Self-assembly of ordered graphene nanodot arrays

<p>Raw data associated with the publication "Self-assembly of ordered graphene nanodot arrays" published in Nature Communications under the DOI: 10.1038/s41467-017-00042-4</p> <p>Abstract: The ability to fabricate nanoscale domains of uniform size in two-dimensional (2D) materials could potentially enable new applications in nanoelectronics and the development of innovative metamaterials. However, achieving even minimal control over the growth of 2D lateral heterostructures at such extreme dimensions has proven exceptionally challenging. Here we show the spontaneous formation of ordered arrays of graphene nano-domains (dots), epitaxially embedded in a 2D boron-carbon-nitrogen alloy. These dots exhibit a strikingly uniform size of 1.6nm ± 0.2nm and strong ordering, and the array periodicity can be tuned by adjusting the growth conditions. We explain this behaviour with a model incorporating dot-boundary energy, a moiré-modulated substrate interaction, and long-range repulsion between dots. This new 2D material, which theory predicts to be an ordered composite of uniform-size semiconducting graphene quantum dots laterally integrated within a larger-bandgap matrix, holds promise for novel electronic and optoelectronic properties, with a variety of potential device applications.</p

Large Single Crystals of Graphene on Melted Copper Using Chemical Vapor Deposition

A simple method is presented for synthesizing large single crystal graphene domains on melted copper using atmospheric pressure chemical vapor deposition (CVD). This is achieved by performing the reaction above the melting point of copper (1090 °C) and using a molybdenum or tungsten support to prevent balling of the copper from dewetting. By controlling the amount of hydrogen during growth, individual single crystal domains of monolayer graphene greater than 200 μm are produced within a continuous film. Stopping growth before a complete film is formed reveals individual hexagonal domains of graphene that are epitaxially aligned in their orientation. Angular resolved photoemission spectroscopy is used to show that the graphene grown on copper exhibits a linear dispersion relationship and no sign of doping. HRTEM and electron diffraction reveal a uniform high quality crystalline atomic structure of monolayer graphene

Direct Measurement of the Tunable Electronic Structure of Bilayer MoS₂ by Interlayer Twist

Using angle-resolved photoemission on micrometer-scale sample areas, we directly measure the interlayer twist angle-dependent electronic band structure of bilayer molybdenum-disulfide (MoS₂). Our measurements, performed on arbitrarily stacked bilayer MoS₂ flakes prepared by chemical vapor deposition, provide direct evidence for a downshift of the quasiparticle energy of the valence band at the Brillouin zone center (Γ̅ point) with the interlayer twist angle, up to a maximum of 120 meV at a twist angle of ∼40°. Our direct measurements of the valence band structure enable the extraction of the hole effective mass as a function of the interlayer twist angle. While our results at Γ̅ agree with recently published photoluminescence data, our measurements of the quasiparticle spectrum over the full 2D Brillouin zone reveal a richer and more complicated change in the electronic structure than previously theoretically predicted. The electronic structure measurements reported here, including the evolution of the effective mass with twist-angle, provide new insight into the physics of twisted transition-metal dichalcogenide bilayers and serve as a guide for the practical design of MoS₂ optoelectronic and spin-/valley-tronic devices

Tin DisulfideAn Emerging Layered Metal Dichalcogenide Semiconductor: Materials Properties and Device Characteristics

Layered metal dichalcogenides have attracted significant interest as a family of single- and few-layer materials that show new physics and are of interest for device applications. Here, we report a comprehensive characterization of the properties of tin disulfide (SnS₂), an emerging semiconducting metal dichalcogenide, down to the monolayer limit. Using flakes exfoliated from layered bulk crystals, we establish the characteristics of single- and few-layer SnS₂ in optical and atomic force microscopy, Raman spectroscopy and transmission electron microscopy. Band structure measurements in conjunction with <i>ab initio</i> calculations and photoluminescence spectroscopy show that SnS₂ is an indirect bandgap semiconductor over the entire thickness range from bulk to single-layer. Field effect transport in SnS₂ supported by SiO₂/Si suggests predominant scattering by centers at the support interface. Ultrathin transistors show on–off current ratios >10⁶, as well as carrier mobilities up to 230 cm²/(V s), minimal hysteresis, and near-ideal subthreshold swing for devices screened by a high-<i>k</i> (deionized water) top gate. SnS₂ transistors are efficient photodetectors but, similar to other metal dichalcogenides, show a relatively slow response to pulsed irradiation, likely due to adsorbate-induced long-lived extrinsic trap states

<i>In Situ</i> Imaging of Cu₂O under Reducing Conditions: Formation of Metallic Fronts by Mass Transfer

Active catalytic sites have traditionally been analyzed based on static representations of surface structures and characterization of materials before or after reactions. We show here by a combination of <i>in situ</i> microscopy and spectroscopy techniques that, in the presence of reactants, an oxide catalyst’s chemical state and morphology are dynamically modified. The reduction of Cu₂O films is studied under ambient pressures (AP) of CO. The use of complementary techniques allows us to identify intermediate surface oxide phases and determine how reaction fronts propagate across the surface by massive mass transfer of Cu atoms released during the reduction of the oxide phase in the presence of CO. High resolution <i>in situ</i> imaging by AP scanning tunneling microscopy (AP-STM) shows that the reduction of the oxide films is initiated at defects both on step edges and the center of oxide terraces

<i>In Situ</i> Imaging of Cu₂O under Reducing Conditions: Formation of Metallic Fronts by Mass Transfer

Active catalytic sites have traditionally been analyzed based on static representations of surface structures and characterization of materials before or after reactions. We show here by a combination of <i>in situ</i> microscopy and spectroscopy techniques that, in the presence of reactants, an oxide catalyst’s chemical state and morphology are dynamically modified. The reduction of Cu₂O films is studied under ambient pressures (AP) of CO. The use of complementary techniques allows us to identify intermediate surface oxide phases and determine how reaction fronts propagate across the surface by massive mass transfer of Cu atoms released during the reduction of the oxide phase in the presence of CO. High resolution <i>in situ</i> imaging by AP scanning tunneling microscopy (AP-STM) shows that the reduction of the oxide films is initiated at defects both on step edges and the center of oxide terraces

<i>In Situ</i> Imaging of Cu₂O under Reducing Conditions: Formation of Metallic Fronts by Mass Transfer

Active catalytic sites have traditionally been analyzed based on static representations of surface structures and characterization of materials before or after reactions. We show here by a combination of <i>in situ</i> microscopy and spectroscopy techniques that, in the presence of reactants, an oxide catalyst’s chemical state and morphology are dynamically modified. The reduction of Cu₂O films is studied under ambient pressures (AP) of CO. The use of complementary techniques allows us to identify intermediate surface oxide phases and determine how reaction fronts propagate across the surface by massive mass transfer of Cu atoms released during the reduction of the oxide phase in the presence of CO. High resolution <i>in situ</i> imaging by AP scanning tunneling microscopy (AP-STM) shows that the reduction of the oxide films is initiated at defects both on step edges and the center of oxide terraces