No abstract

Background: The notion of smart city has grown popular over the past few years. It embraces several dimensions depending on the meaning of the word "smart" and benefits from innovative applications of new kinds of information and communications technology to support communal sharing.Methods: By relying on prior literature, this paper proposes a conceptual framework with three dimensions: (1) human, (2) technology, and (3) organization, and explores a set of fundamental factors that make a city smart from a sharing economy perspective.Results: Using this triangle framework, we discuss what emerging blockchain technology may contribute to these factors and how its elements can help smart cities develop sharing services.Conclusions: This study discusses how blockchain-based sharing services can contribute to smart cities based on a conceptual framework. We hope it can stimulate interest in theory and practice to foster discussions in this area.

We report a systematic empirical study of nanoparticle internalization into cells via non-specific pathways. The nanoparticles were comprised of commercial quantum dots (QDs) that were highly visible under a fluorescence confocal microscope. Surface-modified QDs with basic biologically significant moieties, e.g. carboxyl, amino, and streptavidin, were used, in combination with surface derivatization with polyethylene glycol (PEG) for a range of immortalized cell lines. Internalization rates were derived from image analysis and a detailed discussion about the effect of nanoparticle size, charge and surface groups is presented. We find that PEG derivatization dramatically suppresses the non-specific uptake while PEG-free carboxyl and amine functional groups promote QD internalization. These uptake variations displayed a remarkable consistency across different cell types. The reported results are important for experiments concerned with cellular uptake of surface-functionalized nanomaterials, both when non-specific internalization is undesirable and when it is intended for material to be internalized as efficiently as possible.

Researchers detect individual CO2 physisorption with suspended bilayer graphene based on induced Coulomb impurity scattering.

Motivated by the high expectation for efficient electrostatic modulation of charge transport at very low voltages, atomically thin 2D materials with a range of bandgaps are investigated extensively for use in future semiconductor devices. However, researchers face formidable challenges in 2D device processing mainly originated from the out‐of‐plane van der Waals (vdW) structure of ultrathin 2D materials. As major challenges, untunable Schottky barrier height and the corresponding strong Fermi level pinning (FLP) at metal interfaces are observed unexpectedly with 2D vdW materials, giving rise to unmodulated semiconductor polarity, high contact resistance, and lowered device mobility. Here, FLP observed from recently developed 2D semiconductor devices is addressed differently from those observed from conventional semiconductor devices. It is understood that the observed FLP is attributed to inefficient doping into 2D materials, vdW gap present at the metal interface, and hybridized compounds formed under contacting metals. To provide readers with practical guidelines for the design of 2D devices, the impact of FLP occurring in 2D semiconductor devices is further reviewed by exploring various origins responsible for the FLP, effects of FLP on 2D device performances, and methods for improving metallic contact to 2D materials.

The direct growth of graphene on insulating substrate is highly desirable for the commercial scale integration of graphene due to the potential lower cost and better process control. We report a simple, direct deposition of nanocrystalline graphene (NCG) on insulating substrates via catalyst-free plasma-enhanced chemical vapor deposition at relatively low temperature of ∼800 °C. The parametric study of the process conditions that we conducted reveals the deposition mechanism and allows us to grow high quality films. Based on such film, we demonstrate the fabrication of a large-scale array of nanoelectromechanical (NEM) switches using regular thin film process techniques, with no transfer required. Thanks to ultra-low thickness, good uniformity, and high Young's modulus of ∼0.86 TPa, NCG is considered as a promising material for high performance NEM devices. The high performance is highlighted for the NCG switches, e.g. low pull-in voltage <3 V, reversible operations, minimal leakage current of ∼1 pA, and high on/off ratio of ∼10(5).

van der Waals (vdW) interactions play a central role in the surface-related physics and chemistry. Tuning of the correlated charge fluctuation in a vdW complex is a plausible way of modulating the molecules interaction at the atomic surface. Here, we report the vdW interaction tunability of the graphene-CO2 complex by combining the first-principles calculations with the vdW density functionals and the time evaluation measurements of CO2 molecules adsorption/desorption on graphene under an external electric field. The field-dependent charge transfer within the complex unveils the controllable tuning of CO2 from acceptor to donor. Meanwhile, the configuration of the adsorbed molecule, the equilibrium distance from graphene and O-C-O bonding angle, is modified accordingly. The range of electrical tunability is a unique feature for each type of molecule.

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. The durability of polymer exchange membrane (PEM) fuel cells, under a wide range of operational conditions, has been attracting intensive attention, as durability is one of the largest barriers for commercialization of this promising technology. In the present work, membrane electrode assembly (MEA) degradation of a four-cell stack with Nafion membranes of different thicknesses, including N117, N115, NR212, and NR211, was carried out for 1000 h under idle conditions. By means of several on-line electrochemical measurements, the performance of the individual cells was analyzed at different times during the degradation process. The results indicate that the cells with thinner membranes have a lower open circuit voltage (OCV) due to the higher fuel crossover. Before degradation, the thickness of the membranes correlates with performance of the cell. However, with the advancement of degradation, the performance of cells with thinner membranes degraded much faster than those with thicker membranes, especially after 800 h of operation. The fast performance degradation for thinner membranes is evident by a dramatic increase in hydrogen crossover indicating membrane thinning or pinhole formation. Crown