Figure 2

Time evolution of THz emission from graphene-coated InP in different environmental gases.
(a), Air, (b), vacuum, (c), oxygen and (d), oxygen. In (d), the sample was pre-annealed to remove water before exposure to oxygen. In all cases, after 10 minutes of continuous THz emission measurements (Region I), the sample was illuminated by ultraviolet UV light (365 nm) for 5 minutes (Region II). After the UV light is switched off (Region III), the THz waveform slowly tends towards the original form.