Nanoscale Slits Research Articles

Diffusion/adsorption/dissolution coupling process of methane gas in kerogen nano-slit: Molecular simulation and a chemical potential-based mass transfer model

Understanding the multi-mechanism pore-scale gas transport in shale reservoirs plays a key role in estimating the reserves and production of shale gas. In this work, nano-scale slits confined by two pieces of quasi-planar organic kerogen materials were modeled on the atomic scale. An integrated solution to quantify the complicated mass transfer process was proposed, involving adsorption thermodynamics analyses, diffusion coefficient calculations for free and adsorbed gas, and a chemical potential-based diffusion model to predict the dissolution process. The calculated density distribution in the slit agreed well with the Molecular Dynamics results, which proves the model’s accuracy for various diffusion mechanisms.

Molecular simulation study of liquid sulfur adsorption and diffusion in calcite nanoscale slits under varying temperature and pressure conditions

In the late stages of extensive development of high-sulfur carbonate gas reservoirs, pressure decline leads to sulfur enrichment, and when the temperature exceeds sulfur's melting point, sulfur precipitates in a liquid form, severely restricting the exploitation of high-sulfur carbonate gas reservoirs. However, the adsorption mechanism of sulfur deposition remains poorly understood. In this study, we investigated the microscopic adsorption mechanism of liquid sulfur in calcite nanopores using molecular simulation methods. Our research revealed that liquid sulfur adsorption in calcite nanopores is primarily influenced by pore size. When the pore size is less than 160 Å, multilayer adsorption dominates, with a single-layer sulfur film thickness of approximately 5 Å. At the nanoscale, 1 g of calcite with a 40 Å nanopore structure exhibits excess adsorption of liquid sulfur ranging from 0.00734 to 0.0279 g. As pressure increases, the adsorption of two or more layers intensifies, while the diffusion coefficient decreases. Conversely, as temperature rises, the density of each layer decreases, and the diffusion coefficient increases. Simultaneously, the diffusion coefficient of liquid sulfur in calcite slits exhibits a power function increase as the pore size enlarges. Under a pressure of 15 MPa, when the temperature increases from 420 K to 480 K, the diffusion coefficient increases from 6.96 × 10−11 m²/s to 3.51 × 10−10 m²/s. This study provides valuable insights into the adsorption and diffusion behavior of liquid sulfur in calcite nanopores, which can inform the development of high-sulfur carbonate reservoirs.

Molecular simulation of methane adsorption in nanoscale rough slits

There are large amounts of nanoscale rough pores in shale, which provides the sites for methane adsorption. Proper understanding of the mechanisms of methane adsorption in nanoscale rough slits is important for estimating the shale gas reserves. In this study, graphene was used instead of shale to construct nanoscale slits with different widths and roughness, and the effects of roughness, slit width and pressure on the methane adsorption characteristics are investigated by using the GCMC and molecular dynamics methods. The results showed that the methane adsorption configurations are influenced by the slit width and surface roughness. The adsorption layers in rough slits are discontinuous and weak second adsorption layers are formed in large slits at high pressures. The inaccessible volume increases with the roughness resulting in the reduction of accessible volume. Therefore, both the excess adsorption and absolute adsorption decrease with the roughness, and they increase with the slit width in the microscopic scale due to the increased adsorption. While decrease slightly with the slit width in the mesoscopic scale due to the reduction of adsorbed phase density. The excess adsorption isotherms are well fitted by the Langmuir-Freundlich model. The adsorption is found more stable in smaller and rougher slits due to the superposition of adsorption potentials through the analysis of adsorbate potential energy and adsorption heat.

Machine Learning Techniques for Fluid Flows at the Nanoscale

Simulations of fluid flows at the nanoscale feature massive data production and machine learning (ML) techniques have been developed during recent years to leverage them, presenting unique results. This work facilitates ML tools to provide an insight on properties among molecular dynamics (MD) simulations, covering missing data points and predicting states not previously located by the simulation. Taking the fluid flow of a simple Lennard-Jones liquid in nanoscale slits as a basis, ML regression-based algorithms are exploited to provide an alternative for the calculation of transport properties of fluids, e.g., the diffusion coefficient, shear viscosity and thermal conductivity and the average velocity across the nanochannels. Through appropriate training and testing, ML-predicted values can be extracted for various input variables, such as the geometrical characteristics of the slits, the interaction parameters between particles and the flow driving force. The proposed technique could act in parallel to simulation as a means of enriching the database of material properties, assisting in coupling between scales, and accelerating data-based scientific computations.

Fabrication of Plasmonic Optical Nanoslit Pore Device for Single Molecule Analysis

About 60 years ago, the biological cell counter with an electrical detection technique was invented by Dr. Coulter. The solid state nanopores can be fabricated by using various techniques such as ion sculpting, high energy electron beams such as such as field emission scanning microscopy (FESEM) and transmission electron microscopy (TEM). However, this fabricated portable nanopore device is reported to have too high error rates. The high error rates may be attributed to the electrical double layer formed in the nanopore channel. Considering the fact that most biosensors are utilizing the optical detection technique, the optical pore device can be an excellent candidate for the next generation single molecule sensor. we have also fabricated the nanopore with its diameter ranging from 10 to 3 nm inside the FIB drilled aperture by using various surface treatments including electron beam irradiations and ion beam irradiation. In this report, we will address the fabrication of the optical pores with double slits. We observed the nanoscale Young’s interference from the double slits dependent upon the pitch. With increasing the pitch size, the periodic interference phenomena are observed and the optical intensity through the nanoscale slits are also periodically increasing We also fabricated the (7 x 7) hole array with its diameter of ~ 200 nm dependent upon the pitch between the holes with and without the nano- scale double slits. The highest enhancement of 1.72 at the peak is observed at 530 nm pitch without slits, and enhancement of 8.36 at the peak is also observed from the (7 x 7) hole array with a 530 nm pitch with nanoscale double slits. The enhancement of ~ 4-fold increase at the peak can be attributed to the constructive interference between two surface plasmon waves from hole and slits. This device can be utilized as optical manipulation and characterization for nanobio sensor, especially for single molecule analysis Figure 1

Towards the ultrafast optical nanopore platform for single molecule sensing

Abstract Recently there have been significant interests about fabrication of optical nanopore with its diameter range of 5 nm–10 nm for single molecule analysis and manipulation. However, due to very small amount of the optical intensity through the tiny size of the nano-aperture much smaller than the optical wavelength, the optical intensity enhancement via plasmonic effect by using pore array or periodic groove patterns have been tried. Also, the double slits with nanoscale width are reported to provide the constructive periodic modulation for the transverse-magnetic (TM) wave mode. In this report, the Au aperture arrays sidelined with the nanoscale double slit, and surrounded by 4 nanoscale slits have been fabricated with optical characterization in the visible range.

Pore diameter effects on phase behavior of a gas condensate in graphitic one-and two-dimensional nanopores

Molecular dynamics (MD) simulations were performed on a hydrocarbon mixture representing a typical gas condensate composed mostly of methane and other small molecules with small fractions of heavier hydrocarbons, representative of mixtures found in tight shale reservoirs. The fluid was examined both in bulk and confined to graphitic nano-scale slits and pores. Numerous widths and diameters of slits and pores respectively were examined under variable pressures at 300 K in order to find conditions in which the fluid at the center of the apertures would not be affected by capillary condensation due to the oil-wet walls. For the bulk fluid, retrograde phase behavior was verified by liquid volumes obtained from Voronoi tessellations. In cases of both one and two-dimensional confinement, for the smallest apertures, heavy molecules aggregated inside the pore space and compression of the gas outside the solid structure lead to decreases in density of the confined fluid. Normal density/pressure relationships were observed for slits having gaps of above 3 nm and pores having diameters above 6 nm. At 70 bar, the minimum gap width at which the fluid could pass through the center of slits without condensation effects was predicted to be 6 nm and the corresponding diameter in pores was predicted to be 8 nm. The models suggest that in nanoscale networks involving pores smaller than these limiting dimensions, capillary condensation should significantly impede transmission of natural gases with similar composition.

A Nanoscale-Localized Ion Damage Josephson Junction Using Focused Ion Beam and Ion Implanter.

High-T(c) Josephson junctions were fabricated by nanolithography using focused ion beam (FIB) milling and ion implantation. The junctions were formed in a YBa2Cu3O7-x, thin film in regions defined using a gold-film mask with 50-nm-wide (top) slits, engraved by FIB. The focused ion beam system parameters for dwell time and passes were set to remove gold up to a precise depth. 150 keV oxygen ions were implanted at a nominal dose of up to 5 x 10(13) ions/cm2 into YBa2Cu3O7-x microbridges through the nanoscale slits. The current-voltage curves of the ion implantation junctions exhibit resistive-shunted-junction-like behavior at 77 K. The junction had an approximately linear temperature dependence of critical current. Shapiro steps were observed under microwave irradiation. A 50-nm-wide slit and 0-20-nm-thick buffer layers were chosen in order to make Josephson junctions due to the V-shape of the FIB-milled trench.

A side-illuminated plasmonic planar lens

Planar lens based on nanoscale slits has been demonstrated theoretically and experimentally. In this paper, we propose a 2D model of a similar planar lens but with side-illumination. The lens consists of a main bus waveguide to transport plasmonic wave and grooves functioning as antennas. The shapes and filling materials of the waveguide and grooves are assumed to be invariant in the third direction. The phase retardation needed for wavefront shaping comes from the transverse propagation of the plasmonic wave in the waveguide and the well-designed groove positions. The concept is applied to the design of planar lenses and axicons. The simulation results demonstrate that such structures can work as good diffractive elements. The side-illumination property of such structure enables the potential integration of lens on chip.

Presentation of large DNA molecules for analysis as nanoconfined dumbbells.

The analysis of very large DNA molecules intrinsically supports long-range, phased sequence information, but requires new approaches for their effective presentation as part of any genome analysis platform. Using a multi-pronged approach that marshaled molecular confinement, ionic environment, and DNA elastic properties-but tressed by molecular simulations-we have developed an efficient and scalable approach for presentation of large DNA molecules within nanoscale slits. Our approach relies on the formation of DNA dumbbells, where large segments of the molecules remain outside the nanoslits used to confine them. The low ionic environment, synergizing other features of our approach, enables DNA molecules to adopt a fully stretched conformation, comparable to the contour length, thereby facilitating analysis by optical microscopy. Accordingly, a molecular model is proposed to describe the conformation and dynamics of the DNA molecules within the nanoslits; a Langevin description of the polymer dynamics is adopted in which hydrodynamic effects are included through a Green's function formalism. Our simulations reveal that a delicate balance between electrostatic and hydrodynamic interactions is responsible for the observed molecular conformations. We demonstrate and further confirm that the "Odijk regime" does indeed start when the confinement dimensions size are of the same order of magnitude as the persistence length of the molecule. We also summarize current theories concerning dumbbell dynamics.

Applying a modal technique on a planar lens based on nanoscale slit arrays

A planar lens structure based on an array of nanoscale slits in a metallic film is modeled using a waveguide modal technique. The structure is modeled as a one dimensional lens followed by free space propagation. The obtained results are compared to published experimental results as well as numerical simulations using either the finite difference frequency domain or the transmission line method. A good agreement has been obtained with significant simulation time reduction.

Optical Focusing by Planar Lenses Based on Nano-scale Metallic Slits in Visible Regime

A kind of planar metallic lenses is proposed to realize optical focusing in the visible wavelength through a metallic film with nano-scale slit arrays, which have the same depth but tuning widths. Due to the subwavelength and aperiodic nature of planar metallic lenses, we present the rigorous electromagnetic analysis by using two dimensional finite difference time domain method. The electromagnetic wave transports through the tuning slits in the form of surface plasmon polaritons, and gets the required phase retardations to focusing at the focal plane. We analyze the focusing characteristics of planar dielectric lens and metallic lens with tuning widths that are obtained by generalizing the relevant phase delay, for different incidence polarization waves (TM polarized case and TE polarized case). The computational calculation results show that, extraordinary optical transmission of surface plasmon polaritions through non uniform nano-scale metallic slits is observed, and it has contributions to the optical focusing, but cannot increase the focal energy compared with dielectric planar lens with the same profile, and the metallic lenses are more sensitive to the polarization of incidence wave than that of dielectric lenses. The influence of metallic lenses’ thickness on the focal characteristics has been analyzed also.

Planar Far-Field Lensing with Plasmonic Nano-Slit Arrays

W ith the advent of nanofabrication techniques, such as electron-beam lithography and focused ion beam milling, it is now possible to pattern metallic structures at the nano scale. is enables the exploitation of the plasmonic behavior of metals to create ultra-compact photonic devices for sensing, guiding or focusing.1 In this context, we recently reported on the experimental demonstration of far-fi eld lensing using a plasmonic nano-slit array.2 Refractive lenses are widely used in applications ranging from imaging to concentrating light. e miniaturization of lenses has been essential for the development of modern solid-state image sensors and might have important implications for other opto-electronic applications, including solid-state displays and lighting. e focusing ability of conventional, dielectric-based micro-lenses, however, deteriorates as their physical dimensions are reduced toward a singlewavelength scale. Moreover, the small size limits scientists’ ability to implement devices that are fl exible enough to properly focus light incident at oblique angles directly below the lens. e nano-patterning of optically thick metallic fi lms off ers an alternative that alleviates some of the shortcomings of refractive lenses. In this approach, a “plasmonic” lens is formed by an array of nano-scale slits in a planar metallic fi lm. For a light incident upon such a structure, the phase shift experienced by light as it passes through each individual slit is sensitive to the width.3 With the adjustment of the properties of individual slits, it is possible to create a curved phase front for the transmitted fi eld and thus to achieve focusing behavior. We recently implemented such far-fi eld planar nano-slit lenses using a combination of thin-fi lm deposition methods and focused ion beam milling. We demonstrated with confocal scanning optical microscopy that these structures can act as far-fi eld cylindrical lenses for light at optical frequencies.2 Moreover, we showed excellent agreement between the full electromagnetic fi eld simulations of the design, which include both evanescent and propagating modes, and the far-fi eld, diff ractionlimited confocal measurements. is demonstration is a crucial step in the realization of this potentially important technology, which off ers a range of processing and integration advantages over conventional shaped-based dielectric lenses. For example, the planar geometry facilitates integration using industrystandard semiconductor technology, and the geometry-based design off ers fl exibility that is not easily achieved with refractive lenses at wavelength-size scales. is makes planar “plasmonic” lenses attractive for integrated optoelectronic applications that require angle-compensating micro-lenses. We have shown already that, by introducing position-dependent phase Planar fareld “plasmonic” lens based on nano-slit array in metallic lm. (a) Geometry of the lens consisting of a 400-nm-thick gold lm with air slits of widths between 80 and 150 nm (light blue), sitting on a fused silica substrate (dark blue). (b) Scanning electron micrograph of the structure viewed from the air-side. (c) Focusing pattern measured with a confocal scanning optical microscope (CSOM). (d) Finite-difference frequency-domain simulated focusing pattern of the eld intensity through the center of the slits. (a) (c) (d) 0

Planar metallic nanoscale slit lenses for angle compensation

We demonstrate numerically, using a modified total-field/scattered-field formalism, that metallic lenses, based on arrays of nanoscale slits with varying widths in a planar metallic film, can be used to focus light and compensate for various angles of incidence. These structures could be used as integrated microlenses to improve the efficiency of pixels in solid-state image sensors. Our design guidelines simultaneously accomplish a prism and focusing action. Our results also indicate the importance of the aperture effect for such far-field focusing devices.

Planar Lenses Based on Nanoscale Slit Arrays in a Metallic Film

We experimentally demonstrate planar lenses based on nanoscale slit arrays in a metallic film. Our lens structures consist of optically thick gold films with micron-size arrays of closely spaced, nanoscale slits of varying widths milled using a focused ion beam. We find excellent agreement between electromagnetic simulations of the design and confocal measurements on manufactured structures. We provide guidelines for lens design and show how actual lens behavior deviates from simple theory.