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Both n- and p-type ohmic contact to MoS2 can be obtained via different CuS surfaces, due to the weak metallicity and large work function variation of the CuS surfaces, and due to interface quasi-bonding between CuS and MoS2.

InSb-based materials are promising thermoelectric (TE) alternatives at medium temperature with the high power factor (PF) derived from the intrinsically ultra-high mobility (104–105 cm2 V−1 s−1). N-type InSb-based TE materials have been studied extensively due to the intrinsic Sb vacancies originating from the low formation energy. Based on that π-type TE devices are in favor of P-, N-legs with similar thermal expansivity, P-type InSb-based materials are highly desired. Herein, P-type InSb is synthesized by adjusting the Fermi energy via performing Cd doping. The PF reaches up to ~1.91 × 10−3 W m−1 K−2 at 723 K due to the increased electrical conductivity and inhibited bipolar diffusion effect caused by the high carrier concentration. Furthermore, the lattice thermoelectric conductivity is reduced to 2.0 W m−1 K−1 at 723 K on account of intensive phonon scattering and suppressed bipolar diffusion effect. Finally, benefiting from the simultaneous optimization of the electrical and thermal properties, the optimized figure of merit (zT) value of 0.40 (increased by ~7.0 times) at 723 K was achieved in P-type Cd0.07In0.93Sb, which is comparable with most N-type InSb-based materials. This study could be significant to develop cognate thermostable TE devices using the P-type InSb counterparts.

SnTe has received considerable attention as an environmentally friendly alternative to the representative thermoelectric material of PbTe. However, excessive hole carrier concentration in SnTe results in an extremely low Seebeck coefficient and high thermal conductivity, which makes it exhibit relatively inferior thermoelectric properties. In this work, the thermoelectric performance of p-type SnTe is enhanced through regulating its energy band structures and reducing its electronic thermal conductivity by combining Bi doping with CdSe alloying. First, the carrier concentration of SnTe is successfully suppressed via Bi doping, which significantly decreases the electronic thermal conductivity. Then, the convergence and flattening of the valence band by alloying CdSe effectively improves the effective mass of SnTe while restraining its carrier mobility. Consequently, the electronic thermal conductivity is markedly reduced. Finally, a maximum ZT of ~ 0.87 at 823 K and an average ZT of ~ 0.51 at 300-823 K have been achieved in Sn0.96Bi0.04Te-5%CdSe. Our results indicate that decreasing the electronic thermal conductivity is an effective means of improving the performance of thermoelectric materials with a high carrier concentration.

Ligand-induced chirality in semiconducting nanocrystals has been the subject of extensive study in the past few years and shows potential applications in optics and biology. Yet, the origin of the chiroptical effect in semiconductor nanoparticles is still not fully understood. Here, we examine the effect of the interaction with amino acids on both the fluorescence and the optical activity of chiral semiconductor quantum dots (QDs). A significant fluorescence enhancement is observed for l/d-Cys-CdTe QDs upon interaction with all the tested amino acids, indicating suppression of nonradiative pathways as well as the passivation of surface trap sites brought via the interaction of the amino group with the CdTe QDs’ surface. Heterochiral amino acids are shown to weaken the circular dichroism (CD) signal, which may be attributed to a different binding configuration of cysteine molecules on the QDs’ surface. Furthermore, a red shift of both CD and fluorescence signals in l/d-Cys-CdTe QDs is only observed upon adding cysteine, while other tested amino acids do not exhibit such an effect. We speculate that the thiol group induces orbital hybridization of the highest occupied molecular orbital (HOMOs) of cysteine and the valence band of CdTe QDs, leading to the decrease of the energy band gap and a concomitant red shift of CD and fluorescence spectra. This is further verified by density functional theory calculations. Both the experimental and theoretical findings indicate that the addition of ligands that do not “directly” interact with the valence band (VB) of the QD (noncysteine moieties) changes the QD photophysical properties, as it probably modifies the way cysteine is bound to the surface. Hence, we conclude that it is not only the chemistry of the amino acid ligand that affects both CD and PL but also the exact geometry of binding that modifies these properties. Understanding the relationship between the QD’s surface and chiral amino acid thus provides an additional perspective on the fundamental origin of induced chiroptical effects in semiconductor nanoparticles, potentially enabling us to optimize the design of chiral semiconductor QDs for chiroptic applications.

The phase transitions among polymorphic two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted increasing attention for their potential in enabling distinct functionalities in the same material for making integrated devices. Electron-injection to TMDs has been proved to be a feasible way to drive structural phase transition from the semiconducting H-phase to the semimetal dT-phase. In this contribution, based on density-functional theory (DFT) calculations, firstly we demonstrate that hole-injection drives the transition of the H-phase more efficiently to the metallic T-phase than to the semimetallic dT-phase for group VI-B TMDs (MoS2, WS2, and MoSe2, etc.). The origin can be attributed to the smaller work function of the T-phase than that of the dT-phase. Our work function analysis can distinguish the T and dT phases quantitatively while it is challenging for the commonly used crystal field splitting analysis. In addition, our analysis provides a unified understanding for both hole- and electron-injection induced phase transitions for 2D materials beyond TMDs, such as the newly synthesized MoSi2N4 family. Moreover, the hole-driven T-phase transition mechanism can explain the recent experiment of WS2 phase transition by hole-doping with yttrium (Y) atoms. Using 1/3 Y-doped WS2 and MoSe2 as examples, we show that the Mo and W valency increases to 5+. These above findings open up an avenue to obtain the metallic T-phase, which expands the possible stable phases of 2D materials.

Recent studies have revealed that the interlayer interaction in two-dimensional (2D) layered materials is not simply of van der Waals character but could coexist with quasi-bonding character. Herein, we classify the interlayer quasi-bonding interactions into two main categories (I: homo-occupancy interaction; II: hetero-occupancy interaction) according to the occupancy of the involved energy bands near the Fermi level. We then investigate the quasi-bonding-interaction-induced band structure evolution of several representative 2D materials based on density functional theory calculations. Further calculations confirm that this classification is applicable to generic 2D layered materials and provide a unified understanding of the total strength of interlayer interaction, which is a synergetic effect of the van der Waals attraction and the quasi-bonding interaction. The latter is stabilizing in main category II and destabilizing in main category I. Thus, the total interlayer interaction strength is relatively stronger in category II and weaker in category I.

Iterative initial value of cable force based on influence matrix and linear programming is determined in order to study the cable force of long-span concrete-filled steel tube (CFST) arch b...

The electronic and optical properties of hybrid perovskites CH3NH3SnX3 (X = Br, I) are investigated by first-principles calculations. Our results show that consideration of the weak van der Waals interactions is important for theoretical investigations of Sn-based hybrid materials. During light harvesting, the electron transition will occur between the p states of halogen at the valence band maximum (VBM) and the Sn 5p states at the conduction band minimum (CBM). Comparing with the energy distribution of solar spectra, CH3NH3SnI3 has better absorption characteristics in the visible region than CH3NH3PbI3, which shows promising prospects in realizing lead-free, highly efficient solar cells.

Compression properties and deformation modes of closed-cell foam are investigated at different impact velocity. The contrast of deformation modes indicates that both uniform and negative graded foam have quasi-static mode, transitional mode and impact mode. On the contrary, the positive graded foam only has one mode; the local deformation propagates from impact end towards supported end.

A gate electrode is usually used to controllably tune the carrier concentrations, further modulating the electrical conductivity and the Seebeck coefficient to obtain the optimum thermoelectric figure of merit (ZT) in two-dimensional materials. On the other hand, it is necessary to investigate how an electric field induced by a gate voltage affects the electronic structures, further determining the thermoelectric properties. Therefore, by using density functional calculations in combination with Boltzmann theory, the thermoelectric properties of bilayer MX

Calculating the local stress for the anchorage zone of each part in the tooth plate by establishing two kinds of finite element model: considering concrete effect and not considering concrete effect. The result of the comparative analysis of the two models shows that the local stress considering the concrete effect is smaller than that not considering the concrete effect and the maximum difference is about 170 MPa. The difference is not the same in different parts of the tooth plate. Although the design will be tend to be safe for not considering the concrete effect, the size of the tooth plate may increase. Therefore, in order to reduce the weight of the tooth plate , the concrete effect should be taken into consideration in the design.

We study an inhomogeneous three-orbital Hubbard model for the Cu-substituted iron pnictides using an extended real-space Green's function method combined with density functional calculations. We find that the onsite interactions of the Cu ions are the principal determinant of whether an electron dopant or a hole dopant is caused by the Cu substitution. It is found that the Cu substitution could lead to a hole doping when its onsite interactions are smaller than a critical value, as opposed to an electron doping when the interactions of Cu ions are larger than the critical value, which may explain why the effects of Cu substitution on the carrier density are entirely different in NaFe$_{1-x}$Cu$_x$As and Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$. We also find that the effect of a doping-induced disorder is considerable in the Cu-substituted iron pnictides, and its cooperative effect with electron correlations contributes to the orbital-selective insulating phases in NaFe$_{1-x}$Cu$_x$As and Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$., Comment: 13 pages, 11 figures

The electronic structure of heavy fermion superconductor CeMIn5 (M=Co,Rh,Ir) is studied by density functional theory. Our results indicate that the MIn2 layer plays an important role for stabilizing the layered crystal structure and determining the antiferromagnetic or paramagnetic ground state in this series. When the strong correlation effects of 4f electrons beyond the local density approximation (LDA) are taken into account by the LDA+U approach, the calculated total magnetic moment and band structure of CeRhIn5 yield a good agreement with the experiment. The LDA+U calculation shows that the 4f electrons in this series are located on the border between localization and itineracy.

20 mg/L nonylphenol solution was ozonized. The removal efficiency and the intermediate products were studied during the ozonation of nonylphenol, the possible reaction mechanism of the ozonation of nonylphenol was proposed. The experimental results indicate that there are two kinds of ozonation patterns, the oxidation by molecule O3 alone and by O3/*OH. Both ozonation patterns can remove nonylphenol completely within 18 minutes. However, the combined oxidation can remove 96% of the initial nonylphenol within 4 minutes, and it took 12 minutes in the single O3 molecule oxidation system. The formaldehyde was detected during the ozonation of nonylphenol. The concentration reached stability after 8 minutes during the oxidation by single O3 and gradually increased during the combined oxidation process.

ZnO quantum dots (QDs) with blue emission were synthesized by a sol–gel method. A series of control experiments were conducted to explore the origin of the blue emission. It is found that the blue emission arises from neither the quantum confinement nor intermediate products, and it can be achieved only in the presence of Li+ cations and excessive OH− anions. Moreover, the long decay time of the blue emission suggests a defect-related de-excitation process. On the basis of the experimental and calculation results, possible de-excitation paths for light emission were discussed, and the origin of the blue emission was determined as the electron transition from the conduction band to interstitial oxygen defects. Excessive OH− anions are responsible for the formation of interstitial oxygen defects, and Li+ ions can stabilize the defects by substituting for Zn atoms. Besides, Li+ ions can block the growth of ZnO QDs, broaden their band gap and cause a blue shift of the blue emission.

First-principles calculations were performed to investigate the pressure induced phase transition in SrRuO3 and to compare electronic structures and magnetism of A RuO3 (A= Ca, Sr, and Ba). By combining with the substitutions of Ca(Ba) for Sr in SrRuO3, ferromagnetism evolutions and its origin in A RuO3 are caused by the structural transition induced by the A2+ ionic size. On the (Sr,Ba)RuO3 side, the band broadening induced the decrease of electron–electron exchange interaction is a main reason, while on the (Sr and Ca) RuO3 side, spin–orbital coupling effect and magnetic instability suppress the ferromagnetism.

The electronic structures and magnetic properties induced by the substitution of Mg in MgCNi3 were investigated by performing the first-principles density functional calculations. It is confirmed that AlCNi3, GaCNi3, and InCNi3 are paramagnetic nonsuperconductors resulting from total energy, density of states at Fermi level, and electron-phonon coupling constant. A large peak of density of states lies on the Fermi level, resulting in ferromagnetism rather than superconductivity in NaCNi3. The substitution of dual elements for Mg, such as Al0.5Na0.5CNi3 and Al0.5Li0.5CNi3, was inspected too. Evaluating the electron-phonon coupling interaction, the possible superconductivity exists in near ferromagnetic Al0.5Na0.5CNi3.

The band structure, Fermi surface, and generalized susceptibility χ(q) in the constant-matrix-element approximation for the heavy fermion series CeIn3, CeMIn5(M=Co,Rh,Ir), and PuCoGa5 are studied by density functional calculations to address the relationship among superconductivity, magnetism, and Fermi surface nesting in these compounds. Within the scenario of magnetically mediated d wave superconductivity, our results indicate that the behavior of χ(q) of the Ce class materials favors superconductivity if 4f electrons are treated as core states, since it exhibits broad plateaus with large magnitude around q=(0.5,0.5,0) and (0.5, 0.5, 0.5). In contrast, when the 5f electrons are treated as valence electrons, the χ(q) of PuCoGa5 exhibits a very sharp peak at q=(0.5,0.5,0) due to the strong nesting of hole and electron Fermi surface from the 16th and 17th bands. Not only the large spin fluctuation energy but also the strong nesting of Fermi surface in PuCoGa5 may contribute to the much higher Tc than that ...

The effects on the electronic structure and magnetic property of the Ni site substitution in nonoxide perovskite superconductor MgCNi3 are studied by using density functional calculations. A sharp high peak of Ni d density of states just lies below the Fermi energy in pure MgCNi3. Co-doping results in the onset of ferromagnetism at x=0.083. However, the little energy gain as well as small magnetic moment per atom indicate the weak itinerant ferromagnetism. The strong ferromagnetic spin fluctuation in MgCNi3−xCox leads to quench bulk superconductivity, while the Mn atom forms a local magnetic moment of 1.06 μB at x=0.042 which suppresses superconductivity more seriously than Co does in the low doping case. Cu doping can be well accounted for by the rigid band model, which reduces the density of states at the Fermi level and the Tc.