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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: 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: Elizabeth Lee Radue Publisher: ISBN: Category : Raman spectroscopy Languages : en Pages : 119
Book Description
Vanadium dioxide is an intensely studied material, since it goes through an insulator-metal transition at a critical temperature just above room temperature at 340~K. The dramatic change in conductivity and the easily accessible transition temperature makes it an attractive material for novel technologies. Thin films of VO2 have a reversible transition without any significant degradation in contrast, and depending on the microstructure of the films, the properties of the transition are tunable. In this work, I study the dynamics of the insulator-transition in thin films grown on different substrates using a pump-probe configuration. The energy needed to trigger the transition, as well as the time constants of the change in reflectivity are affected by the strain in the VO2 films. I also characterized the samples using Raman spectroscopy and XRD measurements in order to identify what underlies the differences in behavior. Finally, in collaboration with Dr. Yamaguchi's group at RPI, I show that it is possible to trigger the transition using a THz pulse that directly pumps energy into the lattice, and at lower energies than needed to pump films by photoinducing the electrons across the band gap.
Author: Mengkun Liu Publisher: ISBN: Category : Languages : en Pages : 316
Book Description
Abstract: The metal insulator transition in vanadates has been studied for decades and yet new discoveries still spring up revealing new physics, especially among two of the most studied members: Vanadium sesquioxide (V2 0 3 ) and Vanadium dioxide (VO2 ). Although subtleties abound, both of the materials have first order insulator to metal phase transitions that are considered to be related to strong electron-electron (e-e) correlation. Further, ultrafast spectroscopy of strongly correlated materials has generated great interest in the field given the potential to dynamically distinguish the difference between electronic (spin) response versus lattice responses due to the associated characteristic energy and time scales.In this thesis, I mainly focus on utilizing ultrafast optical and THz spectroscopy to study phase transition dynamics in high quality V2 0 3 and VO2 thin films epitaxially grown on different substrates. The main findings of the thesis are:(1) Despite the fact that the insulator to metal transition (IMT) in V2 03 is electron-correlation driven, lattice distortion plays an important role. Coherent oscillations in the far-infrared conductivity are observed resulting from coherent acoustic phonon modulation of the bandwidth W. The same order of lattice distortion induces less of an effect on the electron transport in VO 2 in comparison to V2 03 . This is directly related to the difference in latent heat of the phase transitions in VO2 and V2 03 .(2) It is possible for the IMT to occur with very little structural change in epitaxial strained VO2 films, like in the case of Cr doped or strained V2 03 . However, in V02 , this necessitates a large strain which is only possible by clamping to a substrate with larger c axis parameter through epitaxial growth. This is demonstrated for VO 2 films on TiO2 substrates.(3) Initiating an ultrafast photo-induced insulator-to-metal transition (IMT) is not only possible with above bandgap excitation, but also possible with high-field far-infrared excitation. With the help of the field enhancement in metamaterial split ring resonator gaps, we obtain picosecond THz electric field transients of several MV/cm which is sufficient to drive the insulator to metal transition in V0 2 .
Author: Shriram Ramanathan Publisher: Springer Science & Business Media ISBN: 1441906649 Category : Technology & Engineering Languages : en Pages : 344
Book Description
Thin Film Metal-Oxides provides a representative account of the fundamental structure-property relations in oxide thin films. Functional properties of thin film oxides are discussed in the context of applications in emerging electronics and renewable energy technologies. Readers will find a detailed description of deposition and characterization of metal oxide thin films, theoretical treatment of select properties and their functional performance in solid state devices, from leading researchers. Scientists and engineers involved with oxide semiconductors, electronic materials and alternative energy will find Thin Film Metal-Oxides a useful reference.
Author: Joseph Woicik Publisher: Springer ISBN: 3319240439 Category : Science Languages : en Pages : 576
Book Description
This book provides the first complete and up-to-date summary of the state of the art in HAXPES and motivates readers to harness its powerful capabilities in their own research. The chapters are written by experts. They include historical work, modern instrumentation, theory and applications. This book spans from physics to chemistry and materials science and engineering. In consideration of the rapid development of the technique, several chapters include highlights illustrating future opportunities as well.
Author: Naga Phani B. Aetukuri Publisher: ISBN: Category : Languages : en Pages :
Book Description
The external control of the conductivity of correlated oxides is one of the most promising avenues towards realizing energy-efficient electronic devices. One of the prime candidates for such devices, vanadium dioxide (VO2), undergoes a temperature-driven metal-insulator transition (MIT) near room temperature (~340 K) with a concomitant change in crystal symmetry. First, using epitaxial strain provided by a variable thickness RuO2 buffer layer, we vary the MIT transition temperature of VO2 (001) films continuously from ~285 to ~345 K. We show, using strain-, polarization- and temperature-dependent x-ray absorption spectroscopy, in conjunction with x-ray diffraction and electrical transport measurements, that the transition temperature (TMIT) of VO2 is controlled by the orbital occupancy in its metallic state. Our results furthermore indicate that the magnitude of the structural distortion across the transition is also directly related to the orbital occupation in the metallic state. This work opens up the possibility of controlling the nature of the conducting state in atomically thin VO2 layers by manipulating the orbital occupancy by, for example, hetero-structural engineering. In a related study, we have used a combination of electron-beam and optical lithography to fabricate lateral two-terminal nano-devices from VO2 films deposited on TiO2 (001) substrates without RuO2 buffer layers. In these devices, we show that the transition can also be engendered by the application of modest electric fields, several orders of magnitude below the electric breakdown field, making this phenomenon potentially useful for two or three terminal switches. The delay time before switching is found to decrease with increasing electric field and temperature. We discuss whether these results indicate the transition is dominated by electronic or by Joule heating effects. These results demonstrate the possibility of triggering an MIT at low voltages and, therefore, at low energies, which is essential for device applications. Finally, we also discuss MIT in VO2-TiO2 based hetero-structures. We show that the temperature-driven MIT persists in VO2 films as thin as 1.8 nm.
Author: Hiroyuki Fujiwara Publisher: John Wiley & Sons ISBN: 9780470060186 Category : Technology & Engineering Languages : en Pages : 388
Book Description
Ellipsometry is a powerful tool used for the characterization of thin films and multi-layer semiconductor structures. This book deals with fundamental principles and applications of spectroscopic ellipsometry (SE). Beginning with an overview of SE technologies the text moves on to focus on the data analysis of results obtained from SE, Fundamental data analyses, principles and physical backgrounds and the various materials used in different fields from LSI industry to biotechnology are described. The final chapter describes the latest developments of real-time monitoring and process control which have attracted significant attention in various scientific and industrial fields.
Author: Vance Morrison Publisher: ISBN: Category : Languages : en Pages :
Book Description
"In this thesis the design and implementation of an ultrafast electron diffractometer with radio frequency compression capabilities is presented. In addition, the results of ultrafast electron diffraction (UED) measurements on the semiconductor to metal phase transition in vanadium dioxide are shown. The ability to perform UED measurements on ultrafast time scales is first demonstrated by observing the expansion and coherent oscillation of the crystal lattice in thin film, single crystal gold. The evolution of the spatio-temporal charge density in ultrashort pulses was then studied using electron-laser cross correlation measurements mediated by the ponderomotive force. These measurements were compared with particle tracing simulations and theoretical models. Similar electron-laser cross correlation measurements were also performed in order to characterize the behaviour of a novel radio-frequency (RF) pulse compression technique. Using an RF cavity, an oscillating, 3 GHz electric field is synchronized to the electron pulse arrival time and allows for the compression of high bunch charge electron pulses (0.1 pC) to 334+/-10 fs. This represents a bunch charge increase of 10^2-10^3 over previous ultrafast electron sources that provide a sub 500 fs impulse response. Finally, the semiconductor to metal transition in vanadium dioxide was studied using RF compressed electron pulses. Here, distinct ultrafast structural and electronic phase transitions were observed providing insight into the long standing debate surrounding the roles of electron-electron interactions and electron-lattice interactions in this phase transition." --
Author: S. L. McBride Publisher: ISBN: Category : Languages : en Pages : 7
Book Description
The electrical resistance of the VO2 film was measured concurrently with the acoustic emissions using the four-lead method. The data show all the main features observed during several hundred cycles of the sample through the transition temperature range. Little variation in the behaviour was observed provided the thermal history of the sample was not irregular. The temperature was cycled between 50C and 90C.
Author: Scott Eric Madaras
Author: Scott Eric Madaras
Author: Elizabeth Lee Radue
Author: Mengkun Liu
Author: Joyeeta Nag
Author: Shriram Ramanathan
Author: Joseph Woicik
Author: Naga Phani B. Aetukuri
Author: Hiroyuki Fujiwara
Author: Vance Morrison
Author: S. L. McBride