Interface and doping in carbon dots influence charge transfer and transport

Nanoscale carbon-based materials have the potential for large-scale optoelectronic and biomedical applications due to their tunable photo-physics. Here, we explore the impact of doping and the role of intervening media on both electron transfer and transport from carbon dots (CD) to an acceptor menadione (MD). In a binary mixture compared to undoped-CD (UCD), the amine-based nitrogen-doped-CD (ACD) reflects significant changes in its photo-physics like excitation-independent fluorescence, enhanced lifetime, along with a distinct drop in electron transfer rate ( k ET ) to MD. With micro-emulsion, k ET from UCD to MD is enhanced while a substantial reduction is observed for ACDs, emphasizing the critical role of doping, surface states, encapsulation, and interfaces of CTAB micelles. The impact of doping and Coulombic interaction at interfaces on the charge transport phenomena with redox-active MD is further investigated by current-sensing atomic force microscopy. For similar bias-voltage, ACD reflects a higher conductance than UCD, and the conductance is enhanced in the presence of CTAB micelles. Moreover, at a low voltage regime, the current-voltage curve shows a linear growth, while at higher voltage, Fowler-Nordheim (F–N) tunneling is observed. The presence of MD, however, leads to an abrupt rise in conductivity resulting in a transition from F–N to direct tunneling.