Materials Literature
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We have synthesized a Ba6Ge25 clathrate, substituting 3 Ge per formula unit by Fe. This chiral clathrate has Ge sites forming a framework of closed cages and helical tunnel networks. Fe atoms randomly occupy these sites, and exhibit high-spin magnetic moments. A ferromagnetic transition is observed with Tc=170 K, the…
Ferromagnetic ${\mathrm{Ni}}_{2}\mathrm{MnGa}$ has unique magnetoelastic properties. These are investigated by detailed computational studies of the phonon-dispersion curves for the non-modulated cubic ${\mathrm{L}2}_{1}$ and tetragonal structures. For the ${\mathrm{L}2}_{1}$ structure, a complete softening of the tra…
Molecular dynamics (MD) simulations of crystalline poly(ethylene oxide) (PEO) have been carried out in order to study its vibrational properties. The vibrational density of states has been calculated using a normal mode analysis (NMA) and also through the velocity autocorrelation function of the atoms. Results agree w…
A perfect two-dimensional porous alumina photonic crystal with 500 nm interpore distance was fabricated on an area of 4 cm2 via imprint methods and subsequent electrochemical anodization. By comparing measured reflectivity with theory, the refractive indices in the oxide layers were determined. The results indicate th…
Graphite is a layered material that is very flexible, in which each layer is able to curve in order to form cages, nanotubes, nanocoils, nanocones, etc. In this paper, we demonstrate that various synthetic routes are capable of producing graphite-like nanomaterials with fascinating electronic and mechanical properties…
Results of torsional oscillation tests are reported that were performed at the temperature T=230C on melts of a hybrid nanocomposite consisting of isotactic polypropylene reinforced with 5 wt.% of montmorillonite clay. Prior to mechanical testing, specimens were annealed at temperatures ranging from 250 to 310C for va…
Motivated by the observed thickness-scaling of the coercive field in ferroelectric films over five decades, we develop a statistical approach towards understanding the conceptual underpinnings of this behavior. Here the scaling exponent is determined by the field-dependence of a known and measured quantity, the nuclea…
We report measurements and analysis of the magnetic critical phenomena in a single crystal of ${\mathrm{La}}_{0.875}{\mathrm{Sr}}_{0.125}{\mathrm{MnO}}_{3}.$ The critical exponents associated with the ferromagnetic transition have been determined from ac susceptibility and dc magnetization data. Techniques like the Ko…
The synthesis, X-ray structures, and magnetic behavior of two new, three-dimensional compounds [W(IV)[(mu-CN)(4)Co(II)(H(2)O)(2)](2).4H(2)O](n) (1) and [[W(V)(CN)(2)](2)[(mu-CN)(4)Co(II)(H(2)O)(2)](3).4H(2)O](n) (2) are presented. Compound 1 crystallizes in the tetragonal system, space group I4/m with cell constants a…
The optical properties of perovskite barium titanate in the core-level spectra are investigated by the first principles under scissor approximation. There are nine peaks at the curve of the imaginary part of dielectric function. The optical spectra are assigned to interband contribution from O 2p valence bands to Ti 3…
Multilayer films have been prepared by the sequential electrostatic adsorption of poly(L-lysine) and hyaluronic acid onto charged silicon surfaces from dilute aqueous solutions under various pH conditions. Microelectrophoresis was used to examine the local acid-base equilibria of the polyelectrolytes within the films…
Nearly monodispersed CoFe2O4 nanoparticles with average sizes between 8 and 100 nm were synthesized by using seed-mediated growth dominant coprecipitation and modified oxidation methods. X-ray diffraction and Mössbauer spectroscopy analyses confirmed the spinel phase and a stoichiometric composition of (Co0.25Fe0.75)[…
The radiative recombination coefficient B(T) of intrinsic crystalline silicon is determined as a function of temperature over the temperature range 77–300 K. We observe that B(T) decreases as a function of temperature and we compare our results to previously published contradictory data from the literature. The radiat…
We report on the photoelectric properties of n-ZnO/p-Si photodiodes which detect UV photons in the depleted n-ZnO and simultaneously detect visible photons in the depleted p-Si. As characterized by I–V measurements in the photon range of 310 to 650 nm our photodiodes exposed to UV photons show a linear increase in pho…
In this work, we report on the growth, fabrication, and device characterization of wide-band-gap heterojunction light-emitting diodes based on the n-ZnO/p-GaN material system. The layer structure is achieved by first growing a Mg-doped GaN film of thickness 1 μm on Al2O3(0001) by molecular-beam epitaxy, then by growin…
Relaxation in supercooled liquids above their glass transition and below the onset temperature of “slow” dynamics involves the correlated motion of neighboring particles. This correlated motion results in the appearance of spatially heterogeneous dynamics or “dynamical heterogeneity.” Traditional two-point time-depend…
Surface-enhanced Raman scattering is capable of providing rich vibrational information at the level of single molecules and single nanoparticles, but the practical applications of this enormous enhancement effect are still a challenge. Here we report a new class of dye-embedded core-shell nanoparticles that are highly…
The photoreduction of silver ions by citrate, catalyzed on silver seeds, is used to synthesize disk-shaped silver nanoparticles in solution. The reaction is characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), optical absorption spectroscopy, and by measuring the silver ion concentra…
Homogeneous carbon nanotube/polymer composites were fabricated using noncovalently functionalized, soluble single-walled carbon nanotubes (SWNTs). These composites showed dramatic improvements in the electrical conductivity with very low percolation threshold (0.05–0.1 wt % of SWNT loading). By significantly improving…
The formation of nearly monodisperse CdTe nanocrystals dots (either zinc blende or wurtzite crystal structure), rods, and tetrapods in a noncoordinating solvent was studied. Several strong ligand effects were observed, and the ligand effects on the monomers were found to play a more important role than the ligand effe…