Anharmonic Effects on Charge and Orbital Order
A Comment on the Letter by Tetsuya Mutou and Hiroushi Kontani, Phys. Rev. Lett. 83, 3685 (1999).
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Optical characterization of CdS nanocrystals in Al2O3 matrices fabricated by ion-beam synthesis
We have studied optical properties of CdS nanocrystals formed by sequential Cd+ and S+ ion implantation into Al2O3 matrices. Two bands related to free excitons in the wurtzite CdS are clearly observed in the absorption spectrum at low temperatures. Efficient photoluminescence (PL) appears near the absorption edge. At…
Semiconductor sieves as nonlinear optical materials
Electrochemical etching techniques were used to fabricate semiconductor sieves of gallium phosphide, i.e., two-dimensionally nanostructured membranes exhibiting an enhanced optical second harmonic generation (SHG) in comparison with the bulk material. The SHG rotational and fundamental polarization dependencies studie…
Detection of volatile organic compound vapors by using a vapochromic material on a tapered optical fiber
A low-cost optical fiber sensor to detect volatile organic compounds has been developed. Changes of up to 13.5 dB in the transmitted optical power have been detected with different concentrations of acetone and dichloromethane vapors. The device uses a standard single-mode fiber. The sensing mechanism relies on a vapo…
Catalytic Action of Ni Atoms in the Formation of Carbon Nanotubes: A Molecular Dynamics Study
Catalytic action of Ni atoms in the growth of single-wall carbon nanotubes is investigated using tight-binding molecular dynamics and ab initio methods. Our results demonstrate this to be a two step process in which the Ni atom first creates and stabilizes defects in nanotubes. The subsequent incorporation of incoming…
Observation of Two Time Scales in the Ferromagnetic ManganiteLa1−xCaxMnO3,x≈0.3
We report new zero-field muon spin relaxation and neutron spin echo measurements in ferromagnetic (FM) (La,Ca)MnO3 which suggest at least two spatially separated regions possessing very different Mn-ion spin dynamics. One region displays diffusive relaxation, "critical slowing down" near T(C) and an increasing volume…
Excitonic gain and stimulated ultraviolet emission in nanocrystalline zinc-oxide powder
We have studied ultraviolet photoluminescence from high-purity zinc-oxide powder over a wide temperature range (2–293 K). At low temperatures, the spontaneous emission is due to radiative recombination of excitons bound to donors and acceptors. At high temperature (>90 K), it mainly consists of recombination of…
Stability of Carbon Nanotubes: How Small Can They Be?
Experimental evidence has been found for the existence of small single wall carbon nanotubes with diameters of 0.5 and 0.33 nm by high resolution transmission electron microscopy, and their mechanical stability was investigated using tight-binding molecular dynamics simulations. It is shown that, while the carbon tube…
(Ga,Mn)As as a digital ferromagnetic heterostructure
(Ga,Mn)As digital ferromagnetic heterostructures are grown by incorporating submonolayer planes of MnAs into GaAs using molecular beam epitaxy. Structural and magnetic measurements indicate single-crystalline superlattice structure and ferromagnetic order with Curie temperatures (TC) up to 50 K. By varying the spacing…
Band-by-band decompositions of the Born effective charges
The Born effective charge, Z *, that describes the polarization created by collective atomic displacements, can be computed from first principles following different techniques. We establish the connections existing between these different formulations, and analyse the related band-by-band decompositions. We show that…
Competing Interactions among Supramolecular Structures on Surfaces
A simple model was constructed to describe the polar ordering of non-centrosymmetric supramolecular aggregates formed by self assembling triblock rodcoil polymers. The aggregates are modeled as dipoles in a lattice with an Ising-like penalty associated with reversing the orientation of nearest neighbor dipoles. The ch…
"Colliding beam" enhancement mechanism of deuteron-deuteron fusion reactions in matter
We suggest a ``ping-pong'' mechanism of enhancement for fusion reactions between a low energy external deuteron beam and the deuterons in a condensed matter or molecular target. The mechanism is based on the possibility of acceleration of a target deuteron by the Coulomb field of a projectile deuteron with its subsequ…
Minimizing Boundary Reflections in Coupled-Domain Simulations
We propose a time-dependent boundary condition coupling an atomistic simulation system to linear surroundings such that reflection of elastic waves across the boundary is minimized. Interdomain interactions expressed in terms of memory kernel functions within linear-response theory are treated in a natural dynamical m…
Does Water Vapor Prevent Upscaling Sonoluminescence?
Experimental results for single-bubble sonoluminescence of air bubbles at very low frequency f = 7.1 kHz are presented: In contrast to the predictions of a recent model [S. Hilgenfeldt and D. Lohse, Phys. Rev. Lett. 82, 1036 (1999)], the bubbles are only as bright (10(4)-10(5) photons per pulse) and the pulses as long…
Molecular Simulation of Ultrathin Polymeric Films near the Glass Transition
Properties such as the glass transition temperature ( T(g)) and the diffusion coefficient of ultrathin polymeric films are shown to depend on the dimensions of the system. In this work, a hard-sphere molecular dynamics methodology has been applied to simulate such systems. We investigate the influence that substrates…
Correlation between Fluorescence Intermittency and Spectral Diffusion in Single Semiconductor Quantum Dots
We find a correlation between the dynamics of fluorescence intermittency and spectral diffusion in the spectroscopy of single CdSe nanocrystal quantum dots (QD). A statistical analysis of the data suggests two populations of blinking events: blinking followed by large spectral diffusion shifts and blinking with small…
Supercapacitor electrodes from multiwalled carbon nanotubes
Electrochemical characteristics of supercapacitors built from multiwalled carbon nanotubes electrodes have been investigated and correlated with microtexture and elemental composition of the materials. Capacitance has been estimated by cyclovoltammetry at different scan rates from 1 to 10 mV/s, galvanostatic discharge…
Inelastic light scattering in B2O3 glasses with different thermal histories
This contribution presents a systematic light scattering study of a series of boron oxide glasses which are characterized by different thermal histories. The thermal treatment was obtained by annealing the samples close to the glass transition temperature for times of several hours. Both low-frequency (0.1–30 cm−1) an…
Phase equilibria in the polydisperse Zwanzig model of hard rods
We study the phase behavior of the Zwanzig model of suspensions of hard rods, allowing for polydispersity in the lengths of the rods. In spite of the simplified nature of the model (rods are restricted to lie along one of three orthogonal axes), the results agree qualitatively with experimental observations: the coexi…
Applications and generalizations of the foam drainage equation
Some new analytic results concerning the foam drainage equation are described. The temporal approach to the equilibrium profile of the foam is shown to be exponential, in agreement with numerical calculations. The effect of including the equilibrium distribution of the liquid fraction as an initial condition is discus…