Today's consumer electronics, such as cell phones, tablets and other portable electronic devices, are typically made of non-renewable, non-biodegradable, and sometimes potentially toxic (for example, gallium arsenide) materials. These consumer electronics are frequently upgraded or discarded, leading to serious environmental contamination. Thus, electronic systems consisting of renewable and biodegradable materials and minimal amount of potentially toxic materials are desirable. Here we report high-performance flexible microwave and digital electronics that consume the smallest amount of potentially toxic materials on biobased, biodegradable and flexible cellulose nanofibril papers. Furthermore, we demonstrate gallium arsenide microwave devices, the consumer wireless workhorse, in a transferrable thin-film form. Successful fabrication of key electrical components on the flexible cellulose nanofibril paper with comparable performance to their rigid counterparts and clear demonstration of fungal biodegradation of the cellulose-nanofibril-based electronics suggest that it is feasible to fabricate high-performance flexible electronics using ecofriendly materials.

Phase transitions in correlated materials can be manipulated at the nanoscale to yield emergent functional properties, promising new paradigms for nanoelectronics and nanophotonics. Vanadium dioxide (VO), an archetypal correlated material, exhibits a metal-insulator transition (MIT) above room temperature. At the thicknesses required for heterostructure applications, such as an optical modulator discussed here, the strain state of VO largely determines the MIT dynamics critical to the device performance. We develop an approach to control the MIT dynamics in epitaxial VO films by employing an intermediate template layer with large lattice mismatch to relieve the interfacial lattice constraints, contrary to conventional thin film epitaxy that favors lattice match between the substrate and the growing film. A combination of phase-field simulation, in situ real-time nanoscale imaging, and electrical measurements reveals robust undisturbed MIT dynamics even at preexisting structural domain boundaries and significantly sharpened MIT in the templated VO films. Utilizing the sharp MIT, we demonstrate a fast, electrically switchable optical waveguide. This study offers unconventional design principles for heteroepitaxial correlated materials, as well as novel insight into their nanoscale phase transitions.

Deep ultraviolet (UV) light-emitting diodes (LEDs) at a wavelength of 226 nm based on AlGaN/ AlN multiple quantum wells using p-type Si as both the hole supplier and the reflective layer are demonstrated. In addition to the description of the hole transport mechanism that allows hole injection from p-type Si into the wide bandgap device, the details of the LED structure which take advantage of the p-type Si layer as a reflective layer to enhance light extraction efficiency (LEE) are elaborated. Fabricated LEDs were characterized both electrically and optically. Owing to the efficient hole injection and enhanced LEE using the p-type Si nanomembranes (NMs), an optical output power of 225 lW was observed at 20 mA continuous current operation (equivalent current density of 15 A/cm 2) without external thermal management. The corresponding external quantum efficiency is 0.2%, higher than any UV LEDs with emission wavelength below 230 nm in the continuous current drive mode. The study demonstrates that adopting p-type Si NMs as both the hole injector and the reflective mirror can enable high-performance UV LEDs with emission wavelengths, output power levels, and efficiencies that were previously inaccessible using conventional p-in structures.

Ultraviolet (UV) light emission at 229 nm wavelength from diode structures based on AlN/Al0.77Ga0.23N quantum wells and using p-type Si to significantly increase hole injection was reported. Both electrical and optical characteristics were measured. Owing to the large concentration of holes from p-Si and efficient hole injection, no efficiency droop was observed up to a current density of 76 A/cm 2 under continuous wave operation and without external thermal management. An optical output power of 160 µW was obtained with corresponding external quantum efficiency of 0.027%. This study demonstrates that by adopting p-type Si nanomembrane contacts as hole injector, practical levels of hole injection can be realized in UV light-emitting diodes with very high Al composition AlGaN quantum wells, enabling emission wavelengths and power levels that were previously inaccessible using traditional p-i-n structures with poor hole injection efficiency.Demand for ultraviolet (UV) light emitting diodes (LEDs) is increasing due to broad applications in biological and chemical detections, decontamination, medical treatment, high density optical recording, and lithography 1-6 . The group III-nitride materials system is the most attractive candidate for UV LEDs spanning the UVA, UVB, and UVC 7-15 owing to its wide bandgap range (GaN: 3.3eV -AlN: ~6.2eV). However, as the wavelength gets shorter, the external quantum efficiency (EQE) becomes significantly degraded. Along with challenges in growth of high Al composition AlxGa1-xN material with low defect densities, the doping concentration limitations and high ionization energy of acceptors for wide gap AlGaN render the p-side of the diode structure quite resistive and the resulting hole injection efficiency is poor. In addition, achieving an Ohmic metal contact to typical p-layers with low contact resistance remains a critical limitation to obtaining an electrically efficient DUV LED. The approach used in this work overcomes both limitations.A variety of approaches have been resorted to circumventing the fundamental p-type doping challenges, such as polarization doping 1,5,16,17 and tunnel junctions [18][19][20] . Both methods require careful control of precursor fluxes for grading Al composition over the growth process, which complicates the epitaxy technique. We have reported a 237 nm UV LED using silicon as an efficient hole injector and postulated that shorter wavelength emission would be obtainable

We present a specially designed materials chemistry that provides ultrathin adhesive layers with persistent tacky surfaces in solid, nonflowable forms for use in transfer printing and related approaches to materials and micro/nanostructure assembly. The material can be photocured after assembly, to yield a robust and highly transparent coating that is also thermally and electrically stable, for applications in electronics, optoelectronics, and other areas of interest.