Stimuli-Responsive Surface Ligands for Direct Lithography of Functional Inorganic Nanomaterials

Wafer-Scale Integration of Metal Oxide Nanocrystals on Gas Sensor Chips via Direct Lithographic Patterning

Nanomaterial-based gas sensors are essential due to their high sensitivity and scalability, enabling efficient gas detection across diverse applications. However, a key challenge hindering their practical applications is the variation in sensing performance between devices. Addressing this requires careful consideration of the relationship between on-chip sensing materials and miniaturized devices. As feature sizes reduce to the microscale, accurately and uniformly positioning sensing nanomaterials onto specific regions of the device electrodes becomes increasingly difficult. This challenge arises from the incompatibility between the bottom-up nanomaterial synthesis methods and the top-down lithography-based fabrication processes. Herein, we introduce a cleanroom-compatible fabrication workflow for chemiresistive gas sensors employing direct lithographic patterning of metal oxide nanocrystals. Gas sensors located across different regions of a 4 in. wafer exhibit highly consistent gas-sensing performances, highlighting the potential of this approach, which integrates the strengths of both top-down and bottom-up approaches. This approach opens new opportunities for integrating a wide range of bottom-up synthesized functional nanomaterials into diverse types of chemical sensors.

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.

Colloidal Chemistry in Molten Inorganic Salts: Direct Synthesis of III-V Quantum Dots via Dehalosilylation of (Me3Si)3Pn (Pn = P, As) with Group III Halides

Gallium pnictides, such as GaAs and GaP, are among the most widely used semiconductors for electronic, optoelectronic, and photonic applications. However, solution syntheses of gallium pnictide nanomaterials are less developed than those of many other colloidal semiconductors, including indium pnictides, II-VI and IV-VI compounds, and lead halide perovskites. In this work, we demonstrate that the Wells dehalosilylation reaction can be carried out in molten inorganic salt solvents to synthesize colloidal GaAs, GaP, and GaP1-xAsx nanocrystals. We demonstrate that discrete colloidal nanocrystals can be nucleated and grown in a molten salt with control over their size and composition. Additionally, we found that reaction temperatures above 400 °C are crucial for annealing structural defects in GaAs nanocrystals. We also highlight the utility of the as-synthesized GaP nanocrystals by showing that GaP can be solution-processed into high-refractive-index coatings and patterned by direct optical lithography with micron resolution. Finally, we demonstrate that dehalosilylation reactions in molten salts can be generalized to synthesize indium pnictide (Pn = As, P) and ternary (In1-xGaxAs and In1-xGaxP) quantum dots.

Ring-Opening Polymerization of Surface Ligands Enables Versatile Optical Patterning and Form Factor Flexibility in Quantum Dot Assemblies

The evolution of display technologies is rapidly transitioning from traditional screens to advanced augmented reality (AR)/virtual reality (VR) and wearable devices, where quantum dots (QDs) serve as crucial pure-color emitters. While solution processing efficiently forms QD solids, challenges emerge in subsequent stages, such as layer deposition, etching, and solvent immersion. These issues become especially pronounced when developing diverse form factors, necessitating innovative patterning methods that are both reversible and sustainable. Herein, a novel approach utilizing lipoic acid (LA) as a ligand is presented, featuring a carboxylic acid group for QD surface attachment and a reversible disulfide ring structure. Upon i-line UV exposure, the LA ligand initiates ring-opening polymerization (ROP), crosslinking the QDs and enhances their solvent resistance. This method enables precise full-color QD patterns with feature sizes as small as 3 µm and pixel densities exceeding 3788 ppi. Additionally, it supports the fabrication of stretchable QD composites using LA-derived monomers. The reversible ROP process allows for flexibility, self-healing, and QD recovery, promoting sustainability and expanding QD applications for ultra-fine patterning and on-silicon displays.

The Accurate Synthesis of a Multiscale Metallic Interface on Graphdiyne

The accurate construction of composite material systems containing graphdiyne (GDY) and other metallic materials has promoted the formation of innovative structures and practical applications in the fields of energy, catalysis, optoelectronics, and biomedicine. To fulfill the practical requirements, the precise formation of multiscale interfaces over a wide range, from single atoms to nanostructures, plays an important role in the optimization of the structural design and properties. The intrinsic correlations between the structure, synthesis process, characteristic properties, and device performance are systematically investigated. This review outlines the current research achievements regarding the controlled formation of multiscale metallic interfaces on GDY. Synthetic strategies for interface regulation, as well as the correlation between the structure and performance, are presented. Furthermore, innovative research ideas for the design and synthesis of functional metal-based materials loaded onto GDY-based substances are also provided, demonstrating the promising application potential of GDY-based materials.

Photothermal Laser Printing of Sub-Micrometer Crystalline ZnO Structures

During light-driven 3D additive manufacturing, an object represented in digital form is initially translated into a spatial distribution of light intensity (sequentially or in parallel), which then results in a spatial material distribution. To date, this process typically proceeds by photoexcitation of small functional molecules, leading to photochemically induced crosslinking of soft materials. Alternatively, thermal triggers can be employed, yet thermal processes are often slow and provide only low spatial localization. Nevertheless, sub-micrometer ZnO structures for functional microelectronic devices have recently been laser-printed. Herein, the photothermal laser-printing of ZnO is advanced by i) introducing single-crystalline rather than amorphous sub-micrometer ZnO shapes that crystallize in the hexagonal ZnO wurtzite structure, ii) employing dimethyl sulfoxide (DMSO) instead of water, enabling higher local process temperatures without micro-bubble formation, and iii) using substrates tailored for light absorption and heat management, resolving the challenge of light to heat conversion. Finally, the herein-demonstrated ZnO printing requires no post-processing and is a cleanroom-free technique for the fabrication of crystalline semiconductors.

Reductive pathways in molten inorganic salts enable colloidal synthesis of III-V semiconductor nanocrystals

Colloidal quantum dots, with their size-tunable optoelectronic properties and scalable synthesis, enable applications in which inexpensive high-performance semiconductors are needed. Synthesis science breakthroughs have been key to the realization of quantum dot technologies, but important group III-group V semiconductors, including colloidal gallium arsenide (GaAs), still cannot be synthesized with existing approaches. The high-temperature molten salt colloidal synthesis introduced in this work enables the preparation of previously intractable colloidal materials. We directly nucleated and grew colloidal quantum dots in molten inorganic salts by harnessing molten salt redox chemistry and using surfactant additives for nanocrystal shape control. Synthesis temperatures above 425°C are critical for realizing photoluminescent GaAs quantum dots, which emphasizes the importance of high temperatures enabled by molten salt solvents. We generalize the methodology and demonstrate nearly a dozen III-V solid-solution nanocrystal compositions that have not been previously reported.

Direct Photopatterning of Colloidal Quantum Dots with Electronically Optimized Diazirine Cross-Linkers

Colloidal quantum dots (QDs) with a wide color gamut and high luminescent efficiency are promising for next-generation electronic and photonic devices. However, precise and scalable patterning of QDs without degrading their properties and their integration into commercially relevant devices, such as digitally addressable QD light-emitting diode (QLED) displays, remain challenging. Here, we develop electronically optimized diazirine-based cross-linkers for nondestructive, direct photopatterning of QDs and, ultimately, building the active-matrix QLED displays. The key to the cross-linker design is the introduction of electron-donating substituents that permit the formation of ground-state singlet carbenes for air-stable and benign QD photopatterning. Under ambient conditions, these cross-linkers enable the patterning of heavy metal-free QDs at a resolution of over 13,000 pixels per inch using commercial i-line photolithography. The patterned QD layers fully preserved their optical and optoelectronic properties. Pixelated electroluminescent devices with patterned InP/ZnSe/ZnS QD layers show a peak external quantum efficiency of 15.3% and a maximum luminance of about 40,000 cd m-2, outperforming those made by existing QD patterning approaches. We further show the seamless integration of patterned QLEDs with thin-film transistor circuits and the fabrication of dual-color active-matrix displays. These results underscore the importance of designing photochemistry for QD patterning, and promise the implementation of direct photopatterning methods in manufacturing commercial QLED displays and other integrated QD device platforms.

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.

Ligand-Assisted Direct Lithography of Upconverting and Avalanching Nanoparticles for Nonlinear Photonics

Upconverting nanoparticles (UCNPs) exhibit unique nonlinear optical properties that can be harnessed in microscopy, sensing, and photonics. However, forming high-resolution nano- and micropatterns of UCNPs with large packing fractions is still challenging. Additionally, there is limited understanding of how nanoparticle patterning chemistries are affected by the particle size. Here, we explore direct patterning chemistries for 6-18 nm Tm3+-, Yb3+/Tm3+-, and Yb3+/Er3+-based UCNPs using ligands that form either new ionic linkages or covalent bonds between UCNPs under ultraviolet (UV), electron-beam (e-beam), and near-infrared (NIR) exposure. We study the effect of UCNP size on these patterning approaches and find that 6 nm UCNPs can be patterned with compact ionic-based ligands. In contrast, patterning larger UCNPs requires long-chain, cross-linkable ligands that provide sufficient interparticle spacing to prevent irreversible aggregation upon film casting. Compared to approaches that use a cross-linkable liquid monomer, our patterning method limits the cross-linking reaction to the ligands bound on UCNPs deposited as a thin film. This highly localized photo-/electron-initiated chemistry enables the fabrication of densely packed UCNP patterns with high resolutions (∼1 μm with UV and NIR exposure; <100 nm with e-beam). Our upconversion NIR lithography approach demonstrates the potential to use inexpensive continuous-wave lasers for high-resolution 2D and 3D lithography of colloidal materials. The deposited UCNP patterns retain their upconverting, avalanching, and photoswitching behaviors, which can be exploited in patterned optical devices for next-generation UCNP applications.