The sub-diffraction imaging of the optical near-field in nanostructures, based on a photochemical technique, is reported. A photosensitive azobenzene-dye polymer is spin coated onto lithographic structures and is subsequently irradiated with laser light. Photoinduced mass transport creates topographic modifications at the polymer film surface that are then measured with atomic force microscopy (AFM). The AFM images correlate with rigorous theoretical calculations of the near-field intensities for a range of different nanostructures and illumination polarizations. This approach is a first step toward additional methods for resolving confined optical near fields, which can augment scanning probe methodologies for high spatial resolution of optical near fields.
The role of surface plasmon in second harmonic generation from arrays of gold nanorod particles excited by femtosecond laser pulses is investigated as a function of incident light polarization and irradiation wavelength. In addition to photoluminescence, a peak of second harmonic is observed and is found to depend on the polarization and wavelength of the fundamental frequency laser beam. In particular, the authors found similarities between extinction spectra of the nanoparticles and spectra of emmitted second harmonic. This behavior can be explained by resonant excitation of localized surface plasmon resonances.
Photodetection in the short-wave infrared (SWIR) spectrum is a challenging task achieved often by costly low bandgap compound semiconductors involving highly toxic elements. In this work, an alternative low-cost approach is reported for SWIR sensors that rely on the plasmonic-induced photothermal effect of solution-processed colloidal gold nanorods (Au NRs). A series of uniform solution-processed Au NRs of various aspect ratios are prepared exhibiting a strong and well-defined longitudinal localized surface plasmon resonance (L-LSPR) maximum from 900 nm to 1.3 µm. A hybrid device structure is fabricated by applying Au NRs on the surface of a thermistor. Under a monochromatic illumination, hybrid Au-NR/thermistor devices exhibit a clear photoresponse in the form of photoinduced resistance drop in the wavelength window from 1.0 to 1.8 µm. The photoresponsivity of such hybrid devices reaches a maximum value of 4.44 × 10 Ω W at λ = 1.4 µm (intensity = 0.28 mW cm ), a wavelength in agreement with the L-LSPR of the Au NRs applied. Colloidal Au NRs, capable to perform fast conversion between photon absorption and thermal energy, thus open an interesting avenue for alternative low-cost SWIR photodetection.
Organic-inorganic hybrid perovskite solar cells have attracted much attention due to their high power conversion efficiency (>25%) and low-cost fabrication. Yet improvements are still needed for more stable and more performing solar cells. In this work, a series of TiO2 nanocolumn photonic structures has been intentionally fabricated on half of the compact TiO2coated fluorine-doped tin oxide substrate by glancing angle deposition with magnetron sputtering, a method particularly suitable for industrial applications due to its high reliability and reduced cost when coating large areas. These vertically aligned nanocolumn arrays were then applied as the electron transport layer (ETL) into triple-cation lead halide perovskite solar cells based on Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3. By comparison to solar cells built onto the same substrate without nanocolumns, the use of TiO2 nanocolumns can significantly enhance the power conversion efficiency of the perovskite solar cells by 7 % and prolong their shelf life. Here, the detailed characterizations on the morphology and the spectroscopic aspects of the nanocolumns, their near-field and far-field optical properties, solar cells characteristics, as well as the charge transport properties, provide mechanistic insights on how 1D TiO2 nanocolumns affect the performance of perovskite halide solar cells in terms of the charge transport, light-harvesting, and stability, knowledge necessary for the future design of more-performing and more-stable perovskite solar cells.
Photon upconversion represents a promising avenue to reduce the spectral mismatch losses limiting the efficiency of solar cells. Here we studied in detail the impact of inserting Yb 3+ /Er 3+ codoped KY 7 F 22 upconversion nanoparticles (UCNPs) into the different interfaces of a solution-processed mixed-cation lead mixedhalide perovskite solar cell. Besides macroscopic photovoltaic characteristics, we quantify the upconversion contribution by the light-beam-induced current/fluorescence mapping technique on devices with only half of their interfaces decorated by UCNPs. Such mapping experiments offer a detailed microscopic and spectroscopic picture allowing a correlation of the electrical and optical contribution of UCNPs together with the solar cell morphology.
We present a near-field optical study of TiO2 nanodisks by fluorescence scanning near-field optical microscopy. The localization of light and the fluorescence enhancement near the dielectric structures are visualized with a lateral resolution of ∼λ/5 using an Er/Yb-codoped fluorescent nanocrystal glued at the end of a sharp scanning tip. We observed that the intensity patterns strongly depend on the disk size, forming lobes for a diameter close to the wavelength and a single bright spot for smaller structures. Although the experiments were performed out of resonance, a maximum fluorescence enhancement of 2.3 was observed near 700 nm-wide disks. The evolution of the fluorescence pattern as a function of the disk size is in good agreement with the near-field maps calculated by the finite-difference time-domain method, in both two and three dimensions above the structures.
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