Elshan A. Akhadov

Low-temperature growth of crystalline GaN films using energetic neutral atomic-beam lithography/epitaxy

Crystalline and polycrystalline gallium nitride films have been grown on bare c-axis-oriented sapphire at low temperatures (100 °C to 500 °C) using energetic neutral atom-beam lithography/epitaxy. Surface chemistry is activated by exposing substrates to nitrogen atoms with kinetic energies between 0.5 and 5.0 eV and a simultaneous flux of Ga metal, allowing low-temperature growth of GaN thin films. The as-grown GaN films show semiconducting properties, a high degree of crystallinity, and excellent epitaxial alignment. This method of low-temperature nitride film growth opens opportunities for integrating novel substrate materials with group III nitride technologies.

Spatial characterization of the magnetic field profile of a probe tip used in magnetic resonance force microscopy

We have developed the experimental approach to characterize spatial distribution of the magnetic field produced by cantilever tips used in magnetic resonance force microscopy (MRFM). We performed MRFM measurements on a well characterized diphenyl-picrylhydrazyl (DPPH) film and mapped the 3D field profile produced by a Nd2Fe14B probe tip. Using our technique field profiles of arbitrarily shaped probe magnets can be imaged.

Gamma-ray waveguides

We have developed an approach for gamma-ray optics using layered structures acting as planar waveguides. Experiments demonstrating channeling of 122keV gamma rays in two prototype waveguides validate the feasibility of this technology. Gamma-ray waveguides allow one to control the direction of radiation up to a few MeV. The waveguides are conceptually similar to polycapillary optics, but can function at higher gamma-ray energies. Optics comprised of these waveguides will be able to collect radiation from small solid angles or concentrate radiation into small area detectors. Gamma-ray waveguides may find applications in medical imaging and treatment, astrophysics, and homeland security.

Innovative approach to nanoscale device fabrication and low-temperature nitride film growth

Energetic neutral beam lithography/epitaxy (ENABLE) was used for etching very high-aspect-ratio nanoscale structures into polymers and for growing templated AlN films at low temperatures. Various methods were used for masking polymeric films for selective etching by energetic oxygen atoms to fabricate sub-100 nm structures with aspect ratios exceeding 35:1. ENABLE was also utilized for low-temperature growth of AlN into previously etched polymer templates to directly form AlN wires. By taking advantage of the unique processing capabilities of ENABLE, new opportunities for making delicate nanostructures are made possible.

Multi-layer planar terahertz electric metamaterials on flexible substrates

Planar electric metamaterials fabricated on thin, flexible substrates are studied using terahertz-time domain spectroscopy. Transmission measurements are performed to analyze dielectric properties on single and multiple stacked samples and reveal strong resonances at 1.2 THz.