There is a demand for the manufacture of two-dimensional (2D) materials with high-quality single crystals of large size. Usually, epitaxial growth is considered the method of choice
in preparing ...single-crystalline thin films, but it requires single-crystal substrates for deposition. Here we present a different approach and report the synthesis of single-crystal-like monolayer graphene films on polycrystalline substrates. The technological realization of the proposed method resembles the Czochralski process and is based on the evolutionary selection
approach, which is now realized in 2D geometry. The method relies on 'self-selection' of the fastest-growing domain orientation, which eventually overwhelms the slower-growing domains and yields a single-crystal continuous 2D film. Here we have used it to synthesize foot-long graphene films at rates up to 2.5 cm h
that possess the quality of a single crystal. We anticipate that the proposed approach could be readily adopted for the synthesis of other 2D materials and heterostructures.
Monolayer hexagonal boron nitride (hBN) attracts significant attention due to the potential to be used as a complementary two-dimensional dielectric in fabrication of functional 2D heterostructures. ...Here we investigate the growth stages of the hBN single crystals and show that hBN crystals change their shape from triangular to truncated triangular and further to hexagonal depending on copper substrate distance from the precursor. We suggest that the observed hBN crystal shape variation is affected by the ratio of boron to nitrogen active species concentrations on the copper surface inside the CVD reactor. Strong temperature dependence reveals the activation energies for the hBN nucleation process of ∼5 eV and crystal growth of ∼3.5 eV. We also show that the resulting h-BN film morphology is strongly affected by the heating method of borazane precursor and the buffer gas. Elucidation of these details facilitated synthesis of high quality large area monolayer hexagonal boron nitride by atmospheric pressure chemical vapor deposition on copper using borazane as a precursor.
By creating nanoscale pores in a layer of graphene, it could be used as an effective separation membrane due to its chemical and mechanical stability, its flexibility and, most importantly, its ...one-atom thickness. Theoretical studies have indicated that the performance of such membranes should be superior to state-of-the-art polymer-based filtration membranes, and experimental studies have recently begun to explore their potential. Here, we show that single-layer porous graphene can be used as a desalination membrane. Nanometre-sized pores are created in a graphene monolayer using an oxygen plasma etching process, which allows the size of the pores to be tuned. The resulting membranes exhibit a salt rejection rate of nearly 100% and rapid water transport. In particular, water fluxes of up to 10(6) g m(-2) s(-1) at 40 °C were measured using pressure difference as a driving force, while water fluxes measured using osmotic pressure as a driving force did not exceed 70 g m(-2) s(-1) atm(-1).
Inspired by recent reports on possible proton conductance through graphene, we have investigated the behavior of pristine graphene and defect engineered graphene membranes for ionic conductance and ...selectivity with the goal of evaluating a possibility of its application as a proton selective membrane. The averaged conductance for pristine chemical vapor deposited (CVD) graphene at pH1 is ∼4 mS/cm2 but varies strongly due to contributions from the unavoidable defects in our CVD graphene. From the variations in the conductance with electrolyte strength and pH, we can conclude that pristine graphene is fairly selective and the conductance is mainly due to protons. Engineering of the defects with ion beam (He+, Ga+) irradiation and plasma (N2 and H2) treatment showed improved areal conductance with high proton selectivity mostly for He-ion beam and H2 plasma treatments, which agrees with primarily vacancy-free type of defects produced in these cases confirmed by Raman analysis.
ABSTRACT
Empirical line lists BRYTS for the open shell molecule 89Y16O (yttrium oxide) and its isotopologues are presented. The line lists cover the six lowest electronic states: $X\, {}^{2}\Sigma ...^{+}$, $A\, {}^{2}\Pi$, $A^{\prime }\, {}^{2}\Delta$, $B\, {}^{2}\Sigma ^{+}$, $C\, {}^{2}\Pi$, and $D\, {}^{2}\Sigma ^{+}$ up to 60 000 cm−1 (<0.167 $\mu$m) for rotational excitation up to J = 400.5. An ab initio spectroscopic model consisting of potential energy curves (PECs), spin–orbit, and electronic angular momentum couplings is refined by fitting to experimentally determined energies of YO, derived from published YO experimental transition frequency data. The model is complemented by empirical spin-rotation and Λ-doubling curves and ab initio dipole moment and transition dipole moment curves computed using multireference configuration interaction (MRCI). The ab initio PECs computed using the complete basis set limit extrapolation and the coupled-cluster CCSD(T) method with its higher quality provide an excellent initial approximation for the refinement. Non-adiabatic coupling curves for two pairs of states of the same symmetry A/C and B/D are computed using a state-averaged complete active space self-consistant field theory (CASSCF) and used to build diabatic representations for the $A\, {}^{2}\Pi$, $C\, {}^{2}\Pi$, $B\, {}^{2}\Sigma ^{+}$, and $D\, {}^{2}\Sigma ^{+}$ curves. The experimentally derived energies of 89Y16O utilized in the fit are used to replace the corresponding calculated energy values in the BRYTS line list. Simulated spectra of YO show excellent agreement with the experiment, where it is available. Calculated lifetimes of YO are tuned to agree well with the experiment, where available. The BRYTS YO line lists are available from the ExoMol database (www.exomol.com).
Voltage-Gated Hydrophobic Nanopores Smirnov, Sergei N; Vlassiouk, Ivan V; Lavrik, Nickolay V
ACS nano,
09/2011, Letnik:
5, Številka:
9
Journal Article
Recenzirano
Hydrophobicity is a fundamental property that is responsible for numerous physical and biophysical aspects of molecular interactions in water. Peculiar behavior is expected for water in the vicinity ...of hydrophobic structures, such as nanopores. Indeed, hydrophobic nanopores can be found in two distinct states, dry and wet, even though the latter is thermodynamically unstable. Transitions between these two states are kinetically hindered in long pores but can be much faster in shorter pores. As it is demonstrated for the first time in this paper, these transitions can be induced by applying a voltage across a membrane with a single hydrophobic nanopore. Such voltage-induced gating in single nanopores can be realized in a reversible manner through electrowetting of inner walls of the nanopores. The resulting I–V curves of such artificial hydrophobic nanopores mimic biological voltage-gated channels.
Proton exchange membranes are at the heart of various technologies utilizing electrochemical storage of intermittent energy sources and powering electrical devices. Current state of the art membranes ...are based on perfluorosulfonic acid, introduced more than a half century ago. Low specificity to protons accompanied by permeance by other species is one of the main impediments for various promising applications in green technologies in an energy sustainable economy. Here we present composite membranes that are exclusively proton selective and do not allow crossover of any ionic or molecular species other than protons. Membranes have high proton conductivity and exceptional mechanical and chemical stability and thus may significantly improve performance of hydrogen-based technologies such as electrolyzers, various kinds of fuel cells, and flow batteries in the future.
pH switchable valves were constructed using nanoporous membranes, the surface of which was modified by mixtures of aminopropyl trimethoxy silane and butyl trimethoxy silane. The modified membranes ...are dry at neutral and basic conditions because of their hydrophobicity but open to flux of aqueous solutions at slightly acidic pH because of protonation of amino groups. The resulting high contrast between the open and the closed states and a high flux in the open state because of large pore size make the approach attractive in applications where pH switching is employed, for example, in drug delivery applications.
Application of non-noble metal electrocatalysts in energy conversion and electrochemical sensing is of utmost importance. Herein, the enhancement in the electrocatalytic water splitting and ...nonenzymatic glucose sensing in alkaline media was realized from the synergistic effect of porous Ni/Co hydr(oxy)oxide structures grown on nickel foam via a facile bubble-templated electrodeposition approach followed by catalytic activation. The effect is likely due to synergy between the low overpotential of nickel and higher adsorption of hydrogen for cobalt in combination with enhanced surface area, where better diffusion of electrolyte in the interconnected pores and low charge-transfer resistance is best realized with the Ni/Co = 1:1 electrode. The overpotential for catalytic current density of 20 mA cm–2 is 132 mV for hydrogen evolution reaction (HER) and 338 mV for oxygen evolution reaction (OER) with the corresponding Tafel slopes of 55.3 and 66.1 mV dec–1, respectively. In a two-electrode configuration, the same Ni/Co = 1:1 electrodes allow the current density of 10 mA cm–2 to be achieved at a stable cell potential of 1.71 V. Moreover, the same electrode shows an excellent glucose sensitivity of 6.6 mA mM–1 cm–2 with minimal interference from uric and ascorbic acids.
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