Nanoscale Channels Research Articles

Confinement Effects and Manipulation Strategies of Nanocomposite Membranes towards Molecular Separation

AbstractMaterials featuring well‐defined nanoscale channels offer inherent advantages in the selective transport of gases, liquids, and ions, making them pivotal in applications such as molecular separation, catalysis and energy storage. A crucial challenge lies in assembling ordered nanochannel structures and translating these microscopic architectures into macroscopic regular distributions to enhance performance. Nanocomposites provide a promising solution by incorporating nanoscale material (e.g., filler) that significantly enhances macroscale properties of matrix (e.g., polymer). In this review, we spotlight nanocomposite membranes nanocomposite membranes that utilize confinement effects between filler and matrix to precisely control nanochannel apertures, surface properties, and channel distribution for efficient separation of target systems. We discussed the underlying design principles, channel architectures, and strategies for optimizing polymer‐filler interfaces and nanochannel manipulation within functional membranes. Emphasis is placed on the fundamental mechanisms of mass transport, and the structure‐property‐performance relationships within the nanocomposite membranes towards molecular separation. This work aims to provide a comprehensive understanding of how these nanocomposite membranes can be further developed to meet the demands of industrial and environmental applications.

Gate-driven transition temperatures of electron hopping behaviors in Hubbard bands formed by dopant-induced QD array in silicon nanowire

Abstract Dopant atoms confined in silicon nanoscale channel can be ionized to form quantum dots (QDs). Several dopant atoms couple with each other forming energy bands, where the electron hopping behavior can be described by the Hubbard model. This characteristic renders dopant-induced QDs particularly appealing for applications in nanoelectronic and quantum devices. Herein we study the gate-driven transition temperatures of electron hopping behavior in the upper Hubbard bands (UHBs) and lower Hubbard bands (LHBs) formed by dopant-induced QD array in junctionless silicon nanowire transistors. The gate-dependent transition temperatures are calculated for three stages of electron hopping behaviors including Efros–Shklovskii Variable Range Hopping (ES-VRH), Mott VRH and Nearest Neighbor Hopping (NNH). Our experimental results indicate that the ES-VRH in arrays of dopant atoms occurs in the domination of a long-range Coulomb interaction, in which the hopping distance relies on the Coulomb gap. Furthermore, the localization length of ES-VRH can be modulated by gate voltages. Those factors lead to the significant difference of transition temperatures between the UHBs and LHBs. In addition, we find that the source–drain bias voltage can effectively modulate the transition temperatures between VRH and NNH by thermal activation energies under different bias voltages Vds.

Water compression induced ionic negative differential resistance in nanopores.

The mass transport behavior through nanoscale channels, greatly influenced by the structures and dynamics of nanoconfined water, plays an essential role in many biophysical processes. However, the dynamics of nanoconfined water under an external field and its effects are still not fully understood. Here, on the basis of molecular dynamics simulations, we theoretically show that the ionic current of [Bmim][PF6] through narrow pores in graphene membrane exhibits an ionic negative differential resistance effect-the ionic current decreases as the voltage increases over a certain threshold. This effect arises from the violation of traditional fluid dynamics as the assumption of continuity and homogeneity of fluids is no longer effective in ultrathin nanopores. The gradient of electric field around the atomic-thin layer produces a strong gradient force on the polarized water inside the nanopore. This dielectrophoretically compressed water leads to a hydrostatic force that repels ions from entering the nanopore. Our findings may advance the understanding of hydrostatic mechanism, which governs ion transport through nanopores.

Piezo-VFETs: Vacuum Field Emission Transistors Controlled by Piezoelectric MEMS Sensors as an Artificial Mechanoreceptor with High Sensitivity and Low Power Consumption.

As one of the most promising electronic devices in the post-Moore era, nanoscale vacuum field emission transistors (VFETs) have garnered significant attention due to their unique electron transport mechanism featuring ballistic transport within vacuum channels. Existing research on these nanoscale vacuum channel devices has primarily focused on structural design for logic circuits. Studies exploring their application potential in other vital fields, such as sensors based on VFET, are more limited. In this study, for the first time, the design of a vacuum field emission transistor (VFET) coupled with a piezoelectric microelectromechanical (MEMS) sensing unit is proposed as the artificial mechanoreceptor for sensing purposes. With a negative threshold voltage similar to an N-channel depletion-mode metal oxide silicon field effect transistor, the proposed VFET has its continuous current tuned by the piezoelectric potential generated by the sensing unit, amplifying the magnitude of signals resulting from electromechanical coupling. Simulations have been conducted to validate the feasibility of such a configuration. As indictable from the simulation results, the proposed piezoelectric VFET exhibits high sensitivity and an electrically adjustable measurement range. Compared to the traditional combination of piezoelectric MEMS sensors and solid-state field effect transistors (FETs), the piezoelectric VFET design has a significantly reduced power consumption thanks to its continuous current that is orders of magnitude smaller. These findings reveal the immense potential of piezoelectric VFET in sensing applications, building up the basis for using VFETs for simple, effective, and low-power pre-amplification of piezoelectric MEMS sensors and broadening the application scope of VFET in general.

Study of Low Temperature-Treated Aldolized Cellulose Nanocrystals for Enhancing Dye Separation and Self-Healing Properties of Graphene Oxide Membranes.

Graphene oxide (GO) membranes with a 2D layered structure and nanoscale channels have great application prospects for dye wastewater purification. In this paper, ethylenediamine (EDA) was grafted onto the surface of GO nanosheets at 70 °C and aldolized cellulose nanocrystals (ICNC) were introduced to form EDA-ICNC hydrogel structures between the GO nanosheets by Schiff base reaction. The interlayer structure of the membrane was determined by adjusting the amount of ICNC added and the degree of aldolization, and the EGOICNC-24 membrane with the best performance was prepared. The water flux is not only 12 times higher than that of GO membrane but also has a good separation ability for dye molecules with a molecular weight around 300. Following the EDA-ICNC-24 hydrogel cross-linking process, the tensile strength of the EGOICNC-24 membrane exhibited a 173% increase relative to that of the GO membrane. Additionally, the dye rejection rate reached 97.16% after 130 h of dye separation. When the surface of the membrane was damaged, it was self-healed by regulating the repair temperature and adding a very small amount of ICNC to undergo a dynamic Schiff base reaction and a synergistic effect of hydrogen bonding.

Ultra‐Fast Weak Light Detectors Based on van der Waals Stacked 2D Semiconductor/h‐BN Heterostructures

AbstractFast and sensitive detectors for weak light are crucial in various fields like real‐time monitoring, medical diagnosis, and astronomy. However, photodetectors using 2D materials face challenges in achieving both a low detection limit for weak light and fast response. Here, a vertical vdW graphene/indium selenide (InSe)/hexagonal boron nitride (h‐BN) heterostructure on a gold electrode is provided, demonstrating an ultra‐low detection limit of 47.4 nW cm−2 and an ultra‐fast response speed of 327 ns. Vertical photodetectors feature nanoscale channel length, thus reducing scattering and recombination of carriers. The high potential barrier of multilayer h‐BN effectively blocks carrier transport, resulting in ultra‐low dark current and minimal power dissipation. Additionally, enhanced light absorption in InSe by the metal‐insulator‐semiconductor structure improves the sensitivity to weak light detection. More importantly, the built‐in field at the graphene/InSe interface can promote the separation of photo‐generated carriers to improve the collection efficiency. These factors jointly reduce the detection limit and response time simultaneously for weak light. This vertical vdW heterostructure comprising a 2D semiconductor/h‐BN offers a solution to make the majority of 2D semiconductors applicable in ultra‐fast weak light detectors.

Low-Frequency Noise in High-Current MoS2 Vertical Field-Effect Transistors with Nanoscale Channel

Low-Frequency Noise in High-Current MoS₂ Vertical Field-Effect Transistors with Nanoscale Channel

Microstructure and reflectance of porous GaN distributed Bragg reflectors on silicon substrates

Distributed Bragg reflectors (DBRs) based on alternating layers of porous and non-porous GaN have previously been fabricated at the wafer-scale in heteroepitaxial GaN layers grown on sapphire substrates. Porosification is achieved via the electrochemical etching of highly Si-doped layers, and the etchant accesses the n+-GaN layers through nanoscale channels arising at threading dislocations that are ubiquitous in the heteroepitaxial growth process. Here, we show that the same process applies to GaN multilayer structures grown on silicon substrates. The reflectance of the resulting DBRs depends on the voltage at which the porosification process is carried out. Etching at higher voltages yields higher porosities. However, while an increase in porosity is theoretically expected to lead to peak reflectance, in practice, the highest reflectance is achieved at a moderate etching voltage because etching at higher voltages leads to pore formation in the nominally non-porous layers, pore coarsening in the porous layers, and in the worst cases layer collapse. We also find that at the high threading dislocation densities present in these samples, not all dislocations participate in the etching process at low and moderate etching voltages. However, the number of dislocations involved in the process increases with etching voltage.

Efficient Li+/Mg2+ separation nanofiltration membranes modified by amine-functionalized TiO2 nanoparticles

Positively charged nanofiltration (NF) membranes are widely used to separate Li+ and Mg2+, which play an important role in extracting lithium from salt lakes. Despite its widespread use, the polyethyleneimine-trimesoyl chloride (PEI-TMC) membrane has attracted attention due to its limited permeance and separation efficiency. To address these challenges, we introduced amine-functionalized titanium dioxide (TiO2-NH2) nanoparticles into the interfacial polymerization (IP) reaction. The introduction of TiO2-NH2 reduced the diffusion rate of PEI and formed nanoscale water channels in the polyamide (PA) layer. This modification effectively modulated the structure of the NF membrane. The NF membrane exhibited high water permeance (9.65 L·m−2·h−1·bar−1) and Li+/Mg2+ selectivity (SLi, Mg = 16.31) when 0.03 wt% TiO2-NH2 was used. The DLVO theory and transition state theory showed that the introduction of TiO2-NH2 improved the rejection of Li+ and Mg2+ by the membrane. Furthermore, the optimized NF membranes demonstrated excellent stability during long-term filtration and in the mixed salt solutions with varying Mg2+/Li+ mass ratios. This work is of great significance for designing and advancing membrane materials that facilitate the efficient separation of lithium from salt lakes with high Mg2+/Li+ mass ratios.

Effect of Membrane Thickness on Ion Transport in pH-Regulated Zero-Depth Interfacial Nanopores.

Zero-depth interfacial nanopores, which are formed by two crossed nanoscale channels at their intersection interface, have been proposed to increase the spatial resolution of solid-state nanopores. However, research on zero-depth interfacial nanopores is still in its early stages. Although it has been shown that the current passing through an interfacial nanopore is largely independent of the membrane thickness, existing studies have not fully considered the impact of membrane thickness on other ion transport characteristics within these nanopores. In this paper, we investigate the electrokinetic ion transport phenomenon in the zero-depth interfacial nanopores, especially focusing on the influence of membrane thickness on the ion transport phenomenon. Our model incorporates the Poisson-Nernst-Planck equations and the Navier-Stokes equations, featuring a pH-regulated surface charge density. We find that when the thickness of the nanochannels is close to the interface size of the formed interfacial nanopore, the phenomenon of ion transport in the interfacial nanopore is similar to that in a conventional cylindrical nanopore. However, when the thickness of the nanochannels is much greater than the interface size of the formed interfacial nanopore, several distinct phenomena occur. The surface charge density on the inner walls of the interfacial nanopores has a small peak at the interface of the two crossing nanochannels, and the anion concentration changes greatly between the two nanochannels; that is, a much greater anion concentration forms in the nanochannel near the anode side than in the nanochannel near the cathode side. When the surface charge is nonzero, the electric field within the interfacial nanopore creates three extreme points, and the directions of the local electric fields are opposite at the ends of the membrane.

Advances in Two-Dimensional Ion-Selective Membranes: Bridging Nanoscale Insights to Industrial-Scale Salinity Gradient Energy Harvesting.

Salinity gradient energy, often referred to as the Gibbs free energy difference between saltwater and freshwater, is recognized as "blue energy" due to its inherent cleanliness, renewability, and continuous availability. Reverse electrodialysis (RED), relying on ion-selective membranes, stands as one of the most prevalent and promising methods for harnessing salinity gradient energy to generate electricity. Nevertheless, conventional RED membranes face challenges such as insufficient ion selectivity and transport rates and the difficulty of achieving the minimum commercial energy density threshold of 5 W/m2. In contrast, two-dimensional nanostructured materials, featuring nanoscale channels and abundant functional groups, offer a breakthrough by facilitating rapid ion transport and heightened selectivity. This comprehensive review delves into the mechanisms of osmotic power generation within a single nanopore and nanochannel, exploring optimal nanopore dimensions and nanochannel lengths. We subsequently examine the current landscape of power generation using two-dimensional nanostructured materials in laboratory-scale settings across various test areas. Furthermore, we address the notable decline in power density observed as test areas expand and propose essential criteria for the industrialization of two-dimensional ion-selective membranes. The review concludes with a forward-looking perspective, outlining future research directions, including scalable membrane fabrication, enhanced environmental adaptability, and integration into multiple industries. This review aims to bridge the gap between previous laboratory-scale investigations of two-dimensional ion-selective membranes in salinity gradient energy conversion and their potential large-scale industrial applications.

Cost-effective moisture-induced electrical power generators for sustainable electrodialysis desalination

To establish a sustainable method for desalination, it is necessary to explore and use renewable energy sources that are cost-effective and unaffected by weather conditions. Therefore, in this study we propose a novel hybrid electrodialysis system for environmentally friendly and cost-effective desalination of blackish water, integrating moisture-induced electrical power generators (MIEPGs). By coating a layer of carbon black on the surface of cellulose acetate fiber columns, which are readily available as cigarette filters, compact MIEPGs can be conveniently fabricated. These MIEPGs can generate electricity from trace amounts of moisture by leveraging the streaming potential induced along nanoscale channels between the carbon black particles. A notable voltage output (13.5–22 V) is achieved from the series connection of 90 cells using a customized module frame. The substantial power output derived from the stacked MIEPGs enables the successful desalination of modeled brackish water with a salt removal ratio of 92%.

Effective mechanical behaviors of transverse isotropic materials containing compressible liquid inclusions with surface effects

Porous media with fluid-saturated microchannels, prevalent in biomaterials, tissue engineering materials and flexible electronic devices, can be modelled as transverse isotropic materials. Surface effects can influence significantly the macro-mechanical responses of such materials, particularly for soft materials with micro- or nano-scale channels. In this study, we first develop constitutive laws for fluid saturated porous materials with microchannels by integrating the top-down (homogenization) approach with the bottom-up (micromechanics) approach. We then explicitly establish a connection between surface effects and macro-mechanical responses. Employing the generalized self-consistent model (GSCM), we estimate the effective parameters (i.e., coefficients in constitutive equations governing macro-mechanical responses), with fluid compressibility and surface effects accounted for. Our findings reveal that, as surface energy increases, the effective transverse shear modulus is enlarged, the effective plane strain bulk modulus, the unit uniaxial straining modulus and the cross modulus are all reduced, but the axial shear modulus remains nearly unchanged. As an application, we characterize the mechanical behaviors of the transverse isotropic fluid-saturated porous material with surface effects by connecting the classic Mandel solution with the estimated effective parameters. The pore pressure exhibits the Mandel-Cryer effect. The insights gained from this study are valuable for comprehending and exploring the intricate ways in which surface effects influence the mechanical responses of transversely isotropic fluid-saturated porous materials featuring sufficiently small channels.

An Experimental Investigation into the Role of an In Situ Microemulsion for Enhancing Oil Recovery in Tight Formations

Surfactant huff-n-puff (HnP) has been shown to be an effective protocol to improve oil recovery in tight and ultratight reservoirs. The success of surfactant HnP for enhanced oil recovery (EOR) process depends on the efficiency of the designed chemical formula, as the formation of an in situ microemulsion by surfactant injection is considered to be the most desirable condition for achieving an ultra-low interfacial tension during the HnP process. In this work, we conducted experimental studies on the mechanism of in situ microemulsion EOR in the Mahu tight oil reservoir. Salinity scan experiments were carried out to compare different surfactants with crude oil from the Mahu reservoir, starting with the assessment of surfactant micellar solutions for their ability to form microemulsions with Mahu crude oil and examining the interfacial characteristics. Subsequently, detailed micromodels representing millimeter-scale fractures, micron-scale pores, and nano-scale channels were utilized to study the imbibition and flowback of various surfactant micellar solutions. Observations of the in situ microemulsion system revealed the mechanisms behind the enhanced oil recovery, which was the emulsification’s near-miscibility effect leading to microemulsion formation and its performance under low-interfacial-tension conditions. During the injection process, notable improvements in the micro-scale pore throat heterogeneity were observed, which improved the pore fluid mobility. The flowback phase improved the channeling between the different media, promoting a uniform movement of the oil–water interface and aiding in the recovery of a significant amount of the oil phase permeability.

Fabrication of SU-8 polymer micro/nanoscale nozzle by hot embossing method

Electrohydrodynamic-jet printing (E-jet printing) is a direct-writing technology for manufacturing micro-nano devices. To further reduce the inner diameter of the nozzle to improve the printing resolution, a large-scale manufacturing method of SU-8 polymer micro/nanoscale nozzle by means of a process combining UV exposure and hot embossing was proposed. To improve the adhesive strength between the UV mask and SU-8, the influence of the oxygen plasma treatment parameters on the water contact angles of the UV mask was analyzed. The effect of hot embossing time and temperature on the replication precision was studied. The influence of UV exposure parameters and thermal bonding parameters on the micro and nanochannel pattern was investigated. The SU-8 polymer nozzles with 188 ± 3 nm wide and 104 ± 2 nm deep nanochannels were successfully fabricated, and the replication precision can reach to 98.5%. The proposed manufacturing method of SU-8 polymer nozzles in this study will significantly advance the research on the transport properties of nanoscale channels in E-jet nozzles and facilitate further advancements in E-jet based applications.

Nanoscale Channel Length MoS2 Vertical Field-Effect Transistor Arrays with Side-Wall Source/Drain Electrodes.

Two-dimensional transition metal dichalcogenides (TMDCs) have natural advantages in overcoming the short-channel effect in field-effect transistors (FETs) and in fabricating three-dimensional FETs, which benefit in increasing device density. However, so far, most reported works related to MoS2 FETs with a sub-100 nm channel employ mechanically exfoliated materials and all of the works involve electron beam lithography (EBL), which may limit their application in fabricating wafer-scale device arrays as demanded in integrated circuits (ICs). In this work, MoS2 FET arrays with a side-wall source and drain electrodes vertically distributed are designed and fabricated. The channel length of the as-fabricated FET is basically determined by the thickness of an insulating layer between the source and drain electrodes. The vertically distributed source and drain electrodes enable to reduce the electrode-occupied area and increase in the device density. The as-fabricated vertical FETs exhibit on/off ratios comparable to those of mechanically exfoliated MoS2 FETs with a nanoscale channel length under identical VDS. In addition, the as-fabricated FETs can work at a VDS as low as 10 mV with a desirable on/off ratio (1.9 × 107), which benefits in developing low-power devices. Moreover, the fabrication process is free from EBL and can be applied to wafer-scale device arrays. The statistical results show that the fabricated FET arrays have a device yield of 87.5% and an average on/off ratio of about 1.7 × 106 at a VDS of 10 mV, with the lowest and highest ones to be about 1.3 × 104 and 1.9 × 107, respectively, demonstrating the good reliability of our fabrication process. Our work promises a bright future for TMDCs in realizing high-density and low-power nanoelectronic devices in ICs.

Shape-influenced non-reciprocal transport of magnetic skyrmions in nanoscale channel

Abstract Skyrmions, with their vortex-like structures and inherent topological protection, play a pivotal role in developing innovative low-power memory and logic devices. The efficient generation and control of skyrmions in geometrically confined systems are of paramount importance for the advancement of skyrmion-based spintronic devices. In this study, we focus on investigating the non-reciprocal transport behavior of skyrmions and their interactions with boundaries of various shapes. The shape of the notch structure in the nanotrack significantly impacts the dynamic behavior of magnetic skyrmions. Through micromagnetic simulation, we explore the non-reciprocal transport properties of skyrmions in nanowires with different notch structure.

Bioinspired Synaptic Branched Network within Quasi-Solid Polymer Electrolyte for High-Performance Microsupercapacitors.

The branched network-driven ion solvating quasi-solid polymer electrolytes (QSPEs) are prepared via one-step photochemical reaction. A poly(ethylene glycol diacrylate) (PEGDA) is combined with an ion-conducting solvate ionic liquid (SIL), where tetraglyme (TEGDME), which acts like interneuron in the human brain and creates branching network points, is mixed with EMIM-NTf2 and Li-NTf2. The QSPE exhibits a unique gyrified morphology, inspired by the cortical surface of human brain, and features well-refined nano-scale ion channels. This human-mimicking method offers excellent ion transport capabilities through a synaptic branched network with high ionic conductivity (σDC ≈ 1.8 mS cm-1 at 298 K), high dielectric constant (εs ≈ 125 at 298 K), and strong ion solvation ability, in addition to superior mechanical flexibility. Furthermore, the interdigitated microsupercapacitors (MSCs) based on the QSPE present excellent electrochemical performance of high energy (E = 5.37 µWh cm-2) and power density (P = 2.2 mW cm-2), long-term cycle stability (≈94% retention after 48 000 cycles), and mechanical stability (>94% retention after continuous bending and compressing deformation). Moreover, these MSC devices have flame-retarding properties and operate effectively in air and water across a wide temperature range (275 to 370 K), offering a promising foundation for high-performance, stable next-generation all-solid-state energy storage devices.

6G THz Propagation Channel Characteristics and Modeling: Recent Developments and Future Challenges

The terahertz (THz) band is expected to play a more important role in the sixth generation (6G) communication networks. It can provide large bandwidth and high-speed transmission rate to support prospective 6G scenarios from space to ground and from macro-scale to nano-scale. However, the THz channel characteristics vary greatly for different scenarios. This paper presents a multi-dimensional overview of propagation channel characteristics and modeling for potential THz communication scenarios, including ground, space, and nano-scale communications. The atmospheric attenuation and propagation mechanisms are firstly discussed for ground scenarios. Then, the channel measurements, characteristics, and models for specific ground scenarios, including indoor office, data center, kiosk, smart rail, and massive MIMO are investigated. Following this, the THz space communication channels are summarized according to the satellite altitude. Futhermore, THz nano-scale communication channels including on-chip and body centric are analyzed. Finally, future research challenges are outlined.

Dual‐Crossbar Configurated Bi2O2Se Device for Multiple Optoelectronic Applications

AbstractTwo‐dimensional (2D) materials are widely used in numerous optoelectronic devices due to their ultra‐thin dimensions and versatile surfaces. However, less attention is paid to distinguishing the light‐matter interactions along the vertical and horizontal paths within the same 2D lattice, as well as comparatively investigating the optoelectronic behaviors between the sensitive top and bottom surfaces. Here, a dual‐crossbar configured architecture is designed and constructed based on Bi2O2Se semiconductor, featuring highly compact three‐in‐one assembly, namely bottom surface horizontal (BSH), middle sandwich vertical (MSV) and top surface horizontal (TSH) devices. The MSV with nanoscale channel possesses efficient separation and transportation of the photogenerated electrons and holes, responding faster to the light stimulation and compared favorably to the BSH and TSH devices. The optoelectric behaviors of the BSH device can be regulated by the characteristics of the substrate due to closer contact. Nevertheless, the performance of the TSH device is more sensitive to the environment, such as dopant absorption and heat dispersion, thus enabling the non‐volatile photoresponse and can be employed as an artificial optoelectronic synapse. This work highlights the importance of designing the device architecture based on the intrinsic structural advantages of 2D materials, paving the way toward integrated optoelectronics.