Exoelectron emission from unexcited metallic glasses Fe40Ni38Mo4B18 during heat treatment

Abstract

In order to elucidate a mechanism for exoelectron emission from metallic glasses during heat treatment, metallic glasses Fe40Ni38Mo4B18, which have a 140 K lower crystallization temperature than the metallic glasses Fe78B13Si9 reported previously, were heated up to 723 K with a constant heating rate of 0.5 K/s under ultrahigh vacuum condition. Although specimens were not excited by ionizing radiations, mechanical treatment, or chemical processes prior to measurements, exoelectrons have been detected for the first heating cycle. However, in the subsequent heating cycles, the counting rate does not exceed the background level. These results agree well with our previous report about metallic glasses Fe78B13Si9, but it is recently found that from the present glasses exoelectrons are emitted from the lower temperature region, and the total number of emitted exoelectrons is larger than that from the previous glasses. An atomic force microscopy (AFM) study reveals many crystallites formed on the surface of the heated specimen, and the spatial density of crystallites on the surface is much higher than that of previous glasses. Both results of exoelectron measurements and AFM observations show that the number of emitted exoelectrons increases with increasing the number of crystallites on the surface. This result implies that exoelectrons are emitted associated with the crystallites formation process on the surface.