Conductive supertips for scanning probe applications

Abstract
Materials machining with the scanning tunneling microscope suffers from poor linewidth compared to the atomic resolution power of the microscope. The trace of the emitted beam is widened due to electron or ion field emission from many tip locations having a low work function. To improve the result emission from a single site that delivers a beam in a confined emission angle is required. Such an emitter is obtained if a supertip is used. It consists of a blunt base tip and an attached supertip of a few nanometers in diameter and height. The supertip delivers the current from one point of field instability only. The attached miniaturized tip generates the high field required for field emission. Electron-beam induced deposition from organometallic gold compounds and a heated substrate is used to build the attached nanocrystalline supertip. Confinement of the emission angle of the emitted beam is confirmed by field emission microscope investigations. An angular confinement of ±7.2° is obtained. Supertips deliver an emission of 0.2 mA/sr as measured, and have therefore at least a tenfold higher angular emission density than conventionally etched tips. Deposited supertips require no single crystalline base and can be placed on any base material. They successfully operate in a scanning tunneling microscope in air.

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