What did you use to write in the trench?

Question: What did you use to write in the trench?
- Keywords:
  trench,
  write
Asked by The Cheetah to Jarrod on 13 Jun 2016.
- Jarrod Hart answered on 13 Jun 2016:
  
  A focussed beam of gallium ions!
  
  I did this at the University of Bristol, where they have clever scientists who spend their days shoots ray guns at stuff and seeing what happens – for science of course!!
  
  http://www.bristol.ac.uk/physics/research/iac/

Question: What did you use to write in the trench?