Defense Date

2009

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Electrical Engineering

First Advisor

Supriyo Bandyopadhyay

Second Advisor

Hadis Morkoc

Third Advisor

Gary Atkinson

Fourth Advisor

Gary Tepper

Fifth Advisor

Ramana Pidaparthi

Abstract

The spin dynamics of electrons in inorganic and organic semiconducting nanostructures has become an area of interest in recent years. The controlled manipulation of an electron’s spin, and in particular its phase, is the primary requirement for applications in quantum information processing. The phase decoheres in a time known as the transverse relaxation time or T2 time. We have carried out a measurement of the ensemble-averaged transverse spin relaxation time (T2*) in bulk and few molecules of the organic semiconductor tris-(8-hydroxyquinolinolato aluminum) or Alq3. The Alq3 system exhibits two characteristic T2* times: the longer of which is temperature independent and the shorter is temperature dependent, indicating that the latter is most likely limited by spin-phonon interaction. Based on the measured data, we infer that the single-particle T2 time in Alq3 is probably long enough to meet Knill's criterion for fault-tolerant quantum computing even at room temperature. Alq3 is also an optically active organic, and we propose a simple optical scheme for spin qubit readout. Moreover, we found that the temperature-dependent T2* time is considerably shorter in bulk Alq3 powder than in few molecules confined in 1–2-nm-sized cavities. Because carriers in organic molecules are localized over individual molecules or atoms but the phonons are delocalized, we believe that this feature is caused by a phonon bottleneck effect. Organic fluorophore molecules, electrosprayed within nanometer sized pores of an anodic alumina film, exhibit unusually large molecule-specific red- or blue-shifts in the fluorescence peak. This molecular specificity allows us to resolve different constituents in a mixture optically, providing a unique new technology for bio- and chemical sensing. We have also observed that the fluorescence efficiency progressively increases with decreasing pore diameter. This trend cannot be explained by the usual photo carrier confinement model since the photo carriers are localized over individual molecules (or atoms) which are much smaller than the pore diameter. A more likely explanation is the metal enhanced fluorescence caused by the plasmon resonance of nanotextured aluminum lying at the bottom of the pores.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

June 2009

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