Scanning tunneling microscope liquid-metal ion source for microfabrication

Abstract

The use of a liquid-metal ion source (LMIS) in a scanning tunneling microscope (STM) embodiment is described. Operation of the LMIS at emitter/target spacings of the order of 100 nm or less is discussed as are also attempts to create microfabrication features on GaAs and Si substrates. The dependence of the threshold voltage for LMIS operation on spacing follows a square root relationship as would be expected from the Taylor theory. Very stable operation of the LMIS was realized at spacings corresponding to threshold voltages <200 V. The use of a proximity focused LMIS allows an exceedingly high current density to be achieved. For example, at 0.1 μm spacing of the emitter from the target and assuming an emission half-angle of 20° a target current density of ∼2300 A/cm2 can be achieved for a Ga LMIS operating at 0.1 μA total current. At closer spacings target current densities are correspondingly greater. Combining the LMIS with an STM embodiment makes possible nanometer fabrication carried out at speeds limited only by the mechanical deflection schemes.