S. Hudlet

Electrostatic forces between metallic tip and semiconductor surfaces

Atomic force microscopy used in the resonant mode is a powerful tool for measuring local surface properties: for example, the quantitative analysis of the electrical forces induced by the application of an electric field between a conductive microscope tip and a surface allows the determination of the tip/surface capacitance and the local surface work function. However, these quantitative analyses require knowledge of tip geometry. In this article, we show that the simple procedure of evaluating the tip curvature radius by fitting the variations of the electrostatic force with the tip‐surface distance is not always adapted to the case where one of the tip‐surface system elements is a semiconductor. However, particular experimental conditions are determined to overcome these difficulties.

Influence of tip modulation on image formation in scanning near-field optical microscopy

Modulation of the probe height in a scanning near-field optical microscope (SNOM) is a technique that is commonly used for both distance control and separation of the near-field signal from a background. Detection of higher harmonic modulated signals has also been used to obtain an improvement in resolution, the elimination of background, or artifacts in the signal. This article presents a theoretical model for the effects induced in SNOM images by modulation of the probe. It is shown that probe modulation introduces a spatial filter into the image, generally suppressing propagating field components and enhancing the strength of evanescent field components. A simple example of detection of a single evanescent field above a prism is studied in some detail, and a complicated dependence on modulation parameters and waveform is shown. Some aspects of the application of this theory in a general experimental situation are discussed. Simulated images are displayed to explicitly show the effects of varying modula...

Van der Waals and capacitive forces in atomic force microscopies

In this article we show that in the atomic force microscopy experiments performed on a metallic surface, there is always a long range electrostatic force in addition to the van der Waals forces. This capacitive force is due to the contact potential between the tip and the surface and exists even without external applied potential. We have calculated this capacitive force for a real geometry of the tip–sample system and compared it to the van der Waals force calculated for the same geometry. We conclude that the electrostatic force is always dominant for a tip–surface distance larger than half of the tip radius of curvature.

Analysis of the interferometric effect of the background light in apertureless scanning near-field optical microscopy

We investigate in detail the interferometric nature of the signal delivered by an apertureless scanning near-field optical microscope (SNOM). This nature is first brought to the fore by near-field images of an integrated waveguide. The detection process of an evanescent wave generated by total internal reflection is then studied by both lateral near-field scans and signal detection as a function of the tip-to-sample distance. This study permits interpretation of fringe patterns appearing in apertureless SNOM images and provides important information about the nature of the signal. In particular, both experimental data and simple calculations show that, because of interference with background light coming from the sample, the detected signal can describe the complex field amplitude, or the field intensity, or a subtle mix of both, depending on the tip environment and the tip position.

In situ measurement of large piezoelectric displacements in resonant atomic force microscopy

In resonant atomic force microscopy (AFMR) the calibration of the tip–sample relative displacement remains a major problem. Commonly used PZT piezoceramics exhibit a nonlinear behavior response for large applied voltages. For low voltages applied to the piezoceramics (i.e., small corrugations), the calibration can be performed by measuring the height of known structures. For large displacements, the interferometric heterodyne detection used in the AFMR provides a relative tip–sample displacement up to 10 μm, without removing the piezo‐tube from the microscope. From these measurements, it was established that the piezosensitivity is not a constant parameter. Its averaged value during an excursion depends linearly on the applied voltage. With this system, routine controls are very easy and an example is given of the displacement corrections related to the nonlinearity of the piezo‐tube for the electrostatic interaction between the tip and a gold surface.

NEAR FIELD MAGNETO-OPTICAL CIRCULAR DICHROISM USING AN APERTURELESS PROBE

We present an original magneto-optical Scanning Near-field-Optical Microscope (SNOM) configuration, using an apertureless probe, and devoted to the characterization in transmission of magnetic samples. Our experimental device provides simultaneously the near and far field optical images, in Magneto-optical Circular Dichroism mode (MCD), and the sample surface topography. The preliminary near field images of an iron garnet test-sample reveal surface modifications in the magnetic domain distribution, unresolved in the far field image, and unrelated to the topographic features. The near field image resolution reaches 240 nm, corresponding to the theoretically estimated size of the smallest magnetic structures.