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You searched for subject:(Quantum Dot Heterostructures). Showing records 1 – 3 of 3 total matches.

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University of Washington

1. Enright, Michael Job. Synthesis of colloidal semiconductor heterostructures for photocatalysis.

Degree: PhD, 2019, University of Washington

The development of colloidal nanoscale semiconductors for next-generation technologies is attractive due to their size-dependent optoelectronic properties and compatibility with solution-based manufacturing methods. This versatile class of nanomaterials holds great promise for light absorption, emission, and energy conversion. However, while the synthesis of single component, isotropic nanocrystals is well developed, the true promise of these materials is in their customization within heterostructure motifs where significant synthetic challenges remain. In particular, colloidal semiconductor nanomaterial heterostructures hold great potential as photocatalysts. Efficient electron-hole recombination is promoted by quantum confinement making traditional quantum dots non-ideal for photocatalytic applications. However, charge carriers can be thermodynamically separated across a nanoheterostructure interface. This prolongs the lifetime of photogenerated charge carriers, paving the way for efficient photoredox chemistry. This thesis uncovers the underlying, generalizable principles for accessing tailor-made heterostructures to provide a roadmap for accessing desirable colloidal semiconductor nanoheterostructures. The generalized rubrics describe strategies and identify potential pitfalls for the synthesis of desirable nanostructures, even if explicit examples of the target structure have not been previously reported. Beyond developing anisotropic heterostructures with rod and tetrapod morphologies, this work demonstrates a new application for nanomaterial photocatalysis by using quantum dots to cleave C-O bonds in biomass model substrates. In all, this thesis makes strides in developing our understanding of how to design and synthesize colloidal semiconductor nanoheterostructures, and of the use of nanomaterials in photolytic applications. Advisors/Committee Members: Cossairt, Brandi M (advisor).

Subjects/Keywords: Anisotropy; Cation exchange; Nanomaterial synthesis; Photocatalysis; Quantum dot; Semiconductor heterostructures; Inorganic chemistry; Chemistry

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Enright, M. J. (2019). Synthesis of colloidal semiconductor heterostructures for photocatalysis. (Doctoral Dissertation). University of Washington. Retrieved from http://hdl.handle.net/1773/44105

Chicago Manual of Style (16th Edition):

Enright, Michael Job. “Synthesis of colloidal semiconductor heterostructures for photocatalysis.” 2019. Doctoral Dissertation, University of Washington. Accessed December 11, 2019. http://hdl.handle.net/1773/44105.

MLA Handbook (7th Edition):

Enright, Michael Job. “Synthesis of colloidal semiconductor heterostructures for photocatalysis.” 2019. Web. 11 Dec 2019.

Vancouver:

Enright MJ. Synthesis of colloidal semiconductor heterostructures for photocatalysis. [Internet] [Doctoral dissertation]. University of Washington; 2019. [cited 2019 Dec 11]. Available from: http://hdl.handle.net/1773/44105.

Council of Science Editors:

Enright MJ. Synthesis of colloidal semiconductor heterostructures for photocatalysis. [Doctoral Dissertation]. University of Washington; 2019. Available from: http://hdl.handle.net/1773/44105


University of Illinois – Urbana-Champaign

2. Oh, Nuri. Incorporating double-heterojunction in anisotropic semiconductor nanocrystals for novel optoelectronic applications.

Degree: PhD, Materials Science & Engr, 2016, University of Illinois – Urbana-Champaign

As semiconductor heterostructures play critical roles in today's electronics and optoelectronics, the introduction of active heterojunctions can impart new and improved capabilities that will enable the use of solution processable colloidal quantum dots (QDs) in future devices. Such heterojunctions incorporated into colloidal nanorods may be especially promising since the inherent shape anisotropy can provide additional benefits of directionality and accessibility in band structure engineering and assembly. Here, we develop double heterojunction nanorods where two distinct semiconductor materials with type II staggered band offset are both in contact with one smaller band gap quantum dot. The double heterojunction can provide independent control over the electron and hole injection/extraction processes while maintaining high photoluminescence yields and shape anisotropy. Developing new synthetic routes for the formation of ideal double heterostructures, we find that unexpected etching of nanocrystals by one of the most commonly used metal precursors, metal oleates. Especially, Zn-oleate is shown to etch CdS nanorods anisotropically, where the length decreases without a significant change in the diameter. Sodium oleate enhances the etch rate whereas oleic acid alone does not cause etching, indicating the importance of counter cation on the rate of oleate induced etching. Subsequent addition of Se precursors to the partially etched nanorod in Zn-oleate solution can lead to epitaxial growth of CdSe particles rather than the expected ZnSe growth despite an excess amount of Zn precursors being present. The composition of this epitaxial growth can be varied from CdSe to ZnSe depending on the amount of excess oleic acid or the reaction temperature. Similar tuning of composition can be observed when starting with collinear CdSe/CdS/CdSe rod/rod/rod heterostructures and spherical CdS (or CdSe/CdS core/shell) nanocrystals. Conversion of collinear rod/rod/rod structures to barbells and interesting rod growth from nearly spherical particles among other structures can also result due to the initial etching effect of metal oleates. These observations have important implications on our understanding of nanocrystal heterostructure synthesis and open up new routes to varying composition and morphology of these materials. One of the most interesting applications of the semiconductor nanocrystals is display device applications such as LEDs incorporating QDs (QD-LEDs) as the electroluminescent layer. Recent advances in QD-LEDs have led to efficiencies and brightness that rival the best organic LEDs. Nearly ideal internal quantum efficiency being achieved leaves light outcoupling as the only remaining means to improve external quantum efficiency (EQE) but that might require radically different device design and reoptimization. However, the current state-of-the-art QD-LEDs are based on spherical core/shell QDs, and the effects of shape and optical anisotropy remain essentially unexplored. Here, we demonstrate… Advisors/Committee Members: Shim, Moonsub (advisor), Shim, Moonsub (Committee Chair), Zuo, Jian-Min (committee member), Schleife, AndrĂ© (committee member), Jain, Prashant (committee member).

Subjects/Keywords: Double-Heterojunction Nanorods; Double Heterostructures; Anisotropic Semiconductor Nanocrystal; Quantum Dot; Quantum dot light emitting diode (QD-LEDs); QLED; Bidirectional Display; Cd-Free Quantum Dots

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Oh, N. (2016). Incorporating double-heterojunction in anisotropic semiconductor nanocrystals for novel optoelectronic applications. (Doctoral Dissertation). University of Illinois – Urbana-Champaign. Retrieved from http://hdl.handle.net/2142/90940

Chicago Manual of Style (16th Edition):

Oh, Nuri. “Incorporating double-heterojunction in anisotropic semiconductor nanocrystals for novel optoelectronic applications.” 2016. Doctoral Dissertation, University of Illinois – Urbana-Champaign. Accessed December 11, 2019. http://hdl.handle.net/2142/90940.

MLA Handbook (7th Edition):

Oh, Nuri. “Incorporating double-heterojunction in anisotropic semiconductor nanocrystals for novel optoelectronic applications.” 2016. Web. 11 Dec 2019.

Vancouver:

Oh N. Incorporating double-heterojunction in anisotropic semiconductor nanocrystals for novel optoelectronic applications. [Internet] [Doctoral dissertation]. University of Illinois – Urbana-Champaign; 2016. [cited 2019 Dec 11]. Available from: http://hdl.handle.net/2142/90940.

Council of Science Editors:

Oh N. Incorporating double-heterojunction in anisotropic semiconductor nanocrystals for novel optoelectronic applications. [Doctoral Dissertation]. University of Illinois – Urbana-Champaign; 2016. Available from: http://hdl.handle.net/2142/90940


Indian Institute of Science

3. Abhale, Atul Prakash. Laser Beam Induced Conductance Modulations as a Potential Microprobe in the Investigation of Defects and Inhomogeneities in Bulk Si and PbS, HgCdTe Quantum Dot Heterostructures.

Degree: 2017, Indian Institute of Science

In this thesis, the strength of the LBIC system is enhanced in different aspects that includes its feasibility as a non-destructive characterization tool, the signal analysis and development of analytical solution to have better understanding on the defects and inhomogeneities in the quantum dot based hetero-structures for device applications, finally understanding its limits due to the size of the laser beam and interpretation of artefacts in the signal appearance due to the presence of co-devices. Chapter#1 provides the introduction and literature survey of the LBIC system. It covers the importance and area of application of the LBIC. Chapter#2 various tools and instrumentation are discussed briefly for the systems that are developed in the lab as well as standard tools utilised for the material characterization. A LBIC instrumentation a novel colloidal quantum dots (CQD) thin film deposition system is discussed. In the last part along with the standard characterization systems a software tool (semiconductor device simulator) is discussed, which is used to visualize and understand the LBIC profile that is obtained experimentally. Chapter#3 provides the information of colloidal synthesis of PbS and HgxCd1-xTe quantum dots. Device fabrication process is explained step by step for the following devices. p-n junction silicon diodes, PbS-CQD/Si hetero-structures, ITO/PbS-CQD/Al crossbar structures and HgCdTe-CQD/Si hetero-structures. Chapter#4 deals with the major constraints imposed on the LBIC due to the need of Ohmic contacts. To overcome this major limitation, in this work, the origin of the signal is studied with the remote contact geometry for silicon p-n junction devices. It was observed that the signals can be collected with the capacitively coupled remote contacts, where LBIC was ultimately demonstrated as contactless measurement tool without any compromise on the measurements and thus obtained physical parameters. The effect of finite laser beam size is also described, which was found to have effect on the actual dimensions measured with the LBIC images. LBIC utility is further enhanced with the Si/CQD based hetero-structure devices, which are the potential candidates in the evolving device technology to be utilized in various modular systems such as PDs and LED applications. Chapter#5 discusses the origin and possible mechanisms for lateral photo-voltage which is closely monitored in the PbS-CQD/Si hetero-junction device systems. Interestingly, it is observed that there are two different line profiles for n and p type Si substrates. Different mechanisms that give rise to this kind of profiles were found to be distinct and are related to the band alignment of the CQD/Si hetero-structure. It lead to the revelation of an interesting phenomenon and believed to be universally observed irrespective of the materials involved in the formation of hetero-junction. Simulations and experimental results are quite consistent and in agreement with each other, which confirm the underlying physical mechanism that… Advisors/Committee Members: Rao, Kota Shiva Rama Koteswara.

Subjects/Keywords: Spatial Mapping; PbS-colloidal Quantum Dot/Si Heterojunctions; Nano Beam Epitaxy; Device Fabrication; LBIC Measurements; Colloidal Quantum Dots; Lead sulfide Colloidal Quantum Dots (PbSCQDs); Photodetectors; HgxCd1-xTe Quantum Dots; Quantum Dot Heterostructures; Physics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Abhale, A. P. (2017). Laser Beam Induced Conductance Modulations as a Potential Microprobe in the Investigation of Defects and Inhomogeneities in Bulk Si and PbS, HgCdTe Quantum Dot Heterostructures. (Thesis). Indian Institute of Science. Retrieved from http://etd.iisc.ernet.in/2005/3557 ; http://etd.iisc.ernet.in/abstracts/4425/G28359-Abs.pdf

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Abhale, Atul Prakash. “Laser Beam Induced Conductance Modulations as a Potential Microprobe in the Investigation of Defects and Inhomogeneities in Bulk Si and PbS, HgCdTe Quantum Dot Heterostructures.” 2017. Thesis, Indian Institute of Science. Accessed December 11, 2019. http://etd.iisc.ernet.in/2005/3557 ; http://etd.iisc.ernet.in/abstracts/4425/G28359-Abs.pdf.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Abhale, Atul Prakash. “Laser Beam Induced Conductance Modulations as a Potential Microprobe in the Investigation of Defects and Inhomogeneities in Bulk Si and PbS, HgCdTe Quantum Dot Heterostructures.” 2017. Web. 11 Dec 2019.

Vancouver:

Abhale AP. Laser Beam Induced Conductance Modulations as a Potential Microprobe in the Investigation of Defects and Inhomogeneities in Bulk Si and PbS, HgCdTe Quantum Dot Heterostructures. [Internet] [Thesis]. Indian Institute of Science; 2017. [cited 2019 Dec 11]. Available from: http://etd.iisc.ernet.in/2005/3557 ; http://etd.iisc.ernet.in/abstracts/4425/G28359-Abs.pdf.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Abhale AP. Laser Beam Induced Conductance Modulations as a Potential Microprobe in the Investigation of Defects and Inhomogeneities in Bulk Si and PbS, HgCdTe Quantum Dot Heterostructures. [Thesis]. Indian Institute of Science; 2017. Available from: http://etd.iisc.ernet.in/2005/3557 ; http://etd.iisc.ernet.in/abstracts/4425/G28359-Abs.pdf

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

.