There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Localized Surface Plasmon Resonance Sensors

The discovery of the photoelectric effect by Heinrich Hertz in 1887 set the foundation for over 125 years of hot carrier science and technology. In the early 1900s it played a critical role in the development of quantum mechanics, but even today the unique properties of these energetic, hot carriers offer new and exciting opportunities for fundamental research and applications. Measurement of the kinetic energy and momentum of photoejected hot electrons can provide valuable information on the electronic structure of materials. The heat generated by hot carriers can be harvested to drive a wide range of physical and chemical processes. Their kinetic energy can be used to harvest solar energy or create sensitive photodetectors and spectrometers. Photoejected charges can also be used to electrically dope two-dimensional materials. Plasmon excitations in metallic nanostructures can be engineered to enhance and provide valuable control over the emission of hot carriers. This Review discusses recent advances in the understanding and application of plasmon-induced hot carrier generation and highlights some of the exciting new directions for the field.

Plasmon-induced hot carrier science and technology

We experimentally demonstrate a perfect plasmonic absorber at λ = 1.6 μm. Its polarization-independent absorbance is 99% at normal incidence and remains very high over a wide angular range of incidence around ±80°. We introduce a novel concept to utilize this perfect absorber as plasmonic sensor for refractive index sensing. This sensing strategy offers great potential to maintain the performance of localized surface plasmon sensors even in nonlaboratory environments due to its simple and robust measurement scheme.

Infrared Perfect Absorber and Its Application As Plasmonic Sensor

Synthesis of metallic nanoparticles using plant extracts.

https://physik.uni-graz.at/~uxh/Publications/mnpbem11.pdf

MNPBEM - A Matlab toolbox for the simulation of plasmonic nanoparticles ✩

The plasmon resonance of metal nanoparticles shifts upon refractive index changes of the surrounding medium through the binding of analytes. The use of this principle allows one to build ultra-small plasmon sensors that can detect analytes (e.g., biomolecules) in volumes down to attoliters. We use simulations based on the boundary element method to determine the sensitivity of gold nanorods of various aspect ratios for plasmonic sensors and find values between 3 and 4 to be optimal. Experiments on single particles confirm these theoretical results. We are able to explain the optimum by showing a corresponding maximum for the quality factor of the plasmon resonance.

/pdf/the-optimal-aspect-ratio-of-gold-nanorods-for-plasmonic-bio-8hw2ty9ojj.pdf

The Optimal Aspect Ratio of Gold Nanorods for Plasmonic Bio-sensing

We demonstrate the ultrafast generation of electrons from tailored metallic nanoparticles and unravel the role of plasmonic field enhancement in this process by comparing resonant and off-resonant particles, as well as different particle geometries. We find that electrons become strongly accelerated within the evanescent fields of the plasmonic nanoparticles and escape along straight trajectories with orientations governed by the particle geometry. These results establish plasmonic nanoparticles as versatile ultrafast, nanoscopic sources of electrons.

Ultrafast strong-field photoemission from plasmonic nanoparticles.

Spatial mapping of optical and acoustic, bulk and surface vibrational modes in magnesium oxide nanocubes is demonstrated using a single electron probe. The vibrational excitations of nanostructures have a fundamental effect on their suitability for various electronic, optical and thermal applications. Maureen Lagos and colleagues probe these excitations, using state-of-the-art electron microscopy to map the vibrational modes both at the surface and within the body of individual nanoparticles. Such information not only contributes to our knowledge of these fundamental vibrational modes, but will also be valuable for the design and optimization of nanostructures for practical use. Imaging of vibrational excitations in and near nanostructures is essential for developing low-loss infrared nanophotonics1, controlling heat transport in thermal nanodevices2,3, inventing new thermoelectric materials4 and understanding nanoscale energy transport. Spatially resolved electron energy loss spectroscopy has previously been used to image plasmonic behaviour in nanostructures in an electron microscope5,6, but hitherto it has not been possible to map vibrational modes directly in a single nanostructure, limiting our understanding of phonon coupling with photons7 and plasmons8. Here we present spatial mapping of optical and acoustic, bulk and surface vibrational modes in magnesium oxide nanocubes using an atom-wide electron beam. We find that the energy and the symmetry of the surface polariton phonon modes depend on the size of the nanocubes, and that they are localized to the surfaces of the nanocube. We also observe a limiting of bulk phonon scattering in the presence of surface phonon modes. Most phonon spectroscopies are selectively sensitive to either surface or bulk excitations; therefore, by demonstrating the excitation of both bulk and surface vibrational modes using a single probe, our work represents advances in the detection and visualization of spatially confined surface and bulk phonons in nanostructures.

Mapping vibrational surface and bulk modes in a single nanocube

We theoretically investigate the strong coupling between a single molecule and a single metallic nanoparticle. A theory suited for the quantum-mechanical description of surface plasmon polaritons (SPPs) is developed. The coupling between these SPPs and a single molecule, and the modified molecular dynamics in the presence of the nanoparticle are described within a combined Drude and boundary-element-method approach. Our results show that strong coupling is possible for single molecules and metallic nanoparticles and can be observed in fluorescence spectroscopy through the splitting of emission peaks.

https://physik.uni-graz.at/~uxh/diploma/truegler.pdf

Andreas Trügler

Papers

MNPBEM - A Matlab toolbox for the simulation of plasmonic nanoparticles ✩

The Optimal Aspect Ratio of Gold Nanorods for Plasmonic Bio-sensing

Ultrafast strong-field photoemission from plasmonic nanoparticles.

Mapping vibrational surface and bulk modes in a single nanocube

Strong coupling between a metallic nanoparticle and a single molecule