Marvin A. Malone

Propagation lengths of surface plasmon polaritons on metal films with arrays of subwavelength holes by infrared imaging spectroscopy

Metal films with arrays of subwavelength holes (mesh) exhibit extraordinary transmission resonances to which many attribute a role for surface plasmon polaritons (SPPs); others debated this point. Experimental measurements of propagation lengths are presented under conditions that pertain to the use of SPPs for surface spectroscopy. The lateral extent of electromagnetic propagation along the mesh surface is measured by recording absorption spectra of a line of latex microspheres as a function of distance away from the line along the mesh. Measurements reveal an exponential functional form for decay of absorption signal laterally from the absorption source. Results at 697 cm(-1), which are closest to the strongest transmission resonance of the mesh, reveal a 1/e propagation distance along the surface of 17.8+/-2.9 microm. This is 40% larger than the lattice spacing implicating the holes as the SPP damping mechanism, however, this is significantly shorter than smooth metal expectations.

Single Airborne Dust Particles using Plasmonic Metal Films with Hole Arrays.

An airborne dust particle is trapped in the hole of a plasmonic metal film with a patterned array of holes (mesh) by pumping air through the mesh. Both scatter-free infrared spectra and scanning electron images are obtained on the same individual airborne dust particle, showing the feasibility of multiple, nondestructive experiments on a single, subwavelength particle. Ultimately, this may help to elucidate the effect of shape, orientation, and crystallinity on IR dust particle spectra.

Infrared spectral model for subwavelength particles of mixed composition based on the spectra of individual particles with calibration data for airborne dust.

A Mie-Bruggeman spectral model is presented which predicts the orientationally averaged, infrared spectra of individual mixed-composition particles or the average spectrum of collections of such particles. The model uses parameters extracted from sets of individual particle spectra of pure materials known to be in subject mixtures. The spectra of both calibrants and subject particles were recorded by trapping size-selected particles in the holes of plasmonic metal mesh. Calibrating data is presented for quartz, calcite, dolomite, three clays, gypsum, polyethylene, and living organic material (yeast cells). The individual particle spectra of these calibrants are averaged to account for crystal orientation effects, fit by a Mie theory model, and tabulated herein as dielectric functions of each component. The component dielectric functions are combined in this model with Bruggeman effective medium theory producing a spectral prediction for mixed-composition particles. The Mie-Bruggeman model was used to analyze the composition of dust from our lab air [K. E. Cilwa et al. J. Phys. Chem. C 2011, 115, 16910] based on the average spectrum of the dust particles. The model does a reasonable job of characterizing the dust in our laboratory air exhibiting promise for future applications. This work presents the model and illustrates potential; however, much more work will be required before its accuracy as a quantitative analytical method is established.

Developing Plasmonics Under the Infrared Microscope: From Ni Nanoparticle Arrays to Infrared Micromesh.

Microscopes typically collect light over large ranges of angles dispersing plasmonic resonances. While this is an advantage for recording spectra of microscopic particles, it is a disadvantage for sensing by resonance shifts. Adaptations are described herein which enable one to identify, manipulate, and examine narrow plasmonic resonances under a microscope. Noting more general familiarity with metal nanoparticle arrays, a useful perspective is offered by relating the optical transmission of small Ni nanoparticle arrays to that of Ni metal films with microhole arrays, i.e., infrared-active mesh. This perspective also includes the connection to traditional dispersion studies, a new microscope method to measure the propagation length of surface-plasmon-polariton-mediated resonances, and the shifting of resonance positions by latex microspheres in the holes of mesh. A useful perspective is offered by relating the optical transmission of small Ni nanoparticle arrays to that of Ni metal films with microhole arrays, i.e., infrared-active mesh.

Plasmonics under the Infrared Microscope: Sensing and Spectra of Single Particles Using Metal Film Hole Arrays

Measurements and modeling of plasmonic resonance positions as a function of orientation are presented in a manner that connects the common geometries with a formalism for all of momentum space. This framework is useful for understanding dispersion studied under an infrared microscope by rotating the sample about the optical axis of the microscope. Applications using the microscope for sensing and spectra of individual particles are presented.

Generalizing thermodynamic properties of bulk single-walled carbon nanotubes.

The enthalpy and Gibbs free energy thermodynamical potentials of single walled carbon nanotubes were studied of all types (armchairs, zig-zags, chirals (n>m), and chiral (n<m)). Bulk values of these thermodynamic potentials were obtained using a previously demonstrated robust method based on semi-empirical PM3 calculations and an extrapolated cluster approach. Those values were used to study the relationship between the thermodynamic potentials and the diameter of the nanotube. Results of this study led to the proposal of a single equation for the thermodynamical potential of [Formula: see text] or [Formula: see text] (assembly of nanotubes from atoms) versus the chiral vector indexes n and m for any given nanotube. The equations show a good level of accuracy in predicting thermodynamic potentials for practical applications.

Plasmonic spectra of individual subwavelength particles under the infrared microscope: cells and airborne dust

A plasmonic metal film with a subwavelength hole array (a mesh) is used to capture an individual subwavelength particle, like a single yeast cell or airborne dust particle, and an imaging infrared (IR) microscope, records a scatterfree, IR absorption spectrum of the particle. Individual spectra of wavelength scale particles usually suffer from large scattering effects. This paper starts by demonstrating the plasmonic nature of the mesh in the infrared, proceeds to how this special form of light (surface plasmon polariton mediated transmission resonance) leads to scatter-free IR absorption spectra of individual, subwavelength particles, and ends with work on yeast cells and dust particles from our laboratory air and a household filter.