Anthony E. McDonald

Three dimensional nickel–graphene core–shell electrodes

The annealing of nickel-coated porous carbon structures results in a new three dimensional nanostructured graphene encapsulated nickel core–shell electrode. A highly interdependent and dynamic process is observed that results in the complete reversal of the spatial orientations of the two component system after the annealing process. We examine the mechanism of carbon diffusion and observe unexpected morphological changes of the nickel in response to carbon crystallization. The new nickel–graphene core–shell electrode demonstrates excellent electrochemical properties with promising applications in micro-batteries and biosensors.

Mitochondrial Correlation Microscopy and Nanolaser Spectroscopy — New Tools for Biophotonic Detection of Cancer in Single Cells

Currently, pathologists rely on labor-intensive microscopic examination of tumor cells using century-old staining methods that can give false readings. Emerging BioMicroNano-technologies have the potential to provide accurate, realtime, high-throughput screening of tumor cells without the need for time-consuming sample preparation. These rapid, nanooptical techniques may play an important role in advancing early detection, diagnosis, and treatment of disease. In this report, we show that laser scanning confocal microscopy can be used to identify a previously unknown property of certain cancer cells that distinguishes them, with single-cell resolution, from closely related normal cells. This property is the correlation of light scattering and the spatial organization of mitochondria. In normal liver cells, mitochondria are highly organized within the cytoplasm and highly scattering, yielding a highly correlated signal. In cancer cells, mitochondria are more chaotically organized and poorly scattering. These differences correlate with important bioenergetic disturbances that are hallmarks of many types of cancer. In addition, we review recent work that exploits the new technology of nanolaser spectroscopy using the biocavity laser to characterize the unique spectral signatures of normal and transformed cells. These optical methods represent powerful new tools that hold promise for detecting cancer at an early stage and may help to limit delays in diagnosis and treatment.

NanoLaser/Microfluidic BioChip for Realtime Tumor Pathology

Through recent interdisciplinary scientific research, modern medicine has significantly advanced the diagnosis and treatment of disease. However, little progress has been made in reducing the death rate due to cancer, which remains the leading cause of death in much of the world. Pathologists routinely rely on microscopic examination of cell morphology using methods that originated over a hundred years ago. These staining methods are labor-intensive, time-consuming, and frequently in error. New micro-analytical methods1 (JBM, 1998; Harrison et al., 1993; Ramsey et al., 1995; Mauro Ferrari, Lynn Jelinski, 1994; Anderson et al., 1996; Carlson et al., 1996) for high speed (real time) automated screening of tissues and cells are critical to advancing pathology and hold the potential for improving diagnosis and treatment of cancer patients.By teaming experts in semiconductor physics, microfabrication, surface chemistry, film synthesis, and fluid mechanics with microbiologists and medical doctors, we are investigating nanostructured biochips to assess the condition of tumor cells by quantifying total protein content. This technique has the potential to quickly identify a cell population that has begun rapid protein synthesis and mitosis, characteristic of tumor cell proliferation. By incorporating microfluidic flow of cells inside the laser microcavity for the first time, we have enabled high throughput screening of cells in their native state, without need of chemical staining, in a sensitive nanodevice.

Oxidation of ultrathin GaSe

Oxidation of exfoliated gallium selenide (GaSe) is investigated through Raman, photoluminescence, Auger, and X-ray photoelectron spectroscopies. Photoluminescence and Raman intensity reductions associated with spectral features of GaSe are shown to coincide with the emergence of signatures emanating from the by-products of the oxidation reaction, namely, Ga2Se3 and amorphous Se. Photoinduced oxidation is initiated over a portion of a flake highlighting the potential for laser based patterning of two-dimensional heterostructures via selective oxidation.

Intracavity spectroscopy in vertical cavity surface‐emitting lasers for micro‐optical‐mechanical systems

We demonstrate lasing action in a novel microcavity laser device based on vertical cavity surface‐emitting laser technology. This laser can be used for intracavity spectroscopy, high contrast imaging of small (10 μm) structures, and is well suited for use in micro‐optical mechanical systems for analysis of particles or fluids. Here, we investigate spectra of intracavity polystyrene spheres. Lasing threshold, single‐mode operation, and multimode operation are all studied. Transverse mode separation in the multimode regime is found to be effective for sizing of the spheres.

Size dictated thermal conductivity of GaN

The thermal conductivity of n- and p-type doped gallium nitride (GaN) epilayers having thicknesses of 3–4 μm was investigated using time domain thermoreflectance. Despite possessing carrier concentrations ranging across 3 decades (1015–1018 cm–3), n-type layers exhibit a nearly constant thermal conductivity of 180 W/mK. The thermal conductivity of p-type epilayers, in contrast, reduces from 160 to 110 W/mK with increased doping. These trends—and their overall reduction relative to bulk—are explained leveraging established scattering models where it is shown that, while the decrease in p-type layers is partly due to the increased impurity levels evolving from its doping, size effects play a primary role in limiting the thermal conductivity of GaN layers tens of microns thick. Device layers, even of pristine quality, will therefore exhibit thermal conductivities less than the bulk value of 240 W/mK owing to their finite thickness.

Optical properties of fractal quantum wells

We report the growth of new fractal quantum‐well structures and the first studies of their optical properties. In these (Al,Ga)As structures the composition is varied in a fractal sequence between layers to create a highly branched, self‐similar distribution of quantum wells. Experimentally, we studied optical absorption, luminescence and excitation spectra, and electron‐hole recombination dynamics. We computed the electron and hole wave functions and transition energies and found good agreement with experiment. The optical and transport properties are strikingly different from those in single or periodic quantum wells. First, the band‐edge absorption slope (change in optical density per unit energy) can be controlled over wide limits simply by modifying the sequence. Second, the transport of carriers across the quantum‐well layers can be adjusted to control the carrier relaxation rate and energy distribution within the quantum wells. These results suggest possible applications of these new materials for ...

A Semiconductor Microlaser for Intracavity Flow Cytometry

Semiconductor microlasers are attractive components for micro- analysis systems because of their ability to emit coherent, intense light from a small aperture. By using a surface- emitting semiconductor geometry, we were able to incorporate fluid flow inside a laser microcavity for the first time. This confers significant advantages for high throughput screening of cells, particulates and fluid analytes in a sensitive microdevice. In this paper we discuss the intracavity microfluidics and present preliminary results with flowing blood and brain cells.

Self-Heating and Failure in Scalable Graphene Devices

Self-heating induced failure of graphene devices synthesized from both chemical vapor deposition (CVD) and epitaxial means is compared using a combination of infrared thermography and Raman imaging. Despite a larger thermal resistance, CVD devices dissipate >3x the amount of power before failure than their epitaxial counterparts. The discrepancy arises due to morphological irregularities implicit to the graphene synthesis method that induce localized heating. Morphology, rather than thermal resistance, therefore dictates power handling limits in graphene devices.

Epitaxial surface-emitting laser on a lattice-mismatched substrate

We have demonstrated continuous‐wave, room‐temperature, photopumped operation of a vertical‐cavity surface‐emitting laser having a 0.8% lattice mismatch with its GaAs substrate. Such mismatch provides flexibility in designing resonators with new lasing wavelengths. The laser resonator comprises lattice‐matched In0.12Ga0.88As and In0.10Al0.90As quarter‐wave layers for mirrors and a strained‐layer superlattice of In0.23Ga0.77As/Al0.35Ga0.65As for an active region. The structure lases in the range 1.05–1.10 μm under continuous‐wave photoexcitation in the wavelength range 900–950 nm. The differential power efficiency is as high as 68% and the threshold is 2 kW/cm2 (1.8 kA/cm2 injection current‐density equivalent). Dislocation line densities observed by photoluminescence microscopy are about 6×102/cm in both the active region and the uppermost mirror layers. The lines predominate along one 〈110〉 direction along which the laser light is preferentially polarized. These observations suggest a way of polarizing su...