Inhomogeneous Phase Transition of Vanadium Oxide on Mesoscopic Scale PDF Download

Author: Siming Wang
Publisher:
ISBN: 9781321324044
Category :
Languages : en
Pages : 126

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Book Description
Vanadium oxides are a prototypical family of materials that exhibit first order metal insulator transitions (MIT). In the past 15 years, the research has been focused on the role of different driving forces and the inhomogeneity in the phase transitions of vanadium oxides. Multiple stimuli, such as voltage, current and laser pulses, have been used to induce a MIT in vanadium oxides. Inhomogeneity can give rise to phase coexistence and multiple avalanches in mesoscopic scale vanadium oxides. In this thesis, I will focus on understanding the MIT of mesoscopic vanadium oxides. I will address the phase transition mechanism through resistance - temperature (R-T) and current - voltage (I-V) characteristics. I will present the R-T characteristic of nano-sized vanadium oxide devices, which exhibits multiple avalanches over two orders of magnitude. Statistics on the avalanches indicate different MIT mechanisms for different vanadium oxides. The I-V characteristic of micro-sized vanadium oxide devices has been previously interpreted as evidence for a voltage induced transition, a non-thermal pure electronic transition in vanadium oxides. I will present a comprehensive study of the I-V characteristic supported by various techniques, including fluorescent local temperature measurement, low temperature scanning electron microscopy and numerical simulation. The results prove that Joule heating plays a significant role in the voltage induced transition of vanadium oxides. I will also discuss the other important aspect of the phase transition, the structural phase transition (SPT) in vanadium oxides. The SPT can be used to manipulate the magnetic properties of ferromagnetic materials, e.g. coercivity and magnetization. In a vanadium oxide/ferromagnet bilayer, the coercivity increases as the SPT occurs, due to the stress anisotropy induced by the SPT. In the special case of a V2O3/Ni bilayer with a smooth interface, a large coercivity enhancement appears at the middle of the V2O3 SPT. This effect is attributed to the phase coexistence in V2O3 at the nanoscale and supported by micromagnetic simulations.

Author: Ilya Valmianski
Publisher:
ISBN:
Category :
Languages : en
Pages : 92

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Book Description
Vanadium oxides are a prototypical family of highly correlated oxides. In his dissertation, I present the study of two vanadium oxides in particular, V2O3 and VO2, which undergo simultaneously both a structural phase transition and a metal to insulator transition. While traditionally these phase transitions were studied in equilibrium, bulk, or in meso/macro-scale devices, in my work I focused on different modalities: fast, small, and strained. In my work on fast time scales during photoexcitation of V2O3 we found a novel meta-stable intermediate state that appears due to symmetry change in the monoclinic phase. This change occurs in the proximity of high temperature rhombohedral domains on length scales similar to those of electronic correlation. Our finding shows that the electronic and structural transitions in V2O3 have similar length scales but very different time scales. In VO2 and V2O3 nanoscale devices, we found a length-scale competition between Joule heating and electric field driven current induced metal to insulator transition. We proposed a novel thermoelectric model and performed simulations using finite element methods. Our modeling showed that the transition is highly inhomogeneous and the resulting filaments are surface bound with thermal gradients generating Seebeck electric fields on the order of 1000 V/cm. Finally, we studied pressurized and strained thin films in V2O3 and discovered strong strain relaxation for pressures of up to 500 MPa, which cause a deviation of thin film Pressure-Temperature phase diagram from bulk behavior. This strain relaxation relies on the difference between the structural and morphological length scales, which allows the formation of strain relaxing creases. Once those creases are fully strained, the thin films respond similarly to bulk samples.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :

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We have systematically studied a variety of vanadium dioxide (VO2) crystalline forms, including bulk single crystals and oriented thin films, using infrared (IR) near-field spectroscopic imaging techniques. By measuring the IR spectroscopic responses of electrons and phonons in VO2 with sub-grain-size spatial resolution (~20nm), we show that epitaxial strain in VO2 thin films not only triggers spontaneous local phase separations, but leads to intermediate electronic and lattice states that are intrinsically different from those found in bulk. Generalized rules of strain- and symmetry-dependent mesoscopic phase inhomogeneity are also discussed. Furthermore, these results set the stage for a comprehensive understanding of complex energy landscapes that may not be readily determined by macroscopic approaches.

Author: Kunal Tiwari
Publisher:
ISBN:
Category :
Languages : en
Pages :

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"The insulator-to-metal transition of vanadium dioxide has attracted the interest of condensed matter physicists for over half a century. In its high-temperature phase, VO2 is metallic with tetragonal rutile crystallography. In its low-temperature phase, it has correlated semiconducting electronic character and a charge-density-wave- like paired monoclinic lattice structure. Determining the relative roles of electron-electron and electron-phonon interactions in the electronic structure of the low temperature phase has been the source of the physics community's interest in VO2.Over the past two decades, it has been shown that the insulator to metal transition may be photoinduced with ultrafast laser pulses. In this thesis we present ultrafast electron diffraction and ultrafast time resolved terahertz spectroscopy measurements of this photoinduced phase transition. Our ultrafast electron diffraction results reveal, at low fluences, a novel metastable phase. This phase has the crystallography of the insulating state, but a dramatically collapsed band gap. A reorganization of valence charge density accompanies this modulated spectroscopic activity.These results have twofold significance. They show that the insulating behavior of the low temperature phase is affected primarily by electron-electron correlations, not by lattice structure. Importantly, they also show that ultrafast electron diffraction may be used to probe both electronic and lattice structure dynamics--it is sensitive to valence charge density reorganizations.Our time resolved terahertz spectroscopy results complement these ultrafast electron diffraction data. We show that, in the novel metastable monoclinic phase, the band gap does not collapse below 50 meV. We also show that dynamics in the time resolved terahertz conductivity through the full photoinduced phase transition occur on two timescales--one fast (240 femtosecond) timescale, characteristic of the coherent athermal photoinduced phase transition; and one slow (picosecond) timescale, characteristic of the astructural transition to the metastable monoclinic phase. In conjunction with our ultrafast electron diffraction measurements, these results suggest that the slow dynamics of the astructural phase transition, and the structural phase transition may be affected by the same underlying mechanism." --

Author:
Publisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 2540

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Here we report on ultrafast optical investigations of the light-induced insulator-to-metal phase transition in vanadium dioxide with controlled disorder generated by substrate mismatch. These results reveal common dynamics of this optically-induced phase transition that are independent of this disorder. Lastly, above the fluence threshold for completing the transition to the rutile crystalline phase, we find a common time scale, independent of sample morphology, of 40.5 ± 2 ps that is consistent with nucleation and growth dynamics of the R phase from the parent M1 ground state.

Author: Fabian I. Ezema
Publisher: Springer Nature
ISBN: 3030684628
Category : Technology & Engineering
Languages : en
Pages : 926

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Book Description
This book guides beginners in the areas of thin film preparation, characterization, and device making, while providing insight into these areas for experts. As chemically deposited metal oxides are currently gaining attention in development of devices such as solar cells, supercapacitors, batteries, sensors, etc., the book illustrates how the chemical deposition route is emerging as a relatively inexpensive, simple, and convenient solution for large area deposition. The advancement in the nanostructured materials for the development of devices is fully discussed.

Author: Sh. Kogan
Publisher: Cambridge University Press
ISBN: 9780521070195
Category : Science
Languages : en
Pages : 376

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Book Description
This book looks at the physics of electronic fluctuations (noise) in solids. The author emphasizes many fundamental experiments that have become classics: physical mechanisms of fluctuations, and the nature and magnitude of noise. He also includes the most comprehensive and complete review of flicker (1/f) noise in the literature. It will be useful to graduate students and researchers in physics and electronic engineering, and especially those carrying out research in the fields of noise phenomena and highly sensitive electronic devices--detectors, electronic devices for low-noise amplifiers, and quantum magnetometers (SQUIDS).

Author: National Research Council
Publisher: National Academies Press
ISBN: 0309147026
Category : Science
Languages : en
Pages : 193

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Book Description
For much of the past 60 years, the U.S. research community dominated the discovery of new crystalline materials and the growth of large single crystals, placing the country at the forefront of fundamental advances in condensed-matter sciences and fueling the development of many of the new technologies at the core of U.S. economic growth. The opportunities offered by future developments in this field remain as promising as the achievements of the past. However, the past 20 years have seen a substantial deterioration in the United States' capability to pursue those opportunities at a time when several European and Asian countries have significantly increased investments in developing their own capacities in these areas. This book seeks both to set out the challenges and opportunities facing those who discover new crystalline materials and grow large crystals and to chart a way for the United States to reinvigorate its efforts and thereby return to a position of leadership in this field.

Author: Asim K. Ray
Publisher: John Wiley & Sons
ISBN: 1119529476
Category : Technology & Engineering
Languages : en
Pages : 628

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Book Description
Oxide Electronics Multiple disciplines converge in this insightful exploration of complex metal oxides and their functions and properties Oxide Electronics delivers a broad and comprehensive exploration of complex metal oxides designed to meet the multidisciplinary needs of electrical and electronic engineers, physicists, and material scientists. The distinguished author eschews complex mathematics whenever possible and focuses on the physical and functional properties of metal oxides in each chapter. Each of the sixteen chapters featured within the book begins with an abstract and an introduction to the topic, clear explanations are presented with graphical illustrations and relevant equations throughout the book. Numerous supporting references are included, and each chapter is self-contained, making them perfect for use both as a reference and as study material. Readers will learn how and why the field of oxide electronics is a key area of research and exploitation in materials science, electrical engineering, and semiconductor physics. The book encompasses every application area where the functional and electronic properties of various genres of oxides are exploited. Readers will also learn from topics like: Thorough discussions of High-k gate oxide for silicon heterostructure MOSFET devices and semiconductor-dielectric interfaces An exploration of printable high-mobility transparent amorphous oxide semiconductors Treatments of graphene oxide electronics, magnetic oxides, ferroelectric oxides, and materials for spin electronics Examinations of the calcium aluminate binary compound, perovoksites for photovoltaics, and oxide 2Degs Analyses of various applications for oxide electronics, including data storage, microprocessors, biomedical devices, LCDs, photovoltaic cells, TFTs, and sensors Suitable for researchers in semiconductor technology or working in materials science, electrical engineering, and physics, Oxide Electronics will also earn a place in the libraries of private industry researchers like device engineers working on electronic applications of oxide electronics. Engineers working on photovoltaics, sensors, or consumer electronics will also benefit from this book.