Insights from Adsorption and Electron Modification Studies of Polyoxometalates on Surfaces for Molecular Memory Applications

Abstract

Metrics & More Article RecommendationsCONSPECTUS: This Account highlights recent experimental and theoretical work focusing on the development of polyoxometalates (POMs) as possible active switching units in what may be called "molecule-based memory cells". Herein, we critically discuss how multiply charged vanadium-containing POMs, which exhibit stable metal−oxo bonds and are characterized by the excellent ability to change their redox states without significant structural distortions of the central polyoxoanion core, can be immobilized best and how they may work optimally at appropriate surfaces. Furthermore, we critically discuss important issues and challenges on the long way toward POM-based nanoelectronics. This Account is divided into four sections shedding light on POM interplay in solution and on surfaces, ion soft-landing of mass-selected POMs on surfaces, electronic modification of POMs on surfaces, and computational modeling of POMs on surfaces. The sections showcase the complex nature of far-reaching POM interactions with the chemical surroundings in solution and the properties of POMs in the macroscopic environment of electrode surfaces. Section 2 describes complex relationships of POMs with their counter-cations, solvent molecules, and water impurities, which have been shown to exhibit a direct impact on the resulting surface morphology, where a concentration-dependent formation of micellar structures can be potentially observed. Section 3 gives insights into the ion softlanding deposition of mass-selected POMs on electrode surfaces, which emerges as an appealing method because the simultaneous deposition of agglomeration-stimulating counter-cations can be avoided. Section 4 provides details of electronic properties of POMs and their modification by external electronic stimuli toward the development of multiple-state resistive (memristive) switches. Section 5 sheds light on issues of the determination of the electronic structure properties of POMs across their interfaces, which is difficult to address by experiment. The studies summarized in these four sections have employed various X-ray-scattering, microscopy, spectroscopy, and computational techniques for imaging of POM interfaces in solution and on surfaces to determine the adsorption type, agglomeration tendency, distribution, and oxidation state of deposited molecules. The presented research findings and conceptual ideas may assist experimentalists and theoreticians to advance the exploration of POM electrical conductivity as a function of metal redox and spin states and to pave the way for a realization of ("brain-inspired") POM-based memory devices, memristive POM-surface device engineering, and energy efficient nonvolatile data storage and processing technologies.

Exploring the Ligand Functionality, Electronic Band Gaps, and Switching Characteristics of Single Wells–Dawson‐Type Polyoxometalates on Gold

“…[10,14,15] In common ReRAM cells often thin films of redoxactive transition metal oxides with extended solid-state structures are exploited as active switching layers, [16] and in principle, they can be scaled down to the low nanometer level. [6] The combination of ReRAMs with stimuli-responsive molecular compounds such as negatively charged metal-oxo clusters (polyoxometalates, POMs) [17,18] can have direct impact on the development of beyond-CMOS technology. Especially, archetypal POMs as building blocks, [19] capable of versatile functionalization and derivatization by organic ligands, [20,21] have emerged as excellent candidates to enable POM-based electronics [22][23][24] due to highly efficient immobilization on surfaces, [25,26] which is however limited to the molecular deposition from solution.…”

“…The combination of ReRAMs with stimuli‐responsive molecular compounds such as negatively charged metal–oxo clusters (polyoxometalates, POMs) [ 17,18 ] can have direct impact on the development of beyond‐CMOS technology. Especially, archetypal POMs as building blocks, [ 19 ] capable of versatile functionalization and derivatization by organic ligands, [ 20,21 ] have emerged as excellent candidates to enable POM‐based electronics [ 22–24 ] due to highly efficient immobilization on surfaces, [ 25,26 ] which is however limited to the molecular deposition from solution.…”

Metalloxidische Materialien

“…Durch die gezielte Verknüpfung von mehreren Speicherzuständen können dabei einfache Rechenprozesse direkt im Speichermedium ablaufen, so wie es auch in neuronalen Netzwerken der Fall ist. Die Entwicklung solcher molekularen Speicher sowie deren kontrollierte Adsorption auf verschiedenen Oberflächen werden unter anderem am Leipziger Leibniz-Institut für Oberflächenmodifizierung (IOM) erforscht [23]. Der ionische Charakter dieser Spezies stellt dabei eine besondere Herausforderung dar, da das Wechselwirkungsverhalten mit den Gegenkationen, dem Lösungsmittel und der Oberfläche mitunter sehr komplex sein kann [24].…”

New phosphotetradecavanadate hybrids: crystal structure, DFT analysis, stability and binding interactions with bio-macromolecules

“…[17][18][19][20][21][22][23][24][25] The size, structure and modifiable load densities of POMs often yield unexpected and interesting behaviours, allowing them to display different physical and chemical properties compared to traditional metal oxides. 26,27 Polyoxidovanadates (POVs) are a relevant subfamily of POMs. The diverse coordination geometries and cluster sizes observed in such vanadium oxide polyhedral shapes and the different oxidation states that vanadium centres can adopt give rise to a great variety of distinct architectures 28 that have attracted increasing attention.…”

“…17–25 The size, structure and modifiable load densities of POMs often yield unexpected and interesting behaviours, allowing them to display different physical and chemical properties compared to traditional metal oxides. 26,27…”