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Large-area nanopore drilling is a major bottleneck in state-of-the-art nanoporous 2D membrane fabrication protocols. In addition, high-quality structural and statistical descriptions of as-fabricated porous membranes are key to predicting the corresponding membrane-wide permeation properties. In this work, we investigate Xe-ion focused ion beam as a tool for scalable, large-area nanopore fabrication on atomically thin, free-standing molybdenum disulfide. The presented irradiation protocol enables designing ultrathin membranes with tunable porosity and pore dimensions, along with spatial uniformity across large-area substrates. Fabricated nanoporous membranes are then characterized using scanning transmission electron microscopy imaging, and the observed nanopore geometries are analyzed through a pore-edge detection and analysis script. We further demonstrate that the obtained structural and statistical data can be readily passed on to computational and analytical tools to predict the permeation properties at both individual pore and membrane-wide scales. As an example, membranes featuring angstrom-scale pores are investigated in terms of their emerging water and ion flow properties through extensive all-atom molecular dynamics simulations. We believe that the combination of experimental and analytical approaches presented here will yield accurate physics-based property estimates and thus potentially enable a true function-by-design approach to fabrication for applications such as osmotic power generation and desalination/filtration.

A sustainable future demands a successful transition from a carbon-energy dependent economy towards renewable energy schemes, many of which ultimately rely on the development of efficient electrocatalysis that either converts chemical energy into electricity or uses electrons to produce chemical energy. In general, electrocatalysis studies focus on the interactions (e.g., electron transfer) between the catalyst surface and the reaction intermediates. However, the role of electron spin, as an intrinsic property of electrons, has commonly been overlooked. Recently, controlling the electron spin polarization at the catalyst’s surface demonstrated the great potential of boosting both reaction activity and product selectivity. Molecule-induced electron spin polarization inspired by the chiral-induced spin selectivity (CISS) effect has started to have a remarkable impact in electrocatalysis. In this compact review, we summarize the latest studies that use molecule-induced electron spin polarization to enhance catalytic performance. We focus on the reactions essential to the so-called hydrogen economy, and discuss the feasibility and limitations of this effect. Finally, we share our perspective regarding the more impactful future applications.

International audience; Adapting optical microscopy methods for nanoscale characterization of defects in two-dimensional (2D) materials is a vital step for photonic on-chip devices. To increase the analysis throughput, waveguide-based on-chip imaging platforms have been recently developed. Their inherent disadvantage, however, is the necessity to transfer the 2D material from the growth substrate to the imaging chip, which introduces nonuniform material coverage and contamination, potentially altering the characterization results. Here we present a unique approach to circumvent these shortfalls by directly growing a widely used 2D material (hexagonal boron nitride, hBN) on silicon nitride chips and optically characterizing the defects in the intact as-grown material. We compare the direct growth approach to the standard PMMA-assisted wet transfer method and confirm the clear advantages of the direct growth. While demonstrated with hBN in the current work, the method can be extended to other 2D materials.

Tailoring the surface properties of 2D materials, such as transition metal dichalcogenides (TMDCs), at the nanoscale is becoming essential in the fabrication of various 2D material-based nanoelectronic devices. Due to the chemical inertness of their basal plane, the surface modification of 2D TMDCs is limited to their defective sites, often requiring special treatments, such as the conversion of the TMDC from its semiconducting into its metallic phase. In this work, we show that the basal plane of a semiconducting 2D TMDC, molybdenum disulfide (MoS2) can be modified electrochemically by electrografting of aryl-diazonium salt. To demonstrate the advantages of this method at the nanoscale, we perform electrografting of 3, 5-bis(trifluoromethyl)benzenediazonium tetrafluoroborate on predefined MoS2 nanoribbons by addressing them individually via a different electrode. The ability to selectively address individually contacted 2D layers opens the possibility for specific surface modification of neighboring 2D nanostructures by different functional groups. This method could be extended to other aryl-diazonium compounds, and other 2D semiconducting materials.

Classical nanopore sensing relies on the measurement of the ion current passing through a nanopore. Whenever a molecule electrophoretically translocates through the narrow constriction, it modulates the ion current. Although this approach allows one to measure single molecules, the access resistance limits the spatial resolution. This physical limitation could potentially be overcome by an alternative sensing scheme taking advantage of the current across the membrane material itself. Such an electronic readout would also allow better temporal resolution than the ionic current. In this work, we present the fabrication of an electrically contacted molybdenum disulfide (MoS2) nanoribbon integrated with a nanopore. DNA molecules are sensed by correlated signals from the ionic current through the nanopore and the transverse current through the nanoribbon. The resulting signal suggests a field-effect sensing scheme where the charge of the molecule is directly sensed by the nanoribbon. We discuss different sensing schemes such as local potential sensing and direct charge sensing. Furthermore, we show that the fabrication of freestanding MoS2 ribbons with metal contacts is reliable and discuss the challenges that arise in the fabrication and usage of these devices.

Atomically thin (2D) nanoporous membranes are an excellent platform for a broad scope of academic research. Their thickness and intrinsic ion selectivity (demonstrated for example in molybdenum disulfide-MoS2) make them particularly attractive for single-molecule biosensing experiments and osmotic energy harvesting membranes. Currently, one of the major challenges associated with the research progress and industrial development of 2D nanopore membrane devices is small-scale thin-film growth and small-area transfer methods. To address these issues, a large-area protocol including a wafer-scale monolayer MoS2 synthesis, Si/SiNx substrate fabrication and wafer-scale material transfer are demonstrated. First, the 7.62 cm wafer-scale MOCVD growth yielding homogenous monolayer MoS2 films are introduced. Second, a large number of devices are fabricated in one batch by employing the wafer-scale thin-film transfer method with high transfer efficiency (>70% device yield). The growth, the transfer quality and cleanliness are investigated using transmission electron microscopy, atomic force microscopy and Raman spectroscopy. Finally, the applicability and robustness of the large-area protocol is demonstrated by performing a set of double-stranded DNA translocation experiments through as-fabricated MoS2 nanopore devices. It is believed that the shown approach will pave the way toward wafer-scale, high-throughput use of 2D nanopores in various applications.

Single-molecule localization microscopy (SMLM) is a powerful tool that is routinely used for nanoscale optical imaging of biological samples. Recently, this approach has been applied to study optically active defects in two-dimensional (2D) materials. Such defects can not only alter the mechanical and optoelectronic properties of 2D materials but also bring new functionalities, which make them a promising platform for integrated nanophotonics and quantum sensing. Most SMLM approaches, however, provide a field of view limited to similar to 50 x 50 mu m(2), which is not sufficient for high-throughput characterization of 2D materials. Moreover, the 2D materials themselves pose an additional challenge as their nanometer-scale thickness prevents efficient far-field excitation of optically active defects. To overcome these limitations, we present here a waveguide-based platform for large field-of-view imaging of 2D materials via total internal reflection excitation. We use this platform to perform large-scale characterization of point defects in chemical vapor deposition-grown hexagonal boron nitride on an area of up to 100 x 1000 mu m(2) and demonstrate its potential for correlative imaging and high throughput characterization of defects in 2D materials.

Blue energy relies on the chemical potential difference generated between solutions of high and low ionic strength and would provide a sun-and-wind independent energy source at estuaries around the world. Converting this osmotic energy through reverse-electrodialysis relies on ion-selective membranes. A novel generation of these membranes is based on atomically thin MoS$_2$ membranes to decrease the resistance to current flow to increase power output. By modulating the surface charge by light we are able to raise the ion selectivity of the membrane by a factor of 5 while staying at a neutral pH. Furthermore, we find that the behavior of small nanopores is dominated by surface conductance. We introduce a formalism based on the Dukhin number to quantify these effects in the case of a concentration gradient system. As a consequence, the charges created by light illumination provoke two important changes. Increased surface charge at the pore rim enhances the ion selectivity and therefore larger osmotic voltage (dominating in small pores), while the increased surface charge of the overall membrane enhances the surface conductance and therefore the osmotic current (dominating in larger pores). The combination of these effects might be able to efficiently boost the energy generation with arrays of nanopores with varying pore sizes.

Among the different developed solid-state nanopores, nanopores constructed in a monolayer of molybdenum disulfide (MoS

A long-standing problem in the application of solid-state nanopores is the lack of the precise control over the geometry of artificially formed pores compared to the well- defined geometry in their biological counterpart, i.e. protein nanopores. To date, experimentally investigated solid-state nanopores have been shown to adopt approximately circular shape. A unique property of hexagonal boron nitride (h-BN) few-layers has been revealed by previous transmission electron microscopy (TEM) studies, where triangular defects or nanopores can be created or enlarged while maintaining their intrinsic triangular shape.1, 2 Here, we investigate the geometrical effect of the nanopore shape on ionic blockage induced by DNA translocation using triangular h-BN nanopores and approximately circular molybdenum disulfide (MoS2) nanopores. We observe a geometry-dependent ion scattering effect, which is further corroborated by a modified ionic blockage model. The well-acknowledged ionic blockage model is derived from uniform ion permeability through the 2D nanopore plane and hemisphere like access region in the nanopore vicinity.3, 4 Based on our experimental results, we propose a modified ionic blockage model, which is highly related to the ionic profile caused by geometrical variations. Our findings shed light on the rational design of 2D nanopores and should be applicable to arbitrary nanopore shapes.

Ultrathin nanopore membranes based on 2D materials have demonstrated ultimate resolution toward DNA sequencing. Among them, molybdenum disulphide (MoS2) shows long-term stability as well as superior sensitivity enabling high throughput performance. The traditional method of fabricating nanopores with nanometer precision is based on the use of focused electron beams in transmission electron microscope (TEM). This nanopore fabrication process is time-consuming, expensive, not scalable and hard to control below 1 nm. Here, we exploited the electrochemical activity of MoS2 and developed a convenient and scalable method to controllably make nanopores in single-layer MoS2 with sub-nanometer precision using electrochemical reaction (ECR). The electrochemical reaction on the surface of single-layer MoS2 is initiated at the location of defects or single atom vacancy, followed by the successive removals of individual atoms or unit cells from single-layer MoS2 lattice and finally formation of a nanopore. Step-like features in the ionic current through the growing nanopore provide direct feedback on the nanopore size inferred from a widely used conductance vs. pore size model. Furthermore, DNA translocations can be detected in-situ when as-fabricated MoS2 nanopores are used. The atomic resolution and accessibility of this approach paves the way for mass production of nanopores in 2D membranes for potential solid-state nanopore sequencing., 13 pages, 4 figures

U ovom radu uspješno su sintetizirane nanočestice kadmijeva sulfida, CdS, u mikroemulziji i sol-gel tankim filmovima. Naglasak rada je bio na optimiranju sinteze u sol-gelu, s ciljem dobivanja tankog sol-gel filma dobrih mehaničkih i optičkih svojstava, s imobiliziranim nanočesticama jednolike raspodjele veličina. Provedeni su različiti eksperimenti u kojima je praćen utjecaj sljedećih parametara: sastava i starosti sol-gel koktela, koncentracije reaktanata a time i molarnog omjera Cd / Si, načina priprave filma i temperature žarenja filma nakon nanošenja. Također je ispitan utjecaj načina miješanja i koncentracije reaktanata na sintezu u mikroemulziji. Karakterizacija je provedena snimanjem apsorpcijskih i fotoluminiscencijskih spektara u UV (ultraljubičastom) i vidljivom području, te usporedbom boje fluorescencije tankih filmova osvijetljenih UV svjetlom. Optimiranjem parametara postignuta je dobra kontrola kinetike sol-gel procesa, te su dobiveni glatki i homogeni filmovi s imobiliziranim nanočesticama široke raspodjele veličina. Sintezom u mikroemulziji dobivene su manje čestice i uža raspodjela veličina nego sol-gel sintezom.

Nanopores in two-dimensional (2D) membranes hold immense potential in single-molecule sensing, osmotic power generation, and information storage. Recent advances in 2D nanopores, especially on single-layer MoS2, focus on the scalable growth and manufacturing of nanopore devices. However, there still remains a bottleneck in controlling the nanopore stability in atomically thin membranes. Here, we evaluate the major factors responsible for the instability of the monolayer MoS2 nanopores. We identify chemical oxidation and delamination of monolayers from their underlying substrates as the major reasons for the instability of MoS2 nanopores. Surface modification of the substrate and reducing the oxygen from the measurement solution improves nanopore stability and dramatically increases their shelf-life. Understanding nanopore growth and stability can provide insights into controlling the pore size, shape and can enable long-term measurements with a high signal-to-noise ratio and engineering durable nanopore devices.

Among the different developed solid-state nanopores, nanopores constructed in a monolayer of molybdenum disulfide (MoS2) stand out as powerful devices for single-molecule analysis or osmotic power generation. Because the ionic current through a nanopore is inversely proportional to the thickness of the pore, ultrathin membranes have the advantage of providing relatively high ionic currents at very small pore sizes. This increases the signal generated during translocation of biomolecules and improves the nanopores' efficiency when used for desalination or reverse electrodialysis applications. The atomic thickness of MoS2 nanopores approaches the inter-base distance of DNA, creating a potential candidate for DNA sequencing. In terms of geometry, MoS2 nanopores have a well-defined vertical profile due to their atomic thickness, which eliminates any unwanted effects associated with uneven pore profiles observed in other materials. This protocol details all the necessary procedures for the fabrication of solid-state devices. We discuss different methods for transfer of monolayer MoS2, different approaches for the creation of nanopores, their applicability in detecting DNA translocations and the analysis of translocation data through open-source programming packages. We present anticipated results through the application of our nanopores in DNA translocations and osmotic power generation. The procedure comprises four parts: fabrication of devices (2-3 d), transfer of MoS2 and cleaning procedure (24 h), the creation of nanopores within MoS2 (30 min) and performing DNA translocations (2-3 h). We anticipate that our protocol will enable large-scale manufacturing of single-molecule-analysis devices as well as next-generation DNA sequencing.

Transition metal dichalcogenides (TMDs) represent a class of semiconducting two-dimensional (2D) materials with exciting properties. In particular, defects in 2D-TMDs and their molecular interactions with the environment can crucially affect their physical and chemical properties. However, mapping the spatial distribution and chemical reactivity of defects in liquid remains a challenge. Here, we demonstrate large area mapping of reactive sulfur-deficient defects in 2D-TMDs in aqueous solutions by coupling single-molecule localization microscopy with fluorescence labeling using thiol chemistry. Our method, reminiscent of PAINT strategies, relies on the specific binding of fluorescent probes hosting a thiol group to sulfur vacancies, allowing localization of the defects with an uncertainty down to 15 nm. Tuning the distance between the fluorophore and the docking thiol site allows us to control Foster resonance energy transfer (FRET) process and reveal grain boundaries and line defects due to the local irregular lattice structure. We further characterize the binding kinetics over a large range of pH conditions, evidencing the reversible adsorption of the thiol probes to the defects with a subsequent transitioning to irreversible binding in basic conditions. Our methodology provides a simple and fast alternative for large-scale mapping of nonradiative defects in 2D materials and can be used for in situ and spatially resolved monitoring of the interaction between chemical agents and defects in 2D materials that has general implications for defect engineering in aqueous condition.

2D semiconducting materials have become the central component of various nanoelectronic devices and sensors. For sensors operating in liquid, it is crucial to efficiently block the electron transfer that occurs between the electrodes contacting the 2D material and the interfering redox species. This reduces current leakages and preserves a good signal-to-noise ratio. Here, a simple electrochemical method is presented for passivating the electrodes contacting a monolayer of MoS2, a representative of transition metal dichalcogenide semiconductors. The method is based on blocking the electrode surface by a thin and compact layer of electronically nonconductive poly(phenylene oxide), PPO, formed by electrochemical polymerization of phenol. Since the phenol polymerization occurs in the potential window where MoS2 is electrochemically inactive, the PPO deposition is area-selective, limited to the electrode surface. The deposited PPO film is characterized by electrochemical, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy techniques. The applicability of this method is demonstrated by coating the electrodes of a MoS2-based field-effect transistor coupled with a nanopore. The highly selective deposition, the simple approach, and the compatibility with MoS2 makes this method a good strategy for efficient insulation of micro- and nanoelectrodes contacting 2D semiconductor-based devices.

Summary Blue energy relies on the chemical potential difference between solutions of high and low ionic concentrations, potentially providing an independent energy source at estuaries around the world. The energy conversion relies on reverse electrodialysis via ion-selective membranes. A novel generation of these membranes is based on nanopores in atomically thin material. Single nanopores in molybdenum disulfide (MoS2)-based membranes have shown record-high power outputs in alkaline conditions. By increasing the surface charge of MoS2 membranes by light, we can double the osmotic power generated by a single nanopore at a neutral pH. The increased surface charge at the pore rim enhances the ion selectivity and leads to a larger osmotic voltage (dominating in small pores), while the increased surface charge of the membrane enhances the surface conductance, leading to a larger osmotic current (dominating in larger pores). The combination of these effects could efficiently boost the energy generation using membranes containing arrays of nanopores of varying sizes.