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This work demonstrates a low-power, light-weight, and cost-efficient vacuum pressure sensor and air leak detector based on 2 mm ×2 mm Cu/HfO2/ p^+ -Si memristor device. The operating principle of the proposed sensor relies on monitoring the off-state resistance ( R_off ) of the device, wherein the experimental results show that the R_off value is inversely proportional to the vacuum pressure. The fabricated sensors demonstrated a sensitivity of 493 Torr-1 and power consumption as low as ∼ 8 nW, when tested in a wide range of sub-atmospheric pressure ( 4.9× 10^-5 - 760 ) Torr, making them highly suitable for low-power applications. Furthermore, it is shown that the sensor can be integrated with a microcontroller-based circuitry to serve as a standalone sensing system.

Compliance current plays a very important role in the retention performance of memristive devices. Although it was established that low and high compliance currents lead to volatile and nonvolatile behavior, respectively, studying the influence of the intermediate compliance current as a method to control the retention has not been widely explored. This is an interesting feature because the memristive devices have captured the attention of the scientific community for the development of a broad spectrum of new applications beyond memory. In this work, the effect of the intermediate compliance current in forming-free Cu/HfO2-based memristive devices is investigated. Here we show the existence of an intermediate compliance current window between the volatile and nonvolatile operating regions wherein the device holds the retention for a short time in a stochastic mode. Furthermore, the variation in the retention time is evaluated with respect to different device electrical parameters including the charge, flux, run history, and ON-state resistance, as well as the switching time of the device. The results show that the retention time controlled by an intermediate compliance current exhibits substantial variation, and the cycle-to-cycle stochasticity in the retention time can be a representative quality parameter for the development of security-related applications.

CO elimination through oxidation over highly active and cost-effective catalysts is a way forward for many processes of industrial and environmental importance. In this study, doped CeO2 with transition metals (TM = Cu, Co, Mn, Fe, Ni, Zr, and Zn) at a level of 20 at. % was tested for CO oxidation. The oxides were prepared using microwave-assisted sol-gel synthesis to improve catalyst's performance for the reaction of interest. The effect of heteroatoms on the physicochemical properties (structure, morphology, porosity, and reducibility) of the binary oxides M-Ce-O was meticulously investigated and correlated to their CO oxidation activity. It was found that the catalytic activity (per gram basis or TOF, s-1) follows the order Cu-Ce-O > Ce-Co-O > Ni-Ce-O > Mn-Ce-O > Fe-Ce-O > Ce-Zn-O > CeO2. Participation of mobile lattice oxygen species in the CO/O2 reaction does occur, the extent of which is heteroatom-dependent. For that, state-of-the-art transient isotopic 18O-labeled experiments involving 16O/18O exchange followed by step-gas CO/Ar or CO/O2/Ar switches were used to quantify the contribution of lattice oxygen to the reaction. SSITKA-DRIFTS studies probed the formation of carbonates while validating the Mars-van Krevelen (MvK) mechanism. Scanning transmission electron microscopy-high-angle annular dark field imaging coupled with energy-dispersive spectroscopy proved that the elemental composition of dopants in the individual nanoparticle of ceria is less than their composition at a larger scale, allowing the assessment of the doping efficacy. Despite the similar structural features of the catalysts, a clear difference in the Olattice mobility was also found as well as its participation (as expressed with the α descriptor) in the reaction, following the order αCu > αCo> αMn > αZn. Kinetic studies showed that it is rather the pre-exponential (entropic) factor and not the lowering of activation energy that justifies the order of activity of the solids. DFT calculations showed that the adsorption of CO on the Cu-doped CeO2 surface is more favorable (-16.63 eV), followed by Co, Mn, Zn (-14.46, -4.90, and -4.24 eV, respectively), and pure CeO2 (-0.63 eV). Also, copper compensates almost three times more charge (0.37e-) compared to Co and Mn, ca. 0.13e- and 0.10e-, respectively, corroborating for its tendency to be reduced. Surface analysis (X-ray photoelectron spectroscopy), apart from the oxidation state of the elements, revealed a heteroatom-ceria surface interaction (Oa species) of different extents and of different populations of Oa species.

This work provides useful insights into the development of HfO2-based memristive systems with a p-type silicon bottom electrode that are compatible with the complementary metal–oxide–semiconductor technology. The results obtained reveal the importance of the top electrode selection to achieve unique device characteristics. The Ag/HfO2/Si devices have exhibited a larger memory window and self-compliance characteristics. On the other hand, the Au/HfO2/Si devices have displayed substantial cycle-to-cycle variation in the ON-state conductance. These device characteristics can be used as an indicator for the design of resistive-switching devices in various scenes such as, memory, security, and sensing. The current–voltage (I–V) characteristics of Ag/HfO2/Si and Au/HfO2/Si devices under positive and negative bias conditions have provided valuable information on the ON and OFF states of the devices and the underlying resistive switching mechanisms. Repeatable, low-power, and forming-free bipolar resistive switching is obtained with both device structures, with the Au/HfO2/Si devices displaying a poorer device-to-device reproducibility. Furthermore, the Au/HfO2/Si devices have exhibited N-type negative differential resistance (NDR), suggesting Joule-heating activated migration of oxygen vacancies to be responsible for the SET process in the unstable unipolar mode.

The ordered open organic frameworks membranes are attractive candidates for flow-assisted molecular separations. The physicochemical properties of such membranes mostly depend on their selectively chosen functional building blocks. In this work, we have introduced a novel concept of functional switchability of three-dimensional covalent organic framework (3D-COF) membranes through a simple solvent-influenced fragmentation method. This room-temperature interfacial synthesis provides free-standing 3D-COF membranes with distinct physicochemical properties from the same building monomers. Notably, the change of solvent from chloroform to ethyl acetate switches the membrane property from hydrophilic (water contact angle 60°) to hydrophobic (water contact angle 142°) nature. The hydrophobic 3D-COF membrane selectively passes oil molecules from an oil-water emulsion with a gravitational flux of 1536 L m

In this work, a new protocol was developed for creating charge-tuned, hydrophilic hybrid ultrafiltration (UF) membranes with high flux, rejection rate, and fouling resistance. The membranes were fabricated using a combination of sulfonated poly(ether sulfone) (SPES) and aminated graphene (GO-SiO

In this paper, the memristive switching behavior of Cu/ HfO2/p++ Si devices fabricated by an organic-polymer-assisted sol-gel spin-coating method, coupled with post-annealing and shadow-mask metal sputtering steps, is examined. HfO2 layers of about 190 nm and 80 nm, are established using cost-effective spin-coating method, at deposition speeds of 2000 and 4000 rotations per minute (RPM), respectively. For two types of devices, the memristive characteristics (Von, Ion, and Vreset) and device-to-device electrical repeatability are primarily discussed in correlation with the oxide layer uniformity and thickness. The devices presented in this work exhibit an electroforming free and bipolar memory-resistive switching behavior that is typical of an Electrochemical Metallization (ECM) I-V fingerprint. The sample devices deposited at 4000 RPM generally show less variation in electrical performance parameters compared to those prepared at halved spin-coating speed. Typically, the samples prepared at 4000 RPM (n = 8) display a mean switching voltage Von of 3.0 V (±0.3) and mean reset voltage Vreset of −1.1 V (±0.5) over 50 consecutive sweep cycles. These devices exhibit a large Roff/Ron window (up to 104), and sufficient electrical endurance and retention properties to be further examined for radiation sensing. As they exhibit less statistical uncertainty compared to the samples fabricated at 2000 RPM, the devices prepared at 4000 RPM are tested for the detection of soft gamma rays (emitted from low-activity Cs-137 and Am-241 radioactive sources), by assessing the variation in the on-state resistance value upon exposure. The analysis of the probability distributions of the logarithmic Ron values measured over repeated ON-OFF cycles, before, during and after exposing the devices to radiation, demonstrate a statistical difference. These results pave the way for the fabrication and development of cost-effective soft-gamma ray detectors.

CO elimination through oxidation over highly active and cost-effective catalysts is a way forward for many processes of industrial and environmental importance. In this study, doped CeO2 with transition metals (TM = Cu, Co, Mn, Fe, Ni, Zr, and Zn) at a level of 20 at. % was tested for CO oxidation. The oxides were prepared using microwave-assisted sol–gel synthesis to improve catalyst’s performance for the reaction of interest. The effect of heteroatoms on the physicochemical properties (structure, morphology, porosity, and reducibility) of the binary oxides M–Ce–O was meticulously investigated and correlated to their CO oxidation activity. It was found that the catalytic activity (per gram basis or TOF, s–1) follows the order Cu–Ce–O > Ce–Co–O > Ni–Ce–O > Mn–Ce–O > Fe–Ce–O > Ce–Zn–O > CeO2. Participation of mobile lattice oxygen species in the CO/O2 reaction does occur, the extent of which is heteroatom-dependent. For that, state-of-the-art transient isotopic 18O-labeled experiments involving 16O/18O exchange followed by step-gas CO/Ar or CO/O2/Ar switches were used to quantify the contribution of lattice oxygen to the reaction. SSITKA-DRIFTS studies probed the formation of carbonates while validating the Mars–van Krevelen (MvK) mechanism. Scanning transmission electron microscopy-high-angle annular dark field imaging coupled with energy-dispersive spectroscopy proved that the elemental composition of dopants in the individual nanoparticle of ceria is less than their composition at a larger scale, allowing the assessment of the doping efficacy. Despite the similar structural features of the catalysts, a clear difference in the Olattice mobility was also found as well as its participation (as expressed with the α descriptor) in the reaction, following the order αCu > αCo> αMn > αZn. Kinetic studies showed that it is rather the pre-exponential (entropic) factor and not the lowering of activation energy that justifies the order of activity of the solids. DFT calculations showed that the adsorption of CO on the Cu-doped CeO2 surface is more favorable (−16.63 eV), followed by Co, Mn, Zn (−14.46, −4.90, and −4.24 eV, respectively), and pure CeO2 (−0.63 eV). Also, copper compensates almost three times more charge (0.37e−) compared to Co and Mn, ca. 0.13e− and 0.10e−, respectively, corroborating for its tendency to be reduced. Surface analysis (X-ray photoelectron spectroscopy), apart from the oxidation state of the elements, revealed a heteroatom–ceria surface interaction (Oa species) of different extents and of different populations of Oa species.

The recent technological advancements in heterogeneous catalysis have extensively focused on tailoring the ubiquitous ceria system into a new class of low-dimensional nanostructured materials with high aspect ratio and unique quantum physicochemical properties to achieve a superior catalytic performance. Among these developments, the electrospun features have become widely targeted, given their ease of nanoscale manipulation with the accessible coupling of the sol-gel process and electrospinning technique. In this review, a plethora of documented electrospun ceria-based nanofibers are mapped for the first time and an emphasis is given to their preparation methods. The nano-architectural engineering of ceria and its related mixed metal-oxide catalysts is surveyed with a main focus on energy production and environmental remediation. A preliminary overview about the primary tunable electrospinning parameters (e.g., solution processing, operating conditions and use of auxiliary configurations) to tailor the morphology, orientation and alignment of the fibers, is discussed. The intercorrelations among the electrospinning conditions and the resulting physicochemical properties and catalytic performance of a variety of low-dimensional CeO2-based systems are elucidated for the first time. Moreover, the benefits of the nanofibrous shape in heterogeneous catalysis are exemplified through applications in oxidation reactions, C1 catalytic chemistry, water-gas shift reaction, photocatalysis, and fuel cells.

Resistive random-access memory (RRAM) technology has been gaining importance due to scalability, low power, non-volatility, and the ability to perform in-memory computing. The RRAM sensing applications have also emerged to enable single RRAM technology platforms which include sensing, data storage, and computing. This paper reports on sol-gel drop coated low-power $\mu $ -thick Ag/TiO2/Cu memristor, named MemSens, developed for radiation sensing. MemSens exhibits a bipolar memristive switching behavior within a small voltage window, ranging up to +0.7 V for the turn-ON, and down to −0.2 V for the turn-OFF. Under these operating conditions, MemSens has 67% less switching voltage, 20% drop in ON switching current, 75% reduced active area and > 3x improved device endurance, compared to the best characteristics reported in the literature for $\mu $ -thick memristors. The device is tested under direct exposure to ionizing Cs-137 662keV $\gamma $ -rays, during which a significant increase in the electrical conductivity of the device is observed. MemSens circuit is proposed to allow a relatively real time and cost-effective radiation detection. This provides a first insight to the advancement of reliable memristors that could potentially be deployed in future low-power radiation sensing technologies for medical, personal protection, and other field applications.

In this paper, we investigate the switching behavior of nano-thick microscale Pd/Hf/HfO2-10nm/Pd memristors. Several key electrical characteristics such as the forming voltage and the SET/RESET IV parameters are studied as a function of the device size, the hafnium-capping thickness and the environmental temperature. The fabricated stack exhibits a unipolar switching behavior that is characteristic of two interfacial oxide and buffer layers consisting of the same transition metal. The average forming voltage value decreases oppositely to the microscale device area while it increases with the Hf-capping layer thickness. The unipolar memristive switching behavior is found to be polarity-dependent due to diverse contributions of the top Hf-buffer layer and the bottom Pd electrode to the switching mechanism. Joule heating effects involving thermophoresis and diffusion are concluded to be predominantly governing the ON/OFF switching events in the positive polarity. Synergistic electric field effects are found to additionally control the unipolar switching behavior in the negative mode. The respective key roles of the top Hf-buffer layer and the bottom Pd electrode in the asymmetric unipolar memristive switching are elucidated at the molecular level according to well-established transport phenomena reported for oxygen vacancies. Given the importance of heat in controlling the conductance state of the proposed stack, the memristor's electrical sensitivity to changes in the ambient temperature is preliminarily investigated for potential temperature sensing applications. Display Omitted The nano-thick microscale Pd/Hf/HfO210nm/Pd memristors exhibit unipolar switching behavior.Increasing the active area can gradually reduce the forming voltage of the fabricated devices.The Hf capping layer plays potential role in dictating the forming voltage.Joule heating effects involving thermophoresis and diffusion are predominantly governing the ON/OFF switching events.The fabricated memristors demonstrate promising electrical sensitivity to changes in the ambient temperature.

Moisture can modulate the resistive switching dynamics in oxide-based electrochemical metallization devices. Unconventional testing environments such as vacuum, could possibly shift the device characteristics, requiring therefore a careful investigation. This work investigates the write/erase behavior of Cu/HfO2(~80-nm-thick)/p+-Si devices in ambient atmosphere and vacuum, under similar electrical bias applied to the top Cu electrode. In vacuum (~5.3 × 10−3 Pa), a parasitic negative SET (N-SET) readily arises during the “erase” operation, unlike in ambient air. The electrical studies and physicochemical analyses of electrically-biased and pristine devices reveal that the “erase” process is sensitive to the environment. Vacuum facilitates the electric-field-controlled generation of an oxygen-vacancy-based path that likely induces a parasitic N-SET at the negative voltage. This path is aided by the presence of partially-ruptured copper filaments at the HfO2/p+-Si interface. The vacuum effects leading to the N-SET are eliminated by introducing a passivating gas environment (zero-air or nitrogen), or device encapsulation.

Memristive crossbar arrays are finding application in a wide range of operations such as memory, in-memory-computing, analog computing, etc. The crossbar performance is limited by a sneak path current, which limits the array size and negatively affects power and noise margin. In this paper, we present a synthesis of one selector and one Memristor device (1S1R) unit based on nonlinear resistive selector connected in series with bipolar Memristor (MR) element. The selector provides a gating function to the MR to reduce the sneak path current. The operation and performance of the MR and the selector devices have been verified individually and when serially connected. The MR cell measurements show good repeatability over multiple SET-RESET cycles with $\mathbf{V}_{\mathbf{on}}\sim \mathbf{2.5}$ to 3 V, $\mathbf{R}_{\mathbf{off}}/\mathbf{R}_{\mathbf{on}}\sim \mathbf{10}^{\mathbf{4}}$ and $\mathbf{V}_{\mathbf{off}}\sim-\mathbf{0.6}$ to −1.5 V. The electrical parameters of the memristor cell have been extracted and correlated mathematically using the Voltage-Threshold Adaptive Model (VTEAM). Various array sizes ranging from $\mathbf{2} \times \mathbf{2}$ to $\mathbf{4,000}\times \mathbf{4,000}$ have been investigated using spice circuit simulator. The results show that the proposed configuration reduces the sneak path by 200 times when compared with a similar size array that does not use a selector device. Also, using the selector increases the crossbar read margin, device selectivity, and enables high memory array density up to $\mathbf{4}\mathbf{k}\times \pmb{4}\mathbf{k}$ compared to $\mathbf{512}\ \mathrm{x}\mathbf{512}$ state of the art. The device allows relatively low voltage operation of 4V/1V (write/read) compared to 5V/2V reported in literature, which makes it attractive for low power applications.

This study introduces the use of choline chloride-urea (ChCl-U) deep eutectic solvent (DES) in polyimide (PI) ultrafiltration (UF) membranes to enhance the filtration removal of aqueous pharmaceuticals such as ibuprofen and paracetamol. The DES is immobilized over silica nanofiller particles by impregnation, and the composite ChCl-U@SiO2 is embedded at different loadings in the preparation of the PI UF membrane case solutions. The effects of ChCl-U@SiO2 loading on the resulting surface roughness, porosity, average pore size, hydrophilicity, and mechanical properties of the membranes were evaluated and correlated with the UF performance. The modified membrane was assessed using dead-end vacuum filtration experiments to measure the water permeate flux, solution permeate flux, and removal efficiency for 50 ppm paracetamol and 50 ppm ibuprofen from synthetic aqueous mixtures. The results showed that a 2 wt% ChCl-U@SiO2 nanofiller loading was necessary to produce membranes with the optimal aforementioned performance characteristics. The ChCl-U@SiO2 (2 wt%) PI UF membrane showed a significant increase in the water flux (250 L/m2 h) compared to the pristine membrane (30 L/m2 h), due to the enhancement of the hydrophilic character of the membrane. The large water flux was accompanied by an outstanding removal efficiency of up to 99.9% for paracetamol, exceeding that of the bare PI membrane (15%) by ~ 6 folds. The rejection removal of ibuprofen (87%) was roughly 7.9 times greater than that for the pristine membrane. This study provided substantial insights for the potential application of DES as a green modifier in the membrane-based removal of pharmaceutical pollutants from water.

Novel composite hydrophilic ultrafiltration (UF) membranes, comprising a polyimide (PI) matrix embedded with silica-based nanofillers are established for the enhanced vacuum-filtration removal of small polar organics such as phenol from water. Spherical silica nanoparticles are first prepared by the surfactant-templated sol–gel approach, then coated with choline chloride-ethylene glycol deep eutectic solvent (DES) by post-impregnation. The modified silica nanofillers are introduced into the PI matrix through the casting solution, which is then used to develop the composite UF membranes by phase inversion. The spectroscopy and high-resolution electron microscopy measurements evidence the presence of DES on the surface of the modified silica nanofillers. The topographical atomic force microscopy studies, dynamic water contact angle, and zeta potential measurements conducted on the native polymer membrane and those embedded with bare-silica and DES-coated silica confirm the successful incorporation of nanofillers into the PI matrix. An optimum nanofiller loading of 2 wt% is found to preserve the membrane structure and give the best mechanical properties as well as for the UF performance characteristics in vacuum-filtration studies at 85 kPa. Consistently, the DES-silica modified PI UF membranes (DES@SiO2@PI) exhibit exceptional water permeate flux (300 L m−2 h−1) and removal efficiency (96%) for 30 mg L−1 aqueous phenol compared with the native polymer and SiO2-modified membranes. The DES-engineered composite membranes can be operated within a wide feed pH window (pH: 2–10) without displaying significant loss in their removal efficiency. The pH and zeta potential results suggest that the interaction of phenol with the optimized membranes is governed by cooperative adsorption/Lewis acid-base mechanisms via hydrogen bonding and assistive ion-exchange interactions with the ethaline coating.

Sol-gel/drop-coated micro-thick TiO 2 memristors were investigated and developed for low-power radiation sensing. Devices constructed with coated aluminum (Al) electrodes exhibited unipolar I-V characteristics with dynamic turn-on voltage, and progressive R OFF /R ON ratio loss under applied bias. Endurance failure of micro-thick Al/Al stacks is ascribed to gradual passivation of Al surface resulting from an electrically-enhanced oxygen-ion diffusion. By exchanging a single Al contact with higher work function copper (Cu) metal, two distinct superimposed TiO 2 phases were formed. The TiO 2 coating on Al surface was carbon-contaminated and amorphous, while that on Cu was found to be additionally doped with Cu (I/II) ions resulting from the corrosion of the surface of the electrode by the amine-based gelation agent. After initial forming, the hybrid stack could achieve a bipolar memristance, with high R OFF /R ON (up to 10 6 ), and over 10 switching cycles at low-operating voltages (±1 V). The enhanced memristive switching properties of Al/Cu devices are explained via cooperative valence-change/electrochemical-metallization processes, involving migration of oxygen and copper species. The advanced micro-thick TiO 2 memristors were exposed to Cs-137 γ-rays, providing for the first time initial insights into their radiation detection capabilities. The sensing mechanism through these devices could be actuated by synergistic radiation-induced and field-driven photo-electric effects.

Bioinspired semiconductor-based devices with adaptive and dynamic properties will have many advantages over conventional static digital silicon-based technologies. The ability to compute, process, and retain information in parallel, without referencing other circuit elements, offers enhanced speed, storage density, energy efficiency, and functionality benefits. A novel crossbar microwire-based device consisting of Nb/NbO/Pt structure that exhibits neural synapse-like adaptive conductivity (i.e., synaptic plasticity) is presented. The neuromorphic memristive junction, formed at the interface between the Pt metal wire and the thermally annealed core–shell Nb–NbO wire, demonstrates 1000 times conductivity change with an effective continuum of resistance levels. The device can also be fully activated to display standard resistance switching between two states. In the subthreshold regime, the voltage flux applied through the ∼400 nm thick NbO junction is shown to have a linear relationship to the charge produc...

The dependency of the calcium sulfate (CaSO4) deposit formation on the presence and concentration of co-precipitating ions, is a fundamental question to the advancement of crystallization science. In this paper, the thermodynamics and kinetics of the static precipitation of 47.5 mM calcium sulfate, in isolation and presence of strontium sulfate (SrSO4) as common co-crystallizing salt, are examined at 30°C. The deposition of pure and composite sulfate scales is studied by varying the salinity of the medium from 0.35 to 1.50 M NaCl. To evaluate the effect of the co-precipitating, strontium ion concentration was altered from 0 to 20.0 mM. In order to elucidate the crystallization mechanism in terms of reaction rate and extent, the concentration of the free scaling ions, including that of Ca2+, SO42− and Sr2+, is systematically monitored at different intervals until equilibrium is achieved. Moreover, crystal deposits collected at regular intervals from the isothermal incubation experiments are characterized for changes in their microstructure, morphology, and elemental distribution, to establish correlations with the data obtained on the evolution of the solution composition. The analysis of the crystallographic properties of the deposits substantiates the dependency of the thermodynamics and kinetics of the CaSO4 precipitation process on the salinity and co-existence of supersaturated SrSO4 in the mixture. Particularly, the morphology of calcium sulfate deposits is altered in the presence of SrSO4, which corroborates the assumption of co-crystal interactions. These results indicate that heterogeneous crystal nucleation and growth of the mixed salts can be prompted at temperatures and salinity conditions as low as 30°C and 0.35 M, when the concentration of Sr2+ is increased up to 20.0 mM. Using the Pitzer model derived ion activity coefficients, discrepant thermodynamic solubility product constant (Ksp) values are also determined for the pure salts when these co-precipitate in mixed systems. Reaction kinetics for calcium sulfate crystallization is also highly sensitive to the ionic strength effect as well as to the presence and concentration of strontium ions. Accordingly, these observations confirm the need to account for both contributing and non-contributing ions in assessing the thermodynamics and kinetics of crystal formation.

Most current techniques for analyzing amino acids require substantial instrumentation and significant sample preprocessing. In this study, we designed, fabricated, and tested a scalable diode-based microdevice that allows for direct sensing of amino acids. The device is based on modulation-doped GaAs heterostructure with a Schottky contact on one side. The relatively high mobility and relatively small dielectric constant of GaAs are naturally helpful in this problem. We also paid attention to a proper etching procedure allowing for substantial modification of the surface properties, thereby further boosting the sensing performance. Transport data (I-V, differential conductance) are presented for three qualitatively different classes of amino acids (i.e., nonpolar with aliphatic R-group, polar uncharged R-group, and charged R-group) with glycine, cysteine, and histidine as specific examples, respectively. The conductance for the GaAs-amino acid interface measured using a scanning tunneling microscope (STM) was previously reported to have distinct spectral features. In this paper, we show that measuring the differential conductance of a GaAs diode, whose surface is in direct contact with an aqueous solution of amino acid, is a simple methodology to access useful information, previously available only through sophisticated and equipment-demanding STM and molecular electronics approaches. Density functional theory calculations were used to examine which adsorption processes were likely responsible for the observed surface conductance modification. Last, in future and ongoing work, we illustrate how it might be possible to employ standard multivariate data analysis techniques to reliably identify distinct (95 %) single amino acid specific features in near-ambient differential conductance data.

The co-doping effect of a rare earth (RE) metal and a transition metal (TM) on ceria oxidation catalysis through the evaluation of samarium-copper co-doped catalysts with Ce-Sm-xCu-O (x: 0–20 at.%, Ce/Sm = 1) nominal compositions, is discussed. The CO oxidation reaction was used as a prototype reaction due to its pivotal role in the fuel cell technology. Ce-Sm-20Cu-O catalyst presented a 64% increase in the CO oxidation activity compared to that of pristine ceria. Diffraction and Raman studies proved that the Cu, Sm co-doping induces many defects related to the dopants (Sm, Cu) and the oxygen vacant sites, while the presence of hybrid CuO/Ce-Sm(Cu)-O fluorite/SmO8 (cubic metastable) phases is the most representative scenario of this oxide microstructure. A size polydispersity of CuO phases was achieved by introducing air cooling during the microwave heating. Cu, Sm atoms were uniformly doped in CeO2 structure according to the HAADF-STEM studies. These results are in agreement with EDS analysis, where Cu, Sm and Ce are located in all the analyzed areas without any preferential distribution. The XPS studies demonstrated the co-presence of Cu2+/Cu1+ and Ce4+/Ce3+ redox couples in agreement with the Bader charge analysis from the ab initio calculations, the latter influencing greatly the oxidation activity of the catalysts. Density functional theory (DFT) calculations shed light on the oxide surface and the underlying mechanism governing the oxidation catalysis taking place. In particular, Cu2+ and Sm3+ dopants were found to be located in the nearest neighbor (NN) sites of oxygen vacancies. Different oxygen vacancies configurations were studied (single vs. double, surface vs. subsurface), where the single vacancies are more stable on the surface, whereas the double vacancies configurations are more stable on the subsurface. Regarding the Ce3+ location, in the presence of single and double oxygen vacancy, the Ce3+ ions prefer to be located in the 1st NN/2nd NN and 2nd NN of the first Ce layer, relative to the oxygen vacancy, respectively. The total Density of States (DOS) analysis of the co-doped systems revealed that the dopants induced new surface states inside the ceria band gap, which can accommodate the unpaired electrons of the vacant oxygen sites. These electronic modifications justify the much lower energy of oxygen vacancy formation (Evf) in both cases, the Sm-doped, and Cu, Sm -doped CeO2 (1 1 1) geometries. Specifically, the Evf lowering upon doping was found to be almost two times larger for the Cu adjacent oxygen vacancies (Cu2+-□) compared to the Sm ones (Sm3+-□), consistent with the CO adsorption trend as the Cu-Sm-CeO2 (1 1 1) system is energetically more favorable than the Sm-CeO2 (1 1 1) and pure CeO2 (1 1 1) surfaces.

(Ce-La-xCu)O2 catalysts with low (3 at.%) and high (10 at.%) Cu content were prepared by conventional microwave (MW) and enhanced microwave methods where air cooling (AC), while heating, was applied. The catalysts were tested for the CO oxidation reaction in the 25–500 °C range using 4%CO/20%O2/He feed gas. Varying spectroscopic, microscopic and catalytic studies were used to probe the effect of synthesis on the nanostructure and the CO oxidation performance. It was found that the synthesis method adopted impacts on the extent of the Cu doping into the (Ce-La)O2 fluorite lattice, hence leading to one and two phases system in the case of catalyst prepared through enhanced (AC) and conventional (MW) microwave methods, respectively. Furthermore, only Ce4+ species were found on the surface of the (Ce-La-10Cu)O2 catalysts synthesized using MW and AC (XPS studies), whereas oxygen vacant sites which are associated with Ce3+ ions were indicated in the sub-surface/bulk (Raman studies). Ultimately, the catalysts with the low and high Cu loading, prepared under the AC-promoted microwave method, presented a superior performance against CO oxidation, exhibiting an overall improvement of the catalytic activity by 16% and 32%, respectively. KP wouldlike to acknowledge the financial support from Abu Dhabi Educational Council (ADEC) through the ADEC 2015 Award for Research Excellence (ADEC B3111 ). KP thanks Khalifa University Core Nanocharacterization Facilities and acknowledges KU and CNCF staff support. AFZ and ASA acknowledges the support of the grant number NPRP 8-1912-1-354 from the Qatar National Research Fund (a member of Qatar Foundation). The microscopy works have been conducted in the �Laboratorio de Microscopias Avanzadas� at �Instituto de Nanociencia de Aragon - Universidad de Zaragoza�. VS acknowledges the LMA-INA for offering access to their instruments and expertise. CIBER-BBN is an initiative funded by the VI National R&D&i Plan 2008-2011 financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund . Scopus

Low cost, high sensitivity and stability are the key features that steer the research and development of glucose sensing. In this paper we report on a low cost metal-insulator- metal (MIM) based sensor that responds to different glucose concentrations. The unique planar Pt/CuO/Pt structure provides large electrochemically active surface area which aids glucose oxidation. The device shows sensitivity to different glucose concentrations, that span low to high blood glucose levels for typical concentrations found in human blood. The fabricated sensor exhibits the ability to detect the glucose concentration at neutral pH (i.e. pH = 7). This eliminates the dilution step needed for most of the existing nonenzymatic glucose sensors to achieve alkaline medium that is essential to perform redox reactions in the absence of glucose oxidase. Unlike the available devices, the fabricated MIM structure involves two metal electrodes in the interaction to improve the sensitivity of the device. This contribution provides new insights into design and fabrication of low cost biomedical sensors.

Nanofluids used in low-flux direct absorption solar collectors (DASCs) typically encounter critical stability issues due to long-term storage, elevated temperatures, high particle concentrations, and fouling from free surfactants. Here, we developed ultrastable nanofluids, and their properties were used to computationally optimize DASC designs. Broadband photothermal absorption was achieved using citrate- (CIT-) and polyethylene glycol-coated (PEG-) gold nanoparticles, circumventing the need for free surfactants. The nanofluids were subjected to long-term ambient storage, high particle concentrations, and incremental heating to analyze their stability and utility in DASCs. Electrosteric stabilization (PEG + CIT) provided superior colloidal stability and more consistent optical properties; chemical and colloidal stability was verified for 16 months, the longest demonstration of stable nanofluids under ambient storage in the solar literature. Optical measurements of the stabilized solar nanofluids were fed into a DASC optimization model. A constrained generalized pattern search (GPS) algorithm simultaneously maximized collector thermal power-gain and minimized nanoparticle mass loading, while maintaining a collector temperature-gain target. Ultimately, by simultaneously developing ultrastable solar nanofluids, minimizing nanoparticle loading requirements, and maximizing collector thermal power gain, the outcomes from this study are considered significant steps towards deploying efficient and reliable low-flux, nanofluid-based DASCs in field applications.

Hydrophilic interaction LC was investigated in hydro-organic and nonaqueous elution modes on a titania column by using a set of N-methyl xanthines as neutral polar probes. To get information regarding the mechanisms that are behind the discrimination of these analytes in hydrophilic interaction, we focused our study on the type and amount of organic modifier as a critical yet rarely explored mobile phase parameter. Several alcohols such as methanol, ethanol, and isopropanol were studied as substitutes to acetonitrile in hydro-organic elution mode. Compared to silica, the investigation of the eluotropic series of these alcohols on titania highlighted a different implication in the retention mechanism of the xanthine derivatives. At low amounts of protic solvents, the adsorption mainly characterized the retention of analytes on bare silica; whereas mixed interactions including adsorption and ligand exchange were identified on native titania. To investigate the peculiar behavior of alcohols on the metal oxide, methanol, ethanol, and ethylene glycol were tested in replacement of water in polar-organic elution mode. Distinctive effects on the chromatographic retention and selectivity of xanthines were noticed for the dihydric alcohol, which was found to be a stronger eluting component than water on titania.

A rewritable micro-thick low power memristor device is presented. The memristor is fabricated based on a novel structure that is composed of Al/TiO 2 /Cu. The device switches at 3X lower voltage compared to the existing bipolar memristor state of the art at the microscale. The fabricated device exhibits unique I-V characteristic among similar devices when operated without prior electroforming. Thus, a new secure communication technique is proposed based on the existence of third trust party (TTP). As each host has unique memristor device, messages can be encrypted and decrypted securely using memristor based keys. In addition, Scyther analysis are provided to prove the security of the proposed technique. This work takes advantage of the inherited variation of memristor device electric characteristics to strengthen security algorithm in cryptographic application.

This paper describes the synthesis of micro-thick hafnium-oxide (∼ 60 μm) memristors using a low-cost sol-gel drop-coating technique, and emphasizes on key parameters to be considered in the development of the microscale technology. The impact of electrode material on the device I-V electrical behavior is screened with the use of different metals, with different work-functions and oxygen affinities such as aluminum (Al), copper (Cu), titanium (Ti) and palladium (Pd) under a symmetric metal-insulator-metal arrangement. The type of metal contact was found to play a vital role in the switching behavior of the devices, highlighting a potential chemical interplay between the drop-coating solution and the electrode surface during the fabrication process. The effect of the sol-gel drying temperature on the I-V curve characteristics is also investigated with similar devices made at 60 °C and 80 °C. For example, the R off /R on ratio of Al/Al-type memristors was found to increase by approximately nine folds when the drying temperature was increased from 60 °C to 80 °C. As depicted from the changes observed in the maximum flowing current within an I-V curve, the drying temperature was generally found to mainly affect the internal resistance of the devices, allowing external control over the R off /R on ratio.

In recent years, metal oxides such as titania have been commercially available as chromatographic beds that can potentially be used to achieve novel separations of polar compounds. For example beta blockers, which are more often encountered in environmental sciences, have a wide range of polarity, and their basic character leads to difficult sample treatment and separation on conventional silica-based sorbents. The contribution of titania to the selective analysis of nine beta blockers was evaluated in terms of retention mechanisms observed in hydrophilic interaction LC using acetonitrile/water mobile phases with various additives. The mobile phase additives enabled to control the beta blocker charge as well as the titania surface charge. Depending on their respective ionic state, various retention mechanisms were identified at low water contents (

Memristors are one of the emerging technologies that can potentially replace state-of-the-art integrated electronic devices for advanced computing and digital and analog circuit applications including neuromorphic networks. Over the past few years, research and development mostly focused on revolutionizing the metal oxide materials, which are used as core components of the popular metal-insulator-metal memristors owing to their highly recognized resistive switching behavior. This paper outlines the recent advancements and characteristics of such memristive devices, with a special focus on (i) their established resistive switching mechanisms and (ii) the key challenges associated with their fabrication processes including the impeding criteria of material adaptation for the electrode, capping, and insulator component layers. Potential applications and an outlook into future development of metal oxide memristive devices are also outlined.

International audience; A design of experiement approach is described for the optimization of the microscopic morphology of macro-mesoporous titania monoliths that were elaborated for the chromatographic enrichment of phosphorylated compounds. The monolithic titania gels were formed via an alkoxy-derived sol-gel route in association with a phase separation mechanism. The synthesis was performed at mild temperatures of gelation using starting mixtures of titanium n-propoxide, hydrochloric acid, N-methylformamide, water, and poly (ethylene oxide). The gelation temperature and the chemical compositions of N-methylformamide, water, and poly (ethylene oxide) were chosen as the most relevant experimental factors of the sol-gel process. Using the sizes of the skeletons and macropores as morphological descriptors of the dried porous monoliths, the statistical analyses simultaneously revealed the effects and interactions between the different factors. Crack-free TiO2 monolithic rods of 8 to 10 cm long with well-defined co-continuous macropores and micro-structured skeletons were obtained after selection of the sol-gel parameters and optimization of the drying and heat-treatment steps of the gels. The bimodal texture of the rods exhibited macropores of 1.5 mu m and mesopores centered at 5.2 nm with a total surface area of 140 m(2) g(-1). The ability of the macro-mesoporous titania rods to selectively bind phosphorylated compounds was demonstrated for O-phosphoamino acids (P-Ser, P-Thr, P-Tyr).

International audience; A new sol-gel protocol was designed and optimized to produce titanium-dioxide-based columns within confined geometries such as monolithic capillary columns and porous-layer open-tubular columns. A surface pre-treatment of the capillary enabled an efficient anchorage of the monolith to the silica capillary wall during the synthesis. The monolith was further synthesized from a solution containing titanium n-propoxide, hydrochloric acid, N-methylformamide, water, and poly(ethylene oxide) as pore template. The chromatographic application of capillary titania-based columns was demonstrated with the separation of a set of phosphorylated nucleotides as probe molecules using aqueous normal-phase liquid chromatography conditions. Capillary titania monoliths offered a compromise between the high permeability and the important loading capacity needed to potentially achieve miniaturized sample preparations. The specificity of the miniaturized titania monolithic support is illustrated with the specific enrichment of 5'-adenosine mono-phosphate. The monolithic column offered a ten times higher loading capacity of 5'-adenosine mono-phosphate compared with that of the capillary titania porous-layer open-tubular geometry.

International audience; The chromatographic behavior of native titania was investigated in aqueous normal phase chromatography using a set of N-methylated xanthines as polar test solutes. In agreement with a hydrophilic interaction on a polar bed, the retention of xanthine models increased mainly along their molecular polarity. Adsorption of these molecules on the hydrated surface of titania prevailed as a retention mechanism for low water contents in the mobile phase. Several N-methylated xanthines could be easily discriminated along the number and position of their methyl groups while the nitrogen atom at position 3 was found deeply involved in the retention on titania. To get further insights on the interactions occurring on the surface of titania, the retention of xanthine derivatives based on ligand-exchange was evaluated as a function of the buffer concentration and type. The separation efficiency of native titania for the set of N-methylated xanthines was comparable to that observed on zirconia but lower than that obtained on native silica due to mixed-mode interactions. However, titania exhibited a superior ability to recognize several isomeric positions of xanthine derivatives in comparison to zirconia and silica.