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Tungsten doped vanadium dioxide via atomic layer deposition with tailored thermochromic electrical and optical response
No full textWith the rise of world temperatures due to global warming, the importance of efficient cooling has increased drastically. Radiative coolers provide a route to effectively emit thermal energy into space. In areas with large diurnal ranges or seasonal temperature variations, however, constant cooling is undesired. Self-adaptive radiative coolers can produce large radiated power at high temperatures and reduced radiated power at low temperatures by passively varying their emissivity (ε). These devices rely upon thermochromic materials, which undergo large changes in their material, optical, and electrical response due to a temperature-driven phase transition. These transitions are induced through the addition of thermal energy by absorbing radiation, Joule heating, or conduction. One such material that exhibits these characteristics is vanadium dioxide - VO2 - a solid-solid phase change material that can reliably switch between its low temperature monoclinic and high-temperature rutile phase around 69 °C. By doping, the thermochromic response can be tailored, extending the material uses to areas including smart windows, memristors, and sensing. For these applications, thin-film devices provide a route for low-cost, lightweight structures with enhanced performance through smart metamaterial and multilayer design. The performance of such devices is highly dependent upon film quality and thickness control. By utilising the novel atomic layer deposition (ALD) of VO2 and W-doped VO2 thin films, devices were produced with adjusted thermochromic responses for a variety of optical and electrical applications. A patterned VO2 metasurface deposited upon an optimised Salisbury screen stack for enhanced infrared IR absorption was fabricated, creating a smart IR emitter with high visual transparency – a smart window. The VO2 thermal emitter demonstrated a tuneable IR emissivity (∆ε) of 0.26, with a 62 % improvement in solar transmittance by the metasurface patterned design compared to its planar counterpart, attributed to the reduced VO2 coverage. The device displays much greater radiated powers under daytime illumination owing to the increased high temperature ε of the device for terrestrial and space applications, displaying the suitability of the design for use in both environments. Reduction of the transition temperature of VO2 films to room temperature was demonstrated through doping with W. By varying the W/V cycle ratio during ALD deposition, five uniform W-doped VO2 stacks with different W concentrations were fabricated and characterised. Predictable control of the transition temperature was shown to be possible while maintaining material and optical performance. By parameterising their temperature dependent electrical response, a novel model was proposed to predict the thermochromic resistivity response of W:VO2 films based on their W doping at.%. Optimised multilayer W:VO2 device designs were then simulated for use as high-sensitivity microbolometers with extended phase transition responses across chosen operating temperature windows.To experimentally demonstrate the extended phase transition of multilayer doped W:VO2 stacks, several films were fabricated with thickness and W doping control using ALD. Three W:VO2 devices on high ε SiO2 were fabricated and optically tested, with each displaying a negative thermochromic ε response for optical stealth. Two additional multilayer W:VO2 devices were manufactured as high-sensitivity microbolometers across two operating temperature windows. Depth-resolved XPS verified a W gradient through the as-deposited films of ∆W ≈ 0.7 and 2.0 at.%. Their electrical thermochromic performances were assessed, with both stacks displaying a convoluted bi-layer response indicative of two distinct W:VO2 layers within a single film. This is the first demonstration of an extended phase transition multilayer W:VO2 device deposited by ALD, opening new pathways for VO2 material control.<br/
Dataset supporting the thesis titled "Tungsten Doped Vanadium Dioxide via Atomic Layer Deposition with Tailored Thermochromic Electrical and Optical Response"
No full textThis dataset supports the thesis entitled 'Tungsten Doped Vanadium Dioxide via Atomic Layer Deposition with Tailored
Thermochromic Electrical and Optical Response', awarded by the University of Southampton in 2024
DESCRIPTION OF THE DATA:
The attached dataset is in support of the data presented in this thesis.
Data presented in Chapters 4 and 5 is published and accessible online, with the DOI's listed in the Related publications section below.
Data is presented in the attached .xlsx file, split by tabs corresponding to the associated Figure number in the thesis.
Ellipsometry data is not inlcuded in these data files.
Data for Figure 32 can be found in full in Figure S2 and 3.
Figures 49, 50, 51 data is extracted from the resistivity data presented in Figure 48.
This dataset contains:
Data collected on a set of W-doped VO2 thin films deposited via ALD for tailored optical and electrical responses.
These were measured using a wide range of spectroscopic and electrical measurement tools including:
Depth resolved and surface X-ray Photoelectron spectroscopy;
Raman spectroscopy;
Hall Probe measurements;
Fourier-Transform Infrared spectroscopy;
Date of data collection: 10/20 - 04/24</span
Dataset in support of the journal article 'Low-temperature vanadium dioxide for CMOS integration and flexible polyimide applications'
No full textArticle published in Optical Materials Express
Figure 1:
Figure 1a: no associated data.
Figure 1b: no associated data.
Figure 1c: no associated data.
Figure 1d: no associated data.
Figure 1e: no associated data.
Figure 1f: no associated data.
Figure 2:Sheet Fig.2 Raman shift vs different anneal temperature.
Figure 3:
Figure 3a: Sheet Fig.3(a) XPS data of unannealed sample.
Figure 3b: Sheet Fig.3(b) XPS data of 250 °C annealed sample.
Figure 3c: Sheet Fig.3(c) XPS data of 300 °C annealed sample.
Figure 3d: Sheet Fig.3(d) XPS data of 350 °C annealed sample.
Figure 3e: Sheet Fig.3(e) XPS data of 400 °C annealed sample.
Figure 4:
Figure 4a: Sheet Fig.4(a) FTIR reflectance spectra at different temperatures (250C anneal temperature).
Figure 4b: Sheet Fig.4(b) FTIR reflectance spectra at different temperatures (300C anneal temperature).
Figure 4c: Sheet Fig.4(c) FTIR reflectance spectra at different temperatures (350C anneal temperature).
Figure 4d: Sheet Fig.4(d) FTIR reflectance spectra at different temperatures (400C anneal temperature).
Figure 4e: Sheet Fig.4(e) IR emissivity hysteresis for anneals at 300 °C
Figure 4f: Sheet Fig.4(f) IR emissivity hysteresis for anneals at 350 °C
Figure 5:
Figure 5a: no associated data.
Figure 5b: Sheet Fig.5(b) Raman shift of Kapton comparing with VO2 and V2O5 reference samples.
Figure 5c: Sheet Fig.5(c) FTIR reflectance spectra on Kapton (300C anneal temperature).
Figure 5d: Sheet Fig.5(d) IR emissivity hysteresis for Kapton anneals at 300C.
Supporting Information
Figure S1: no associated data.
Figure S2: Sheet Fig.S2, COMSOL simulated FTIR reflectance spectra under different SiO2 thickness.</span
Low-temperature vanadium dioxide for CMOS integration and flexible polyimide applications
No full textVanadium dioxide (VO2) is a popular phase-transition material with broad applications ranging from thermal management in smart windows to neuromorphic computing. Currently, VO2 thin films are usually fabricated at high temperatures, making them incompatible in forming on top of CMOS and flexible polyimide substrates. This study explores a low-temperature VO2 thin film formation approach that combines atomic layer deposition (ALD) with a post-deposition anneal. With systematic material characterizations, we clearly demonstrate high-quality VO2 film formation on Si substrates at a significantly reduced annealing temperature of 300 °C. Further reducing the annealing temperature to 250 oC is shown to lead to insufficient VO2 crystallization whilst elevating the temperature to 400 oC results in overoxidation into V2O5. We implement our method on polyimide substrates and demonstrate that the high-quality phase transition is indeed preserved. This work demonstrates the ability of low-temperature formation of VO2 thin films, and it will accelerate the adoption of VO2 in emerging electronic devices as well as photonic applications
Dataset in support of the paper 'Multilayer W-doped VO2 thermal sensors with extended operation region'
No full textThis dataset contains:
Figure Data for Fig 1a,1b,1c, 1d, 1e, 1h, 3c, 3e, 3f, 5a-d, 6, S1, S2, S3, S7,S8, S9, S10, S11, S12 in Excel format
Article to be published in IScience</span
Dataset to support the journal article: VO2 Metasurface Smart Thermal Emitter with High Visual Transparency for Passive Radiative Cooling Regulation in Space and Terrestrial Applications
No full textSimulation results and optical spectra of devices, the dataset consists of a single excel file with spreadsheet for each subfigure/figure presented in the paper</span
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dataset supporting an article: Room Temperature Phase Transition of W-doped VO2 by Atomic Layer Deposition on 200 mm Si Wafers and Flexible Substrates
No full textThis dataset supports the journal publication
Room Temperature Phase Transition of W-doped VO2 by Atomic Layer Deposition on 200 mm Si Wafers and Flexible Substrates
:Advanced Optical Materials
https://doi.org/10.1002/adom.202201326
The data is in Excel format</span
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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