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We carried out calculations based on density functional theory to investigate the electronic, vibrational, and dielectric properties of mixed halide perovskites CH3NH3 AI3-xClx with A = Pb and Sn. Computed free energies indicated that Cl mixed systems may be formed only for Cl concentrations not exceeding 1019 cm-3, and phonon calculations showed that the disorder induced in the host lattice by the presence of a smaller halogen is responsible for mechanical instabilities. However, we found that the presence of chloride may be beneficial to the electronic properties of the perovskites. Chloride anions cause the organic cations to be displaced from the center of the cage; such a displacement induces preferential orientations of the cation dipole, which in turn are responsible for notable changes in the dielectric properties of the material and possibly for the formation of local ferroelectric domains. The latter are instrumental in separating electron hole pairs and hence in contributing to long charge-carrier diffusion lengths, in spite of polarons being more likely formed in mixed perovksites than in CH3NH3AI3. [ABSTRACT FROM AUTHOR]

Hybrid organic/inorganic CH3NH3AI3(A = Pb and Sn) perovskites have beenrecognized as promising photovoltaicmaterials. Using ab initio calculations, we showed that these systemsmay also be promising materials for solar thermoelectric applications.We found that their large carrier mobilities mainly originate froma combination of the small effective masses of electrons and holesand a relatively weak carrier–phonon interaction. We proposethat by tuning the carrier concentration to values of the order of∼1018cm–3, the thermoelectricfigure of merit of Sn and Pb based perovskites may reach values rangingfrom 1 to 2, which could possibly be further increased by optimizingthe lattice thermal conductivity through engineering perovskite superlattices. [ABSTRACT FROM AUTHOR]

Using first-principles calculations,we investigated the thermoelectricproperties of a newly synthesized Si-based ternary clathrate K8Al8Si38, composed of ∼1 nm hollowcages with a metal atom inside. This compound contains solely Earthabundant elements. We found that, similar to other nanostructuredtype I clathrates, this system is a semiconductor and has a low thermalconductivity (∼1 W/mK). It was long believed that the merepresence of rattling centers was responsible for the low lattice thermalconductivity of type I clathrates. We found instead that the cagestructural disorder induced by atomic substitution plays a crucialrole in determining the conductivity of these materials, in additionto the dynamics of the guest atoms. Our calculations showed that thelatter is substantially affected by the charge transfer between themetal and the cages. Our results provide design rules for the searchof new types of promising nanocage structured thermoelectric materials. [ABSTRACT FROM AUTHOR]

A well-aligned composition-graded CuSi nanorod array structure has been fabricated by a simple oblique angle codeposition technique in a physical vapor deposition system. The Cu and Si graded composition distribution in the nanorods was confirmed by their elemental mapping and depth profiles. The crystal structure evolution with the nanorod length was revealed by both electron and X-ray diffractions. The size evolution of the CuSi nanorods followed a power law, which results from the combination effects of geometric shadowing and limited surface atomic diffusion. Such a graded composition distribution could relax the stress between the nanorods and the substrate, and is promising for applications where improved nanorod−substrate adhesion is required. A well-controlled and well-aligned composition-graded CuSi nanorod array has been fabricated by an oblique angle codeposition (OACD) technique through dynamically tuning the relative deposition rates of Cu and Si during coevaporation. The Cu and Si graded composition distribution, and the crystal structure and morphology evolution with the nanorod length have been investigated by SEM, EDX, XRD, TEM, and SAED. [ABSTRACT FROM AUTHOR]

Emerging applications of metal-organic frameworks (MOFs) in electronic devices will benefit from the design and synthesis of intrinsically, highly electronically conductive MOFs. However, very few are known to exist. It is a challenging task to search for electronically conductive MOFs within the tens of thousands of reported MOF structures. Using a new strategy (i.e., transfer learning) of combining machine learning techniques, statistical multivoting, and ab initio calculations, we screened 2932 MOFs and identified 6 MOF crystal structures that are metallic at the level of semilocal DFT band theory: Mn 2 [Re 6 X 8 (CN) 6 ] 4 (X = S, Se,Te), Mn[Re 3 Te 4 (CN) 3 ], Hg[SCN] 4 Co[NCS] 4 , and CdC 4 . Five of these structures have been synthesized and reported in the literature, but their electrical characterization has not been reported. Our work demonstrates the potential power of machine learning in materials science to aid in down-selecting from large numbers of potential candidates and provides the information and guidance to accelerate the discovery of novel advanced materials.

To avoid fraudulent substitutions in fish markets, the proper methods are needed to test the authenticity of the ingredients. As a preferable methodology, a quantitative real-time polymerase chain reaction (qPCR) method was used in this study to identify species from the Salmonidae family based on the salmon growth hormone gene. Fish samples of six genera from the Salmonidae family were tested to identify the specificity, sensitivity, and applicability of the established method. Results showed that the method was highly specific for salmonid detection. Ct values were obtained only from 31 Salmonidae fish species samples. The relative and absolute limits of detection were 0.01% and 25 pg of genomic DNA, respectively, which could meet with the requirements of routine detections. To test the applicability of the method, the content of salmonid ingredients in 16 commercial food products was quantified from standard curves constructed from DNA of two Salmonidae species. The results revealed that the salmonid ingredient was detected in 12 samples, indicating that 25% of the labels are inauthentic. These results demonstrate that the developed qPCR method is suitable for identification of Salmonidae ingredients.

Using molecular dynamics simulations, we show that the thermal conductivity (κ) of Si(0.5)Ge(0.5) can be reduced by more than one order of magnitude by etching nanometer-sized holes in the material, and it becomes almost constant as a function of temperature between 300 and 1100 K for samples with 1 nm wide pores. In nanoporous SiGe, thermal conduction is largely determined by mass disorder and boundary scattering, and thus the dependence of κ on pore distance and on structural, atomistic disorder is much weaker than in the case of nanoporous Si. This indicates that one may minimize κ of the alloy with less stringent morphological constraints than for pure Si.

We present molecular and lattice dynamics calculations of the thermal conductivity of nanoporous silicon, and we show that it may attain values 10-20 times smaller than in bulk Si for porosities and surface-to-volume ratios similar to those obtained in recently fabricated nanomeshes. Further reduction of almost an order of magnitude is obtained in thin films with thickness of 20 nm, in agreement with experiment. We show that the presence of pores has two main effects on heat carriers: appearance of non-propagating, diffusive modes and reduction of the group velocity of propagating modes. The former effect is enhanced by the presence of disorder at the pore surfaces, while the latter is enhanced by decreasing film thickness.

Using a geometric shadowing effect, a thin catalyst layer can be coated asymmetrically on the side of a nanorod backbone. Combining with substrate rotation, a dynamic shadowing growth technique has been developed to fabricate catalytic nanomotors such as rotary Si/Pt nanorods, rotary L-shaped Si/Pt and Si/Ag nanorods, and rolling Si/Ag nanosprings, and their autonomous motions have been demonstrated in a diluted H2O2 solution. This fabrication method reveals an optimistic step toward designing integrated nanomachines.