It is always helpful to do a little Google search. If you search for Google Scholar for 'nano onions synthesis' you can find as the first hit the paper:

Nanotechnology: Synthesis of carbon 'onions' in water

Nature 414(6863):506-507 · November 2001

DOI: 10.1038/35107141

Abstract

The fabrication of carbon nanomaterials usually calls for expensive vacuum systems to generate plasmas and yields are disappointingly low. Here we describe a simple method for producing high-quality spherical carbon nano-'onions' in large quantities without the use of vacuum equipment. The nanoparticles, which have C60 cores surrounded by onion-like nested particles, are generated by an arc discharge between two graphite electrodes submerged in water. This technique is economical and environmentally benign, and produces uncontaminated nanoparticles which may be useful in many applications.

This should be simple enough: water and no vacuum.

thanks dear Fernando

my mean was the best and easiest way