Photocurrent studies on multi-walled WS$_{2}$ nanotube devices

Multi-walled WS$_{2}$ nanotubes were used for transport and photo response studies. The nanotubes were structurally characterized by scanning electron microscopy, high resolution transmission electron microscopy and Raman spectroscopy. Nanotube devices in field effect transistor geometry were fabricated on Si/SiO$_{2}$ substrates using nano lithography techniques. I-V measurements of these devices were carried out in ambient conditions. A confocal microscope system was used to study the photo response of the devices to 633 nm and 532 nm laser wavelengths using lock-in technique. Photocurrent map of the devices was obtained and studied as a function of applied bias voltage and gate voltage. The devices showed non-linear increase in photocurrent with increasing bias voltage and light intensity. Further, heterostructure devices of graphene and WS$_{2}$ nanotubes were fabricated for enhanced field effect behavior. Results of the photo response studies of these devices will also be presented.