The probe-surface interaction underlying the ‘‘shear-force’’ distance control commonly used in near-field microscopy has been studied in detail by measuring dither resonance profiles and approach curves in vacuum and liquid helium. Simulations based on a nonlinear oscillator model considering the probe geometry, its elastic properties, adiabatic short-range probe-surface contact, and the surface tilt angle, are in excellent agreement with the experiments. We prove conclusively that a nonlinear bending force mechanism with parametric mode conversion is responsible for the observed phenomena.

Hydroxyapatite nanocrystals in natural form are a major component of bone- a known piezoelectric material. Synthetic hydroxyapatite is widely used in bone grafts and prosthetic pyroelectric coatings as it binds strongly with natural bone. Nanocrystalline synthetic hydroxyapatite films have recently been found to exhibit strong piezoelectricity and pyroelectricity. While a spontaneous polarization in hydroxyapatite has been predicted since 2005, the reversibility of this polarization (i.e. ferroelectricity) requires experimental evidence. Here we use piezoresponse force microscopy to demonstrate that nanocrystalline hydroxyapatite indeed exhibits ferroelectricity: a reversal of polarization under an electrical field. This finding will strengthen investigations on the role of electrical polarization in biomineralization and bone-density related diseases. As hydroxyapatite is one of the most common biocompatible materials, our findings will also stimulate systematic exploration of lead and rare-metal free ferroelectric devices for potential applications in areas as diverse as in vivo and ex vivo energy harvesting, biosensing and electronics.

Fast highly-sensitive room-temperature semiconductor gas sensor based on the nanoscale Pt-TiO 2 -Pt sandwich, Sensors and Actuators B: Chemical (2014), http://dx. AbstractDevelopment of fast highly-sensitive semiconductor gas sensors operating at room temperature, which would be compatible with semiconductor technology, remains a challenge for researchers.Here we present such sensor based on a nanoscale Pt-TiO 2 -Pt sandwich. The sensor consists of a thin (~30 nm) nanocrystalline TiO 2 layer with ~10 nm grains, placed between the bottom Pt electrode layer and top Pt electrode shaped as a long narrow (width w down to 80 nm) stripe. If we decrease w to ~100 nm and below, the sensor exposed to air with 1% H 2 exhibits the increase of response (R air / ) up to ~ 10 7 and decrease of the reaction time to only a few seconds even at room temperature. The sensitivity increase is due to a nontrivial non-ohmic effect, a sudden decrease (by three orders of magnitude) of the electrical resistance with decreasing w for w ~ 100nm. This non-ohmic effect is explained as a consequence of two nanoscale-related effects: the hydrogen-diffusion-controlled spatially-inhomogeneous resistivity of the TiO 2 layer, combinedPage 2 of 41 A c c e p t e d M a n u s c r i p t 2 with onset of the hot-electron-temperature instability when the tiny grains are subjected to high electric field.

Hydroxyapatite (HA) is the major component of bone and is used in artificial form in many biomedical applications. It was once believed to have a centrosymmetric crystal structure. In theoretical and experimental studies published in 2005, it was shown to have a monoclinic P21 structure. In the work reported here, 500 nm films of HA were spin-coated on silicon wafers. The materials were not poled. They had a nonuniform polarization distribution and exhibited pyroelectricity, piezoelectricity, and photoeffects. Structures of this type may have a number of technological applications.