The effects of an uncapped nanocrystal on a simulated induced current collected by a nano-contact

The effects of the charge capture process by an isolated and uncapped nanocrystal on the electron beam induced current are studied by the use of the Monte Carlo simulation. In the calculation, the current is created by an electron beam irradiation and is collected by a hemispherical nano-contact. The nanocrystal is considered as a recombination center, and the surface recombination velocity at the free surface is assumed to be equal to zero. The diffusion length is taken out from the fitting of simulated collection efficiency profiles, and studied as a function of the electron beam energy. The diffusion length rapidly decreases at very low energy (≤∼5 keV), increases to reach a maximum at middle energies (∼13 keV), and then decreases to reach saturation for high energy (≥∼25 keV). The effect of the isolated nanocrystal at the surface is highlighted at high energy, when the diffusion length becomes energy independent. This situation leads to determination of effective surface recombination velocities the values of which underline the trapping process in the nanocrystal.