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Theory of Electronic Transport and Novel Modeling of Amorphous Materials

Subedi, Kashi
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1640014277883479

Abstract Details

2022, Doctor of Philosophy (PhD), Ohio University, Physics and Astronomy (Arts and Sciences).
Amorphous materials have myriad applications. There are persistent challenges in understanding their structure due to the absence of long range order. Ab initio methods are useful tools to model these materials and determine their microscopic properties. To utilize materials for technological applications, understanding of electronic transport is of central importance. More specifically, for a heterogeneous system, determining conduction-active sites in the network may provide an insight to engineer the material for a desired application. In this dissertation, we describe and develop a novel method to project electronic conductivity onto real-space grids and visualize conduction-active sites in selected materials. To implement the method, we utilize the Kohn-Sham eigenvalues and eigenfunctions obtained from hybrid functional calculations. We then apply the method to study conduction mechanisms in insulating, semi-conducting, metallic and mixed systems. In this dissertation, we also describe atomistic modeling of two promising resistive memory materials: amorphous aluminum oxide (a-Al2O3) and silicon suboxide (a-SiOx). For the former case, we study the impact of transition metal Cu in a highly ionic host a-Al2O3 and discuss its effect to electronic structure and transport in the material. We reveal that the Cu atoms segregate and form a cluster or chain-like structure in the oxide host. We find that such Cu-cluster/chain like network forms the major conduction-active sites in the material. For the latter case, we present a-SiOx models with x = 1.7, 1.5 and 1.3 and study their structure and electronic transport. In our study, we find that the decrease in x results in the complexity of the network with different tetrahedral structures of the form SiSiyO4−y where y = 0 to 4. This results in different types of oxygen (O)-vacancy sites in the material. We propose that a-SiOx also has a potential as a computer security device: physical unclonable functions (PUFs) due to the inherent randomness in its structure, particularly for low x. In the last section of the dissertation, we employ the building-block method to model sodium silicate glasses among the most important glasses for practical application. We provide a detailed study of structural, electronic and thermal properties with varying concentration of modifier (Na2O) in the glass (SiO2). For the first time (to our knowledge), we have computed the linear thermal expansion coefficient using first principles and our results find close agreement with experiments.
David Drabold (Advisor)
Sumit Sharma (Committee Member)
Eric Stinaff (Committee Member)
Martin Kordesch (Committee Member)
Gang Chen (Committee Member)
127 p.
Physics
Kubo-Greenwood formula; Electronic conductivity; Conduction matrix; Space-projected conductivity; resistive memory devices; physical unclonable functions; building-block method; sodium silicate glasses

Recommended Citations

Citations

  • Subedi, K. (2022). Theory of Electronic Transport and Novel Modeling of Amorphous Materials [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1640014277883479

    APA Style (7th edition)

  • Subedi, Kashi. Theory of Electronic Transport and Novel Modeling of Amorphous Materials. 2022. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1640014277883479.

    MLA Style (8th edition)

  • Subedi, Kashi. "Theory of Electronic Transport and Novel Modeling of Amorphous Materials." Doctoral dissertation, Ohio University, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1640014277883479

    Chicago Manual of Style (17th edition)

ohiou1640014277883479
179
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This open access ETD is published by Ohio University and OhioLINK.