The transport gap of nanoparticle-passivated Si substrates is measured by scanning tunneling microscopy. Passivation is achieved using a monolayer of CdSe nanoparticles. It is shown that the transport gap and conduction-band edge of the system change upon passivation. The size of the nanoparticles that passivate the Si substrate is varied to study its effect on the transport gap of the system. Plots of the tunneling current versus voltage show that the transport gap of the system can be tuned by the binding of just a monolayer of suitable nanoparticles. From the normalized density of states, it is shown that the conduction-band edge of the system responds to the size of the nanoparticles. Here, a monolayer of the nanoparticles, which were capped with suitable functional groups, has been formed via electrostatic adsorption with the substrate
