Controlled Lattice Thermal Conductivity of Transparent Conductive Oxide Thin Film via Localized Vibration of Doping Atoms.

Amorphization using impurity doping is a promising approach to improve the thermoelectric properties of tin-doped indium oxide (ITO) thin films. However, an abnormal phenomenon has been observed where an excessive concentration of doped atoms increases the lattice thermal conductivity (κl). To elucidate this paradox, we propose two hypotheses: (1) metal hydroxide formation due to the low bond enthalpy energy of O and metal atoms and (2) localized vibration due to excessive impurity doping. To verify these hypotheses, we doped ZnO and CeO2, which have low and high bond enthalpies with oxygen, respectively, into the ITO thin film. Regardless of the bond enthalpy energy, the κl values of the two thin films increased due to excessive doping. Fourier transform infrared spectroscopy was conducted to determine the metal hydroxide formation. There was no significant difference in wave absorbance originating from the OH stretching vibration. Therefore, the increase in κl due to the excessive doping was due to the formation of localized regions in the thin film. These results could be valuable for various applications using other transparent conductive oxides and guide the control of the properties of thin films.

Extreme-Pressure Imprint Lithography for Heat and Ultraviolet-Free Direct Patterning of Rigid Nanoscale Features.

Nanoimprint lithography (NIL) is typically performed by filling up of molds by heated polymers or UV-curable liquid resists, inevitably requiring subsequent pattern-transfer processes. Although direct NIL techniques have been suggested alternatively, they usually require precursors or ink-type resists containing undesired organic components. Here, we demonstrate extreme-pressure imprint lithography (EPIL) that effectively produces well-defined multiscale structures with a wide range from 10 nm to 10 mm on diverse surfaces even including pure or alloy metals without using any precursors, heating, UV exposure, or pattern transfer. In particular, EPIL is accomplished through precise control of room-temperature plastic deformation in nanoscale volumes, which is elucidated by finite element analyses and molecular dynamics simulations. In addition to scalability to macroscopic areas, we confirm the outstanding versatility of EPIL via its successful applications to Ni, Cu, steel, and organics. We expect that the state-of-the-art EPIL process combined with other emerging nanopatterning technologies will be extendable to the future large-area nanofabrication of various devices.

Hierarchical multi-level block copolymer patterns by multiple self-assembly.

Uniform, well-ordered sub-20 nm patterns can be generated by the templated self-assembly of block copolymers (BCPs) with a high Flory-Huggins interaction parameter (χ). However, the self-assembled BCP monolayers remain limited in the possible structural geometries. Here, we introduce a multiple self-assembly method which uses di-BCPs to produce diverse morphologies, such as dot, dot-in-honeycomb, line-on-dot, double-dot, pondering, dot-in-pondering, and line-on-pondering patterns. To improve the diversity of BCP morphological structures, we employed sphere-forming and cylinder-forming poly(styrene-block-dimethylsiloxane) (PS-b-PDMS) BCPs with a high χ. The self-assembled mono-layer and double-layer SiOx dot patterns were modified at a high temperature (∼800 °C), showing hexagonally arranged (dot) and double-hexagonally arranged (pondering) SiOx patterns, respectively. We successfully obtained additional new nanostructures (big-dot, dot-in-honeycomb, line-on-dot, pondering, dot-in-pondering, and line-on-pondering types) through a second self-assembly of cylinder-forming BCPs using the dot and pondering patterns as guiding templates. This simple approach can likely be extended to the multiple self-assembly of many other BCPs with good functionality, significantly contributing to the development of various nanodevices.

Enhancing the Directed Self-assembly Kinetics of Block Copolymers Using Binary Solvent Mixtures.

The rapid pattern formation of well-ordered block copolymer (BCP) nanostructures is practical for next-generation nanolithography applications. However, there remain critical hurdles to achieve the rapid self-assembly of BCPs with a high Flory-Huggins interaction parameter (χ), owing to their slow kinetics. In this article, we report that a binary solvent vapor annealing methodology can significantly accelerate the self-assembly kinetics of poly(dimethylsiloxane-b-styrene) (PDMS-b-PS) BCPs with a high-χ. In particular, we systemically analyzed the effects of the mixing ratio of a binary solvent composed of a PDMS-selective solvent (heptane) and a PS-selective solvent (toluene), showing an ultrafast self-assembly time (≤1 min) to obtain a well-ordered nanostructure. Moreover, we successfully accomplished extremely fast generation of sub-20 nm dot patterns within an annealing time of 10 s in a 300 nm-wide trench by means of binary solvent annealing. We believe that these results are also applicable to other solvent-based annealing systems of BCPs and that they will contribute to the realization of next-generation ultrafine lithography applications.