Photocurrent study of all-printed photodetectors on paper made of different transition metal dichalcogenide nanosheets

We have inkjet-printed in-plane 'metal-semiconductor-metal' type photodetectors on paper, one of the cheapest flexible substrates, which is also recyclable and foldable, in contrast to traditional plastic substrates. The photodetectors are made by using graphene as electrodes and various transition metal dichalcogenides (TMDs) as photoactive component. In particular, we have tested MoS2, WS2, MoSe2 and MoTe2. Large differences in responsivity and sensitivity were observed for all of the TMDs measured, with MoS2 showing the highest sensitivity and MoTe2 producing the largest response. However, photodetectors made of MoTe2 show large decreases in responsivity after one week of exposure to air. The wavelength dependence of the responsivity in MoS2 based devices was further analyzed using a supercontinuum photocurrent spectroscopy setup, with the results suggesting a bolometric or photoelectric origin of the signal. We also report some simple approaches to enhance the device performance and tune the energy range at which the maximum in responsivity or sensitivity is observed

X-ray reflectivity of ultra-thin diamond-like carbon films

Grazing incidence x-ray reflectivity has been employed to investigate ultra-thin films of tetrahedral amorphous carbon (ta-C) grown with an S-bend filtered cathodic vacuum arc. The results indicate that x-ray reflectivity can be used as a metrological tool for thickness measurements on films as thin as 0.5 nm, which is lower than the range required for carbon overcoats for magnetic hard disks and sliders if they are to reach storage densities of 100 Gbits/in2. The density of the films was derived from the best-fit to simulated reflectivity profiles from models for the structural parameters. In such thin films, the x-rays are reflected mainly at the film substrate interface, rather than the outer surface, so that the film density is derived from analysis of the oscillations of the post-critical angle reflectivity