Download or read book Scanning Tunneling Microscopy Investigation of the Vanadium Dioxide Surface and Its Related Metal insulator Transition MIT written by Wenjing Yin and published by . This book was released on 2009 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Phase Field Study of Metal Insulator Transition in Strongly Correlated Vanadium Dioxide written by Yin Shi and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Vanadium dioxide (VO2) is a strongly correlated system which exhibits an intriguing metal-insulator transition (MIT) accompanied by a structural transition at a temperature slightly above the room temperature. It offers potential novel device applications such as sensors, Mott field-effect transistors, and memristors, which desire guidance from mesoscopic theoretical modeling. Based on symmetry consideration, we formulate a mesoscopic phase-field model of the MIT explicitly incorporating both structural and electronic instabilities as well as free electrons and holes. We employ this model to investigate the MIT in mesoscale VO2 subject to various stimuli such as heat, stress/strain, electric field, doping, electric current, and light. First, the temperature-stress/strain phase diagrams of VO2 nanobeams and thin films under different mechanical boundary conditions are calculated consistently, which show good agreement with existing experimental observations. We also calculate the temperature-radius phase diagrams of VO2 nanoparticles and nanofibers. Second, in a VO2 slab under an electric field in an open-circuit configuration, an abrupt universal resistive transition is shown to occur inside the supercooling region, in sharp contrast to the conventional Landau-Zener smooth electric breakdown. Third, the temperature-dopant-concentration phase diagrams of VO2 doped with various metal ions are calculated consistent with the experiments. Furthermore, hole doping in VO2 may induce a metastable metallic monoclinic phase, which could be stabilized through geometrical confinement and the size effect in VO2-VO_{2-delta} bilayers leading to the decoupling of the electronic and structural phase transitions. Fourth, we demonstrate that the electric current may drive the MIT isothermally via the current-induced electron correlation weakening, inducing a few-nanosecond ultrafast resistive switching consistent with experimental measurements. The isothermal temperature-current phase diagram is further calculated and the current is also found able to drive domain walls to move. Fifth, dynamic processes of the MIT in VO2 illuminated by femtosecond laser pulses are simulated, showing the emergence of the transient metallic monoclinic phase and the bias-induced shrinkage of the photoinduced metallic phase. We also prove that during a generic metal-insulator transition, a nonequilibrium homogeneous state may be unstable against charge density modulations with certain wavelengths, and thus evolves to the equilibrium phase through transient electronic phase separation. This transient electronic phase separation is shown to take place in VO2 upon photoexcitation.
Download or read book A Theoretical Exploration of the Metal Insulator Transition in Vanadium Dioxide with an Eye Towards Applications A First Principles Approach written by and published by . This book was released on 2009 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vanadium oxides are very interesting compounds which exhibit exotic transport phenomena. In particular vanadium dioxide (VO2) undergoes a first-order transition from a high-temperature metallic phase to a low-temperature insulating phase at almost the room temperature (T = 340 K). The resistivity jumps by several orders of magnitude through this transition, and the crystal structure changes from rutile (R-phase) at high-temperature to monoclinic (so-called M1-phase) at low-temperature. The latter is characterized by a dimerization of the vanadium atoms into pairs, as well as a tilting of these pairs with respect to the c-axis. VO2 has also attracted a great deal of attention for its ultrafast optical response, switching between the R and the M1 phase. Despite the large number of experimental studies focusing on this material the physics driving this phase transition and the resulting optical properties is still mysterious. There are intensive reports around the world to make devices such as switches, transistors, detectors, varistors, phase change memory, exploiting the unique properties of VO2. Two physical effects, Peierls, i.e. dimerization, and the Mott mechanism due to strong Coulomb repulsion are important in the metal-insulator transition (MIT) of VO2. Understanding the detailed interplay and the relative importance of both Peierls and Mott mechanism is important for controlling this material with an eye towards applications. For example, whether the driving force of this transition is electronic (i.e. occurring on femtosecond timescales) or structural (occurring on the picosecond timescale) is important to understand the speed of the switching from the M1 to the rutile phase. The insights obtained in this study together with the computational machinery developed, will serve as a basis for rational material design of VO2 based applications.
Download or read book Scanning Tunneling Microscopy in Surface Science Nanoscience and Catalysis written by Michael Bowker and published by John Wiley & Sons. This book was released on 2009-11-11 with total page 258 pages. Available in PDF, EPUB and Kindle. Book excerpt: Here, top international authors in the field of STM and surface science present first-class contributions on this hot topic, bringing the reader up to date with the latest developments in this rapidly advancing field. The focus is on the nanoscale, particularly in relation to catalysis, involving developments in our understanding of the nature of the surfaces of oxides and nanoparticulate materials, as well as adsorption, and includes in-situ studies of catalysis on such model materials. Of high interest to practitioners of surface science, nanoscience, STM and catalysis.
Download or read book Scanning Tunneling Microscopy written by and published by Academic Press. This book was released on 1993-03-25 with total page 481 pages. Available in PDF, EPUB and Kindle. Book excerpt: Scanning tunneling microscopy (STM) and its extensions have become revolutionary tools in the fields of physics, materials science, chemistry, and biology. These new microscopies have evolved from their beginnings asresearch aids to their current use as commercial tools in the laboratory and on the factory floor. New wonders continue to unfold as STM delivers atomic scale imaging and electrical characterization of the newly emerging nanometer world. This volume in the METHODS OF EXPERIMENTAL PHYSICS Series describes the basics of scanning tunneling microscopy, provides a fundamental theoretical understanding of the technique and a thorough description of the instrumentation, and examines numerous examples and applications. Written by the pioneers of the field, this volume is an essential handbook for researchers and users of STM, as well as a valuable resource for libraries.
Download or read book Scanning Tunneling Microscopy in Surface Science written by Michael Bowker and published by Wiley-VCH. This book was released on 2010-02-01 with total page 258 pages. Available in PDF, EPUB and Kindle. Book excerpt: Here, top international authors in the field of STM and surface science present first-class contributions on this hot topic, bringing the reader up to date with the latest developments in this rapidly advancing field. The focus is on the nanoscale, particularly in relation to catalysis, involving developments in our understanding of the nature of the surfaces of oxides and nanoparticulate materials, as well as adsorption, and includes in-situ studies of catalysis on such model materials. Of high interest to practitioners of surface science, nanoscience, STM and catalysis.
Download or read book Metallization of Vanadium Dioxide Driven by Large Phonon Entropy written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Phase competition underlies many remarkable and technologically important phenomena in transition-metal oxides. Vanadium dioxide exhibits a first-order metal-insulator transition (MIT) near room temperature, where conductivity is suppressed and the lattice changes from tetragonal to monoclinic on cooling. Ongoing attempts to explain this coupled structural and electronic transition begin with two classic starting points: a Peierls MIT driven by instabilities in electron-lattice dynamics versus a Mott MIT where strong electron-electron correlations drive charge localization1-10. A key-missing piece of the VO2 puzzle is the role of lattice vibrations. Moreover, a comprehensive thermodynamic treatment must integrate both entropic and energetic aspects of the transition. Our measurements establish that the entropy driving the MIT is dominated by strongly anharmonic phonons rather than electronic contributions, and provide a direct determination of phonon dispersions. Our calculations identify softer bonding as the origin of the large vibrational entropy stabilizing the metallic rutile phase. They further reveal how a balance between higher entropy in the metal and orbital-driven lower energy in the insulator fully describes the thermodynamic forces controlling the MIT. This study illustrates the critical role of anharmonic lattice dynamics in metal-oxide phase competition, and provides guidance for the predictive design of new materials.
Download or read book Scanning Tunneling Microscopy and Computational Chemistry Studies for Controlled Reactions on Silicon written by Dimitri B. Skliar and published by ProQuest. This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The understanding of the chemistry of silicon surfaces has been one of the major contributors in development and improvement of silicon based microelectronic devices in the past several decades. Progressively, the dimensions of devices have reduced by several orders of magnitude, presently at the length scale of few tens of nanometers, and are expected to decrease in size even more. For chemistry based film growth methods such as chemical vapor deposition (CVD) or atomic layer deposition (ALD), control of film structure and composition in this spatial regime requires a very detailed nanoscopic understanding of silicon surface chemistry. A combined experimental and theoretical approach, utilizing ultra high vacuum scanning tunneling microscopy (UHV-STM) and density functional theory (DFT), to understanding the surface chemistry of Si(100) is illustrated in the context of ALD development for high dielectric constant metal oxides. As a first possible route to controllably deposit monolayer thick metal layer, the reaction of the metal-organic molecule with bare silicon surface is considered. The interaction of the protonated b-diketonate ligand, 2,2,6,6-tetramethyl-3,5-heptanedione (dpmH), which is a byproduct of the strontium metal-organic precursor vaporization, with Si(100)-2x1 surface is investigated. Two aspects of the molecule's interactions were addressed: the adsorption at room temperature as well as its thermal decomposition. By combination of the experiments with DFT calculations of adsorbate geometry, STM image simulations, and reaction pathways it was possible to propose unique binding configurations that match the experimentally observed adsorption features. Theoretical analysis of multiple competing reaction pathways showed that hydroxyl dissociation via a 1,7 H-shift mechanism is the dominant adsorption pathway. Several other pathways including [2+4] addition, [2+2] C=O intra-dimer addition, [2+2] C=O intra-dimer addition with OH dissociation on an adjacent dimer, [2+2] C=C intra-dimer addition, and "ene" addition are found to be barrierless with respect to the entrance channel, and have small barriers relative to a hypothesized adsorption precursor intermediate. Pathways involving 1,3 and 1,2 intra-molecular H-shifts are found to be highly activated and are expected to be inaccessible at room temperature. Several state inter-conversions are found to be unlikely as well. These results provide insight to the competitive adsorption pathways for multifunctional molecules on silicon. Investigations of thermally induced decomposition of adsorbed dpmH molecules showed that there are no significant products of desorption of carbon containing fragments of the molecule, i.e. most of the carbon atoms incorporate into the silicon surface causing it to reconstruct to a c(4x4) phase at exposures below ~ 0.15 L. At higher exposures formation of SiC islands is observed. These findings demonstrate that schemes to deposit materials from organometallic compounds containing b-diketone ligands onto clean Si(100)-2x1 surface cannot result in an ordered interfacial structure as carbon incorporation into the substrate is inevitable. An alternative strategy for depositing metal template layer is proposed, where the initial reacting surface will be terminated by water at room temperature. The stability of surface hydroxyl groups and mechanisms of their decomposition in 300-600K temperature range are analyzed. It is found that surface oxidation does not follow first order kinetics with respect to the hydroxyl groups. DFT calculations of oxygen insertion pathways point towards a catalytic effect of the dangling bonds and suggest that in the 500-550K range the insertion events should occur predominantly next to unoccupied surface silicon sites. A model is proposed, where diffusing dangling bonds act as moving catalysts for hydroxyl group decomposition. Kinetic Monte Carlo (kMC) simulations are used to compare the results of this model with experimental data. A strategy to increase hydroxyl group stability is demonstrated where the initial concentration of surface dangling bonds is decreased by water termination at 130K.
Download or read book Scattering of Vibrationally Excited NO from Vanadium Dioxide written by Artur Meling and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work investigates the surface dynamics of vanadium dioxide with nitric oxide in dependence of its metal-to-insulator transition (MIT) at 68 °C. At lower temperatures VO2 has a monoclinic lattice structure which has low electrical conductance. VO2(M) is therefore considered an insulator. At higher temperature it is found in its rutile phase, which shows several orders of magnitude more electrical conductance than the monoclinic phase. VO2(R) is therefore considered a metal. In previous works it was found that when vibrationally excited NO scatters from metal surfaces, such as Au(111) an ...
Download or read book Scanning Tunneling Microscopy Studies of Chemisorbed Layers of Metal Surfaces written by David Mark Zeglinski and published by . This book was released on 1990 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Imaging Competing Electronic Phases During Metal Insulator Transitions in Transition Metal Oxides Using Microwave Impedance Microscopy written by Ashish Gangshettiwar and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Metal-Insulator transitions are accompanied by huge resistivity changes, sometimes over ten orders of magnitude, and are widely observed in condensed-matter systems. Particularly important are the transitions driven by correlation effects associated with the electron-electron interaction. The insulating phase caused by the correlation effects is known as the Mott Insulator. Despite a long history of investigations, the driving force of the MIT and the exact nature of the ground state are still controversial. Using microwave impedance microscopy, we will study the coexisting metallic and insulating phases in different strongly correlated compounds which might carry important information on the transition in these materials. In this dissertation, I will begin by discussing Microwave Impedance Microscopy which will be the prime research tool used in the study of these materials. I will present the technical specifications of this tool and how it can be modified to be used on cryogenic setups, mainly, using tuning fork microscopy for topography feedback. The application of MIM to study Metal-Insulator Phase transitions in strongly correlated systems is demonstrated by studying doped Ruthenate oxides. Chapter 4 describes the insights gathered on Ti doped Bilayer Calcium Ruthenates which includes the discovery of a new stripe-phase at the MIT phase boundary. Followed by a chapter discussing the comparison with the MIT in Mn-doped bilayer Calcium ruthenate. I will conclude the dissertation with a short summary of our contribution to the field and an outlook where I would highlight the directions needed to pursue further research and come up with an overall picture of the phase transition in this class of material
Download or read book Scanning Tunneling Microscopy Studies of Growth and Adsorption on Transition Metal Surfaces written by Morten Østergaard Pedersen and published by . This book was released on 1998 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scanning Tunneling Microscope Investigation of Fullerene metal Interactions for Vanadium and Tungsten written by Harmonie Ai-Vi Sahalov and published by . This book was released on 2011 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Terahertz Scanning Tunneling Microscopy of Metal and Superconductor Surfaces written by Howe Simpson and published by . This book was released on 2021 with total page 90 pages. Available in PDF, EPUB and Kindle. Book excerpt: The advent of the terahertz scanning tunneling microscope (THz-STM) brings with it a new method of observing and characterizing the ultrafast dynamics of materials. The sub-nanometer spatial resolution of an ultra-high vacuum scanning tunneling microscope (UHV-STM) coupled with the sub-picosecond time resolution from a terahertz (THz) pulse allows for ultrafast measurements of surface dynamics across varying surface features down to the atomic scale. This thesis explores STM and THz-STM of metal and superconductor surfaces. High critical temperature superconductivity has been an area Bi2Sr2CaCu2O8 is an excellent candidate to study the superconductive process due to its high critical temperature of 95 K and ease of cleaving. STM and scanning tunneling spectroscopy measurements on the high-temperature superconductor Bi2Sr2CaCu2O8 are performed at 100 K and 55 K. STM and STS measurements were also performed on the surface of flat Au(111). Given gold's versatility as a substrate for many STM measurements, it is important to ensure that the STM system used in this study can replicate results that coincide with many other studies done on the surface of gold. The characteristics of the substrate such as flatness and cleanliness prior to deposition of other materials were investigated. The herringbone surface reconstruction of Au(111) was imaged and the topography was analysed with good agreement compared to other studies. Finally, optical-pump/THz-STM-probe measurements are performed on a silver-coated gold surface. These measurements, with tip-sample distances outside of the typical tunneling regime of the THz-STM, use photo-excited electrons from an optical pump beam to tunnel between the sample and tip. A THz pulse is then focused onto the junction between the sample and tip. The results show an interesting behaviour in the regime where the pump beam is not focused on the junction but elsewhere on the surface of the sample. These preliminary results may help gain a better understanding of the photoemission-based THz waveform measurements, as well as demonstrate a new use of the THz-STM for propagation dynamics of surface excitations.
Download or read book Surfaces in Motion written by Mischa Sebastiaan Hoogeman and published by . This book was released on 1998 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scanning Tunneling Microscopy Investigations of Metal Dichalcogenide Materials written by and published by . This book was released on 1993 with total page 45 pages. Available in PDF, EPUB and Kindle. Book excerpt: Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) have been used to characterize the atomic level structure of electronic properties, reactivity and wear of metal dichalcogenide materials that are or have potential as solid state lubricants. Single crystals Of MoS2, Ni(x)Mo(l-x) S2, MoS(2-x)Se(x) and MoS(2-x)Te(x) have been prepared to determine how chemical modifications affect the local structure and electronic properties of this lubricant. STM images of Ni-doped MoS2 show localized electronic states due to the Ni atoms, while images of Se- and Te-doped materials indicate that anion substitution is electronically delocalized. AFM studies of Te-doped MoS2 show, however, that the tellurium dopants form atomic scale structural protrusions that may reduce sliding friction. AFM has also been used to characterize nanometer scale wear and oxidation on MoS2 and NbSe2 surfaces. In atmosphere at room-temperature AFM studies showed that NbSe2 wears approximately three times faster than MoS2. Furthermore, oxidation studies demonstrated that NbSe2 was significantly more reactive than MoS2 with molecular oxygen. These results indicate that the intrinsic stability of the MoS2 surface make it an effective lubricant, AFM was also used to elucidate the growth of MoO3 on the surface Of MoS2 during oxidation, and to study wear properties of these MoO3 crystallites. The AFM tip was used to define lines with 10 nm resolution in MoO3 and to manipulate distinct MoO3 structures on the MoS2 surface. In addition, metal- substitution in TaS2 has been studied systematically using STM and theoretical methods.
Download or read book Scanning Tunneling Microscopy at Metal Surfaces written by Christoph A. Lang and published by . This book was released on 1990 with total page 346 pages. Available in PDF, EPUB and Kindle. Book excerpt:
