Solvent-free bottom-up patterning of zeolitic imidazolate frameworks

Direct Photopatterning of Zeolitic Imidazolate Frameworks via Photoinduced Fluorination

Precise and effective patterning strategies are essential for integrating metal-organic frameworks (MOFs) into microelectronics, photonics, sensors, and other solid-state devices. Direct lithography of MOFs with light and other irradiation sources has emerged as a promising patterning strategy. However, existing direct lithography methods often rely on the irradiation-induced amorphization of the MOFs structures and the breaking of strong covalent bonds in their organic linkers. High-energy sources (such as X-rays or electron beams) and large irradiation doses - conditions unfavorable for scalable patterning - are thus required. Here, we report a photoinduced fluorination chemistry for patterning various zeolitic imidazolate frameworks (ZIFs) under mild UV irradiation. Using UV doses as low as 10 mJ cm-2, light-sensitive fluorine-containing molecules covalently bond to ZIFs and enhance their stability in water. This creates a water-stability contrast between ZIFs in exposed and unexposed regions, enabling scalable direct photolithography of ZIFs with high resolution (2 μm) on 4-inch wafers and flexible substrates. The patterned ZIFs preserve their original crystallinity and porous properties while gaining increased hydrophobicity. This allows for the demonstration of a water-responsive fluorescent MOFs array with implications in sensing and multicolor information encryption.

Nanoscale Resist-Free Patterning of Halogenated Zeolitic Imidazolate Frameworks by Extreme UV Lithography

Advancements in patterning techniques for metal-organic frameworks (MOFs) are crucial for their integration into microelectronics. However, achieving precise nanoscale control of MOF structures remains challenging. In this work, a resist-free method for patterning MOFs is demonstrated using extreme ultraviolet (EUV) lithography with a resolution of 40 nm. The role of halogen atoms in the linker and the effect of humidity are analyzed through in situ and near-ambient pressure synchrotron X-ray photoelectron spectroscopy. In addition to facilitating the integration of MOFs, the results offer valuable insights for developing the highly sought-after positive-tone EUV photoresists.

Accurately Tunable AuNC-ZIF Content Architecture Based on Coordination-Dissociation Mechanism Enables Highly Brightness Dual-Site Fluorescent Biosensor

The quantum yield and fluorescence intensity of gold nanocluster (AuNC) nanocarriers are critical parameters for developing ultrasensitive biosensors. In this study, AuNCs-zeolitic-imidazolate-framework (Au-ZIF) nanocomposites are systematically constructed by impregnating AuNCs onto the ZIF-8 surface through a coordination-dissociation mechanism, resulting in a dual-site fluorescence-loaded structure. In this configuration, AuNCs are anchored to the external surface while the integrity of the inner cavity remains intact. The surface of ZIF-8 induces a confinement effect on the configuration and electrons of AuNCs, significantly enhancing luminescence (18-fold increase). The quantum yield of AuNCs exhibits an increase of more than 13-fold, from 2.80% to 38.1%. This approach demonstrates broad applicability and maintains strong fluorescence across different ZIFs. Additionally, a novel nanocomposite, Au-ZIF@carbon-dots (CDs), is synthesized by encapsulating CDs into the inner cavity of Au-ZIF. A ratiometric fluorescence detection platform is subsequently developed and incorporated into hydrogels for the quantitative detection of the pesticide triazophos. By employing an image-processing algorithm, quantitative detection is achieved with a detection limit of 0.07 ng mL⁻1. The findings provide crucial insights into the relationship between the assembly and performance of AuNCs and ZIFs, offering guidance for designing ultrasensitive multifunctional biosensors applicable in the field of biosensing.

Micropattern Fabricated by Acropetal Migration Controlled through Sequential Photo and Thermal Polymerization

Bottom-up patterning technology plays a significant role in both nature and synthetic materials, owing to its inherent advantages such as ease of implementation, spontaneity, and noncontact attributes, etc. However, constrained by the uncontrollability of molecular movement, energy interaction, and stress, obtained micropatterns tend to exhibit an inevitable arched outline, resulting in the limitation of applicability. Herein, inspired by auxin's action mode in apical dominance, a versatile strategy is proposed for fabricating precision self-organizing micropatterns with impressive height based on polymerization-induced acropetal migration. The copolymer containing fluorocarbon chains (low surface energy) and tertiary amine (coinitiator) is designed to self-assemble on the surface of the photo-curing system. The selective exposure under a photomask establishes a photocuring boundary and the radicals would be generated on the surface, which is pivotal in generating a vertical concentration difference of monomer. Subsequent heating treatment activates the material continuously transfers from the unexposed area to the exposed area and is accompanied by the obviously vertical upward mass transfer, resulting in the manufacture of a rectilinear profile micropattern. This strategy significantly broadens the applicability of self-organizing patterns, offering the potential to mitigate the complexity and time-consuming limitations associated with top-down methods.

Reactive Extrusion Printing of Zeolitic Imidazolate Framework Films

An outstanding challenge for the field of metal-organic frameworks (MOFs) is structuring to form forms with greater useability. Reactive extrusion printing (REP) is a technique for the direct formation of films from their molecular components on-demand and on-location. Here we apply REP for the first time to zeolitic imidazolate frameworks (ZIFs) and study the interplay of solvent and molarity ratio on the phase distribution between ZIF-8 and ZIF-L in reactive printed films. Our results show that REP controllably directs phase formation between ZIF-L and ZIF-8 and that REP also gives control over crystal size and that high-quality ZIF-8 films, in particular, are produced in low-dispersity interconnected nanoparticulate form. Importantly, we show that REP is responsive to established surface-functionalization techniques to control important printing parameters of line width and thickness. This work expands the repertoire of REP to the important class of ZIFs.

Direct Optical Patterning of Metal-Organic Frameworks via Photoacid-Induced Etching

Metal-organic frameworks (MOFs) are a class of porous materials constructed from organic linkers and inorganic building blocks. Coordinative competition labilizes some MOFs under harsh chemical conditions because of their weak bonding. However, instability is not always a negative property of a material. In this study, we demonstrated the use of the acidic lability of MOFs for direct optical patterning. The controllable acid release from the photoacid generator at the exposed area causes bond cleavage between the linkers and metal ions/clusters, leading to solubility changes and pattern formation after development. This process avoids redundant steps and possible contamination in traditional photolithography, while maintaining the original properties of patterned MOFs. The preserved porosity and crystallinity promoted the development of MOFs for gas sensors and solid displays.

ZIF-8 Vibrational Spectra: Peak Assignments and Defect Signals

Zeolitic imidazolate framework (ZIF-8) is a promising material for gas separation applications. It also serves as a prototype for numerous ZIFs, including amorphous ones, with a broader range of possible applications, including sensors, catalysis, and lithography. It consists of zinc coordinated with 2-methylimidazolate (2mIm) and has been synthesized with methods ranging from liquid-phase to solvent-free synthesis, which aim to control its crystal size and shape, film thickness and microstructure, and incorporation into nanocomposites. Depending on the synthesis method and postsynthesis treatments, ZIF-8 materials may deviate from the nominal defect-free ZIF-8 crystal structure due to defects like missing 2mIm, missing zinc, and physically adsorbed 2mIm trapped in the ZIF-8 pores, which may alter its performance and stability. Infrared (IR) spectroscopy has been used to assess the presence of defects in ZIF-8 and related materials. However, conflicting interpretations by various authors persist in the literature. Here, we systematically investigate ZIF-8 vibrational spectra by combining experimental IR spectroscopy and first-principles molecular dynamics simulations, focusing on assigning peaks and elucidating the spectroscopic signals of putative defects present in the ZIF-8 material. We attempt to resolve conflicting assignments from the literature and to provide a comprehensive understanding of the vibrational spectra of ZIF-8 and its defect-induced variations, aiming toward more precise quality control and design of ZIF-8-based materials for emerging applications.

Crosslinking-induced patterning of MOFs by direct photo- and electron-beam lithography

Metal-organic frameworks (MOFs) with diverse chemistry, structures, and properties have emerged as appealing materials for miniaturized solid-state devices. The incorporation of MOF films in these devices, such as the integrated microelectronics and nanophotonics, requires robust patterning methods. However, existing MOF patterning methods suffer from some combinations of limited material adaptability, compromised patterning resolution and scalability, and degraded properties. Here we report a universal, crosslinking-induced patterning approach for various MOFs, termed as CLIP-MOF. Via resist-free, direct photo- and electron-beam (e-beam) lithography, the ligand crosslinking chemistry leads to drastically reduced solubility of colloidal MOFs, permitting selective removal of unexposed MOF films with developer solvents. This enables scalable, micro-/nanoscale (≈70 nm resolution), and multimaterial patterning of MOFs on large-area, rigid or flexible substrates. Patterned MOF films preserve their crystallinity, porosity, and other properties tailored for targeted applications, such as diffractive gas sensors and electrochromic pixels. The combined features of CLIP-MOF create more possibilities in the system-level integration of MOFs in various electronic, photonic, and biomedical devices.

Porous organic framework membranes based on interface-induced polymerisation: design, synthesis and applications

Porous organic frameworks (POFs) are novel porous materials that have attracted much attention due to their extraordinary properties, such as high specific surface area, tunable pore size, high stability and ease of functionalisation. However, conventional synthesised POFs are mostly large-sized particles or insoluble powders, which are difficult to recycle and have low mass transfer efficiencies, limiting the development of their cutting-edge applications. Therefore, processing POF materials into membrane structures is of great significance. In recent years, interface engineering strategies have proved to be efficient methods for the formation of POF membranes. In this perspective, recent advances in the use of interfaces to prepare POF membranes are reviewed. The challenges of this strategy and the potential applications of the formed POF membranes are discussed.

Borosilicate-Based Framework: Synthesis, Single-Crystal Structure Study, and Physical Properties

Herein, we report the synthesis, crystal structure, and optical properties of a metal-free three-dimensional (3D) inorganic covalent framework ((H2en)[Si(B4O9)], named CityU-11, where H2en is the abbreviation for ethanediamine). With the assistance of a tiny amount of F- ions and the selection of SiO2 as Si sources, single crystals of CityU-11 can be successfully prepared under solvothermal conditions. The precise structure information on CityU-11 has been disclosed through both single-crystal X-ray diffraction (SCXRD) and low-dose high-resolution transmission electron microscopy (LD-HRTEM). The SCXRD results showed that CityU-11 crystallized in the noncentrosymmetric space group of Pnn2, while LD-HRTEM suggested that CityU-11 possessed almost the same interplanar distances of 0.6 nm for both (200) and (020) crystal planes, which finely matched with the double peaks of 2θ = 15° in the pattern of its powder X-ray diffraction (PXRD). CityU-11 also displayed an interesting optical property with a moderate birefringence of 0.0258@550 nm.

An Overview of Metal-organic Framework Based Electrocatalysts: Design and Synthesis for Electrochemical Hydrogen Evolution, Oxygen Evolution, and Carbon Dioxide Reduction Reactions

Due to the increasing global energy demands, scarce fossil fuel supplies, and environmental issues, the pursued goals of energy technologies are being sustainable, more efficient, accessible, and produce near zero greenhouse gas emissions. Electrochemical water splitting is considered as a highly viable and eco-friendly energy technology. Further, electrochemical carbon dioxide (CO2 ) reduction reaction (CO2 RR) is a cleaner strategy for CO2 utilization and conversion to stable energy (fuels). One of the critical issues in these cleaner technologies is the development of efficient and economical electrocatalyst. Among various materials, metal-organic frameworks (MOFs) are becoming increasingly popular because of their structural tunability, such as pre- and post- synthetic modifications, flexibility in ligand design and its functional groups, and incorporation of different metal nodes, that allows for the design of suitable MOFs with desired quality required for each process. In this review, the design of MOF was discussed for specific process together with different synthetic methods and their effects on the MOF properties. The MOFs as electrocatalysts were highlighted with their performances from the aspects of hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and electrochemical CO2 RR. Finally, the challenges and opportunities in this field are discussed.

Unit-cell-thick zeolitic imidazolate framework films for membrane application

Zeolitic imidazolate frameworks (ZIFs) are a subset of metal-organic frameworks with more than 200 characterized crystalline and amorphous networks made of divalent transition metal centres (for example, Zn2+ and Co2+) linked by imidazolate linkers. ZIF thin films have been intensively pursued, motivated by the desire to prepare membranes for selective gas and liquid separations. To achieve membranes with high throughput, as in ångström-scale biological channels with nanometre-scale path lengths, ZIF films with the minimum possible thickness-down to just one unit cell-are highly desired. However, the state-of-the-art methods yield membranes where ZIF films have thickness exceeding 50 nm. Here we report a crystallization method from ultradilute precursor mixtures, which exploits registry with the underlying crystalline substrate, yielding (within minutes) crystalline ZIF films with thickness down to that of a single structural building unit (2 nm). The film crystallized on graphene has a rigid aperture made of a six-membered zinc imidazolate coordination ring, enabling high-permselective H2 separation performance. The method reported here will probably accelerate the development of two-dimensional metal-organic framework films for efficient membrane separation.

Metal-organic framework template-guided electrochemical lithography on substrates for SERS sensing applications

The templating method holds great promise for fabricating surface nanopatterns. To enhance the manufacturing capabilities of complex surface nanopatterns, it is important to explore new modes of the templates beyond their conventional masking and molding modes. Here, we employed the metal-organic framework (MOF) microparticles assembled monolayer films as templates for metal electrodeposition and revealed a previously unidentified guiding growth mode enabling the precise growth of metallic films exclusively underneath the MOF microparticles. The guiding growth mode was induced by the fast ion transportation within the nanochannels of the MOF templates. The MOF template could be repeatedly used, allowing for the creation of identical metallic surface nanopatterns for multiple times on different substrates. The MOF template-guided electrochemical growth mode provided a robust route towards cost-effective fabrication of complex metallic surface nanopatterns with promising applications in metamaterials, plasmonics, and surface-enhanced Raman spectroscopy (SERS) sensing fields.

Wrinkled Interfaces: Taking Advantage of Anisotropic Wrinkling to Periodically Pattern Polymer Surfaces

Periodically patterned surfaces can cause special surface properties and are employed as functional building blocks in many devices, yet remaining challenges in fabrication. Advancements in fabricating structured polymer surfaces for obtaining periodic patterns are accomplished by adopting "top-down" strategies based on self-assembly or physico-chemical growth of atoms, molecules, or particles or "bottom-up" strategies ranging from traditional micromolding (embossing) or micro/nanoimprinting to novel laser-induced periodic surface structure, soft lithography, or direct laser interference patterning among others. Thus, technological advances directly promote higher resolution capabilities. Contrasted with the above techniques requiring highly sophisticated tools, surface instabilities taking advantage of the intrinsic properties of polymers induce surface wrinkling in order to fabricate periodically oriented wrinkled patterns. Such abundant and elaborate patterns are obtained as a result of self-organizing processes that are rather difficult if not impossible to fabricate through conventional patterning techniques. Focusing on oriented wrinkles, this review thoroughly describes the formation mechanisms and fabrication approaches for oriented wrinkles, as well as their fine-tuning in the wavelength, amplitude, and orientation control. Finally, the major applications in which oriented wrinkled interfaces are already in use or may be prospective in the near future are overviewed.

Chemical Vapor Deposition and High-Resolution Patterning of a Highly Conductive Two-Dimensional Coordination Polymer Film

Crystalline coordination polymers with high electrical conductivities and charge carrier mobilities might open new opportunities for electronic devices. However, current solvent-based synthesis methods hinder compatibility with microfabrication standards. Here, we describe a solvent-free chemical vapor deposition method to prepare high-quality films of the two-dimensional conjugated coordination polymer Cu-BHT (BHT = benzenehexanothiolate). This approach involves the conversion of a metal oxide precursor into Cu-BHT nanofilms with a controllable thickness (20-85 nm) and low roughness (<10 nm) through exposure to the vaporized organic linker. Moreover, the restricted metal ion mobility during the vapor-solid reaction enables high-resolution patterning via both bottom-up lithography, including the fabrication of micron-sized Hall bar and electrode patterns to accurately evaluate the conductivity and mobility values of the Cu-BHT films.