Charge distribution from SKPM images.

Inferring the surface charge distribution from experimental Kelvin probe microscopy measurements is usually a hard task. Although several approximations have been proposed in order to estimate the effect of these charges, the real inverse problem has not been addressed so far. In this paper, we propose a fast and intuitive method based on Fast Fourier Transform algorithms that allows the surface charge distribution to be obtained directly from the experimental Kelvin voltage measurements. With this method, quantitative physical information such as the total charge and charge position is accessible even in complex charge distributions such as highly insulating polymer surfaces. Moreover, one of the strongest points is that sub-tip resolution is achieved, and therefore the usually unknown charge size can be estimated.

Localized charge imaging with scanning Kelvin probe microscopy.

In this work, we propose an intuitive and easily implementable approach to model and interpret scanning Kelvin probe microscopy images of insulating samples with localized charges. The method, based on the image charges method, has been validated by a systematic comparison of its predictions with experimental measurements performed on charge domains of different sizes, injected in polymethyl methacrylate discontinuous films. The agreement between predictions and experimental lateral profiles, as well as with spectroscopy tip-sample distance curves, supports its consistency. The proposed procedure allows obtaining quantitative information such as total charge and the size of a charge domain and allows estimating the most adequate measurement parameters.

Nanoscale surface photovoltage of organic semiconductors with two pass Kelvin probe microscopy.

Kelvin probe microscopy implemented with controlled sample illumination is used to study nanoscale surface photovoltage effects. With this objective a two trace method, where each scanning line is measured with and without external illumination, is proposed. This methodology allows a direct comparison of the contact potential images acquired in darkness and under illumination and, therefore, the surface photovoltage is simply inferred. Combined with an appropriate data analysis, the temporal and spatial evolution of reversible and irreversible photo-induced processes can be obtained. The potential and versatility of this technique is applied to MEH-PPV thin films. Photo-physical phenomena such as the mesoscale polymer electronic light-induced response as well as the local nanoscale electro-optical properties are studied.

Contrast inversion in non-contact Dynamic Scanning Force Microscopy: what is high and what is low?

The present work proves that when non-contact Dynamic Scanning Force Microscopy (DSFM) is performed in ambient conditions wrong height measurements of heterogeneous samples can be obtained. In some extreme cases even contrast inversion can be observed. Alkanethiol islands on Au (111) have been used as model system, where contrast inversion is observed with different DSFM modes and various data acquisition parameters. To understand this effect, spectroscopy measurements have been used to show that contrast inversion is really a consequence of the differences in the interaction measured between tip and sample on the bare Au substrate and on the alkanethiol islands. We propose that this interaction is mainly induced by liquid necks forming between tip and sample, which is much stronger on the hydrophilic Au substrate than on the hydrophobic alkanethiol islands.

Anisotropic chemical etching of semipolar [1011]/[101+1] ZnO crystallographic planes: polarity versus dangling bonds.

ZnO thin films grown by metal-organic vapor phase epitaxy along the nonpolar [formula: see text] direction and exhibiting semipolar [formula: see text] facets have been chemically etched with HCl. In order to get an insight into the influence of the ZnO wurtzite structure in the chemical reactivity of the material, Kelvin probe microscopy and convergent beam electron diffraction have been employed to unambiguously determine the absolute polarity of the facets, showing that [formula: see text] facets are unstable upon etching in an HCl solution and transform into [formula: see text] planes. In contrast, [formula: see text] facets undergo homogeneous chemical etching perpendicular to the initial crystallographic plane. The observed etching behavior has been explained in terms of surface oxygen dangling bond density, suggesting that the macroscopic polarity plays a secondary role in the etching process.

Enhancing dynamic scanning force microscopy in air: as close as possible.

Frequency modulation dynamic scanning force microscopy has been implemented in ambient conditions using low oscillation amplitudes (<1 nm) to simultaneously record not only topographic but also additional channels of information, in particular contact potential images. The performance of this mode as compared to the conventional amplitude modulation mode is analyzed in detail using a biological molecule, turning yellow mosaic virus RNA, as the model sample. On the basis of scanning force microscopy imaging as well as spectroscopy experiments, we find that for such very small samples the frequency modulation mode is superior since it can be operated with smaller tip-sample interaction, smaller effective tip-sample distance and lower forces. Combined with Kelvin probe microscopy it results not only in considerably higher electrostatic resolution, but also in correct quantitative values for the contact potential as compared to traditional amplitude modulation scanning force microscopy.

Surface potential domains on lamellar P3OT structures.

In this work the electrostatic properties of poly(3-octylthiophene) thin films have been studied on a nanometer scale by means of electrostatic force microscopy and Kelvin probe microscopy (KPM). The KPM images reveal that different surface contact potential domains coexist on the polymer surface. This result, together with additional capacitance measurements, indicates that the potential domains are related to the existence of dipoles due to different molecular arrangements. Finally, capacitance measurements as a function of the tip-sample bias voltage show that in all regions large band bending effects take place.