title: Low-Dimensional Polyoxometalate Molecules/Tantalum Oxide Hybrids for Non-Volatile Capacitive Memories.
abstract: Transition-metal-oxide hybrids composed of high surface-to-volume ratio Ta2O5 matrices and a molecular analogue of transition metal oxides, tungsten polyoxometalates ([PW12O40](3-)), are introduced herein as a charge storage medium in molecular nonvolatile capacitive memory cells. The polyoxometalate molecules are electrostatically self-assembled on a low-dimensional Ta2O5 matrix, functionalized with an aminosilane molecule with primary amines as the anchoring moiety. The charge trapping sites are located onto the metal framework of the electron-accepting molecular entities as well as on the molecule/oxide interfaces which can immobilize negatively charged mobile oxygen vacancies. The memory characteristics of this novel nanocomposite were tested using no blocking oxide for extraction of structure-specific characteristics. The film was formed on top of the 3.1 nm-thick SiO2/n-Si(001) substrates and has been found to serve as both SiO2/Si interface states' reducer (i.e., quality enhancer) and electron storage medium. The device with the polyoxometalates sandwiched between two Ta2O5 films results in enhanced internal scattering of carriers. Thanks to this, it exhibits a significantly larger memory window than the one containing the plain hybrid and comparable retention time, resulting in a memory window of 4.0 V for the write state and a retention time around 10(4) s without blocking medium. Differential distance of molecular trapping centers from the cell's gate and electronic coupling to the space charge region of the underlying Si substrate were identified as critical parameters for enhanced electron trapping for the first time in such devices. Implementing a numerical electrostatic model incorporating structural and electronic characteristics of the molecular nodes derived from scanning probe and spectroscopic characterization, we are able to interpret the hybrid's electrical response and gain some insight into the electrostatics of the trapping medium.
authors.affiliation: Institute of Nanoscience and Nanotechnology, NCSR Demokritos , Aghia Paraskevi, Athens 153 10, Greece.|Department of Chemical Sciences, School of Chemical Engineering, National Technical University of Athens , Iroon Polytexneiou 9, Athens 157 80, Greece.
authors.forename: Angelika
authors.initials: A
authors.lastname: Balliou
authors.affiliation: Institute of Nanoscience and Nanotechnology, NCSR Demokritos , Aghia Paraskevi, Athens 153 10, Greece.
authors.forename: Giorgos
authors.initials: G
authors.lastname: Papadimitropoulos
authors.affiliation: Department of Chemical Engineering, University of Patras , University Campus, Patras 26504, Greece.
authors.forename: George
authors.initials: G
authors.lastname: Skoulatakis
authors.affiliation: Department of Chemical Engineering, University of Patras , University Campus, Patras 26504, Greece.
authors.forename: Stella
authors.initials: S
authors.lastname: Kennou
authors.affiliation: Institute of Nanoscience and Nanotechnology, NCSR Demokritos , Aghia Paraskevi, Athens 153 10, Greece.
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Davazoglou
authors.affiliation: Department of Solid State Physics, National and Kapodistrian University of Athens , University Campus, Zografos, Athens 157 84, Greece.
authors.forename: Spiros
authors.initials: S
authors.lastname: Gardelis
authors.affiliation: Institute of Nanoscience and Nanotechnology, NCSR Demokritos , Aghia Paraskevi, Athens 153 10, Greece.
authors.forename: Nikos
authors.initials: N
authors.lastname: Glezos
keywords: CMOS-compatible technology; electron trapping; interface engineering; molecular capacitive memories; self-assembled molecular layers; transition metal oxide/molecular hybrids