We report a new kind of experimental realization of a molecular rectifier, which is based on a single azafullerene C59N molecule in a double-barrier tunnel junction via the single electron tunneling effect. An obvious rectifying effect is observed. The positive onset voltage is about 0.5-0.7 V, while the negative onset voltage is about 1.6-1.8 V. Theoretical analyses show that the half-occupied molecular orbital of the C59N molecule and the asymmetric shift of the molecular Fermi level when the molecule is charged are responsible for the molecular rectification.

Low-cost and earth-abundant PbS-based thermoelectrics are expected to be an alternative for PbTe, and have attracted extensive attentions from thermoelectric community. Herein, a maximum ZT (ZT max ) ≈ 1.3 at 923 K in n-type PbS is obtained through synergistically optimizing quality factor with Sn alloying and PbTe phase incorporation. It is found that Sn alloying in PbS can sharpen the conduction band shape to balance the contradictory interrelationship between carrier mobility and effective mass, accordingly, a peak power factor of ∼19.8 μWcm −1 K −2 is achieved. Besides band sharpening, Sn alloying can also narrow the band gap of PbS so as to make the conduction band position between Pb 0.94 Sn 0.06 S and PbTe well aligned, which can benefit high carrier mobility. Therefore, incorporating the PbTe phase into the Pb 0.94 Sn 0.06 S matrix can not only favorably maintain the carrier mobility at ∼150 cm 2 V −1 s −1 but also suppress the lattice thermal conductivity to ∼0.61 Wm −1 K −1 in Pb 0.94 Sn 0.06 S-8%PbTe, which contributes to a largely enhanced quality factor. Consequently, an average ZT (ZT ave ) ≈ 0.72 in 300−923 K is achieved in Pb 0.94 Sn 0.06 S-8%PbTe that outperforms other n-type PbSbased thermoelectric materials.

The generalized energy-based fragmentation (GEBF) approach has been implemented for the explicitly correlated F12a of coupled-cluster with the noniterative triples corrections [CCSD(T)-F12a] method for medium- and large-sized systems. By combining the canonical Hartree-Fock (HF) total energies and the GEBF-X correlation energies, the GEBF-X/HF method is illustrated to be more accurate than the origin GEBF-X method, where X could be any electron correlation method, such as second-order Møller-Plesset perturbation theory (MP2), MP2-F12, CCSD(T), and CCSD(T)-F12a. By combining the GEBF-X/HF results at the MP2-F12 and CCSD(T)-F12a levels, we can approximately achieve the CCSD(T) complete basis set (CBS) limit. Our test calculations for 10 low-energy isomers of water 20-mers show that for the relative energies of large water clusters, both the basis set and high-level electron correlation effects should be taken into account, in which the former is even more important. In addition, the GEBF-CCSD(T)/HF method at the CBS limit is used to evaluate 32 levels of density functional theory (DFT) methods. The results show that the DFT methods are difficult to predict the relative energies between the isomers of water 20-mers. The GEBF-CCSD(T)/HF method at the CBS limit is expected to be a benchmark for DFT and other electron correlation methods for medium- and large-sized systems with complex structures, in which both the basis set and electron correlation effects are important.

Scanning tunneling spectroscopy measurements of Pb islands on Si(111) at high energy resolution reveal a novel pseudogap, or a pseudopeak in special cases, around the Fermi level in addition to the usual quantum well states. These gap or peak features persist to temperatures as high as approximately 80 K and are uniquely related to the quantum well nanostructure of the Pb islands. A systematic analysis indicates that electron-phonon scattering is responsible for the observed electronic structure.

As a storage material for Li-ion batteries, graphene/molybdenum disulfide (Gr/MoS 2 ) composites have been intensively studied in experiments. But the relevant theoretical works from first-principles are lacking. In the current work, van-der-Waals-corrected density functional theory calculations are performed to investigate the interaction of Li in Gr/MoS 2 composites. Three interesting features are revealed for the intercalated Gr/Li(n)/MoS 2 composites (n = 1 to 9). One is the reason for large Li storage capacity of Gr/MoS 2 : due to the binding energies per Li atom increase with the increasing number of intercalated Li atoms. Secondly, the band gap opening of Gr is found, and the band gap is enlarged with the increasing number of intercalated Li atoms, up to 160 meV with nine Li; hence these results suggest an efficient way to tune the band gap of graphene. Thirdly, the Dirac cone of Gr always preserve for different number of ionic bonded Li atoms. TOC Graphic:

Ligand-stabilized palladium amorphous nanoparticles with various monodispersed sizes ranging from 2 to 6 nm were synthesized and compared with palladium crystalline nanoparticles. The nanoparticles were characterized by high-resolution electron microscopy (HREM), X-ray photoelectron spectroscopy, and scanning tunneling microscopy/spectroscopy (STM/STS). Both HREM images and electron diffraction patterns show quite clear differences in structures between crystalline and amorphous palladium nanoparticles. STS spectra exhibit fine structures in addition to the Coulomb blockade and the Coulomb staircases in the current-voltage (I-V) curves for the crystalline Pd nanoparticles when the diameters are smaller than 4 nm but only pure effect of Coulomb blockade and Coulomb staircases for amorphous Pd nanoparticles, which further indicates the differences in electronic structures.

A low temperature scanning tunneling microscope (STM) has been employed to investigate the insulating alkanethiol self-assembled monolayers chemisorbed on Au(111) substrates. The STM images show clear intramolecular patterns, which are voltage- and site-dependent. Theoretical simulations, using the density functional theory, reproduce the experimental STM images. Our results show that due to the chemisorption, there are new states appeared in the energy gap of the alkanethiol, and they are mainly composed of Au and S orbitals, mixed with a small amount of orbitals at the alkyl part. The STM only images the states localized at the tail carbon–hydrogen groups since the Au and S atoms are located farther from the STM tip, and the images can reflect the surface topography of such standing molecular layers.

The recent discovered intrinsic magnetic topological insulator MnBi2Te4 have been met with unusual success in hosting emergent phenomena such as the quantum anomalous Hall effect and the axion insulator states. However, the surface-bulk correspondence of the Mn-Bi-Te family, composed by the superlattice-like MnBi2Te4/(Bi2Te3)n (n = 0, 1, 2, 3…) layered structure, remains intriguing but elusive. Here, by using scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) techniques, we unambiguously assign the two distinct surface states of MnBi4Te7 (n = 1) to the quintuple-layer (QL) Bi2Te3 termination and the septuplelayer (SL) MnBi2Te4 termination, respectively. A comparison of the experimental observations with theoretical calculations reveals the diverging topological behaviors, especially the hybridization effect between magnetic and nonmagnetic layers, on the two terminations: a gap on the QL termination originating from the topological surface states of the QL hybridizing with the bands of the beneath SL, and a gapless Dirac-cone band structure on the SL termination with timereversal symmetry. The quasi-particle interference patterns further confirm the topological nature of the surface states for both terminations, continuing far above the Fermi energy. The QL termination carries a spin-helical Dirac state with hexagonal warping, while at the SL termination, a strongly canted helical state from the surface lies between a pair of Rashba-split states from its neighboring layer. Our work elucidates an unprecedented hybridization effect between the building blocks of the topological surface states, and also reveals the termination-dependent timereversal symmetry breaking in a magnetic topological insulator, rendering an ideal platform to realize the half-integer quantum Hall effect and relevant quantum phenomena.