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Elucidation of Charge Density Wave Stability and Defect Interactions in the Highly-Ordered Structural Transition Metal Dichalcogenide System 1T-TaS2.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Elucidation of Charge Density Wave Stability and Defect Interactions in the Highly-Ordered Structural Transition Metal Dichalcogenide System 1T-TaS2./
Author:	Engen, Paige Ela.
Description:	1 online resource (198 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-01, Section: B.
Contained By:	Dissertations Abstracts International85-01B.
Subject:	Materials science. -
Online resource:	click for full text (PQDT)
ISBN:	9798379944377

Elucidation of Charge Density Wave Stability and Defect Interactions in the Highly-Ordered Structural Transition Metal Dichalcogenide System 1T-TaS2.
Engen, Paige Ela.

Elucidation of Charge Density Wave Stability and Defect Interactions in the Highly-Ordered Structural Transition Metal Dichalcogenide System 1T-TaS2. - 1 online resource (198 pages)

Source: Dissertations Abstracts International, Volume: 85-01, Section: B.

Thesis (Ph.D.)--University of Minnesota, 2023.

Includes bibliographical references

The 1T phase of tantalum disulfide (1T-TaS2) has a rich and complex charge density wave (CDW) phase character that has been broadly studied. CDWs are a highly correlated state between electron density and lattice distortion, originally predicted to only exist in one dimension. The discovery of CDWs in two-dimensional systems spiked interest in uncovering the various phases and phase interactions. Understanding the phase interactions is of fundamental interest to better comprehend the nature of complicated CDW behaviors. 1T-TaS2 has three thermally-dependent primary CDW phases that show increased commensurability to the underlying lattice with decreasing temperature. This dissertation focuses on the room temperature nearly-commensurate (NC) phase, along with some investigation into the high temperature incommensurate (IC) phase. The work presented in this dissertation starts to elucidate the CDW stability using high-resolution and in situ transition electron microscopy (TEM).Direct observation of the CDWs allows for characterizing the interaction between the superlattice and the underlying lattice, including topological defects. Various methods have been used to visualize the CDW supercells, lattice distortion, and domain structure. However, many of these techniques lack atomic resolution, require additional image processing, or complicate the direct observation of long-range order. Here, high-resolution, bright-field TEM was used to directly observe CDW-associated moire contrast. This methodology allows for atomic resolution of the tantalum atoms and identification of long-range CDW superlattice ordering. Investigation into the superlattice moire contrast revealed a variety of edge dislocation topological defects within the CDW phase. Dislocations in the CDW superlattice are poorly understood, and the work presented in this dissertation is one of the first reports of edge dislocation-like topological defects. Determination of the underlying cause of the topological defect remains elusive, but preliminary analysis of the defect stability is explored.The stability and dynamics of the three primary phases have been extensively studied to extract thermal and photoexcited transitions. Defects and various specimen morphologies have been shown to destabilize and suppress the CDW phases. However, much of the previous work used techniques that spatially average out the interactions and lose the precise morphological interactions. Regionally-selective NC-IC phase transitions were investigated to determine the role of higher-order structural defects, such as crystalline step edges and ripplocations, on CDW stability. The phase transition temperature is directly related to the stability of the CDW in the various regions. Decreases in the transition temperature are correlated with a reduction in phase stability. It is shown that local variations in the identity and concentration of higher-dimensional defects will modify the NC-IC phase transition temperatures within a single specimen. It is clear that defects' local effects directly influence the CDW phase behavior and have interesting implications for understanding CDW dynamics.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798379944377Subjects--Topical Terms:

557839
Materials science.
Subjects--Index Terms:

Tantalum disulfideIndex Terms--Genre/Form:

554714
Electronic books.

Elucidation of Charge Density Wave Stability and Defect Interactions in the Highly-Ordered Structural Transition Metal Dichalcogenide System 1T-TaS2.
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520 $a The 1T phase of tantalum disulfide (1T-TaS2) has a rich and complex charge density wave (CDW) phase character that has been broadly studied. CDWs are a highly correlated state between electron density and lattice distortion, originally predicted to only exist in one dimension. The discovery of CDWs in two-dimensional systems spiked interest in uncovering the various phases and phase interactions. Understanding the phase interactions is of fundamental interest to better comprehend the nature of complicated CDW behaviors. 1T-TaS2 has three thermally-dependent primary CDW phases that show increased commensurability to the underlying lattice with decreasing temperature. This dissertation focuses on the room temperature nearly-commensurate (NC) phase, along with some investigation into the high temperature incommensurate (IC) phase. The work presented in this dissertation starts to elucidate the CDW stability using high-resolution and in situ transition electron microscopy (TEM).Direct observation of the CDWs allows for characterizing the interaction between the superlattice and the underlying lattice, including topological defects. Various methods have been used to visualize the CDW supercells, lattice distortion, and domain structure. However, many of these techniques lack atomic resolution, require additional image processing, or complicate the direct observation of long-range order. Here, high-resolution, bright-field TEM was used to directly observe CDW-associated moire contrast. This methodology allows for atomic resolution of the tantalum atoms and identification of long-range CDW superlattice ordering. Investigation into the superlattice moire contrast revealed a variety of edge dislocation topological defects within the CDW phase. Dislocations in the CDW superlattice are poorly understood, and the work presented in this dissertation is one of the first reports of edge dislocation-like topological defects. Determination of the underlying cause of the topological defect remains elusive, but preliminary analysis of the defect stability is explored.The stability and dynamics of the three primary phases have been extensively studied to extract thermal and photoexcited transitions. Defects and various specimen morphologies have been shown to destabilize and suppress the CDW phases. However, much of the previous work used techniques that spatially average out the interactions and lose the precise morphological interactions. Regionally-selective NC-IC phase transitions were investigated to determine the role of higher-order structural defects, such as crystalline step edges and ripplocations, on CDW stability. The phase transition temperature is directly related to the stability of the CDW in the various regions. Decreases in the transition temperature are correlated with a reduction in phase stability. It is shown that local variations in the identity and concentration of higher-dimensional defects will modify the NC-IC phase transition temperatures within a single specimen. It is clear that defects' local effects directly influence the CDW phase behavior and have interesting implications for understanding CDW dynamics.
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