Electron Microscopy Characterization of Vanadium Dioxide Thin Films and Nanoparticles
Vanadium dioxide (VO_2) is a material of particular interest due to its exhibited metal to insulator phase transition at 68°C that is accompanied by an abrupt and significant change in its electronic and optical properties. Since this material can exhibit a reversible drop in resistivity of up to fi...
Main Author: | |
---|---|
Format: | Others |
Published: |
BYU ScholarsArchive
2012
|
Subjects: | |
Online Access: | https://scholarsarchive.byu.edu/etd/2975 https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=3974&context=etd |
id |
ndltd-BGMYU2-oai-scholarsarchive.byu.edu-etd-3974 |
---|---|
record_format |
oai_dc |
spelling |
ndltd-BGMYU2-oai-scholarsarchive.byu.edu-etd-39742019-05-16T03:04:07Z Electron Microscopy Characterization of Vanadium Dioxide Thin Films and Nanoparticles Rivera, Felipe Vanadium dioxide (VO_2) is a material of particular interest due to its exhibited metal to insulator phase transition at 68°C that is accompanied by an abrupt and significant change in its electronic and optical properties. Since this material can exhibit a reversible drop in resistivity of up to five orders of magnitude and a reversible drop in infrared optical transmission of up to 80%, this material holds promise in several technological applications. Solid phase crystallization of VO_2 thin films was obtained by a post-deposition annealing process of a VO_{x,x approx 2} amorphous film sputtered on an amorphous silicon dioxide (SiO_2) layer. Scanning electron microscopy (SEM) and electron-backscattered diffraction (EBSD) were utilized to study the morphology of the solid phase crystallization that resulted from this post-deposition annealing process. The annealing parameters ranged in temperature from 300°C up to 1000°C and in time from 5 minutes up to 12 hours. Depending on the annealing parameters, EBSD showed that this process yielded polycrystalline vanadium dioxide thin films, semi-continuous thin films, and films of isolated single-crystal particles. In addition to these films on SiO_2, other VO_2 thin films were deposited onto a-, c-, and r-cuts of sapphire and on TiO_2(001) heated single-crystal substrates by pulsed-laser deposition (PLD). The temperature of the substrates was kept at ~500°C during deposition. EBSD maps and orientation imaging microscopy were used to study the epitaxy and orientation of the VO_2 grains deposited on the single crystal substrates, as well as on the amorphous SiO_2 layer. The EBSD/OIM results showed that: 1) For all the sapphire substrates analyzed, there is a predominant family of crystallographic relationships wherein the rutile VO_2{001} planes tend to lie parallel to the sapphire's {10-10} and the rutile VO_2{100} planes lie parallel to the sapphire's {1-210} and {0001}. Furthermore, while this family of relationships accounts for the majority of the VO_2 grains observed, due to the sapphire substrate's geometry there were variations within these rules that changed the orientation of VO_2 grains with respect to the substrate's normal direction. 2) For the TiO_2, a substrate with a lower lattice mismatch, we observe the expected relationship where the rutile VO_2 [100], [110], and [001] crystal directions lie parallel to the TiO_2 substrate's [100], [110], and [001] crystal directions respectively. 3) For the amorphous SiO_2 layer, all VO_2 crystals that were measurable (those that grew to the thickness of the deposited film) had a preferred orientation with the the rutile VO_2[001] crystal direction tending to lie parallel to the plane of the specimen. The use of transmission electron microscopy (TEM) is presented as a tool for further characterization studies of this material and its applications. In this work TEM diffraction patterns taken from cross-sections of particles of the a- and r-cut sapphire substrates not only solidified the predominant family mentioned, but also helped lift the ambiguity present in the rutile VO_2{100} axes. Finally, a focused-ion beam technique for preparation of cross-sectional TEM samples of metallic thin films deposited on polymer substrates is demonstrated. 2012-03-01T08:00:00Z text application/pdf https://scholarsarchive.byu.edu/etd/2975 https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=3974&context=etd http://lib.byu.edu/about/copyright/ All Theses and Dissertations BYU ScholarsArchive vanadium dioxide electron microscopy SEM TEM FIB focused ion beam thin films characterization Astrophysics and Astronomy Physics |
collection |
NDLTD |
format |
Others
|
sources |
NDLTD |
topic |
vanadium dioxide electron microscopy SEM TEM FIB focused ion beam thin films characterization Astrophysics and Astronomy Physics |
spellingShingle |
vanadium dioxide electron microscopy SEM TEM FIB focused ion beam thin films characterization Astrophysics and Astronomy Physics Rivera, Felipe Electron Microscopy Characterization of Vanadium Dioxide Thin Films and Nanoparticles |
description |
Vanadium dioxide (VO_2) is a material of particular interest due to its exhibited metal to insulator phase transition at 68°C that is accompanied by an abrupt and significant change in its electronic and optical properties. Since this material can exhibit a reversible drop in resistivity of up to five orders of magnitude and a reversible drop in infrared optical transmission of up to 80%, this material holds promise in several technological applications. Solid phase crystallization of VO_2 thin films was obtained by a post-deposition annealing process of a VO_{x,x approx 2} amorphous film sputtered on an amorphous silicon dioxide (SiO_2) layer. Scanning electron microscopy (SEM) and electron-backscattered diffraction (EBSD) were utilized to study the morphology of the solid phase crystallization that resulted from this post-deposition annealing process. The annealing parameters ranged in temperature from 300°C up to 1000°C and in time from 5 minutes up to 12 hours. Depending on the annealing parameters, EBSD showed that this process yielded polycrystalline vanadium dioxide thin films, semi-continuous thin films, and films of isolated single-crystal particles. In addition to these films on SiO_2, other VO_2 thin films were deposited onto a-, c-, and r-cuts of sapphire and on TiO_2(001) heated single-crystal substrates by pulsed-laser deposition (PLD). The temperature of the substrates was kept at ~500°C during deposition. EBSD maps and orientation imaging microscopy were used to study the epitaxy and orientation of the VO_2 grains deposited on the single crystal substrates, as well as on the amorphous SiO_2 layer. The EBSD/OIM results showed that: 1) For all the sapphire substrates analyzed, there is a predominant family of crystallographic relationships wherein the rutile VO_2{001} planes tend to lie parallel to the sapphire's {10-10} and the rutile VO_2{100} planes lie parallel to the sapphire's {1-210} and {0001}. Furthermore, while this family of relationships accounts for the majority of the VO_2 grains observed, due to the sapphire substrate's geometry there were variations within these rules that changed the orientation of VO_2 grains with respect to the substrate's normal direction. 2) For the TiO_2, a substrate with a lower lattice mismatch, we observe the expected relationship where the rutile VO_2 [100], [110], and [001] crystal directions lie parallel to the TiO_2 substrate's [100], [110], and [001] crystal directions respectively. 3) For the amorphous SiO_2 layer, all VO_2 crystals that were measurable (those that grew to the thickness of the deposited film) had a preferred orientation with the the rutile VO_2[001] crystal direction tending to lie parallel to the plane of the specimen. The use of transmission electron microscopy (TEM) is presented as a tool for further characterization studies of this material and its applications. In this work TEM diffraction patterns taken from cross-sections of particles of the a- and r-cut sapphire substrates not only solidified the predominant family mentioned, but also helped lift the ambiguity present in the rutile VO_2{100} axes. Finally, a focused-ion beam technique for preparation of cross-sectional TEM samples of metallic thin films deposited on polymer substrates is demonstrated. |
author |
Rivera, Felipe |
author_facet |
Rivera, Felipe |
author_sort |
Rivera, Felipe |
title |
Electron Microscopy Characterization of Vanadium Dioxide Thin Films and Nanoparticles |
title_short |
Electron Microscopy Characterization of Vanadium Dioxide Thin Films and Nanoparticles |
title_full |
Electron Microscopy Characterization of Vanadium Dioxide Thin Films and Nanoparticles |
title_fullStr |
Electron Microscopy Characterization of Vanadium Dioxide Thin Films and Nanoparticles |
title_full_unstemmed |
Electron Microscopy Characterization of Vanadium Dioxide Thin Films and Nanoparticles |
title_sort |
electron microscopy characterization of vanadium dioxide thin films and nanoparticles |
publisher |
BYU ScholarsArchive |
publishDate |
2012 |
url |
https://scholarsarchive.byu.edu/etd/2975 https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=3974&context=etd |
work_keys_str_mv |
AT riverafelipe electronmicroscopycharacterizationofvanadiumdioxidethinfilmsandnanoparticles |
_version_ |
1719184015797256192 |