# Fabrication and structural characterization of diamond-coated tungsten tips

## TL;DR

This paper presents a method for fabricating and characterizing diamond-coated tungsten tips, achieving nanometer-thin, dense nanocrystalline diamond coatings with controlled growth at the apex for potential photocathode applications.

## Contribution

It introduces a novel fabrication recipe for uniformly coating tungsten tips with nanocrystalline diamond using plasma-enhanced chemical vapor deposition and seed migration control.

## Key findings

- Achieved nanometer-thin diamond coatings within 1 μm of the apex.
- Confirmed dense nanocrystalline structure with 20 nm grains.
- Controlled diamond growth at the apex via nitrogen gas flow.

## Abstract

Coating metal nanotips with a negative electron affinity material like hydrogen-terminated diamond bears promise for a high brightness photocathode. We report a recipe on the fabrication of diamond coated tungsten tips. A tungsten wire is etched electrochemically to a nanometer sharp tip, dip-seeded in diamond suspension and subsequently overgrown with a diamond film by plasma-enhanced chemical vapor deposition. With dip-seeding only, the seeding density declines towards the tip apex due to seed migration during solvent evaporation. The migration of seeds can be counteracted by nitrogen gas flow towards the apex, which makes coating of the apex with nanometer-thin diamond possible. At moderate gas flow, diamond grows homogeneously at shaft and apex whereas at high flow diamond grows in the apex region only. With this technique, we achieve a thickness of a few tens of nanometers of diamond coating within less than 1 $\mu$m away from the apex. Conventional transmission electron microscopy (TEM), electron diffraction and electron energy loss spectroscopy confirm that the coating is composed of dense nanocrystalline diamond with a typical grain size of 20 nm. High resolution TEM reveals graphitic paths between the diamond grains.