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In this article, we report on a room-temperature humidity sensing device using graphene oxide (GO) thin films synthesized by chemical exfoliation. Changes in the device conductivity are measured for varying relative humidity in the experimental chamber. Experiments are carried out for relative humidity varying from 30% to 95%. We observe a difference in the results obtained for low relative humidity (<50%) and high relative humidity (>50%), and propose a sensing mechanism to explain this difference. Although the sensor exhibits some hysteresis at high relative humidities, a method to "reset" the sensor is also proposed. The sensing device has high sensitivity and fast response time.

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In the present study, we report on an efficient method for large-area photoreduction of graphene oxide flexible films. The laser-based reduction can be carried out in situ and can be tuned to attain the properties required. A systematic study has been conducted to evaluate the variation of the degree of reduction with the actual reduction temperature, which is measured using an infrared thermal camera. Local reduction temperature is varied up to 350˚C, and the degree of reduction is measured using the C/O ratio. The C/O ratio is increased from 2:1 for graphene oxide to 10:1 for reduced graphene oxide. This high degree of reduction is observed at low temperatures, and also in a short period of time. Thermal conductivity properties calculated using the temperature distribution shows the in-plane thermal conductivities of graphene oxide and reduced graphene oxide are a few orders of magnitude lower than single layer graphene. This can be attributed to oxygen-defect scattering, and also due to the heat conduction through the thickness of the sample by way of contact between adjacent flakes. This photoreduction method provides a way for roll-to-roll scalable production of graphene-based flexible films.