Patterned Sandwich-Type Silver Nanowire-Based Flexible Electrode by Photolithography

Facile Transfer of a Transparent Silver Nanowire Pattern to a Soft Substrate Using Graphene Oxide as a Double-Sided Adhesion-Tuning Layer

Silver nanowires (AgNWs) have been employed in various optoelectronic devices as transparent electrodes. However, it remains a great challenge to facilely pattern silver nanowires to realize desirable soft skin devices. Here, we develop an intact transfer method via a double-layered adhesion regulator of graphene oxide (GO) enabling complete transfer of a silver nanowire pattern from a tough substrate onto soft polydimethylsiloxane (PDMS) and flexible polyethylene (PE). We achieve positive and negative patterns simultaneously when selectively transferring silver nanowire patterns. The resulting patterned AgNW electrodes have uniform conductivity and long-term stability. The underlying mechanism of the clean transfer is thoroughly investigated via transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). GO plays a role in reducing the adhesion of AgNW to the donor tough substrate and enhancing adhesion of AgNW to the target soft substrate simultaneously. Finally, we demonstrate the utility of the patterned electrodes as transparent sensors detecting body motion. This work offers an effective solution to the challenging patterning problem of silver nanowires on a hydrophobic soft substrate, which is compatible with the soft component in emerging smart skin or wearable electronics.

Scalable Fabrication of Nanogratings on GaP for Efficient Diffraction of Near-Infrared Pulses and Enhanced Terahertz Generation by Optical Rectification

We present a process flow for wafer-scale fabrication of a surface phase grating with sub-micron feature sizes from a single semiconductor material. We demonstrate this technique using a 110-oriented GaP semiconductor wafer with second-order nonlinearity to obtain a nanostructured device (800 nm lateral feature size and a 245 nm height modulation) with applications relevant to near-infrared optical diffraction and time-resolved terahertz (THz) technologies. The fabrication process involves a plasma-enhanced chemical deposition of a SiO2 layer on the wafer followed by contact photolithography and inductively coupled plasma reactive ion etching (ICP-RIE). We discuss the required radiation dosage, exposure times, temperatures and other key parameters to achieve high-quality nanogratings in terms of filling ratio, edge profile, and overall shape. The phase-grating properties, such as the pitch, spatial homogeneity, and phase retardation, are characterized with an atomic force microscope, scanning electron microscope and a non-invasive optical evaluation of the optical diffraction efficiency into different orders. We demonstrate an application of this device in a time-domain THz spectroscopy scheme, where an enhanced THz spectral bandwidth is achieved by optical rectification of near-infrared laser pulses incident on the grating and efficiently diffracted into the first orders. Finally, the reported process flow has the potential to be applied to various materials by considering only slight adjustments to the ICP-RIE etching steps, paving the way to scalable fabrication of sub-micron patterns on a large range of substrates.