Sheffer Meltzer

Plasmonics—A Route to Nanoscale Optical Devices

The further integration of optical devices will require the fabrication of waveguides for electromagnetic energy below the diffraction limit of light. We investigate the possibility of using arrays of closely spaced metal nanoparticles for this purpose. Coupling between adjacent particles sets up coupled plasmon modes that give rise to coherent propagation of energy along the array. A point dipole analysis predicts group velocities of energy transport that exceed 0.1c along straight arrays and shows that energy transmission and switching through chain networks such as corners (see Figure) and tee structures is possible at high efficiencies. Radiation losses into the far field are expected to be negligible due to the near-field nature of the coupling, and resistive heating leads to transmission losses of about 6 dB/lm for gold and silver particles. We analyze macroscopic analogues operating in the microwave regime consisting of closely spaced metal rods by experiments and full field electrodynamic simulations. The guiding structures show a high confinement of the electromagnetic energy and allow for highly variable geometries and switching. Also, we have fabricated gold nanoparticle arrays using electron beam lithography and atomic force microscopy manipulation. These plasmon waveguides and switches could be the smallest devices with optical functionality.

Manipulation of gold nanoparticles in liquid environments using scanning force microscopy

Precise and controlled manipulation of individual gold nanoparticles (deposited on a Si/SiO2 surface) in liquid environments using the tip of a scanning force microscope is reported for the first time. Experiments were performed in deionized water and in ethanol as a prototype for an organic solvent. Analysis of the amplitude signal of the cantilever before and during manipulation reveals that the particles are pushed across the surface, similar to the manipulation of nanoparticles in air.

Manipulation of nanoscale components with the AFM: principles and applications

Bottom-up construction of nanostructures from molecular-sized components is a promising approach to nanofabrication. This paper discusses bottom-up techniques that involve positioning of nanoparticles or nanorods with an Atomic Force Microscope (AFM), and, for certain applications, chemical linking of such components. The physical principles of nanomanipulation with an AFM are described, with an emphasis on Dynamic Force Microscopy (DFM). Sources of spatial uncertainty are discussed. It is shown that nanoparticles and nanorods can be reliably positioned on a surface by pushing them with the tip of an AFM. Typical nanomanipulation operations are conducted at room temperature, in ambient air or in a liquid. For many applications nanostructures composed of nanoparticles or nanorods must be linked together. This can be done by using self-assembling linkers or by electroless deposition. The ability to immobilize the particles on a surface also is important in some applications. Again, self-assembly techniques can be used to imbed the particles in deposited layers.

Observation of coupled plasmon-polariton modes of plasmon waveguides for electromagnetic energy transport below the diffraction limit

We investigate the possibility of using arrays of closely spaced metal nanoparticles as plasmon waveguides for electromagnetic energy below the diffraction limit of light. Far-field spectroscopy on arrays of closely spaced 50 nm Au particles fabricated using electron beam lithography reveals the presence of near-field optical particle interactions that lead to shifts in the plasmon resonance frequencies for longitudinal and transverse excitations. We link this observation to a point-dipole model for energy transfer in plasmon waveguides and give an estimate of the expected group velocities and energy decay lengths for the fabricated structures. A near-field optical excitation and detection scheme for energy transport is proposed and demonstrated. The fabricated structures show a high propagation loss of about 3 dB / 15 nm which renders a direct experimental observation of energy transfer impossible. The nature of the loss and ways to decrease it by an order of magnitude are discussed. We also present finite-difference time-domain simulations on the energy transfer properties of plasmon waveguides.

Layered nanoassembly of three-dimensional structures

NEMS (nanoelectromechanical systems) loom beyond the MEMS horizon as the new frontier in miniaturization. Nanorobots and other NEMS are expected to find revolutionary applications in science, engineering and everyday life. Until now, nanostructures have been built primarily in 2D, because of the difficulties of 3D fabrication. This paper describes a promising approach to the construction of 3D nanostructures by working in successive layers, much like the rapid prototyping techniques used in the macroscopic world. Each object nanolayer is built by nanomanipulation, or possibly by programmed self-assembly, and then surrounded by a sacrificial layer that planarizes the sample and serves as a substrate for the deposition of the next object nanolayer. Initial experimental results which show that the approach is feasible are presented.

Energy transport in metal nanoparticle plasmon waveguides

We investigate the optical properties of arrays of closely spaced metal nanoparticles in view of their potential to guide electromagnetic energy with a lateral mode confinement below the diffraction limit of light. Finite-difference time-domain simulations of short arrays of noble metal nanospheres show that electromagnetic pulses at optical frequencies can propagate along the arrays due to near-field interactions between plasmon-polariton modes of adjacent nanoparticles. Near-field microscopy enables the study of energy transport in these plasmon waveguides and shows experimental evidence for energy propagation over a distance of 0.5 µm for plasmon waveguides consisting of spheroidal silver particles fabricated using electron beam lithography.