Grafting of aryl layers derived from aryl diazonium salts onto glassy carbon electrodes can be observed by time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The grafting occurs spontaneously when a glassy carbon plate is immersed into a solution of aryl diazonium salt and can be enhanced by biasing the carbon plate at a potential a little more negative than the diazonium salt reduction.