Biorealistic Neuronal Temperature-Sensitive Dynamics within Threshold Switching Memristors: Toward Neuromorphic Thermosensation.

Neuromorphic nanoelectronic devices that can emulate the temperature-sensitive dynamics of biological neurons are of great interest for bioinspired robotics and advanced applications such as in silico neuroscience. In this work, we demonstrate the biomimetic thermosensitive properties of two-terminal V3O5 memristive devices and showcase their similarity to the firing characteristics of thermosensitive biological neurons. The temperature-dependent electrical characteristics of V3O5-based memristors are used to understand the spiking response of a simple relaxation oscillator. The temperature-dependent dynamics of these oscillators are then compared with those of biological neurons through numerical simulations of a conductance-based neuron model, the Morris-Lecar neuron model. Finally, we demonstrate a robust neuromorphic thermosensation system inspired by biological thermoreceptors for bioinspired thermal perception and representation. These results not only demonstrate the biorealistic emulative potential of threshold-switching memristors but also establish V3O5 as a functional material for realizing solid-state neurons for neuromorphic computing and sensing applications.

Optically Tunable Electrical Oscillations in Oxide-Based Memristors for Neuromorphic Computing.

The application of hardware-based neural networks can be enhanced by integrating sensory neurons and synapses that enable direct input from external stimuli. This work reports direct optical control of an oscillatory neuron based on volatile threshold switching in V3O5. The devices exhibit electroforming-free operation with switching parameters that can be tuned by optical illumination. Using temperature-dependent electrical measurements, conductive atomic force microscopy (C-AFM), in situ thermal imaging, and lumped element modelling, it is shown that the changes in switching parameters, including threshold and hold voltages, arise from overall conductivity increase of the oxide film due to the contribution of both photoconductive and bolometric characteristics of V3O5, which eventually affects the oscillation dynamics. Furthermore, V3O5 is identified as a new bolometric material with a temperature coefficient of resistance (TCR) as high as -4.6% K-1 at 423 K. The utility of these devices is illustrated by demonstrating in-sensor reservoir computing with reduced computational effort and an optical encoding layer for spiking neural network (SNN), respectively, using a simulated array of devices.

Physical Origin of Negative Differential Resistance in V3 O5 and Its Application as a Solid-State Oscillator.

Oxides that exhibit an insulator-metal transition can be used to fabricate energy-efficient relaxation oscillators for use in hardware-based neural networks but there are very few oxides with transition temperatures above room temperature. Here the structural, electrical, and thermal properties of V3 O5 thin films and their application as the functional oxide in metal/oxide/metal relaxation oscillators are reported. The V3 O5 devices show electroforming-free volatile threshold switching and negative differential resistance (NDR) with stable (<3% variation) cycle-to-cycle operation. The physical mechanisms underpinning these characteristics are investigated using a combination of electrical measurements, in situ thermal imaging, and device modeling. This shows that conduction is confined to a narrow filamentary path due to self-confinement of the current distribution and that the NDR response is initiated at temperatures well below the insulator-metal transition temperature where it is dominated by the temperature-dependent conductivity of the insulating phase. Finally, the dynamics of individual and coupled V3 O5 -based relaxation oscillators is reported, showing that capacitively coupled devices exhibit rich non-linear dynamics, including frequency and phase synchronization. These results establish V3 O5 as a new functional material for volatile threshold switching and advance the development of robust solid-state neurons for neuromorphic computing.

Large non-thermal contribution to picosecond strain pulse generation using the photo-induced phase transition in VO2.

Picosecond strain pulses are a versatile tool for investigation of mechanical properties of meso- and nano-scale objects with high temporal and spatial resolutions. Generation of such pulses is traditionally realized via ultrafast laser excitation of a light-to-strain transducer involving thermoelastic, deformation potential, or inverse piezoelectric effects. These approaches unavoidably lead to heat dissipation and a temperature rise, which can modify delicate specimens, like biological tissues, and ultimately destroy the transducer itself limiting the amplitude of generated picosecond strain. Here we propose a non-thermal mechanism for generating picosecond strain pulses via ultrafast photo-induced first-order phase transitions (PIPTs). We perform experiments on vanadium dioxide VO2 films, which exhibit a first-order PIPT accompanied by a lattice change. We demonstrate that during femtosecond optical excitation of VO2 the PIPT alone contributes to ultrafast expansion of this material as large as 0.45%, which is not accompanied by heat dissipation, and, for excitation density of 8 mJ cm-2, exceeds the contribution from thermoelastic effect by a factor of five.

Photoinduced surface plasmon switching at VO2/Au interface.

Angle-resolved reflection, light scattering and ultrafast pump-probe spectroscopy combined with a surface plasmon-polariton (SPP) resonance technique in attenuated total reflection geometry was used to investigate the light-induced plasmonic switching in a photorefractive VO2/Au hybrid structure. Measurements of SPP scattering and reflection shows that the optically-induced formation of metallic state in a vanadium dioxide layer deposited on a gold film significantly alters the electromagnetic field enhancement and SPP propagation length at the VO2/Au interface. The ultrafast optical manipulation of SPP resonance is shown on a picosecond timescale. Obtained results demonstrate high potential of photorefractive vanadium oxides as efficient plasmonic modulating materials for ultrafast optoelectronic devices.

Ultrafast Excited-State Dynamics of V_{3}O_{5} as a Signature of a Photoinduced Insulator-Metal Phase Transition.

The ultrafast elastic light scattering technique is applied to reveal the strong nonlinearity of V_{3}O_{5} associated with a photoinduced insulator-metal phase transition. Observation of time-domain relaxation dynamics suggests several stages of structural transition. We discuss the nonequilibrium processes in V_{3}O_{5} in terms of photoinduced melting of a polaronic Wigner crystal, coalescence of V-O octahedra, and photogeneration of acoustical phonons in the low-T and high-T phases of V_{3}O_{5}. A molecular dynamics computation supports experimentally observed stages of V_{3}O_{5} relaxation dynamics.

Super-resolution in diffractive imaging from hemispherical elastic light scattering data.

Angle-resolved hemispherical elastic light scattering techniques have been used to reconstruct the surface profile of two-dimensional photonic crystals with submicron resolution and metrological precision. Iterative algorithms permit subsequent calculation of a surface autocorrelation function with additional numerical approximation of the power spectrum and then yield final reconstruction of the surface shape. The proposed method enables filtering out unwanted scattering background, precluding the convergence of phase-retrieval algorithms. The estimation of higher harmonics in the power spectrum provides the reconstruction of a realistic surface achieving subwavelength resolution.

Investigation of dynamics in BMIM TFSA ionic liquid through variable temperature and pressure NMR relaxometry and diffusometry.

A comprehensive variable temperature, pressure and frequency multinuclear (1H, 2H, and 19F) magnetic resonance study was undertaken on selectively deuterated 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIM TFSA) ionic liquid isotopologues. This study builds on our earlier investigation of the effects of increasing alkyl chain length on diffusion and dynamics in imidazolium-based TFSA ionic liquids. Fast field cycling 1H T1 data revealed multiple modes of motion. Through calculation of diffusion coefficient (D) values and activation energies, the low- and high-field regimes were assigned to the translational and reorientation dynamics respectively. Variable-pressure 2H T1 measurements reveal site-dependent interactions in the cation with strengths in the order MD3 > CD3 > CD2, indicating dissimilarities in the electric field gradients along the alkyl chain, with the CD2 sites having the largest gradient. Additionally, the α saturation effect in T1 vs. P was observed for all three sites, suggesting significant reduction of the short-range rapid reorientational dynamics. This reduction was also deduced from the variable pressure 1H T1 data, which showed an approach to saturation for both the methyl and butyl group terminal methyl sites. Pressure-dependent D measurements show independent motions for both cations and anions, with the cations having greater D values over the entire pressure range.

Do TFSA Anions Slither? Pressure Exposes the Role of TFSA Conformational Exchange in Self-Diffusion.

Multinuclear ((1)H, (2)H, and (19)F) magnetic resonance spectroscopy techniques as functions of temperature and pressure were applied to the study of selectively deuterated 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (EMIM TFSA) ionic liquid isotopologues and related ionic liquids. For EMIM TFSA, temperature-dependent (2)H T1 data indicate stronger electric field gradients in the alkyl chain region compared to the imidazolium ring. Most significantly, the pressure dependences of the EMIM and TFSA self-diffusion coefficients revealed that the displacements of the cations and anions are independent, with diffusion of the TFSA anions being slowed much more by increasing pressure than for the EMIM cations, as shown by their respective activation volumes (28.8 ± 2.5 cm(3)/mol for TFSA vs 14.6 ± 1.3 cm(3)/mol for EMIM). Increasing pressure may lower the mobility of the TFSA anion by hindering its interconversion between trans and cis conformers, a process that is coupled to diffusion according to published molecular dynamics simulations. Measured activation volumes (ΔV(‡)) for ion self-diffusion in EMIM bis(fluoromethylsulfonyl)amide and EMIM tetrafluoroborate support this hypothesis. In addition, (2)H T1 data suggest increased ordering with increasing pressure, with two T1 regimes observed for the MD3 and D2 isotopologues between 0.1-100 and 100-250 MPa, respectively. The activation volumes for T1 were 21 and 25 cm(3)/mol (0-100 MPa) and 11 and 12 cm(3)/mol (100-250 MPa) for the MD3 and D2 isotopologues, respectively.

Photoinduced insulator-to-metal transition and surface statistics of VO2 monitored by elastic light scattering.

Measurements of ultrafast light scattering within a hemisphere are performed for statistical analysis of nonequilibrium processes in VO2 epitaxial film. A Gerchberg-Saxton error reduction algorithm is applied for accurate calculation of a surface autocorrelation function from light scattering data and for partial reconstruction of a power spectral density function. Upon ultrafast photoinduced phase transition of VO2, the elastic light scattering reveals anisotropic grain-size-dependent dynamics. It was found that the transition rate depends on the optical absorption and orientation of VO2 grains with respect to polarization of the pump pulse. An observed stepwise evolution of surface autocorrelation length and transient anisotropy of the scattering field presumably originates from complex multistage transformation of VO2 lattice on a subpicosecond time scale.

Formulación y evaluación de la calidad proteínica de una harina de mezcla de desechos del fileteado de tiburones y cabezas de camarón / Formulation and evaluation of the protein quality of a mixture flour from shark filleting by products and shrimp's heads

Este estudio informa sobre una harina formulada con desechos del fileteado de tiburón (dt) y subproductos de camarón (cc) en la relación de 1.0:l.15, con el propósito de utilizarla en alimentación avícola. El contenido de proteína cruda era de 55.66%, con una relación Ca:P de 5.76. La distribuición de aminoácidos esenciales fue similar a la de harina de pescado y de la carne de tiburón tollo, siendo en todos los casos la metionina el primer limitante. Con excepción de los subproductos de camarón, los materiales pesqueros acusaron niveles adecuados de lisina disponible (entre 337 y 383 mg/gN). La distribución porcentual de partícula de la harina cc-dt referida al calibre de cedazo estádar estadounidense, arrojó un valor de módulo más fino (M. F.) de 3.95, con un diámetro promedio de partícula de 0.0175 de pulgada (0.444 mm) y un grado de uniformidad de 1 parte gruesa: 5 partes medianas: 4 partes finas. La calidad proteínica de la harina cc-dt en ratas se evaluó por los métodos de PER, NPR, PV y NGI. Se utilizaron dietas de caseínas y carne de tiburón tollo como fuentes de proteínas de referencia. La harina cc-dt presentó los menores valores de PER (1.60), NGI (2.46), PV (2.49) y DA (88.80), estadísticamente significativos (P <0.05) con los valores de caseínas y de la harina de carne de tiburón tollo, respectivamente