Condensed Matter Physics

Single and Mixed Phase TiO2 Powders by Excess Hydrolysis of Titanium Alkoxide

by Material Science

To investigate excess-hydrolysis of titanium alkoxides, TiO2 powders were fabricated from titanium-tetra-isopropoxide... more To investigate excess-hydrolysis of titanium alkoxides, TiO2 powders were fabricated from titanium-tetra-isopropoxide using 6:1 and 100:1 H2O:Ti (r) ratios. Powders were dried and fired at a range of temperatures (≤800ºC). Hydroxylation and organic content in powders were characterised using ATR-FTIR, laser Raman microspectroscopy, and elemental microanalysis; surface area and pore size distribution were evaluated using N2 gas adsorption; phase composition was analysed using XRD and laser Raman microspectroscopy; and crystallite size was evaluated by XRD, TEM and SEM. Results showed near-complete hydrolysis in a predominantly aqueous medium (r = 100), resulting in precipitated crystalline powders exhibiting brookite and anatase, which begin to transform to rutile below 500°C. Powders precipitated in a predominantly organic medium (r = 6) underwent partial hydrolysis, were highly porous and exhibited an amorphous structure, with crystallisation of anatase occurring at ~300°C and transformation to rutile beginning at 500°-600°C.

Quantum Quench in the Transverse Field Ising chain I: Time evolution of order parameter correlators

by Maurizio Fagotti

Co-authored with Pasquale Calabrese and Fabian Essler

We consider the time evolution of order parameter correlation functions after a sudden quantum quench of the magnetic... more We consider the time evolution of order parameter correlation functions after a sudden quantum quench of the magnetic field in the transverse field Ising chain. Using two novel methods based on determinants and form factor sums respectively, we derive analytic expressions for the asymptotic behaviour of one and two point correlators. We discuss quenches within the ordered and disordered phases as well as quenches between the phases and to the quantum critical point. We give detailed account of both methods.

Encoding Universal Computation in the Ground States of Ising Lattices

by Mile Gu

Chiral Photonic and Plasmonic Structures

by Kin Hung Fung

Zeeman Splitting of Photonic Angular Momentum States in Gyromagnetic Cylinder

by Kin Hung Fung

Spin polarization of two-dimensional electrons in GaAs quantum wells around Landau level filling ν = 1 from NMR measurements of gallium nuclei

by Sorin Melinte

Different quantum phases have different computational power

by Mile Gu

ハーフメタリック強磁性体材料マグネタイトを用いた有機EL素子

by Takuya Noguchi

20070904

ハーフメタリック強磁性体材料を電極に用いた有機EL構造の作製

by Takuya Noguchi

20070327

ペンタセン・磁性体接合の輸送特性とXMCD測定

by Takuya Noguchi

20060829

Rectification at Graphene-Semiconductor Interfaces: Zero-Gap Semiconductor-Based Diodes

by Sefaattin Tongay

Extinction of ferromagnetism in highly ordered pyrolytic graphite by annealing

by Sefaattin Tongay

Etymology and Barangay History

by Historically Digitized

Atomic collisions, elastic recombination, and thermal diffusion during thin-film growth from low-energy ion beams

by Nicole Herbots

N. Herbots *, 0. Vancauwenberghe **, O.C. Hellman + and Y.C. Joo ++
Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Volumes 59-60, Part 1, 1 July 1991, Pages 326-331
doi:10.1016/0168-583X(91)95233-4 |

Low-energy (< 1 keV) ions are used in a variety of thin-film techniques. When low-energy ions are used during... more Low-energy (< 1 keV) ions are used in a variety of thin-film techniques. When low-energy ions are used during growth, the atomic mobility is athermally enhanced. This can lead to a significant lowering of the temperature necessary to induce epitaxial growth and chemical reactions. Athermal enhancement of atomic mobility in semiconductors can be described below the temperature for plastic deformation (T = 540-degrees-C in Si) by classifying the mechanisms involved into three categories according to their respective timescale: collisions, elastic recombination, and thermal diffusion. A quantitative model can then be derived to predict the conditions of temperature, dose rate, and energy to obtain thin film growth, and oxidation in techniques such as ion beam deposition (IBD), and ion beam oxidation (IBO). Using computer simulations, the dynamics of defect generation and redistribution, and the resulting thin-film growth rate can be investigated. Energies below 200 eV are found not only to minimize damage and sputtering, but also create defect distributions that favor surface recombination and hence growth. This elucidates the mechanism of thin-film formation with high atomic density, oxidation with a sharp inteface with the substrate and epitaxial growth, and experimental findings on the energy dependence of IBD and IBO.

Quantum ring models and action-angle variables

by Vahagn Yeghikyan

Co-authored with Stefano Bellucci, Armen Nersessian and Armen Saghatelian

We suggest to use the action-angle variables for the study of properties of (quasi)particles in quantum
rings.... more We suggest to use the action-angle variables for the study of properties of (quasi)particles in quantum
rings. For this purpose we present the action-angle variables for three two-dimensional singular oscillator
systems. The first one is the usual (Euclidean) singular oscillator, which plays the role of the confinement
potential for the quantum ring. We also propose two singular spherical oscillator models for the role of
the confinement system for the spherical ring. The first one is based on the standard Higgs oscillator
potential. We show that, in spite of the presence of a hidden symmetry, it is not convenient for the study
of the system’s behaviour in a magnetic field. The second model is based on the so-called CP1 oscillator
potential and respects the inclusion of a constant magnetic field.

Dipole transitions and Stark effect in the charge-dyon bound system

by Vahagn Yeghikyan

Co-authored with  L.Mardoyan, A.Nersessian, H.Sarkisyan published in J. Phys.A40 (2007), 5973-5980

We consider the dipole transitions and the linear and quadratic Stark effect in the MICZ-Kepler system interpreting as... more We consider the dipole transitions and the linear and quadratic Stark effect in the MICZ-Kepler system interpreting as a charge-dyon system. We show, that while the linear Stark effect in the ground state is proportional to azimuth quantum number(and to the sign of monopole number), the quadratic Stark effect in the ground state is independent on the signs of azimuth and monopole numbers.

Derivation of model Hamiltonians: Exchange Hamiltonian for H_ {2}

by Carlos E. Solivérez

New insights into the entanglement of disjoint blocks

by Maurizio Fagotti

Journal-ref: 2012 EPL 97 17007

We study the entanglement of two disjoint blocks in spin-1/2 chains obtained by merging solvable models, such as XX... more We study the entanglement of two disjoint blocks in spin-1/2 chains obtained by merging solvable models, such as XX and Ising models. We compute the universal function F_2(x) of the R\'enyi entropy S_2=-\log\mathrm{Tr}\rho^2 and deduce the small-length expansion of F_{v.N.}(x), corresponding to the von Neumann entropy. We show that F_\alpha(x)-1 and F_{v.N.}(x) can be smaller than 0, in contrast to what observed in all models examined so far. An exact relation between the entanglement of disjoint subsystems in the XX model and that in a chain embodying two Ising models is a by-product of our investigations.

Atomic displacement free interfaces and atomic registry in SiO2/(1x1) Si(100). Journal of Applied Physics. Vol 100. No 10 (2006) 104109-10410.

by Nicole Herbots

Shaw, J. M. ; Herbots, N. ; Hurst, Q. B. ; Bradley, D. ; Culbertson, R. J. ; Atluri, V. ; Queeney, K. T.

JOURNAL OF APPLIED PHYSICS Volume: 100 Issue: 10 Article Number: 104109 DOI: 10.1063/1.2358835 Published: NOV 15 2006

We use ion beam analysis to probe the structure and interface of ultrathin thermal oxide films grown on (1x1) Si(100)... more We use ion beam analysis to probe the structure and interface of ultrathin thermal oxide films grown on (1x1) Si(100) surfaces prepared using the Herbots-Atluri [U.S. patent No. 6,613,677 (Sept. 2, 2003)] wet chemical clean. We discover that these oxide layers are structurally registered with the substrate lattice with no interfacial structural disorder. Registry of Si atoms is most pronounced along < 111 > directions relative to the Si substrate, consistent with a beta-cristobalite epitaxial phase. This structurally registered phase transitions to an amorphous structure approximately 2 nm from the interface.(c) 2006

US patent 7,851,365 issued 12/14/10: "Methods for preparing semiconductor substrates & interfacial oxides there on

by Nicole Herbots

N. Herbots, J.D. Bradley, J.M. Shaw, R.J. Culbertson and V. Atluri


This patent is a result of my research in nanophases, surfaces and thin films and analysis from a 10-year collaboration using my materials synthesis expertise to create the nanophases and characterizing them with Prof. R. J. Culbertson. The second author is our former graduate student Dr. J.D. Bradley, whose PhD research contributed to this patent, and who brought applications via his expertise as engineer working on medical electronics processing and modeling. He is now employed at Medtronic. The third author is another PhD physics graduate student J.M. Shaw (ASU ’06), whose doctoral research also contributed to the concept of this patent and its application in semiconductor physics. Dr. J.M Shaw is now a permanent member of the research staff at NIST. He was trained by Prof. R.J. Culbertson as a physics undergraduate researcher in Ion Beam Analysis to his PhD research in advanced IBA technique and heteroepitaxy. The fifth author is our former graduate student V. Atluri, a chemical engineer who completed his PhD thesis in Materials Science on the chemical synthesis of ordered and passivated oxides with Profs. Herbots and Culbertson in 1998. He is now manager at Intel Corp, in charge of semiconductor technology integration with high density packaging. The keypoint of this patent is the discovery of a new, ordered, silicon nanophase akin to beta-cristobalite identified in part via ion beam analysis, using channeling, surface peak analysis, areal density calculations and Monte-Carlo computer simulations of channeling and blocking to identify the spatial geometry of these new nanophases.

FIELD OF THE INVENTION
This invention relates to methods for preparing semiconductor substrates, the... more FIELD OF THE INVENTION
This invention relates to methods for preparing semiconductor substrates, the semiconductor oxides grown thereon, and more specifically, to epitaxial oxides grown on the surface of semiconductors, and the interfacial layer formed between the oxide and the semiconductor.
BACKGROUND OF THE INVENTION
Ever since the first integrated circuit was demonstrated, one goal of the electronics industry has been to increase the density of individual devices in an integrated circuit. Ultimately, as smaller devices are made, the devices can be packed more densely, which reduces transmission between devices and also allows for faster operation. Metal oxide semiconductor (MOS) technology forms the basis for a large part of chip manufacturing. In typical MOS transistor technology, silicon dioxide (SiO2) is grown on a silicon substrate so as to form part of a metal oxide semiconductor gate. SiO2
so formed is commonly referred to as a gate oxide or a gate oxide dielectric.

Until recently, SiO2 grown on MOS transistor gates has always been thought of as amorphous with little ordering in the first atomic layers at the interface between the silicon substrate and the oxide layer.

Silicon has been used commercially as a semiconductor preferentially over other materials because it readily forms stable oxide dielectric layers with a lower interface defect density than other semiconductors and their oxides. The stability of Si/SiO2 having a low interface defect density enables the manufacture of transistors with better electrical properties than is attainable with other semiconductors. The desire for lower dimension devices presents a basic problem: as devices get The desire for lower dimension devices presents a basic problem: as devices get smaller in three dimensions, the dielectric layer must get both narrower and thinner and continue to function as a dielectric. Silicon does not always provide the optimum physical and electronic properties, such as a low interface defect density or a high dielectric constant, necessary to or tailored to fill a particular need. A desire for materials that have better tailored physical and electronic properties creates another problem: growth of dielectric layers on multi-element semiconductors is difficult. These two problems become essentially insurmountable when one desires a small device made out of a semiconductor other than doped silicon. Conceptually, a solution would lie in producing either a well-ordered ultra-thin oxide on top of the multi-element semiconductor, or at least a more ordered interface between the semiconductor and the dielectric layers. Doing so without elemental or phase separation is extremely difficult especially in chemical systems where the defect generation rate is higher than silicon, and as the physical sizes involved approach atomic dimensions. Any improvement in ordering at the interface or in
the material will improve the interface defect density. It will be appreciated that, as smaller devices demand thinner dielectric layers, interface characteristics become increasingly important.
Another goal of electronic device processing is the growth of heterodielectrics or other materials listed below on a semiconductor substrate. While this goal is achievable
for some systems, in general, growth of ordered films of a material on a semiconductor substrate is difficult. US 6,613,677, incorporated herein by reference, discloses long range ordered semiconductor interface phase and oxides that can improve many properties of oxides, and in particular SiO2 grown on Si. However, the growth of epitaxial, or continuous crystalline films on semiconductor substrates remains elusive. Herein, are described novel methods for preparing semiconductor substrates and forming epitaxial interfacial layers of oxides thereon.