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In this paper, a range of sputtered ternary and quaternary (Si)(Ge)As x Te 3 layers (x: 2 or 5) and (Si)(Ge)As 2 Se 3 layers are examined using Raman spectroscopy. The results are linked to the Ovonic Threshold Switching properties of these materials when incorporated in selector devices, as observed in separate studies. In case of both the As-rich and As-poor tellurides, a large amount of homopolar bonds are present as the spectra are dominated by peaks associated with As–As and Te–Te bonds. Such homopolar bonds are commonly linked with drift in OTS properties. In the case of the selenides the spectra are dominated by modes associated with heteropolar As–Se bond vibrations. Adding Ge as an alloying element has a significant impact on the bond structure for both material systems. In contrast, Si has a much less pronounced impact and will mostly bond with itself. Time-resolved Raman measurements were also performed to determine the stability of the layers under micro-Raman laser excitation. At the regular exposure settings, no significant changes in the spectra were observed during the measurement. At elevated exposure settings, however, persistent changes in the bond structure can be induced for certain compositions. [ABSTRACT FROM AUTHOR]

The increasing availability of computational data from quantum-chemical calculations on the reactivity and electronic structure of catalytically active oxidic systems make a revisitation of the classical questions on chemical bonding aspects of catalytically reactive systems useful. This Perspective paper starts with a short review of the different available systems. The elementary reactions that are part of the selective oxidation catalysis, such as substrate bond activation or oxygen insertion, are introduced. This is followed by a discussion of basic electronic features of the valence electron structure of oxide materials. We will initially compare the chemical bonding and reactivity of compounds with dominantly ionic versus covalent bonding. Surface reactivity descriptors for the two types of chemical bonds are indicated. It will appear that, except for longer range ionic interactions, binding to the metal cations is dominated by local covalent interactions and that ligand field theory type atomic orbital splitting as well as rehybridisation are important. Trends in bonding as a function of position of reducible metal in the periodic system are emphasized throughout the paper. At the surface, in addition to the changes in electronic structure, atom position relaxation and surface reconstruction effects may also have a large influence on the differences in reactivity. The reactivity of the oxygen atoms varies. They can be proton acceptors and generate Brønsted acidity, can assist heterolytic or radical type C H bond activation or when electrophilic will insert into hydrocarbon double bonds. At the end of the paper trends in catalytic reactivity are analyzed. The double volcano type curve found for the dependence of catalytic reactivity on the position of cation in the third row of the periodic system is shown to relate to the distribution of electrons with high spin over the ligand field split atomic orbitals of the respective cations. This will be discussed in the context of classical catalytic results that are based on Balandin type volcano plots of reactivity versus the catalyst material reactivity parameters. [ABSTRACT FROM AUTHOR]

[Display omitted] • Broadband absorption of SiAlON films caused by chemical intermixing. • One-step magnetron co-sputtering method for fabricating SiAlON films. • Alterable IR optical properties based upon tunable compositions. • Flexible optical constants/absorbing bands that enables IR absorbers optimization. Broadband infrared absorbers have been intensively developed in recent decades due to their wide range of applications. Current infrared absorbers usually adapt complicated photonic designs to meet increasing demands, since natural infrared material (e.g., dielectrics, polymers, and metals) can hardly realize broadband and spectrally selective absorption simultaneously. In this paper, a novel infrared absorbing composite SiAlON is proposed and successfully fabricated by co-sputtering Si 3 N 4 and AlN. Its wide-band absorption characteristics across through 8 to 16 μm can be tuned simply via adjusting its deposition conditions. The corresponding optical and composition analyses confirm that the broadband features with spectral selectivity are attributed to chemical composition control and the chemical bonding state tunability. This work extends the bandwidth and improves the absorbing flexibility of single material, making a step forward to develop broadband infrared absorbers with simpler structure. [ABSTRACT FROM AUTHOR]

[Display omitted] First-principles molecular dynamics simulations were used to investigate pressure- and temperature-induced phase transitions in different TaN polymorphs. The driving forces and intermediate structures were established for the CoSn-like TaN (ε phase) to WC-type TaN (θ phase) and ε to NaCl type-TaN (δ phase) structural transformations that were observed in experiments and for the θ to hP4-194, θ to cP2-221, δ to cP2-221 and δ to tP4-129 phase transitions that were predicted in this investigation. Other possible TaN polytypes were systematically investigated and five new prospective phases were found: oP8-25, oP12-25, hP8-194, tP8-105 and tI8-109. All new structures are thermodynamically, dynamically and mechanically stable, and their formation energy is only slightly higher than that of the θ phase (by 0.014–0.032 eV/atom). The relative stability, electronic structure, chemical bonding, vibrational spectra, elastic moduli and their spatial anisotropy, Vickers hardness, fracture toughness, Debye temperature and optical properties (real and imaginary parts of the dielectric function, reflectivity spectrum) of the tantalum mononitrides mentioned above were systematically calculated and discussed. The oP12-25, tP8-105 and tI8-109 novel phases exhibit the Vickers hardness (33.1–34.2 GPa), fracture toughness (5.52–5.59 MPa m1/2) and Debye temperatures (609.7–616.1 K) that are higher compared to those of the known TaN structures. The TaN polytypes with the strong Ta-N bonds with minimal fraction of ionicity were found to possess the best mechanical properties. Further experimental investigations are highly desirable to confirm the results presented in this paper. [ABSTRACT FROM AUTHOR]

The aerospace industry uses aluminum alloys which have a good strength-to-weight ratio, but they have poor corrosion resistance. Additionally, in some cases the aluminum surface may need to be exposed to the adhesive and attached to other equipment. Therefore, it is necessary to have a coating with both adhesive bonding and corrosion resistance. Most effectively, anodized coatings are used to achieve these goals. Oxides made by anodizing are porous and can improve the adhesive bonding of surfaces due to their porous structure. Anodizing is done by using various electrolytes and processes that affect adhesive bonding and adhesion strength dramatically. In this paper, we describe methods to assess the adhesive bonding of anodized surfaces. The evaluation methods are divided into two categories. Chemical analysis is performed on anodized surfaces in the first category, and in the second category, mechanical interlocking is evaluated. [ABSTRACT FROM AUTHOR]

The chemical bonding is usually not avoidable at a welding or fusion interface and sometimes is desirable to enhance the mechanical strength, while it might strongly affect the thermal contact resistance which plays a critical role in hindering heat dissipation of electronic devices. In this paper, we employ a non-equilibrium molecular dynamics method to study the effect of chemical bonding on the thermal contact resistance. Results show that the chemical bonding can greatly affect the thermal contact resistance. With the increase of the chemical bonding ratios, the thermal contact resistance firstly drops dramatically until arrives at a bonding ratio of about 20% where the thermal contact resistance is only about 15% that with a bonding ratio of 0%, and then gradually decreases to 0. Analyzing the spectral energy density of phonons at the interface, we conclude that the increase of the phonon velocity should be responsible for the decrease of the thermal contact resistance. By simulating the thermal contact resistance of silica with different morphologies (crystalline or amorphous silica), we found that different morphologies could lead to different thermal contact resistances, although this difference is less than 6%. This study is expected to provide references for managing thermal transport at a welding or fusion interface. [ABSTRACT FROM AUTHOR]

This paper reports on the results of comparative investigations of Si-C-N films prepared by using both plasma enhanced chemical vapor deposition (PECVD) and DC magnetron sputtering (MS) at different nitrogen flow rates (F N2 ). The films were characterized by an atomic force microscope, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, nanoindentation and photoluminescence spectroscopy. All the deposited films were X-ray amorphous. For the PECVD films, nanohardness (H) and elastic module (E) increase with F N2 , which can be assigned to decreasing the hydrogen content. On the contrary, for the films, deposited by magnetron sputtering, the values of H and E decrease, when F N2 increases. The latter is supposed to be due to decreasing a number of strong Si-C bonds and to increasing a number of weak Si N and C N bonds. The surface roughness of two types of the films is smaller compared to that of silicon substrates. An increase in nitrogen flow rate causes the smoothing of the film surfaces. The PECVD films deposited at high F N2 exhibit bright photoemission with the main peak at ∼440 nm. The intensity of this peak increases with increasing nitrogen content. [ABSTRACT FROM AUTHOR]

[Display omitted] • The bicapped pentagonal prism and icosahedral geometry were found. • The species exhibit high stabilities, especially for closed-shell anionic clusters. • The enhanced stability of clusters can be explained by spherical aromaticity. • The delocalized bondings (4c-2e) are important in the clusters revealed by AdNDP. • The Au@Sn 12 cluster possesses the largest AEA value (3.00 eV). Group-14 (Ge, Sn, Pb) clusters have attracted a lot of attention not only because of their unique structural models but also the outstanding building blocks as cluster-assembled materials. In this paper, we have systematically investigated the structure, chemical stability, electronic property, spherical aromaticity, and bonding of neutral Au@X 12 (X = Ge, Sn, Pb) clusters and their anions using density-functional theory (DFT) calculations. It is found that the Au@Ge 12 cluster displays bicapped pentagonal prism geometry, whereas Au@X 12 (X = Sn, Pb) possess the perfect icosahedral geometry. Analysis of binding energy reveals that the species exhibit high chemical stabilities, especially for closed-shell anionic clusters, which contain 60 valence electrons. The hybridization between cage and Au enhances the chemical stability of clusters, while the enhanced stability can be explained by spherical aromaticity, confirmed by largely negative NICS values, of which eight π electrons satisfy 2(N + 1)2 counting rule, forming 2S22P6 set. The AdNDP analysis reveals that the delocalized chemical bonding is responsible for structural stabilization of clusters, e.g., eight delocalized 4c-2e σ-bonds on inner shell and five delocalized 4c-2e σ-bonds on outer shell. To summarize, the calculated results will provide further understanding for the design of novel building blocks as cluster-assembled nanomaterials. [ABSTRACT FROM AUTHOR]

[Display omitted] • A direct Z-scheme heterojunction of NU/CC was fabricated for CO 2 photoreduction. • The heterojunction of NH 2 -UiO-66/CeCO 3 OH was featured with O-Zr-CO 3 2- bond. • The rate of electron consumption of NU/CC is 152.8 μmol/g h, 5-fold of that of NU. NH 2 -UiO-66 is recently regarded as a potential photocatalyst for CO 2 reduction reaction due to the high CO 2 adsorption capacity, high UV–vis light absorption capacity and chemical stability. Aiming to further improve its activity, in this paper, a composite of NH 2 -UiO-66 and CeCO 3 OH (NU/CC) was fabricated via an in-situ growth method of NH 2 -UiO-66 on CeCO 3 OH. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) characterizations indicated that a direct Z-scheme heterojunction between CeCO 3 OH and NH 2 -UiO-66 was formed via the formation of O-Zr-CO 3 2- bond. The CO 2 adsorption measurement, UV–vis DRS spectra and photo(electro)chemical measurements indicated that the optimal composite NU/CC-1.6–90 exhibited the higher CO 2 adsorption capacity, stronger respond and wider absorption range to UV–vis light, as well as the significantly delayed recombination of photogenerated electron-hole pairs, compared with other control samples. As a result, NU/CC-1.6–90 delivered the obviously enhanced photocatalytic activity of CO 2 to both CO and CH 4 , and the rate of electron consumption reached 152.8 μmol/g h, 5-fold of that of NH 2 -UiO-66. [ABSTRACT FROM AUTHOR]

• High-temperature non-Arrhenius dynamical crossover is probed in a Au-based metallic glass melt by nuclear magnetic resonance. • The dynamical crossover temperature is about 2.3 times of the glass-transition temperature. • The tendency to form covalent bonds become increasingly strong below the crossover temperature. • The emergence of strong covalent bonds may be responsible for such a non-Arrhenius behavior by promoting the spatial connectivity of energetically preferred short-range clusters. The structure and dynamics of melts have critical influence on the glass formation and solidification of crystals, which attracts broad interest to clarify the underlying mechanisms. In this paper, the quadrupolar spin-lattice relaxation rates of 63Cu and 65Cu nuclei in a Au 50 Cu 25.5 Ag 7.5 Si 17 metallic glass melt are studied by using a home-designed high-precision high-temperature NMR equipment. The relaxation rates follow the Arrhenius behavior at high temperatures above 870 K, but become non-Arrhenius at low temperatures, which indicates a non-Arrhenius dynamical crossover. The crossover temperature T A is about 2.3 times of the glass-transition temperature (T g =378 K). Based on the analysis of Knight shift and magnetic relaxation rates, Cu and Si atoms are found to tend to form stronger covalent-like bonds below T A. Such an increase in bonding strength may promote the connectivity of energetically preferred short-range clusters, which is responsible for the observed sluggish dynamics. [ABSTRACT FROM AUTHOR]

• The electrostatic interaction dominant bonding mechanism for uranyl-ligand, with some covalent bonding character. • The equatorial σ-type orbital interactions between U 5 f 6 d 7 s AOs and O, N, S- n p AOs result in substantial covalency. • The binding ability of [AmO 2 ]2+ to both ligands of PDA and PDTA is stronger than that of [UO 2 ]2+. • The large orbital interactions in [AmO 2 ]2+ complexes arise from significant participant of Am 5 f in chemical bonding. In this paper, we studied the electronic structure and chemical bonding in a series tridentate ligand-actinyl complexes, [AnO 2 (L) 2 ]2+ (An: U and Am; L: pyridine-2,6-dicarboxamide (PDA), pyridine-2,6-dicarboxthioamide (PDTA) and furan-2,6-dicarboxamide (FDA)) via using relativistic density functional theory. According to the calculation results, it is found that the actinyl is coordinated by two ligands via six donor atoms with the formation of a 1:2 complex. Among these thermodynamic achievable complexes, the [UO 2 (PDA) 2 ]2+ species generally show the largest thermal stability, and differences in stability mainly arise from differences in the valence shell levels of the donor atoms. The main U − Ligand bonding character in uranyl complexes favors electrostatic interaction over orbital interaction. We subsequently assessed the bonding difference of uranium and americium in [AnO 2 (L) 2 ]2+ (L: PDA and PDTA), finding out that binding ability of [AmO 2 ]2+ to both ligands of PDA and PDTA is stronger than that of [UO 2 ]2+, due to the larger orbital interactions in [AmO 2 (L) 2 ]2+ complexes, which arises from significant participant of Am 5 f in chemical bonding. This finding provides a fundamentally qualitative understanding of bonding nature in actinyl complexes and could provide some guidelines when selection of ligands for the best complexation behaviors toward actinyl. [ABSTRACT FROM AUTHOR]

Abstract: Developments in the application of quantum mechanics to the understanding of the chemical bond are traced with a view to examining the evolving conception of the covalent bond. Beginning with the first quantum mechanical resolution of the apparent paradox in Lewis’s conception of a shared electron pair bond by Heitler and London, the ensuing account takes up the challenge molecular orbital theory seemed to pose to the classical conception of the bond. We will see that the threat of delocalisation can be overstated, although it is questionable whether this should be seen as reinstating the issue of the existence of the chemical bond. More salient are some recent developments in a longstanding discussion of how to understand the causal aspects of the bonding interaction—the nature of the force involved in the covalent link—which are taken up in the latter part of the paper. [Copyright &y& Elsevier]

Highlights: [•] The stability and elastic constants of carbides are studied by first principles. [•] The rules of modulus of MC compounds are discussed by their group. [•] The hardness of carbides is estimated in this paper at the first time. [ABSTRACT FROM AUTHOR]

Abstract: This work was motivated by the desire to improve the long-term durability of E-glass/Hysol 9394 epoxy/Al-6XN stainless steel joints whose fracture energy in a previous study was shown to fall from ∼950J/m2 (ambient) to a mere ∼88J/m2 after only two days of exposure to a 90%RH, 50°C environment. This paper reports a new polyurea chemistry to bond the E-glass and steel sections with very promising results. The fracture energy under ambient condition was measured to be 1232±15J/m2 using a double cantilever beam experiment. This value degraded by only 13% to 1070±35J/m2 in samples that were conditioned for 30days at 90%RH and 50°C. The failure in all samples was cohesive, within the first ply of the E-glass composite that neighbored the polyurea interface. The intrinsic fracture energy measurements, devoid of inelastic effects, were also carried out by submerging samples in a liquid nitrogen bath. Values of 590±25J/m2 were obtained, which can be used by the designers to set the local failure condition in design simulations of large-scale structures. [Copyright &y& Elsevier]

Abstract: Finding an alternative way to fabricate higher performance and more cost effective diamond tools can revolutionize tooling industry. Laser cladding due to its unique features such as low interaction time and high cooling rate can be a better alternative. In this paper the deposition of metal matrix diamond composite on mild steel substrate is investigated. Pre-mixed powders of copper, tin, titanium, and diamond with the weight ratio of 54%, 13.5%, 7.5%, and 25%, respectively, were deposited on mild steel substrates by the use of pre-placed laser cladding using a continuous wave and a pulsed laser. The effect of scanning speed and laser power on the clad–substrate bonding, porosity and micro-cracks in the deposit, diamond graphitization, chemical bondings between diamond particles and the matrix, and distribution of diamond particles are discussed. Development of an interfacial layer between diamond particles and the matrix was detected. The layer was characterized as titanium carbide by the use of EDS analysis and nanoindentation. The effects of scanning speed and laser power on the thickness of the titanium carbide layer are discussed. Results of deposition by a continuous wave laser are compared with those of a pulsed laser and it is concluded that with the same laser power and scanning speed, the deposit by the pulsed laser had a slightly lower diamond graphitization and thinner TiC layers. [Copyright &y& Elsevier]

This paper aims to determine the effect of conceptual change texts accompanied with computer animations on 11th grade students’ understanding and alternative conceptions related to chemical bonding. One experimental group (EG; N =28) and one comparison group (CG; N =30) were used in the study. While the comparison group taught traditional instruction, the experimental group received conceptual change text accompanied with computer animations instruction. Chemical bonding achievement test was applied as pre-test, post-test and delayed test to collect data. The results of the study indicated that while there is no statistically significant difference between groups in pre-test, performance of EG students is greater than the CG ones in post-test and delayed test. And also, the EG students are better in remediating their alternative conceptions related to chemical bonding. Based on the study, it is concluded that conceptual change texts combined with computer animations can be effective instructional tools to improve students’ conceptual understanding of chemical concepts. [Copyright &y& Elsevier]

Abstract: We show in this paper by using quantum chemical methods how added hydrogen to cyclic triborane forms a 3c–2e bond to two boron atoms. Attached ammonia renders the storaged hydrogen more easily detached. The optimization of the structures were carried out at the MP2/6-311++G∗∗ level of theory and the bonding properties were then analyzed by topological methods applied to charge density as well as by the methods based upon natural bonding orbital theory. [Copyright &y& Elsevier]

This paper reports the microstructure of LiXPO4 (X=Ni, Co, Mn) materials prepared by solid state chemical reaction. The variation in microstructure of these phospho-olivines is mainly due to a difference in the XO6 cationic octahedral environment, which is discussed using a molecular vibration model to elucidate the bonding between various structural units. A direct relationship is established between the vibrational frequencies and the second ionisation potential of the metal (X) in LiXPO4. [Copyright &y& Elsevier]

Abstract: The paper is a review of some cathode materials used in lithium batteries. A correlation between chemical bonding, electronic structure, and electrochemical properties of the cathode materials LixMaXb (M=transition metal; X=O, S) has been demonstrated. [Copyright &y& Elsevier]