A number of important commercial applications would benefit from the introduction of easily manufactured devices that exhibit current-controlled, or “S-type,” negative differential resistance (NDR). A leading example is emerging non-volatile memory based on crossbar array architectures. Due to the inherently linear current vs. voltage characteristics of candidate non-volatile memristor memory elements, individual memory cells in these crossbar arrays can be addressed only if a highly non-linear circuit element, termed a “selector,” is incorporated in the cell. Selectors based on a layer of niobium oxide sandwiched between two electrodes have been investigated by a number of groups because the NDR they exhibit provides a promisingly large non-linearity. We have developed a highly accurate compact dynamical model for their electrical conduction that shows that the NDR in these devices results from a thermal feedback mechanism. A series of electrothermal measurements and numerical simulations corroborate this model. These results reveal that the leakage currents can be minimized by thermally isolating the selector or by incorporating materials with larger activation energies for electron motion.

Reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), vibrating sample magnetometry, and other physical property measurements are used to investigate the structure, morphology, magnetic, and magnetotransport properties of (001)-oriented Cr2Te3 thin films grown on Al2O3(0001) and Si(111)-(7×7) surfaces by molecular beam epitaxy. Streaky RHEED patterns indicate flat smooth film growth on both substrates. STM studies show the hexagonal arrangements of surface atoms. Determination of the lattice parameter from the atomically resolved STM image is consistent with the bulk crystal structures. Magnetic measurements show the film is ferromagnetic, having a Curie temperature of about 180 K, and a spin glass-like behavior was observed below 35 K. Magnetotransport measurements show the metallic nature of the film with a perpendicular magnetic anisotropy along the c-axis.

We report here the study of two-photon induced luminescence of 11-mercaptoundecanoic acid functionalized quantum-sized Au nanodots (11MUA-Au nanodots). The X-ray absorption near-edge structure (XANES) measurement at the gold L III edge indicates that the oxidation state of the surface of 11MUA-Au nanodots is best described as Au + . The two-photon absorption (TPA) property of 11MUA-Au nanodots was then investigated via an open aperture Z-scan method. Together with a precise extinction coefficient (i.e., onephoton absorption) extracted from inductively coupled plasma mass spectrometry, the TPA cross section, σ, was deduced to be 8761 ( 175 GM (800 nm) for 11MUA-Au nanodots (diameter 1.33 ( 0.12) in water. Upon dextran encapsulation, 11MUA-Au nanodots was proved to be highly water-soluble, stable, and low in toxicity, which demonstrated its power in two-photon imaging toward human mesenchymal stem cells (hMSCs) in vitro.

A memristor is a two-terminal 'memory resistor' electronic device, in which a metal oxide switching layer is sandwiched between two metal electrodes [1][2][3][4]. In general, memristors offer non-linear switching characteristics, and materials and process compatibility with advanced silicon manufacturing. These attributes have spurred the exploration of memristors as synaptic devices for realizing spike-based hardware learning systems that are capable of processing unstructured, temporal data [5][6][7][8][9][10]. However, for memristor-based technologies to be viable, the device should exhibit several key characteristics. It should have a compact nanoscale footprint, operate at a voltage close to 1V that is compatible with complementary metal oxide semiconductor (CMOS) technology, have reproducible electrical characteristics, and possess high switching speed to minimize the energy consumption [11]. Furthermore, the hardware integration of synaptic connections in advanced neural networks requires memristors with multiple resistive states [12,13]. These are challenging requirements and are difficult to implement without significant innovations.The phenomenological principle of memristor device operation is based on the change in the physical properties of a conductive filament (associated with the presence of oxygen vacancies) by applying an electric field across the metal oxide switching layer [14][15][16]. The resulting motion of the oxygen vacancies alters the device resistance between low (Set) and high (Reset) states, depending on the direction and the amplitude of the electric field. So far, a variety of structures from a large set of materials (various metal oxide switching layers and metal electrodes) have been studied in the literature [4,17,18]. Several key findings can be drawn from those studies regarding the performance, energy and scalability of this type of devices. The most important finding reveals the trade-off between the switching energy and the data retention time-that is often referred to as voltage-time dilemma [19]. This trade-off is associated with the energy barrier of the device structure. For example, devices made of metal oxides with small energy bandgap (E g ), such as titanium oxide (TiO x , E g~3 .4eV), generally exhibit low operating voltage and compromised data retention [20], while those with large bandgap, such as hafnium oxide (HfO x , E g~5 .4eV) demonstrate the opposite [21]. However, the fabrication of devices with bilayer switching stacks has shown to be effective in mitigating this trade-off. In particular, the improvement in data retention was obtained by the incorporation of an ultra-thin wide bandgap metal oxide capping layer (for example aluminum oxide) [22]. On the other hand, the addition of a reactive capping metal (for example titanium, hafnium, etc.) as an oxygen scavenging layer provided a pathway for reducing the operating voltage of the devices [23,24]. Despite significant advances, a sub-1V memristive device that simultaneously affords built-in analog behavior...

Performance stability and functional reliability in bipolar resistive switching of bilayer ceria based resistive random access memory devices Dual operation characteristics of resistance random access memory in indium-gallium-zinc-oxide thin film transistors Appl. Phys. Lett.Electrical characteristics and carrier transport mechanisms of write-once-read-many-times memory elements based on graphene oxide diodes

No abstract

In an aim to harvest UV-near-visible (360-440 nm) photons as well as to increase the morphology in the bulk heterojunction solar cells, we report herein the strategic design, synthesis, and characterization of a novel excited-state intramolecular proton-transfer dye, 3-hydroxy-2-(5-(5-(5-(3-hydroxy-4-oxo-4H-chromen-2-yl)thiophen-2-yl)thiophen-2-yl)thiophen-2-yl)-4H-chromen-4-one (FT), which bears two key functional groups, namely 3-hydroxychromone chromophore and trithiophene backbone and is then exploited into the blends of regioregular poly(3-hexylthiophene) (RR-P3HT) and phenyl-C(61)-butyric acid methyl ester (PCBM). FT acts as an excellent UV-near visible absorber, which then undergoes excited-state intramolecular proton transfer, giving rise to an orange-red proton-transfer emission that was reabsorbed by P3HT via a Forster type of energy transfer. Introduction of FT to P3HT/PCBM blend films also improves the morphology of phase separated structure, in particular, enhances the interaction of P3HT chains and the hole mobility. In this work, under the optimized condition of P3HT: PCBM:FT of 15:9:2 in weight ratio, the best performance of the device B-FT2 revealed consistent enhancements in the efficiency (eta) 4.28% and short-circuit current (J(sc)) 12.53 mAcm(-2), which are higher than that (3.68% and 10.28 mAcm(-2)) of the best performance of the control device B (P3HT:PCBM 15:9 in weight ratio) by 16 and 22%, respectively.

No abstract