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"Surfaces and Interfaces"
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Interactive textures for architecture and landscaping : digital elements and technologies
\"This book addresses the phenomenon called \"interactive architecture that challenges artists, architects, designers, theorists, and geographers to develop a language and designs toward the \"use\" of these environments\"--Provided by publisher.
Book
Imaging Bond Formation Between a Gold Atom and Pentacene on an Insulating Surface
A covalent bond between an individual pentacene molecule and a gold atom was formed by means of single-molecule chemistry inside a scanning tunneling microscope junction. The bond formation is reversible, and different structural isomers can be produced. The single-molecule synthesis was done on ultrathin insulating films that electronically isolated the reactants and products from their environment. Direct imaging of the orbital hybridization upon bond formation provides insight into the energetic shifts and occupation of the molecular resonances.
Journal Article
Sharp-interface limit of the Cahn–Hilliard model for moving contact lines
Diffuse-interface models may be used to compute moving contact lines because the Cahn–Hilliard diffusion regularizes the singularity at the contact line. This paper investigates the basic questions underlying this approach. Through scaling arguments and numerical computations, we demonstrate that the Cahn–Hilliard model approaches a sharp-interface limit when the interfacial thickness is reduced below a threshold while other parameters are fixed. In this limit, the contact line has a diffusion length that is related to the slip length in sharp-interface models. Based on the numerical results, we propose a criterion for attaining the sharp-interface limit in computing moving contact lines.
Journal Article
An ab Initio Molecular Dynamics Study of the Aqueous Liquid-Vapor Interface
We present an ab initio molecular dynamics simulation of the aqueous liquid-vapor interface. Having successfully stabilized a region of bulk water in the center of a water slab, we were able to reproduce and further quantify the experimentally observed abundance of surface \"acceptor-only\" (19%) and \"single-donor\" (66%) moieties as well as substantial surface relaxation approaching the liquid-vapor interface. Examination of the orientational dynamics points to a faster relaxation in the interfacial region. Furthermore, the average value of the dipole decreases and the average value of the highest occupied molecular orbital for each water molecule increases approaching the liquid-vapor interface. Our results support the idea that the surface contains, on average, far more reactive states than the bulk.
Journal Article
Steric Effects in the Chemisorption of Vibrationally Excited Methane on Ni(100)
Newly available, powerful infrared laser sources enable the preparation of intense molecular beams of quantum-state prepared and aligned molecules for gas/surface reaction dynamics experiments. We present a stereodynamics study of the chemisorption of vibrationally excited methane on the (100) surface of nickel. Using linearly polarized infrared excitation of the C-H stretch modes of two methane isotopologues [CH₄(ν₃) and CD₃H(ν₁)], we aligned methane's angular momentum and vibrational transition dipole moment in the laboratory frame. An increase in methane reactivity of as much as 60% is observed when the laser polarization is parallel rather than normal to the surface. The dependence of the alignment effect on the rotational branch used for excitation indicates that alignment of the vibrational transition dipole moment of methane is responsible for the steric effect. Potential explanations for the steric effect in terms of an alignment-dependent reaction barrier height or electronically nonadiabatic effects are discussed.
Journal Article
Plethora of tunable Weyl fermions in kagome magnet Fe3Sn2 thin films
Interplay of magnetism and electronic band topology in unconventional magnets enables the creation and fine control of novel electronic phenomena. In this work, we use scanning tunneling microscopy and spectroscopy to study thin films of a prototypical kagome magnet Fe3Sn2. Our experiments reveal an unusually large number of densely-spaced spectroscopic features straddling the Fermi level. These are consistent with signatures of low-energy Weyl fermions and associated topological Fermi arc surface states predicted by theory. By measuring their response as a function of magnetic field, we discover a pronounced evolution in energy tied to the magnetization direction. Electron scattering and interference imaging further demonstrates the tunable nature of a subset of related electronic states. Our experiments provide a direct visualization of how in-situ spin reorientation drives changes in the electronic density of states of the Weyl fermion band structure. Combined with previous reports of massive Dirac fermions, flat bands, and electronic nematicity, our work establishes Fe3Sn2 as an interesting platform that harbors an extraordinarily wide array of topological and correlated electron phenomena.
Journal Article
Preferential Growth of Single-Walled Carbon Nanotubes with Metallic Conductivity
Single-walled carbon nanotubes can be classified as either metallic or semiconducting, depending on their conductivity, which is determined by their chirality. Existing synthesis methods cannot controllably grow nanotubes with a specific type of conductivity. By varying the noble gas ambient during thermal annealing of the catalyst, and in combination with oxidative and reductive species, we altered the fraction of tubes with metallic conductivity from one-third of the population to a maximum of 91%. In situ transmission electron microscopy studies reveal that this variation leads to differences in both morphology and coarsening behavior of the nanoparticles that we used to nucleate nanotubes. These catalyst rearrangements demonstrate that there are correlations between catalyst morphology and resulting nanotube electronic structure and indicate that chiral-selective growth may be possible.
Journal Article
Formation of Warm Dense Matter: Experimental Evidence for Electronic Bond Hardening in Gold
Under strong optical excitation conditions, it is possible to create highly nonequilibrium states of matter. The nuclear response is determined by the rate of energy transfer from the excited electrons to the nuclei and the instantaneous effect of change in electron distribution on the interatomic potential energy landscape. We used femtosecond electron diffraction to follow the structural evolution of strongly excited gold under these transient electronic conditions. Generally, materials become softer with excitation. In contrast, the rate of disordering of the gold lattice is found to be retarded at excitation levels up to 2.85 megajoules per kilogram with respect to the degree of lattice heating, which is indicative of increased lattice stability at high effective electronic temperatures, a predicted effect that illustrates the strong correlation between electronic structure and lattice bonding.
Journal Article
A review of spurious currents in the lattice Boltzmann method for multiphase flows
A spurious current is a small-amplitude artificial velocity field which arises from an imbalance between discretized forces in multiphase/multi-component flows. If it occurs, the velocity field may persist indefinitely, preventing the achievement of a true equilibrium state. Spurious velocities can sometimes be as large as the characteristic velocities of the problem, causing severe instability and ambiguity between physical and spurious velocities. They are typically exacerbated by large values of numerical surface tension or when the two fluids being simulated have large density ratios. The resulting instability can restrict what parameters may be simulated. To varying degrees, spurious currents are found in all multiphase flow models of the lattice Boltzmann method (LBM). There have been many studies of the occurrence of the phenomenon, and many suggestions on how to eliminate it. This paper reviews the three main models of simulating multiphase/multi-component flow in the lattice Boltzmann method, as well as the subsequent modifications made in order to reduce or eliminate spurious currents.
Journal Article
The interface between silicon and a high-k oxide
The ability of the semiconductor industry to continue scaling microelectronic devices to ever smaller dimensions (a trend known as Moore's Law
1
) is limited by quantum mechanical effects: as the thickness of conventional silicon dioxide (SiO
2
) gate insulators is reduced to just a few atomic layers, electrons can tunnel directly through the films. Continued device scaling will therefore probably require the replacement of the insulator with high-dielectric-constant (high-
k
) oxides
2
, to increase its thickness, thus preventing tunnelling currents while retaining the electronic properties of an ultrathin SiO
2
film. Ultimately, such insulators will require an atomically defined interface with silicon without an interfacial SiO
2
layer for optimal performance. Following the first reports of epitaxial growth of AO and ABO
3
compounds on silicon
3
,
4
,
5
,
6
,
7
, the formation of an atomically abrupt crystalline interface between strontium titanate and silicon was demonstrated
8
,
9
,
10
. However, the atomic structure proposed for this interface is questionable because it requires silicon atoms that have coordinations rarely found elsewhere in nature. Here we describe first-principles calculations of the formation of the interface between silicon and strontium titanate and its atomic structure. Our study shows that atomic control of the interfacial structure by altering the chemical environment can dramatically improve the electronic properties of the interface to meet technological requirements. The interface structure and its chemistry may provide guidance for the selection process of other high-
k
gate oxides and for controlling their growth.
Journal Article