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Colorado State University
1.
Shepherd, Douglas Parker.
Extending single molecule spectroscopic techniques to multi-particle systems of semiconductor nanocrystals.
Degree: PhD, Physics, 2011, Colorado State University
URL: http://hdl.handle.net/10217/48177 
► This dissertation describes the application of single molecule spectroscopic techniques to individual semiconductor nanocrystals (NCs), small clusters of NCs, and NCs used as the light…
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▼ This dissertation describes the application of single molecule spectroscopic techniques to individual semiconductor nanocrystals (NCs), small clusters of NCs, and NCs used as the light harvesting layer in sensitized solar cells. We first examine how coupling between close-packed NCs may alter their photophysical properties by studying isolated NCs and small clusters of NCs via single molecule time-correlated single-photon counting, from which fluorescence intensity trajectories, autocorrelation functions, decay histograms, and lifetime-intensity distributions have been constructed. These measurements confirm that NC clusters exhibit unique photoluminescence behavior not observed in isolated NCs. In particular, the NC clusters exhibit a short-lifetime component in their photoluminescence decay that is correlated with low photoluminescence intensity of the cluster. A model based on radiative energy transfer to NCs within a cluster that have smaller energy gaps, combined with independent blinking for the NCs in a cluster, accounts for the main experimental features. This energy transfer may lead to energy sinks when an excitation is transferred to a NC that is in the off
state. We then examine a model photovoltaic system where a sub-monolayer film of NCs is chemically coupled to a single crystal semiconductor (TiO2 or ZnO) substrate through a variety of capping ligands. Again, utilizing time-correlated single photon counting and internal photon conversion efficiency we have studied both the photoluminescence intensity, photoluminescence decay time, and sensitized photocurrents. We find that for all configurations of capping ligands and substrate the photoluminescence decay rate is quenched compared to the free NCs in solution; whereas, only the short chain capping ligands that promote electron coupling to the substrate produce photocurrents. The longer chain capping groups both inhibit the electron injection and promote NC clustering on the surface where interactions between the individual NCs or the NCs and substrate alter the radiative rate. This result confirms that the possibility of NC clusters leading to a loss of energy due to inter-NC coupling is present in devices and warrants further study.
Advisors/Committee Members: Gelfand, Martin Paul (advisor), Van Orden, Alan K. (advisor), Roberts, Jacob Lyman (committee member), Prieto, Amy Lucia (committee member).
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APA (6th Edition):
Shepherd, D. P. (2011). Extending single molecule spectroscopic techniques to multi-particle systems of semiconductor nanocrystals. (Doctoral Dissertation). Colorado State University. Retrieved from http://hdl.handle.net/10217/48177
Chicago Manual of Style (16th Edition):
Shepherd, Douglas Parker. “Extending single molecule spectroscopic techniques to multi-particle systems of semiconductor nanocrystals.” 2011. Doctoral Dissertation, Colorado State University. Accessed April 13, 2021.
http://hdl.handle.net/10217/48177.
MLA Handbook (7th Edition):
Shepherd, Douglas Parker. “Extending single molecule spectroscopic techniques to multi-particle systems of semiconductor nanocrystals.” 2011. Web. 13 Apr 2021.
Vancouver:
Shepherd DP. Extending single molecule spectroscopic techniques to multi-particle systems of semiconductor nanocrystals. [Internet] [Doctoral dissertation]. Colorado State University; 2011. [cited 2021 Apr 13].
Available from: http://hdl.handle.net/10217/48177.
Council of Science Editors:
Shepherd DP. Extending single molecule spectroscopic techniques to multi-particle systems of semiconductor nanocrystals. [Doctoral Dissertation]. Colorado State University; 2011. Available from: http://hdl.handle.net/10217/48177
Colorado State University
2.
Farnell, Shawn.
Artin-Schreier curves.
Degree: PhD, Mathematics, 2010, Colorado State University
URL: http://hdl.handle.net/10217/44957
► Let k be an algebraically closed field of characteristic p where p is a prime number. The main focus of this work is on properties…
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▼ Let k be an algebraically closed field of characteristic p where p is a prime number. The main focus of this work is on properties of Artin-Schreier curves. In particular, we study two invariants of the p-torsion of the Jacobian of these curves: the p-rank and the a-number. In the main result, we demonstrate a family of Artin-Schreier curves for which the a-number is constant. We also give a result concerning the existence of deformations of Artin-Schreier curves with varying p-rank.
Advisors/Committee Members: Pries, Rachel (advisor), Achter, Jeffrey D. (committee member), Peterson, Christopher Scott, 1963- (committee member), Gelfand, Martin Paul (committee member).
Subjects/Keywords: Artin-Schreier; moduli; invariant; deformation; curve; Curves, Algebraic; Deformations of singularities; Moduli theory; Smooth affine curves; Jacobians
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APA (6th Edition):
Farnell, S. (2010). Artin-Schreier curves. (Doctoral Dissertation). Colorado State University. Retrieved from http://hdl.handle.net/10217/44957
Chicago Manual of Style (16th Edition):
Farnell, Shawn. “Artin-Schreier curves.” 2010. Doctoral Dissertation, Colorado State University. Accessed April 13, 2021.
http://hdl.handle.net/10217/44957.
MLA Handbook (7th Edition):
Farnell, Shawn. “Artin-Schreier curves.” 2010. Web. 13 Apr 2021.
Vancouver:
Farnell S. Artin-Schreier curves. [Internet] [Doctoral dissertation]. Colorado State University; 2010. [cited 2021 Apr 13].
Available from: http://hdl.handle.net/10217/44957.
Council of Science Editors:
Farnell S. Artin-Schreier curves. [Doctoral Dissertation]. Colorado State University; 2010. Available from: http://hdl.handle.net/10217/44957
Colorado State University
3.
Sweeney, Mark Charles.
Vortex phases in type-I superconductors.
Degree: PhD, Physics, 2010, Colorado State University
URL: http://hdl.handle.net/10217/44985
► Sufficiently thin films of type-I superconductor in a perpendicular magnetic field exhibit a triangular vortex lattice, while thick films develop an intermediate state. To elucidate…
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▼ Sufficiently thin films of type-I superconductor in a perpendicular magnetic field exhibit a triangular vortex lattice, while thick films develop an intermediate
state. To elucidate what happens between these two regimes, precise numerical calculations have been made within Ginzburg-Landau theory at κ=0.5 and 0.25 for a variety of vortex lattice structures with one flux quantum per unit cell. The phase diagram in the space of mean induction and film thickness includes a narrow wedge in which a square lattice is stable, surrounded by the domain of stability of the triangular lattice at thinner films/lower fields and, on the other side, rectangular lattices with continuously varying aspect ratio. The vortex lattice has an anomalously small shear modulus within and close to the square lattice phase. Solutions of the Ginzburg-Landau equations have also been obtained for bulk systems and thin films for vortex lattices with one vortex but two flux quanta per square or triangular unit cell. These lattices of double fluxoid vortices are thermodynamically unstable in bulk in both type-I and type-II superconductors, as expected. In type-I films the situation is less clear, because the corresponding calculations for more complicated vortex lattice structures are not yet possible.
Advisors/Committee Members: Gelfand, Martin Paul (advisor), Mueller, Jennifer L. (committee member), Bradley, Richard M. (committee member), Field, Stuart B. (committee member).
Subjects/Keywords: superconductors; Vortex-motion; Thin films; Superconductivity; Superconductors – Magnetic fields
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APA (6th Edition):
Sweeney, M. C. (2010). Vortex phases in type-I superconductors. (Doctoral Dissertation). Colorado State University. Retrieved from http://hdl.handle.net/10217/44985
Chicago Manual of Style (16th Edition):
Sweeney, Mark Charles. “Vortex phases in type-I superconductors.” 2010. Doctoral Dissertation, Colorado State University. Accessed April 13, 2021.
http://hdl.handle.net/10217/44985.
MLA Handbook (7th Edition):
Sweeney, Mark Charles. “Vortex phases in type-I superconductors.” 2010. Web. 13 Apr 2021.
Vancouver:
Sweeney MC. Vortex phases in type-I superconductors. [Internet] [Doctoral dissertation]. Colorado State University; 2010. [cited 2021 Apr 13].
Available from: http://hdl.handle.net/10217/44985.
Council of Science Editors:
Sweeney MC. Vortex phases in type-I superconductors. [Doctoral Dissertation]. Colorado State University; 2010. Available from: http://hdl.handle.net/10217/44985
Colorado State University
4.
Whitfield, JaDon Saeed.
Simplicial homotopy group model for K2 of a ring, A.
Degree: PhD, Mathematics, 2010, Colorado State University
URL: http://hdl.handle.net/10217/45975
► We construct an isomorphism between the group K2(R) from classical, algebraic K-Theory for a ring R and a simplicial homotopy group constructed using simplicial homotopy…
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▼ We construct an isomorphism between the group K2(R) from classical, algebraic K-Theory for a ring R and a simplicial homotopy group constructed using simplicial homotopy theory based on that same ring R. First I describe the basic aspects of simplicial homotopy theory. Special attention is paid to the use of category theory, which will be applied to the construction of a simplicial set. K-Theory for K0(R), K1(R) and K2(R) is then described before we set to work describing explicitly the nature of isomorphisms for K0(R) and K1(R) based on previous work. After introducing some theory related to K-Theory, some considerations and corrections on previous work motivate more new theory that helps the isomorphism with K2(R). Such theory is developed, mainly with regards to finitely generated projective modules over R and then elementary matrices with entries from R, culminating in the description of the Steinberg Relations that are central to the understanding of K2(R) in terms of homotopy classes. We then use new considerations on the previous work to show that a map whose image is constructed through this article is an isomorphism since it is the composition of isomorphisms.
Advisors/Committee Members: Duflot, Jeanne (advisor), Miranda, Rick (committee member), Achter, Jeffrey D. (committee member), Gelfand, Martin Paul (committee member).
Subjects/Keywords: algebra; topology; simplicial homotopy; Homotopy groups; K-theory; Loop spaces; Isomorphisms (Mathematics)
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APA ·
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APA (6th Edition):
Whitfield, J. S. (2010). Simplicial homotopy group model for K2 of a ring, A. (Doctoral Dissertation). Colorado State University. Retrieved from http://hdl.handle.net/10217/45975
Chicago Manual of Style (16th Edition):
Whitfield, JaDon Saeed. “Simplicial homotopy group model for K2 of a ring, A.” 2010. Doctoral Dissertation, Colorado State University. Accessed April 13, 2021.
http://hdl.handle.net/10217/45975.
MLA Handbook (7th Edition):
Whitfield, JaDon Saeed. “Simplicial homotopy group model for K2 of a ring, A.” 2010. Web. 13 Apr 2021.
Vancouver:
Whitfield JS. Simplicial homotopy group model for K2 of a ring, A. [Internet] [Doctoral dissertation]. Colorado State University; 2010. [cited 2021 Apr 13].
Available from: http://hdl.handle.net/10217/45975.
Council of Science Editors:
Whitfield JS. Simplicial homotopy group model for K2 of a ring, A. [Doctoral Dissertation]. Colorado State University; 2010. Available from: http://hdl.handle.net/10217/45975
Colorado State University
5.
Hsiao, Kuo-Jui.
Electron-reflector strategy for CdTe thin-film solar cells.
Degree: PhD, Physics, 2010, Colorado State University
URL: http://hdl.handle.net/10217/39057
► The CdTe thin-film solar cell has a large absorption coefficient and high theoretical efficiency. Moreover, large-area photovoltaic panels can be economically fabricated. These features potentially…
(more)
▼ The CdTe thin-film solar cell has a large absorption coefficient and high theoretical efficiency. Moreover, large-area photovoltaic panels can be economically fabricated. These features potentially make the CdTe thin-film solar cell the leading alternative energy source. However, the record CdTe efficiency (16.5%) is much less than its theoretical maximum efficiency (29%), primarily because the open-circuit voltage (0.845 V) is well below what is expected for its band gap (1.5 eV). The incorporation of an electron reflector is a strategy to improve the open-circuit voltage of solar cells, and thus a strong possibility to improve the efficiency of CdTe thin-film solar cells. An electron reflector is a conduction-band energy barrier at the back surface of the solar cell, which can reduce the recombination due to the electron flow to the back surface. Different methods to create an electron reflector are explained in the thesis: (1) expanded band gap, either an expanded-band-gap layer or a bulk-band-gap reduction, and (2) alteration to the band bending through a reversed back barrier or a heavily-doped back surface. Investigation shows that the expanded-band-gap layer is the most efficient and practical mechanism for an electron reflector, and the combination of any two mechanisms does not yield additional improvement. To have the optimal effect from the electron-reflector strategy, reasonable CdTe lifetime (1 ns or above) and full depletion of the CdTe layer are required to ensure high carrier collection. Furthermore, a good-quality reflector interface between the p-type CdTe layer and the electron-reflector layer is essential. Preliminary experimental evidence has shown that CdTe cells with a ZnTe back layer do have a slightly higher open-circuit voltage. An electron reflector should be particularly beneficial for thin (less than 2 μm) CdTe cells which have a fully-depleted CdTe absorber layer. Thin CdTe cells can also benefit from the optical reflection at the back surface. To investigate the possibility of still higher efficiency, both electron and optical reflection were numerically applied to the CdTe record-cell baseline model. However, there is little improvement for CdTe thicknesses greater than 2 μm. To have the optimal effect from combined electron and optical reflection, cells approximately one micron thick are required. Even without the improvement to the current quality of CdTe, cell efficiency above 19% should be achievable with a 0.2-eV electron reflector. Moreover, efficiency above 20% should be possible if one can also achieve large optical back reflection. At the same time, competitive CdTe cell performance at a thickness as thin as 0.4 um should be possible. This thesis gives a comprehensive numerical investigation of the electron-reflector strategy for CdTe thin-film solar cells.
Advisors/Committee Members: Sites, James R. (advisor), Sampath, W. S. (Walajabad S.) (committee member), Gelfand, Martin Paul (committee member), Leisure, Robert Glenn, 1938- (committee member).
Subjects/Keywords: Solar cells – Reliability; Thin films; Photovoltaic cells
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Record Details
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APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Hsiao, K. (2010). Electron-reflector strategy for CdTe thin-film solar cells. (Doctoral Dissertation). Colorado State University. Retrieved from http://hdl.handle.net/10217/39057
Chicago Manual of Style (16th Edition):
Hsiao, Kuo-Jui. “Electron-reflector strategy for CdTe thin-film solar cells.” 2010. Doctoral Dissertation, Colorado State University. Accessed April 13, 2021.
http://hdl.handle.net/10217/39057.
MLA Handbook (7th Edition):
Hsiao, Kuo-Jui. “Electron-reflector strategy for CdTe thin-film solar cells.” 2010. Web. 13 Apr 2021.
Vancouver:
Hsiao K. Electron-reflector strategy for CdTe thin-film solar cells. [Internet] [Doctoral dissertation]. Colorado State University; 2010. [cited 2021 Apr 13].
Available from: http://hdl.handle.net/10217/39057.
Council of Science Editors:
Hsiao K. Electron-reflector strategy for CdTe thin-film solar cells. [Doctoral Dissertation]. Colorado State University; 2010. Available from: http://hdl.handle.net/10217/39057
. 
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