Atomic structure and charge-density waves of blue bronze K0.3MoO3 (20[overline 1]) by variable-temperature scanning tunneling microscopy

Blue bronze (K0.3MoO3) has been the focus of a number of scattering, transport, scanning tunneling microscopy (STM), and theoretical studies that have provided insight into the relation between atomic structure and charge-density wave (CDW) formation. However, the full extent of a relation of the CDWs to the atomic lattice and the microscopic origin of CDW pinning are still not completely resolved. In this study STM is used to distinguish the atomic structure and CDWs at the (201) surface. Within the STM\u27s spatial resolution, the CDWs are incommensurate with the lattice at midrange temperatures and approach commensurability at low temperatures. Incommensurate CDWs are present on the surface and the degree of the incommensurability between blue bronze lattice and CDW lattice agree well with those determined from bulk scattering technique

Photo-induced Charge Dynamics on BaTIO\u3csub\u3e3\u3c/sub\u3e (001) Surface Characterized by Surface Probe Microscopy

The surface potential of a multidomain BaTiO3 (001) surface was imaged in the presence and absence of ultraviolet (UV) illumination. The UV radiation induces a decrease in the surface potential contrast between c+ and c− domains with a time constant of a few seconds due to redistribution of photocarriers and screening. A slower process of recovery was observed after illumination. In addition, scanning a conducting atomic force microscopy tip in contact under UV illumination destabilizes some ferroelectric domains

Probing Polarization and Dielectric Function of Molecules with Higher Order Harmonics in Scattering-near-field Scanning Optical Microscopy

The idealized system of an atomically flat metallic surface [highly oriented pyrolytic graphite (HOPG)] and an organic monolayer (porphyrin) was used to determine whether the dielectric function and associated properties of thin films can be accessed with scanning–near-field scanning optical microscopy (s-NSOM). Here, we demonstrate the use of harmonics up to fourth order and the polarization dependence of incident light to probe dielectric properties on idealized samples of monolayers of organic molecules on atomically smooth substrates. An analytical treatment of light/ sample interaction using the s-NSOM tip was developed in order to quantify the dielectric properties. The theoretical analysis and numerical modeling, as well as experimental data, demonstrate that higher order harmonic scattering can be used to extract the dielectric properties of materials with tens of nanometer spatial resolution. To date, the third harmonic provides the best lateral resolution(~50 nm) and dielectric constant contrast for a porphyrin film on HOPG

An Electrochemical Method for CuO Thin Film Deposition from Aqueous Solution

An electrochemical procedure is described for the anodic deposition of CuO thin films from solution precursors at 25-30°C in an alkaline medium (pH \u3e 13). The deposition bath was similar to Fehling\u27s solution using tartrate ions as a complexing agent for Cu(II). Cupric oxide deposited onto a platinum substrate at an anodic current density of 5 mA cm-2 has a preferred orientation of [010]. Rietveld refinement of the powder diffraction pattern reveals pure Cu(II) oxide with no trace of other copper oxides. The suggested mechanism involves the irreversible electrochemical oxidation of the tartrate ligand of the Cu(II) complex leading to the CuO precipitation. The same bath can also be used to deposit Cu₂O films using a cathodic electrodeposition process. In this case, cuprous oxide deposited onto a platinum electrode has a [111] preferred orientation

Supramolecular Conjugated Block Copolymers

While the performance of polymer–polymer bulk heterojunction organic photovoltaics (OPVs) is poor compared with polymer–fullerene OPVs, reducing or eliminating micrometer-scale phase separation in all-polymer OPVs may dramatically improve performance. Herein, we demonstrate that 2-ureido-4­[1<i>H</i>]-pyrimidinone (UPy) quadruple hydrogen bonding interactions can be used to prevent micrometer-scale phase separation at temperatures and processing conditions typically used to prepare bulk heterojunction OPVs. UPy-terminated polymers are synthesized by coupling hydroxyl or primary amine terminated polymers to a reactive isocyanate–UPy group in a one-step reaction. Polymer blend films are subsequently prepared by solution blending, casting onto a surface, and thermal and/or solvent annealing. Film microstructure including the presence of phase-separated domains and polymer crystallinity is analyzed by optical microscopy, atomic force microscopy (AFM), and grazing-incidence wide-angle X-ray scattering (GIWAXS). In contrast to unmodified polymer blends, blends of UPy-terminated polymers do not exhibit micrometer-scale phase separation after extended thermal annealing. AFM reveals the presence of crystalline nanofibers and, in some cases, 100–300 nm phase-separated domains in UPy-mediated polymer blends. Fluorescence measurements indicate that UPy modification increases fluorescence quenching in solutions of donor and acceptor polymers, due to hydrogen-bonding associations which reduce the average distance for energy and/or electron transfer. These results show that UPy-mediated interactions can suppress micrometer-scale phase separation in bulk heterojunction polymer blends at temperatures and processing conditions typically used to prepare bulk-heterojunction OPVs. As a result, UPy functionalization may be a powerful route for improving the performance of all-polymer OPVs

Enantiospecific Electrodeposition of Chiral CuO Films from Copper(II) Complexes of Tartaric and Amino Acids on Single-Crystal Au(001)

Chiral films of CuO were electrochemically deposited onto achiral Au(001) using chiral precursors such as tartaric acid and the amino acids alanine and valine to complex the Cu(II). The chirality of the electrodeposited films was dictated by the chiral solution precursor. X-ray diffraction pole figures and azimuthal scans, in conjunction with stereographic projections, were used to determine the absolute configuration and enantiomeric excess of the chiral CuO films. CuO films grown from L-tartaric acid have a (1) orientation with an enantiomeric excess of 95%, while the films grown from D-tartaric acid have a (11) orientation with an enantiomeric excess of 93%. CuO films grown from chiral amino acids have two types of chiral orientations, each showing lower enantiomeric excess compared with the films deposited from tartaric acid. The films grown from L-alanine and L-valine solution have an excess of the (11) and () orientations, while the films grown from D-alanine and D-valine have an excess of (1) and (111). Films of CuO deposited from a solution of achiral glycine consist of a racemic mixture of the (11) and (1) orientations. Chiral CuO films deposited on both single-crystal Au(001) and polycrystalline Au films were shown to exhibit chiral recognition for the electrochemical oxidation of tartaric acid

Radio frequency radiation-induced hyperthermia using Si nanoparticle-based sensitizers for mild cancer therapy

International audienceOffering mild, non-invasive and deep cancer therapy modality, radio frequency (RF) radiation-induced hyperthermia lacks for efficient biodegradable RF sensitizers to selectively target cancer cells and thus avoid side effects. Here, we assess crystalline silicon (Si) based nanomaterials as sensitizers for the RF-induced therapy. Using nanoparticles produced by mechanical grinding of porous silicon and ultraclean laser- ablative synthesis, we report efficient RF-induced heating of aqueous suspensions of the nanoparticles to temperatures above 45-50 degrees C under relatively low nanoparticle concentrations (< 1 mg/mL) and RF radiation intensities (1-5 W/cm(2)). For both types of nanoparticles the heating rate was linearly dependent on nanoparticle concentration, while laser-ablated nanoparticles demonstrated a remarkably higher heating rate than porous silicon-based ones for the whole range of the used concentrations from 0.01 to 0.4 mg/mL. The observed effect is explained by the Joule heating due to the generation of electrical currents at the nanoparticle/water interface. Profiting from the nanoparticle-based hyperthermia, we demonstrate an efficient treatment of Lewis lung carcinomain in vivo. Combined with the possibility of involvement of parallel imaging and treatment channels based on unique optical properties of Si-based nanomaterials, the proposed method promises a new landmark in the development of new modalities for mild cancer therapy