We present the simulation, fabrication and optical characterization of plasmonic gold bowtie nanoantennas on a semiconducting GaAs substrate as geometrical parameters such as size, feed gap, height and polarization of the incident light are varied. The surface plasmon resonance was probed using white light reflectivity on an array of nominally identical, 35 nm thick Au antennas. To elucidate the influence of the semiconducting, high refractive index substrate, all experiments were compared using nominally identical structures on glass. Besides a linear shift of the surface plasmon resonance from 1.08 eV to 1.58 eV when decreasing the triangle size from 170 nm to 100 nm on GaAs, we observed a global redshift by 0.25 ± 0.05 eV with respect to nominally identical structures on glass. By performing polarization resolved measurements and comparing results with finite difference time domain simulations, we determined the near field coupling between the two triangles composing the bowtie antenna to be ∼8× stronger when the antenna is on a glass substrate compared to when it is on a GaAs substrate. The results obtained are of strong relevance for the integration of lithographically defined plasmonic nanoantennas on semiconducting substrates and, therefore, for the development of novel optically active plasmonic-semiconducting nanostructures.
We compared the parental age at birth of patients with Alzheimer disease (AD) with that of cognitively healthy control subjects. Within 206 carefully diagnosed AD patients, two groups were distinguished according to the likelihood of carrying a major gene for AD (MGAD). This likelihood was calculated by applying a Bayesian approach which incorporates data on aggregation of the disease, age at onset, and "censoring" ages within the family. All AD patients were ranked by MGAD probability. According to the sample's quartiles, two subgroups were defined representing the 52 individuals with the lowest and the 52 with the highest MGAD probability. Age at onset of dementia, education, and apolipoprotein E epsilon4 allele frequencies were not statistically different between the two groups. Fathers of patients with a low MGAD probability were significantly older (35.7+/-8.1 years) than fathers of both other groups (high MGAD probability 31.3+/-6.9 years, P=0.004; controls 32.6+/-6.8 years, P=0.04, n=50). The differences for mothers were less pronounced and not statistically significant. These findings suggest that increased paternal age is a risk factor for AD in the absence of a major gene, whereas increased maternal age and AD are associated only weakly and independently of genetic disposition.
Abstract. We present a combined experimental and simulation study of a single self-assembled InGaAs quantum dot coupled to a nearby (∼ 25 ) plasmonic antenna. Micro-photoluminescence spectroscopy shows a ∼ 2.4× increase of intensity, which is attributed to spatial far-field redistribution of the emission from the quantum dot-antenna system. Power-dependent studies show similar saturation powers of 2.5for both coupled and uncoupled quantum dot emission in polarization-resolved measurements. Moreover, time-resolved spectroscopy reveals the absence of Purcell-enhancement of the quantum dot coupled to the antenna as compared to an uncoupled dot, yielding comparable exciton lifetimes of ∼ 0.5 . This observation is supported by numerical simulations, suggesting only minor Purcelleffects of < 2× for emitter-antenna separations > 25 . The observed increased emission from a coupled quantum dot-plasmonic antenna system is found to be in good qualitative agreement with numerical simulations and will lead to a better understanding of light-matter-coupling in such novel semiconductor-plasmonic hybrid systems
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