Transparent electrodes that can remain electrically conductive and stable under large mechanical deformations are highly desirable for applications in flexible and wearable electronics. This paper describes a comprehensive study of the electrical, optical, and mechanical properties of hybrid nanostructures based on two-dimensional graphene and networks of one-dimensional metal nanowires, and their use as transparent and stretchable electrodes. Low sheet resistance (33 Ω/sq) with high transmittance (94% in visible range), robust stability against electric breakdown and oxidation, and superb flexibility (27% in bending strain) and stretchability (100% in tensile strain) are observed, and these multiple functionalities of the hybrid structures suggest a future promise for next generation electronics. The use of hybrid electrodes to fabricate oxide semiconductor transistors and single-pixel displays integrated on wearable soft contact lenses with in vivo tests are demonstrated.

We report on the formation of good Pt Schottky contacts on the Zn-terminated n-type ZnO (0001) surfaces (∼2×1017cm−3) using surface treatment with a hydrogen peroxide solution. The Pt contacts on organic solvent-cleaned ZnO (0001) show leaky behavior with a high leakage current of ∼−0.05A under −5V reverse bias voltage, whereas the hydrogen peroxide-treated contacts show Schottky behavior with very low leakage current of ∼−6.5×10−8A under −5V reverse bias voltage. Schottky barrier heights estimated from current-voltage and capacitance-voltage characteristics are 0.89 and 0.93eV, respectively. Room-temperature photoluminescence results show that the hydrogen peroxide treatment is fairly effective in removing deep-level defects near the ZnO surface region. In addition, the preliminary deep-level transient spectroscopy result is also presented.

We have investigated Ti/Au ͑30/50 nm͒ ohmic contacts to n-ZnO:Al. The samples are annealed at temperatures of 300 and 500°C for 60 s in a flowing N 2 atmosphere. Current-voltage measurements show that the as-deposited sample is ohmic with a specific contact resistance of 2 ϫ 10 Ϫ2 ⍀ cm 2 . However, annealing of the sample at 300°C results in much better ohmic behavior with a contact resistance of 2 ϫ 10 Ϫ4 ⍀ cm 2 . Further increase in annealing temperature ͑500°C͒ causes the degradation of the ohmic property. Glancing angle X-ray diffraction and Auger electron spectroscopy are used to investigate interfacial reactions between the Ti/Au and ZnO layers. It is shown that both rutile and srilankite TiO 2 phases are formed in the as-deposited and annealed samples. It is further shown that annealing at 500°C results in the formation of new phases such as Ti 3 Au and TiAu 2 . A possible explanation is given to describe the annealing temperature dependence of the specific contact resistance.

Various wearable electronic devices have been developed for extensive outdoor activities. The key metrics for these wearable devices are high touch sensitivity and good mechanical and thermal stability of the flexible touchscreen panels (TSPs). Their dielectric constants (k) are important for high touch sensitivities. Thus, studies on flexible and transparent cover layers that have high k with outstanding mechanical and thermal reliabilities are essential. Herein, an unconventional approach for forming flexible and transparent cellulose nanofiber (CNF) films is reported. These films are used to embed ultralong metal nanofibers that serve as nanofillers to increase k significantly (above 9.2 with high transmittance of 90%). Also, by controlling the dimensions and aspect ratios of these fillers, the effects of their nanostructures and contents on the optical and dielectric properties of the films have been studied. The length of the nanofibers can be controlled using a stretching method to break the highly aligned, ultralong nanofibers. These nanofiber-embedded, high-k films are mechanically and thermally stable, and they have better Young's modulus and tensile strength with lower thermal expansion than commercial transparent plastics. The demonstration of highly sensitive TSPs using high-k CNF film for smartphones suggests that this film has significant potential for next-generation, portable electronic devices.

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