Nanoplasmon-enabled macroscopic thermal management

In numerous applications of energy harvesting via transformation of light into heat the focus recently shifted towards highly absorptive materials featuring nanoplasmons. It is currently established that noble metals-based absorptive plasmonic platforms deliver significant light-capturing capability and can be viewed as super-absorbers of optical radiation. However, direct experimental evidence of plasmon-enabled macroscopic temperature increase that would result from these efficient absorptive properties is scarce. Here we derive a general quantitative method of characterizing light-capturing properties of a given heat-generating absorptive layer by macroscopic thermal imaging. We further monitor macroscopic areas that are homogeneously heated by several degrees with plasmon nanostructures that occupy a mere 8% of the surface, leaving it essentially transparent and evidencing significant heat generation capability of nanoplasmon-enabled light capture. This has a direct bearing to thermophotovoltaics and other applications where thermal management is crucial

Mode-specific directional emission from hybridized particle-on-a-film plasmons

We investigate the electromagnetic interaction between a gold nanoparticle and a thin gold film on a glass substrate. The coupling between the particle plasmons and the surface plasmon polaritons of the film leads to the formation of two localized hybrid modes, one low-energy. film-like. plasmon and one high-energy plasmon dominated by the nanoparticle. We find that the two modes have completely different directional scattering patterns on the glass side of the film. The high-energy mode displays a characteristic dipole emission pattern while the low-energy mode sends out a substantial part of its radiation in directions parallel to the particle dipole moment. The relative strength of the two radiation patterns vary strongly with the distance between the particle and the film, as determined by the degree of particle-film hybridization

Plasmon-Interband Coupling in Nickel Nanoantennas

Plasmonic excitations are usually attributed to the free electron response at visible frequencies in the classic plasmonic metals Au and Ag. However, the vast majority of metals exhibit spectrally localized interband transitions or broad interband transition backgrounds in the energy range of interest for nanoplasmonics. Nevertheless, the interaction of interband transitions with localized plasmons in optical nanoantennas has hitherto received relatively little attention, probably because interband transitions are regarded as highly unwanted due to their strong damping effect on the localized plasmons. However, with an increasing number of metals (beyond Au and Ag) being considered for nanoplasmonic applications such as hydrogen sensing (Pd), UV-SERS (Al), or magnetoplasmonics (Ni, Fe, Co), a deeper conceptual understanding of the interactions between a localized plasmon mode and an interband transition is very important. Here, as a generic example, we examine the interaction of a localized (in energy space) interband transition with spectrally tunable localized plasmonic excitations and unearth the underlying physics in a phenomenological approach for the case of Ni disk nanoantennas. We find that plasmon interband interactions can be understood in the classical picture of two coupled harmonic oscillators, exhibiting the typical energy anticrossing fingerprint of a coupled system approaching the strong-coupling regime

Tunnel Junction Sensing of TATP Explosive at the Single-Molecule Level

Triacetone triperoxide (TATP) is a homemade, potent explosive and, unfortunately, is used in many terrorist attacks. It is hard to detect, and present techniques for its sensing do not offer portability. Fortunately, TATP is volatile, and gas-sensing-based devices for TATP detection would provide a higher level of safety. Here, we explore the possibility of single molecule TATP detection in the air by tunneling current measurement in the N-terminated carbon-based nanogaps, at the DFT+NEGF level of theory. We found TATP averaged current amplitude of tens nano amperes, with a discrimination ratio with respect to prevalent indoor volatile organic compounds (VOC) of a few orders of magnitude. That high tunneling current is due to specific TATP HOMO contributions to electronic transport. The transport facilitates the strong, in-gap electrical field generated by N-C polar bonds from electrode ends and TATP electrode hybridization, spurred by oxygen atoms from a probed molecule

Simulations of directionality effects and optical forces in plasmonic nanostructures

With the rapid development of nanoscience and nanotechnology, surface plasmonics based on metal nanoparticles and nanostructures gain increasing interest, not only for fundamental scientific studies, but also for optical and sensor applications. At the nanoscale, the physical and chemical properties of metal particles, especially their optical properties, strongly depend on size and shape, as well as on the surrounding media and structures. By modifying those features, one may design novel functional materials and devices. This thesis deals with investigations of light-induced effects at the nanoscale, focusing on optically induced forces on plasmonic nanostructures and angular distribution of light due to the particle-substrate interactions. Nanoparticles trapped within an optically induced potential energy well (e.g. using optical tweezers) will interact with each other by mutual forces. This can lead tothe self-organization of the nanoparticles within the trap, an effect known as optical binding. In this thesis I have theoretically investigated the optical forces between the metal nanoparticles for different polarization configurations. In addition to the optical forces, there are other contributions to the total interaction forces betweenthe particles, such as the Coulomb repulsion and van der Waals attraction. These contributions have been investigated in the case of two strongly interacting gold particles through the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). The thesis also contains a study of optical manipulation (trapping, rotation and spinning) of elongated plasmonic particles, such as rods, dimers and micrometer long nanowires. The other main theme of the thesis is the angular distribution of light scattered from the nanoparticles and the nanowires. The scattering properties of these structures are strongly affected by the presence of the substrate. It is shown that the dipolar angular distribution of light scattered from a single dipolar emitter in a homogeneous medium is highly modified when the emitter is brought close to a glass substrate (and even more so when the emitter is brought close to a thin metal film).In addition to nanoparticles, the thesis deals with nanowires, structures that support plasmonic Fabry-Perot resonances due to multiple reflection of the plasmonspropagating along their interfaces. It is shown that nanowires can scatter light in a rather narrow angular distribution thanks to the phase retardation of the plasmonpropagating along the wire, which is dictated by the wire diameter, length and surrounding medium

Simulations of directionality effects and optical forces in plasmonic nanostructures

With the rapid development of nanoscience and nanotechnology, surface plasmonics based on metal nanoparticles and nanostructures gain increasing interest, not only for fundamental scientific studies, but also for optical and sensor applications. At the nanoscale, the physical and chemical properties of metal particles, especially their optical properties, strongly depend on size and shape, as well as on the surrounding media and structures. By modifying those features, one may design novel functional materials and devices. This thesis deals with investigations of light-induced effects at the nanoscale, focusing on optically induced forces on plasmonic nanostructures and angular distribution of light due to the particle-substrate interactions. Nanoparticles trapped within an optically induced potential energy well (e.g. using optical tweezers) will interact with each other by mutual forces. This can lead tothe self-organization of the nanoparticles within the trap, an effect known as optical binding. In this thesis I have theoretically investigated the optical forces between the metal nanoparticles for different polarization configurations. In addition to the optical forces, there are other contributions to the total interaction forces betweenthe particles, such as the Coulomb repulsion and van der Waals attraction. These contributions have been investigated in the case of two strongly interacting gold particles through the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). The thesis also contains a study of optical manipulation (trapping, rotation and spinning) of elongated plasmonic particles, such as rods, dimers and micrometer long nanowires. The other main theme of the thesis is the angular distribution of light scattered from the nanoparticles and the nanowires. The scattering properties of these structures are strongly affected by the presence of the substrate. It is shown that the dipolar angular distribution of light scattered from a single dipolar emitter in a homogeneous medium is highly modified when the emitter is brought close to a glass substrate (and even more so when the emitter is brought close to a thin metal film).In addition to nanoparticles, the thesis deals with nanowires, structures that support plasmonic Fabry-Perot resonances due to multiple reflection of the plasmonspropagating along their interfaces. It is shown that nanowires can scatter light in a rather narrow angular distribution thanks to the phase retardation of the plasmonpropagating along the wire, which is dictated by the wire diameter, length and surrounding medium

Optical manipulation of plasmonic nanoparticles using laser tweezers

Plasmonic nanoparticles, typically gold and silver colloids, can be trapped by a highly focused Gaussian beam. The behavior of the particles in an optical trap, such as the alignment, stability and interaction between particles, depends on their plasmonic nature, determined by the correlation between the size, shape and material of the particles, and the wavelength and polarization of the trapping laser. For instance, an elongated nanoparticle aligns parallel to the polarization of a NIR trapping laser to minimize the optical potential energy. However, nanowires tend to align perpendicular to the polarization. A dimer of two isotropic nanoparticles in principle acts similar to a nanorod with its "long axis" (dimer axis) parallel to the laser polarization. These results are evidenced by dark-field scattering imaging and spectra, and agree well with discrete dipole approximation simulations of the near-fields around different nanostructures. Elongated nanoparticles, dimers and nanowires all rotate when the laser polarization is rotated. Irradiated under a circularly polarized laser, trapped objects spin spontaneously due to the transfer of angular momentum from the incident photons. The interaction between two gold nanoparticles in a dimer is complex because it involves the optical potential and the DLVO potential. The latter can be probed to some extent using dark-field scattering spectroscopy. \ua9 2010 SPIE

Alignment, Rotation, and Spinning of Single Plasmonic Nanoparticles and Nanowires Using Polarization Dependent Optical Forces

We demonstrate optical alignment and rotation of individual plasmonic nanostructures with lengths from Lens of nanometers to several micrometers using a single beam of linearly polarized near-infrared laser light. Silver nanorods and dimers of gold nanoparticles align parallel to the laser polarization because of the high long-axis dipole polarizability. Silver nanowires, in contrast, spontaneously turn perpendicular to the incident polarization and predominantly attach at the wire ends, in agreement with electrodynamics simulations. Wires, rods, and dimers all rotate if the incident polarization is turned. In the case of nanowires, we demonstrate spinning at an angular frequency of similar to 1 Hz due to transfer of spin angular momentum from circularly polarized light