Dominic Zerulla

The design of efficient surface-plasmon-enhanced ultra-thin polymer-based solar cells

Polymer based solar cells are particularly attractive because of their mechanical flexibility and potential for low-cost fabrication. Although significant progress has been made, their efficiency is reduced strongly due to recombination processes that scale with the thickness of the active layer. A theoretical study of periodic plasmonic solar cell enhancement is presented, including a design for demonstrating high efficiency while using a significantly reduced active layer thicknesses. This is achieved through the superposition of toothgrating structures of multiple periodicities along a silver reflecting layer. Through finite-difference time-domain calculations, it was possible to optimize the overall spectral response of the cell yielding surface plasmon resonances at predetermined wavelengths. The improved solar cell design results in a system with increased absorption, allowing for the desired reduction in active layer thickness while also enhancing the performance of the cell over a wide wavelength ...

Competing interaction of different thiol species on gold surfaces

Abstract Self-assembled monolayers (SAMs) of thiol molecules show very interesting properties. We have investigated the possibilities of creating mixed thiol films, consisting of two structurally and chemically very different thiol species. We used the aliphatic hexadecanethiol and the aromatic 2-mercapto-benzothiazol (MBT). The interaction of both species after successive adsorption on gold was investigated using XPS. We found, that hexadecanethiol displaces the MBT from gold surfaces, similar to the removal of carbon contamination by the alkanethiol. In contrast, MBT cannot replace the adsorbed alkanethiol layer. Therefore, the creation of mixed films has to start with a partial coverage of hexadecanethiol, followed by the MBT, which now can assemble to the uncovered surface without disturbing the alkanethiol.

Magnetic Manipulation and Optical Imaging of an Active Plasmonic Single-Particle Fe-Au Nanorod

Superparamagnetic microbeads play an important role in a number of scientific and biotechnology applications including single-molecule force measurements, affinity separation, and in vivo and in vitro diagnostics. Magneto-optically active nanorods composed of single-crystalline Au and polycrystalline Fe segments were synthesized with diameters of 60 or 295 nm using templated electrodeposition. The Fe section was magnetically soft and had a saturation magnetization of approximately 200 emu/g, resulting in a 10-fold increase in magnetization relative to that iron oxide nanoparticles. The strong plasmonic response of the Au segment of the rod in both the longitudinal and transverse directions made it possible to detect the orientation of a single rod in a polarized light microscope with nanometer resolution. These nanorods provide significantly improved physical properties over iron oxide superparamagnetic beads, making it possible to simultaneously manipulate and monitor the orientation of biomolecules with well-defined forces at the nanometer scale.

Plasmonic Enhancement of Dye Sensitized Solar Cells via a Tailored Size-Distribution of Chemically Functionalized Gold Nanoparticles

A substantial and stable increase of the current density Jsc of ruthenium (Ru) dye sensitized solar cells (DSC) of up to 16.18% and of the power efficiency of up to 25.5% is demonstrated in this article via plasmonic enhancement. The key aspect of this work is the use of a tailored bimodal size distribution of functionalized gold nanoparticles (AuNPs) that have been chemically immobilized onto the mesoporous titanium dioxide (TiO2) layer via short, stable dithiodibutyric acid linkers. The size distribution of the AuNPs is a result of theoretical calculations that aimed at the perfection of the absorption characteristics of the complete solar cell system over a wide range of wavelengths. The functionalization of the AuNPs serves to bind them at a close but defined distance to TiO2-particles and additionally to chemically protect them against potential corrosion by the electrolyte. Simulations of near field (enhanced absorption) and far field (scattering) contributions have been used to tailor a complex AuNPs bimodal size distribution that had subsequently demonstrated experimentally a close to optimum improvement of the absorbance over a wide wavelength range (500–675 nm) and therefore an impressive DSC efficiency enhancement. Finally, the modified DSCs are exhibiting pronounced longevity and stable performance as confirmed via long time measurements. In summary, the presented systems show increased performance compared to non plasmonic enhanced cells with otherwise identical composition, and are demonstrating a previously unpublished longevity for iodide electrolyte/AuNPs combinations.

Nanoscale infrared absorption imaging permits non-destructive intracellular photosensitizer localization for subcellular uptake analysis

The most immediate biological and medical advantages of therapeutic agent localization on the nanoscale arise from the increased understanding of targeted delivery, selectivity and intracellular distribution that are gained by imaging at the resolution scale of individual nanovectors and therapeutic agents themselves. This paper reports on the use of a nanoscale resolution chemical imaging method, infrared (IR) nanospectral absorption imaging, used to map the subcellular localization of a photoactive therapeutic agent - toluidine blue-conjugated gold nanoparticles (TBO) within nanoscale subsections of single colon adenocarcinoma cells. By comparison of photosensitizer distribution with diffraction limited optical imaging, the benefits of IR nanospectral localization are highlighted and the spatial and spectral accuracy of the non-destructive IR imaging method is confirmed. IR spectral ratio imaging is presented as a means to map intracellular nanoparticle density at sub 50 nm lateral resolution with IR nanospectroscopy enabling distinction of nanoparticle seeded cells from a control group with 95% confidence. In this way we illustrate that IR absorption nanoimaging combined with IR point source data does not only yield intracellular drug detection on the order of nanometres, but also permits extension of the AFM-IR technique from subcellular analysis up to studies of cell numbers that are statistically significant.

Quantifying nanoscale biochemical heterogeneity in human epithelial cancer cells using combined AFM and PTIR absorption nanoimaging

Subcellular chemical heterogeneity plays a key role in cell organization and function. However the biomechanics underlying the structure-function relationship is governed by cell substructures which are poorly resolved using conventional chemical imaging methods. To date, advances in sub-diffraction limited infrared (IR) nanoscopy have permitted intracellular chemical mapping. In this work we report how image analysis applied to a combination of IR absorption nanoimaging and topographic data permits quantification of chemical complexity at the nanoscale, enabling the analysis of biochemical heterogeneity in mammalian cancer cells on the scale of subcellular features.

Tailoring surface plasmon polariton propagation via specific symmetry properties of nanostructures

We report on an experimental investigation on surface plasmon polariton (SPP) propagation and interaction on two-dimensional arrays of differing symmetry properties. Providing the required symmetry variations and forming the basis of the arrays are tailor designed nanostructures. We demonstrate that as a result of a 120° symmetry presence, our triquetra-rotor nanostructures can be used for SPP guiding and propagation direction control. As a result, the polarization angle at which the far field SPP related minimum reflectivity occurs can be predetermined by design characteristics and orientation of the nanostructures.

The extreme low-frequency Raman spectrum of liquid water.

Not merely sloshing around: The chemical and physical properties of water are very important. In contrast to its simplistic chemical formula, water possesses a complex dynamic behaviour (see picture). The bend, torsion, symmetric and asymmetric stretch modes of liquid water, close to the wavelength of the laser line have been predicted. Here, the low-frequency Raman spectrum of liquid water is presented confirming the presence of all four modes in the restricted translational region (35–300 cm −1 ).

Highly ordered Fe-Au heterostructured nanorod arrays and their exceptional near-infrared plasmonic signature.

The potential of highly ordered array nanostructures in sensing applications is well recognized, particularly with the ability to define the structural composition and arrangement of the individual nanorods accurately. The use of heterogeneous nanostructures generates an additional degree of freedom, which can be used to tailor the optical response of such arrays. In this article, we report on the fabrication and characterization of well-defined Fe-Au bisegmented nanorod arrays in a repeating hexagonal arrangement. Through an asymmetric etching method, free-standing Fe-Au nanorod arrays on a gold-coated substrate were produced with an inter-rod spacing of 26 nm. This separation distance renders the array capable of sustaining resonant electromagnetic wave coupling between individual rods. Owing to this coupling, the subwavelength arrangement, and the structural heterogeneity, the nanorod arrays exhibit unique plasmonic responses in the near-infrared (NIR) range. Enhanced sensitivity in this spectral region has not been identified for gold-only nanorods of equivalent dimensions. The NIR response offers confirmation of the potential of these highly ordered, high-density arrays for biomedical relevant applications, such as subcutaneous spectroscopy and biosensing.

Angular-resolved XANES measurements of the polar and azimuthal orientation of alkanethiols on InP(110)

Abstract This Letter describes investigations of the X-ray absorption near-edge structure of adsorbed hexadecanethiol monolayers on InP(110). The angular (azimuthal and polar)-resolved measurements reveal the substrate-dependent tilt-angle of the alkyl C–C backbone (about 34° from normal). A unique feature observed on these monolayers is the nearly complete alignment of the alkyl chains with respect to the azimuthal orientation. We suggest that this adsorbate system represents the case of a single-domain organic monolayer. We interpret this behaviour, which deviates strongly from the well-known thiol films on gold, silver or copper, in terms of structural constraints and dangling-bond-induced pre-orientation of the alkanethiol chains.