Spatially Extended Charge Density Wave Switching by Nanoscale Local Manipulation in a VTe Monolayer.

Monolayer transition metal dichalcogenide VTe exhibits multiple charge density wave (CDW) phases, mainly (4 × 4) and (4 × 1). Here we report facile dynamic and tens-of-nanometer scale switching between these CDW phases with gentle bias pulses in scanning tunneling microscopy. Bias pulses purposely stimulate a reversible random CDW symmetry change between the isotropic (4 × 4) and anisotropic (4 × 1) CDWs, as well as CDW phase slips and rotation.

Identification and Manipulation of Defects in Black Phosphorus.

We identify and manipulate commonly occurring defects in black phosphorus, combining scanning tunneling microscopy experiments with density functional theory calculations. A ubiquitous defect, imaged at negative bias as a bright dumbbell extending over several nanometers, is shown to arise from a substitutional Sn impurity in the second sublayer. Another frequently observed defect type is identified as arising from an interstitial Sn atom; this defect can be switched to a more stable configuration consisting of a Sn substitutional defect + P adatom, by application of an electrical pulse via the STM tip.

Unique Gap Structure and Symmetry of the Charge Density Wave in Single-Layer VSe_{2}.

Single layers of transition metal dichalcogenides (TMDCs) are excellent candidates for electronic applications beyond the graphene platform; many of them exhibit novel properties including charge density waves (CDWs) and magnetic ordering. CDWs in these single layers are generally a planar projection of the corresponding bulk CDWs because of the quasi-two-dimensional nature of TMDCs; a different CDW symmetry is unexpected. We report herein the successful creation of pristine single-layer VSe_{2}, which shows a (sqrt[7]×sqrt[3]) CDW in contrast to the (4×4) CDW for the layers in bulk VSe_{2}.

Large quantum-spin-Hall gap in single-layer 1T' WSe.

Two-dimensional (2D) topological insulators (TIs) are promising platforms for low-dissipation spintronic devices based on the quantum-spin-Hall (QSH) effect, but experimental realization of such systems with a large band gap suitable for room-temperature applications has proven difficult. Here, we report the successful growth on bilayer graphene of a quasi-freestanding WSe single layer with the 1T' structure that does not exist in the bulk form of WSe. Using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS), we observe a gap of 129 meV in the 1T' layer and an in-gap edge state located near the layer boundary.

Near room temperature chemical vapor deposition of graphene with diluted methane and molten gallium catalyst.

Direct growth of graphene integrated into electronic devices is highly desirable but difficult due to the nominal ~1000 °C chemical vapor deposition (CVD) temperature, which can seriously deteriorate the substrates. Here we report a great reduction of graphene CVD temperature, down to 50 °C on sapphire and 100 °C on polycarbonate, by using dilute methane as the source and molten gallium (Ga) as catalysts. The very low temperature graphene synthesis is made possible by carbon attachment to the island edges of pre-existing graphene nuclei islands, and causes no damages to the substrates.

Emergence of charge density waves and a pseudogap in single-layer TiTe.

Two-dimensional materials constitute a promising platform for developing nanoscale devices and systems. Their physical properties can be very different from those of the corresponding three-dimensional materials because of extreme quantum confinement and dimensional reduction. Here we report a study of TiTe from the single-layer to the bulk limit.

Tuning the Magnetic Anisotropy at a Molecule-Metal Interface.

We demonstrate that a C(60) overlayer enhances the perpendicular magnetic anisotropy of a Co thin film, inducing an inverse spin reorientation transition from in plane to out of plane. The driving force is the (60)/Co interfacial magnetic anisotropy that we have measured quantitatively in situ as a function of the (60) coverage. Comparison with state-of-the-art ab initio calculations show that this interfacial anisotropy mainly arises from the local hybridization between (60) p(z) and Co d(z(2)) orbitals.

Optimal electron doping of a C60 monolayer on Cu(111) via interface reconstruction.

We demonstrate the charge state of C60 on a Cu(111) surface can be made optimal, i.e., forming C60(3-) as required for superconductivity in bulk alkali-doped C60, purely through interface reconstruction rather than with foreign dopants.

Fluorescence enhancement and lifetime modification of single nanodiamonds near a nanocrystalline silver surface.

Fluorescent nanodiamond (FND) contains nitrogen-vacancy defect centers as fluorophores. The intensity of its fluorescence can be significantly enhanced after deposition of the particle (35 or 140 nm in size) on a nanocrystalline Ag film without a buffer layer. The excellent photostability (i.

Sodium ion ordering and vacancy cluster formation in NaxCoO2 (x=0.71 and 0.84) single crystals by synchrotron X-Ray diffraction.

In the rich phase diagram of NaxCoO2, x=0.71 enjoys special stability and is called the Curie-Weiss metal due to its anomalous properties. Similarly, x=0.

Sodium trimer ordering on a NaxCoO2 surface.

Sodium ion ordering on an in situ cleaved NaxCoO2 (x=0.84) surface has been studied by ultrahigh vacuum scanning tunneling microscopy at room temperature. Three main phases, with p(3 x 3), ( radical7 x radical7), and (2 radical3 x 2 radical3) hexagonal unit cells and a surface Na concentration of 1/3, 3/7, 1/2, respectively, were identified.

Anomalous surface diffusion of C60 and anisotropic growth of nano islands on Ni(111).

The migration behavior of C60 on Ni(111) has been inferred from its growth morphology at various substrate temperatures, as observed with scanning tunneling microscopy. The number density of islands increased and their average sizes decreased anomalously in the temperature range of approximately 573 K to approximately 973 K. This trend contradicts the prediction in conventional nucleation theory.

Dislocation emission around nanoindentations on a (001) fcc metal surface studied by scanning tunneling microscopy and atomistic simulations.

We present a combined study by scanning tunneling microscopy and atomistic simulations of the emission of dissociated dislocation loops by nanoindentation on a (001) fcc surface. The latter consist of two stacking-fault ribbons bounded by Shockley partials and a stair-rod dislocation. These dissociated loops, which intersect the surface, are shown to originate from loops of interstitial character emitted along the <110> directions and are usually located at hundreds of angstroms away from the indentation point.

Evolution of two-dimensional wormlike nanoclusters on metal surfaces.

A pinch-off phenomenon is discovered in the evolution of 2D wormlike nanoclusters formed in homoepitaxial adlayers. This feature is shown to distinguish mass transport via periphery diffusion from other mechanisms. Continuum modeling of such evolution accurately describes experimental observations, particularly if one incorporates the anisotropy in step-edge line tension.