The optical properties in visible – near infrared range of Pd nano-hole arrays (PNA) and Pd thin films under hydrogen absorption – desorption processes have been investigated. The PNA samples show plasmonic resonances with about three times more transmission than that of the Pd thin film samples with a similar thickness. Remarkably, due to the plasmonic effect the PNA samples exhibit two times larger transmission change, normalized to the Pd cover area, under the hydrogen absorption/desorption processes at the Wood’s anomaly positions. The PNA sample can be used as a hydrogen sensor that has a better signal-to-noise ratio than the one based on the corresponding Pd thin film. The experimental results are confirmed by the finite-difference time domain (FDTD) calculations.
Hyperfine interaction (HFI) has been considered as a dominant spin mixing mechanism in conventional semiconducting polymers causing large magnetoconductance (MC) in organic diodes. However, the relationship between the MC width or HFI strength and the MC magnitude has not been investigated. We studied the correlation between the width and the magnitude of the MC response in organic diodes made by several conventional π-conjugated semiconducting polymers. First, by comparing the MC responses in electron- and hole-only unipolar devices made by the same polymer, we found that the electron-only device with a larger MC width always show a larger MC magnitude than that in the corresponding hole-only device. Second, we intentionally decreased and increased the charge localization or HFI strength in these unipolar devices by controlling their annealing temperature and UV irradiation, respectively. We found that the MC magnitude in these unipolar devices generally increases when the HFI strength increases but with different rates. We conclude that the width of MC or HFI strength is a crucial but not a unique factor that influences the MC magnitude. Finally, although the HFI in bipolar devices is smaller than that in the corresponding electron-only devices, the MC magnitude in bipolar devices is always larger than that in the electron-only devices suggesting that their underlying mechanisms are different.
Recent advances in spin response of organic semiconductors include long polaron spin coherence time measured
by optically detected magnetic resonance (ODMR); substantive room-temperature magneto-electroluminescence
and magneto-conductance obtained in organic light emitting diodes (OLED); and spin-polarized carrier injection
from ferromagnetic electrodes in organic spin valves (OSV). Although the hyperfine interaction (HFI) has been
foreseen to play an important role in organic spin response, clear experimental evidence has been lacking. Using
the chemical versatility advantage of the organics, we studied and compared spin responses in films, OLED and
OSV devices based on π-conjugated polymers made of protonated, H-, and deuterated, D-hydrogen having a
weaker HFI strength. We demonstrate that the HFI plays a crucial role in all three spin responses. OLEDs and
films based on the D-polymers show substantial narrower magneto-electroluminescence, magneto-conductivity
and ODMR responses; whereas due to the longer spin diffusion, OSV devices based on D-polymers show
substantially larger magnetoresistance that reaches ~330% at small bias voltage and low temperatures.
The phenomenon of anomalous transmission through subwavelength aperture arrays in metallic films (plasmonic
lattices) is thought to be mediated by surface plasmon polaritons (SPP) on the film surfaces. Using terahertz time-domain
spectroscopy we systematically studied the anomalous transmission spectrum through plasmonic lattices as a
function of the incidence angle, θ of the impinging beam. We observed splitting of the various transmission resonances
into two resonance branches when θ deviates from normal incidence that depends on the polarization direction of the
beam respect to the plane of incidence and θ. We show that the transmission resonance splitting is not related to
dispersion relation of different SPP branches, but rather is associated to the interference properties of the SPP waves on
the metal surface. The dependence of the split resonant frequencies vs. θ is fit with a theoretical formula that takes into
account the effective dielectric function of the plasmonic lattice vs. θ, which emphasizes the important role of the Fanotype
anti-resonances in the transmission spectrum. Finally, we introduced a simple way for making an efficient notch
filter with high Q factor exploiting the splitting of transmission resonance under rotation.