Gate-Defined Quantum Confinement in CVD 2D WS2.

Temperature-dependent transport measurements are performed on the same set of chemical vapor deposition (CVD)-grown WS2 single- and bilayer devices before and after atomic layer deposition (ALD) of HfO2 . This isolates the influence of HfO2 deposition on low-temperature carrier transport and shows that carrier mobility is not charge impurity limited as commonly thought, but due to another important but commonly overlooked factor: interface roughness. This finding is corroborated by circular dichroic photoluminescence spectroscopy, X-ray photoemission spectroscopy, cross-sectional scanning transmission electron microscopy, carrier-transport modeling, and density functional modeling. Finally, electrostatic gate-defined quantum confinement is demonstrated using a scalable approach of large-area CVD-grown bilayer WS2 and ALD-grown HfO2 . The high dielectric constant and low leakage current enabled by HfO2 allows an estimated quantum dot size as small as 58 nm. The ability to lithographically define increasingly smaller devices is especially important for transition metal dichalcogenides due to their large effective masses, and should pave the way toward their use in quantum information processing applications.

Flexible Modulation of CO-Release Using Various Nuclearity of Metal Carbonyl Clusters on Graphene Oxide for Stroke Remediation.

Utilizing the size-dependent adsorption properties of ruthenium carbonyl clusters (Ru-carbon monoxide (CO)) onto graphene oxide (GO), a facile CO-release platform for in situ vasodilation as a treatment for stroke-related vascular diseases is developed. The rate and amount of formation of the CO-release-active RuII (CO)2 species can be modulated by a simple mixing procedure at room temperature. The subsequent thermally induced oxidation of RuII (CO)2 to RuO2 on the GO surface results in the release of CO. Further modulation of thermal and CO-release properties can be achieved via a hybridization of medium- and high-nuclearity of Ru-CO clusters that produces a RuO2 /RuII (CO)2 /6 Ru-CO-GO composite, where 6 Ru-CO-GO provides a photothermally activated reservoir of RuII (CO)2 species and the combined infrared absorption properties of GO and RuO2 provides photothermal response for in situ CO-release. The RuO2 /RuII (CO)2 /6 Ru-CO-GO composite does not produce any cytotoxicity and the efficacy of the composite is further demonstrated in a cortical photothrombotic ischemia rat model.

The stability of aluminium oxide monolayer and its interface with two-dimensional materials.

The miniaturization of future electronic devices requires the knowledge of interfacial properties between two-dimensional channel materials and high-κ dielectrics in the limit of one atomic layer thickness. In this report, by combining particle-swarm optimization method with first-principles calculations, we present a detailed study of structural, electronic, mechanical, and dielectric properties of Al2O3 monolayer. We predict that planar Al2O3 monolayer is globally stable with a direct band gap of 5.99 eV and thermal stability up to 1100 K. The stability of this high-κ oxide monolayer can be enhanced by substrates such as graphene, for which the interfacial interaction is found to be weak. The band offsets between the Al2O3 monolayer and graphene are large enough for electronic applications. Our results not only predict a stable high-κ oxide monolayer, but also improve the understanding of interfacial properties between a high-κ dielectric monolayer and two-dimensional material.

Optical charge-transfer in iron(III)hexacyanoferrate(II): electro-intercalated cations induce lattice-energy-dependent ground-state energies.

The maximum of the color-conferring charge-transfer (CT) band in Prussian Blue (PB) varies with the electrochemically introduced cation M(z+) incorporated (as "supernumerary") for charge neutrality, and the dependence on particular properties of the M(z+) has been sought. With alkali-metal ions, the CT-maximum shifts are in the same sequence as the PB mass changes on M+ insertion; the effect on the CT ground state of the intra-lattice interaction of an M+ with the ferrocyanide CN- moiety (competing with cation hydration), is then implicated in shifts of the maxima, as the ferrocyanide is the donor center in the optical CT. More definitely, for M2+ and Ag+, solubility-products of the insoluble M(z+) ferrocyanides (that provide direct indicators of the intra-lattice M(z+)-[Fe(II)(CN)(6)](4- interactions) show a strong correlation with the spectral shifts. The determining interaction of M(z+) with ferrocyanide within PB is enhanced in some cases by the accessibility of M(z+) oxidation states +/- 1 different from the common values. PB lattice energies and the ground states of the optical CTs thus appear closely interlinked. The electrochemical uptake of appreciable amounts of the M(z+) within the lattices was confirmed by XPS.

Charge-transfer band shifts in iron(III) hexacyanoferrate(II) by electro-intercalated cations via ground state-energy/lattice-energy link.

It is currently important to achieve and understand adjustments of optical properties: "guest cation" induced CT spectral shifts in Prussian Blue are shown to be driven (via its specific effect on the Fe(CN)6 CT-donor entity) by the cation lattice-energy interaction, as inferred from microgravimetry of introduced alkali-metal ions, and from independent solubility correlations for other intercalated cations.