Two-Dimensional Stacked Composites of Self-Assembled Alkane Layers and Graphene for Transparent Gas Barrier Films with Low Permeability

Principles for fabricating moisture barrier films via stacked Janus graphene layers

The excellent impermeability makes graphene film an ideal candidate for thin film encapsulation technology. However, current chemical vapor deposition (CVD) graphene-based barrier films can not provide sufficient moisture barrier performance, suggesting a lack of understanding in mechanism that dominates water diffusion in/through graphene stacks. Herein, we fabricate large-area graphene barrier films with a record-low water vapor transmission rate (WVTR) of 5 × 10-5 g/(m2·day), two orders of magnitude lower than previous works, in which two stacked Janus graphene films are intercalated by toluidine blue O (TBO) sub-monolayer: one side of graphene is decorated with fluorine- and oxygen-containing groups to allow crack-free transfer, while the other side is functionalized with hydroxyl groups to trap water. The intercalated TBO further blocks water transport due to a strong water-TBO interaction. Our work opens a route for surface/interface engineering of CVD graphene and promises its exciting future in the applications for advanced packaging.

Protocol for lateral patterning of van der Waals heterostructures using sequential chemical vapor deposition

Previous work demonstrates that scalable area-selective deposition of van der Waals monolayers enables tunable design of atomically thin electronic and photonic platforms. Here, we present a protocol for lateral patterning of MoS2-WS2 heterostructures using sequential chemical vapor deposition. We describe steps for constructing patterned lateral heterostructures with alternating channels from nanometers to micrometers. This protocol has potential application in next-generation atomically thin electronic circuits. For complete details on the use and execution of this protocol, please refer to Lee et al.1.

Controlled Vapor-Phase Synthesis of VSe2 via Selenium-Driven Gradual Transformation of Single-Crystalline V2O5 Nanosheets

We report a gas-phase precursor modulation strategy for the controlled synthesis of 1T-phase vanadium diselenide (VSe2) from vanadium pentoxide (V2O5) nanosheets by systematically adjusting the vapor pressure of selenium. By controlling the selenium vapor pressure, selenium-free vapor transport of vanadium dioxide led to the spontaneous oxidation and formation of tens-of-micrometer-sized rectangular V2O5 crystals, while moderate selenium introduction produced intermediate oxygen-rich phases with trapezoidal crystal facets, and a highly selenium-rich environment yielded trigonal VSe2 crystals. Raman scattering measurements confirmed the stepwise transformation from V2O5 to VSe2, and atomic force microscopy revealed well-defined layered morphologies and distinct conformation within an atomically thin regime. Additionally, high-resolution transmission electron microscopy validated the orthorhombic and trigonal crystal structures of V2O5 and VSe2, respectively. This work demonstrates the versatility of fine-tuned vapor-phase growth conditions in vanadium-based layered compounds, providing useful platforms to optimize structural composition with atomic precision.

Enhancing barrier properties of cellulose propionate films through the integration of ionic liquid: A study on water pressure resistance

This study pioneers the production of porous cellulose propionate (CP) films enhanced with tetrabutylammonium styrenesulfonate ([N4444][SS]), an ionic liquid, to bolster their resistance against water pressure. In contrast to polymer films with ionic liquids that have high moisture permeability, the CP/[N4444][SS] films exhibit remarkable water resistance even under 8 bar pressure. This is due to the physical cross-linking between the [N4444] ions and CP's polar groups, limiting CP chain mobility and thus reducing water interaction. Fourier-transform infrared spectroscopy confirmed these interactions, while scanning electron microscopy revealed a dense, unconnected porous structure. Thermogravimetric and differential scanning calorimetry analyses showed that adding [N4444][SS] increases the CP film's glass transition temperature, indicating enhanced thermal stability. Overall, the study demonstrates that integrating an ionic liquid into CP films significantly improves their barrier capabilities against water and pressure, which has broad implications for various industrial applications.

High Moisture-Barrier Performance of Double-Layer Graphene Enabled by Conformal and Clean Transfer

Graphene films that can theoretically block almost all molecules have emerged as promising candidate materials for moisture barrier films in the applications of organic photonic devices and gas storage. However, the current barrier performance of graphene films does not reach the ideal value. Here, we reveal that the interlayer distance of the large-area stacked multilayer graphene is the key factor that suppresses water permeation. We show that by minimizing the gap between the two monolayers, the water vapor transmission rate of double-layer graphene can be as low as 5 × 10-3 g/(m2 d) over an A4-sized region. The high barrier performance was achieved by the absence of interfacial contamination and conformal contact between graphene layers during layer-by-layer transfer. Our work reveals the moisture permeation mechanism through graphene layers, and with this approach, we can tailor the interlayer coupling of manually stacked two-dimensional materials for new physics and applications.

A Graphene-Based Polymer-Dispersed Liquid Crystal Device Enabled through a Water-Induced Interface Cleaning Process

We report the use of four-layer graphene (4LG) as a highly reliable transparent conductive electrode (TCE) for polymer-dispersed liquid crystal (PDLC)-based smart window devices. The adhesion between 4LG and the substrate was successfully improved through a water-induced interface-cleaning (WIIC) process. We compared the performance of a device with a WIIC-processed 4LG electrode with that of devices with a conventional indium tin oxide (ITO) electrode and a 4LG electrode without a WIIC. With the application of the WIIC process, the PDLC smart window with a 4LG electrode exhibited reduced turn-on voltage and haze compared to 4LG without the WIIC process and characteristics comparable to those of the ITO electrode. The WIIC-processed 4LG electrode demonstrated enhanced electrical properties and better optical performance, leading to improved device efficiency and reliability. Furthermore, our study revealed that the WIIC process not only improved the adhesion between 4LG and the substrate but also enhanced the compatibility and interfacial interactions, resulting in the superior performance of the smart window device. These findings suggest that 4LG with WIIC holds great promise as a transparent conductive electrode for flexible smart windows, offering a cost-effective and efficient alternative to conventional ITO electrodes.

Selective Blocking of Graphene Defects Using Polyvinyl Alcohol through Hydrophilicity Difference

Defects on graphene over a micrometer in size were selectively blocked using polyvinyl alcohol through the formation of hydrogen bonding with defects. Because this hydrophilic PVA does not prefer to be located on the hydrophobic graphene surface, PVA selectively filled hydrophilic defects on graphene after the process of deposition through the solution. The mechanism of the selective deposition via hydrophilic-hydrophilic interactions was also supported by scanning tunneling microscopy and atomic force microscopy analysis of selective deposition of hydrophobic alkanes on hydrophobic graphene surface and observation of PVA initial growth at defect edges.

The composition and structure of the ubiquitous hydrocarbon contamination on van der Waals materials

The behavior of single layer van der Waals (vdW) materials is profoundly influenced by the immediate atomic environment at their surface, a prime example being the myriad of emergent properties in artificial heterostructures. Equally significant are adsorbates deposited onto their surface from ambient. While vdW interfaces are well understood, our knowledge regarding atmospheric contamination is severely limited. Here we show that the common ambient contamination on the surface of: graphene, graphite, hBN and MoS₂ is composed of a self-organized molecular layer, which forms during a few days of ambient exposure. Using low-temperature STM measurements we image the atomic structure of this adlayer and in combination with infrared spectroscopy identify the contaminant molecules as normal alkanes with lengths of 20-26 carbon atoms. Through its ability to self-organize, the alkane layer displaces the manifold other airborne contaminant species, capping the surface of vdW materials and possibly dominating their interaction with the environment.

Here, the authors attribute the ambient surface contamination of van der Waals materials to a self-organized molecular layer of normal alkanes with lengths of 20-26 carbon atoms. The alkane adlayer displaces the manifold other airborne contaminant species, capping the surface of graphene, graphite, hBN and MoS₂.