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Author: Raul Torrico Publisher: ISBN: 9781321834154 Category : Phase transformations (Statistical physics) Languages : en Pages : 491
Book Description
Abstract: Vanadium Dioxide (VO2) has been garnering a lot of attention because of its ability to undergo a phase transition from insulator to metal when heated and to switch back to insulator when cooled. Here we use the scattering-type Near-Field Optical Microscope to study the changes caused in the optical properties by the phase transition in near-field regime of VO2 . We observe the growth of metallic VO2 puddles at varying temperatures from room temperature up to a critical temperature around 358 K. The insulator to metal transition causes the optical constants in VO2 to drastically change. Taking advantage of the change, coupling VO2 with plasmonic structures has the interesting effect of combining to form optical metamaterials. These man-made materials exhibit behaviors not found in nature. Using the Lumerical Solutions software, it is possible to model and simulate those optical behaviors for different types of noble metal plasmonic structures using insulating and metallic VO2 at different light sources. These metamaterials can be categorized as hybrid-tunable metamaterials which can be designed to filter certain resonance frequencies without having to change plasmonic structure.
Author: Raul Torrico Publisher: ISBN: 9781321834154 Category : Phase transformations (Statistical physics) Languages : en Pages : 491
Book Description
Abstract: Vanadium Dioxide (VO2) has been garnering a lot of attention because of its ability to undergo a phase transition from insulator to metal when heated and to switch back to insulator when cooled. Here we use the scattering-type Near-Field Optical Microscope to study the changes caused in the optical properties by the phase transition in near-field regime of VO2 . We observe the growth of metallic VO2 puddles at varying temperatures from room temperature up to a critical temperature around 358 K. The insulator to metal transition causes the optical constants in VO2 to drastically change. Taking advantage of the change, coupling VO2 with plasmonic structures has the interesting effect of combining to form optical metamaterials. These man-made materials exhibit behaviors not found in nature. Using the Lumerical Solutions software, it is possible to model and simulate those optical behaviors for different types of noble metal plasmonic structures using insulating and metallic VO2 at different light sources. These metamaterials can be categorized as hybrid-tunable metamaterials which can be designed to filter certain resonance frequencies without having to change plasmonic structure.
Author: Scott Eric Madaras Publisher: ISBN: Category : Thin films Languages : en Pages : 146
Book Description
Vanadium Dioxide (VO2) is a strongly correlated material which has been studied for many decades. VO2 has been proposed for uses in technologies such as optical modulators, IR modulators, optical switches and Mott memory devices. These technologies are taking advantage of VO2’s insulator to metal transition (IMT) and the corresponding changes to the optical and material properties. The insulator to metal transition in VO2 can be accessed by thermal heating, applied electric field, or ultra-fast photo induced processes. Recently, thin films of VO2 grown on Titanium Dioxide doped with Niobium (TiO2:Nb), have shown promise as a possible UV photo detector with high quantum efficiency which utilizes a heterostructure between these two materials. In this work, the dynamics of the IMT on thin films of VO2 is explored. We show that surface plasmons generated in an Au thin film can induce the insulator to metal transition in a thin film of VO2 due to the enhanced electric field as well as help detect the IMT via changes in its resonance condition. Time resolved pump probe studies were also done on thin films of VO2 grown on TiO2 and TiO2:Nb, using UV photon energy of 3.1 eV (400nm wavelength). The fluence threshold of the IMT at 3.1 eV was significantly lower than published values for the 1.55 eV pump fluence. The time response of the IMT shows uncommon reflectivity dynamics in these samples. The response was partially attributed to internal interference of the reflected probe beam from the inhomogeneous layers formed inside the film by different phases of VO2, and can be elucidated by a diffusion model with respect to its optical properties. Finally, the photocurrent generation time constants for the sample with highest quantum efficiency are given and compared to its ultrafast photo induced IMT time constants.
Author: Tyler J. Huffman Publisher: ISBN: Category : Physics Languages : en Pages :
Book Description
The salient feature of the familiar structural transition accompanying the thermally-driven metal-insulator transition in bulk vanadium dioxide (VO2) is a pairing of all the vanadium ions in the monoclinic M¬1 insulating phase. Whether this pairing (unit cell doubling) alone is sufficient to open the energy gap has been the central question of a classic debate which has continued for almost sixty years. Interestingly, there are two less familiar insulating states, monoclinic M2 and triclinic, which are accessible via strain or chemical doping. These phases are noteworthy in that they exhibit distinctly different V-V pairing. With infrared and optical photon spectroscopy, we investigate how the changes in crystal structure affect the electronic structure. We find that the energy gap and optical inter-band transitions are insensitive to changes in the vanadium-vanadium pairing. This result is confirmed by DFT+U and HSE calculations. Hence, our work conclusively establishes that intra-atomic Coulomb repulsion between electrons provides the dominant contribution to the energy gap in all insulating phases of VO2. VO2 is a candidate material for novel technologies, including ultrafast data storage, memristors, photonic switches, smart windows, and transistors which move beyond the limitations of silicon. The attractiveness of correlated materials for technological application is due to their novel properties that can be tuned by external factors such as strain, chemical doping, and applied fields. For advances in fundamental physics and applications, it is imperative that these properties be measured over a wide range of regimes. Towards this end, we study a single domain VO2 crystal with polarized light to characterize the anisotropy of the optical properties. In addition, we study the effects of compressive strain in a VO2 thin film in which we observe remarkable changes in electronic structure and transition temperature. Furthermore, we find evidence that electronic correlations are active in the metallic rutile phase as well. VO2 films exhibit phase coexistence in the vicinity of the metal-insulator transition. Using scanning near-field infrared microscopy, we have studied the patterns of phase coexistence in the same area on repeated heating and cooling cycles. We find that the pattern formation is reproducible each time. This is an unexpected result from the viewpoint of classical nucleation theory that anticipates some degree of randomness. The completely deterministic nature of nucleation and growth of domains in a VO2 film with imperfections is a fundamental finding. This result also holds promise for producing reliable nanoscale VO2 devices.
Author: Soumyadipta Basu Publisher: William Andrew ISBN: 0323429769 Category : Science Languages : en Pages : 478
Book Description
Near-Field Radiative Heat Transfer across Nanometer Vacuum Gaps provides an in-depth description of fundamentals and application of near-field radiative heat transfer. When the vacuum gap between two media is on the order of nanometers, heat transfer can exceed that between blackbodies. This book investigates near-field heat transfer between different materials and geometries highlighting interplay between optics, material thermophysical properties and electromagnetism. The book also highlights the application of near-field thermal radiation in the field of power generation, imaging, and thermal systems as an analog of electronic devices. - Brings together research in near-field radiative heat transfer in a focused and comprehensive manner, allowing those new to the topic to gain a thorough understanding of the science and how it can be used - Offers focused coverage of heat transfer in near-field radiation, which other books do not - Outlines the interplay between optics, electromagnetics, basic thermodynamics, and thermophysical properties of materials during near-field heat transfer
Author: Zhuomin M. Zhang Publisher: Springer Nature ISBN: 3030450392 Category : Science Languages : en Pages : 780
Book Description
This substantially updated and augmented second edition adds over 200 pages of text covering and an array of newer developments in nanoscale thermal transport. In Nano/Microscale Heat Transfer, 2nd edition, Dr. Zhang expands his classroom-proven text to incorporate thermal conductivity spectroscopy, time-domain and frequency-domain thermoreflectance techniques, quantum size effect on specific heat, coherent phonon, minimum thermal conductivity, interface thermal conductance, thermal interface materials, 2D sheet materials and their unique thermal properties, soft materials, first-principles simulation, hyperbolic metamaterials, magnetic polaritons, and new near-field radiation experiments and numerical simulations. Informed by over 12 years use, the author’s research experience, and feedback from teaching faculty, the book has been reorganized in many sections and enriched with more examples and homework problems. Solutions for selected problems are also available to qualified faculty via a password-protected website.• Substantially updates and augments the widely adopted original edition, adding over 200 pages and many new illustrations;• Incorporates student and faculty feedback from a decade of classroom use;• Elucidates concepts explained with many examples and illustrations;• Supports student application of theory with 300 homework problems;• Maximizes reader understanding of micro/nanoscale thermophysical properties and processes and how to apply them to thermal science and engineering;• Features MATLAB codes for working with size and temperature effects on thermal conductivity, specific heat of nanostructures, thin-film optics, RCWA, and near-field radiation.
Author: Felipe Rivera Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 222
Book 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: Raul Torrico
Author: Raul Torrico
Author: Scott Eric Madaras
Author: Valter Kiisk
Author: Lukas Novotny
Author: Tyler J. Huffman
Author: Scott H. Beasor
Author: 
Author: Soumyadipta Basu
Author: Zhuomin M. Zhang
Author: Felipe Rivera