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The recent emerging significance of the Internet of Things (IoT) demands sensor devices to be integrated with many different functional structures and devices while conserving their original functionalities. To this end, optical transparency and mechanical flexibility of sensor devices are critical requirements for optimal integration as well as high sensitivity. In this work, a transparent, flexible, and sensitive gas sensor building platform is introduced by using multilevel self-assembly of block copolymers (BCPs) and polystyrene (PS) colloids. For the demonstration of an H

Air pollution is on the priority list of global safety issues, with the concern of fatal environmental and public health deterioration. 2D materials are potential adsorbent materials for environmental decontamination, owing to their high surface area, manageable interlayer binding, large surface-to-volume ratio, specific binding capability, and chemical, thermal, and mechanistic stability. Specifically, graphene oxide and reduced graphene oxide have been attracting attention, taking advantage of their low cost synthesis, excessive oxygen containing surface functionalities, and intrinsic aqueous dispersibility, making them desirable for the development of cost-effective, high performance air filters. Many different material designs have been proposed to expand their filtration capability, including the functionalization and integration with other metals and metal oxides, which act not only as binding agents to the target pollutants but also as antimicrobial agents. This review highlights the advantages and drawbacks of 2D materials for air filtration and summarizes the interrelationships among various strategies and the resultant filtration performance in terms of structural engineering, morphology control, and material compositions. Finally, potential future directions are suggested toward the idealized designs of 2D material based air filters.

Hardware-based cryptography that exploits physical unclonable functions is required for the secure identification and authentication of devices in the Internet of Things. However, physical unclonable functions are typically based on anticounterfeit identifiers created from randomized microscale patterns or non-predictable fluctuations of electrical response in semiconductor devices, and the validation of an encrypted signature relies on a single-purpose method such as microscopy or electrical measurement. Here we report nanoscale physical unclonable function labels that exploit non-deterministic molecular self-assembly. The labels are created from the multilayer superpositions of metallic nanopatterns replicated from self-assembled block copolymer nanotemplates. Due to the nanoscale dimensions and diverse material options of the system, physical unclonable functions are intrinsically difficult to replicate, robust for authentication and resistant to external disturbance. Multiple, independently operating keys—which use electrical resistance, optical dichroism or Raman signals—can be generated from a single physical unclonable function, offering millisecond-level validation speeds. We also show that our physical unclonable function labels can be used on a range of different surfaces including dollar bills, human hair and microscopic bacteria.

Two-dimensional (2D) MXenes have attracted significant attention in electromagnetic interference (EMI) shielding applications due to their unique properties, such as excellent metallic conductivity, high surface area, 2D geometry, tunable surface chemistry, and solution processability. In this study, we present a simple and versatile way for introducing multiple internal interfaces into the Ti3C2T x MXenes using insulating graphene oxide (GO) intercalants to enhance internal scattering, resulting in improved absorption loss and EMI shielding effectiveness (SE). Amine-functionalized MXene flakes exhibit a positive surface charge, while GO flakes have a negative charge at acidic pH levels. The functionalized MXene and GO flakes electrostatically self-assemble to form 2D/2D heterostack of MXene/GO nanosheets, and simultaneously generate multiple internal interfaces with significant impedance mismatch. The 2D/2D alternating heterostack of MXene/GO enhances the internal scattering of incident EM waves. Interestingly, despite their inferior electrical conductivity, the MXene/GO heterostack films exhibit higher EMI SE values than the randomly mixed hybrid films, and even outperform pristine MXene with larger electrical conductivity. This enhancement is attributed to enhanced absorption of electromagnetic waves resulting from strong internal scattering at the multiple internal interfaces in the heterostack film.

Graphene fiber is emerging as a new class of carbon-based fiber with distinctive material properties particularly useful for electroconductive components for wearable devices. Presently, stretchable and bendable graphene fibers are principally employing soft dielectric additives, such as polymers, which can significantly deteriorate the genuine electrical properties of pristine graphene-based structures. We report molecular-level lubricating nanodiamonds as an effective physical property modifier to improve the mechanical flexibility of graphene fibers by relieving the tight interlayer stacking among graphene sheets. Nanoscale-sized NDs effectively increase the tensile strain and bending strain of graphene/nanodiamond composite fibers while maintaining the genuine electrical conductivity of pristine graphene-based fibers. The molecular-level lubricating mechanism is elucidated by friction force microscopy on the nanoscale as well as by shear stress measurement on the macroscopic scale. The resultant highly bendable graphene/nanodiamond composite fiber is successfully weaved into all graphene fiber-based textiles and wearable Joule heaters, proposing the potential for reliable wearable applications.

Block copolymer (BCP) nanopatterning has emerged as a versatile nanoscale fabrication tool for semiconductor devices and other applications, because of its ability to organize well-defined, periodic nanostructures with a critical dimension of 5-100 nm. While the most promising application field of BCP nanopatterning has been semiconductor devices, the versatility of BCPs has also led to enormous interest from a broad spectrum of other application areas. In particular, the intrinsically low cost and straightforward processing of BCP nanopatterning have been widely recognized for their large-area parallel formation of dense nanoscale features, which clearly contrasts that of sophisticated processing steps of the typical photolithographic process, including EUV lithography. In this Review, we highlight the recent progress in the field of BCP nanopatterning for various nonsemiconductor applications. Notable examples relying on BCP nanopatterning, including nanocatalysts, sensors, optics, energy devices, membranes, surface modifications and other emerging applications, are summarized. We further discuss the current limitations of BCP nanopatterning and suggest future research directions to open up new potential application fields.

Nanoscale shape engineering is an essential requirement for the practical use of 2D materials, aiming at precisely customizing optimal structures and properties. In this work, sub-10-nm-scale block copolymer (BCP) self-assembled nanopatterns finely aligned along the atomic edge of 2D flakes, including graphene, MoS

The long-range alignment of supramolecular structures must be engineered as a first step toward advanced nanopatterning processes aimed at miniaturizing features to dimensions below 5 nm. This study introduces a facile method of directing the orientation of supramolecular columns over wafer-scale areas using faceted surfaces. Supramolecular columns with features on the sub-5 nm scale were highly aligned in a direction orthogonal to that of the facet patterning on unidirectional and nanoscopic faceted surface patterns. This unidirectional alignment of supramolecular columns is also observed by varying the thickness of the supramolecular film or by altering the dimensions of the facet pattern. The ordering behavior of the supramolecular columns can be attributed to the triangular depth profile of the bottom facet pattern. Furthermore, this directed self-assembly principle allows for the continuous alignment of supramolecular structures across ultralarge distances on flexible patterned substrates.

Graphene oxide (GO)-a chemical derivative of graphene with numerous oxygen functional groups on its surface-has attracted considerable interest because of its intriguing properties in relation to those of pristine graphene. In addition to the inherent wide lateral size distribution of GO sheets arising from the typical oxidative exfoliation of graphite, control of the lateral size of GO is critical for desired GO-based applications. Herein, flow/hyperlayer field-flow fractionation (flow/hyperlayer FFF) is optimized to separate GO sheets by lateral dimensions. Optimized fractionation is achieved by investigating the influences of carrier solvent, channel thickness, and flow rate conditions on the steric/hyperlayer separation of GO sheets by flow FFF. Due to the strong hydrodynamic lift forces of extremely thin GO sheets, a thick flow FFF channel (w = 350 μm) and a very low field strength are required to retain the GO sheets within the channel. GO sheets with narrow size fractions are successfully collected from two different graphite sources during flow/hyperlayer FFF runs and are examined to verify the size evolution. Considering the average lateral diameter of the GO fraction calculated on the basis of the assumption of a circular disk shape, the retention of the GO sheets is 2.2-5.0 times faster than that of spherical particles of the same diameter. This study demonstrates that through flow/hyperlayer FFF, the size distribution of GO sheets can be determined and narrow size fractions can be collected (which is desirable for GO-based applications), which are commonly influenced by the GO lateral dimension.

An effective pathway to build macroscopic scale functional architectures bearing diverse structural dimensions is one of the critical challenges in the two-dimensional (2D) MXene research area. Unfortunately, assembling MXene without adhesive binder is largely limited due to its innate brittle nature and the relatively weak inter-flake van der Waals contact, in contrast to other mechanically compliant 2D materials such as graphene. Herein, an electrochemical self-assembly of pure Ti3C2Tx MXenes is presented for functional multidimensional MXene structures, effectively driven by layer-by-layer spontaneous interfacial reduction at metal template surfaces and subsequent defunctionalization. A three-dimensional open porous aerogel as well as 2D highly stacked thin film structures could be readily obtained in this approach, along with largely enhanced electrical properties induced by spontaneous removal of charge-trapping oxygen functional groups. Accordingly, supercapacitors and electromagnetic interference shielding films based on the multidimensional assembly demonstrate excellent performances.

Hybridization of low-dimensional components with diverse geometrical dimensions should offer an opportunity for the discovery of synergistic nanocomposite structures. In this regard, how to establish a reliable interfacial interaction is the key requirement for the successful integration of geometrically different components. Here, we present 1D/2D heterodimensional hybrids via dopant induced hybridization of 2D Ti3C2Tx MXene with 1D nitrogen-doped graphene nanoribbon. Edge abundant nanoribbon structures allow a high level nitrogen doping (∼6.8 at%), desirable for the strong coordination interaction with Ti3C2Tx MXene surface. For piezoresistive pressure sensor application, strong adhesion between the conductive layers and at the conductive layer/elastomer interface significantly diminishes the sensing hysteresis down to 1.33% and enhances the sensing stability up to 10 000 cycles at high pressure (100 kPa). Moreover, large-area pressure sensor array reveals a high potential for smart seat cushion-based posture monitoring application with high accuracy (>95%) by exploiting machine learning algorithm.

Graphene Oxides (GOs) have been frequently employed as fillers in polymer-based applications. While GO is known to nucleate polymer crystallization in GO-polymer composites reinforcing the mechanical properties of semicrystalline polymers, its counter effect on how polymer crystallization can alter the microstructure of GO has rarely been systematically studied yet. In this work, we study the GO nematic liquid crystal (LC) phase during polymer crystallization focusing on their hierarchical structures by employing in situ small/wide-angle X-ray scattering/diffraction (SAXS/WAXD) techniques. We found that GO LC and polymer crystals co-exist in the GO/polymer complex, where the overall liquid crystallinity is influenced by polymer crystallization. While polymer crystallizes in bulk or at the interface depending on the cooling rate, the interfacial crystallization of poly(ethylene glycol) (PEG) on GO improves both GO alignment and orientation of PEG crystal. This work provides an opportunity to develop a hierarchical structure of GO-based crystalline polymer nanocomposites, whose directionality can be controlled by polymer crystallization under proper cooling rates.

Many interesting properties of 2D materials and their assembled structures are strongly dependent on the lateral size and size distribution of 2D materials. Accordingly, effective size separation of polydisperse 2D sheets is critical for desirable applications. Here, we introduce flow field-flow fractionation (FlFFF) for a wide-range size fractionation of graphene oxide (GO) up to 100 μm. Two different separation mechanisms are identified for FlFFF, including normal mode and steric/hyperlayer mode, to size fractionate wide size-distributed GOs while employing a crossflow field for either diffusion or size-controlled migration of GO. Obviously, the 2D GO sheet reveals size separation behavior distinctive from typical spherical particles arising from its innate planar geometry. We also investigate 2D sheet size-dependent mechanical and electrical properties of three different graphene fibers produced from size-fractionated GOs. This FlFFF-based size selection methodology can be used as a generic approach for effective wide-range size separation for 2D materials, including rGO, TMDs, and MXene.

Despite the ability to precisely tune their bandgap energies, mixed halide perovskites (MHPs) suffer from significant spectral instability, which obstructs their utilization for the rational design of light-emitting diodes. Here, we investigate the origin of the electroluminescence peak shifts in layered MHPs containing bromide and iodide. X-ray diffraction and steady-state absorption measurements prove effective integration of iodide into the cubic lattice and the spatially uniform distribution of halides in the ambient environment. However, the applied electric field during the device operation is found to drive the systematic halide migration. Quantum mechanical density functional theory calculations reveal that the different activation energies required for directional ion hopping lead to the redistribution of anions. In-depth analyses of the electroluminescence spectra indicate that the spectral shifting rate is dependent on the drift velocity of halides. Finally, it is suggested from our study that the dominant red emission is ascribed to the thermodynamically favorable selective hole injection. Our mechanistic study provides insights into the fundamental reason for the spectral instability of devices based on MHPs.

Oxygen evolution (OER) and oxygen reduction (ORR) reactions are the key electrocatalytic redox couple for advanced energy storage/conversion, including rechargeable metal-air batteries and regenerative fuel cells. Heteroatom doped carbon catalysts propose a promising candidate for such purposes along with the superior durability and cost-effectiveness. Unfortunately, exact identification of the catalytic site as well as the critical role of dopants is still controversial in the catalytic mechanism. Here we present bifunctional catalytic site of nitrogen pair-doped graphene nanoribbons for precisely switchable OER and ORR. Pyrazolated N2-edges of graphene nanoribbon serve as switchable dual-functional active sites for OER/ORR with efficient activities and extraordinary durability. Theoretical calculation reveals genuine catalytic mechanism originating from the electrochemical potential-dependent molecular absorption and conversion at the atomic level dopant site. This judiciously controllable bifunctional electrocatalytic activity of dopant catalyst fundamentally addresses the interference between ORR and OER and attains highly stable rechargeable metal-air battery with long-term stability.

Two-dimensional (2D) MXene has shown enormous potential in scientific fields, including energy storage and electromagnetic interference (EMI) shielding. Unfortunately, MXene-based material structures generally suffer from mechanical fragility and vulnerability to oxidation. Herein, mussel-inspired dopamine successfully addresses those weaknesses by improving interflake interaction and ordering in MXene assembled films. Dopamine undergoes in situ polymerization and binding at MXene flake surfaces by spontaneous interfacial charge transfer, yielding an ultrathin adhesive layer. Resultant nanocomposites with highly aligned tight layer structures achieve approximately seven times enhanced tensile strength with a simultaneous increase of elongation. Ambient stability of MXene films is also greatly improved by the effective screening of oxygen and moisture. Interestingly, angstrom thick polydopamine further promotes the innate high electrical conductivity and excellent EMI shielding properties of MXene films. This synergistic concurrent enhancement of physical properties proposes MXene/polydopamine hybrids as a general platform for MXene based reliable applications.

Passive component-based soft resonators have been spotlighted in the field of wearable and implantable devices due to their remote operation capability and tunable properties. As the output signal ...

Perovskite nanocrystals are promising luminescent materials with synthetic feasibility and band gap tunability. Nonetheless, application of the perovskite nanocrystals to light-emitting devices has been challenging because of the intrinsic poor colloidal stability and environmental vulnerability issues. Here, we introduce a new protocol for highly air-stable perovskite nanocrystal layers with a tunable band gap via a simple nanocrystal pinning process. The nanocrystals were composed of CH3NH3PbBr3 (MAPbBr3) mixed with (vinylbenzylamine)2PbBr4 ((VBzA)2PbBr4), which contains a photopolymerizable structure-directing ligand. Along with the compostion of (VBzA)2PbBr4, the band gap of the perovskite layer continuously increased with the reduction of the nanocrystal size and also lattice distortion. The nanocrystal film readily polymerized upon exposure to visible light was highly stable under humid air more than 15 days. Its application to bluish-green light-emitting diodes is demonstrated.

Graphene fibers (GFs) are promising elements for flexible conductors and energy storage devices, while translating the extraordinary properties of individual graphene sheets into the macroscopically assembled 1D structures. We report that a small amount of water addition to the graphene oxide (GO) N-methyl-2-pyrrolidone (NMP) dispersion has significant influences on the mesophase structures and physical properties of wet-spun GFs. Notably, 2 wt % of water successfully hydrates GO flakes in NMP dope to form a stable graphene oxide liquid crystal (GOLC) phase. Furthermore, 4 wt % of water addition causes spontaneous planarization of wet-spun GFs. Motivated from these interesting findings, we develop highly electroconductive and mechanically strong flat GFs by introducing highly crystalline electrochemically exfoliated graphene (EG) in the wet-spinning of NMP-based GOLC fibers. The resultant high-performance hybrid GFs can be sewn on cloth, taking advantage of the mechanical robustness and high flexibility., A small amount of water can hydrate graphene oxide dispersed in organic solvents, resulting in formation of a liquid crystal phase and spontaneous rearrangement of graphene fibers in a flat geometry.

Graphene-fiber (GF) supercapacitors have attracted significant research attention in the field of wearable devices. However, there is still a need for active materials with high energy density. Transition Metal Nitrides (TMNs) are promising candidates for this purpose compared with conventional Transition Metal Oxides (TMOs) or conducting polymers (CPs) owing to their higher electrical conductivity, stability and relevant electrochemical properties. We have successfully integrated Tungsten Nitride (WN) with reduced graphene oxide fibers (rGOF) and developed high-performance hybrid fiber (WN-rGOF) supercapacitors. These hybrid supercapacitors attained a high capacitance of 16.29 F cm-3 at 0.05 A cm-3 and an energy density of 1.448 mW h cm-3, which is 7.5 and 1.75 times higher than those of the pure rGOF supercapacitor and the Tungsten Oxide/rGO hybrid fiber (WO3-rGOF) supercapacitor, respectively. The energy density readily increased up to 2.896 mW h cm-3 when three WN-rGOF supercapacitors were connected in series. The WN-rGOF supercapacitor also showed high capacitance retention of 84.7% after 10 000 cycles along with appreciable performance under severe mechanical deformation.

Artificial muscles are indispensable components for next-generation robotics capable of mimicking sophisticated movements of living systems. However, an optimal combination of actuation parameters, including strain, stress, energy density and high mechanical strength, is required for their practical applications. Here we report mammalian-skeletal-muscle-inspired single fibres and bundles with large and strong contractive actuation. The use of exfoliated graphene fillers within a uniaxial liquid crystalline matrix enables photothermal actuation with large work capacity and rapid response. Moreover, the reversible percolation of graphene fillers induced by the thermodynamic conformational transition of mesoscale structures can be in situ monitored by electrical switching. Such a dynamic percolation behaviour effectively strengthens the mechanical properties of the actuator fibres, particularly in the contracted actuation state, enabling mammalian-muscle-like reliable reversible actuation. Taking advantage of a mechanically compliant fibre structure, smart actuators are readily integrated into strong bundles as well as high-power soft robotics with light-driven remote control.

A reliable method for preparing a conformal amorphous carbon (a-C) layer with a thickness of 1-nm-level, is tested as a possible Cu diffusion barrier layer for next-generation ultrahigh-density semiconductor device miniaturization. A polystyrene brush of uniform thickness is grafted onto 4-inch SiO

Two-dimensional (2D) materials are promising components for defect passivation of metal halide perovskites. Unfortunately, commonly used polydisperse liquid-exfoliated 2D materials generally suffer from heterogeneous structures and properties while incorporated into perovskite films. We introduce monodisperse multifunctional 2D crystalline carbon nitride, poly(triazine imide) (PTI), as an effective defect passivation agent in perovskite films via typical solution processing. Incorporation of PTI into perovskite film can be readily attained by simple solution mixing of PTI dispersions with perovskite precursor solutions, resulting in the highly selective distribution of PTI localized at the defective crystal grain boundaries and layer interfaces in the functional perovskite layer. Several chemical, optical, and electronic characterizations, in conjunction with density functional theory calculations, reveal multiple beneficial roles from PTI: passivation of undercoordinated organic cations at the surface of perovskite crystal, suppression of ion migration by blocking diffusion channels, and prevention of hole quenching at perovskite/SnO

Graphene oxide (GO) has become a key component for high-performance carbon-based films or fibers based on its dispersibility and liquid crystallinity in an aqueous suspension. While the superior performance of GO-based fiber relies on their alignment at the submicrometer level, fine control of the microstructure is often hampered, in particular, under dynamic nature of GO-processing involving shear. Here, we systemically studied the structural variation of GO suspensions under shear conditions via in situ rheo-scattering and shear-polarized optical microscope analysis. The evolution of GO alignment under shear is indeed complex. However, we found that the shear-dependent structural equilibrium exists. GO showed a nonlinear structural transition with shear, yet there is a "universal" shear threshold for the best alignment, resulting in graphene fiber achieved an improvement in mechanical properties by ∼54% without any chemical modification. This finding challenges the conventional concept that high shear stress is required for the good alignment of particles and their best performance.

Energy storage system (ESS) can mediate the smart distribution of local energy to reduce the overall carbon footprint in the environment. South Korea is actively involved in the integration of ESS into renewable energy development. This perspective highlights the research and development status of ESS in South Korea. We provide an overview of different ESS technologies practiced in South Korea with a special emphasise on the electrochemical energy storage systems. We also discuss the possible strategies for the sustainable development of ESS in South Korea.

High specific capacity materials that can store potassium (K) are essential for next-generation K-ion batteries. One such candidate material is phosphorene (the 2D allotrope of phosphorus (P)), but the potassiation capability of phosphorene has not yet been established. Here we systematically investigate the alloying of few-layer phosphorene (FLP) with K. Unlike lithium (Li) and sodium (Na), which form Li3P and Na3P, FLP alloys with K to form K4P3, which was confirmed by ex situ X-ray characterization as well as density functional theory calculations. The formation of K4P3 results in high specific capacity (∼1200 mAh g-1) but poor cyclic stability (only ∼9% capacity retention in subsequent cycles). We show that this capacity fade can be successfully mitigated by the use of reduced graphene oxide (rGO) as buffer layers to suppress the pulverization of FLP. We studied the performance of rGO and single-walled carbon nanotubes (sCNTs) as buffer materials and found that rGO being a 2D material can better encapsulate and protect FLP relative to 1D sCNTs. The half-cell performance of FLP/rGO could also be successfully reproduced in a full-cell configuration, indicating the possibility of high-performance K-ion batteries that could offer a sustainable and low-cost alternative to Li-ion technology.

Br-doped Li4Ti5O12-xBrx (“x” = 0, 0.1, 0.3, 0.5 and 0.7) anode materials were synthesized by a conventional solid-state reaction technique using precursors of Li2CO3, TiO2 and LiBr, and the doping behavior and related electrochemical properties of these materials were studied. In our investigation, quantitative instrumental analyses revealed that most of the Br ions are situated on the surfaces/interfaces of agglomerated particles rather than in the bulk lattice. Narrow conduction paths of electron and Li-ion were, thus, formed on their surfaces/interfaces. During charging/discharging process, the presence of these narrow surface electrical conduits increased the rate-capability of the LTOBr samples. The LTOBr0.5 sample showed the highest capacity of 125 mAh/g at 1C compared to 115 mAh/g for pure LTO. A highly Br-doped sample (LTOBr0.7), however, showed a slight reduction in capacity. This was explained with the formation of fine precipitations (Br-containing second phase) on the surfaces of the LTO particles due to high Br addition.

Unzipping carbon nanotubes (CNTs) may offer a valuable route to synthesize graphene nanoribbon (GNR) structures with semiconducting properties. Unfortunately, currently available unzipping methods commonly rely on a random harsh chemical reaction and thereby cause significant degradation of the crystalline structure and electrical properties of GNRs. Herein, crystalline semiconducting GNRs are achieved by a synergistic, judiciously designed two-step unzipping method for N-doped CNTs (NCNTs). NCNTs are effectively unzipped by damage-minimized, dopant-specific electrochemical unzipping and subsequent sonochemical treatment into long ribbon-like nanostructures with crystalline basal planes. Owing to the nanoscale dimension originating from the dense nucleation of the unzipping reaction at highly NCNTs, the resultant GNRs demonstrate semiconducting properties, which can be exploited for chemiresistor-type gas-sensing devices and many other applications.

We report ultrafast recrystallization of perovskite (methylammonium lead tribromide, MAPbBr3) by flash light annealing (FLA) for light-emitting diode (LED) application. Intense near-infrared (NIR) peak spectrum (830 and 900 nm) of flash light could rapidly heat MAPbBr3 based LED structures over ∼320 °C without radiative damage. Cuboidal morphology of the perovskite active layer was evolved into the dense recrystallized structure with a noticeably small grain size (∼38 nm) by FLA, which significantly promoted the radiative recombination. Surface roughness (root mean square (RMS)) of the perovskite layer was decreased by 62% (from 8.47 to 3.22 nm) via FLA, while inhibiting the leakage current that limit current efficiency (CE) of perovskite LED (PeLED). Three dimensional temperature simulation was investigated for the mechanism of flash-induced MAPbBr3 recrystallization. Finally, FLA was successfully exploited for the flexible PeLEDs on polyethylene naphthalate substrates, which exhibited 252% larger CE compared to thermally annealed counterpart.

A nanosquare array is an indispensable element for the integrated circuit design of electronic devices. Block copolymer (BCP) lithography, a promising bottom-up approach for sub-10 nm patterning, has revealed a generic difficulty in the production of square symmetry because of the thermodynamically favored hexagonal packing of self-assembled sphere or cylinder arrays in thin-film geometry. Here, we demonstrate a simple route to square arrays via the orthogonal self-assembly of two lamellar layers on topographically patterned substrates. While bottom lamellar layers within a topographic trench are aligned parallel to the sidewalls, top layers above the trench are perpendicularly oriented to relieve the interfacial energy between grain boundaries. The size and period of the square symmetry are readily controllable with the molecular weight of BCPs. Moreover, such an orthogonal self-assembly can be applied to the formation of complex nanopatterns for advanced applications, including metal nanodot square arrays.

Natural photosystems (PSs) have received much attention as a biological solar energy harvester because of their high quantum efficiency for energy transfer. However, the PSs hybridized with solid electrodes exhibit low light-harvesting efficiencies because of poor interface properties and random orientations of PSs, all of which interfere with efficient charge extraction and transfer. Herein, we report the linker-free, oriented self-assembly of natural PSs with nitrogen-doped carbon nanotubes (NCNTs) via electrostatic interaction. Protonated nitrogen-doped sites on the NCNTs facilitate spontaneous immobilization of the negatively charged stroma side of PSs, which provides a favorable orientation for electron transfer without electrically insulating polymer linkers. The resulting PS/NCNT hybrids exhibit a photocurrent density of 1.25 ± 0.08 μA cm