Professor Robert Taylor

Abstract:

Er3N@C,, exhibits sharp optical emission lines in the near-infrared attributed to fluorescence from the Er3+ ion. Here we demonstrate that high magnetic fields cause this spectrum to split, corresponding to transitions from the lowest field-split Kramers doublet of the I-4(13/2) manifold to the four lowest field-split levels of the I-4(15/2) manifold. The internal structure of these fullerenes can be spatially aligned with a preferred orientation under high magnetic field; the effect of alignment is to reduce the broadening associated with the isotropic spatial averaging characteristic of powder or frozen-solution spectra. Using a tunable 1.5 mu m laser, we directly observe non-cage-mediated optical interactions with the Er3+ ion. This spectroscopic method provides the opportunity to map the energy level structure of the incarcerated ion and to coherently control its quantum state. These qualities suggest that rare-earth endohedral fullerenes have characteristics that could be employed as a readout pathway for fullerene-based quantum information processing.

Abstract:

The endohedral fullerene Er3N@C80 shows characteristic 1.5 μm photoluminescence at cryogenic temperatures associated with radiative relaxation from the crystal-field split Er3+ 4I13/2 manifold to the 4I15/2 manifold. Previous observations of this luminescence were carried out by photoexcitation of the fullerene cage states leading to relaxation via the ionic states. We present direct non-cage-mediated optical interaction with the erbium ion. We have used this interaction to complete a photoluminescence-excitation map of the Er3+ 4I13/2 manifold. This ability to interact directly with the states of an incarcerated ion suggests the possibility of coherently manipulating fullerene qubit states with light. © 2006 Elsevier B.V. All rights reserved.

Abstract:

We have studied the microscopic surface morphology of AlN which was revealed by using an atomic force microscopy (AFM). AlN was sputtered on Si (111) and Si (100) substrates for 30 and 60 minutes. AlN was observed to crystallize as cubic-AlN at an annealing temperature of 900 °C and an annealing time of 60 minutes. We present a model to explain this cubic AlN bonding configuration. GaN was grown on AlN/Si(111) and AlN/Si(100) substrates by using a hydride vapor phase epitaxy technique. A terrace with saw-tooth-shaped formations was observed on the GaN surface and could be explained in terms of the lattice mismatch and the gas diffusion rate.

Abstract:

The dynamics of carriers in GaN epilayers is investigated using femtosecond pump-probe spectroscopy. After the residual chirp on the continuum probe is removed, the normalized difference spectra (NDS) for different probe energies are synchronized, recovering the full time resolution of our laser pulse. Our Monte-Carlo simulation agrees well with the unchirped NDS spectrum, which shows the development of the carrier distribution at early times, where phonon satellites are seen, together with a strong non-thermal electron distribution in the region of the LO-phonon energy arising from the remarkably strong electron-LO phonon interaction. Employing a new technique which involves the integration of the normalized NDS multiplied by the corresponding energy, a measure of the mean energy of the carriers in non-thermal states is obtained. By comparing the time-dependent energy loss with the theoretical energy loss rate, we estimate the effective temperature of the phonon modes as well as the population of phonons. © 2005 Elsevier B.V. All rights reserved.