Healable Anti-Corrosive and Wear-Resistant Silicone-Oil-Impregnated Porous Oxide Layer of Aluminum Alloy by Plasma Electrolytic Oxidation.

Lubricant (or oil)-impregnated porous surface has been considered as a promising surface treatment to realize multifunctionality. In this study, silicone oil was impregnated into a hard porous oxide layer created by the plasma electrolytic oxidation (PEO) of aluminum (Al) alloys. The monolayer of polydimethylsiloxane (PDMS) from silicone oil is formed on a porous oxide layer; thus, a water-repellent slippery oil-impregnated surface is realized on Al alloy, showing a low contact angle hysteresis of less than 5°. This water repellency significantly enhanced the corrosion resistance by more than four orders of magnitude compared to that of the PEO-treated Al alloy without silicone oil impregnation. The silicone oil within the porous oxide layer also provides a lubricating effect to improve wear resistance by reducing friction coefficients from ~0.6 to ~0.1. In addition, because the PDMS monolayer can be restored by frictional heat, the water-repellent surface is tolerant to physical damage to the oxide surface. Hence, the results of this fundamental study provide a new approach for the post-treatment of PEO for Al alloys.

Influence of Tempering Temperature and Time on Microstructure and Mechanical Properties of Additively Manufactured H13 Tool Steel.

Among various processes for manufacturing complex-shaped metal parts, additive manufacturing is highlighted as a process capable of reducing the wastage of materials without requiring a post-process, such as machining and finishing. In particular, it is a suitable new manufacturing technology for producing AISI H13 tool steel for hot-worked molds with complex cooling channels. In this study, we manufactured AISI H13 tool steel using the laser power bed fusion (LPBF) process and investigated the effects of tempering temperature and holding time on its microstructure and mechanical properties. The mechanical properties of the sub-grain cell microstructure of the AISI H13 tool steel manufactured using the LPBF process were superior to that of the H13 tool steel manufactured using the conventional method. These sub-grain cells decomposed and disappeared during the austenitizing process; however, the mechanical properties could be restored at a tempering temperature of 500 °C or higher owing to the secondary hardening and distribution of carbides. Furthermore, the mechanical properties deteriorated because of the decomposition of the martensite phase and the accumulation and coarsening of carbides when over-tempering occurred at 500 °C for 5 h and 550 °C for 3 h.

Icephobic Coating through a Self-Formed Superhydrophobic Surface Using a Polymer and Microsized Particles.

Icephobic coatings have been extensively studied for decades to overcome the potential damage associated with ice formation in various devices that are operated under harsh weather conditions. Superhydrophobic surface coatings have been applied for icephobic coating applications owing to their low surface energy. In this study, an icephobic coating of a self-formed superhydrophobic surface using polydimethylsiloxane (PDMS) and SiO2 powder was investigated. The effect of superhydrophobicity on icephobicity was determined by varying the experimental parameters. Polyvinylidene fluoride (PVDF) was added to the PDMS solution to improve the mechanical properties of the icephobic layer. The PDMS-PVDF solution also showed a self-formation behavior into a superhydrophobic surface. In addition, the icephobicity and mechanical properties of the PDMS-PVDF mixture coating improved because of the multilevel nanostructure formed by physical and chemical interactions between the mixture and SiO2 powder. We believe that the proposed approach will be a suitable candidate for various practical applications of icephobicity and a model system to understand the correlation between superhydrophobicity and icephobicity.

A Hybrid Gate Dielectrics of Ion Gel with Ultra-Thin Passivation Layer for High-Performance Transistors Based on Two-Dimensional Semiconductor Channels.

We propose a hybrid gate structure for ion gel dielectrics using an ultra-thin Al2O3 passivation layer for realizing high-performance devices based on electric-double-layer capacitors. Electric-double-layer transistors can be applied to practical devices with flexibility and transparency as well as research on the fundamental physical properties of channel materials; however, they suffer from inherent unwanted leakage currents between electrodes, especially for channel materials with low off-currents. Therefore, the Al2O3 passivation layer was introduced between the metal electrodes and ion gel film as a leakage current barrier; this simple approach effectively reduced the leakage current without capacitance degradation. In addition, we confirmed that a monolayer MoS2 transistor fabricated with the proposed hybrid gate dielectric exhibited remarkably enhanced device properties compared to a transistor using a normal ion gel gate dielectric. Our findings on a simple method to improve the leakage current properties of ion gels could be applied extensively to realize high-performance electric-double-layer transistors utilizing various channel materials.

Atomic layer deposition of 1D and 2D nickel nanostructures on graphite.

One-dimensional (1D) nanowires (NWs) and two-dimensional (2D) thin films of Ni were deposited on highly ordered pyrolytic graphite (HOPG) by atomic layer deposition (ALD), using NH3 as a counter reactant. Thermal ALD using NH3 gas forms 1D NWs along step edges, while NH3 plasma enables the deposition of a continuous 2D film over the whole surface. The lateral and vertical growth rates of the Ni NWs are numerically modeled as a function of the number of ALD cycles. Pretreatment with NH3 gas promotes selectivity in deposition by the reduction of oxygenated functionalities on the HOPG surface. On the other hand, NH3 plasma pretreatment generates surface nitrogen species, and results in a morphological change in the basal plane of graphite, leading to active nucleation across the surface during ALD. The effects of surface nitrogen species on the nucleation of ALD Ni were theoretically studied by density functional theory calculations. Our results suggest that the properties of Ni NWs, such as their density and width, and the formation of Ni thin films on carbon surfaces can be controlled by appropriate use of NH3.

Nanodomain swelling block copolymer lithography for morphology tunable metal nanopatterning.

Ordered metal nanopatterns are crucial requirements for electronics, magnetics, catalysts, photonics, and so on. Despite considerable progress in the synthetic route to metal nanostructures, highly ordered metal nanopatterning over a large-area is still challenging. Nanodomain swelling block copolymer lithography is presented as a general route to the systematic morphology tuning of metal nanopatterns from amphiphilic diblock copolymer self-assembly. Selective swelling of hydrophilic nanocylinder domains in amphiphilic block copolymer films during metal precursor loading and subsequent oxygen based etching generates diverse shapes of metal nanopatterns, including hexagonal nanoring array and hexagonal nanomesh and double line array in addition to common nanodot and nanowire arrays. Solvent annealing condition of block copolymer templates, selective swelling of hydrophilic cylinder nanodomains, block copolymer template thickness, and oxygen based etching methods are the decisive parameters for systematic morphology evolution. The plasmonic properties of ordered Au nanopatterns are characterized and analyzed with finite differential time domain calculation. This approach offers unprecedented opportunity for diverse metal nanopatterns from commonly used diblock copolymer self-assembly.

Device-oriented graphene nanopatterning by mussel-inspired directed block copolymer self-assembly.

Directed self-assembly of a block copolymer is successfully employed to fabricate device-oriented graphene nanostructures from CVD grown graphene. We implemented mussel-inspired polydopamine adhesive in conjunction with the graphoepitaxy principle to tailor graphene nanoribbon arrays and a graphene nanomesh located between metal electrodes. Polydopamine adhesive was utilized for facile and damage-free surface treatment to complement the low surface energy of pristine graphene. Our process minimizes the damage to the ideal graphitic structures and electrical properties of graphene during the nanopatterning process. Multi-channel graphene nanoribbon arrays and a graphene nanomesh were successfully fabricated between metal electrodes.

Biomimetic mineralization of vertical N-doped carbon nanotubes.

Biomimetic mineralization of vertical N-doped carbon nanotubes is demonstrated as a straightforward route for carbon-based mineral nanocomposites. The N-doped sites along the carbon nanotube backbone play the role of nucleation sites for mineralization.

One-dimensional metal nanowire assembly via block copolymer soft graphoepitaxy.

We accomplished a facile and scalable route to linearly stacked, one-dimensional metal nanowire assembly via soft graphoepitaxy of block copolymers. A one-dimensional nanoscale lamellar stack could be achieved by controlling the block copolymer film thickness self-assembled within the disposable topographic confinement and utilized as a template to generate linear metal nanowire assembly. The mechanism underlying this interesting morhpology evolution was investigated by self-consistent field theory. The optical properties of metal nanowire assembly involved with surface plasmon polariton were investigated by first principle calculations.

Ultralarge-area block copolymer lithography enabled by disposable photoresist prepatterning.

We accomplished truly scalable, low cost, arbitrarily large-area block copolymer lithography, synergistically integrating the two principles of graphoepitaxy and epitaxial self-assembly. Graphoepitaxy morphology composed of highly aligned lamellar block copolymer film that self-assembled within a disposable photoresist trench pattern was prepared by conventional I-line lithography and utilized as a chemical nanopatterning mask for the underlying substrate. After the block copolymer film and disposable photoresist layer were removed, the same lamellar block copolymer film was epitaxially assembled on the exposed chemically patterned substrate. Highly oriented lamellar morphology was attained without any trace of structure directing the photoresist pattern over an arbitrarily large area.

Peptide-templating dye-sensitized solar cells.

A hollow TiO(2) nanoribbon network electrode for dye-sensitized solar cells (DSSC) was fabricated by a biotemplating process combining peptide self-assembly and atomic layer deposition (ALD). An aromatic peptide of diphenylalanine was assembled into a three-dimensional network consisting of highly entangled nanoribbons. A thin TiO(2) layer was deposited at the surface of the peptide template via the ALD process. After the pyrolysis of the peptide template, a highly entangled nanotubular TiO(2) framework was successfully prepared. Evolution of the crystal phase and crystallite size of the TiO(2) nanostructure was exploited by controlling the calcination temperature. Finally, the hollow TiO(2) nanoribbon network electrode was integrated into DSSC devices and their photochemical performances were investigated. Hollow TiO(2) nanoribbon-based DSSCs exhibited a power conversion efficiency of 3.8%, which is comparable to the conventional TiO(2) nanoparticle-based DSSCs (3.5%). Our approach offers a novel pathway for DSSCs consisting of TiO(2) electrodes via biotemplating.

Soft graphoepitaxy of block copolymer assembly with disposable photoresist confinement.

We demonstrate soft graphoepitaxy of block copolymer assembly as a facile, scalable nanolithography for highly ordered sub-30-nm scale features. Various morphologies of hierarchical block copolymer assembly were achieved by means of disposable topographic confinement of photoresist pattern. Unlike usual graphoepitaxy, soft graphoepitaxy generates the functional nanostructures of metal and semiconductor nanowire arrays without any trace of structure-directing topographic pattern. Our novel approach is potentially advantageous for multilayer overlay processing required for complex device architectures.

Fabrication and electrochemical characterization of TiO2 three-dimensional nanonetwork based on peptide assembly.

The three-dimensional network of TiO(2) hollow nanoribbons designed from a peptide assembly using atomic layer deposition is demonstrated as a promising Li secondary battery electrode in this study. The nanoribbon network ensures effective transport of electrons and Li ions due to (i) a well-connected network of nanoribbons and (ii) the hollow structure of each nanoribbon itself, into which Li ions in the electrolyte can readily diffuse. The improved specific capacity, rate capability, and cyclability of the nanonetwork show that the utilization of a nanonetwork of individual hollow ribbons can serve as a promising strategy toward the development of high-performance electrode for Li secondary batteries.