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 Title: Scanning tunneling microscopy of quasi-one-dimensional charge-density wave materials Author(s): Gammie, Gordon Doctoral Committee Chair(s): Tucker, John R. Department / Program: Electrical and Computer Engineering Discipline: Electrical Engineering Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Engineering, Electronics and Electrical Physics, Condensed Matter Engineering, Materials Science Abstract: Scanning tunneling microscopy (STM) has been used to study the atomic and electronic structures of quasi-one-dimensional charge-density wave (CDW) materials. The two materials chosen for this study, NbSe$\sb3$ and o-TaS$\sb3$, exhibit numerous interesting characteristics associated with the formation and motion of the CDW. The purpose of these studies is to determine if the surface characteristics are sufficiently similar to the bulk characteristics to learn something about the microscopics of CDWs and their dynamics.Room temperature studies of NbSe$\sb3$ show that at least two different surface structures are possible. The first is a slightly relaxed form of the bulk crystal structure, while the second suggests the presence of an additional atom on the type-I chains. The detailed structure of o-TaS$\sb3$ is not known, but STM studies show that it is more closely related to the ZrSe$\sb3$ structure than that of NbSe$\sb3$ and m-TaS$\sb3$, as had previously been assumed. The difference in the strength of the chalcogen pairing in the chains of o-TaS$\sb3$ is much less than that of m-TaS$\sb3$, with all chains exhibiting intermediate strength pairing.Low temperature studies of the two surfaces of NbSe$\sb3$ show that the relaxed surface forms a faint CDW, while the adatom surface does not. One-dimensional fluctuations above the CDW transition temperature in o-TaS$\sb3$ can be seen in STM images. Below the transition, the CDW is imaged and agrees well with the known wavevector. There are two uniformly distributed CDW maxima per unit cell along the b$\sb{\rm o}$-axis which, in conjunction with the room temperature lattice images, explains some of the differences between the CDW characteristics of o-TaS$\sb3$ and m-TaS$\sb3$. All attempts to slide the CDW on the surfaces of these materials have been unsuccessful. Issue Date: 1991 Type: Text Language: English URI: http://hdl.handle.net/2142/20448 Rights Information: Copyright 1991 Gammie, Gordon Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9210808 OCLC Identifier: (UMI)AAI9210808
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