F. Johann

Depth resolution of piezoresponse force microscopy

Given that a ferroelectric domain is generally a three dimensional entity, the determination of its area as well as its depth is mandatory for full characterization. Piezoresponse force microscopy (PFM) is known for its ability to map the lateral dimensions of ferroelectric domains with high accuracy. However, no depth profile information has been readily available so far. Here, we have used ferroelectric domains of known depth profile to determine the dependence of the PFM response on the depth of the domain, and thus effectively the depth resolution of PFM detection.

Impact of electrostatic forces in contact-mode scanning force microscopy

In this contribution we address the question to what extent surface charges affect contact-mode scanning force microscopy measurements. We therefore designed samples where we could generate localized electric-field distributions near the surface as and when required. We performed a series of experiments where we varied the load of the tip, the stiffness of the cantilever and the hardness of the sample surface. It turned out that only for soft cantilevers could an electrostatic interaction between tip and surface charges be detected, irrespective of the surface properties, i.e., basically regardless its hardness. We explain these results through a model based on the alteration of the tip-sample potential by the additional electric field between charged tip and surface charges.

Ultra-smooth lithium niobate photonic micro-structures by surface tension reshaping

Annealing of micro-structured lithium niobate substrates at temperatures close to, but below the melting point, allows surface tension to reshape preferentially melted surface zones of the crystal. The reshaped surface re-crystallizes upon cooling to form a single crystal again as it is seeded by the bulk which remains solid throughout the process. This procedure yields ultra-smooth single crystal superstructures suitable for the fabrication of photonic micro-components with low scattering loss.

Quantitative measurement of the surface charge density

We present a method of measuring the charge density on dielectric surfaces. Similar to electrostatic force microscopy we record the electrostatic interaction between the probe and the sample surface, but at large tip-sample distances. For calibration we use a pyroelectric sample which allows us to alter the surface charge density by a known amount via a controlled temperature change. For proof of principle, we determined the surface charge density under ambient conditions of ferroelectric lithium niobate.

Spectral and electro-optic response of UV-written waveguides in LiNbO3 single crystals.

An experimental study of the spectral and electro-optic response of direct UV-written waveguides in LiNbO3 is reported. The waveguides were written using c.w. laser radiation at 275, 300.3, 302, and 305 nm wavelengths with various writing powers (35-60 mW) and scan speeds (0.1-1.0 mm/sec). Spectral analysis was used to determine the multimode and single mode wavelength regions and, the cut-off point of the fabricated waveguides. Electro-optic characterization of these waveguides reveals that the electro-optic coefficient (r33) decreases for longer writing wavelengths, with a maximum of 31 pm/V for 275 nm and, is reduced to 14 pm/V for waveguides written with 305 nm.

Sol-gel derived ferroelectric nanoparticles investigated by piezoresponse force microscopy

Piezoresponse force microscopy (PFM) was used to investigate the ferroelectric properties of sol-gel derived LiNbO3 nanoparticles. To determine the degree of ferroelectricity we took large-area images and performed statistical image-analysis. The ferroelectric behavior of single nanoparticles was verified by poling experiments using the PFM tip. Finally we carried out simultaneous measurements of the in-plane and the out-of-plane piezoresponse of the nanoparticles, followed by measurements of the same area after rotation of the sample by 90° and 180°. Such measurements basically allow to determine the direction of polarization of every single particle.

Lateral signals in piezoresponse force microscopy at domain boundaries of ferroelectric crystals

In piezoresponse force microscopy a lateral signal at the domain boundaries is occasionally observed. In recent years, a couple of experiments have been reported and varying explanations for the origin of this lateral signal have been proposed. Additionally, elaborated theoretical modeling for this particular issue has been carried out. Here we present experimental data obtained on different crystallographic cuts of

Ultra-smooth lithium niobate single crystal photonic micro-structures

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UV laser-induced poling inhibition in lithium niobate crystals

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Ultra-smooth lithium niobate micro-resonators by surface tension reshaping

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