Ab initio Molecular Dynamics Investigation on the Permeation of Sodium and Chloride Ions through Nanopores in Graphene and Hexagonal Boron Nitride Membranes.

Nanoporous membranes promise energy-efficient water desalination. Hexagonal boron nitride (h-BN), like graphene, exhibits outstanding physical and chemical properties, making it a promising candidate for water treatment. We employed Car-Parrinello molecular dynamics simulations to establish an accurate modeling of Na+ and Cl- permeation through hydrogen passivated nanopores in graphene and h-BN membranes. We demonstrate that ion separation works well for the h-BN system by imposing a barrier of 0.13 eV and 0.24 eV for Na+ and Cl- permeation, respectively. In contrast, for permation of the graphene nanopore, the Cl- ion faces a minimum of energy of 0.68 eV in the nanopore plane and is prone toward blockade of the nanopore, while the Na+ ion experiences a slight minimum of 0.03 eV. Overall, the desalination performance of h-BN nanopores surpasses that of their graphene counterparts.

Exploring the dynamics of DNA nucleotides in graphene/h-BN nanopores: insights from ab initio molecular dynamics.

Nanopore devices based on graphene and h-BN heterostructures show outstanding electrical and physical characteristics for high throughput label-free DNA sequencing. On top of their suitability for DNA sequencing with the ionic current method, G/h-BN nanostructures are promising for DNA sequencing by employing the in-plane electronic current. The influence of the nucleotide/device interaction on the in-plane current has been widely explored for static-optimized geometries. Therefore, it is essential to investigate the dynamics of the nucleotides within the G/h-BN nanopores to gain a comprehensive view of their interaction with the nanopores. In this study, we investigated the dynamic interaction between nucleotides and nanopores in horizontal graphene/h-BN/graphene heterostructures. The insulating h-BN layer, where the nanopores are implemented, changes the in-plane charge transport mechanism into the quantum mechanical tunneling regime. We employed the Car-Parrinello molecular dynamics (CPMD) formalism to investigate the interaction of the nucleotides with nanopores in a vacuum as well as in an aqueous environment. The simulation was performed in the NVE canonical ensemble with an initial temperature of 300 K. The results indicate that the interaction between the electronegative ends of the nucleotides and the atoms at the nanopore edge is essential for the dynamic behavior of the nucleotides. Moreover, water molecules have a substantial effect on the dynamics and interactions of the nucleotides with nanopores.

In-plane graphene/h-BN/graphene heterostructures with nanopores for electrical detection of DNA nucleotides.

The in-plane heterostructure of graphene and h-BN has unique physical and electrical characteristics, which can be exploited for single-molecule DNA sequencing. On this account, we propose a nanostructure based on a nanopore in graphene/h-BN/graphene heterostructures as a viable approach for in-plane electrical detection. The insulating h-BN layer changes the charge transport to the quantum tunneling regime, which is very sensitive to the electrostatic interactions induced by nucleotides during their translocation through the nanopore. Density functional theory (DFT) is utilized to study the membrane/nanopore interactions as well as their interactions with different nucleotides (dAMP, dGMP, dCMP, and dTMP). The results indicate that the nucleotides show stronger interactions with nanopores in h-BN rather than nanopores in pristine graphene. For the calculation of electronic transport, non-equilibrium Green's function (NEGF) formalism at the first principles level is employed. The in-plane currents at different applied voltages are calculated in the presence of different nucleotides in the nanopore. The sensitivity of the proposed nanostructure towards different nucleotides is measured based on the current modulation induced by each nucleotide. The graphene/h-BN/graphene heterostructure shows higher sensitivity toward different nucleotides compared to a similar structure consisting of pristine graphene and can be considered as a promising candidate for DNA sequencing applications.

Wireless, miniaturized, semi-implantable electrocorticography microsystem validated in vivo.

This paper reports on the design, development, and test of a multi-channel wireless micro-electrocorticography (µECoG) system. The system consists of a semi-implantable, ultra-compact recording unit and an external unit, interfaced through a 2.4 GHz radio frequency data telemetry link with 2 Mbps (partially used) data transfer rate. Encased in a 3D-printed 2.9 cm × 2.9 cm × 2.5 cm cubic package, the semi-implantable recording unit consists of a microelectrode array, a vertically-stacked PCB platform containing off-the-shelf components, and commercially-available small-size 3.7-V, 50 mAh lithium-ion batteries. Two versions of microelectrode array were developed for the recording unit: a rigid 4 × 2 microelectrode array, and a flexible 12 × 6 microelectrode array, 36 of which routed to bonding pads for actual recording. The external unit comprises a transceiver board, a data acquisition board, and a host computer, on which reconstruction of the received signals is performed. After development, assembly, and integration, the system was tested and validated in vivo on anesthetized rats. The system successfully recorded both spontaneous and evoked activities from the brain of the subject.

Ab-Initio Molecular Dynamics Simulation of Condensed-Phase Reactivity: The Electrolysis of Amino Acids and Peptides.

Electrolysis is a potential candidate for a quick method of wastewater cleansing. However, it is necessary to know what compounds might be formed from bioorganic matter. We want to know if there are toxic intermediates and if it is possible to influence the product formation by the variation in initial conditions. In the present study, we use Car-Parrinello molecular dynamics to simulate the fastest reaction steps under such circumstances. We investigate the behavior of amino acids and peptides under anodic conditions. Such highly reactive situations lead to chemical reactions within picoseconds, and we can model the reaction mechanisms in full detail. The role of the electric current is to discharge charged species and, hence, to produce radicals from ions. This leads to ultra-fast radical reactions in a bulk environment, which can also be seen as redox reactions as the oxidation states change. In the case of amino acids, the educts can be zwitterionic, so we also observe complex acid-base chemistry. Hence, we obtain the full spectrum of condensed-phase chemistry.

Electronic properties of graphene-ZnO interface: a density functional theory investigation.

Electronic properties of graphene/ZnO interface have been theoretically investigated by applying first principles density functional theory calculations. This interface is demonstrated to have interesting electrical, optical and chemical properties and therefore, is employed in different applications. In our investigation the interface between graphene and different ZnO surfaces such as polar Zn-terminated [Formula: see text] and O-terminated [Formula: see text] surfaces as well as nonpolar [Formula: see text] surface are considered. Different interface properties such as equilibrium atomic structure, binding energy, charge transfer and band alignment are calculated for these interfaces. The calculated binding energies between graphene and different ZnO surfaces are within the range of van der Waals or physical adsorption. The results clearly reveal the essential role of oxygen density at the interface. The O- and Zn-terminated ZnO surfaces show the lowest and highest binding energies, respectively. The amount of charge transfer and the direction of interfacial dipole are also dominated by the number of oxygen atoms at the graphene/ZnO interface. Calculations for the interfacial band alignment reveal that a high/low density of oxygen atoms at the interface results in a Schottky/Ohmic contact. It is also shown that inducing oxygen vacancies at an oxygen rich interface leads to the lowering of the Schottky barrier.

Electronic properties of Ag-doped ZnO: DFT hybrid functional study.

Studying the possibility of a p-type conduction mechanism in the Ag-doped ZnO can clarify persisting ambiguities in the related materials and devices. Here, utilizing the first principles study by hybrid functional calculations, we conclude that the potential acceptor defects AgZn and VZn are rare in the low Fermi level conditions required for p-type conduction and, hence, can hardly contribute to the hole generation in ZnO regardless of the assumed O-rich condition. Our results also reveal the exothermicity of the reaction between VO and AgZn to form the complex defect VO-2AgZn which is shown to be a less effective donor than VO. The conversion of the VO to a less electronically effective complex defect is proposed as the mechanism responsible for the conductivity instabilities in the silver doped zinc oxide.

Interaction of oxygen vacancies and lanthanum in Hf-based high-k dielectrics: an ab initio investigation.

The interaction between oxygen vacancies and La atoms in the La doped HfO(2) dielectric were studied using first principles total energy calculations. La dopants in the vicinity of a neutral oxygen vacancy (V(O)) show lower formation energy compared to the La defects far from V(O) centres. La doping in HfO(2) leads to the shift of the defect states of oxygen vacancies towards the conduction band edge. A statistical average of this shift over several possible configurations of La atoms and V(O) shows that the incorporation of La effectively passivates the V(O) induced defect states leading to the reduction of the gate leakage current and improvement of the device reliability.