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Synthesis, optical and electronic properties of group IV semiconductor nanocrystals

Citation

Shcheglov, Kirill V. (1997) Synthesis, optical and electronic properties of group IV semiconductor nanocrystals. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-01172008-081522

Abstract

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Every operating control system must deal with constraints. On the one hand, the range and rate of change of the input or manipulated variable is limited by the physical nature of the actuator (saturation limits). On the other hand, process state variables or outputs (pressures, temperatures, voltages) may not be allowed to exceed certain bounds arising from equipment limitation, safety considerations, or environmental regulations.

A rich theory exists for designing controllers - both linear ([...],LQG, LTR, pole-placement) and nonlinear (nonlinear [...], control, feedback linearization, sliding mode control, gain scheduling). However, none of these popular and fashionable controller design techniques account for the presence of input or output constraints. Although occasionally these constraints may be neglected, in general, they lead to design and operating problems unless they are accounted for properly.

In traditional control practice, overrides or mode selection schemes are used to deal with output constraints: they switch between a "bank" of controllers, each of which is designed to achieve a specific objective. In both cases (saturation limit and mode selection), a control input nonlinearity is introduced into the operating system.

Despite its significance, the study of the constrained control problem has received far less attention than the traditional unconstrained (linear and nonlinear) control theory. With few exceptions, most of the controller design techniques for constrained systems are by-and-large ad-hoc, with very little guarantees of stability, performance and robustness to plant model uncertainty.

The objective of this thesis is to take a broad approach towards the constrained control problem. One part of the thesis is devoted to the development of a systematic and unifying theory for studying the so-called Anti-Windup Bumpless Transfer (AWBT) problem. The other part aims towards the development of a general novel approach for the synthesis of a robust model predictive control (MPC) algorithm.

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.

Group IV semiconductor (Si, Ge and Sn) nanocrystals were synthesized in dielectric matrixes by ion implantation of the respective species into the matrix to form a supersaturated solid solution and subsequent precipitation by thermal annealing. The resulting structure was characterized by Transmission Electron Microscopy and Raman spectroscopy. It was found that nanocrystals of these materials can be effectively synthesized with diameters in the nanometer range. Ge nanocrystals in SiO[...] were extensively characterized, particle size distributions were counted from TEM results and were used to compare experimental photoluminescence spectra with theoretical predictions. Unusual nanostructures were formed in samples co-implanted with Ge and Sn and annealed at 600°C. Raman spectroscopy indicated a possibility of significant alloying of Ge and Sn in these nanostructures. Optical properties of Si nanocrystals in silicon dioxide were investigated by photoluminescence spectroscopy as well. It was found that while Ge nanocrystal system luminescence is mostly due to defects in the matrix produced by ion implantation, Si nanocrystal sample luminescence is due to the Si nanocrystals themselves. The luminescence is above the bulk Si bandgap and supports the quantum confined excitonic luminescence theory. Light emitting devices were fabricated using both systems. Electroluminescence was observed for both Si and Ge, albeit with rather low efficiency, in the 10[...] - 10[...] range. Electroluminescence from Si nanocrystal containing devices was spectrally similar to photoluminescence from that system, with a band about 800 nm, consistent with electronic excitation of radiative transitions in Si nanocrystals. Cubic nonlinearities were measured for both Ge and Si nanocrystals and found to be 10[...] - 10[...] esu range. Finally, an interesting interferometric arrangement which has a potential to be useful for investigating nanoscale structures was theoretically described.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Applied Physics
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Atwater, Harry Albert
Thesis Committee:
  • Atwater, Harry Albert (chair)
  • Vahala, Kerry J.
  • Bridges, William B.
  • McGill, Thomas C.
  • Quake, Stephen R.
Defense Date:2 May 1997
Record Number:CaltechETD:etd-01172008-081522
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-01172008-081522
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:211
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:13 Feb 2008
Last Modified:26 Dec 2012 02:28

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