COMPUTATIONAL STUDY OF CARBON NANOMATERIALS: NANOTHREADS AND NANOPOROUS CARBON
Open Access
- Author:
- Xu, Enshi
- Graduate Program:
- Physics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 15, 2016
- Committee Members:
- Vincent Henry Crespi, Dissertation Advisor/Co-Advisor
Mauricio Terrones Maldonado, Committee Member
Jorge Osvaldo Sofo, Committee Member
John V. Badding, Outside Member - Keywords:
- Nanothread
Density Functional Theory
Carbon Nano-materials
Schwarzites
Raman Spectroscopy - Abstract:
- % Place abstract below. Carbon nano-materials can be categorized by their hybridization and dimension: whether they are sp$^2$ or sp$^3$ hybridized, and whether they are zero, one, two or three dimensional material. A recent experiment breakthrough, cold compression of solid benzene into ordered product that is stable back to ambient condition, brought to the front stage a new sp$^3$ hybridized material which is also one dimensional, and this material, belonging in the category of one dimensional sp$^3$ carbon, has certain advantages over the previously considered polymers or nanowires: polymers have too much structural flexibility, nanowires are too wide that most of the atoms are still in the diamond bulk state. We name the material ``carbon nanothread''. Following a concise introduction in Chapter 1 of the structures and basic properties of carbon material classified by their hybridization and dimensionality and a practical introduction in Chapter 2 to the simulation methods used in studying carbon nanothreads, the author presents a systematic enumeration scheme to generate all the structure candidates for carbon nanothreads in Chapter 3, a work that has been published in early 2015. The visualization of the lowest energy structures and a brief discussion of their properties follow the enumeration scheme. In the later sections of Chapter 3, the author shows possible chemical reactions leading to these carbon nanothreads starting from benzene, along with the structures of intermediates, a work done not by the author himself but by the author's collaborators and a work that is an important and integral part to understand the whole picture of nanothreads. Some on-going and proposed directions to utilize the physical properties of carbon nanothreads for applications are proposed in Chapter 3 as well. With the structure candidates at hand, we are equipped to analyze the sample synthesized in experiments, by comparing the calculated observables of the candidate structures to the experiments, a topic of Chapter 4. Raman spectrum analysis is the most extensively studied one, and other experiments are also briefly mentioned. This part of the work is an on-going, unpublished effort. Tuning the reactions pathways by using different precursors will be interesting, and boron nitride nanothreads naturally comes into consideration by the analog of boron nitride nanotube. Chapter 5 focuses on the structures of boron nitride versions of nanothreads, starting from a proposed molecular precursor and covering all the possible intermediates and mapping out potential reaction pathways. Due to the partial ionic nature of boron nitride compound and symmetry breaking, some aspects of the polarization of BN nanothread, having a density as large as the common ferroelectric material BaTiO$_3$, are discussed, envisioning possible applications. In Chapter 6, the author's work prior to the nanothread efforts is presented. The work focuses on another category of carbon material: sp$^2$ hybridized carbon with true three-dimensional structures called ``Schwarzite'', a 3D structure with pores. A new structure design in this family of materials arises from the inclusion of a local carbon atom defect that has four nearest carbon neighbours but is embedded in the graphitic network. The role of such a defect in the possible synthesis of ordered Schwarzite structures is discussed.