Nanoantennas

Metal nanoparticles have also been included into MIPs. Such particles can be used, for example, as nanoantennae for the enhancement of electromagnetic waves (plasmonic enhancement). It has been shown by He et al. [122] that a thin layer (20-120 nm) of testosterone-imprinted silica could be synthesized around 350 nm silver particles in a controlled way. The composite material showed specific binding of the testosterone target. Matsui et al. [123] reported a molecularly imprinted polymer with immobilized Au nanoparticles as a sensing material for spectrometry. The sensing mechanism is based on the variable proximity of the Au nanoparticles... 

Fromm, D.P., A. Sundaramurthy, P.J. Schuck, G.S. Kino, and W.E. Moerner. 2004. Gap-dependent optical coupling of single bowtie nanoantennas resonant in the visible. Nano Lett. 4 957-961. 

Kiihn, S., Hakanson, U., Rogobete, L., and Sandoghdar, V. (2006). Enhancement of ingle-Molecule Fluorescence Using a Gold Nanoparticle as an Optical Nanoantenna. Phys. Rev. Lett. 97 017402-1-4 see also Supplementary info. 

Muskens, O. L., Giannini, V., Sanchez-Gil, J. A., and Rivast, J. G. (2007). Strong enhancement of the radiative decay rate of emitters by single plasmonic nanoantennas. Nano Letters 7 2871-2875. 

Metal nanoparticles can increase the modulation band of semiconductor LEDs. This is demonstrated theoretically on example of nano-LED (NEED) composed of a single q-dot and nanoparticle (nanoantenna). NEED is analogous to dipole nano-laser (DNL)... 

Here we discuss an example of elementary NEED composed of a single q-dot and nanoantenna , that is a metal nanoparticle, following the approach of dipole nano-laser (DNL) [1,4]. We show that the nanoparticle increases not only the brightness [4], but also the modulation band of emission of a single q-dot, which is important for applications in optical information processing. Q-dot structures are considered as promising materials for LEDs [5]. 

Jackel, F., Kinkhabwala, A.A., and Moerner, W.E. (2007) Gold bowtie nanoantennas for surface-enhanced Raman scattering under controlled electrochemical potential. Chemical Physics Letters, 446, 339-343. 

One of the striking features of NANOM TMC -200 ) is a domination of quantum dots, nanoclusters and carbon nanotubes at different aspects. Their unique properties extensively studied last years have led to an avalanche of theoretical and experimental papers. Properties of these nanostructures have been predicted and often tested for wide range applications extending from more or less traditional fluorescent marks and elements of nanophotonics to unique nanocontainers, thermal nanoantennas and elements for spintronics and quantum computing. Many examples can be found in this book collecting invited reviews and short notes of contributions to the Conference. 

Maas. H. Calzaferri, G. Trapping energy from and injecting energy into dye-zeolite nanoantennae. Angew. 22. Chem. Int. Ed. 2002. 41 (13). 2284-2288. 

As was diseussed earlier, there are many other ways of preparing metallic particles with different morphologies such as nanoshells,nanoprisms, nanorods, nanoantennas, " nanocresents, and nanoparticle arrays. The reader is reeommended to follow the preparative techniques that are described in the relevant papers for a detailed description of these procedures. 

G.W. Bryant, E.J. Garcia de Abajo, J. Aizpurua, Mapping the plasmon resonances of metallic nanoantennas. Nano Lett. 8, 631-636 (2008)... 

Hawaldar R, Mulik U, PatU K, Pasricha R, Sathaye S, Lewis A, et al. Growth of PhS nanopyramidal particulate films for potential applications in quantum-dot photovoltaics and nanoantennas. Mater Res Bull 2005 40 1353-60. 

P. J. Schuck et al.. Improving the mismatch between light and nanoscale objects with gold bowtie nanoantennas, Physical Review Letters, 94(1), 017402-017404 (2005). 

Some examples of potential converging LH nanoantennas based on QDs as ET acceptors were investigated by Matloussi and coworkers (Figure 29). Different organic donors were examined, and the ET process resulted to be, in aU cases, too slow to compete with the unimolecular deactivation of the donors and hence quite inefficient. 

Besides nanoparticles and nanovoids as scatterers and nanoantennas, different diffractive structures can be used (gratings, lattices) [129] for field coupling into... 

Contrary to the conventional antennas for radio waves, nanoantennas are not connected to any feeding circuitry. They are standalone structures and are used in large arrays. They enhance scattering of electromagnetic waves, the more so the nearer they are to resonance. The literature describes various types of nanoantennas that were experimentally produced. Figure 2.61 shows some of the basic geometries. 

The simplest and the most basic nanoantenna is the nanosphere. This structure actually behaves like a dipole. Its scattering properties can be calculated using the Mie theory [266]. Noble metal nanoparticles are often fabricated in spherical form. This makes them the simplest nanoantennas. 

Another very often met nanoantenna stmcture is the bowtie nanoantenna [313]. It consists of two triangles aligned along their symmetry axes. A feed gap is formed between their tips. Bowtie antennas have a broader bandwidth together and at the same time ensure large field localizations in the feed gap. A similar type of antenna is the diabolo-type nanoantenna [314], where the triangles overlap. 

Among the nanoantennas mentioned in the literature are spiral nanoantennas [316] and those with fractal geometries [317]. Many other shapes can be used. Basically, all particles used to fabricate metamaterials can also function as nanoantennas. This includes single and double split rings, crescent antennas, etc. 

An important group of nanoantennas are those based on the Babinet principle. A metal shape surrounded by dielectric and a dielectric-filled hole in metal with identical shape and size have identical diliiaction patterns. Thus bowtie shaped holes in metal can be used, two holes are a Babinet equivalent of a nanodimer, arrays of nanoholes are equivalent of arrays of nanoparticles, crossed arrays of nanoholes correspond to crossed arrays of nanoparticles, etc. [318]. 

Nanoantennas are used in photodetection to couple propagating and localized modes and to localize fields. Especially, strong localizations are those in the feed gaps between coupled nanostructures. Photodetector enhancement by nanoantennas is a hot topic and numerous works have been published on it [243]. Earliest publications date as far as 1970s [319]. 

One of the approaches to the use of nanoantennas in photodetection is to use a Schottky metal-semiconductor junction. An optical antenna forms flie metal part of the metal-dielectric contact at the semiconductor detector surface [320]. Photoexcitation generates hot electron-hole pairs by plasmon decay and the electrons are injected over the Schottky barrier, thus directly generating photocurrent. A problem with this approach is its low efficiency. 

As the simplest nanoantennas, plasmonic nanoparticles can be utilized to enhance the absorption within thin-film solar cells [243]. They couple incoming waves with the localized SPP field, have increased scattering cross-section and strongly localize electromagnetic field just in the thin active region of the detector. Fig. 2.62. The same principle is applicable for infrared detection [321]. This cannot be done with pure noble metal nanoparticles since their surface plasmon resonance is in ultraviolet or visible part of the spectrum. Because of that their response must be redshifted. In this part, two approaches to such redshifting are described. 

T. Grosjean, M. Mivelle, F.I. Baida, G.W. Burr, U.C. Fischer, Diabolo nanoantenna for enhancing and confining the magnetic optical field. Nano Lett. 11(3), 1009-1013 (2011)... 

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