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.