subject:(Nanocrystals Electric properties)

Michigan State University

1. Peng, Wei-Tao. Ab initio molecular dynamics : applications to defective silicon nanocrystals and developments toward dense manifold systems.

Degree: 2019, Michigan State University

URL: http://etd.lib.msu.edu/islandora/object/etd:48205

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Thesis Ph. D. Michigan State University. Chemistry 2019.

Ab initio molecular dynamics (AIMD) methods consider the nuclear motions under the potential generated by electronic wavefunctions… (more)

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Thesis Ph. D. Michigan State University. Chemistry 2019.

Ab initio molecular dynamics (AIMD) methods consider the nuclear motions under the potential generated by electronic wavefunctions which are determined from ab initio quantum mechanical calculations on-the-fly. AIMD methods allow researchers to investigate chemical processes without prior knowledge or assumptions about the shape of the potential energy surface (PES). In this thesis, we applied AIMD methods to study silicon nanocrystals with dangling bond defects (DB-SiNCs). DB defects on SiNCs have been known as nonradiative (NR) decay centers. However, the atomistic mechanism for the decay process is unclear. Previously, researchers considered a pyramidalization mode surrounding the DB site involved in the process. Based on our AIMD calculations on the first excited state and the static analysis of the PESs of SiNC systems, we discovered that asymmetrical Si-Si bond stretching modes surrounding DB sites are important, in addition to pyramidalization. Most importantly, we found a low-lying defect-induced conical intersection (DICI) in the neutral DB system. The minimum energy conical intersection (MECI) is estimated to be 1.74 eV above the ground state minimum energy geometry by application of multi-state complete active space second-order perturbation theory (MS-CASPT2) to a small cluster model system. In addition, the roles of charged DBs on NR decay process are investigated. We found DICIs for both positively and negatively charged DB systems. The MECI energies are 2.10 eV and 2.65 eV respectively. The rationalization of the existence of conical intersections and detailed dynamics after excitation of these systems are discussed in the thesis. Additionally, to study the possible defect-defect interactions during the NR recombination process, we considered slab models with two DB defects at short (4 0303A) and long (100303 A) separations. According to our simulations, the NR recombination process is localized on a single DB site, regardless the defect-defect distances. However, energy transfer between defect sites with short separations is possible.For the defective SiNC systems, we demonstrated the power of the AIMD method to investigate the dynamics after excitations. However, the applications of AIMD to high-lying states are much more challenging, due to the dense manifold of states that cause immense computational effort. In the thesis, we developed several methods toward the application to such systems. First, we developed a time-dependent configuration interaction (TD-CI) method that can simulate the electron dynamics under a strong field efficiently. The method is based on the direct scheme to form the vector, , which can be accelerated by a graphical processing unit. A TD-CI calculation with 853776 determinants requires only 20.1 hours to propagate to 100 fs with 1 attosecond (10-18 second) time steps. On the other hand, when the field is strong enough, the electrons can be driven to the boundary of the basis set, which would cause unphysical…

Advisors/Committee Members: Levine, Benjamin G., Hunt, Katharine C., Dantus, Marcos, Piecuch, Piotr.

Subjects/Keywords: Nanosilicon – Electric properties – Mathematical models; Silicon crystals – Electric properties – Mathematical models; Nanocrystals – Electric properties – Mathematical models; Molecular dynamics – Mathematical models; Chemistry

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APA (6^th Edition):

Peng, W. (2019). Ab initio molecular dynamics : applications to defective silicon nanocrystals and developments toward dense manifold systems. (Thesis). Michigan State University. Retrieved from http://etd.lib.msu.edu/islandora/object/etd:48205

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

Chicago Manual of Style (16^th Edition):

Peng, Wei-Tao. “Ab initio molecular dynamics : applications to defective silicon nanocrystals and developments toward dense manifold systems.” 2019. Thesis, Michigan State University. Accessed January 21, 2021. http://etd.lib.msu.edu/islandora/object/etd:48205.

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

MLA Handbook (7^th Edition):

Peng, Wei-Tao. “Ab initio molecular dynamics : applications to defective silicon nanocrystals and developments toward dense manifold systems.” 2019. Web. 21 Jan 2021.

Vancouver:

Peng W. Ab initio molecular dynamics : applications to defective silicon nanocrystals and developments toward dense manifold systems. [Internet] [Thesis]. Michigan State University; 2019. [cited 2021 Jan 21]. Available from: http://etd.lib.msu.edu/islandora/object/etd:48205.

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

Council of Science Editors:

Peng W. Ab initio molecular dynamics : applications to defective silicon nanocrystals and developments toward dense manifold systems. [Thesis]. Michigan State University; 2019. Available from: http://etd.lib.msu.edu/islandora/object/etd:48205

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

Columbia University

2. Clark, Michael. Quantitative Theories of Nanocrystal Growth Processes.

Degree: 2013, Columbia University

URL: https://doi.org/10.7916/D8PK0MVR

► Nanocrystals are an important field of study in the 21st century. Crystallites that are nanometers in size have very different properties from their bulk analogs… (more)

▼ Nanocrystals are an important field of study in the 21st century. Crystallites that are nanometers in size have very different properties from their bulk analogs because quantum mechanical effects become dominant at such small length scales. When a crystallite becomes small enough, the quantum confinement of electrons in the material manifests as a size-dependence of the nanocrystal's properties. Electrical and optical properties such as absorbance, surface plasmon resonance, and photoluminescence are sensitive to the size of the nanocrystal and proffer an array of technological applications for nanocrystals in such fields as biological imaging, laser technology, solar power enhancement, LED modification, chemical sensors, and quantum computation.The synthesis of size-controlled nanocrystals is critical to using nanocrystal in applications for their size-dependent properties. The development of nanocrystal synthesis techniques has been its own entire field of study for two decades or more, and several successes have established novel, utilitarian protocols for the mass-production of nanocrystals with controlled size and very low polydispersity. However, the experimental successes are generally poorly understood and no theoretical framework exists to explain the dynamics of these processes and how to better control or optimize them. It is the goal of this thesis to develop novel theories of nanocrystal synthesis processes to describe these phenomena in theoretical detail and extract meaningful correlations and driving forces that provide the necessary insight to improve the technology and enhance our understanding of nanocrystal growth. Chapter 4, 5 and 6 comprise all the novel research conducted for this thesis, with Chapters 1, 2 and 3 serving as necessary background to understanding the current state of the art. In Chapter 4, we develop a quantitative describe of the process of size focusing, in which a population of polydisperse nanocrystals, which are useless for applications, can be made more monodisperse by the injection of new crystallizable material. We derive mass balance equations that relate the rate of new-material generation to changes in the growth patterns of the nanocrystals. Specifically, we determine that only when the rate of crystal-material production is sustained at a high level can size focusing occur and a monodisperse sample of nanocrystals be produced. Quantitative criteria are provided for how high the rate of production must be, and the quantitative effects on the nanocrystal size distribution function for various magnitudes of the production rate. The effect of the production rate on every facet of the size distribution function is evaluated analytically and confirmed numerically. Furthermore, through comparison of the theory to experimental data, it is determined that a typical nanocrystal synthesis accidentally correlates two variables that are critical to the phenomenon of size focusing. The unknowingly correlated variables have frustrated experimental investigations of the same…

Subjects/Keywords: Crystal growth; Surface active agents; Nanostructured materials; Nanostructured materials – Optical properties; Nanostructured materials – Electric properties; Nanocrystals; Chemical engineering; Nanotechnology

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

APA (6^th Edition):

Clark, M. (2013). Quantitative Theories of Nanocrystal Growth Processes. (Doctoral Dissertation). Columbia University. Retrieved from https://doi.org/10.7916/D8PK0MVR

Chicago Manual of Style (16^th Edition):

Clark, Michael. “Quantitative Theories of Nanocrystal Growth Processes.” 2013. Doctoral Dissertation, Columbia University. Accessed January 21, 2021. https://doi.org/10.7916/D8PK0MVR.

MLA Handbook (7^th Edition):

Clark, Michael. “Quantitative Theories of Nanocrystal Growth Processes.” 2013. Web. 21 Jan 2021.

Vancouver:

Clark M. Quantitative Theories of Nanocrystal Growth Processes. [Internet] [Doctoral dissertation]. Columbia University; 2013. [cited 2021 Jan 21]. Available from: https://doi.org/10.7916/D8PK0MVR.

Council of Science Editors:

Clark M. Quantitative Theories of Nanocrystal Growth Processes. [Doctoral Dissertation]. Columbia University; 2013. Available from: https://doi.org/10.7916/D8PK0MVR

University of Texas – Austin

3. Lee, Doh Chang, 1978-. Silicon nanowires, carbon nanotubes, and magnetic nanocrystals: synthesis, properties, and applications.

Degree: PhD, Chemical Engineering, 2007, University of Texas – Austin

URL: http://hdl.handle.net/2152/3229

► Central to the practical use of nanoscale materials is the controlled growth in technologically meaningful quantities. Many of the proposed applications of the nanomaterials potentially… (more)

▼ Central to the practical use of nanoscale materials is the controlled growth in technologically meaningful quantities. Many of the proposed applications of the nanomaterials potentially require inexpensive production of the building blocks. Solution-based synthetic approach offers controllability, high throughput, and scalability, which make the process attractive for the potential scale-up. Growth kinetics could be readily influenced by chemical interactions between the precursor and the solvent. In order to fully utilize its benefits, it is therefore pivotal to understand the decomposition chemistry of the precursors used in the reactions. Supercritical fluids were used as solvent in which high temperature reactions could take place. Silicon nanowires with diameters of 20~30 nm was synthesized in supercritical fluids with metal nanocrystals as seeds for the nanowire growth. To unravel the effect of silicon precursors, several silicon precursors were reacted and the resulting products were investigated. The scalability of the system is discussed based on the experimental data. The nanowires were characterized with various characterization tools, including high-resolution transmission electron microscopy and electron energy loss spectroscopy. The crystallographic signatures were analyzed through the transmission electron microscopic study, and fundamental electrical and optical properties were probed by electron energy loss spectroscopy. Carbon nanotubes were prepared by reacting carbon-containing chemicals in supercritical fluids with organometallic compounds that form metal seed particles in-situ. A batch reaction, in which the temperature control was relatively poor, yielded a mixture of multiwall nanotubes and amorphous carbon nanofilaments with a low selectivity of nanotubes in the product. When reaction parameters were translated into a continuous flow-through reaction, nanotube selectivity as well as the throughput of the total product significantly improved. Magnetic properties of various metal nanocrystals were also studied. Colloidal synthesis enables the growth of FePt and MnPt3 nanocrystals with size uniformity. The as-synthesized nanocrystals, however, had compositionally disordered soft-magnetic phases. To obtain hard magnetic layered phase, the nanocrystals must be annealed at high temperatures, which led to sintering of the inorganic cores. To prevent sintering, the nanocrystals were encapsulated with silica layer prior to annealing. Interparticle magnetic interactions were also explored using particles with varying silica thickness. Advisors/Committee Members: Korgel, Brian A., 1969- (advisor).

Subjects/Keywords: Nanostructured materials; Nanocrystals – Magnetic properties; Nanostructured materials – Electric properties; Nanostructured materials – Optical properties

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

APA (6^th Edition):

Lee, Doh Chang, 1. (2007). Silicon nanowires, carbon nanotubes, and magnetic nanocrystals: synthesis, properties, and applications. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/3229

Chicago Manual of Style (16^th Edition):

Lee, Doh Chang, 1978-. “Silicon nanowires, carbon nanotubes, and magnetic nanocrystals: synthesis, properties, and applications.” 2007. Doctoral Dissertation, University of Texas – Austin. Accessed January 21, 2021. http://hdl.handle.net/2152/3229.

MLA Handbook (7^th Edition):

Lee, Doh Chang, 1978-. “Silicon nanowires, carbon nanotubes, and magnetic nanocrystals: synthesis, properties, and applications.” 2007. Web. 21 Jan 2021.

Vancouver:

Lee, Doh Chang 1. Silicon nanowires, carbon nanotubes, and magnetic nanocrystals: synthesis, properties, and applications. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2007. [cited 2021 Jan 21]. Available from: http://hdl.handle.net/2152/3229.

Council of Science Editors:

Lee, Doh Chang 1. Silicon nanowires, carbon nanotubes, and magnetic nanocrystals: synthesis, properties, and applications. [Doctoral Dissertation]. University of Texas – Austin; 2007. Available from: http://hdl.handle.net/2152/3229

Georgia Tech

4. Schill, Alexander Wilhem. Interesting Electronic and Dynamic Properties of Quantum Dot Quantum Wells and other Semiconductor Nanocrystal Heterostructures.

Degree: PhD, Chemistry and Biochemistry, 2006, Georgia Tech

URL: http://hdl.handle.net/1853/11514

► Some interesting electronic and dynamic properties of semiconductor nanocrystal heterostructures have been investigated using various spectroscopic methods. Semiconductor nanocrystal heterostructures were prepared using colloidal synthesis… (more)

Subjects/Keywords: Ultrafast; Hot electron relaxation; Colloids; Nanoparticles; Femtosecond; Charge transfer; Semiconductor nanocrystals; Quantum wells; Quantum dots; Nanocrystals Electric properties

Record Details Similar Records Cite « Share

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

APA (6^th Edition):

Schill, A. W. (2006). Interesting Electronic and Dynamic Properties of Quantum Dot Quantum Wells and other Semiconductor Nanocrystal Heterostructures. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/11514

Chicago Manual of Style (16^th Edition):

Schill, Alexander Wilhem. “Interesting Electronic and Dynamic Properties of Quantum Dot Quantum Wells and other Semiconductor Nanocrystal Heterostructures.” 2006. Doctoral Dissertation, Georgia Tech. Accessed January 21, 2021. http://hdl.handle.net/1853/11514.

MLA Handbook (7^th Edition):

Schill, Alexander Wilhem. “Interesting Electronic and Dynamic Properties of Quantum Dot Quantum Wells and other Semiconductor Nanocrystal Heterostructures.” 2006. Web. 21 Jan 2021.

Vancouver:

Schill AW. Interesting Electronic and Dynamic Properties of Quantum Dot Quantum Wells and other Semiconductor Nanocrystal Heterostructures. [Internet] [Doctoral dissertation]. Georgia Tech; 2006. [cited 2021 Jan 21]. Available from: http://hdl.handle.net/1853/11514.

Council of Science Editors:

Schill AW. Interesting Electronic and Dynamic Properties of Quantum Dot Quantum Wells and other Semiconductor Nanocrystal Heterostructures. [Doctoral Dissertation]. Georgia Tech; 2006. Available from: http://hdl.handle.net/1853/11514

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