Recently, tetramantane, a member of diamondoid series (C4n+6H4n+12), has shown to exhibit negative-electron-affinity effect which has a potential use for efficient electron emitting devices. Here, we explore the electronic property of adamantane (C10H16), the smallest member of the series. We prepare adamantane films on Si(1 1 1) substrates and then study their electronic structure with photoemission spectroscopy. Photoelectron spectra of adamantane on Si(1 1 1) have shown a peak at low-kinetic energy which could be a generic property of diamondoids. The possibility of the negative-electron-affinity effect in adamantane is further discussed. (C) 2009 Elsevier B.V. All rights reserved.