Regular Aligned 1D Single‐Crystalline Supramolecular Arrays for Photodetectors

Solution‐processed semiconductor single‐crystal patterns possess unique advantages of large scale and low cost, leading to potential applications toward high‐performance optoelectronic devices. To integrate organic semiconductor micro/nanostructures into devices, various patterning techniques have been developed. However, previous patterning techniques suffer from trade‐offs between precision, scalability, crystallinity, and orientation. Herein, a patterning method is reported based on an asymmetric‐wettability micropillar‐structured template. Large‐scale 1D single‐crystalline supramolecular arrays with strict alignment, pure crystallographic orientation, and precise position can be obtained. The wettability difference between tops and sidewalls of micropillars gives rise to the confinement of organic solutions in discrete capillary tubes followed by dewetting and formation of capillary trailing. The capillary trailing enables unidirectional dewetting, regulated mass transport, and confined crystal growth. Owing to the high crystallinity and pure crystallographic orientation with Pt atomic chains parallel to the substrate, the photodetectors based on the 1D arrays exhibit improved responsivity. The work not only provides fundamental understanding on the patterning and crystallization of supramolecular structures but also develops a large‐scale assembly technique for patterning single‐crystalline micro/nanostructures.     

Monitoring Nanocrystal Self‐Assembly in Real Time Using In Situ Small‐Angle X‐Ray Scattering

Self‐assembled nanocrystal superlattices have attracted large scientific attention due to their potential technological applications. However, the nucleation and growth mechanisms of superlattice assemblies remain largely unresolved due to experimental difficulties to monitor intermediate states. Here, the self‐assembly of colloidal PbS nanocrystals is studied in real time by a combination of controlled solvent evaporation from the bulk solution and in situ small‐angle X‐ray scattering (SAXS) in transmission geometry. For the first time for the investigated system a hexagonal closed‐packed (hcp) superlattice formed in a solvent vapor saturated atmosphere is observed during slow solvent evaporation from a colloidal suspension. The highly ordered hcp superlattice is followed by a transition into the final body‐centered cubic superlattice upon complete drying. Additionally, X‐ray cross‐correlation analysis of Bragg reflections is applied to access information on precursor structures in the assembly process, which is not evident from conventional SAXS analysis. The detailed evolution of the crystal structure with time provides key results for understanding the assembly mechanism and the role of ligand–solvent interactions, which is important both for fundamental research and for fabrication of superlattices with desired properties.     

Directed Self‐Assembly of Liquid‐Crystalline Molecular Building Blocks for Sub‐5 nm Nanopatterning

The thin‐film directed self‐assembly of molecular building blocks into oriented nanostructure arrays enables next‐generation lithography at the sub‐5 nm scale. Currently, the fabrication of inorganic arrays from molecular building blocks is restricted by the limited long‐range order and orientation of the materials, as well as suitable methodologies for creating lithographic templates at sub‐5 nm dimensions. In recent years, higher‐order liquid crystals have emerged as functional thin films for organic electronics, nanoporous membranes, and templated synthesis, which provide opportunities for their use as lithographic templates. By choosing examples from these fields, recent progress toward the design of molecular building blocks is highlighted, with an emphasis on liquid crystals, to access sub‐5 nm features, their directed self‐assembly into oriented thin films, and, importantly, the fabrication of inorganic arrays. Finally, future challenges regarding sub‐5 nm patterning with liquid crystals are discussed.     

Ultrathin Alumina Membranes for Surface Nanopatterning in Fabricating Quantum‐Sized Nanodots

Using ultrathin alumina membranes (UTAMs) as evaporation or etching masks large‐scale ordered arrays of surface nanostructures can be synthesized on substrates. However, it is a challenge for this technique to synthesize quantum‐sized surface structures. Here an innovative approach to prepare UTAMs with regularly arrayed pores in the quantum size range is reported. This new approach is based on a well‐controlled pore‐opening process and a modulated anodization process. Using UTAMs with quantum‐sized pores for the surface patterning process, ordered arrays of quantum dots are synthesized on silicon substrates. This is the first time in realizing large‐scale regularly arrayed surface structures in the quantum size range using the UTAM technique, which is an important breakthrough in the field of surface nanopatterning.     

Colloidal Self‐Assembly Meets Nanofabrication: From Two‐Dimensional Colloidal Crystals to Nanostructure Arrays

Self‐assembly of colloidal microspheres or nanospheres is an effective strategy for fabrication of ordered nanostructures. By combination of colloidal self‐assembly with nanofabrication techniques, two‐dimensional (2D) colloidal crystals have been employed as masks or templates for evaporation, deposition, etching, and imprinting, etc. These methods are defined as “colloidal lithography”, which is now recognized as a facile, inexpensive, and repeatable nanofabrication technique. This paper presents an overview of 2D colloidal crystals and nanostructure arrays fabricated by colloidal lithography. First, different methods for fabricating self‐assembled 2D colloidal crystals and complex 2D colloidal crystal structures are summarized. After that, according to the nanofabrication strategy employed in colloidal lithography, related works are reviewed as colloidal‐crystal‐assisted evaporation, deposition, etching, imprinting, and dewetting, respectively.     

In‐Plane Direct‐Write Assembly of Iridescent Colloidal Crystals

Materials made by directed self‐assembly of colloids can exhibit a rich spectrum of optical phenomena, including photonic bandgaps, coherent scattering, collective plasmonic resonance, and wave guiding. The assembly of colloidal particles with spatial selectivity is critical for studying these phenomena and for practical device fabrication. While there are well‐established techniques for patterning colloidal crystals, these often require multiple steps including the fabrication of a physical template for masking, etching, stamping, or directing dewetting. Here, the direct‐writing of colloidal suspensions is presented as a technique for fabrication of iridescent colloidal crystals in arbitrary 2D patterns. Leveraging the principles of convective assembly, the process can be optimized for high writing speeds (≈600 µm s^?1) at mild process temperature (30 °C) while maintaining long‐range (cm‐scale) order in the colloidal crystals. The crystals exhibit structural color by grating diffraction, and analysis of diffraction allows particle size, relative grain size, and grain orientation to be deduced. The effect of write trajectory on particle ordering is discussed and insights for developing 3D printing techniques for colloidal crystals via layer‐wise printing and sintering are provided.     

Interfacial Capillary‐Force‐Driven Self‐Assembly of Monolayer Colloidal Crystals for Supersensitive Plasmonic Sensors

Colloidal lithography technology based on monolayer colloidal crystals (MCCs) is considered as an outstanding candidate for fabricating large‐area patterned functional nanostructures and devices. Although many efforts have been devoted to achieve various novel applicatons, the quality of MCCs, a key factor for the controllability and reproducibility of the patterned nanostructures, is often overlooked. In this work, an interfacial capillary‐force‐driven self‐assembly strategy (ICFDS) is designed to realize a high‐quality and highly‐ordered hexagonal monolayer MCCs array by resorting the capillary effect of the interfacial water film at substrate surface as well as controlling the zeta potential of the polystyrene particles. Compared with the conventional self‐assembly method, this approach can realize the reself‐assembly process on the substrate surface with few colloidal aggregates, vacancy, and crystal boundary defects. Furthermore, various typical large‐scale nanostructure arrays are achieved by combining reactive ion etching, metal‐assisted chemical etching, and so forth. Specifically, benefiting from the as‐fabricated high‐quality 2D hexagonal colloidal crystals, the surface plasmon resonance (SPR) sensors achieve an excellent refractive index sensitivity value of 3497 nm RIU^?1, which is competent for detecting bovine serum albumin with an ultralow concentration of 10^?8 m . This work opens a window to prepare high‐quality MCCs for more potential applications.     

Flash Light Millisecond Self‐Assembly of High χ Block Copolymers for Wafer‐Scale Sub‐10 nm Nanopatterning

One of the fundamental challenges encountered in successful incorporation of directed self‐assembly in sub‐10 nm scale practical nanolithography is the process compatibility of block copolymers with a high Flory–Huggins interaction parameter (χ). Herein, reliable, fab‐compatible, and ultrafast directed self‐assembly of high‐χ block copolymers is achieved with intense flash light. The instantaneous heating/quenching process over an extremely high temperature (over 600 °C) by flash light irradiation enables large grain growth of sub‐10 nm scale self‐assembled nanopatterns without thermal degradation or dewetting in a millisecond time scale. A rapid self‐assembly mechanism for a highly ordered morphology is identified based on the kinetics and thermodynamics of the block copolymers with strong segregation. Furthermore, this novel self‐assembly mechanism is combined with graphoepitaxy to demonstrate the feasibility of ultrafast directed self‐assembly of sub‐10 nm nanopatterns over a large area. A chemically modified graphene film is used as a flexible and conformal light‐absorbing layer. Subsequently, transparent and mechanically flexible nanolithography with a millisecond photothermal process is achieved leading the way for roll‐to‐roll processability.     

Patterning of Discotic Liquid Crystals with Tunable Molecular Orientation for Electronic Applications

The large‐area formation of functional micropatterns with liquid crystals is of great significance for diversified applications in interdisciplinary fields. Meanwhile, the control of molecular alignment in the patterns is fundamental and prerequisite for the adequate exploitation of their photoelectric properties. However, it would be extremely complicated and challenging for discotic liquid crystals (DLCs) to achieve the goal, because they are insensitive to external fields and surface chemistry. Herein, a simple method of patterning and aligning DLCs on flat substrates is disclosed through precise control of the formation and dewetting of the capillary liquid bridges, within which the DLC molecules are confined. Large‐area uniform alignment occurs spontaneously due to directional shearing force when the solvent is slowly evaporated and programmable patterns could be directly generated on desired substrates. Moreover, the in‐plane column direction of DLCs is tunable by slightly tailoring their chemical structures which changes their self‐assembly behaviors in liquid bridges. The patterned DLCs show molecular orientation–dependent charge transport properties and are promising for templating self‐assembly of other materials. The study provides a facile method for manipulation of the macroscopic patterns and microscopic molecular orientation which opens up new opportunities for electronic applications of DLCs.     

Self‐Assembly of CoPt Magnetic Nanoparticle Arrays and its Underlying Forces

Nanoparticles covered with surfactants are often used to study particle motion patterns and self‐assembly processes in solutions. Surfactants have influence on the interparticle interactions and therefore on the particle motion tracks and final patterns. In this study, CoPt nanoparticles are synthesized in aqueous solution without any surfactant. In situ transmission electron microscopy observation is performed to monitor the self‐assemble process. Two types of magnetic nanoparticle superlattice arrays are formed: hexagonal equal distance superlattice arrays when particle size is 3 nm, and tight unequal distance superlattice arrays when particle size is 4.5 nm. It is interesting to observe that two small arrays merge into a large one through rotational and translational movements. A Monte Carlo simulation is carried out which successfully restores the whole process. It is identified that the underlying forces are van der Waals and magnetic dipolar interactions. The latter is responsible for orientation of each particle during the whole process. This investigation leads to a better understanding of the formation mechanism of magnetic nanoparticle superlattice arrays.     

Nanopatterning self-assembled nanoparticle superlattices by moulding microdroplets

Highly ordered arrays of nanoparticles exhibit many properties that are not found in their disordered counterparts. However, these nanoparticle superlattices usually form in a far-from-equilibrium dewetting process, which precludes the use of conventional patterning methods owing to a lack of control over the local dewetting dynamics. Here, we report a simple yet efficient approach for patterning such superlattices that involves moulding microdroplets containing the nanoparticles and spatially regulating their dewetting process. This approach can provide rational control over the local nucleation and growth of the nanoparticle superlattices. Using DNA-capped gold nanoparticles as a model system, we have patterned nanoparticle superlattices over large areas into a number of versatile structures with high degrees of internal order, including single-particle-width corrals, single-particle-thickness microdiscs and submicrometre-sized 'supra-crystals'. Remarkably, these features could be addressed by micropatterned electrode arrays, suggesting potential applications in bottom-up nanodevices.     

Precise Patterning of Organic Single Crystals via Capillary‐Assisted Alternating‐Electric Field

Owing to the extraordinary properties, organic micro/nanocrystals are important building blocks for future low‐cost and high‐performance organic electronic devices. However, integrated device application of the organic micro/nanocrystals is hampered by the difficulty in high‐throughput, high‐precision patterning of the micro/nanocrystals. In this study, the authors demonstrate, for the first time, a facile capillary‐assisted alternating‐electric field method for the large‐scale assembling and patterning of both 0D and 1D organic crystals. These crystals can be precisely patterned at the photolithography defined holes/channels at the substrate with the yield up to 95% in 1 mm². The mechanism of assembly kinetics is systematically studied by the electric field distribution simulation and experimental investigations. By using the strategy, various organic micro/nanocrystal patterns are obtained by simply altering the geometries of the photoresist patterns on substrates. Moreover, ultraviolet photodetectors based on the patterned Alq3 micro/nanocrystals exhibit visible–blind photoresponse with high sensitivity as well as excellent stability and reproducibility. This work paves the way toward high‐integration, high‐performance organic electronic, and optoelectronic devices from the organic micro/nanocrystals.     

Interface‐Directed Self‐Assembly of Cell‐Laden Microgels

Cell‐laden hydrogels show great promise for creating engineered tissues. However, a major shortcoming with these systems has been the inability to fabricate structures with controlled micrometer‐scale features on a biologically relevant length scale. In this Full Paper, a rapid method is demonstrated for creating centimeter‐scale, cell‐laden hydrogels through the assembly of shape‐controlled microgels or a liquid–air interface. Cell‐laden microgels of specific shapes are randomly placed on the surface of a high‐density, hydrophobic solution, induced to aggregate and then crosslinked into macroscale tissue‐like structures. The resulting assemblies are cell‐laden hydrogel sheets consisting of tightly packed, ordered microgel units. In addition, a hierarchical approach creates complex multigel building blocks, which are then assembled into tissues with precise spatial control over the cell distribution. The results demonstrate that forces at an air–liquid interface can be used to self‐assemble spatially controllable, cocultured tissue‐like structures.     

Temperature‐Enhanced Solvent Vapor Annealing of a C3 Symmetric Hexa‐peri‐Hexabenzocoronene: Controlling the Self‐Assembly from Nano‐ to Macroscale

Temperature‐enhanced solvent vapor annealing (TESVA) is used to self‐assemble functionalized polycyclic aromatic hydrocarbon molecules into ordered macroscopic layers and crystals on solid surfaces. A novel C₃ symmetric hexa‐peri‐hexabenzocoronene functionalized with alternating hydrophilic and hydrophobic side chains is used as a model system since its multivalent character can be expected to offer unique self‐assembly properties and behavior in different solvents. TESVA promotes the molecule's long‐range mobility, as proven by their diffusion on a Si/SiO_x surface on a scale of hundreds of micrometers. This leads to self‐assembly into large, ordered crystals featuring an edge‐on columnar type of arrangement, which differs from the morphologies obtained using conventional solution‐processing methods such as spin‐coating or drop‐casting. The temperature modulation in the TESVA makes it possible to achieve an additional control over the role of hydrodynamic forces in the self‐assembly at surfaces, leading to a macroscopic self‐healing within the adsorbed film notably improved as compared to conventional solvent vapor annealing. This surface re‐organization can be monitored in real time by optical and atomic force microscopy.     

Cobalt Nanoparticle Arrays made by Templated Solid‐State Dewetting

Self‐assembled cobalt particle arrays are formed by annealing, which cause agglomeration (dewetting) of thin Co films on oxidized silicon substrates that are topographically prepatterned with an array of 200‐nm‐period pits. The Co nanoparticle size and uniformity are related to the initial film thickness, annealing temperature, and template geometry. One particle per 200‐nm‐period pit is formed from a 15‐nm film annealed at 850 °C; on a smooth substrate, the same annealing process forms particles with an average interparticle distance of 200 nm. Laser annealing enables templated dewetting of 5‐nm‐thick films to give one particle per pit. Although the as‐deposited films exhibit a mixture of hexagonal close‐packed and face‐centered cubic (fcc) phases, the ordered cobalt particles are predominantly twinned fcc crystals with weak magnetic anisotropy. Templated dewetting is shown to provide a method for forming arrays of nanoparticles with well‐controlled sizes and positions.     

A Lithography‐Free and Field‐Programmable Photonic Metacanvas

The unique correspondence between mathematical operators and photonic elements in wave optics enables quantitative analysis of light manipulation with individual optical devices. Phase‐transition materials are able to provide real‐time reconfigurability of these devices, which would create new optical functionalities via (re)compilation of photonic operators, as those achieved in other fields such as field‐programmable gate arrays (FPGA). Here, by exploiting the hysteretic phase transition of vanadium dioxide, an all‐solid, rewritable metacanvas on which nearly arbitrary photonic devices can be rapidly and repeatedly written and erased is presented. The writing is performed with a low‐power laser and the entire process stays below 90 °C. Using the metacanvas, dynamic manipulation of optical waves is demonstrated for light propagation, polarization, and reconstruction. The metacanvas supports physical (re)compilation of photonic operators akin to that of FPGA, opening up possibilities where photonic elements can be field programmed to deliver complex, system‐level functionalities.     

Guiding the Dewetting of Thin Polymer Films by Colloidal Imprinting

Micropatterned surfaces are important in many biomedical and bioengineering applications, such as the development of biosensors. An approach for the creation of ordered surface patterns, fabricated combining colloidal crystals, consisting of ordered layers of micrometric particles, with dewetting of bilayers of thin polymer films is introduced. The produced patterns are both topographical and chemical in nature, consisting of ordered arrays of microscale holes imprinted in a polymer film, with tunable size. The spontaneous dewetting of the polymer film enables this tunability, with a maximum sevenfold increase in lateral size of the holes and sixfold increase in depth from imprinting to coalescence with neighboring holes. Polymer dewetting and layer inversion are seen to compete during the annealing of the polymer bilayers, and the optimal conditions for hole growth are identified. An in‐depth investigation highlights the effects of UV‐ozone treatment on the long‐range ordering of the colloidal crystals and on preventing the dewetting of the imprinted bilayers. Ordered patterns of different size and depth are produced over large areas by tuning of the colloidal crystal assembly, UV surface treatment and dewetting conditions. Potential applications of the micropatterns produced in the present work include microarrays for single cell studies and biosensors.     

Molecular Self‐Assembly on Graphene

The formation of ordered arrays of molecules via self‐assembly is a rapid, scalable route towards the realization of nanoscale architectures with tailored properties. In recent years, graphene has emerged as an appealing substrate for molecular self‐assembly in two dimensions. Here, the first five years of progress in supramolecular organization on graphene are reviewed. The self‐assembly process can vary depending on the type of graphene employed: epitaxial graphene, grown in situ on a metal surface, and non‐epitaxial graphene, transferred onto an arbitrary substrate, can have different effects on the final structure. On epitaxial graphene, the process is sensitive to the interaction between the graphene and the substrate on which it is grown. In the case of graphene that strongly interacts with its substrate, such as graphene/Ru(0001), the inhomogeneous adsorption landscape of the graphene moiré superlattice provides a unique opportunity for guiding molecular organization, since molecules experience spatially constrained diffusion and adsorption. On weaker‐interacting epitaxial graphene films, and on non‐epitaxial graphene transferred onto a host substrate, self‐assembly leads to films similar to those obtained on graphite surfaces. The efficacy of a graphene layer for facilitating planar adsorption of aromatic molecules has been repeatedly demonstrated, indicating that it can be used to direct molecular adsorption, and therefore carrier transport, in a certain orientation, and suggesting that the use of transferred graphene may allow for predictible molecular self‐assembly on a wide range of surfaces.     

Programmable Liquid Adhesion on Bio‐Inspired Re‐Entrant Structures

Surfaces combining antispreading and high adhesion can find wide applications in the manipulation of liquid droplets, generation of micropatterns and liquid enrichment. To fabricate such surfaces, almost all the traditional methods demand multi‐step processes and chemical modification. And even so, most of them cannot be applied for some liquids with extremely low surface energy. In the past decade, multiply re‐entrant structures have aroused much attention because of their universal and modification‐independent antiadhesion or antipenetration ability. Unfortunately, theories and applications about their liquid adhesion behavior are still rare. In this work, inspired by the springtail skin and gecko feet in the adhered state, it is demonstrated that programmable liquid adhesion is realized on the 3D‐printed micro doubly re‐entrant arrays. By arranging the arrays reasonably, three different Cassie adhesion behaviors can be obtained: I) no residue adhesion, II) tunable adhesion, and III) absolute adhesion. Furthermore, various arrays are designed to tune macro/micro liquid droplet manipulation, which can find applications in the transportation of liquid droplets, liquid enrichment, generation of tiny droplets, and micropatterns.     

Nanoimprint Lithography for Functional Three‐Dimensional Patterns

Nanoimprint lithography (NIL) is viewed as an alternative nanopatterning technique to traditional photolithography, allowing micrometer‐scale and sub‐hundred‐nanometer resolution as well as three‐dimensional structure fabrication. In this Research News article we highlight current activities towards the use of NIL in patterning active or functional materials, and the application of NIL in patterning materials that present both chemistry and structure/topo­graphy in the patterned structures, which provide scaffolds for subsequent manipulation. We discuss and give examples of the various materials and chemistries that have been used to create functional patterns and their implication in various fields as electronic and magnetic devices, optically relevant structures, biologically important surfaces, and 3D particles.