A novel true random number generator based on a stochastic diffusive memristor

The intrinsic variability of switching behavior in memristors has been a major obstacle to their adoption as the next generation universal memory. On the other hand, this natural stochasticity can be valuable for hardware security applications. Here we propose and demonstrate a novel true random number generator (TRNG) utilizing the stochastic delay time of threshold switching in a Ag:SiO2 diffusive memristor, which exhibits evident advantages in scalability, circuit complexity and power consumption. The random bits generated by the diffusive memristor TRNG passed all 15 NIST randomness tests without any post-processing, a first for memristive-switching TRNGs. Based on nanoparticle dynamic simulation and analytical estimates, we attributed the stochasticity in delay time to the probabilistic process by which Ag particles detach from a Ag reservoir. This work paves the way for memristors in hardware security applications for the era of Internet of Things (IoT)

Memristors with diffusive dynamics as synaptic emulators for neuromorphic computing

The accumulation and extrusion of Ca2+ in the pre- and postsynaptic compartments play a critical role in initiating plastic changes in biological synapses. To emulate this fundamental process in electronic devices, we developed diffusive Ag-in-oxide memristors with a temporal response during and after stimulation similar to that of the synaptic Ca2+ dynamics. In situ high-resolution transmission electron microscopy and nanoparticle dynamics simulations both demonstrate that Ag atoms disperse under electrical bias and regroup spontaneously under zero bias because of interfacial energy minimization, closely resembling synaptic influx and extrusion of Ca2+, respectively. The diffusive memristor and its dynamics enable a direct emulation of both short- and long-term plasticity of biological synapses and represent a major advancement in hardware implementation of neuromorphic functionalities

Anatomy of Ag/Hafnia‐Based Selectors with 1010 Nonlinearity

Sneak path current is a significant remaining obstacle to the utilization of large crossbar arrays for non-volatile memories and other applications of memristors. A two-terminal selector device with an extremely large current-voltage nonlinearity and low leakage current could solve this problem. We present here a Ag/oxide-based threshold switching (TS) device with attractive features such as high current-voltage nonlinearity (~1010 ), steep turn-on slope (less than 1 mV/dec), low OFF-state leakage current (~10-14 A), fast turn ON/OFF speeds (108 cycles). The feasibility of using this selector with a typical memristor has been demonstrated by physically integrating them into a multilayered 1S1R cell. Structural analysis of the nanoscale crosspoint device suggests that elongation of a Ag nanoparticle under voltage bias followed by spontaneous reformation of a more spherical shape after power off is responsible for the observed threshold switching of the device. Such mechanism has been quantitatively verified by the Ag nanoparticle dynamics simulation based on thermal diffusion assisted by bipolar electrode effect and interfacial energy minimization

Mixed Diacetylene/Octadecyl Melamine Nanowires Formed at the Air/Water Interface Exhibit Unique Structural and Colorimetric Properties

Polydiacetylene (PDA) assemblies exhibit interesting photophysical properties, specifically, visible colorimetric transformations. A considerable body of work has focused on the formation and characterization of PDA Langmuir monolayer systems, and the overwhelming majority of reports so far have indicated that the adoption of 2D sheetlike structures associated with a hydrogen bond network between the diacetylene headgroups is a prerequisite for polymerization and chromatic properties. Here we report for the first time on the assembly of nanowire networks in mixed Langmuir monolayers comprising diacetylene monomers and octadecyl melamine surfactants. Structural and physical analysis indicates that the nanowires are composed of a helical organization of stacked diacetylene/octadecyl melamine building blocks assembled through hydrogen bonds between the melamine residues and the carboxylic termini of the diacetylenes. Following ultraviolet-induced polymerization, the PDA/octadecyl melamine nanowires exhibited unusual chromatic properties, specifically, an absence of the ubiquitous “blue” phase, rather transforming into a new “purple” PDA phase. This study demonstrates that the incorporation of surfactant constituents within diacetylene frameworks provides a means for modulating the structural and chromatic features of PDA assemblies, giving rise to new morphologies and unique optical properties

Scalable Inkjet-Based Structural Color Printing by Molding Transparent Gratings on Multilayer Nanostructured Surfaces

To enable customized manufacturing of structural colors for commercial applications, up-scalable, low-cost, rapid, and versatile printing techniques are highly demanded. In this paper, we introduce a viable strategy for scaling up production of custom-input images by patterning individual structural colors on separate layers, which are then vertically stacked and recombined into full-color images. By applying this strategy on molded-ink-on-nanostructured-surface printing, we present an industry-applicable inkjet structural color printing technique termed multilayer molded-ink-on-nanostructured-surface (M-MIONS) printing, in which structural color pixels are molded on multiple layers of nanostructured surfaces. Transparent colorless titanium dioxide nanoparticles were inkjet-printed onto three separate transparent polymer substrates, and each substrate surface has one specific subwavelength grating pattern for molding the deposited nanoparticles into structural color pixels of red, green, or blue primary color. After index-matching lamination, the three layers were vertically stacked and bonded to display a color image. Each primary color can be printed into a range of different shades controlled through a half-tone process, and full colors were achieved by mixing primary colors from three layers. In our experiments, an image size as big as 10 cm by 10 cm was effortlessly achieved, and even larger images can potentially be printed on recombined grating surfaces. In one application example, the M-MIONS technique was used for printing customizable transparent color optical variable devices for protecting personalized security documents. In another example, a transparent diffractive color image printed with the M-MIONS technique was pasted onto a transparent panel for overlaying colorful information onto one’s view of reality

Scalable Inkjet-Based Structural Color Printing by Molding Transparent Gratings on Multilayer Nanostructured Surfaces

To enable customized manufacturing of structural colors for commercial applications, up-scalable, low-cost, rapid, and versatile printing techniques are highly demanded. In this paper, we introduce a viable strategy for scaling up production of custom-input images by patterning individual structural colors on separate layers, which are then vertically stacked and recombined into full-color images. By applying this strategy on molded-ink-on-nanostructured-surface printing, we present an industry-applicable inkjet structural color printing technique termed multilayer molded-ink-on-nanostructured-surface (M-MIONS) printing, in which structural color pixels are molded on multiple layers of nanostructured surfaces. Transparent colorless titanium dioxide nanoparticles were inkjet-printed onto three separate transparent polymer substrates, and each substrate surface has one specific subwavelength grating pattern for molding the deposited nanoparticles into structural color pixels of red, green, or blue primary color. After index-matching lamination, the three layers were vertically stacked and bonded to display a color image. Each primary color can be printed into a range of different shades controlled through a half-tone process, and full colors were achieved by mixing primary colors from three layers. In our experiments, an image size as big as 10 cm by 10 cm was effortlessly achieved, and even larger images can potentially be printed on recombined grating surfaces. In one application example, the M-MIONS technique was used for printing customizable transparent color optical variable devices for protecting personalized security documents. In another example, a transparent diffractive color image printed with the M-MIONS technique was pasted onto a transparent panel for overlaying colorful information onto one’s view of reality

Using Dopants to Tune Oxygen Vacancy Formation in Transition Metal Oxide Resistive Memory

Introducing dopants is an important way to tailor and improve electronic properties of transition metal oxides used as high-k dielectric thin films and resistance switching layers in leading memory technologies, such as dynamic and resistive random access memory (ReRAM). Ta₂O₅ has recently received increasing interest because Ta₂O₅-based ReRAM demonstrates high switching speed, long endurance, and low operating voltage. However, advances in optimizing device characteristics with dopants have been hindered by limited and contradictory experiments in this field. We report on a systematic study on how various metal dopants affect oxygen vacancy formation in crystalline and amorphous Ta₂O₅ from first principles. We find that isoelectronic dopants and weak n-type dopants have little impact on neutral vacancy formation energy and that p-type dopants can lower the formation energy significantly by introducing holes into the system. In contrast, n-type dopants have a deleterious effect and actually increase the formation energy for charged oxygen vacancies. Given the similar doping trend reported for other binary transition metal oxides, this doping trend should be universally valid for typical binary transition metal oxides. Based on this guideline, we propose that p-type dopants (Al, Hf, Zr, and Ti) can lower the forming/set voltage and improve retention properties of Ta₂O₅ ReRAM

Ruthenium-Catalyzed Redox-Neutral C–H Activation via N–N Cleavage: Synthesis of N‑Substituted Indoles

The first Ru-catalyzed redox-neutral C–H activation reaction via N–N bond cleavage is reported. Pyrazolidin-3-one is demonstrated as an internally oxidative directing group that enables C–H annulation reactions with a broad scope of alkynes, including previously incompetent terminal alkynes. Pharmacologically privileged 3-(1<i>H</i>-indol-1-yl)­propanamides were synthesized in high yields

Single-Stranded DNA as a Cleavable Linker for Bioorthogonal Click Chemistry-Based Proteomics

In this communication, we report a new class of cleavable linker based on automatically synthesized, single-stranded DNAs. We incorporated a DNA oligo into an azide-functionalized biotin (biotin-DNA-N₃) and used the probe to enrich for alkyne-tagged glycoproteins from mammalian cell lysates. Highly efficient and selective release of the captured proteins from streptavidin agarose resins was achieved using DNase treatment under very mild conditions. A total of 36 sialylated glycoproteins were identified from the lysates of HL60 cells, an acute human promyeloid leukemia cell line. These sialylated glycoproteins were involved in many different biological processes ranging from glycan biosynthesis to cell adhesion events

Phase Equilibria of Water/CO₂ and Water/<i>n</i>‑Alkane Mixtures from Polarizable Models

Phase equilibria of water/CO₂ and water/<i>n</i>-alkane mixtures over a range of temperatures and pressures were obtained from Monte Carlo simulations in the Gibbs ensemble. Three sets of Drude-type polarizable models for water, namely the BK3, GCP, and HBP models, were combined with a polarizable Gaussian charge CO₂ (PGC) model to represent the water/CO₂ mixture. The HBP water model describes hydrogen bonds between water and CO₂ explicitly. All models underestimate CO₂ solubility in water if standard combining rules are used for the dispersion interactions between water and CO₂. With the dispersion parameters optimized to phase compositions, the BK3 and GCP models were able to represent the CO₂ solubility in water, however, the water composition in CO₂-rich phase is systematically underestimated. Accurate representation of compositions for both water- and CO₂-rich phases cannot be achieved even after optimizing the cross interaction parameters. By contrast, accurate compositions for both water- and CO₂-rich phases were obtained with hydrogen bonding parameters determined from the second virial coefficient for water/CO₂. Phase equilibria of water/<i>n</i>-alkane mixtures were also studied using the HBP water and an exponenial-6 united-atom <i>n</i>-alkanes model. The dispersion interactions between water and <i>n</i>-alkanes were optimized to Henry’s constants of methane and ethane in water. The HBP water and united-atom <i>n</i>-alkane models underestimate water content in the <i>n</i>-alkane-rich phase; this underestimation is likely due to the neglect of electrostatic and induction energies in the united-atom model