We investigated the effect of small-molecule electron-transport (Alq(3)) and hole-transport (alpha-NPD) bilayers on the nonvolatile memory characteristics of small-molecule memory cells embedded with Ni nanocrystals. With increasing thickness of the hole-transport layer, the on-state current (I(on)) and memory margin (I(on)/I(off) ratio) decreased, the retention time decreased, and the standard deviation of I(on) and I(off) during erase-and-program cycles increased. These results indicate that the N,N'-bis (1-naphthalene)-1,1'biphenyl4,4 '' diamine layer in small-molecule-bilayer memory cells behaves as an electron-transport layer rather a hole-transport layer and that the dominant carriers in those memory cells are electrons rather than holes. (C) 2009 Elsevier B.V. All rights reserved.