title: Optical diffraction for measurements of nano-mechanical bending.
abstract: We explore and exploit diffraction effects that have been previously neglected when modelling optical measurement techniques for the bending of micro-mechanical transducers such as cantilevers for atomic force microscopy. The illumination of a cantilever edge causes an asymmetric diffraction pattern at the photo-detector affecting the calibration of the measured signal in the popular optical beam deflection technique (OBDT). The conditions that avoid such detection artefacts conflict with the use of smaller cantilevers. Embracing diffraction patterns as data yields a potent detection technique that decouples tilt and curvature and simultaneously relaxes the requirements on the illumination alignment and detector position through a measurable which is invariant to translation and rotation. We show analytical results, numerical simulations and physiologically relevant experimental data demonstrating the utility of the diffraction patterns. We offer experimental design guidelines and quantify possible sources of systematic error in OBDT. We demonstrate a new nanometre resolution detection method that can replace OBDT, where diffraction effects from finite sized or patterned cantilevers are exploited. Such effects are readily generalized to cantilever arrays, and allow transmission detection of mechanical curvature, enabling instrumentation with simpler geometry. We highlight the comparative advantages over OBDT by detecting molecular activity of antibiotic Vancomycin.
authors.affiliation: London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, UK.|Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: Rodolfo I
authors.initials: RI
authors.lastname: Hermans
authors.affiliation: London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, UK.|Leica Camera AG, Am Leitz-Park 5, 35578 Wetzlar, Germany.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Dueck
authors.affiliation: London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, UK.|Jomo Kenyatta University of Agriculture and Technology, Department of Chemistry, PO Box 62000, Nairobi, Kenya.
authors.forename: Joseph Wafula
authors.initials: JW
authors.lastname: Ndieyira
authors.affiliation: London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, UK.|Jomo Kenyatta University of Agriculture and Technology, Department of Chemistry, PO Box 62000, Nairobi, Kenya.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: McKendry
authors.affiliation: London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, UK.|Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK.|Division of Medicine, Rayne Institute, 5 University Street, London WC1E 6JF, UK.|Departments of Physics, ETH Zürich, CH-8093 Zürich, Switzerland and École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Aeppli