The application of carbon nanotube electron sources to the electron microscope

The promising field emission properties of carbon nanotubes, or CNTs, have resulted in them being identified as desirable sources for electron microscopes and other electron beam equipment. A new process to grow single CNTs aligned to the electron-optical axis inside electron source modules has been developed. The process involves putting the entire source-suppressor module inside a plasma-enhanced chemical vapour deposition reaction chamber. This is a process which can be scaled up to mass production. The resultant CNT electron sources were inserted into an electron microscope for imaging. Though current stability was found to be comparable to the tungsten cold-field emitter (with a maximum-minimum variation of 3-7% of the mean current over one hour), the reduced brightness was found to be an order of magnitude greater than a typical Schottky source (at 3 x 10(9) Acm(2)sr(-1)) with a kinetic energy spread of 0.28 eV. Imaging with a CNT source has produced a marked improvement in resolution when compared to a Schottky source using the same electron-optics. The properties measured show that the CNT source compares favourably with and in some cases improves upon other sources available today. In particular, the CNT source would be of most benefit to low-voltage, high-resolution microscopy.