Multistate resistive switching in silver nanoparticle films.

Resistive switching devices have garnered significant consideration for their potential use in nanoelectronics and non-volatile memory applications. Here we investigate the nonlinear current-voltage behavior and resistive switching properties of composite nanoparticle films comprising a large collective of metal-insulator-metal junctions. Silver nanoparticles prepared via the polyol process and coated with an insulating polymer layer of tetraethylene glycol were deposited onto silicon oxide substrates. Activation required a forming step achieved through application of a bias voltage. Once activated, the nanoparticle films exhibited controllable resistive switching between multiple discrete low resistance states that depended on operational parameters including the applied bias voltage, temperature and sweep frequency. The films' resistance switching behavior is shown here to be the result of nanofilament formation due to formative electromigration effects. Because of their tunable and distinct resistance states, scalability and ease of fabrication, nanoparticle films have a potential place in memory technology as resistive random access memory cells

Multicomponent bionanocomposites based on clay nanoarchitectures for electrochemical devices

Based on the unique ability of defibrillated sepiolite (SEP) to form stable and homogeneous colloidal dispersions of diverse types of nanoparticles in aqueous media under ultrasonication, multicomponent conductive nanoarchitectured materials integrating halloysite nanotubes (HNTs), graphene nanoplatelets (GNPs) and chitosan (CHI) have been developed. The resulting nanohybrid suspensions could be easily formed into films or foams, where each individual component plays a critical role in the biocomposite: HNTs act as nanocontainers for bioactive species, GNPs provide electrical conductivity (enhanced by doping with MWCNTs) and, the CHI polymer matrix introduces mechanical and membrane properties that are of key significance for the development of electrochemical devices. The resulting characteristics allow for a possible application of these active elements as integrated multicomponent materials for advanced electrochemical devices such as biosensors and enzymatic biofuel cells. This strategy can be regarded as an "a la carte" menu, where the selection of the nanocomponents exhibiting different properties will determine a functional set of predetermined utility with SEP maintaining stable colloidal dispersions of different nanoparticles and polymers in water

Strong Electron Confinement By Stacking-fault Induced Fractional Steps on Ag(111) Surfaces

The electron reflection amplitude $R$ at stacking-fault (SF) induced fractional steps is determined for Ag(111) surface states using a low temperature scanning tunneling microscope. Unexpectedly, $R$ remains as high as $0.6 \sim 0.8$ as energy increases from 0 to 0.5 eV, which is in clear contrast to its rapidly decreasing behavior for monatomic (MA) steps [L. B{\"u}rgi et al., Phys. Rev. Lett. \textbf{81}, 5370 (1998)]. Tight-binding calculations based on {\em ab-initio} derived band structures confirm the experimental finding. Furthermore, the phase shifts at descending SF steps are found to be systematically larger than counterparts for ascending steps by $\approx 0.4 \pi$. These results indicate that the subsurface SF plane significantly contributes to the reflection of surface states

Electrochemical nanoarchitectonics through polyaminobenzylamine-dodecyl phosphate complexes: Redox activity and mesoscopic organization in self-assembled nanofilms

Molecular design and preparation of redox active films displaying mesoscopic levels of organization represents one of the most actively pursued research areas in nanochemistry. These mesostructured materials are not only of great interest at the fundamental level because of their unique properties but they can also be employed for a wide range of applications such as electrocatalysts, electronic devices, and electrochemical energy conversion and storage. Herein, we introduce a simple and straightforward strategy to chemically modify electrode surfaces with self-assembled electroactive polyelectrolyte-surfactant complexes. These assemblies are composed of amino-appended polyaniline and monododecyl phosphate. The complexes were deposited by spin-coating and the films were characterized by spectroscopic and X-ray-based techniques: XRR, GISAXS, WAXS, and XPS. The films presented a well-defined lamellar structure, directed by the strong interaction between the phosphate groups and the positively charged amine groups in the polyelectrolyte. These films also displayed intrinsic electroactivity in both acidic and neutral solutions, showing that the polymer remains electroactive and ionic transport is still possible through the stratified and hydrophobic coatings. The stability and enhanced electroactivity in neutral solutions make these assembled films promising building blocks for the construction of nanostructured electrochemical platforms.Fil: Lorenzo, Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Marmisollé, Waldemar Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Maza, Eliana María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Ceolin, Marcelo Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Azzaroni, Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin

Locality and lateral modulations of quantum well states in Ag(100) thin films studied using a scanning tunneling microscope

We investigate Ag(100) thin films epitaxially grown on a Fe(100) substrate using a low-temperature scanning tunneling microscope. Fabrication of a wedge structure by evaporating Ag through a shadow mask allows us to observe systematic evolution of quantum well (QW) states for layer thicknesses varying from 3 to 16 monolayers (ML). Close inspection of differential conductance spectra and images reveal significant modulations of QW states in the lateral directions, presumably due to the local defects at the Ag/Fe interface. The area where QW states are modulated extends over ~ 5 nm. In clear contrast, near a surface atomic step, QW states exhibit negligible changes at least up to 1 nm away from the step, leaving unmixed the two sets of neighboring QW states belonging to different thicknesses. The results are discussed in terms of a simple electron wave diffraction model.Comment: 17 pages, 5 figure

Tuning the van der Waals Interaction of Graphene with Molecules via Doping

We use scanning tunneling microscopy to visualize and thermal desorption spectroscopy to quantitatively measure that the binding of naphthalene molecules to graphene (Gr), a case of pure van der Waals (vdW) interaction, strengthens with $n$- and weakens with $p$-doping of Gr. Density functional theory calculations that include the vdW interaction in a seamless, ab initio way accurately reproduce the observed trend in binding energies. Based on a model calculation, we propose that the vdW interaction is modified by changing the spatial extent of Gr's $\pi$ orbitals via doping