title: Long-range transport in an assembly of ZnO quantum dots: the effects of quantum confinement, Coulomb repulsion and structural disorder.
abstract: We have studied the storage and long-range transport of electrons in a porous assembly of weakly coupled ZnO quantum dots permeated with an aqueous and a propylene carbonate electrolyte solution. The number of electrons per ZnO quantum dot is controlled by the electrochemical potential of the assembly; the charge of the electrons is compensated by ions present in the pores. We show with optical and electrical measurements that the injected electrons occupy the S, P, and D type conduction electron levels of the quantum dots; electron storage in surface states is not important. With this method of three-dimensional charge compensation, up to ten electrons per quantum-dot can be stored if the assembly is permeated with an aqueous electrolyte. The screening of the electron charge is less effective in the case of an assembly permeated with a propylene carbonate electrolyte solution. Long-range electron transport is studied with a transistor set-up. In the case of ZnO assemblies permeated with an aqueous electrolyte, two quantum regimes are observed corresponding to multiple tunnelling between the S orbitals (at a low occupation) and P orbitals (at a higher occupation). In a ZnO quantum-dot assembly permeated with a propylene carbonate electrolyte solution, there is a strong overlap between these two regimes.
authors.affiliation: Debye Institute, Utrecht University, P.O. Box 80 000, 3508 TA Utrecht, The Netherlands.
authors.forename: Aarnoud L
authors.initials: AL
authors.lastname: Roest
authors.forename: Alexander
authors.initials: A
authors.lastname: Germeau
authors.forename: John J
authors.initials: JJ
authors.lastname: Kelly
authors.forename: Daniël
authors.initials: D
authors.lastname: Vanmaekelbergh
authors.forename: Guy
authors.initials: G
authors.lastname: Allan
authors.forename: Eric A
authors.initials: EA
authors.lastname: Meulenkamp