James H. Rice

InGaN quantum dots grown by metalorganic vapor phase epitaxy employing a post-growth nitrogen anneal

We describe the growth of InGaN quantum dots (QDs) by metalorganic vapor phase epitaxy. A thin InGaN epilayer is grown on a GaN buffer layer and then annealed at the growth temperature in molecular nitrogen inducing quantum dot formation. Microphotoluminescence studies of these QDs reveal sharp peaks with typical linewidths of ∼700 μeV at 4.2 K, the linewidth being limited by the spectral resolution. Time-resolved photoluminescence suggests that the excitons in these structures have lifetimes in excess of 2 ns at 4.2 K.

Quantum dot emission from site-controlled InGaN/GaN micropyramid arrays

InxGa1−xN quantum dots have been fabricated by the selective growth of GaN micropyramid arrays topped with InGaN∕GaN quantum wells. The spatially, spectrally, and time-resolved emission properties of these structures were measured using cathodoluminescence hyperspectral imaging and low-temperature microphotoluminescence spectroscopy. The presence of InGaN quantum dots was confirmed directly by the observation of sharp peaks in the emission spectrum at the pyramid apices. These luminescence peaks exhibit decay lifetimes of approximately 0.5ns, with linewidths down to 650μeV (limited by the spectrometer resolution).

Time-resolved dynamics in single InGaN quantum dots

We present measurements of photoluminescence decay dynamics for single InGaN quantum dots. The recombination is shown to be characterized by a single exponential decay, in contrast to the nonexponential recombination dynamics seen in the two-dimensional wetting layer. The lifetimes of single dots in the temperature range 4 to 60 K decrease with increasing temperature.

Photoreduction of SERS-Active Metallic Nanostructures on Chemically Patterned Ferroelectric Crystals

Photodeposition of metallic nanostructures onto ferroelectric surfaces is typically based on patterning local surface reactivity via electric field poling. Here, we demonstrate metal deposition onto substrates which have been chemically patterned via proton exchange (i.e., without polarization reversal). The chemical patterning provides the ability to tailor the electrostatic fields near the surface of lithium niobate crystals, and these engineered fields are used to fabricate metallic nanostructures. The effect of the proton exchange process on the piezoelectric and electrostatic properties of the surface is characterized using voltage-modulated atomic force microscopy techniques, which, combined with modeling of the electric fields at the surface of the crystal, reveal that the deposition occurs preferentially along the boundary between ferroelectric and proton-exchanged regions. The metallic nanostructures have been further functionalized with a target probe molecule, 4-aminothiophenol, from which surface-enhanced Raman scattering (SERS) signal is detected, demonstrating the suitability of chemically patterned ferroelectrics as SERS-active templates.

Temporal variation in photoluminescence from single InGaN quantum dots

We report measurements of optical transitions in single III/V (InGaN) quantum dots as a function of time. Temporal fluctuations in microphotoluminescence peak position and linewidth are demonstrated and attributed to spectral diffusion processes. The origin of this temporal variation is ascribed to randomly generated local electric fields inducing a Stark shift in the optical emission peaks of the InGaN quantum dots.

Quantum-confined Stark effect in a single InGaN quantum dot under a lateral electric field

The effect of an externally applied lateral electric field upon an exciton confined in a single InGaN quantum dot is studied using microphotoluminescence spectroscopy. The quantum-confined Stark effect causes a shift in the exciton energy of more than 5 meV, accompanied by a reduction in the exciton oscillator strength. The shift has both linear and quadratic terms as a function of the applied field.

Nanoscale solid-state quantum computing

Most experts agree that it is too early to say how quantum computers will eventually be built, and several nanoscale solid–state schemes are being implemented in a range of materials. Nanofabricated quantum dots can be made in designer configurations, with established technology for controlling interactions and for reading out results. Epitaxial quantum dots can be grown in vertical arrays in semiconductors, and ultrafast optical techniques are available for controlling and measuring their excitations. Single–walled carbon nanotubes can be used for molecular self–assembly of endohedral fullerenes, which can embody quantum information in the electron spin. The challenges of individual addressing in such tiny structures could rapidly become intractable with increasing numbers of qubits, but these schemes are amenable to global addressing methods for computation.

Submicrometer infrared surface imaging using a scanning-probe microscope and an optical parametric oscillator laser

Submicrometer IR surface imaging was performed with a resolution better than the diffraction limit. The apparatus was based on an IR optical parametric oscillator laser and a commercial atomic force microscope and used, as the detection mechanism, induced resonant oscillations in an atomic force microscopy (AFM) cantilever. For the first time to our knowledge this was achieved with top-down illumination and a benchtop IR source, thus extending the range of potential applications of this technique. IR absorption and AFM topography images of polystyrene beads were recorded simultaneously with an image resolution of 200 nm.

Beyond the diffraction limit: far-field fluorescence imaging with ultrahigh resolution

Fluorescence microscopy is an important and extensively utilised tool for imaging biological systems. However, the image resolution that can be obtained has a limit as defined through the laws of diffraction. Demand for improved resolution has stimulated research into developing methods to image beyond the diffraction limit based on far-field fluorescence microscopy techniques. Rapid progress is being made in this area of science with methods emerging that enable fluorescence imaging in the far-field to possess a resolution well beyond the diffraction limit. This review outlines developments in far-field fluorescence methods which enable ultrahigh resolution imaging and application of these techniques to biology. Future possible trends and directions in far-field fluorescence imaging with ultrahigh resolution are also outlined.

Site selective surface enhanced Raman on nanostructured cavities

Presented here are angle dependence studies on the surface enhanced Raman (SER) signal obtained from dye placed on plasmon active nanocavity arrays. A comparative study was carried out between two modified array supports. One array had dye placed only on the interior walls of the cavities in the array. The other array had dye placed only on its top flat surface. Results show that Raman intensities as a function of angle depend on the location of the dye on the array; this was interpreted to arise from the presence of different plasmon polariton modes in these sites.