Self-Organized Phase-Composite Nanocrystal Solids with Superior Charge Transport.

Interparticle electronic coupling is essential for self-assembled colloidal nanocrystal (NC) solid semiconductors to fulfill their wide-tunable electrical and optoelectrical properties, but it has been limited by disorders. Here, a disorder-tolerant coupling approach is presented by synthesizing self-organized NC solids based on amorphous/nanocrystalline phase-composites. The ZnO amorphous matrix, which infills the space between the less regularly ordered ZnO NCs, enables robust electronic coupling between neighboring NCs via the resonant wave function overlap, leading to a disorder-tolerant resonant conducting state. Field-effect transistors based on phase-composite semiconductors show delocalized band-like transport with superior field-effect mobility values (∼75 cm2 V-1 s-1), compared to amorphous or polycrystalline ZnO semiconductors. Furthermore, the broad amorphous matrix can mitigate interfacial defects between crystalline regions through atomic relaxation, in contrast to narrow grain boundaries in polycrystalline films, resulting in a significantly low interface trap density for phase-composite NC solids. Density function theory calculations and quantum transport simulations using the nonequilibrium Green's function formalism elucidate the origins of superior and highly disorder-tolerant electron transport in phase-composite NC solids. Our report introduces a new class of NC solids complementary to the colloidal counterpart and will be applicable to CMOS-compatible emerging device technologies.

MIL-101-NH2(Fe)-Coated Nylon Microfibers for Immobilized Photocatalysts in RhB and Cr(VI) Removal.

MIL-101-NH2(Fe) is one of the effective photocatalytic metal-organic frameworks (MOFs) working under visible light. However, its powder-type form inhibits reusability in practical applications. In this study, we immobilized MIL-101-NH2(Fe) on a polymeric microfiber mesh to improve reusability while minimizing the loss of catalytic performance. To overcome the lack of surface functionality of the nylon fibers, an atomic layer deposition Al2O3 layer and NH2-BDC linker were introduced to facilitate uniform coating of the MOF on the fiber surface. The reactions of the metal precursor to the nylon substrate and NH2-BDC ligand of the MOF allow chemical bonding from the core to the shell of the entire hybrid catalytic materials. The resulting fiber-immobilized MOFs (Nylon@Al2O3@MOF) demonstrated high photocatalytic performance in the removal of RhB and Cr(VI) as representatives of organic dyes and heavy metals, respectively, while retaining over 85% of its efficiency after five cycles.

Super-Resolution Fluorescence Imaging for Semiconductor Nanoscale Metrology and Inspection.

The increase in the number and complexity of process levels in semiconductor production has driven the need for the development of new measurement methods that can evaluate semiconductor devices at the critical dimensions of fine patterns and simultaneously inspect nanoscale contaminants or defects. However, conventional optical inspection methods often fail to resolve device patterns or defects at the level of tens of nanometers required for device development owing to their diffraction-limited resolutions. In this study, we used the stochastic optical reconstruction microscopy (STORM) technique to image semiconductor nanostructures with feature sizes as small as 30 nm and detect individual 20 nm-diameter contaminants. STORM imaging of semiconductor nanopatterns is based on the development of a selective labeling method of fluorophores for a negative silicon oxide surface using the charge interaction of positive polyethylenimine molecules. This study demonstrates the potential of STORM for nanoscale metrology and in-line defect inspection of semiconductor integrated circuits.

Eutectic friction transfer lithography: a facile solid-state route for highly crystalline semiconducting polymers.

Herein, we report a solid-state lithography technique utilizing eutectic friction transfer lithography (EFTL). The EFTL technique employs eutectic pellets made of semiconducting polymers and volatile organic solid matrices. Using frictional heating and eutectic melting, various semiconducting polymer crystals were formed by a simple rubbing process under mild conditions. The strong anisotropic optical properties suggest that J-type packing is dominant in EFTL microwires because of the highly extended and planarized crystal structures.

Complementary Hybrid Semiconducting Superlattices with Multiple Channels and Mutual Stabilization.

An organic-inorganic hybrid superlattice with near perfect synergistic integration of organic and inorganic constituents was developed to produce properties vastly superior to those of either moiety alone. The complementary hybrid superlattice is composed of multiple quantum wells of 4-mercaptophenol organic monolayers and amorphous ZnO nanolayers. Within the superlattice, multichannel formation was demonstrated at the organic-inorganic interfaces to produce an excellent-performance field effect transistor exhibiting outstanding field-effect mobility with band-like transport and steep subthreshold swing. Furthermore, mutual stabilizations between organic monolayers and ZnO effectively reduced the performance degradation notorious in exclusively organic and ZnO transistors.

Dynamic band alignment modulation of ultrathin WOx/ZnO stack for high on/off ratio field-effect switching applications.

A two-dimensional (2D) WOx/ZnO stack reveals a unique carrier transport behavior, which can be utilized as a novel device element to achieve a very high on/off ratio (>106) and an off current density lower than 1 nA cm-2. These unique behaviors are explained by a dynamic band alignment between WOx and ZnO, which can be actively modulated by a gate bias. The performance of FET utilizing the WOx/ZnO stack is comparable to those of other 2D heterojunction devices; however, it has a unique benefit in terms of process integration because of very low temperature process capability (T < 110 °C). The high on/off switching with extremely low off current density utilizing the dynamic band alignment modulation at the WOx/ZnO stack can be a very useful element for future device applications, especially in monolithic 3D integration or flexible electronics.

Selective Infiltration in Polymer Hybrid Thin Films as a Gas-Encapsulation Layer for Stretchable Electronics.

The infiltration depth and water vapor transmission rate (WVTR) were explored in a variety of Al2O3-polymer hybrid layers as thin gas barrier films by filling the free volumes of polymers in the subsurface region with Al2O3 using the atomic layer infiltration (ALI) method. Among all, the prepared Al2O3-polyethylene terephthalate (PET), Al2O3-polyimide, and Al2O3-Nylon 6 hybrid thin layers with the infiltration depth in the nanometer ranges showed extremely low WVTR values (<10-6 g m-2 day-1) in a Ca dot corrosion test. Furthermore, we observed selective infiltration among the two polymers [perfluoroalkoxy alkane (PFA) and PET] by a preferential growth of Al2O3 in the PET polymer that might be based on effective functional group anchoring in the ALI process. Then, we demonstrated a novel strategy by employing such a selective infiltration procedure and encapsulating individual segments of 144 Ca dots by Al2O3-PET hybrid thin films on the PFA polymer substrate rather than wrapping the whole thing together for the stretchable gas-encapsulation film. Regardless of stretching, it showed an extremely low WVTR (<10-7 g m-2 day-1) and is proposed as a highly promising hermetic sealing alternative in stretchable, flexible, and foldable electronic display technologies.

Realization of Spatially Addressable Library by a Novel Combinatorial Approach on Atomic Layer Deposition: A Case Study of Zinc Oxide.

Though the synthesis of libraries of multicomponent metal oxide systems is prevalent using the combinatorial approach, the combinatorial approach has been rarely realized in studying simple metal oxides, especially applied to the atomic layer deposition (ALD) technique. In this literature, a novel combinatorial approach technique is utilized within an ALD grown simple metal oxide to synthesize a "spatially addressable combinatorial library". The two key factors in gradients were defined during the ALD process: (1) the process temperature and (2) a nonuniform flow of pulsed gases inside a cross-flow reactor. To validate the feasibility of our novel combinatorial approach, a case study of zinc oxide (ZnO), a simple metal oxide whose properties are well-known, is performed. Because of the induced gradient, the ZnO (002) crystallite size was found to gradually vary across a 100 mm wafer (∼10-20 nm) with a corresponding increase in the normalized Raman E2/A1 peak intensity ratio. The findings agree well with the visible grain size observed from scanning electron microscope. The novel combinatorial approach provides a means of systematical interpretation of the combined effect of the two gradients, especially in the analysis of the microstructure of ZnO crystals. Moreover, the combinatorial library reveals that the process temperature, rather than the crystal size, plays the most significant role in determining the electrical conductivity of ZnO.

ZnO composite nanolayer with mobility edge quantization for multi-value logic transistors.

A quantum confined transport based on a zinc oxide composite nanolayer that has conducting states with mobility edge quantization is proposed and was applied to develop multi-value logic transistors with stable intermediate states. A composite nanolayer with zinc oxide quantum dots embedded in amorphous zinc oxide domains generated quantized conducting states at the mobility edge, which we refer to as "mobility edge quantization". The unique quantized conducting state effectively restricted the occupied number of carriers due to its low density of states, which enable current saturation. Multi-value logic transistors were realized by applying a hybrid superlattice consisting of zinc oxide composite nanolayers and organic barriers as channels in the transistor. The superlattice channels produced multiple states due to current saturation of the quantized conducting state in the composite nanolayers. Our multi-value transistors exhibited excellent performance characteristics, stable and reliable operation with no current fluctuation, and adjustable multi-level states.

Single-Crystal Poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']dithiophen-2-yl)- alt-[1,2,5]thiadiazolo[3,4- c]pyridine] Nanowires with Ultrahigh Mobility.

We fabricated single-crystal poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']-dithiophen-2-yl)- alt-[1,2,5]thiadiazolo-[3,4- c]pyridine] (PCDTPT) nanowires with ultrahigh mobility using a liquid-bridge-mediated nanotransfer molding method. The structural analysis of the single-crystal PCDTPT nanowires reveals that PCDTPT crystals have a triclinic structure, and the nanowires grow parallel to PCDTPT backbone chains, which provide important insights into its intrinsic charge transport. The single-crystal PCDTPT nanowire exhibits a superior charge carrier mobility of 72.94 ± 18.02 cm2 V-1 s-1 (maximum mobility up to 92.64 cm2 V-1 s-1), which is a record high value among conjugated polymers to date. In the single-crystal PCDTPT nanowire, the backbone chains in the linear structure along the nanowire growth axis lead to strong backbone delocalization, resulting in highly conductive polymer backbones and a drastic increase in charge carrier mobility. In addition, the single-crystal PCDTPT nanowire shows good environmental stability under air conditions compared to small-molecule organic semiconductors.

Ultra Gas-Proof Polymer Hybrid Thin Layer.

Hermetic sealing is an important technology for isolating and protecting air-sensitive materials and is key in the development of foldable and stretchable electronic devices. Here we report an ultra gas-proof polymer hybrid thin layer prepared by filling the free volume of the polymer with Al2O3 using gas-phase atomic layer infiltration. The high-density polymer-inorganic hybrid shows extremely low gas transmission rate, below the detection limit of the Ca corrosion test (water vapor transmission rate <10-7 g m-2 day-1). Furthermore, because of the remarkable nanometer-scale thinness of the complete polymer-inorganic hybrid, it is highly flexible, which makes it useful for hermetic sealing of stretchable and foldable devices.

Fluorescence-based immunosensor using three-dimensional CNT network structure for sensitive and reproducible detection of oral squamous cell carcinoma biomarker.

A hierarchical three-dimensional network of carbon nanotubes on Si pillar substrate (3DN-CNTs) was developed for the accurate detection of oral squamous cell carcinoma (OSCC) in clinical saliva samples. The 3DN-CNTs were uniformly coated with a layer of aluminum oxides to enhance structural stability during biomarker detection. Cytokeratin-19 antigen (Cyfra 21-1) was utilized as a model biomarker of OSCC for fluorescence-based immunosensor using 3DN-CNTs (3DN-CNTs sensor). The 3DN-CNTs sensor enhances the sensitivity of Cyfra 21-1 detection by increasing the density of immobilized antibody through high surface area of 3DN-CNTs and enhancing the accessibility of biomolecules through the ordered pathway of hierarchical structure. The reliable detection limit for sensing of Cyfra 21-1 was estimated as in the level of 0.5 ng/mL and the quantitative estimation of Cyfra 21-1 was analyzed by 4-parameter logistic (4-PL) model for curve-fitting analysis. Clinical applicability of 3DN-CNTs sensor was evaluated through correlation with the commercially available electrochemiluminescence (ECL) detection system in the hospital. The assay results of the two systems for clinical saliva samples showed a good linear correlation. The 3DN-CNTs sensor offers great potential for accurate diagnosis of OSCC using Cyfra 21-1 biomarker in clinical fluids.

Highly Sensitive Ammonia Gas Sensor Based on Single-Crystal Poly(3-hexylthiophene) (P3HT) Organic Field Effect Transistor.

A highly sensitive organic field-effect transistor (OFET)-based sensor for ammonia in the range of 0.01 to 25 ppm was developed. The sensor was fabricated by employing an array of single-crystal poly(3-hexylthiophene) (P3HT) nanowires as the organic semiconductor (OSC) layer of an OFET with a top-contact geometry. The electrical characteristics (field-effect mobility, on/off current ratio) of the single-crystal P3HT nanowire OFET were about 2 orders of magnitude larger than those of the P3HT thin film OFET with the same geometry. The P3HT nanowire OFET showed excellent sensitivity to ammonia, about 3 times higher than that of the P3HT thin film OFET at 25 ppm ammonia. The ammonia response of the OFET was reversible and was not affected by changes in relative humidity from 45 to 100%. The high ammonia sensitivity of the P3HT nanowire OFET is believed to result from the single crystal nature and high surface/volume ratio of the P3HT nanowire used in the OSC layer.

Extremely High Barrier Performance of Organic-Inorganic Nanolaminated Thin Films for Organic Light-Emitting Diodes.

This work presents a novel barrier thin film based on an organic-inorganic nanolaminate, which consists of alternating nanolayers of self-assembled organic layers (SAOLs) and Al2O3. The SAOLs-Al2O3 nanolaminated films were deposited using a combination of molecular layer deposition and atomic layer deposition techniques at 80 °C. Modulation of the relative thickness ratio of the SAOLs and Al2O3 enabled control over the elastic modulus and stress in the films. Furthermore, the SAOLs-Al2O3 thin film achieved a high degree of mechanical flexibility, excellent transmittance (>95%), and an ultralow water-vapor transmission rate (2.99 × 10-7 g m-2 day-1), which represents one of the lowest permeability levels ever achieved by thin film encapsulation. On the basis of its outstanding barrier properties with high flexibility and transparency, the nanolaminated film was applied to a commercial OLEDs panel as a gas-diffusion barrier film. The results showed defect propagation could be significantly inhibited by incorporating the SAOLs layers, which enhanced the durability of the panel.

Heterogeneous Monolithic Integration of Single-Crystal Organic Materials.

Manufacturing high-performance organic electronic circuits requires the effective heterogeneous integration of different nanoscale organic materials with uniform morphology and high crystallinity in a desired arrangement. In particular, the development of high-performance organic electronic and optoelectronic devices relies on high-quality single crystals that show optimal intrinsic charge-transport properties and electrical performance. Moreover, the heterogeneous integration of organic materials on a single substrate in a monolithic way is highly demanded for the production of fundamental organic electronic components as well as complex integrated circuits. Many of the various methods that have been designed to pattern multiple heterogeneous organic materials on a substrate and the heterogeneous integration of organic single crystals with their crystal growth are described here. Critical issues that have been encountered in the development of high-performance organic integrated electronics are also addressed.

Intramolecular and Intermolecular Interactions in Hybrid Organic-Inorganic Alucone Films Grown by Molecular Layer Deposition.

Investigation of molecular interactions in polymeric films is crucial for understanding and engineering multiscale physical phenomena correlated to device function and performance, but this often involves a compromise between theoretical and experimental data, because of poor film uniformity. Here, we report the intramolecular and intermolecular interactions inside the ultrathin and conformal hybrid organic-inorganic alucone films grown by molecular layer deposition, based on sequential and self-limiting surface reactions. Varying the carbon chain length of organic precursors, which affects their molecular flexibility, caused intramolecular interactions such as double reactions by bending of the molecular backbone, resulting in formation of hole vacancies in the films. Furthermore, intermolecular interactions in alucone polymeric films are dependent on the thermal kinetics of molecules, leading to binding failures and cross-linking at low and high growth temperatures, respectively. We illustrate these key interactions and identify molecular geometries and potential energies by density functional theory calculations.

Controlled Growth of Rubrene Nanowires by Eutectic Melt Crystallization.

Organic semiconductors including rubrene, Alq3, copper phthalocyanine and pentacene are crystallized by the eutectic melt crystallization. Those organic semiconductors form good eutectic systems with the various volatile crystallizable additives such as benzoic acid, salicylic acid, naphthalene and 1,3,5-trichlorobenzene. Due to the formation of the eutectic system, organic semiconductors having originally high melting point (Tm > 300 °C) are melted and crystallized at low temperature (Te = 40.8-133 °C). The volatile crystallizable additives are easily removed by sublimation. For a model system using rubrene, single crystalline rubrene nanowires are prepared by the eutectic melt crystallization and the eutectic-melt-assisted nanoimpinting (EMAN) technique. It is demonstrated that crystal structure and the growth direction of rubrene can be controlled by using different volatile crystallizable additives. The field effect mobility of rubrene nanowires prepared using several different crystallizable additives are measured and compared.

A non-destructive n-doping method for graphene with precise control of electronic properties via atomic layer deposition.

Graphene applications require high precision control of the Fermi level and carrier concentration via a nondestructive doping method. Here, we develop an effective n-doping technique using atomic layer deposition (ALD) of ZnO thin films on graphene through a reactive molecular layer. This ALD doping method is nondestructive, simple, and precise. The ZnO thin films on graphene are uniform, conformal, of good quality with a low density of pinholes, and finely tunable in thickness with 1 Å resolution. We demonstrate graphene transistor control in terms of the Dirac point, carrier density, and doping state as a function of the ZnO thickness. Moreover, ZnO functions as an effective thin-film barrier against air-borne water and oxygen on the graphene, resulting in extraordinary stability in air for graphene devices. ZnO ALD was also applied to other two-dimensional materials including MoS2 and WSe2, which substantially enhanced electron mobility.

Inkjet-Assisted Nanotransfer Printing for Large-Scale Integrated Nanopatterns of Various Single-Crystal Organic Materials.

Inkjet-assisted nanotransfer printing (inkjet-NTP) facilitates spatial control of many arrays of various organic functional materials on a single substrate with a high-throughput integration process, enabling monolithic integration of various organic nanopatterns. Inkjet-NTP enables wafer-scale organic electronic circuits composed of field-effect transistors, complementary inverters, and p-n diodes, demonstrating its capability to produce a high-performance, multifunctional organic chip.

Wafer-scale single-domain-like graphene by defect-selective atomic layer deposition of hexagonal ZnO.

Large-area graphene films produced by means of chemical vapor deposition (CVD) are polycrystalline and thus contain numerous grain boundaries that can greatly degrade their performance and produce inhomogeneous properties. A better grain boundary engineering in CVD graphene is essential to realize the full potential of graphene in large-scale applications. Here, we report a defect-selective atomic layer deposition (ALD) for stitching grain boundaries of CVD graphene with ZnO so as to increase the connectivity between grains. In the present ALD process, ZnO with a hexagonal wurtzite structure was selectively grown mainly on the defect-rich grain boundaries to produce ZnO-stitched CVD graphene with well-connected grains. For the CVD graphene film after ZnO stitching, the inter-grain mobility is notably improved with only a little change in the free carrier density. We also demonstrate how ZnO-stitched CVD graphene can be successfully integrated into wafer-scale arrays of top-gated field-effect transistors on 4-inch Si and polymer substrates, revealing remarkable device-to-device uniformity.