Molecular Memory Cells Research Articles

Site-Selective Photoswitching of Two Distinct Magnetic Chromophores in a Propeller-Like Molecule To Achieve Four Different Magnetic States

Magnetic photoswitching is a highly important but relatively rare phenomenon for enabling optical writing/reading of the magnetic state of a molecule. In this work, an unprecedented site-selective double photoswitching is reported from the assembly of two different "photomagnetic chromophores" into a single hexanuclear molecule: namely, a spin-crossover Fe(II) center exhibiting light-induced excited spin state trapping (LIESST) and a photochemically active octacyanometalate(IV) unit. Four different magnetization levels are accessible through the appropriate combination of violet/red light and temperature, results that highlight the potential of photomagnetic molecules as future molecular memory cells.

Silicon-Immobilized Ferrocenyl Monolayers for All-Solid Molecular Charge Storage and Logic

The functionalization of technologically relevant conducting surfaces, such as oxide-free, hydrogen-terminated silicon (H-Si), with high-quality ferrocene (Fc) [1] and metal-complexed porphyrin [2] -terminated monolayers has been demonstrated to be a powerful bottom-up approach for the fabrication of electrically addressable charge-storage devices with low-power consumption.Compared with metalloporphyrins, Fc is a much smaller molecule (average diameter of tetraphenylporphyrin and Fc are about 18 and 6.6 Å, respectively), and consequently is immobilized on silicon with a higher surface coverage, which gives rise to higher charge densities. Indeed, the surface coverages reached for high-quality ferrocenyl monolayers are in the range of (2.0–5.0) ×10-10 mol cm-2. This does not only allow for an extremely fast electron communication between the electroactive groups [3], but also yields charge densities in the range of 20–50 mC cm-2. These values are thus much higher than those measured for Si/SiO2 capacitors currently used in Dynamic Random Access Memories (5–10 mC cm-2).Very recently, we also demonstrated that tailor-made micrometer-sized patterns of such redox-active monolayers could behave as light-activated molecular memory cells operating at low voltages with unprecedented capacitance performances [4]. The characteristics of this stimuli-responsive device are of great scientific interest for data-processing applications, such as redox-based Boolean logic gates [5]. In our system, the switching of the capacitance upon light irradiation that is observed only at a certain electrical potential constitutes the principle of all-solid two-input AND logic gate without the need of chemical inputs in solution. Such performances can be ascribed to the judicious combination between a photoswitchable conducting/insulating silicon substrate and high-quality microstamped redox-active assemblies.[1] Fabre, B. Acc. Chem. Res. 2010, 43, 1509–1518.[2] Lindsey, J. S.; Bocian, D. F. Acc. Chem. Res. 2011, 44, 638–650.[3] a) Hauquier, F.; Ghilane, J.; Fabre, B.; Hapiot, P. J. Am. Chem. Soc. 2008, 130, 2748–2749. b) Zigah, D.; Herrier, C.; Scheres, L.; Giesbers, M.; Fabre, B.; Hapiot, P.; Zuilhof, H. Angew. Chem. Int. Ed. 2010, 49, 3157–3160.[4] Fabre, B.; Li, Y.; Scheres, L.; Pujari, S. P.; Zuilhof, H. Angew. Chem. Int. Ed. 2013, 52, 12024-12027.[5] de Ruiter, G.; van der Boom, M. E. Acc. Chem. Res. 2011, 44, 563–573.

A room-temperature non-volatile CNT-based molecular memory cell

Recent experiments with a carbon nanotube (CNT) system confirmed that the innertube can oscillate back-and-forth even under a room-temperature excitation. This demonstration of relative motion suggests that it is now feasible to build a CNT-based molecular memory cell (MC), and the key to bring the concept to reality is the precision control of the moving tube for sustained and reliable read/write (RW) operations. Here, we show that by using a 2-section outertube design, we are able to suitably recalibrate the system energetics and obtain the designed performance characteristics of a MC. Further, the resulting energy modification enables the MC to operate as a non-volatile memory element at room temperatures. Our paper explores a fundamental understanding of a MC and its response at the molecular level to roadmap a novel approach in memory technologies that can be harnessed to overcome the miniaturization limit and memory volatility in memory technologies.

Impedance Spectroscopy of a Molecular Memory Cell with a Redox-Active Component

We report the frequency dependent impedance spectroscopy of an Al/Al2O3/ASA-15 monolayer/Ti/Al molecular memory cell. As a result of comparing the memory cell with a control device that does not contain ASA-15 molecules, we confirmed that its impedance properties were originated from the ASA-15 monolayer. By examining the Cole-Cole plot for the fabricated memory cell, we also found that the response of the memory cell can be explained in terms of an equivalent circuit model with a contact resistance R(s) in series with an impedance Z(ox) at the Al oxide layer and an impedance Z(LB) at the ASA-15 monolayer.

Molecular wires, switches, and memories.

Design and measurements of molecular wires, switches, and memories offer an increased device capability with reduced elements. We report: Measurements on through-bond electronic transport properties of nanoscale metal-1,4-phenylene diisocyanide-metal junctions are reported, where nonohmic thermionic emission is the dominant process, with isocyanide-Pd showing the lowest thermionic barrier of 0.22 eV; robust and large reversible switching behavior in an electronic device that utilizes molecules containing redox centers as the active component, exhibiting negative differential resistance (NDR) and large on-off peak-to-valley ratio (PVR) are realized; erasable storage of higher conductivity states in these redox-center-containing molecular devices are observed; and a two-terminal electronically programmable and erasable molecular memory cell with long bit retention time is demonstrated.

Molecular analogue memory cell based on electrical switching and memory in molecular thin films

The structure of a molecular memory cell with its work based on the phenomenon of structural instability of one-dimensional conductive molecular systems is offered. Electrophysical parameters of the molecular analogue memory cell were investigated. It was established that a memory cell has an S-shaped voltage–current characteristic with memory. Any impedance of the memory cell can be obtained in the interval between ∼10MΩ and ∼100Ω depending on the switching condition. A conclusion is drawn that the design of memory chips based on the molecular analogue memory cell is promising.