The concept of realizing electronic applications on elastically stretchable "skins" that conform to irregularly shaped surfaces is revolutionizing fundamental research into mechanics and materials that can enable high performance stretchable devices. The ability to operate electronic devices under various mechanically stressed states can provide a set of unique functionalities that are beyond the capabilities of conventional rigid electronics. Here, a distinctive microtectonic effect enabled oxygen-deficient, nanopatterned zinc oxide (ZnO) thin films on an elastomeric substrate are introduced to realize large area, stretchable, transparent, and ultraportable sensors. The unique surface structures are exploited to create stretchable gas and ultraviolet light sensors, where the functional oxide itself is stretchable, both of which outperform their rigid counterparts under room temperature conditions. Nanoscale ZnO features are embedded in an elastomeric matrix function as tunable diffraction gratings, capable of sensing displacements with nanometre accuracy. These devices and the microtectonic oxide thin film approach show promise in enabling functional, transparent, and wearable electronics.

This work demonstrates an optofluidic system, where dielectrophoretically controlled suspended nanoparticles are used to manipulate the properties of an optical waveguide. This optofluidic device is composed of a multimode polymeric rib waveguide and a microfluidic channel as its upper cladding. This channel integrates dielectrophoretic (DEP) microelectrodes and is infiltrated with suspended silica and tungsten trioxide nanoparticles. By applying electrical signals with various intensities and frequencies to the DEP microelectrodes, the nanoparticles can be concentrated close to the waveguide surface significantly altering the optical properties in this region. Depending on the particle refractive indices, concentrations, positions and dimensions, the light remains confined or is scattered into the surrounding media in the microfluidic channel.

COMMUNICATION posed grating, we fabricated TiO 2 gratings using the transfer technique presented by Gutruf et al. [ 21 ] This transfer technique enables the incorporation of oxides in elastomeric substrates by utilizing the weak adhesion of platinum to silicon. For our experiments we chose a small grating period of 1 µm which allows for detection of nanometer changes within the grating and is greater than the laser wavelength to stay within the diffraction mode of the grating. [ 22 ] Figure 1 shows a step-wise schematic of the fabrication process used to create the dot gratings (a detailed description of the synthesis can be found in the Experimental Section). Special precaution needs to be taken to conduct the step shown in Figure 1 d. Here, a compressive stress is introduced by curing the PDMS at an elevated temperature (120 °C). This stress results in a negative strain of ≈4% while peeling the structure off the host substrate. The fabricated grating period reduces by 4% as a direct result of this effect. As such, the chosen 1.00 µm grating period shrinks to a 0.96 µm period when released from the rigid carrier.In order to test the performance of the fabricated diffraction grating, it was placed in a uniaxial stretching stage and studied under two laser wavelengths (543.5 and 668.3 nm). A schematic is presented in Figure 2 , with full details presented in the Experimental Section.Once the laser transmits through the grating, a diffraction pattern can be observed on a screen placed behind the grating. The locations of the fi rst order diffraction spots of the laser were measured for compressive (negative) and tensile (positive) applied strains ranging from −4% to 18%. Photographs of the diffraction images obtained as a function of strain for the green laser illumination are presented in Figure 3 a. The diffraction image under red laser illumination is displayed

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S. Sriram, M. Bhaskaran, and co‐workers utilise oxygen‐deficient zinc oxide in stretchable devices to demonstrate sensing and photonic applications. On page 4532, interactions with the environment or with stimuli modify oxygen adsorption and, thereby, the carrier concentration. The resulting technology enables wearable UV and toxic gas sensors.

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