Spin-transfer torque magnetic memory (STT-MRAM) is currently under intense academic and industrial development, since it features non-volatility, high write and read speed and high endurance. In this work, we show that when used in a non-conventional regime, it can additionally act as a stochastic memristive device, appropriate to implement a "synaptic" function. We introduce basic concepts relating to spin-transfer torque magnetic tunnel junction (STT-MTJ, the STT-MRAM cell) behavior and its possible use to implement learning-capable synapses. Three programming regimes (low, intermediate and high current) are identified and compared. System-level simulations on a task of vehicle counting highlight the potential of the technology for learning systems. Monte Carlo simulations show its robustness to device variations. The simulations also allow comparing system operation when the different programming regimes of STT-MTJs are used. In comparison to the high and low current regimes, the intermediate current regime allows minimization of energy consumption, while retaining a high robustness to device variations. These results open the way for unexplored applications of STT-MTJs in robust, low power, cognitive-type systems.

Recently, VIB-group layered transition metal dichalcogenides (TMDs), MX 2 (M = Mo, W; X = S, Se, Te), attracted extensive attention due to rich physiochemical properties, ranging from catalysis, [1][2][3] topological states, [4][5][6][7][8][9][10][11][12][13][14][15][16] valley polarization, [17][18][19][20][21][22] even to superconductivity. [23][24][25][26][27][28] These multiple electronic properties essentially originate from varied crystal structures of TMD materials. The typical crystal structure in TMD materials is the 2H-type structure with [X-M-X] atoms in ABA stacking in each monolayer (Figure S1a, Supporting Information). Usually, 2H MX 2 materials are semiconducting, such as, 2H MoS 2 , where the valley polarization was widely studied. [17][18][19] Also, Ising superconductivity was observed when the TMD materials are reduced down to a few or even oneRecently the metastable 1T′-type VIB-group transition metal dichalcogenides (TMDs) have attracted extensive attention due to their rich and intriguing physical properties, including superconductivity, valleytronics physics, and topological physics. Here, a new layered WS 2 dubbed "2M" WS 2 , is constructed from 1T′ WS 2 monolayers, is synthesized. Its phase is defined as 2M based on the number of layers in each unit cell and the subordinate crystallographic system. Intrinsic superconductivity is observed in 2M WS 2 with a transition temperature T c of 8.8 K, which is the highest among TMDs not subject to any fine-tuning process. Furthermore, the electronic structure of 2M WS 2 is found by Shubnikov-de Haas oscillations and first-principles calculations to have a strong anisotropy. In addition, topological surface states with a single Dirac cone, protected by topological invariant Z 2 , are predicted through first-principles calculations. These findings reveal that the new 2M WS 2 might be an interesting topological superconductor candidate from the VIB-group transition metal dichalcogenides.

The green emission of poly(9,9′′‐dioctylfluorenyl‐2,7′′‐diyl), end‐capped by polyhedral oligomeric silsequioxanes, (PFO‐POSS) has been investigated by photoluminescence (PL) and photoexcitation (PE), gel permeation chromatography (GPC), and transmission Fourier transform infrared (FTIR) spectroscopy. The green emission is closely correlated with thermal oxidation degradation and crosslinking of the polymer and is enhanced by annealing at elevated temperatures. The green‐to‐blue emission intensity ratio, used to assess the emission properties of thin (90 nm) films, was 3.70, 4.35, and 1.54 for an air‐annealed film, its insoluble residue (crosslinked), and a film cast from its soluble portion, respectively. For thick (5–6 μm) film, the ratios are 13.33, 13.33, and 0.79, respectively. However, FTIR spectroscopy of thick films leads to the conclusion that the carbonyl‐to‐aromatic ring concentration ratio are 0.018, 0.015, and 0.032, respectively. Focusing on the recast films, the green emission is relatively low while the carbonyl concentration is relatively high. This suggests that the energy traps at crosslinked chains play an important role in green emission. It is likely that the crosslinking enhances the excitation energy migration and energy transfer to the defects by hindering chain segment twisting.

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Since interface superconductivity was discovered at the interface between two insulating layers LaAlO and SrTiO, such interface-induced superconducting systems have been a research hotspot in superconductivity. Here, we report homogeneous interfaces formed by stacking chemically exfoliated monolayer TaS nanosheets randomly. Enhanced superconductivity of T = 3 K is observed, compared with 0.8 K of parent 2H-TaS. The measurement of heat capacity shows the increase of electronic specific-heat coefficient γ of restacked TaS nanosheets compared to parent 2H-TaS crystals. Density functional theory calculations indicate that increase and delocalization of electron states near the Fermi surface due to the homogeneous interfaces effects could account for the enhanced superconductivity.

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Binding of lead (Pb) to soil fulvic acid (JGFA), soil humic acids (JGHA, JLHA), and lignite-based humic acid (PAHA) was investigated through binding isotherms and XAFS. Pb binding to humic substances (HS) increased with increasing pH and decreasing ionic strength. The NICA-Donnan model described Pb binding to the HS satisfactorily. The comparison of the model parameters showed substantial differences in median Pb affinity constants among JGFA, PAHA, and the soil HAs. Milne's "generic" parameters did not provide an adequate prediction for the soil samples. The Pb binding prediction with generic parameters for the soil HAs was improved significantly by using the value n(Pb1) = 0.92 instead of the generic value n(Pb1) = 0.60. The n(Pb1)/n(H1) ratios obtained were relatively high, indicating monodentate Pb binding to the carboxylic-type groups. The nPb2/nH2 ratios depended somewhat on the method of optimization, but the values were distinctly lower than the n(Pb1)/nH1 ratios, especially when the optimization was based on Pb bound vs log [Pb(2+)]. These low values indicate bidentate binding to the phenolic-type groups at high Pb concentration. The NICA-Donnan model does not consider bidentate binding of Pb to a carboxylic- and a phenolic-type group. The EXAFS results at high Pb loading testified that Pb was bound in bidentate complexes of one carboxylic and one phenolic group (salicylate-type) or two phenolic groups (catechol-type) in ortho position.

This report describes new findings of an investigation of a bifunctional nanocomposite probe for the detection of cancer biomarkers, demonstrating the viability of magnetic focusing and SERS detection in a microfluidic platform. The nanocomposite probe consists of a magnetic nickel-iron core and a gold shell. Upon bioconjugation, the nanoprobes are magnetically focused on a specific spot in a microfluidic channel, enabling an enrichment of "hot spots" for surface enhanced Raman scattering detection of the targeted carcinoembryonic antigen. The detection sensitivity, with a limit of detection of ∼0.1 pM, is shown to scale with the magnetic focusing time and the nanoparticle size. The latter is also shown to exhibit an excellent agreement between the experimental data and the theoretical simulation. Implications of the findings to the development of rapid and sensitive microfluidic detection of cancer biomarkers are also discussed.