ABSTRACT
Photonic devices can be advanced by increasing the density of the integrated optical components. As the integration density increases, the potential for signal interference between adjacent components, optical crosstalk, becomes a concern. To address the crosstalk issue, it is crucial to identify the emission directionality of the integrated optical components. In this study, we investigate the emission directionality of 3D printed light-emitting nano/microwires. We experimentally and numerically showed that when the diameter is reduced below the single-mode cutoff, the emission becomes noticeably directional. In addition, our demonstrations on pairs of closely positioned wires show that optical crosstalk can be effectively avoided by reducing the diameter to the nanoscale to exploit the strong directionality of its emission. We expect that our study can be applied to various fundamental research and applications in the fields of photonics, optical communication, sensing, and imaging, where the directionality of the emissions is crucial.
ABSTRACT
Structural colors are produced by the diffraction of light from microstructures. The collective arrangement of substructures is a simple and cost-effective approach for structural coloration represented by colloidal self-assembly. Nanofabrication methods enable precise and flexible coloration by processing individual nanostructures, but these methods are expensive or complex. Direct integration of desired structural coloration remains difficult because of the limited resolution, material-specificity, or complexity. Here, we demonstrate three-dimensional printing of structural colors by direct writing of nanowire gratings using a femtoliter meniscus of polymer ink. This method combines a simple process, desired coloration, and direct integration at a low cost. Precise and flexible coloration is demonstrated by printing the desired structural colors and shapes. In addition, alignment-resolved selective reflection is shown for displayed image control and color synthesis. The direct integration facilitates structural coloration on various substrates, including quartz, silicon, platinum, gold, and flexible polymer films. We expect that our contribution can expand the utility of diffraction gratings across various disciplines such as surface-integrated strain sensors, transparent reflective displays, fiber-integrated spectrometers, anticounterfeiting, biological assays, and environmental sensors.
ABSTRACT
The pixel is the minimum unit used to represent or record information in photonic devices. The size of the pixel determines the density of the integrated information, such as the resolution of displays or cameras. Most methods used to produce display pixels are based on two-dimensional patterning of light-emitting materials. However, the brightness of the pixels is limited when they are miniaturized to nanoscale dimensions owing to their limited volume. Herein, we demonstrate the production of three-dimensional (3D) pixels with nanoscale dimensions based on the 3D printing of quantum dots embedded in polymer nanowires. In particular, a femtoliter meniscus was used to guide the solidification of liquid inks to form vertically freestanding nanopillar structures. Based on the 3D layout, we show high-density integration of color pixels, with a lateral dimension of 620 nm and a pitch of 3 µm for each of the red, green, and blue colors. The 3D structure enabled a 2-fold increase in brightness without significant effects on the spatial resolution of the pixels. In addition, we demonstrate individual control of the brightness based on a simple adjustment of the height of the 3D pixels. This method can be used to achieve super-high-resolution display devices and various photonic applications across a range of disciplines.
ABSTRACT
Photoelectrochemical (PEC) water splitting is an alternative to fossil fuel combustion involving the generation of renewable hydrogen without environmental pollution or greenhouse gas emissions. Cuprous oxide (Cu2O) is a promising semiconducting material for the simple reduction of hydrogen from water, in which the conduction band edge is slightly negative compared to the water reduction potential. However, the solar-to-hydrogen conversion efficiency of Cu2O is lower than the theoretical value due to a short carrier-diffusion length under the effective light absorption depth. Thus, increasing light absorption in the electrode-electrolyte interfacial layer of a Cu2O photoelectrode can enhance PEC performance. In this study, a Cu2O 3D photoelectrode comprised of pyramid arrays was fabricated using a two-step method involving direct-ink-writing of graphene structures. This was followed by the electrodeposition of a Cu current-collecting layer and a p-n homojunction Cu2O photocatalyst layer onto the printed structures. The performance for PEC water splitting was enhanced by increasing the total light absorption area (A a) of the photoelectrode via controlling the electrode topography. The 3D photoelectrode (A a = 3.2 cm2) printed on the substrate area of 1.0 cm2 exhibited a photocurrent (I ph) of -3.01 mA at 0.02 V (vs. RHE), which is approximately three times higher than that of a planar photoelectrode with an A a = 1.0 cm2 (I ph = -0.91 mA). Our 3D printing strategy provides a flexible approach for the design and the fabrication of highly efficient PEC photoelectrodes.
