Doping of traditional semiconductors has enabled technological applications in modern electronics by tailoring their chemical, optical and electronic properties. However, substitutional doping in two-dimensional semiconductors is at a comparatively early stage, and the resultant effects are less explored. In this work, we report unusual effects of degenerate doping with Nb on structural, electronic and optical characteristics of MoS2 crystals. The doping readily induces a structural transformation from naturally occurring 2H stacking to 3R stacking. Electronically, a strong interaction of the Nb impurity states with the host valence bands drastically and nonlinearly modifies the electronic band structure with the valence band maximum of multilayer MoS2 at the Γ point pushed upward by hybridization with the Nb states. When thinned down to monolayers, in stark contrast, such significant nonlinear effect vanishes, instead resulting in strong and broadband photoluminescence via the formation of exciton complexes tightly bound to neutral acceptors.

Combining both density functional theory and the cluster expansion method, we investigate 3 binary MXene alloy systems of semiconducting Ti 2 CO 2 , Zr 2 CO 2 , and Hf 2 CO 2 , where the transition metals substitute one another (i.e., Ti 2(1−x) Zr 2x CO 2 , Ti 2(1−x) Hf 2x CO 2 , and Zr 2(1−x) Hf 2x CO 2 ). We show that this group of MXene alloys forms the solidsolution phase across all compositions. Special quasirandom structures are generated to model the solid-solution phase of these alloys, using which we demonstrate how their structural, mechanical, electronic, and optical properties are tuned via stoichiometry engineering. These alloys exhibit outstanding mechanical strength and stability. They possess indirect band gaps of 1.25−1.80 eV. For Ti 2(1−x) Zr 2x CO 2 and Ti 2(1−x) Hf 2x CO 2 , they display higher absorbance in the solar spectrum than their constituent Zr 2 CO 2 and Hf 2 CO 2 , respectively. Most of the MXene alloys also show appropriately aligned band edges for water splitting. We predict the Ti 2(1−x) Zr 2x CO 2 alloy with x = 0.2778 to be the most promising water-splitting photocatalyst among the MXenes studied here, outperforming its constituents, Ti 2 CO 2 and Zr 2 CO 2 , when solar absorbance performance and band-edge alignments are simultaneously considered. This work demonstrates that alloying can be used to effectively tune photocatalytic performance.

At elevated temperatures, bimetallic nanomaterials change their morphologies because of the interdiffusion of atomic species, which also alters their properties. The Kirkendall effect (KE) is a well-known phenomenon associated with such interdiffusion. Here, we show how KE can manifest in bimetallic nanoparticles (NPs) by following core–shell NPs of Au and Pd during heat treatment with in situ transmission electron microscopy. Unlike monometallic NPs, these core–shell NPs did not evolve into hollow core NPs. Instead, nanoscale voids formed at the bimetallic interface and then, migrated to the NP surface. Our results show that: (1) the direction of vacancy flow during interdiffusion reverses due to the higher vacancy formation energy of Pd compared to Au, and (2) nanoscale voids migrate during heating, contrary to conventional assumptions of immobile voids and void shrinkage through vacancy emission. Our results illustrate how void behavior in bimetallic NPs can differ from an idealized picture based on atomic fluxes and have important implications for the design of these materials for high-temperature applications.

A computationally efficient first-principles approach to predict intrinsic semiconductor charge transport properties is proposed. By using a generalized Eliashberg function for short-range electron–phonon scattering and analytical expressions for long-range electron–phonon and electron–impurity scattering, fast and reliable prediction of carrier mobility and electronic thermoelectric properties is realized without empirical parameters. This method, which is christened “Energy-dependent Phonon- and Impurity-limited Carrier Scattering Time AppRoximation (EPIC STAR)” approach, is validated by comparing with experimental measurements and other theoretical approaches for several representative semiconductors, from which quantitative agreement for both polar and non-polar, isotropic and anisotropic materials is achieved. The efficiency and robustness of this approach facilitate automated and unsupervised predictions, allowing high-throughput screening and materials discovery of semiconductor materials for conducting, thermoelectric, and other electronic applications.

As a unique class of molecular electronic materials, organic donor–acceptor complexes now exhibit tantalizing prospect for heat–electricity interconversion. Over the past decades, in design of these materials for thermoelectric applications, consistent efforts have been made to synthesize a wide variety of structures and to characterize their properties. However, hitherto, one of the paramount conundrums, namely lack of systematic molecular design principles, has not been addressed yet. Here, based on ab initio calculations, and by comprehensively examining the underlying correlation among thermoelectric power factors, non-intuitive transport processes, and fundamental chemical structures for 13 prototypical organic donor–acceptor complexes, we establish a unified roadmap for rational development of these materials with increased thermoelectric response. We corroborate that the energy levels of frontier molecular orbitals in the isolated donor and acceptor molecules control the charge transfer, electronic property, charge transport, and thermoelectric performance in the solid-state complexes. Our results demonstrate that tailoring a suitable energy-level difference between donor’s highest occupied molecular orbital and acceptor’s lowest unoccupied molecular orbital holds the key to achieving an outstanding power factor. Moreover, we reveal that the charge-transfer-caused Coulomb scattering governs the charge and thermoelectric transport in organic donor–acceptor complexes.

PEDOT:PSS doped with a series of functionalized sulfoxides exhibits enhanced electrical conductivity and Seebeck coefficient.

In article number 2000015, new insights into thermoelectric transport in conducting polymers based on first‐principles calculations and new material design guidelines are presented by Shuo‐Wang Yang and co‐workers. They demonstrate that in the crystalline domains, the counterion scattering controls the power factor, and in the polycrystalline domains, the crystallite orientations and the grain sizes strongly affect the power factor.

A fundamental understanding of the atomic and electronic structures of metallic nanowires (NWs) on semiconductors is critical for micro- or molecular electronics. The deposition of Au atoms on Ge(001) surfaces can trigger the self-assembly of atomic NWs extending for hundreds of nanometers, and these NWs raised much controversy on their atomic/electronic configurations. In this work, different types of NWs were characterized on Au/Ge(001) surfaces via scanning tunneling microscopy (STM). Combined with density functional theory (DFT) calculations, the atomic structures of Au-induced NWs on Ge(001) surfaces were decoded, including the NWs-H/L and complex chevron and zigzag (V–W) reconstructions, where simulated V–W patterns at filled states transform to triplets at empty states. Moreover, a quasi-one-dimensional (1D) electronic behavior and anisotropic two-dimensional (2D) electronic states are uncovered in the Au–Ge-modified-dimer-row (AGMDR) and Au-NWs-in-trench (ANT) models, respectively, reconciling the previous controversy about electronic behaviors of NWs on Au/Ge(001) surfaces. Because of the quantum instability, 1D electron systems undergo a transition from metallic to nonconducting, while the atomic NWs (i.e., NWs-H and NWs-L) in the ANT model are metallic, rendering them good conductive channels for micro- or molecular electronics. Our findings provide insights into ascertaining the atomic structures of self-assembled NWs and understanding the discrepancies of the Au/Ge(001) material system.