Carl E. Bonner

Controlling spontaneous emission with metamaterials

We have observed, in metamaterial with hyperbolic dispersion (an array of silver nanowires in alumina membrane), a sixfold reduction of the emission lifetime of dye deposited onto the metamaterials surface. This serves as evidence of an anomalously high density of photonic states in hyperbolic metamaterials, demonstrates the feasibility of an earlier-predicted single-photon gun, and paves the road for the use of metamaterials in quantum optics.

Control of spontaneous emission in a volume of functionalized hyperbolic metamaterial

We have developed a simple method to fabricate lamellar metal-dielectric hyperbolic metamaterials on flat, flexible, and curvilinear substrates, which allows for functionalization of dielectric layers by dye molecules. The control of spontaneous emission of dye molecules with hyperbolic metamaterials has been studied in two different sample configurations, and the effect has been found to be much stronger when emitters are placed inside the metamaterial rather than on its surface.

Pulsed-laser deposited Er:ZnO films for 1.54μm emission

High-quality Er:ZnO films were grown by the pulsed-laser deposition technique at high temperature followed by in situ annealing. The films demonstrate remarkable crystalline quality and array of self-assembled grains. Although the films show very low electrical resistivity (∼6.41×10−4Ωcm) at room temperature, a semiconductor-metal transition was observed at 190K for low doping in contrast to semiconductor behavior for high doping. The films show pronounced room temperature emission at 1.54μm, illustrating the activation of Er3+ ions in ZnO matrix. Furthermore, no quenching effects in 1.54μm emission characteristics were observed up to 2wt% of Er doping in ZnO at room temperature.

Crystal growth, spectroscopic characterization, and laser performance of a new efficient laser material Nd:Ba5(PO4)3F

High quality single crystals of neodymium doped barium fluorapatite have been grown by the Czochralski technique and evaluated as an optical gain medium. A product of the emission cross section and lifetime of Nd3+ luminescence of more than 1.8×10−22 cm2 s at 1055 nm, and laser performance with slope efficiency up to 65% have been obtained.

Influence of doping rate in Er3+:ZnO films on emission characteristics.

High-quality Er(3+):ZnO films were grown by the pulsed-laser deposition technique for 0.5 and 2 wt. % Er doping. Two peaks were observed at approximately 1.54 microm in the photoluminescence spectra of samples with 2 wt. % doping contrary to only one peak in the 0.5 wt. % doped sample. Both peaks were found to be strongly temperature dependent. The microscopic studies clearly illustrate that the appearance of the additional peak is attributed to the environment of Er(3+) ions in the form of ErO(6) clusters, which are optically active centers in the ZnO matrix. These results are very important for designing waveguides for telecommunications.

Conjugated Block Copolymers for Opto-Electronic Functions

A novel block copolymer system containing a conjugated donor block (RO-PPV) and a conjugated acceptor block (SF-PPV) coupled by a non-conjugated bridge unit has been synthesized and characterized. While the donor block film has a strong PL emission at around 570 nm, and acceptor block film has a strong PL emission at around 590 nm, the PL emissions of -DBAB- block copolymer films were quenched by over 99%. Preliminary thin film electron microscopy studies revealed certain regular morphological pattern, possibly due to block copolymer microphase separation.

Effective third-order nonlinearities in metallic refractory titanium nitride thin films

Nanophotonic devices offer an unprecedented ability to concentrate light into small volumes which can greatly increase nonlinear effects. However, traditional plasmonic materials suffer from low damage thresholds and are not compatible with standard semiconductor technology. Here we study the nonlinear optical properties in the novel refractory plasmonic material titanium nitride using the Z scan method at 1550 nm and 780 nm. We compare the extracted nonlinear parameters for TiN with previous works on noble metals and note a similarly large nonlinear optical response. However, TiN films have been shown to exhibit a damage threshold up to an order of magnitude higher than gold films of a similar thickness, while also being robust, cost-efficient, bio- and CMOS compatible. Together, these properties make TiN a promising material for metal-based nonlinear optics.

Enhancing Eu 3+ magnetic dipole emission by resonant plasmonic nanostructures

We demonstrate the enhancement of magnetic dipole spontaneous emission from Eu3+ ions by an engineered plasmonic nanostructure that controls the electromagnetic environment of the emitter. Using an optical microscope setup, an enhancement in the intensity of the Eu3+ magnetic dipole emission was observed for emitters located in close vicinity to a gold nanohole array designed to support plasmonic resonances overlapping with the emission spectrum of the ions.

In vitro stability study of organophosphonic self assembled monolayers (SAMs) on cobalt chromium (Co-Cr) alloy

Surface modification of cobalt chromium (Co-Cr) alloy is being investigated as a possible solution to the biomedical challenges arising from its usage. Self assembled monolayers (SAMs) of organophosphonic octadecylphosphonic acid (ODPA) were formed on the oxide surface of Co-Cr alloy by chemisorption using the solution deposition technique. High quality and well-ordered SAMs were formed which were characterized using Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle measurements and ellipsometry. The resulting monolayers were then exposed to in vitro conditions using phosphate buffered saline (PBS) solution. The samples were analyzed for a period of 1, 3, 7 and 14 days. The resulting samples were characterized using XPS, AFM and Contact angle measurements. XPS atomic concentrations and detailed high energy elemental scans gave an insight into the trends of elemental concentrations over the duration of the study. SAMs were found to be strongly bound to the oxide surface after PBS exposure. AFM gave the topographic details of SAMs presence by island formation before and after SAM formation and also over the duration of the PBS exposure. Contact Angle Measurements confirmed the hydrophobicity of the surface after SAM formation and indicated a slight disorder of the SAM alkyl chain upon exposure to PBS. Thus, ODPA SAMs were successfully coated on Cobalt Chromium (Co-Cr) alloy surface and were found to be stable and strongly bound after PBS exposure.

Gyroidal titanium nitride as nonmetallic metamaterial

We have synthesized gyroidal TiN metamaterials, studied their optical properties, and compared them with the optical properties of the TiN thin films fabricated using reactive magnetron sputtering. The plasma frequency, ωp, and the corresponding free carrier concentration, N, in the gyroid samples were found to be much lower than those in thin films. Furthermore, the plasma frequency in TiN gyroids was comparable to or smaller than the damping rate, γD. This makes the studied TiN gyroid a poor plasmonic material. At the same time, TiN gyroidal samples have demonstrated bright rainbow pattern in the optical microscopy reflectance study. This phenomenon is tentatively explained by different orientations of the gyroid domains.