Spatial and electronic manipulation of silicon nanocrystals by atomic force microscopy

Summary form only given. As Si-based devices shrink, interest is increasing in fast, low-power devices sensitive to small numbers of electrons. MOS structures with large Si nanocrystal arrays comprising a floating gate can be extremely fast, reliable and nonvolatile relative to conventional floating gate memories. Approximately one electron is stored per nanocrystal. Despite promising initial results, current devices have a charge transit time distribution during nanocrystal ensemble writing which limits speed. This behaviour is not completely understood, but may be due to dispersion in oxide thicknesses, nanocrystal interface states, or electronic bound state shifts due to size variations. To address these limitations, we developed an aerosol vapor synthesis/deposition technique for Si nanocrystals with active size classification, enabling narrow nanocrystal size distributions (~10-15% of particles in 2-10 nm range). The first goal of the experiments was to use scanning probe techniques for particle manipulation and to characterize particle electronic properties and charging on a single-particle basis. Si nanocrystal structures were formed by contact mode operation and imaged in noncontact mode without further particle motion. Single nanocrystal charging by a conducting AFM tip was observed, detected as an apparent height change due to electrostatic force, followed by slow relaxation as the stored charge dissipates. Ongoing and future efforts are discussed, including nanocrystal size distribution narrowing, nanocrystal oxide thickness control, and measurement of electron transport through individual particles and ensembles