Azimuthal rotation-controlled nanoinscribing for continuous patterning of period- and shape-tunable asymmetric nanogratings.

We present an azimuthal-rotation-controlled dynamic nanoinscribing (ARC-DNI) process for continuous and scalable fabrication of asymmetric nanograting structures with tunable periods and shape profiles. A sliced edge of a nanograting mold, which typically has a rectangular grating profile, slides over a polymeric substrate to induce its burr-free plastic deformation into a linear nanopattern. During this continuous nanoinscribing process, the "azimuthal angle," that is, the angle between the moving direction of the polymeric substrate and the mold's grating line orientation, can be controlled to tailor the period, geometrical shape, and profile of the inscribed nanopatterns. By modulating the azimuthal angle, along with other important ARC-DNI parameters such as temperature, force, and inscribing speed, we demonstrate that the mold-opening profile and temperature- and time-dependent viscoelastic polymer reflow can be controlled to fabricate asymmetric, blazed, and slanted nanogratings that have diverse geometrical profiles such as trapezoidal, triangular, and parallelogrammatic. Finally, period- and profile-tunable ARC-DNI can be utilized for the practical fabrication of diverse optical devices, as is exemplified by asymmetric diffractive optical elements in this study.

Size-Selective Sub-micrometer-Particle Confinement Utilizing Ionic Entropy-Directed Trapping in Inscribed Nanovoid Patterns.

We have developed a single-step, high-throughput methodology to selectively confine sub-micrometer particles of a specific size into sequentially inscribed nanovoid patterns by utilizing electrostatic and entropic particle-void interactions in an ionic solution. The nanovoid patterns can be rendered positively charged by coating with an aluminum oxide layer, which can then localize negatively charged particles of a specific size into ordered arrays defined by the nanovoid topography. On the basis of the Poisson-Boltzmann model, the size-selective localization of particles in the voids is directed by the interplay between particle-nanovoid geometry, electrostatic interactions, and ionic entropy change induced by charge regulation in the electrical double layer overlapping region. The underlying principle and developed method could potentially be extended to size-selective trapping, separation, and patterning of many other objects including biological structures.

Piezo-Actuated One-Axis Vibrational Patterning for Mold-Free Continuous Fabrication of High-Precision Period-Programmable Micro- and Nanopatterns.

We present a mold-free high-resolution nanopatterning technology named piezo-actuated one-axis vibrational patterning (POP) that enables continuous and scalable fabrication of micro- and nanopatterns with precisely programmable periods and dimensions. POP utilizes the piezoelectric stack-actuated high-precision uniaxial vibration of a flat, pattern-free rigid tool edge to conduct sub-50 nm-periodic indentations on various compliant substrates laterally fed underneath. By controlling the tool vibration frequency, tool temperature, and substrate feed rate and by combining sequential tool strokes along multiple directions, diverse functional micro- and nanopatterns with variable periods and depths and multidimensional profiles can be continuously created without resorting to mold prefabrication. With its simple but universal principle, excellent scalability, and versatile processability, POP can be practically applied to many functional devices particularly requiring large-area micro- and nanopatterns with specifically designed periods and dimensions.