A Multi-mode Transverse Dynamic Force Microscope - Design, Identification and Control

This is the author accepted manuscript. The final version is available from IEEE via the DOI in this record.The transverse dynamic force microscope (TDFM) and its shear force sensing principle permit true non-contact force detection in contrast to typical atomic force microscopes. The two TDFM measurement signals for the cantilever allow, in principle, two different scanning modes of which, in particular, the second presented here permits a full-scale non-contact scan. Previous research mainly focused on developing the sensing mechanism, whereas this work investigates the vertical axis dynamics for advanced robust closed-loop control. This paper presents a new TDFM digital control solution, built on field-programmable gate array (FPGA) equipment running at high implementation frequencies. The integrated control system allows the implementation of online customizable controllers, and raster-scans in two modes at very high detection bandwidth and nano-precision. Robust control algorithms are designed, implemented, and practically assessed. The two realized scanning modes are experimentally evaluated by imaging nano-spheres with known dimensions in wet conditions.Engineering and Physical Sciences Research Council (EPSRC

High-speed AFM with a light touch

No abstract available

Real-time sliding mode observer scheme for shear force estimation in a transverse dynamic force microscope

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.This paper describes a sliding mode observer scheme for estimation of the shear force affecting the cantilever in a Transverse Dynamic Force Microscope (TDFM). The vertically oriented cantilever is oscillated in proximity to the specimen under investigation. The amplitude of oscillation of the cantilever tip is affected by these shear forces. They are created by the ordered-water layer above the specimen. The oscillation amplitude is therefore a measure of distance between the tip and the surface of the specimen. Consequently, the estimation of the shear forces provides useful information about the specimen characteristics. For estimating the shear forces, an approximate finite dimensional model of the cantilever is created using the method of lines. This model is subsequently reduced for its model order. An unknown input sliding mode observer has been used to reconstruct the unknown shear forces using only tip position measurements and the cantilever excitation. This paper describes the development of the sliding mode scheme and presents experimental results from the TDFM set up at the Centre for Nanoscience and Quantum Information (NSQI) at Bristol University

Real-time force reconstruction in a transverse dynamic force microscope

This is the author accepted manuscript. The final version is available from IEEE via the DOI in this recordOne major functionality of force microscopes is their ability to measure forces at a high sensitivity, thereby, allowing understanding of vital mechanisms: for instance, in bio-specimens. The investigation of a specimen’s viscoelasticity on nano-scale can have significant scientific impact, but has been inhibited by the lack of fast, comprehensive scanning instruments. In principle, transverse dynamic force microscopes (TDFMs) permit the measurement of interaction forces within delicate samples in a non-contact manner. The force measurements are reconstructed via complicated offline analysis in TDFMs, therefore, they can hardly be utilised as an online force measuring tool. This paper introduces a novel integrated robust design for practical scanning using the TDFM system. The digital design is implemented in fixed-point arithmetic using Field Programmable Gate Array (FPGA) devices, thereby, permitting measurement of the interaction force at a high sampling rate. The novel digital design tackles different implementation issues achieving fast and robust force measuring performance. This enables a new force-scan mode for the TDFM, realising for the first time, online force mapping of sample-surfaces in real-time.Engineering and Physical Sciences Research Council (EPSRC

A super-twisting observer for atomic-force reconstruction in a probe microscope

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordThis paper presents a new methodology employing a super-twisting sliding mode observer to reconstruct un-measureable atomic-forces at nano-Newton precision in a Vertically Oriented Probe Microscope (VOPM). The VOPM senses the deflection of a vertically oriented cantilever, caused by shear-force interaction with a confined water layer above the sample-substrate. The paper describes the development of a model and the subsequent experimental process for computing its parameters. This forms the basis for the design of a super-twisting observer to estimate the unknown shear-forces. The reconstructed force can be decomposed into elastic and viscous components ,which are important in biological research.Engineering and Physical Sciences Research Council (EPSRC

The cylindrical envelope projection model applied to SE images of curved surfaces and comparison with AFM evaluations

The Cylindrical Envelope Projection Model (CEPM) has been extended to images of curved objects (e.g., spheres), obtained in a SEM by means of SEs, in order to improve the accuracy of measurements (down to a few %). The test objects have been calibrated by means of an AFM equipped with home-made nanotips. A simple rule for measuring the diameter of spheres and cylinders from SE y-modulated traces is given. The rule is applicable to specimens of medium $(Z\geq 25)$ and high atomic number