Suppressing Thermal Conductivity in SrTiO by Introducing Oxygen Isotope Disorder.

Transition metal oxides are promising candidates in the field of thermoelectricity, which can convert heat and electricity into each other and realize the efficient utilization of waste energy. For the figure of merit = σ/(κ + κ), a lower thermal conductivity is desired for an enhanced , and cation doping is an appropriate way to regulate the thermal transport properties. However, because , σ, and κ are strongly coupled with each other, cation doping for one parameter modification can generate compensation with others, making regulation more difficult.

Synthesis, Characterization, X-ray Molecular Structure, Antioxidant, Antifungal, and Allelopathic Activity of a New Isonicotinate-Derived -Tetraarylporphyrin.

The present article describes the synthesis of an isonicotinate-derived -arylporphyrin, that has been fully characterized by spectroscopic methods (including fluorescence spectroscopy), as well as elemental analysis and HR-MS. The structure of an -hexane monosolvate has been determined by single-crystal X-ray diffraction analysis. The radical scavenging activity of this new porphyrin against the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical has been measured.

Effects of vacancies on the thermal conductivity of Si nanowires.

Point defects can be used to tailor the properties of semiconductors, but can also have undesired effects on electronic and thermal transport, particularly in ultrascaled nanostructures, such as nanowires. Here we use all-atom molecular dynamics to study the effect that different concentrations and spatial distributions of vacancies have on the thermal conductivity of Si nanowires, overcoming the limitations of previous studies. Although vacancies are not as effective as the nanovoids found in porous Si, they can still reduce the thermal conductivity in ultrathin Si nanowires by more than a factor of two, when found in concentrations smaller than 1%.

Synthesis of New Amino-Functionalized Porphyrins:Preliminary Study of Their Organophotocatalytic Activity.

The design, synthesis, and initial study of amino-functionalized porphyrins as a new class of bifunctional catalysts for asymmetric organophotocatalysis is described. Two new types of amine-porphyrin hybrids derived from 5,10,15,20-tetraphenylporphyrin (TPPH), in which a cyclic secondary amine moiety is covalently linked either to a β-pyrrolic position (Type A) or to the -position of one of the phenyl groups (Type B), were prepared by condensation, reductive amination, or amidation reactions from the suitable porphyrins (either formyl or methanamine derivatives) with readily available chiral amines. A preliminary study of the possible use of Type A amine-porphyrin hybrids as asymmetric, bifunctional organophotocatalysts was performed using the chiral, imidazolidinone-catalyzed Diels-Alder cycloaddition between cyclopentadiene 28 and -cinnamaldehyde 29 as a benchmark reaction.

Descriptors of intrinsic hydrodynamic thermal transport: screening a phonon database in a machine learning approach.

Machine learning techniques are used to explore the intrinsic origins of the hydrodynamic thermal transport and to find new materials interesting for science and engineering. The hydrodynamic thermal transport is governed intrinsically by the hydrodynamic scale and the thermal conductivity. The correlations between these intrinsic properties and harmonic and anharmonic properties, and a large number of compositional (290) and structural (1224) descriptors of 131 crystal compound materials are obtained, revealing some of the key descriptors that determines the magnitude of the intrinsic hydrodynamic effects, most of them related with the phonon relaxation times.

Chiral Amphiphilic Secondary Amine-Porphyrin Hybrids for Aqueous Organocatalysis.

Two chiral proline-derived amphiphilic 5-substituted-10,15,20-tris(4-sulfonatophenyl)porphyrins were prepared, and their pH-dependent supramolecular behavior was studied. In neutral aqueous solutions, the free-base form of the hybrids is highly soluble, allowing enamine-based organocatalysis to take place, whereas under acidic conditions, the porphyrinic protonated core of the hybrid leads to the formation of self-assembled structures, so that the hybrids flocculate and their catalytic activity is fully suppressed. The low degree of chirality transfer observed for aqueous Michael and aldol reactions strongly suggests that these reactions take place under true "in water" organocatalytic conditions.

Ballistic Phonons in Ultrathin Nanowires.

According to Fourier's law, a temperature difference across a material results in a linear temperature profile and a thermal conductance that decreases inversely proportional to the system length. These are the hallmarks of diffusive heat flow. Here, we report heat flow in ultrathin (25 nm) GaP nanowires in the absence of a temperature gradient within the wire and find that the heat conductance is independent of wire length.

Giant Electrophononic Response in PbTiO_{3} by Strain Engineering.

We demonstrate theoretically how, by imposing epitaxial strain in a ferroelectric perovskite, it is possible to achieve a dynamical control of phonon propagation by means of external electric fields, which yields a giant electrophononic response, i.e., the dependence of the lattice thermal conductivity on external electric fields.

Collective thermal transport in pure and alloy semiconductors.

Conventional models for predicting thermal conductivity of alloys usually assume a pure kinetic regime as alloy scattering dominates normal processes. However, some discrepancies between these models and experiments at very small alloy concentrations have been reported. In this work, we use the full first principles kinetic collective model (KCM) to calculate the thermal conductivity of SiGe and InGaAs alloys.

Full-field thermal imaging of quasiballistic crosstalk reduction in nanoscale devices.

Understanding nanoscale thermal transport is of substantial importance for designing contemporary semiconductor technologies. Heat removal from small sources is well established to be severely impeded compared to diffusive predictions due to the ballistic nature of the dominant heat carriers. Experimental observations are commonly interpreted through a reduction of effective thermal conductivity, even though most measurements only probe a single aggregate thermal metric.

Growth of Highly Epitaxial YBa2Cu3O(7-δ) Films from a Simple Propionate-Based Solution.

Intensive investigations have been conducted to develop epitaxial oxide thin films with superior electromagnetic performance by low-cost chemical solution deposition routes. In this paper, a novel propionate-based precursor solution without involving any other additive was proposed and employed to grow superconducting YBa2Cu3O(7-δ) (YBCO) films on LaAlO3 (LAO) single crystals. The precursor solutions are stable with a long shelf life of up to several months.