A method to form and manipulate the properties of nanometer-size liquid bridges by an external electric field is discussed. The properties of bridges are shown to be the result of an interplay among the field-induced polarization of the water layer adsorbed on the surface, the surface energy, and the water condensation from the humid air. For a given tip-sample separation, a simple model predicts the existence of a threshold voltage V(th) to form the bridge in full agreement with experiments.
A detailed analysis of electrostatic interactions between a dc-biased tip and a metallic or insulating sample is presented. By using a simple method to calculate capacitances and forces, tip shape effects on the force versus tip-sample distance curves are dicussed in detail. For metallic samples the force law, except for a constant background, only depends on the tip radius of curvature. In contrast, for dielectric samples the forces depend on the overall geometry of the tip. Interestingly, we found that the contact (adhesion) force does not depend on the tip size and is bound by a simple expression which only depends on the applied bias and the sample dielectric constant.
A detailed analysis of electrostatic interactions between a
dc-biased tip and a metallic or insulating sample is presented.
For inhomogeneous thin dielectric films, the scanning probe
signal is shown to be proportional to the convolution between an
effective surface profile and a response function of the
microscope. Based on the properties of the response function,
tip-shape effects on the lateral resolution in electrostatic
force microscopy are discussed. For tip-sample distances D
smaller than the tip radius R, the resolution is found to be
proportional to (DR)1/2.
Abstract. A theoretical approach to electrostatic scanning probe microscopy is presented. We show that a simple perturbation formula, originally derived in the context of scattering theory of electromagnetic waves, can be used to obtain the capacitance and the electrostatic force between a metallic tip and an inhomogeneous dielectric sample. For inhomogeneous thin dielectric films, the scanning probe signal is shown to be proportional to the convolution between an effective surface profile and a response function of the microscope. This provides a rigorous framework to address the resolution issue and the inverse problem.
We present a study
of the effect of gold nanoparticles (Au NPs)
on TiO
2
on charge generation and trapping during illumination
with photons of energy larger than the substrate band gap. We used
a novel characterization technique, photoassisted Kelvin probe force
microscopy, to study the process at the single Au NP level. We found
that the photoinduced electron transfer from TiO
2
to the
Au NP increases logarithmically with light intensity due to the combined
contribution of electron–hole pair generation in the space
charge region in the TiO
2
–air interface and in the
metal–semiconductor junction. Our measurements on single particles
provide direct evidence for electron trapping that hinders electron–hole
recombination, a key factor in the enhancement of photo(electro)catalytic
activity.
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