Photovoltaic and photothermal effects induced by visible laser radiation in atomic force microscopy probes.

Excitation of electrons into higher energy states in solid state materials can be induced by absorption of visible light, a physical process generally studied by optical absorption spectroscopy. A promising approach for improving the spatial resolution of optical absorption spectroscopy beyond the diffraction limit is the detection of photoinduced forces by an atomic force microscope operating under wavelength-dependent light irradiation. Here, we report on a combined photovoltaic/photothermal effect induced by the absorption of visible light by the microscope probes.

Photonic Excitation of a Micromechanical Cantilever in Electrostatic Fields.

We present a specific near-field configuration where an electrostatic force gradient is found to strongly enhance the optomechanical driving of an atomic force microscope cantilever sensor. It is shown that incident photons generate a photothermal effect that couples with electrostatic fields even at tip-surface separations as large as several wavelengths, dominating the cantilever dynamics. The effect is the result of resonant phenomena where the photothermal-induced parametric driving acts conjointly (or against, depending on electric field direction) with a photovoltage generation in the cantilever.

From Chains to Monolayers: Nanoparticle Assembly Driven by Smectic Topological Defects.

In this Letter, we show how advanced hierarchical structures of topological defects in the so-called smectic oily streaks can be used to sequentially transfer their geometrical features to gold nanospheres. We use two kinds of topological defects, 1D dislocations and 2D ribbon-like topological defects. The large trapping efficiency of the smectic dislocation cores not only surpasses that of the elastically distorted zones around the cores but also surpasses the one of the 2D ribbon-like topological defect.

Magnetic force fields of isolated small nanoparticle clusters.

The usage of magnetic nanoparticles (NPs) in applications necessitates a precise mastering of their properties at the single nanoparticle level. There has been a lot of progress in the understanding of the magnetic properties of NPs, but incomparably less when interparticle interactions govern the overall magnetic response. Here, we present a quantitative investigation of magnetic fields generated by small clusters of NPs assembled on a dielectric non-magnetic surface.

Nonlinear Phase Imaging of Gold Nanoparticles Embedded in Organic Thin Films.

The phase detection in the dynamic mode of the atomic force microscopes is a known technique for mapping nanoscale surface heterogeneities. We present here an additional functionality of this technique, which allows high-resolution imaging of embedded inorganic nanoparticles with diameter and interparticle distances of a few nanometers. The method is based on a highly nonlinear tip-sample interaction occurring markedly above the nanoparticles, giving thus a high phase contrast between zones with and without nanoparticles.