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Theoretical study of focused field emission of electrons from a point source.

We clarify basic mechanisms for focused field emission of electrons from a point source. The effective potential barrier arising from the lateral confinement of current carrying states is shown to be essential for subband filtering. A hornlike opening at the emission plane further improves the collimation even if the transport is not adiabatic. We predict novel source- and field-dependent resonance effects which can affect the emission characteristics.