Two-dimensional transition metal dichalcogenides (e.g. MoS) have recently emerged as a promising material system for electronic and optoelectronic applications. A major challenge for these materials, however, is to realize bipolar electrical transport properties (i.e. both p-type and n-type conduction), which is critical for enhancing device performance and functionalities. Here, we demonstrate the transition metal zinc as a p-type dopant in the otherwise n-type MoS, through systematic characterizations of large area Zn-doped MoS thin films grown by a one-step chemical vapor deposition (CVD) approach. Raman characterization and X-ray photoelectron spectroscopy studies identified millimeter-scale, monolayer films with 1-2% Zn as dopants. Zinc doping suppresses n-type conductivity in MoS and shifts its Fermi level downwards. The stability and p-type nature of Zn dopants were further confirmed by density-functional-theory calculations of formation energies and electronic band structures. The electrical transport properties of Zn-MoS films can be influenced by stoichiometry, and p-type gate transfer characteristics were realized by thermal treatment under a sulfur atmosphere. Our work highlights transition-metal doping followed by sulfur vacancy elimination in CVD grown films as a promising route for achieving large area p-type transition metal dichalcogenide films that are essential for practical applications in electronics and optoelectronics.

By means of electronic transport, we study the transverse magnetic anisotropy of an individual Fe4 single-molecule magnet (SMM) embedded in a three-terminal junction. In particular, we determine in situ the transverse anisotropy of the molecule from the pronounced intensity modulations of the linear conductance, which are observed as a function of applied magnetic field. The proposed technique works at temperatures exceeding the energy scale of the tunnel splittings of the SMM. We deduce that the transverse anisotropy for a single Fe4 molecule captured in a junction is substantially larger than the bulk value.

Bi 2 Se 3 is a three-dimensional topological insulator which has been extensively studied because it has a single Dirac cone on the surface, inside a relatively large bulk band gap. However, the effect of two-dimensional topological insulator Bi bilayers on the properties of Bi 2 Se 3 and vice versa, has not been explored much. Bi bilayers are often present between the quintuple layers of Bi 2 Se 3 , since (Bi 2 ) n (Bi 2 Se 3 ) m form stable ground-state structures. Moreover, Bi 2 Se 3 is a good substrate for growing ultrathin Bi bilayers. By first-principles techniques, we first show that there is no preferable surface termination by either Bi or Se. Next, we investigate the electronic structure of Bi bilayers on top of, or inside a Bi 2 Se 3 slab. If the Bi bilayers are on top, we observe a charge transfer to the quintuple layers that increases the binding energy of the surface Dirac cones. The extra states, originating from the Bi bilayers, were declared to form a topological Dirac cone, but here we show that these are ordinary Rashba-split states. This result, together with the appearance of a new Dirac cone that is localized slightly deeper, might necessitate the reinterpretation of several experimental results. When the Bi bilayers are located inside the Bi 2 Se 3 slab, they tend to split the slab into two topological insulators with clear surface states. Interface states can also be observed, but an energy gap persists because of strong coupling between the neighboring quintuple layers and the Bi bilayers.

We investigate how the electron-vibron coupling influences electron transport via an anisotropic magnetic molecule, such as a single-molecule magnet (SMM) Fe 4 , by using a model Hamiltonian with parameter values obtained from density-functional theory (DFT). Magnetic anisotropy parameters, vibrational energies, and electron-vibron coupling strengths of the Fe 4 are computed using DFT. A giant spin model is applied to the Fe 4 with only two charge states, specifically a neutral state with the total spin S = 5 and a singly charged state with S = 9/2, which is consistent with our DFT result and experiments on Fe 4 single-molecule transistors. In sequential electron tunneling, we find that the magnetic anisotropy gives rise to new features in conductance peaks arising from vibrational excitations. In particular, the peak height shows a strong, unusual dependence on the direction as well as magnitude of applied B field. The magnetic anisotropy also introduces vibrational satellite peaks whose position and height are modified with the direction and magnitude of applied B field. Furthermore, when multiple vibrational modes with considerable electron-vibron coupling have energies close to one another, a low-bias current is suppressed, independently of gate voltage and applied B field, although that is not the case for a single mode with the similar electron-vibron coupling. In the former case, the conductance peaks reveal a stronger B-field dependence than in the latter case. The new features appear because the magnetic anisotropy barrier is of the same order of magnitude as the energies of vibrational modes with significant electron-vibron coupling. Our findings clearly show the interesting interplay between magnetic anisotropy and electron-vibron coupling in electron transport via the Fe 4 . The similar behavior can be observed in transport via other anisotropic magnetic molecules.

The nanoscopic structure and the stationary propagation velocity of ͑1+1͒-dimensional solid-on-solid interfaces in an Ising lattice-gas model, which are driven far from equilibrium by an applied force, such as a magnetic field or a difference in ͑electro͒chemical potential, are studied by an analytic nonlinear-response approximation ͓P. A. Rikvold and M. Kolesik, J. Stat. Phys. 100, 377 ͑2000͔͒ together with kinetic Monte Carlo simulations. Here, we consider the case that the system is coupled to a two-dimensional phonon bath. In the resulting dynamic ͓K. Saito et al., Phys. Rev. E 61, 2397 ͑2000͒; K. Park and M. A. Novotny, Comput. Phys. Commun. 147, 737 ͑2002͔͒, transitions that conserve the system energy are forbidden, and the effects of the applied force and the interaction energies do not factorize ͑a so-called hard dynamic͒. In full agreement with previous general theoretical results, we find that the local interface width changes dramatically with the applied force. However, in contrast with other hard dynamics, this change is nonmonotonic in the driving force. Results are also obtained for the force dependence and anisotropy of the interface velocity, which also show differences in good agreement with the theoretical expectations for the differences between soft and hard dynamics. However, significant differences between theory and simulation are found near two special values of the driving force, where certain transitions allowed by the solid-on-solid model become forbidden by the phonon-assisted dynamic. Our results show that different stochastic interface dynamics that all obey detailed balance and the same conservation laws nevertheless can lead to radically different interface responses to an applied force. Thus, they represent a significant step toward providing a solid physical foundation for kinetic Monte Carlo simulations.