Thermal Evolution of Compound Nanoparticles on Moulds Machined by Focused-Ion-Beam for Micro/Nano Lithography

Abstract

Focused-ion-beam (FIB) milling is a modern fabrication technique by using focused energetic ions to ablate material and generate features with nanometer resolution. FIB system with Ga ion source was used in our lab to make moulds for laser-based micro/nano lithography. For FIB milling on glassy carbon, particles in the range of tens of nanometers up to 400 nm can often be found around the area subject to milling, with the composition of carbon and gallium. As the laser-based micro/nano lithography involves thermal process, it is important to identify the dynamic process of those compound nanoparticles during heat treatment. Glassy carbon moulds after FIB milling have been heated in air from room temperature up to 550 oC with temperature ramp rate of 10 oC/min. Scanning Electron Microscope (SEM) was used to record the morphology of the machined surface after heat treatments. Energy dispersive X-ray spectroscopy (EDS) was used for elemental analysis. Particles increase their size before the heating temperature reaches 200 oC. With further temperature increase, new particles nucleate, and grow at the neighbouring of the existing particles via coalescence and Ostwald ripening. When the temperature is over 400 oC, the morphology of nanoparticles changes, due to the evaporation of gallium. When the in air heating reaches 525 oC, cracking starts on the surface of glassy carbon. It is suggested that for in air lithographic application, heating temperature should not exceed 500 oC.