Spelling suggestions: "subject:"superlattices as materials"" "subject:"supperlattices as materials""
31 |
Neutron diffraction studies of organic and magnetic layered structuresHamacher, Klaus A. January 1998 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 179-190). Also available on the Internet.
|
32 |
Fabrication, characterization and modeling of a superlattice base hot electron transistorChoo, Andrew Hua-kuang 27 October 1992 (has links)
Graduation date: 1993
|
33 |
Optical Properties of Superlattice Photonic CrystalsNeff, Curtis Wayne 22 September 2005 (has links)
Photonic band gap materials, commonly referred to as photonic crystals (PCs), have been a topic of great interest for almost two decades due to their promise of unprecedented control over the propagation and generation of light. We report investigations of the optical properties of a new PC structure based upon a triangular lattice in which adjacent [i, j] rows of holes possess different properties, creating a superlattice (SL) periodicity. Symmetry arguments predicted and quot;band folding and quot; and band splitting behaviors, both of which are direct consequences of the new basis that converts the Brillouin zone from hexagonal (six-fold) to rectangular (two-fold). Plane wave expansion and finite-difference time-domain (FDTD) numerical calculations were used to explore the effects of the new structure on the photonic dispersion relationship of the SL PC. Electron beam lithography and inductively coupled plasma dry etching were used to fabricate 1 mm2 PC areas (lattice constant, a =358 nm and 480 nm) with hole radius ratios ranging from 1.0 (triangular) to 0.585 (r2/r1 = 73.26 nm/125.26 nm) on Silicon-on-insulator wafers. The effects of modifying structural parameters (such as hole size, lattice constant, and SL strength) were measured using the coupled resonant band technique, confirming the SL symmetry arguments and corroborating the band structure calculations. Analysis of the dispersion contours of the static SL (SSL) PC predicted both giant refraction (change in beam propagation angle of 110 for an 8 change in incident angle) and superprism behavior (change in beam propagation angle of 108 for a 12% change in normalized frequency) in these structures. Dynamic control of these refraction effects was also investigated by incorporating electro-optic and nonlinear materials into the SSL PC structure. Wave vector analyses on these structures predicted a change in beam propagation angle and gt;96 when the refractive index inside of the holes of the structure changed from n=1.5 to 1.7. Through this investigation, the first successful measurement of the band folding effect in multidimensional PCs as well as the first explicit measurement of the dielectric band of a 2D PC were reported. In addition, the SL PCs impact on new opto-electronic devices was explored.
|
34 |
Optical properties of the square superlattice photonic crystal structure and optical invisibility cloakingBlair, John L. 27 August 2010 (has links)
The refraction properties of photonic crystal lattices offers methods to control the beam steering of light through use of non-linear dispersion contours. In this thesis new photonic crystal structures, such as the square and triangular superlattices, that provide novel refractive properties are analyzed. The property difference between rows in these structures is the hole radius Δr. The difference in hole sizes leads to observation of the superlattice effect, that is, a change in the refractive index Δn between opposite rows of holes. The index difference becomes a function of the size of the smaller r2 hole area or volume due to the addition of the higher index background material compared to the larger r1 holes. The difference in hole radii Δr = r1 - r2 is referred to as the static superlattice strength and is designated by the ratio of r2/r1. The superlattice strength increases as the ratio of r2/r1 decreases.
The hole size modulation creates modified dispersion contours that can be used to fabricate advanced beam steering devices through the introduction of electro-optical materials and a controlled bias. A discussion of these superlattice structures and their optical properties will be covered, followed by both static and dynamic tunable device constructions utilizing these designs. Also, static tuning of the devices through the use of atomic layer deposition, as well as active tuning methods utilizing liquid crystal (LC) infiltration, sealed LC cells, and the addition of electro-optic material will be discussed.
Also in this thesis we present designs to implement a simpler demonstration of cloaking, the carpet cloak, in which a curved reflective surface is compressed into a flat reflective surface, effectively shielding objects behind the curve from view with respect to the incoming radiation source. This approach eliminates the need for metallic resonant elements. These structures can now be fabricated using only high index dielectric materials by the use of electron beam lithography and standard cleanroom technologies. The design method, simulation analysis, device fabrication, and near field optical microscopy (NSOM) characterization results are presented for devices designed to operate in the 1400-1600nm wavelength range. Improvements to device performance by the deposition/infiltration of linear, and potentially non-linear optical materials, were investigated.
|
35 |
Magnetic properties and interlayer coupling of ZnTe/MnTe superlattices /Lin, Jun, January 2000 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 139-143). Also available on the Internet.
|
36 |
Magnetic properties and interlayer coupling of ZnTe/MnTe superlatticesLin, Jun, January 2000 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 139-143). Also available on the Internet.
|
37 |
Characterization and modeling of strained layers grown on V-grooved substrates /Gupta, Archana. January 1997 (has links)
Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references. Also available via World Wide Web.
|
38 |
Diffusion studies in InGaAs/GaAs and AIGaAs/GaAs quantum well structures /Ramanujachar, Kartik. January 1998 (has links)
Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references (leaves 185-191). Also available via World Wide Web.
|
39 |
The chemical and magnetic structures of rare-earth superlattices and thin filmsSwaddling, Paul January 1994 (has links)
No description available.
|
40 |
An optical investigation of implantation damage as GaAs superlatticesHaile, Kibreab Mebrahtom 26 April 2005 (has links)
In this work tunability, implantation damage and recovery of GaAs doping superlattices implanted with hydrogen ions were studied. The applicability of two models of the optical properties of semiconductors was also investigated. GaAs doping superlattices were implanted with 0.5 MeV hydrogen ions at doses of 1012 cm-2, 1014 cm-2 and 1016 cm-2. This gradually modifies their optical characteristics from superlattice behaviour to something resembling the bulk material and beyond. Such a processing technique therefore provides a convenient way of tuning the optical properties of a superlattice semi-permanently. A combined result of ellipsometry and near infrared reflectance measurements showed that a single effective oscillator as well as a more advanced three-parameter model could be applied to the virgin and ion-implanted doping superlattices. This allowed us to determine the dose dependent effective band gap as well as other model parameters. Photoluminescence as well as normal and resonance Raman techniques were applied to study hydrogen ion implantation damage and its recovery. These techniques showed that implantation damage could be reversed to a large extent by a simple thermal annealing step. / Dissertation (MSc)--University of Pretoria, 2006. / Physics / unrestricted
|
Page generated in 0.0908 seconds