Search

Waterflooding is one of the geotechniques used to recover fuel sources from nanoporous geological formations. The scientific understanding of the process that involves the multiphase flow of nanoconfined fluids, however, has lagged, mainly due to the complex nanopore geometries and chemical compositions. To enable the benchmarked flow of nanoconfined fluids, architected geomaterials, such as synthesized mesoporous silica with tunable pore shapes and surface chemical properties, are used for designing and conducting experiments and simulations. This work uses a modified many-body dissipative particle dynamics (mDPD) model with accurately calibrated parameters to perform parametric flow simulations for studying the influences of waterflooding-driven power, pore shape, surface roughness, and surface wettability on the multiphase flow in heptane-saturated silica nanochannels. Remarkably, up to an 80% reduction in the effective permeability is found for water-driven heptane flow in a baseline 4.5-nm-wide slit channel when compared with the Hagen–Poiseuille equation. In the 4.5-nm-wide channels with architected surface roughness, the flow rate is found to be either higher or lower than the baseline case, depending on the shape and size of cross sections. High wettability of the solid surface by water is essential for achieving a high recovery of heptane, regardless of surface roughness. When the solid surface is less wetting or nonwetting to water, the existence of an optimal waterflooding-driven power is found to allow for the highest possible recovery. A detailed analysis of the evolution of the transient water–heptane interface in those nanochannels is presented to elucidate the underlying mechanisms that impact or dictate the multiphase flow behaviors.

A modified many-body dissipative particle dynamics (mDPD) model is rigorously calibrated to achieve realistic fluid–fluid/solid interphase properties and applied for mesoscale flow simulations to elucidate the transport mechanisms of heptane liquid and water, respectively, through pore networks formed by packed silica nanoparticles with a uniform diameter of 30 nm. Two million CPU core hours were used to complete the simulation studies. Results show reduction of permeability by 54–64% in heptane flow and by 88–91% in water flow, respectively, compared to the Kozeny–Carman equation. In these nanopores, a large portion of the fluids are in the near-wall regions and thus not mobile due to the confinement effect, resulting in reduced hydraulic conductivity. Moreover, intense oscillations in the calculated flow velocities also indicate the confinement effect that contests the external driven force to flow. The generic form of Darcy’s law is considered valid for flow through homogeneous nanopore networks, while permeability depends collectively on pore size and surface wettability. This fluid-permeability dependency is unique to flow in nanopores. In addition, potential dependence of permeability on pore connectivity is observed when the porosity remains the same in different core specimens.

Silicon is the cornerstone of electronics and photonics. In this context, almost all integrated devices derived from two-dimensional (2D) materials stay rooted in silicon technology. However, as the growth substrate, silicon has long been thought to be a hindrance for growing 2D materials through bottom-up methods that require high growth temperatures, and thus, indirect routes are usually considered instead. Although promising growth of large-area 2D materials on silicon has been demonstrated, the direct growth of single-crystalline materials using low-thermal-budget synthesis methods remains challenging. Here, we report the room-temperature growth of millimeter-scale single-crystal 2D metal halides on silicon substrates with a hydroxyl-terminated surface. Theoretical calculations reveal that the activation energy for surface diffusion can be reduced by an order of magnitude by terminating the surface with hydroxyl groups, from which on-silicon growth is greatly facilitated at room temperature and enables a 4-order-of-magnitude increase in area. The high quality and uniformity of the resulting single crystals are further evidenced. The optoelectronic devices employing the as-grown materials show an ultralow dark current of 10–13A and a high detectivity of 1013Jones, thereby corroborating a weak-light detection ability. These results would point to a rich space of surface modulation that can be used to surmount current limitations and demonstrate a promising strategy for growing 2D materials directly on silicon at room temperature to produce large single crystals.

The phase behavior of hydrocarbon fluids confined in porous media has been reported to deviate significantly from that in the bulk environment due to the existence of sub-10 nm pores. Though experiments and simulations have measured the bubble/dew points and sorption isotherms of hydrocarbons confined in both natural and synthetic nanopores, the confinement effects in terms of the strength of fluid–pore interactions tuned by surface wettability and chemistry have received comparably less discussion. More importantly, the underlying physics of confinement-induced phenomena remain obfuscated. In this work, we studied the phase behavior and capillary condensation of n-hexane to understand the effects of confinement at the molecular level. To systematically investigate the pore effects, we constructed two types of wall confinements; one is a structureless virtual wall described by the Steele potential and the other one is an all-atom amorphous silica structure with surface modified by hydroxyl groups. Our numerical results demonstrated the importance of fluid–pore interaction, pore size, and pore morphology effects in mediating the pressure–volume–temperature (PVT) properties of hydrocarbons. The most remarkable finding of this work was that the saturation pressure predicted from the van der Waals-type adsorption isothermal loop could be elevated or suppressed relative to the bulk phase, as illustrated in the graphical abstract. As the surface energy (i.e., fluid–pore interaction) decreased, the isothermal vapor pressure increased, indicating a greater preference for the fluid to exist in the vapor state. Sufficient reduction of the fluid–pore interactions could even elevate the vapor pressure above that of the bulk fluid.

The synapse is one of the fundamental elements in human brain performing functions such as learning, memorizing, and visual processing. The implementation of synaptic devices to realize neuromorphic computing and sensing tasks is a key step to artificial intelligence, which, however, has been bottlenecked by the complex circuitry and device integration. We report a high-performance charge-trapping memory synaptic device based on two-dimensional (2D) MoS2and high-k Ta2O5–TiO2(TTO) composite to build efficient and reliable neuromorphic system, which can be modulated by both electrical and optical stimuli. Significant and essential synaptic behaviors including short-term plasticity, long-term potentiation, and long-term depression have been emulated. Such excellent synaptic behaviors originated from the good nonvolatile memory performance due to the high density of defect states in the engineered TTO composite. The 2D synaptic device also exhibits effective switching by incident light tuning, which further enables pattern recognition with accuracy rate reaching 100%. Such experimental demonstration paves a robust way toward a multitask neuromorphic system and opens up potential applications in future artificial intelligence and sensing technology.

Bismuth triiodide, BiI3, is one of the promising 2D layered materials from the family of metal halides. The unique electronic structure and properties make it an attractive material for the room-temperature gamma/X-ray detectors, high-efficiency photovoltaic absorbers, and Bi-based organic–inorganic hybrid perovskites. Other possibilities including optoelectronic devices and optical circuits are envisioned but rarely experimentally confirmed yet. Here, we report the synthesis of vertical 2D BiI3nanoplates using the physical vapor deposition mechanism. The obtained products were found easy to be separated and transferred to other substrates. Photodetectors employing such 2D nanoplates on polyethylene terephthalate substrate are demonstrated to be quite sensitive to red light (635 nm) with good responsivity (2.8 A W–1), fast stable photoresponse (3/9 ms for raise/decay times), and remarkable specific detectivity (1.2 × 1012jones), which attest to high comparability of the assembled components with many latest 2D nanostructured light sensors. In addition, such photodetectors exhibit outstanding mechanical stability and durability under different bending strains within the theoretically affordable levels, suggesting a variety of potential applications of 2D BiI3for flexible devices.

A third-order accurate reconstructed discontinuous Galerkin method, namely rDG(P 1 P 2 ), is presented to solve the Reynolds-Averaged Navier–Stokes (RANS) equations, along with the modified one-equation model of Spalart and Allmaras (SA) on 3D curved grids. In this method, a piecewise quadratic polynomial solution (P 2 ) is obtained using a least-squares method from the underlying piecewise linear DG(P 1 ) solution. The reconstructed quadratic polynomial solution is then used for computing the inviscid and the viscous fluxes. Furthermore, Hermite Weighted Essentially Non-Oscillatory (WENO) reconstruction is used to guarantee the stability of the developed rDG method. A number of benchmark test cases based on a set of uniformly refined quadratic curved meshes are presented to assess the performance of the resultant rDG(P 1 P 2 ) method for turbulent flow problems. The numerical results demonstrate that the rDG(P 1 P 2 ) method is able to obtain reliable and accurate solutions to 3D compressible turbulent flows at a cost slightly higher than its underlying second-order DG(P 1 ) method. [ABSTRACT FROM AUTHOR]

Highlights: [•] A third-order, parallel, implicit reconstructed discontinuous Galerkin method. [•] Significant lower memory requirement versus third-order implicit DG (P2). [•] Jacobian formulation based on automatic differentiation is easy and robust. [•] For the compressible Euler and NavierStokes equations on 3D hybrid grids. [•] Fast convergence for a wide rage of flow problems including complex configurations. [Copyright &y& Elsevier]

Highlights: [•] An implicit method for a Hermite WENO reconstruction-based DG method, IRDG (P1P2), is developed. [•] It adds one order of accuracy to the underlying implicit DG (P1) without much extra computing cost. [•] It can achieve the 3rd-order accuracy at a much lower memory requirement than implicit DG (P2). [•] The approximate Jacobian matrix is simply based on the underlying DG (P1), which is easy to assemble. [•] The fast convergence property is shown in a variety of test cases, including complex configurations. [Copyright &y& Elsevier]

On the basis of first-principles density functional calculations, we predict that Li-decorated graphyne can serve as a promising candidate for hydrogen storage, with a largest storage capacity of 18.6 wt %. The average adsorption energy of hydrogen is about −0.27 eV/H2, indicating that the doped system is an ideal hydrogen storage material at ambient conditions. It is proposed that the polarization mechanism, which stems from the electric field induced by the ionic Li coated on the graphyne, plays a key role in the adsorption of H2molecules. Furthermore, the formation of the hydrogen–hydrogen complex also stabilizes the adopted hydrogen molecules.

The microstructure of room‐temperature silver selenide thin films prepared by pulsed laser deposition (PLD) was investigated by transmission electron microscope (TEM). Two phases existed in room‐temperature silver selenide. One was orthorhombic phase (O) and the other was identified as monoclinic phase (M) by TEM tilting experiments. The monoclinic phase can transform to orthorhombic phase along [100]Mdirection under the irradiation of electron beam. Thermal stress induced by the difference of coefficient of thermal expansion (CTE) of Ag2Se and Cu gridding/NaCl substrate is thought to play an important role in this phase transformation.

The thermodynamic state and kinetic process of low-temperature deoxygenation reaction of graphene oxide (GO) have been investigated for better understanding on the reduction mechanism by using Differential Scanning Calorimetry (DSC), Thermogravimetry-Mass Spectrometry (TG-MS), and X-ray Photo-electron Spectroscopy (XPS). It is found that the thermal reduction reaction of GO is exothermic with degassing of CO2, CO and H2O. Graphene is thermodynamically more stable than GO. The deoxygenation reaction of GO is kinetically controlled and the activation energy for GO is calculated to be 167kJ/mol (1.73 eV/atom).

The amorphous/crystalline phase change behavior of (AGT) electrolyte was investigated. Satisfactory electrolytic resistive switching phenomena were observed in the memory cells composed of amorphous or crystalline AGT films sandwiched between Ag and Pt electrodes. The measured high and low resistance values of amorphous/crystalline cells are distinguishable and in different order of magnitudes. The electrically driven amorphous/crystalline phase change was also demonstrated in the cells sandwiched between two Pt electrodes. It is proposed that by controlling and using the electrolytic resistive switching in amorphous/crystalline cells and the electrically driven amorphous/crystalline phase change of these cells, a new type of four-state memory might be created.

Memory properties of p-Si/ultrathin /metal capacitors have been investigated, in which all the high- dielectric films were derived by atomic layer deposition technique. Using a film as the charge trapping layer, a large memory window of and a high charge trap density of have been achieved. A 53% initial memory window can still be maintained after of retention even after adopting an ultrathin tunneling layer of . The experimental results also demonstrated that adding into films can improve the memory characteristics as compared with the memory capacitors employing pure as the charge trapping layer.

Organic field-effect transistors (OFETs) as nonvolatile memory units are essential for lightweight and flexible electronics, yet the practical application remains a great challenge. The positively charged defects in pentacene film at the interface between pentacene and polymer caused by environmental conditions, as revealed by theoretical and experimental research works, result in unacceptable high programming/erasing (P/E) gate voltages in pentacene OFETs with polymer charge-trapping dielectric. Here, we report a pentacene OFET in which an n-type semiconductor layer was intercalated between a polymer and a blocking insulator. In this structure, the hole barrier caused by the defect layer can be adjusted by the thickness and charge-carrier density of the n-type semiconductor interlayer based on the electrostatic induction theory. This idea was implemented in an OFET structure Cu/pentacene/poly(2-vinyl naphthalene) (PVN)/ZnO/SiO2/Si(p+), which shows low P/E gate voltages, large field-effect mobility (0.73 cm2V–1s–1), fast P/E speeds (responding to a pulse width of 5 × 10–4s), and long retention time in air.

Mesoscopic simulations of hydrocarbon flow in source shales are challenging, in part due to the heterogeneous shale pores with sizes ranging from a few nanometers to a few micrometers. Additionally, the sub-continuum fluid–fluid and fluid–solid interactions in nano- to micro-scale shale pores, which are physically and chemically sophisticated, must be captured. To address those challenges, we present a GPU-accelerated package for simulation of flow in nano- to micro-pore networks with a many-body dissipative particle dynamics (mDPD) mesoscale model. Based on a fully distributed parallel paradigm, the code offloads all intensive workloads on GPUs. Other advancements, such as smart particle packing and no-slip boundary condition in complex pore geometries, are also implemented for the construction and the simulation of the realistic shale pores from 3D nanometer-resolution stack images. Our code is validated for accuracy and compared against the CPU counterpart for speedup. In our benchmark tests, the code delivers nearly perfect strong scaling and weak scaling (with up to 512 million particles) on up to 512 K20X GPUs on Oak Ridge National Laboratory's (ORNL) Titan supercomputer. Moreover, a single-GPU benchmark on ORNL's SummitDev and IBM's AC922 suggests that the host-to-device NVLink can boost performance over PCIe by a remarkable 40%. Lastly, we demonstrate, through a flow simulation in realistic shale pores, that the CPU counterpart requires 840 Power9 cores to rival the performance delivered by our package with four V100 GPUs on ORNL's Summit architecture. This simulation package enables quick-turnaround and high-throughput mesoscopic numerical simulations for investigating complex flow phenomena in nano- to micro-porous rocks with realistic pore geometries. Program title: USER MESO 2.5 Program files doi: http://dx.doi.org/10.17632/zzpv74bz9m.1 Licensing provisions: GNU General Public License 3 Programming language: CUDA C/C++ with MPI and OpenMP Nature of problem: Particle-based simulation of multiphase flow and fluid–solid interaction in nano- to micro-scale pore networks of arbitrary pore geometries. Solution method: Fluid particles and solid wall particles are modeled with a many-body dissipative particle dynamics (mDPD) model – a mesoscopic model for coarse-grained fluid and solid molecules. The pore surface wall boundary for arbitrary surface geometries is modeled with a no-slip boundary condition for fluid particles that prevents fluid particles from indefinitely penetrating in the walls. The time evolution of the system is integrated using the Velocity-Verlet algorithm. Restrictions: The code is compatible with NVIDIA GPUs with compute capability 3.0 and above. Unusual features: The code is implemented on GPGPUs with significantly improved speed. • A GPU-accelerated DPD simulator for nano to micro-pore flow. • Good weak and strong-scalability on Titan at ORNL. • Advanced device-to-host interconnects help significant speedup. • Performance on V100 GPUs suggests good scalability on Summit at ORNL. • Demonstrated code capability for realistic shale rock analysis. [ABSTRACT FROM AUTHOR]

The roles of moisture in resistive switching (RS) devices are closely related to the RS mechanism. In principle, the nonpolar RS promises symmetric behaviors independent of the polarities of operating voltages. However, the effect of humidity on the RS characteristics of Pt/TiO2?x/Pt nonpolar cells is confirmed to be polarity-dependent. The positive electroforming threshold voltage decreases when humidity increases, whereas the negative one is unaffected. This asymmetric phenomenon can be attributed to the polarity-associated rule of current varying with humidity before electroforming. The voltage distribution in the device and then the electroforming threshold voltage are modified.

On the basis of the density functional theory coupled with the Boltzmann transport equation with relaxation time approximation, we investigate the electronic structure and predict the electron mobility of few-layer InSe. Few-layer InSe has a tunable band gap on thickness. At the same time, it possesses a high carrier mobility on the order of 103cm2V?1s?1. As we demonstrated, few-layer InSe has potential applications for next-generation electronic materials owing to its considerable band gap and high carrier mobility.

A reconstructed discontinuous Galerkin (rDG(P1P2)) method, originally introduced for the compressible Euler equations, is developed for the solution of the compressible Navier–Stokes equations on 3D hybrid grids. In this method, a piecewise quadratic polynomial solution is obtained from the underlying piecewise linear DG solution using a hierarchical Weighted Essentially Non-Oscillatory (WENO) reconstruction. The reconstructed quadratic polynomial solution is then used for the computation of the inviscid fluxes and the viscous fluxes using the second formulation of Bassi and Reay (Bassi–Rebay II). The developed rDG(P 1 P 2 ) method is used to compute a variety of flow problems to assess its accuracy, efficiency, and robustness. The numerical results demonstrate that the rDG(P 1 P 2 ) method is able to achieve the designed third-order of accuracy at a cost slightly higher than its underlying second-order DG method, outperform the third order DG method in terms of both computing costs and storage requirements, and obtain reliable and accurate solutions to the direct numerical simulation (DNS) of compressible turbulent flows. [ABSTRACT FROM AUTHOR]

The amorphous/crystalline phase change behavior of Ag10Ge15Te75(AGT) electrolyte was investigated. Satisfactory electrolytic resistive switching phenomena were observed in the memory cells composed of amorphous or crystalline AGT films sandwiched between Ag and Pt electrodes. The measured high and low resistance values of amorphous/crystalline cells are distinguishable and in different order of magnitudes. The electrically driven amorphous/crystalline phase change was also demonstrated in the cells sandwiched between two Pt electrodes. It is proposed that by controlling and using the electrolytic resistive switching in amorphous/crystalline cells and the electrically driven amorphous/crystalline phase change of these cells, a new type of four-state memory might be created.

Memory properties of p-Si/ultrathin Al2O3∕(HfO2)0.8(Al2O3)0.2∕Al2O3/metal capacitors have been investigated, in which all the high-kdielectric films were derived by atomic layer deposition technique. Using a (HfO2)0.8(Al2O3)0.2film as the charge trapping layer, a large memory window of 5.7Vand a high charge trap density of 2.4×1013cm−2have been achieved. A 53% initial memory window can still be maintained after 10yearsof retention even after adopting an ultrathin tunneling Al2O3layer of 2nm. The experimental results also demonstrated that adding Al2O3into HfO2films can improve the memory characteristics as compared with the memory capacitors employing pure HfO2as the charge trapping layer.