3 research outputs found
Control over Memory Performance of Layer-by-Layer Assembled Metal Phthalocyanine Multilayers via Molecular-Level Manipulation
We herein report on the nonvolatile memory properties
of iron phthalocyanine
multilayers prepared using an electrostatic layer-by-layer assembly
method. Cationic polyÂ(allylamine hydrochloride) (PAH) and anionic
ironÂ(III) phthalocyanine-4, 4,′ 4″, 4′″-tetrasulfonic
acid (Fe-TsPc) were alternately deposited onto quartz glass, indium
tin oxide (ITO), or platinum-coated silicon substrates via electrostatic
interactions. The electrochemical response of the PAH/Fe-TsPc, which
was obtained from cyclic voltammograms (CV) in solution, indicated
that redox reactions occurred at the phthalocyanine unit and at the
metallic center. It was found that these redox reactions of the PAH/Fe-TsPc
multilayer films in solution could be extended to resistive switching
nonvolatile memory based on a charge trap/release mechanism in air.
The PAH/Fe-TsPc multilayers sandwiched between the bottom (platinum)
and top (Ag or tungsten) electrodes exhibited the characteristics
of a resistive switching memory at a relatively low operating voltage
of less than 2 V, with a switching speed of about 100 ns and an ON/OFF
current ratio of ∼10<sup>3</sup>. Additionally, it is confirmed
using kelvin probe force microscopy (KPFM) that the reversible resistance
changes in the PAH/Fe-TsPc multilayers are mainly caused by the externally
applied voltage as a result of the trapping and release of charges
at redox sites within the Fe-TsPc. Furthermore, in the case where
insulating layers of about 2 nm in thickness are inserted between
adjacent Fe-TsPc layers, it is demonstrated that these devices can
exhibit further improvements in memory performance (ON/OFF current
ratio of ∼10<sup>6</sup>) and a lower power consumption in
comparison with PAH/Fe-TsPc multilayers
Electrically Bistable Properties of Layer-by-Layer Assembled Multilayers Based on Protein Nanoparticles
Electrochemical properties of redox proteins, which can cause the reversible changes in the resistance according to their redox reactions in solution, are of the fundamental and practical importance in bioelectrochemical applications. These redox properties often depend on the chemical activity of transition metal ions as cofactors within the active sites of proteins. Here, we demonstrate for the first time that the reversible resistance changes in dried protein films based on ferritin nanoparticles can be caused by the externally applied voltage as a result of charge trap/release of Fe<sup>III</sup>/Fe<sup>II</sup> redox couples. We also show that one ferritin nanoparticle of about 12 nm size can be operated as a nanoscale-memory device, and furthermore the layer-by-layer assembled protein multilayer devices can be extended to bioinspired electronics with adjustable memory performance <i>via</i> molecular level manipulation
Hydrophobic Nanoparticle-Based Nanocomposite Films Using <i>In Situ</i> Ligand Exchange Layer-by-Layer Assembly and Their Nonvolatile Memory Applications
A robust method for preparing nanocomposite multilayers was developed to facilitate the assembly of well-defined hydrophobic nanoparticles (<i>i.e.</i>, metal and transition metal oxide NPs) with a wide range of functionalities. The resulting multilayers were stable in both organic and aqueous media and were characterized by a high NP packing density. For example, inorganic NPs (including Ag, Au, Pd, Fe<sub>3</sub>O<sub>4</sub>, MnO<sub>2</sub>, BaTiO<sub>3</sub>) dispersed in organic media were shown to undergo layer-by-layer assembly with amine-functionalized polymers to form nanocomposite multilayers while incurring minimal physical and chemical degradation of the inorganic NPs. In addition, the nanocomposite multilayer films formed onto flat and colloidal substrates could directly induce the adsorption of the electrostatically charged layers without the need for additional surface treatments. This approach is applicable to the preparation of electronic film devices, such as nonvolatile memory devices requiring a high memory performance (ON/OFF current ratio >10<sup>3</sup> and good memory stability)