher efficiency.
Using a combination of photoemission electron microscopy and numerical simulations, we investigated the angular moment transfer in strongly enhanced optical near-fields of artificially fabricated optical antennas. The polarization dependence of the optical near-field enhancement has been measured in a maximum symmetric geometry, i.e., excitation by a normal incident planar wave. Finite-difference time-domain simulations for the realistic antenna geometries as determined by high-resolution electron microscopy reveal a very good agreement with experimental data. The agreement confirms that the geometrical asymmetries and inhomogeneities due to the nanoscale fabrication process preserve the circular polarization in the gap regions with strong near-field enhancement.
The conventional TiO{sub 2} photoelectrode for water splitting was integrated with ordered mesoporous carbon material (CMK-3) and Au metal nanoparticles (NPs) to improve the photocatalytic efficiency under visible light irradiation. Compared to TiO{sub 2}, Au/TiO{sub 2}-CMK-3 photoelectrode demonstrated over two orders of magnitude enhancement of photocurrent under 532 nm laser irradiation due to the generation of hot electron and near field from Au NPs. Furthermore, the improvement of free carrier transport and additional long-wavelength absorption can be achieved by exploiting the superior conductivity and blackbody-like property of CMK-3. This proposed enhancement mechanism was proved by the measurements of photoluminescence emission spectrum and electrochemical impedance spectroscopy.
No abstract prepared.
No abstract prepared.