High-speed AFM with a light touch

No abstract available

Estimation of the shear force in transverse dynamic force microscopy using a sliding mode observer

Open access journalIn this paper, the problem of estimating the shear force affecting the tip of the cantilever in a Transverse Dynamic Force Microscope (TDFM) using a real-time implementable sliding mode observer is addressed. The behaviour of a vertically oriented oscillated cantilever, in close proximity to a specimen surface, facilitates the imaging of the specimen at nano-metre scale. Distance changes between the cantilever tip and the specimen can be inferred from the oscillation amplitudes, but also from the shear force acting at the tip. Thus, the problem of accurately estimating the shear force is of significance when specimen images and mechanical properties need to be obtained at submolecular precision. A low order dynamic model of the cantilever is derived using the method of lines, for the purpose of estimating the shear force. Based on this model, an estimator using sliding mode techniques is presented to reconstruct the unknown shear force, from only tip position measurements and knowledge of the excitation signal applied to the top of the cantilever. Comparisons to methods assuming a quasi-static harmonic balance are made.Engineering and Physical Sciences Research Council (EPSRC

Direct measurements of the extraordinary optical momentum and transverse spin-dependent force using a nano-cantilever

Known since Kepler's observation that a comet's tail is oriented away from the sun, radiation pressure stimulated remarkable discoveries in electromagnetism, quantum physics and relativity [1,2]. This phenomenon plays a crucial role in a variety of systems, from atomic [3-5] to astronomical [6] scales. The pressure of light is associated with the momentum of photons, and it is usually assumed that both the optical momentum and the radiation-pressure force are naturally aligned with the propagation of light, i.e., its wavevector. Here we report the direct observation of an extraordinary optical momentum and force directed perpendicular to the wavevector, and proportional to the optical spin (i.e., degree of circular polarization). Such optical force was recently predicted for evanescent waves [7] and other structured fields [8]. It can be associated with the enigmatic "spin-momentum" part of the Poynting vector, which was introduced by Belinfante in field theory 75 years ago [9-11]. We measure this unusual transverse momentum using a nano-cantilever capable of femto-Newton resolution, which is immersed in an evanescent optical field above the total-internal-reflecting glass surface. Furthermore, the transverse force we measure exhibits another polarization-dependent contribution determined by the imaginary part of the complex Poynting vector. By revealing new types of optical forces in structured fields, our experimental findings revisit fundamental momentum properties of light and bring a new twist to optomechanics.Comment: 9 pages, 3 figures, Supplementary Informatio

Fabrication of Nano-Tips by Carbon Contamination in a Scanning Electron Microscope for Use in Scanning Probe Microscopy and Field Emission

Results are reported on a systematic study addressed to an effective fabrication of nano-tips by means of carbon contamination in a scanning electron microscope. Nano-tips with angular aperture of 10°, apical radius of about 5 nm, 1$\mu$m long can be efficiently produced by our method in less than 60 s of electron beam exposure; it involves, in particular, successive focusing during tip growth and the use of a carbon block as a source of contaminant. These tips have been used as high aspect ratio and low capillary force probes in atomic force microscopy, and as nano-sized field emitters for electron guns