Showing papers by "Shengli Zhang published in 2020"

Tackling the Activity and Selectivity Challenges of Electrocatalysts toward the Nitrogen Reduction Reaction via Atomically Dispersed Biatom Catalysts

Abstract: Developing efficient catalysts for nitrogen fixation is becoming increasingly important but is still challenging due to the lack of robust design criteria for tackling the activity and selectivity problems, especially for electrochemical nitrogen reduction reaction (NRR). Herein, by means of large-scale density functional theory (DFT) computations, we reported a descriptor-based design principle to explore the large composition space of two-dimensional (2D) biatom catalysts (BACs), namely, metal dimers supported on 2D expanded phthalocyanine (M2-Pc or MM'-Pc), toward the NRR at the acid conditions. We sampled both homonuclear (M2-Pc) and heteronuclear (MM'-Pc) BACs and constructed the activity map of BACs by using N2H* adsorption energy as the activity descriptor, which reduces the number of promising catalyst candidates from over 900 to less than 100. This strategy allowed us to readily identify 3 homonuclear and 28 heteronuclear BACs, which could break the metal-based activity benchmark toward the efficient NRR. Particularly, using the free energy difference of H* and N2H* as a selectivity descriptor, we screened out five systems, including Ti2-Pc, V2-Pc, TiV-Pc, VCr-Pc, and VTa-Pc, which exhibit a strong capability of suppressing the competitive hydrogen evolution reaction (HER) with favorable limiting potential of -0.75, -0.39, -0.74, -0.85, and -0.47 V, respectively. This work not only broadens the possibility of discovering more efficient BACs toward N2 fixation but also provides a feasible strategy for rational design of NRR electrocatalysts and helps pave the way to fast screening and design of efficient BACs for the NRR and other electrochemical reactions.

Near-Complete Suppression of Oxygen Evolution for Photoelectrochemical H2O Oxidative H2O2 Synthesis

Abstract: Solar energy-assisted water oxidative hydrogen peroxide (H2O2) production on an anode combined with H2 production on a cathode increases the value of solar water splitting, but the challenge of the...

Advances of 2D bismuth in energy sciences.

Abstract: Since graphene has been successfully exfoliated, two-dimensional (2D) materials constitute a vibrant research field and open vast perspectives in high-performance applications. Among them, bismuthene and 2D bismuth (Bi) are unique with superior properties to fabricate state-of-the-art energy saving, storage and conversion devices. The largest experimentally determined bulk gap, even larger than those of stanene and antimonene, allows 2D Bi to be the most promising candidate to construct room-temperature topological insulators. Moreover, 2D Bi exhibits cyclability for high-performance sodium-ion batteries, and the enlarged surface together with the good electrochemical activity renders it an efficient electrocatalyst for energy conversion. Also, the air-stability of 2D Bi is better than that of silicene, germanene, phosphorene and arsenene, which could enable more practical applications. This review aims to thoroughly explore the fundamentals of 2D Bi and its improved fabrication methods, in order to further bridge gaps between theoretical predictions and experimental achievements in its energy-related applications. We begin with an introduction of the status of 2D Bi in the 2D-material family, which is followed by descriptions of its intrinsic properties along with various fabrication methods. The vast implications of 2D Bi for high-performance devices can be envisioned to add a new pillar in energy sciences. In addition, in the context of recent pioneering studies on moire superlattices of other 2D materials, we hope that the improved manipulation techniques of bismuthene, along with its unique properties, might even enable 2D Bi to play an important role in future energy-related twistronics.

Designing sub-10-nm Metal-Oxide-Semiconductor Field-Effect Transistors via Ballistic Transport and Disparate Effective Mass: The Case of Two-Dimensional Bi N

Abstract: In the post-Moore era, improving energy efficiency is an urgent requirement for microelectronics moving towards the Internet of Things, artificial intelligence, and 5G. In particular, two-dimensional (2D) materials with natural passivation, gate electrostatics, and high mobility have attracted significant attention for integrated circuits in the race towards next-generation field-effect transistors (FETs). Here, by coupling first-principles and nonequilibrium-Green's-function approaches, we obtain a physical understanding of the ballistic transport properties of a V-V binary bismuth nitride ($\mathrm{Bi}\mathrm{N}$) material. Promisingly, monolayer $\mathrm{Bi}\mathrm{N}$ has sharp conduction-band and flat valence-band edges, which exhibit disparate effective masses. Simulated sub-10-nm monolayer $\mathrm{Bi}\mathrm{N}$ transistors show potential device performance and fulfill the high-performance and low-power requirements of the goals of the International Technology Roadmap for Semiconductors 2028 with their optimal parameters. Furthermore, by comprehensively analyzing the effective mass, density of states, on-state current, subthreshold swing, etc., we show that materials whose band dispersions have an extreme character have advantages for transistors. Also, benchmarking of the energy-delay product confirms that $\mathrm{Bi}\mathrm{N}$ FETs possess sufficient competitiveness against other 2D FETs. We believe that this could be a guide for designing potential channel materials for next-generation FETs.

Two-Dimensional BAs/InTe: A Promising Tandem Solar Cell with High Power Conversion Efficiency

Abstract: Tandem solar cells (SCs) connecting two subcells with different absorption bands have the potential to reach the commercialized photovoltaic standard. However, the performance improvement of tandem architectures is still a challenge, primarily owing to the mismatch of band gaps in two subcells. Here, we demonstrate a two-dimensional (2D) BAs/InTe-based tandem SC, which could achieve solar-to-electric conversion efficiency higher than 30%. First, the narrow band gap of hexagonal single-layer BX (X = P and As) and wide band gap of single-layer YZ (Y = Ga and In, Z = S, Se, and Te) are found to have high thermodynamic stability based on density functional theory calculations. Next, considering narrow and wide band gaps at the HSE06 functional, single-layer BX/YZ-based tandem SCs are built to effectively capture a broad-band solar spectrum by combining such two subcells. Since the band gap of single-layer BAs matches well with that of the InTe monolayer, the power conversion efficiency of BAs/InTe-based tande...

Ultrascaled Double-Gate Monolayer Sn S 2 MOSFETs for High-Performance and Low-Power Applications

Abstract: The shrinking of field-effect transistors (FETs) is in great demand for next-generation integrated circuits. However, traditional silicon FETs are reaching the scaling limits, and it is therefore urgent to explore alternative paradigms. Two-dimensional (2D) materials attract great research enthusiasm, owing to their abilities to suppress short-channel effects. Herein, we evaluate the electronic properties and device performance of ultrascaled 2D ${\mathrm{Sn}\mathrm{S}}_{2}$ metal-oxide-semiconductor FETs (MOSFETs) via ab initio simulations. Specifically, the ${I}_{\mathrm{on}}$ value of the 5.5 nm monolayer ${\mathrm{Sn}\mathrm{S}}_{2}$ n-MOSFETs is ultrahigh, up to 3400 \textmu{}A/\textmu{}m, as a result of the small effective masses of the conduction-band minimum of monolayer ${\mathrm{Sn}\mathrm{S}}_{2}$. Until the channel length is scaled down to 4 nm, the MOSFETs can fulfill the standards of ${I}_{\mathrm{on}}$, delay time, and power dissipation product of the International Roadmap for Devices and Systems (IRDS) 2018 goals for high-performance devices. Moreover, the 5.5 nm monolayer ${\mathrm{Sn}\mathrm{S}}_{2}$ n-MOSFETs can also fulfill the IRDS 2018 requirements for the 2028 horizon for low-power applications. This work demonstrates that monolayer ${\mathrm{Sn}\mathrm{S}}_{2}$ is a favorable channel material for future competitive ultrascaled devices.

Structural transition, metallization, and superconductivity in quasi-two-dimensional layered Pd S 2 under compression

Abstract: Based on first-principles simulations and calculations, we explore the evolutions of crystal structure, electronic structure, and transport properties of quasi-two-dimensional layered $\mathrm{Pd}{\mathrm{S}}_{2}$ under compression by uniaxial stress and hydrostatic pressure. An interesting ferroelastic phase transition with lattice reorientation is revealed under uniaxial compressive stress, which originates from the bond reconstructions of the unusual $\mathrm{Pd}{\mathrm{S}}_{4}$ square-planar coordination. By contrast, the layered structure transforms into a three-dimensional cubic pyrite-type structure under hydrostatic pressure. In contrary to the experimentally proposed coexistence of layered $\mathrm{Pd}{\mathrm{S}}_{2}$-type structure with cubic pyrite-type structure at intermediate pressure range, we predict that the compression-induced intermediate phase will show the same structure symmetry as the ambient phase, except for sharply shrinking interlayer distances. The coordination of the Pd ions not only plays crucial roles in the structural transition, but also leads to electronic structure and transport property variations, which changes from square planar to distorted octahedron in the intermediate phase, resulting in bandwidth broadening and orbital-selective metallization. In addition, the superconductivity in the cubic pyrite-type structure comes from the strong electron-phonon coupling in the presence of topological nodal-line states. The strong interplay between structural transition, metallization, and superconductivity in $\mathrm{Pd}{\mathrm{S}}_{2}$ provides a good platform to study the fundamental physics of the interactions between crystal structure and transport behavior, and the competition or cooperation between diverse phases.

Ballistic Transport in High-Performance and Low-Power Sub-5 nm Two-Dimensional ZrNBr MOSFETs

Abstract: Here, the electronic properties and ballistic transport properties of two-dimensional (2D) ZrNBr are comprehensively investigated by the nonequilibrium Green’s function coupled with density functional theory. 2D ZrNBr has a wide direct band gap of 1.82 eV with the highest mobility of 8700cm $^{{2}}\text{V}^{-{1}}\text{s}^{-{1}}$ . Both the n- and p-type 2D ZrNBr MOSFETs with 5-nm channel length hold the on-currents above $2300~\mu \text{A}/\mu \text{m}$ for high-performance devices and an on/off ratio exceeding 106 for low-power applications, which is of great value for the design of complementary circuits in 2D electronics. In addition, the energy-delay products of the single 2D ZrNBr MOSFETs and the 32-bit Arithmetic Logic Unit show more potential compared to other 2D materials and CMOS proposals. Thus, this work broadens a promising path towards beyond-silicon electronic systems.

High-performance vertical field-effect transistors based on all-inorganic perovskite microplatelets

Abstract: All-inorganic halide perovskites have made significant achievements in electronics, optoelectronics, and other fields due to their unique physical and chemical properties. However, the researchers focus on the traditional planar field-effect transistors, which have limited electrical performance and applications due to their planar structure with a long channel length. Here, we report a vertical field-effect transistor (VFET) based on the CsPbBr3 microplatelet grown by van der Waals epitaxial growth. The VFET is achieved by a direct evaporation method utilizing the height difference between the CsPbBr3 single-crystal and the graphene substrate. Compared with the traditional planar structure transistors, the device exhibits more excellent performance, such as a high current density of 12.3 A cm−2 and a high on/off ratio over 106 at room temperature. The trap-state density of the CsPbBr3 single-crystal is calculated to be as low as 2.3 × 1015 cm−3 by space-charge-limited currents, which further proves its excellent crystallinity. Also, we have firstly fabricated a MoS2/CsPbBr3 heterostructure inverter with a vertical structure, which could implement the “No” function in logic operations. This work opens a new pathway for practical application of all-inorganic halide perovskites in future electronics.

High-performance monolayer Na3Sb shrinking transistors: a DFT-NEGF study

Abstract: 2D materials with direct bandgaps and high carrier mobility are considered excellent candidates for next-generation electronic and optoelectronic devices. Here, a new 2D semiconductor, Na3Sb, is proposed and investigated for the performance limits of FETs by ab initio quantum-transport simulations. Monolayer Na3Sb shows a direct bandgap of 0.89 eV and a high phonon-limited electron mobility of up to 1.25 × 103 cm2 V−1 s−1. We evaluated the impact of channel lengths, gate underlaps, oxide thicknesses, and dielectrics on devices. The major figures of merits for FETs are also assessed in terms of the On–Off ratio, subthreshold swing, gate capacitance, delay time, power dissipation, and field-effect mobility, fulfilling the requirements of the International Roadmap for Devices and Systems (IRDS) for high-performance (HP) devices and demonstrating great potential for electronics with novel 2D Na3Sb.

Transferable High-Quality Inorganic Perovskites for Optoelectronic Devices by Weak Interaction Heteroepitaxy

Abstract: Transferable semiconductors with superior light-emitting properties are important for developing flexible and integrated optoelectronics. However, finding such a qualified candidate remains challen...

DFT coupled with NEGF study of the electronic properties and ballistic transport performances of 2D SbSiTe3

Abstract: Identifying novel 2D semiconductors with promising electronic properties and transport performances for the development of electronic and optoelectronic applications is of utmost importance. Here, we show a detailed study of the electronic properties and ballistic quantum transport performance of a new 2D semiconductor, SbSiTe3, based on density functional theory (DFT) and non-equilibrium Green's function (NEGF) formalism. Promisingly, monolayer SbSiTe3 owns an indirect band gap of 1.61 eV with a light electron effective mass (0.13m0) and an anisotropic hole effective mass (0.49m0 and 1.34m0). The ballistic performance simulations indicate that the 10 nm monolayer SbSiTe3 n- and p-MOSFETs display a steep subthreshold swing of about 80 mV dec-1 and a high on/off ratio (106), which indicate a good gate-controlling capability. As the channel length of SbSiTe3 decreases to 5 nm, its p-MOSFET also effectively suppresses the intra-band tunneling. Therefore, 2D SbSiTe3 is a potential semiconductor for future nanoelectronics.

First-principle study of puckered arsenene MOSFET

Abstract: Two-dimensional material has been regarded as a competitive silicon-alternative with a gate length approaching sub-10 nm, due to its unique atomic thickness and outstanding electronic properties. Herein, we provide a comprehensively study on the electronic and ballistic transport properties of the puckered arsenene by the density functional theory coupled with nonequilibrium Green’s function formalism. The puckered arsenene exhibits an anisotropic characteristic, as effective mass for the electron/hole in the armchair and zigzag directions is 0.35/0.16 m0 and 1.26/0.32 m0. And it also holds a high electron mobility, as the highest value can reach 20 045 cm2V–1s–1. Moreover, the puckered arsenene FETs with a 10-nm channel length possess high on/off ratio above 105 and a steep subthreshold swing below 75 mV/dec, which have the potential to design high-performance electronic devices. Interestingly, the channel length limit for arsenene FETs can reach 7-nm. Furthermore, the benchmarking of the intrinsic arsenene FETs and the 32-bit arithmetic logic unit circuits also shows that the devices possess high switching speed and low energy dissipation, which can be comparable to the CMOS technologies and other CMOS alternatives. Therefore, the puckered arsenene is an attractive channel material in next-generation electronics.