Fig. 4

Effect of the direct deposition of the merocyanine isomer. a Schematics of the experiment. Transfer characteristics (I_DS–V_GS) are measured for clean graphene and MoS₂ devices before and after the deposition of a merocyanine film. b I_DS–V_GS of a clean graphene device (in black) and of the same device covered by a directly deposited merocyanine (MC) assembly (in blue). c I_DS–V_GS of a clean MoS₂ device (in black) and of the same device covered by a directly deposited MC assembly (in blue). The directly deposited MC layer introduced significant n-type doping in both graphene and MoS₂, qualitatively and quantitatively similar to that observed upon irradiation of the spiropyran assembly on the devices. The transfer curves were measured applying a drain source voltage V_DS = 10 mV for graphene and V_DS = 1 V for MoS₂.  Channel length L = 4.6 µm and width W = 10.6 µm (graphene); L = 1.4 µm, W = 1.0 µm (MoS₂). d Scanning tunneling microscope height image of the assembly of a directly deposited MC film on highly oriented pyrolytic graphite. Measured unit cell parameters: a = 3.9 ± 0.2 nm, b = 1.1 ± 0.1 nm, and α = 90 ± 2°, therefore leading to an area A = 4.2 ± 0.2 nm². Inset: Calculated MC assembly on the basis of molecular dynamics simulations. Tunneling parameters: average tunneling current I_t = 20 pA, tip bias voltage V_t = 600 mV. In the three cases, the SP→MC isomerization was obtained through irradiation of an SP solution with UV light immediately before spin coating