Monolayer molybdenum disulfide (MoS2) has attracted great interest due to its potential applications in electronics and optoelectronics. Ideally, single-crystal growth over a large area is necessary to preserve its intrinsic figure of merit but is very challenging to achieve. Here, we report an oxygen-assisted chemical vapor deposition method for growth of single-crystal monolayer MoS2. We found that the growth of MoS2 domains can be greatly improved by introducing a small amount of oxygen into the growth environment. Triangular monolayer MoS2 domains can be achieved with sizes up to ∼350 μm and a room-temperature mobility up to ∼90 cm(2)/(V·s) on SiO2. The role of oxygen is not only to effectively prevent the poisoning of precursors but also to eliminate defects during the growth. Our work provides an advanced method for high-quality single-crystal monolayer MoS2 growth.

Growth mechanisms of ZnO(0001) investigated using the first-principles calculation J. Appl. Phys. 112, 064301 (2012) Generation of silver-anatase nanocomposite by excimer laser-assisted processing AIP Advances 2, 032171 (2012) Degradation and passivation of CuInSe2

Tellurium (Te) films with monolayer and few-layer thickness are obtained by molecular beam epitaxy on a graphene/6H-SiC(0001) substrate and investigated by in situ scanning tunneling microscopy and spectroscopy (STM/STS). We reveal that the Te films are composed of parallel-arranged helical Te chains flat-lying on the graphene surface, exposing the (1 × 1) facet of (101̅0) of the bulk crystal. The band gap of Te films increases monotonically with decreasing thickness, reaching the near-infrared band for the monolayer Te. An explicit band bending at the edge between the monolayer Te and graphene substrate is visualized. With the thickness controlled in the atomic scale, Te films show potential applications of electronics and optoelectronics.

The significant role of interfacial coupling on the superconductivity enhancement in FeSe films on SrTiO3 has been widely recognized. But the explicit origination of this coupling is yet to be identified. Here by surface phonon measurements using high resolution electron energy loss spectroscopy, we found electric field generated by Fuchs-Kliewer (F-K) phonon modes of SrTiO3 can penetrate into FeSe films and strongly interact with electrons therein. The mode-specific electronphonon coupling (EPC) constant for the ∼92 meV F-K phonon is ∼ 0.25 in the single-layer FeSe on SrTiO3. With increasing FeSe thickness, the penetrating field intensity decays exponentially, which matches well the observed exponential decay of the superconducting gap. It is unambiguously shown that the SrTiO3 F-K phonon penetrating into FeSe is essential in the interfacial superconductivity enhancement.

At the interface between monolayer FeSe films and SrTiO3 substrates the superconducting transition temperature (Tc) is unexpectedly high, triggering a surge of excitement. The mechanism for the Tc enhancement has been the central question, as it may present a new strategy for seeking out higher Tc materials. To reveal this enigmatic mechanism, by combining advances in high quality interface growth, 16O 18O isotope substitution, and extensive data from angle resolved photoemission spectroscopy, we provide striking evidence that the high Tc in FeSe/SrTiO3 is the cooperative effect of the intrinsic pairing mechanism in the FeSe and interactions between the FeSe electrons and SrTiO3 phonons. Furthermore, our results point to the promising prospect that similar cooperation between different Cooper pairing channels may be a general framework to understand and design high-temperature superconductors.

was measured with a physical property measurement system. The electrical resistivity shows the MIT at T c = 154 K on cooling (Fig. 1) and exhibits large thermal hysteresis behavior indicating a first-order character of the MIT. Ca 1.9 Sr 0.1 RuO 4 crystals for scanning tunneling microscopy (STM), LEED, and HREELS measurements were mounted on the sample plates with conducting silver epoxy, and a small metal post was glued on top. The crystal was cleaved by knocking off the post in ultrahigh vacuum with a base pressure of 1.0 × 10 −10 torr, producing a flat shiny [001] surface that yielded a sharp LEED pattern. The STM images of the freshly cleaved surfaces show large micrometer-sized terraces. Both the LEED pattern and atomically resolved STM images indicate that the surface has a well-ordered lattice structure. All surface steps are integral multiples of ~6.4 A ˚ , which is the spacing between two nearest-neighbor RuO6 octahedron layers (Fig. 1). LEED I-V analysis shows that the surface is composed of Ca/Sr-O terminations. 13. Ismail et al., Phys. Rev. B 67, 035407 (2003). 14. J. H. Jung et al., Phys. Rev. Lett. 91, 056403 (2003). 15. A. V. Puchkov et al., Phys. Rev. Lett. 81, 2747 (1998). 16. S. Nakatsuji et al., Phys. Rev. Lett. 93, 146401 (2003). 17. Detailed spectral data analysis methods were as follows: The Drude weight is the integrated intensity obtained from the difference between the left and right sides of the quasi-elastic peak through a Lorentzian function. The phonon energy, intensity, and linewidth were obtained by fitting the phonon spectra with a Lorentzian function and were deconvoluted from the Drude tail and instrumentation-resolution function. More details of the surface phonons can be found in (32). 18. M. A. Van Hove et al., Low-Energy Electron Diffraction Experiment, Theory and Surface Structure Determination Carbohydrate recognition is biologically important but intrinsically challenging, for both nature and host-guest chemists. Saccharides are complex, subtly variable, and camouflaged by hydroxyl groups that hinder discrimination between substrate and water. We have developed a rational strategy for the biomimetic recognition of carbohydrates with all-equatorial stereochemistry (b-glucose, analogs, and homologs) and have now applied it to disaccharides such as cellobiose. Our synthetic receptor showed good affinities, not unlike those of some lectins (carbohydrate-binding proteins). Binding was demonstrated by nuclear magnetic resonance, induced circular dichroism, fluorescence spectroscopy, and calorimetry, all methods giving self-consistent results. Selectivity for the target substrates was exceptional; minor changes to disaccharide structure (for instance, cellobiose to lactose) caused almost complete suppression of complex formation. C arbohydrates are challenging substrates for host-guest chemistry (1-4). They possess extended, complex structures that require large receptor frameworks for full encapsulation. The differences between them are often subtle (e.g., the stereochemistry o...

No abstract

No abstract