Few-molecule reservoir computing experimentally demonstrated with surface enhanced Raman scattering and ion-gating stimulation

Reservoir computing (RC) is a promising solution for achieving low power consumption neuromorphic computing, although the large volume of the physical reservoirs reported to date has been a serious drawback in their practical application. Here, we report the development of a few-molecule RC that employs the molecular vibration dynamics in the para-mercaptobenzoic acid (pMBA) detected by surface enhanced Raman scattering (SERS) with tungsten oxide nanorod/silver nanoparticles (WOx@Ag-NPs). The Raman signals of the pMBA molecules, adsorbed at the SERS active site of WOx@Ag-NPs, were reversibly perturbated by the application of voltage-induced local pH changes in the vicinity of the molecules, and then used to perform RC of pattern recognition and prediction tasks. In spite of the small number of molecules employed, our system achieved good performance, including 95.1% to 97.7% accuracy in various nonlinear waveform transformations and 94.3% accuracy in solving a second-order nonlinear dynamic equation task. Our work provides a new concept of molecular computing with practical computation capabilities.Comment: 22 pages, 4 figure

Improved electrical conductance through self-assembly of bioinspired peptides into nanoscale fibers

We investigated the electrical conductance of films consisting of bio-inspired peptide molecules and of their extended form, self-assembled nanoscale fibers. Here, the entirely natural and novel peptide sequence, GFPRFAGFP, was designed based on naturally occurring fibrous proteins. To attain electrical conductance, we implemented phenylalanine residues in the sequence such that the aromatic rings are present along face of the molecule. We confirmed self-assembly of nanoscale fibers in pure water after incubating the peptides at 37 °C by AFM. The morphology and conformation of the incubated peptide fibers were studied using AFM, fluorescence spectroscopy and circular dichroism spectroscopy. It was shown that very thin fibers with a single-molecule-level diameter form. The helical feature of the peptide backbone and enhanced stacking of aromatic residues were also investigated. This aromatic stacking is important to our electrical measurements as, even in vacuum environment, films of non-incubated GFPRFAGFP sometimes show apparent conductance while those containing self-assembled nanoscale fibers show stable and improved conductance. We propose that this effect may be due to extended stacking of aromatic residues providing π - π conjugation along the fiber

Dual‐Gate Anti‐Ambipolar Transistor with Van der Waals ReS2/WSe2 Heterojunction for Reconfigurable Logic Operations

Abstract A dual‐gate anti‐ambipolar transistor (AAT) with a two‐dimensional ReS2 and WSe2 heterojunction is developed. The characteristic Λ‐shaped transfer curves yielded by the bottom‐gate voltage are effectively controlled by the top‐gate voltage. This feature is applied to logic operations, with the bottom‐ and top‐gate voltages acting as two input signals and the drain current (Id) monitored as an output signal. Importantly, a single dual‐gate AAT exhibits all the two‐input logic operations (AND, OR, XOR, NAND, NOR, and XNOR) under optimized input voltages. Additionally, drain voltage (Vd)‐induced switching between AND and OR logic operations is achieved. These features are advantageous for simplifying circuit design

Emergent dynamics of neuromorphic nanowire networks.

Neuromorphic networks are formed by random self-assembly of silver nanowires. Silver nanowires are coated with a polymer layer after synthesis in which junctions between two nanowires act as resistive switches, often compared with neurosynapses. We analyze the role of single junction switching in the dynamical properties of the neuromorphic network. Network transitions to a high-conductance state under the application of a voltage bias higher than a threshold value. The stability and permanence of this state is studied by shifting the voltage bias in order to activate or deactivate the network. A model of the electrical network with atomic switches reproduces the relation between individual nanowire junctions switching events with current pathway formation or destruction. This relation is further manifested in changes in 1/f power-law scaling of the spectral distribution of current. The current fluctuations involved in this scaling shift are considered to arise from an essential equilibrium between formation, stochastic-mediated breakdown of individual nanowire-nanowire junctions and the onset of different current pathways that optimize power dissipation. This emergent dynamics shown by polymer-coated Ag nanowire networks places this system in the class of optimal transport networks, from which new fundamental parallels with neural dynamics and natural computing problem-solving can be drawn

Metallic versus Semiconducting SWCNT Chemiresistors: A Case for Separated SWCNTs Wrapped by a Metallosupramolecular Polymer

As-synthesized single-walled carbon nanotubes (SWCNTs) are a mixture of metallic and semiconducting tubes, and separation is essential to improve the performances of SWCNT-based electric devices. Our chemical sensor monitors the conductivity of an SWCNT network, wherein each tube is wrapped by an insulating metallosupramolecular polymer (MSP). Vapors of strong electrophiles such as diethyl chlorophosphate (DECP), a nerve agent simulant, can trigger the disassembly of MSPs, resulting in conductive SWCNT pathways. Herein, we report that separated SWCNTs have a large impact on the sensitivity and selectivity of chemical sensors. Semiconducting SWCNT (S-SWCNT) sensors are the most sensitive to DECP (up to 10000% increase in conductivity). By contrast, the responses of metallic SWCNT (M-SWCNT) sensors were smaller but less susceptible to interfering signals. For saturated water vapor, increasing and decreasing conductivities were observed for S- and M-SWCNT sensors, respectively. Mixtures of M- and S-SWCNTs revealed reduced responses to saturated water vapor as a result of canceling effects. Our results reveal that S- and M-SWCNTs compensate sensitivity and selectivity, and the combined use of separated SWCNTs, either in arrays or in single sensors, offers advantages in sensing systems