First-principles studies on the electronic and contact properties of monolayer Ga2STe-metal contacts.

Monolayer (ML) Janus III-VI compounds have attracted the use of multiple competitive platforms for future-generation functional electronics, including non-volatile memories, field effect transistors, and sensors. In this work, the electronic and interfacial properties of ML Ga2STe-metal (Au, Ag, Cu, and Al) contacts are systematically investigated using first-principles calculations combined with the non-equilibrium Green's function method. The ML Ga2STe-Au/Ag/Al contacts exhibit weak electronic orbital hybridization at the interface, while the ML Ga2STe-Cu contact exhibits strong electronic orbital hybridization. The Te surface is more conducive to electron injection than the S surface in ML Ga2STe-metal contact. Quantum transport calculations revealed that when the Te side of the ML Ga2STe is in contact with Au, Ag and Cu electrodes, p-type Schottky contacts are formed. When in contact with the Al electrode, an n-type Schottky contact is formed with an electron SBH of 0.079 eV. When the S side of ML Ga2STe is in contact with Au and Al electrodes, p-type Schottky contacts are formed, and when it is in contact with Ag and Cu electrodes, n-type Schottky contacts are formed. Our study will guide the selection of appropriate metal electrodes for constructing ML Ga2STe devices.

Optimizing ultrashort pulse in fiber laser based on artificial intelligence algorithm.

Ultrashort pulses, characterized by their short pulse duration, diverse spectral content, and high peak power, are widely used in fields including laser processing, optical storage, biomedical sciences, and laser imaging. The complex, highly-nonlinear process of ultrashort pulse evolution within fiber lasers is influenced by numerous aspects such as dispersion, loss, gain, and nonlinear effects. Traditionally, the split-step Fourier transforms method is employed for simulating ultrashort pulses in fiber lasers, which involves traversing multiple parameters within the fiber to attain the pulse's optimal state. The simulation is a significantly time-consuming process. Here, we use a neural network model to fit and predict the impact of multiple parameters on the pulse characteristics within fiber lasers, enabling parameter optimization through genetic algorithms to determine the optimal pulse duration, pulse energy, and peak power. Integrating artificial intelligence algorithms simplifies the acquisition of optimal pulse parameters and enhances our understanding of multiple parameters' impact on the pulse characteristics. The investigation of ultrashort pulse optimization based on artificial intelligence holds immense potential for laser design.

Mutations influence the conformational dynamics of the GDP/KRAS complex.

Mutations near allosteric sites can have a significant impact on the function of KRAS. Three specific mutations, K104Q, G12D/K104Q, and G12D/G75A, which are located near allosteric positions, were selected to investigate the molecular mechanisms behind mutation-induced influences on the activity of KRAS. Gaussian accelerated molecular dynamics (GaMD) simulations followed by the principal component analysis (PCA) were performed to improve the sampling of conformational states. The results revealed that these mutations significantly alter the structural flexibility, correlated motions, and dynamic behavior of the switch regions that are essential for KRAS binding to effectors or regulators. Furthermore, the mutations have a significant impact on the hydrogen bonding interactions between GDP and the switch regions, as well as on the electrostatic interactions of magnesium ions (Mg2+) with these regions. Our results verified that these mutations strongly influence the binding of KRAS to its effectors or regulators and allosterically regulate the activity. We believe that this work can provide valuable theoretical insights into a deeper understanding of KRAS function.Communicated by Ramaswamy H. Sarma.

Interfacial electronic states and self-formed asymmetric Schottky contacts in polar α-In2Se3/Au contacts.

In recent years, the two-dimensional (2D) semiconductor α-In2Se3 has great potential for applications in the fields of electronics and optoelectronics due to its spontaneous iron electrolysis properties. Through ab initio electronic structure calculations and quantum transport simulations, the interface properties and transport properties of α-In2Se3/Au contacts with different polarization directions are studied, and a two-dimensional α-In2Se3 asymmetric metal contact design is proposed. When α-In2Se3 is polarized upward, it forms an n-type Schottky contact with Au. While when α-In2Se3 is polarized downward, it forms a p-type Schottky contact with Au. More importantly, significant rectification effect is found in the asymmetric Au/α-In2Se3/Au field-effect transistor. The carrier transports under positive and negative bias voltages are found to be dominated by thermionic excitation and tunneling, respectively. These findings provide guidance for the further design of 2D α-In2Se3-based transistors.

Theoretical screening of a graphyne-supported transition metal single-atom catalyst for the N2 reduction reaction.

The electrocatalytic nitrogen reduction reaction (NRR) is a promising technology for the synthesis of NH3 in an ambient environment. However, developing low-cost and high-efficiency electrocatalysts still remains a long-standing challenge. In this work, density function theory (DFT) calculations are done to systematically investigate the NRR catalytic activity of transition metals (TM = Sc-Cu, Y-Ag, and Hf-Au) supported on monolayer graphyne (GY). TM@GY (TM = Sc, V, Mn, Y, Tc, and Os) with excellent NRR performance are demonstrated. The mixed pathway is the most favorable for Sc, V, Y, and Os@GY with the potentials of -0.37, -0.27, -0.40, and -0.36 V, respectively, while the distal reaction pathway is most favorable for Mn and Tc@GY with the potentials of -0.37 and -0.42 V. Most strikingly, Mn, Tc, and Os@GY exhibit high NRR selectivity. This work provides a screening scheme for exploring highly efficient electrocatalysts for the electrochemical NRR under ambient conditions.

Optical reflection characteristic-based emissivity analysis of a pyramid array flat-plate blackbody for remote sensor calibration.

The flat-plate blackbody (FPB) is the core device in infrared remote sensing radiometric calibration for providing accurate infrared radiation energy. The emissivity of an FPB is an important parameter that directly affects calibration accuracy. This paper uses a pyramid array structure based on the regulated optical reflection characteristics to analyze the FPB's emissivity quantitatively. The analysis is accomplished by performing emissivity simulations based on the Monte Carlo method. The effects of specular reflection (SR), near-specular reflection (NSR), and diffuse reflection (DR) on the emissivity of an FPB with pyramid arrays are analyzed. In addition, various patterns of normal emissivity, small-angle directional emissivity, and emissivity uniformity are examined under different reflection characteristics. Further, the blackbodies with the NSR and DR are fabricated and tested experimentally. The experimental results show a good agreement with the corresponding simulation results. The emissivity of the FPB with the NSR can reach 0.996 in the 8-14 µm waveband. Finally, the emissivity uniformity of FPB samples at all tested positions and angles is better than 0.005 and 0.002, respectively. The standard uncertainty of experimental measurement of waveband emissivity and spectral emissivity are 0.47% and 0.38% respectively, and the simulation uncertainty is 0.10%.

First-principles study on electronic states of In2Se3/Au heterostructure controlled by strain engineering.

The development of low-dimensional multifunctional devices has become increasingly important as the size of field-effect transistors decreases. In recent years, the two-dimensional (2D) semiconductor In2Se3 has emerged as a promising candidate for applications in the fields of electronics and optoelectronics owing to its remarkable spontaneous polarization properties. Through first-principles calculations, the effects of the polarization direction and biaxial tensile strain on the electronic and contact properties of In2Se3/Au heterostructures are investigated. The contact type of In2Se3/Au heterostructures depends on the polarization direction of In2Se3. The more charge transfers from the metal to the space charge region, the biaxial tensile strain increases. Moreover, the upward polarized In2Se3 in contact with Au maintains a constant n-type Schottky contact as the biaxial tensile strain increases, with a barrier height Φ SB,n of only 0.086 eV at 6% strain, which is close to ohmic contact. On the other hand, the downward polarized In2Se3 in contact with Au can be transformed from p-type to n-type by applying a biaxial tensile strain. Our calculation results can provide a reference for the design and fabrication of In2Se3-based field effect transistors.

TEM Investigation of Asymmetric Deposition-Driven Crystalline-to-Amorphous Transition in Silicon Nanowires.

Controlling the shape and internal strain of nanowires (NWs) is critical for their safe and reliable use and for the exploration of novel functionalities of nanodevices. In this work, transmission electron microscopy was employed to examine bent Si NWs prepared by asymmetric electron-beam evaporation. The asymmetric deposition of Cr caused the formation of nanosized amorphous-Si domains; the non-crystallinity of the Si NWs was controlled by the bending radius. No other intermediate crystalline phase was present during the crystalline-to-amorphous transition, indicating a direct phase transition from the original crystalline phase to the amorphous phase. Moreover, amorphous microstructures caused by compressive stress, such as amorphous Cr domains and boxes, were also observed in the asymmetric Cr layer used to induce bending, and the local non-crystallinity of Cr was lower than that of Si under the same bending radius.

First principles studies on the electronic and contact properties of single layer 2H-MoS2/1T'-MX2 heterojunctions.

Constructed via in-plane heterojunction contacts between the semiconducting 2H phase (as the channel) and the metallic 1T' phase (as the electrode), two-dimensional (2D) transition metal dichalcogenide (TMD) field-effect transistors (FETs) have received much recent attention because they significantly reduce contact resistance. In this paper, ab initio quantum transport simulation is done to study and predict the electronic states and contact properties of the 2H-MoS2/1T'-MX2 (WS2, TaSe2, NbSe2, MoSe2, TaS2, and NbS2) in-plane heterojunctions. It is found that the interfacial states are not obvious and the fluctuation of the average electron density at the 1T'/2H phase boundary is small for all 2H-MoS2/1T'-MX2 heterojunctions. The average electrostatic potential differences (ΔV) are all negative, which is beneficial to promote the charge transfer from 1T'-MX2 to 2H-MoS2. Moreover, the p-type Schottky contact of the 2H-MoS2/1T'-MX2 heterojunctions is formed and the ΦSB,P values are 0.609 eV, 0.625 eV, 0.641 eV, 0.617 eV, 0.469 eV and 0.477 eV for 1T'-WS2, 1T'-TaSe2, 1T'-NbSe2, 1T'-MoSe2, 1T'-TaS2, and 1T'-NbS2, respectively. The results provide theoretical guidance for designing two-dimensional material devices.

The configuration effect on the exciton dynamics of zinc chlorin aggregates.

Excitonic energy transfer among the zinc chlorin molecules is significant for the photovoltaic process because of their high sensitivities to harvesting sunlight. Zinc chlorin monomers and dimers can be synthesized experimentally, and they can form various self-assembled structures. Using the realistic parameters of zinc chlorin molecules, we assume that 20 molecules with J-, H- or J-H aggregation are arranged in a line and we investigate their dipole configuration effect on exciton dynamics. The expectation value approximation of operators is applied to derive the equations of motion of multi-exciton states. The temporal evolution of multi-exciton states is analyzed in the scheme of density matrix theory. Our simulations show that the inter-molecular coupling results in an exciton band and the wave-packet progressing excited by the resonant laser pulse exhibits attractive or repulsive behavior at the exciton level due to the dipole configuration effect. In the defined J-H coupling, the coherent wave-packet cannot overcome the configuration barrier to the no-excited part. The exciton dynamics revealed here might be helpful to better understand the energy transfer process in organic photovoltaic devices.

Non-invasively improving the Schottky barrier of MoS2/metal contacts by inserting a SiC layer.

The applications of two-dimensional (2D) materials in electronics, optoelectronics, and spintronics are limited by the high contact resistance at the metal/semiconductor interface owing to the strong Fermi-level pinning. In this study, an interlayer insertion strategy is proposed to solve this problem, and first principles calculations are done to study the influences of inserting a SiC layer on the Schottky barrier and electronic properties of MoS2/metals (Mg, Al, In, Cu, Ag, Au, Pd, Ti, and Sc). The average charge value substantially increased (≥0.060 e) at the interface between SiC and MoS2 layers, and then no tunneling barrier appeared except for the MoS2/Au contact by inserting the SiC layer. Moreover, ΦSB,N almost decreases for the MoS2/metal contacts by inserting the SiC layer. When Ti, Cu, Au, and Pd are used as electrodes, the n-type Schottky barrier is formed with the ΦSB,N values of 0.479 eV, -0.073 eV, 0.498 eV, and 0.225 eV, respectively. However, if Al, In, Mg, and Ag are used as electrodes, the systems are transformed into Ohmic contact. These findings provide a practical guideline for depinning the Fermi level at contact interfaces and designing the high performance TMD-based nanoelectronic devices.

Driving interference control by side carbon chains in molecular and two-dimensional nano-constrictions.

The quantum interference effect offers a unique route to control the charge transport through nanoscale constrictions. The carbon atomic chain, which is an sp-hybridized carbon allotrope, has recently stimulated interest to construct ultimate nano-devices. Instead of using the carbon atomic chain as an electron transmitting channel interconnecting nano-components, we explore the possibility of using side carbon chains to change the phase of the transmitting electrons and influence the interference pattern of the nano-device. Interference pattern modulation is a general phenomenon which is demonstrated in a benzene molecular device, a zigzag graphene nanoribbon device and a SiC nanoribbon device. Odd-even oscillation dependence of the conductance on the length of the side carbon chain is found. Two criteria, i.e. large magnitude of the local state in the side carbon chain and proper length of the side carbon chain, must be satisfied simultaneously to achieve effective interference modulation. By carefully choosing the position and length of the side carbon chains, the transmission zero can be moved to the Fermi energy. Moreover, the transmission zero induced by destructive interference at the Fermi energy can be very robust against strain. This work provides a new possibility to construct nano-devices with carbon atomic chains.

Perfect Spin Filter in a Tailored Zigzag Graphene Nanoribbon.

Zigzag graphene nanoribbons (ZGNRs) are expected to serve as the promising component in the all-carbon spintronic device. It remains challenging to fabricate a device based on ZGNRs with high spin-filter efficiency and low experimental complexity. Using density functional theory combined with nonequilibrium Green's function technique, we studied the spin-dependent transport properties of the tailored zigzag graphene nanoribbon. A perfect spin-filtering effect is found in the tailored structure of ZGNR. The nearly 100% spin-polarized current and high magneto-resistance ratio can be obtained by applying a homogeneous magnetic field across the device. The distribution of spin up and spin down states at the bridge carbon atom plays a dominant role in the perfect spin filtering. The tailoring of ZGNR provides a new effective approach to graphene-based spintronics.