Direct observation of surface charge redistribution in active nanoscale conducting channels by Kelvin Probe Force Microscopy.

Surface-exposed uniformly doped silicon-on-insulator channels are fabricated to evaluate the accuracy of Kelvin Probe Force Microscopy (KPFM) measured surface potential and reveals the role of surface charge on the exposed channel operated in the ambient environment. First, the quality of the potential profile probed in the vacuum environment is assessed by the consistency of converted resistivity from KPFM result to the resistivity extracted by the other three methods. Second, in contrast to the simulated and vacuum surface potential profile and image, the ambient surface potential is bent excessively at the terminals of the channel. The excessive bending can be explained by the movement of surface charge under the drive of geometry induced strong local electric field from the channel and results in non-uniform distribution. The dynamic movement of surface charges is proved by the observation of time-dependent potential drift in the ambient measurement. The result suggests the surface charge effect should be taken into account of the measurement of the surface potential in the ambient environment and the design of charge sensitive devices whose surfaces are exposed to air or in ambient conditions in their operation.