194 research outputs found
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/HafniaāBased 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 āblueā phase, rather transforming
into a new āpurpleā 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 oneās 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 oneās 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). Ta<sub>2</sub>O<sub>5</sub> has recently received increasing interest because Ta<sub>2</sub>O<sub>5</sub>-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 Ta<sub>2</sub>O<sub>5</sub> 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 Ta<sub>2</sub>O<sub>5</sub> ReRAM
Ruthenium-Catalyzed Redox-Neutral CāH Activation via NāN Cleavage: Synthesis of NāSubstituted Indoles
The first Ru-catalyzed redox-neutral
CāH activation reaction
via NāN bond cleavage is reported. Pyrazolidin-3-one is demonstrated
as an internally oxidative directing group that enables CāH
annulation reactions with a broad scope of alkynes, including previously
incompetent terminal alkynes. Pharmacologically privileged 3-(1<i>H</i>-indol-1-yl)Āpropanamides 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-N<sub>3</sub>) 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/CO<sub>2</sub> and Water/<i>n</i>āAlkane Mixtures from Polarizable Models
Phase equilibria
of water/CO<sub>2</sub> 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 CO<sub>2</sub> (PGC) model to represent the water/CO<sub>2</sub> mixture.
The HBP water model describes hydrogen bonds between water and CO<sub>2</sub> explicitly. All models underestimate CO<sub>2</sub> solubility
in water if standard combining rules are used for the dispersion interactions
between water and CO<sub>2</sub>. With the dispersion parameters optimized
to phase compositions, the BK3 and GCP models were able to represent
the CO<sub>2</sub> solubility in water, however, the water composition
in CO<sub>2</sub>-rich phase is systematically underestimated. Accurate
representation of compositions for both water- and CO<sub>2</sub>-rich
phases cannot be achieved even after optimizing the cross interaction
parameters. By contrast, accurate compositions for both water- and
CO<sub>2</sub>-rich phases were obtained with hydrogen bonding parameters
determined from the second virial coefficient for water/CO<sub>2</sub>. 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 Henryās 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
- ā¦