Piezonuclear neutrons from fracturing of inert solids

Neutron emission measurements by means of helium-3 neutron detectors were performed on solid test specimens during crushing failure. The materials used were marble and granite, selected in that they present a different behaviour in compression failure (i.e., a different brittleness index) and a different iron content. All the test specimens were of the same size and shape. Neutron emissions from the granite test specimens were found to be of about one order of magnitude higher than the natural background level at the time of failure. These neutron emissions should be caused by nucleolysis or piezonuclear “fissions” that occurred in the granite, but did not occur in the marble: . The present natural abundance of aluminum (7-8% in the Earth crust), which is less favoured than iron from a nuclear point of view, is possibly due to the above piezonuclear fission reaction. Despite the apparently low statistical relevance of the results presented in this Letter, it is useful to present them in order to give to other teams the possibility to repeat the experiment.     

LiB6Si: An indirect band gap semiconductor

Using first-principle calculations, mechanical properties, electronic structure, and Raman spectra of LiB₆Si structure were investigated. The band structures calculated by GGA-PBE and HSE06 methods reveal that LiB₆Si is an indirect band gap semiconductor. The band gap estimated by HSE06 method is about 2.24 eV, which is in good agreement with that of experimental value 2.27 eV. The calculated tensile stress-strain curves of LiB₆Si reveal that [010] direction is the cleavage direction under tensile strains. The calculated Raman spectra of LiB₆Si are also in good agreement with that of measured. The position of the band gap may provide a basis for further photocatalysis research on LiB₆Si.     

On the behavior of spallation neutrons from extended Pb targets plus moderator: A comparison between SSNTD measurements and calculation

Thick Pb targets of different lengths were irradiated by 1 GeV protons at the Nuclotron accelerator of the High Energy Laboratory, JINR, Dubna. To favor transmutation via (n,γ) reactions a paraffin moderator is used. Solid-state nuclear track detectors (SSNTDs) measured neutron distribution. A comparison of experimental results with calculation on the moderator surface is given.     

Composites of multiwall carbon nanotubes and conducting polyaniline: Bulk samples and films produced from a solution in chloroform

Multiwall carbon nanotubes and conducting polyaniline, doped with dodecylbenzenesulfonic acid, are blended by employing the solubility of both materials in chloroform. Pellets are made by pressing the dried powder of the obtained composite, and films by sedimentary deposition onto a plastic substrate. In these composites, the advantageous properties of carbon nanotubes can be utilized in fully conducting bulk and planar structures while the strong decrease of the conductivity of doped polyaniline at low temperatures is simultaneously suppressed. The nanotube content in pellets can be as high as 40% by weight, and this wide range leads to a control over the shape and magnitude of the conductivity versus temperature curves. As the nanotube content grows, the temperature dependence of the conductivity becomes less steep, which is similar to the effect of annealing temperature on the conductivity of certain polycrystalline graphene films. In our case, this change is most likely caused by the increase of the density of highly conducting channels and not by homogeneous delocalization effects.     

An alternative method for measurement of charge carrier mobility in semiconductors using photocurrent transient response

We report here a simple alternative method for measuring charge carrier drift mobilities in semiconductor devices. A typical falling photocurrent transient formula for switch-off-state was adjusted to obtain simultaneously electron and hole mobilities. For both undoped ZnO film and InAlAs/InGaAs quantum well structure, electron mobilities extracted from our model were compared with those obtained from maximum-entropy mobility-spectrum analysis method (ME-MSA). Our results demonstrated that electron mobility obtained from our photocurrent response model could serve as substitutes for a representative mobility obtained from ME-MSA.     

Quantum diffraction of position-momentum entangled photons from a sharp edge

In this paper, an experiment of quantum diffraction of position-momentum entangled photons from a straight sharp edge is presented. Path of a single photon of an entangled pair is partially blocked by a sharp edge whereas the other photon is detected at a stationary location without revealing the which-path information of the other photon. Quantum diffraction pattern of the sharp edge is revealed only in the correlated conditional detection of spatially separated photons and no diffraction pattern is formed in local detections of individual photons. Theoretical analysis of the quantum diffraction of position-momentum entangled photons from a sharp edge is also presented in this paper. Experimental measurements of the quantum diffraction pattern are compared with theoretically calculated quantum diffraction pattern of position-momentum entangled photons.     

Stabilization of E-type antiferromagnetic ordering in La and Y substituted orthorhombic LuMnO3: A first-principles study

We carry out first principles density functional theory calculations of non-lone pairs, namely, La and Y substituted orthorhombic LuMnO₃, to verify the generality of symmetry breaking effects observed in the lone pair cations substituted orthorhombic rare earth manganites. Our calculations revealed that similar to lone pair cations ordering at the A-site of LuMnO₃, non-lone pair cations ordering also results in the lowering of the symmetry thereby proving that the symmetry breaking with A-site ordering is a generic effect. Interestingly, we were able to stabilize the large radius La substituted LuMnO₃ into an E-type antiferromagnetic (E-AFM) phase, in contrast to the normally expected A-type antiferromagnetic (A-AFM) phase of large radius rare earth manganites such as LaMnO₃.     

The migration of alkali metal (Na+, Li+, and K+) ions in single crystalline vanadate nanowires: Rasch-Hinrichsen resistivity

We report the synthesis of single crystalline alkali metal vanadate nanowires, Li-vanadate (Li₄V₁₀O₂₇), Na-vanadate (NaV₆O₁₅), and K-vanadate (KV₄O₁₀) and their electrical properties in a single nanowire configuration. Alkali metal vanadate nanowires were obtained by a simple thermal annealing process with vanadium hydroxides(V(OH)₃) nanoparticles containing Li⁺, Na⁺, and K⁺ ions and further the analysis of the migration of charged particles (Li⁺, Na⁺, and K⁺) in vanadate by measuring the conductivity of them. We found that their ionic conductivities can be empirically explained by the Rasch-Hinrichsen resistivity and interpreted on the basis of transition state theory. Our results thus indicate that the Li ion shows the lowest potential barrier of ionic conduction due to its small ionic size. Additionally, Na-vanadate has the lowest ion number per unit V₂O₅, resulting in increased distance to move without collision, and ultimately in low resistivity at room temperature.     

Improving the charge transfer performance of Si nanomaterial through C surface modification: A first-principles study

Models of oxidized Si (111) surface under different C coverage were established to study the charge transfer ability of Si nanomaterial from strategy of C surface modification using first-principles calculation. The calculated formation energies show that structures of C surface-modified oxidized Si (111) surface are stable. The electronic properties present that the interaction between C and Si atoms is mainly contributed by the hybridization of C-2p and Si-3p states. And the interaction between C and Si atoms increases firstly and then decreases with the increasing C coverage rate. The transfer charge between C and Si reaches a maximum when C coverage rate is 0.5. We speculate that the conductivity of experimentally prepared Si nanomaterial does not monotonously enhance with the increasing C concentration, which would reach a maximum at a certain C concentration, and then decreases.     

First-principles study of two-dimensional van der Waals heterostructure based on ZnO and Mg(OH)2: A potential photocatalyst for water splitting

In this study, the structural, electronic and optical properties of the two-dimensional heterostructure based on ZnO and Mg(OH)₂ are investigated by first-principle calculations. The ZnO/Mg(OH)₂ heterostructure, formed by van der Waals (vdW) interaction, possesses a type-II band structure, which can separate the photogenerated electron–holes constantly. The heterostructure has decent band edge positions for the redox reaction to decompose the water at pH 0 and 7. As for the interfacial properties of the heterostructure, the trend of band bending of the ZnO and Mg(OH)₂ layers in the heterostructure is addressed, which will result a built-in electric field. Besides, the charge-density difference and potential drop across the interface of the ZnO/Mg(OH)₂ vdW heterostructure are also calculated. Finally, the heterostructure is demonstrated that it not only has excellent ability to capture the light near the visible spectrum region, but also can improve the optical performance for the monolayered ZnO and Mg(OH)₂.     

Infrared induced visible emission from porous silicon: the mechanism of anodic oxidation

The visible luminescence caused by anodic oxidation of p-type porous silicon has been studied. It is shown that similar luminescence can be observed in n-type material by illumination with near-infrared light. Addition of a suitable reducing agent to the electrolyte solution can both suppress the oxidation of the porous layer and quench its luminescence. These results confirm a previously suggested mechanism, in which the capture of a valence band hole in a surface bond of the porous semiconductor gives rise to a surface state intermediate capable of thermally injecting an electron into the conduction band.     

Investigation of half-metallic ferromagnetism in hafnium and tantalum doped NiO for spintronic applications: A DFT study

Full Potential Linearised Augmented Plane Wave (FP-LAPW) method was used to investigate the electronic and magnetic properties of NiO doped with Hf and Ta within the frame work of density functional theory (DFT). NiO is found to be stable in rock salt structure. NiO shows conducting characteristics for the lattice constant of 4.155 Å. Doping Hf and Ta in the metallic super cell of NiO separately in the doping concentration of 12.5%, the compounds Hf_0.125Ni_0.875O and Ta_0.125Ni_0.875O are formed. These compounds of Hf_0.125Ni_0.875O and Ta_0.125Ni_0.875O are predicted to exhibit stability in the ferromagnetic phase. The density of states and band structure plots predict that these compounds exhibit half metallic character with formation of energy gap in one of the spins at the Fermi level. The total spin magnetic moments found in these compounds are 12.00689 μ_B and 10.97628 μ_B.     

An even magneto-optic effect: Linear polarization of the spectral thermal emission from ferromagnetic iron

The thermal spectral emission from ferromagnetic iron observed at normal incidence and with the magnetization parallel to its surface is partially linearly polarized. Measurements of the new even magneto-optic effect have been performed in the spectral range from 1.8 m to 5 m wave-length.     

Prediction of two-dimensional monochalcogenides: MoS and WS

Using density functional theory, we explore the possibility of two monolayer monochalcogenides, namely, MoS and WS. From the energetics, buckled and puckered structures are found to be more probable configurations. Our results on cohesive energy and phonon dispersion predict that the buckled structures of both MoS and WS are stable. On the other hand, while the puckered structure of WS clearly shows a dynamical instability, the same for MoS may have a stable configuration. Charge analyses predict ionic-like bonding in these systems. Density of states and band structure reveal a non-magnetic metallic nature for MoS in the stable configurations. However, for the buckled WS, our study predicts a non-magnetic semi-metallic nature. Further, semi-metal to indirect semiconductor transition has been observed for tensile strain of 5%, 6% and 8%.     

Impact of substituents in the NN ligand on the emission wavelength of Cu(I) complexes: Insight from experimental and theoretical approach

Three mononuclear Cu(I) complexes [Cu(bop)(PPh₃)₂][BF₄], [Cu(fop)(PPh₃)₂][BF₄] and [Cu (pop)(PPh₃)₂][BF₄] were synthesized, where 2-(5-tert-butyl-1,3,4-oxadiazol-2-yl)pyridine (bop), 2-(5-(trifluoromethyl)-1,3,4-oxadiazol-2-yl)pyridine (fop) or 2-(5-phenyl-1,3,4-oxadiazol-2-yl)pyridine (pop) was used as N^∧N chelate ligand and triphenylphosphine was used as ancillary ligand. Several substituents with different electronic effects, such as tert-butyl (t-Bu), trifluoromethyl (CF₃) and phenyl (Ph) groups, were introduced into the 1,3,4-oxadiazole moiety of the N^∧N chelate ligands. The photophysical properties of the complexes were examined by UV-vis absorption and photoluminescence (PL) spectroscopies. The complex [Cu(fop)(PPh₃)₂][BF₄] with a CF₃ group in the N^∧N chelate ligand exhibited the lowest energy absorption and emission band. Electrochemical analyses combined with density functional theory (DFT) calculations established that the introduction of electron withdrawing group (CF₃) decreases the HOMO-LUMO energy gap, and the introduction of electron donating group (t-Bu) into the 1,3,4-oxadiazole moiety has a similar effect on the emission wavelength as that of the introduction of a phenyl group with a π-conjugation.     

Electronic and optical properties of vacancy and B,N, O and F doped graphene: DFT study

Structural and optical properties of graphene with a vacancy and B, N, O and F doped graphene have been investigated computationally using density functional theory (DFT). We find that B is a p-type while N, O and F doped graphene layers, as well as graphene with a vacancy are n-type semiconductors. Optical properties for both cases of in plane $\left(E\perp c\right)$ and out of plane $\left(E6c\right)$ polarization of light are investigated. It is observed that with the increase in the number of electrons entering the supercell, the amount of absorption of the system decreases and the absorption peaks are transferred to higher energies (blue shift).     

In-operando spectroscopic ellipsometry studies of IrO2 dynamic instabilities: Guide to in-situ growth of pyrochlore iridate thin films

The instability of iridium oxide at high temperature has long been a bottleneck for in growing pyrochlore iridate thin films in a vacuum chamber. To overcome this problem, we investigated the chemical instability of IrO₂ thin films, which are the simplest form of iridate, via in-operando spectroscopic ellipsometry (SE). We observed that IrO₂ thin films undergo IrO₂ dissociation and IrO₃ gas formation depending on the thermodynamic conditions. The chemical kinetics observations of IrO₂ were confirmed by ex-situ X-ray diffraction and atomic force microscopy. SE experimental data were compared with models used to describe the evolution of the two chemical reactions. Real-time in-operando SE analysis based on the Maxwell Garnett theory yielded a precise IrO₂ dissociation speed for the given thermodynamic conditions. Moreover, the real-time in-operando SE technique allowed us to observe the phase transition from solid IrO₂ to gaseous IrO₃. This study on the chemical instability of IrO₂ at high temperature affords insights into a new method for in-situ pyrochlore iridate and other iridates thin-film growth.     

Influence of dilution on magnetization properties of geometrically frustrated magnetic systems: Effective-field theory cluster approximations on kagome lattice

The influence of the site dilution on the magnetization properties of the antiferromagnetic spin-1/2 Ising model on the kagome lattice is systematically investigated using various n-site cluster effective-field theory approximations up to the cluster size $n=12$. It is shown that, regardless of the cluster approximation, the site dilution of the system leads, in addition to the existence of the standard saturated ground state, to the formation of four nontrivial plateau ground states together with five single-point ground states that separate them in the zero temperature limit. It is also shown that, while magnetization properties of the saturated ground state and two single-point ground states are stable with respect to the used cluster approximation, the magnetization properties of all four nontrivial plateau ground states and three single-point ground states that separate them strongly depend on the used approximation and have tendency to approach each other with increasing of the cluster approximation.     

Heteroduplex mobility assay (HMA) pre-screening: An improved strategy for the rapid identification of inserts selected from phage-displayed peptide libraries

Phage-displayed peptide libraries represent an efficient toolto isolate peptides that bind a given target molecule. Afterseveral selection rounds, generally a large pool of targetbinding phages is obtained. Conventional analysis of theselected phage population involves extensive sequencing of many clones, mostof which can be identical. We have adapted the HeteroduplexMobility Assay (HMA) for pre-screening of phage inserts thatwere amplified by direct colony PCR of ELISA-positive clones.This strategy allowed for the rapid and reproducible assignment ofinsert sequences to different `heteroduplex migration groups'.Sequence analysis of only one representative of each HMAmigration group then completes the characterisation of thebinding phage population. In our model experiments,only 16% of HMA pre-screenedclones required further sequence analysis.     

Surface chemistry and catalysis of oxide model catalysts from single crystals to nanocrystals

Fundamental understandings of surface chemistry and catalysis of solid catalysts are of great importance for the developments of efficient catalysts and corresponding catalytic processes, but have been remaining as a challenge due to the complex nature of heterogeneous catalysis. Model catalysts approach based on catalytic materials with uniform and well-defined surface structures is an effective strategy. Single crystals-based model catalysts have been successfully used for surface chemistry studies of solid catalysts, but encounter the so-called “materials gap” and “pressure gap” when applied for catalysis studies of solid catalysts. Recently catalytic nanocrystals with uniform and well-defined surface structures have emerged as a novel type of model catalysts whose surface chemistry and catalysis can be studied under the same operational reaction condition as working powder catalysts, and they are recognized as a novel type of model catalysts that can bridge the “materials gap” and “pressure gap” between single crystals-based model catalysts and powder catalysts. Herein we review recent progress of surface chemistry and catalysis of important oxide catalysts including CeO₂, TiO₂ and Cu₂O acquired by model catalysts from single crystals to nanocrystals with an aim at summarizing the commonalities and discussing the differences among model catalysts with complexities at different levels. Firstly, the complex nature of surface chemistry and catalysis of solid catalysts is briefly introduced. In the following sections, the model catalysts approach is described and surface chemistry and catalysis of CeO₂, TiO₂ and Cu₂O single crystal and nanocrystal model catalysts are reviewed. Finally, concluding remarks and future prospects are given on a comprehensive approach of model catalysts from single crystals to nanocrystals for the investigations of surface chemistry and catalysis of powder catalysts approaching the working conditions as closely as possible.