J. J. Yoon

Interband transitions of InAsxSb1−x alloy films

We report pseudodielectric-function spectra from 1.5 to 6.0 eV of InAsxSb1−x ternary alloys obtained by spectroscopic ellipsometry. Energies of the E1, E1+Δ1, E0′, E0′+Δ0′, E2, E2+Δ2, E2′, E2′+Δ2, and E1′ critical points (CPs) were obtained from numerically calculated second derivatives, and identifications established by band-structure calculations using the linear augmented Slater-type orbital method. The E2, E2+Δ2, E2′, and E2′+Δ2 CP structures cross with increasing As-composition. Two saddle-point transitions, Δ5cu-Δ5vu and Δ5cl−Δ5vu, are found for InSb.

Model dielectric functions for AlxGa1−xAs alloys of arbitrary compositions

Many optical models have been used to construct analytic composition-dependent dielectric functions of AlxGa1−xAs alloys. However, these models incorporate various unphysical assumptions to improve their fits to data. Here, we provide the parameters needed to calculate dielectric functions of AlxGa1−xAs for 1.5≤E≤6.0u2002eV and 0≤x≤1 by means of the parametric model of Johs et al. [Thin Solid Films 313–314, 137 (1998)], which eliminates these problems. A representative example concerning interface analysis is discussed, where it is necessary to construct a dielectric function of an alloy of essentially arbitrary composition.

Optical properties of InxAl1−xAs alloy films

Pseudodielectric functions ⟨e⟩ of InxAl1−xAs ternary alloy films were determined from 1.5to6.0eV by spectroscopic ellipsometry. We minimized overlayer effects by performing wet-chemical etching to more accurately determine intrinsic bulk dielectric responses. Energies of the E1, E1+Δ1, E0′, E2, E2+Δ2 and E2′ critical points (CPs) were identified by band structure calculations of the linear augmented Slater-type orbital method. These calculations also showed a crossing of the E0′ and E2 CP structures with increasing In composition and a new saddle point in the AlAs band structure.

Dielectric functions and interband transitions of In1−xAlxSb alloys

Pseudodielectric functions ⟨e⟩ of In1−xAlxSb ternary alloy films were determined from 1.5 to 6.0 eV by spectroscopic ellipsometry. Overlayer effects were minimized by performing in situ chemical etching to more accurately determine intrinsic bulk dielectric responses. Critical-point (CP) energies of structures were determined from numerically calculated second energy derivatives. Where necessary, Brillouin-zone origins were identified by electronic band structure calculations done with the linear augmented Slater-type orbital method. These calculations also showed increasing separation of the E2 and E2′ CP structures with increasing Al-composition

Self-organization of maze-like structures via guided wrinkling

A novel self-organization approach for constructing maze-like structures is presented by controlling wrinkling on a microparticle. Sophisticated three-dimensional (3D) structures found in nature are self-organized by bottom-up natural processes. To artificially construct these complex systems, various bottom-up fabrication methods, designed to transform 2D structures into 3D structures, have been developed as alternatives to conventional top-down lithography processes. We present a different self-organization approach, where we construct microstructures with periodic and ordered, but with random architecture, like mazes. For this purpose, we transformed planar surfaces using wrinkling to directly use randomly generated ridges as maze walls. Highly regular maze structures, consisting of several tessellations with customized designs, were fabricated by precisely controlling wrinkling with the ridge-guiding structure, analogous to the creases in origami. The method presented here could have widespread applications in various material systems with multiple length scales.

Interband transitions and dielectric functions of InGaSb alloys

We report pseudodielectric functions of In1−xGaxSb ternary alloy films from 1.5 to 6.0u2009eV determined by spectroscopic ellipsometry. Artifacts were minimized by real-time assessment of overlayer removal, leading to accurate representations of the bulk dielectric responses of these materials. Critical-point (CP) energies were obtained from numerically calculated second energy derivatives, and their Brillouin-zone origins identified by band-structure calculations. The E2′ and E2u2009+u2009Δ2 CP energies cross with increasing In content as a result of increasing spin-orbit splitting Δ2.

Optical properties of AlAsxSb1−x alloys determined by in situ ellipsometry

We report pseudodielectric function data xa0⟨e⟩u2009=u2009⟨e1⟩u2009+u2009i⟨e2⟩ from 0.74 to 6.48u2009eV of oxide-free AlAsSb alloys that are the closest representation to date of the intrinsic bulk dielectric response e of the material. Measurements were performed on 1.3u2009μm thick films grown on (001) GaAs substrates by molecular beam epitaxy. Data were obtained with the films in situ to avoid oxidation artifacts. Critical-point structures were identified by band-structure calculations done with the linear augmented Slater-type orbital method. Crossings of transitions at the Γ- and X-points and the Γ- and L-points with composition were observed.

Lithographic resolution enhancement of a maskless lithography system based on a wobulation technique for flow lithography

We present a method for improving the lithographic resolution of digital micromirror devices for flow-lithography using a wobulation technique. While maintaining the area of UV exposure, the lithographic resolution was improved using a wobulation technique, which is a large screen display technique that enhances resolution via overlapping pixels by half a pixel. The edges of a diagonal pattern in a microstructure were smoothly generated with additional sub-patterns compared to conventional single pattern-exposure. In addition, the surface roughness of the microstructure was improved because the gaps between pixels were filled by the overlapping patterns.

Dielectric function analysis of ZnSe and CdSe using parametric semiconductor model

We present the dielectric function spectra of ZnSe and CdSe at room temperature between 0.7 and 9eV obtained by vacuum ultra-violet ellipsometry measurement. We have observed the E1, E1+Δ1, E2, E2+Δ2, E0, E0, and E1 bandgaps that had been predicted in previous theoretical calculation. The experimental data were analyzed with parametric semiconductor model which represents the dielectric function as sum of asymmetric critical point lineshapes. The traditional 2nd derivative method analysis was also performed to confirm the quality of parametric model fit.

Modulated grayscale UV pattern for uniform photopolymerization based on a digital micromirror device system

We present an essential method for generating microparticles uniformly in a single ultraviolet (UV) light exposure area for optofluidic maskless lithography. In the optofluidic maskless lithography process, the productivity of monodisperse microparticles depends on the size of the UV exposure area. An effective fabrication area is determined by the size of the UV intensity profile map, satisfying the required uniformity of UV intensity. To increase the productivity of monodisperse microparticles in optofluidic maskless lithography, we expanded the effective UV exposure area by modulating the intensity of the desired UV light pattern based on the premeasured UV intensity profile map. We verified the improvement of the uniformity of the microparticles generated by the proposed modulation technique, providing histogram analyses of the conjugated fluorescent intensities and the sizes of the microparticles. Additionally, we demonstrated the generation of DNA uniformly encapsulated in microparticles.