Materials Literature
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Biomineralizing organisms use organic molecules to generate species-specific mineral patterns. Here, we describe the chemical structure of long-chain polyamines (up to 20 repeated units), which represent the main organic constituent of diatom biosilica. These substances are the longest polyamine chains found in nature…
A re-examination of the status of the monotypic genus Saniella Hilliard & Burtt (Hypoxidaceae) was inspired by the rediscovery of Empodium occidentale on Hantam Mountain in Calvinia Division, SW Cape. This plant does not belong to Empodium, and has critical features that show that it is better placed as a second s…
In this letter we employ null ellipsometry on Langmuir Blodgett multilayers of a glass forming photosensitive side chain polymer to investigate both the structural changes and the related time relaxation as a function of temperature and sample thickness following isothermal optical perturbation. Below a thickness of a…
We report tunable, narrow, directional, and enhanced erbium emission from one-dimensional photonic band gap structures. The structures are prepared by anodic etching of crystalline silicon and consist of two highly reflecting porous silicon Bragg reflectors sandwiching an active layer. The cavities are doped by cathod…
Silver nanowires of diameter ∼40 nm and length ∼0.3 mm have been grown by electrodeposition within the pores of silica gels which were heat treated in the temperature range 523 to 823 K and, subsequently, soaked in a silver nitrate solution. A staircase current–voltage characteristic was observed in the direction of e…
The site vacancy responsible for the manifestation of a spontaneous normal-to-relaxor transition was investigated using La-modified PbTiO3 as a model perovskite system. The two cation-site defects relevant to the present study are the A-site (Pb site) and B-site (Ti site) vacancies. To clearly elucidate the type of va…
Experimental results on the temperature-dependent cross-plane thermal conductivity of skutterudite thin films are presented. The films examined include IrSb3, CoSb3, and Ir0.5Co0.5Sb3 single layers, and IrSb3/CoSb3 superlattices that are grown by pulsed-laser deposition. A differential 3ω method is used to measure the…
In this letter, the reversible and irreversible polarization contributions in donor-doped Pb(Zr,Ti)O3 are investigated using conventional capacitance–voltage (C–V) and hysteresis measurements. The dependence of the Rayleigh coefficient in the subcoercive regime on the doping concentration is investigated and shown to…
We have examined the atomic structure, composition, and bonding at a nominally undoped 58° [001] tilt grain boundary in SrTiO3 in order to develop an understanding of the control that the grain boundary plane exerts over the bulk properties. Room temperature and in situ heating experiments show that there is a segrega…
We investigate, through first-principles calculations, lattice instabilities induced in diamond by the application of high shear stresses. For shear stresses as low as 95 GPa a lattice instability will occur, leading to graphitelike layered structures. This effect is highly anisotropic. The reversal of the direction o…
We report highly substrate-site selective growth of carbon nanotubes by chemical vapor deposition from precursors of ferrocene and xylene mixtures. The technique allows us to grow well-aligned multiwalled carbon nanotubes preferentially on the SiO2 regions of patterned SiO2/Si substrates prepared by conventional litho…
Theoretical aspects of x-ray standing wave method for investigation of the real structure of crystals are considered in this review paper. Starting from the general approach of the secondary radiation yield from deformed crystals this theory is applied to different concreat cases. Various models of deformed crystals l…
We propose an explanation of anomalies observed in the behavior of deformation hardening of Invars. An extremely strong volume magnetostriction, typical of Invars, results in an enhancement of the exchange contribution to the energy of the dislocation system by about three orders of magnitude with respect to its value…
Diffusing-wave spectroscopy (DWS) was used to follow the sol-gel transition of concentrated colloidal suspensions. We present a new technique based on a sandwich of two scattering cells aimed to overcome the problem of nonergodicity in DWS of solidlike systems. Using this technique we obtain quantitative information a…
Charged closed-cell microporous polypropylene foams are shown to exhibit piezoelectric resonance modes in the dielectric function, coupled with a large anisotropy in the electromechanical and elastic material properties. Strong direct and converse dynamic piezoelectricity with a piezoelectric d33 coefficient of 140 pC…
Tunneling of Bloch electrons through a vacuum barrier introduces new physical effects in comparison with the textbook case of free (plane wave) electrons. For the latter, the exponential decay rate in the vacuum is minimal for electrons with the parallel component of momentum ${\bf k}_\parallel=0$, and the prefactor i…
A theory for longitudinal (T1) and transverse (T2) electron spin coherence times in zincblende semiconductor quantum wells is developed based on a non-perturbative nanostructure model solved in a fourteen-band restricted basis set. Distinctly different dependences of coherence times on mobility, quantization energy, a…
Relative $K$ x-ray intensities of $Mn$ in $Mn$, $MnO_{2}$, $LaMnO_{3}$ and $La_{0.7}B_{0.3}MnO_{3}$ ($B$ = $Ca$, $Sr$, and $Ce$) systems have been measured following excitation by 59.54 keV $γ$-rays from a 200 mCi $^{241}$Am point-source. The measured results for the compounds deviate significantly from the results of…
We have investigated the structural and optical properties of Ga-doped ZnO films grown on GaN templates by plasma-assisted molecular-beam epitaxy. The carrier concentration in Ga-doped ZnO films can be controlled from 1.33×1018/cm3 to 1.13×1020/cm3. Despite high Ga incorporation, the linewidth of (0002) ω-rocking curv…
We consider an equilibrium structure of a monolayer formed by weakly charged polyelectrolyte chains tethered to the oppositely charged interface. The interface is characterized by an immobile charge spatially distributed in a sublayer of finite thickness submerging tethered polyions. The Coulomb attraction of tethered…