A recently developed experimental method of producing quantum dots covered with a carbon layer has been applied to Pt clusters to make carbon-coated materials. Pt clusters with the size of 1-5 nm embedded in carbon quantum balls with the size of 10 nm order have been produced by the advanced gas evaporation method in He gas at 10 kPa. The carbon layer covering Pt clusters was similar to 3 nm in thickness. The stability and usefulness of electron emission as functional materials have been discussed with respect to the electron beam irradiation effect and contact potentials between the metallic cluster and carbon layer. (C) 2004 Elsevier B.V. All rights reserved.