1,353 research outputs found
Attraction between like-charged colloidal particles induced by a surface a density - functional analysis
We show that the first non-linear correction to the linearised
Poisson-Boltzman n (or DLVO) theory of effective pair interactions between
charge-stabilised, co lloidal particles near a charged wall leads to an
attractive component of entro pic origin. The position and depth of the
potential compare favourably with rec ent experimental measurementsComment: 12 pages including 2 figures. submitted to physical review letter
Position and Mode Dependent Optical Detection Back-Action in Cantilever Beam Resonators
Optical detection back-action in cantilever resonant or static detection
presents a challenge when striving for state-of-the-art performance. The origin
and possible routes for minimizing optical back-action have received little
attention in literature. Here, we investigate the position and mode dependent
optical back-action on cantilever beam resonators. A high power heating laser
(100 {\mu}W) is scanned across a silicon nitride cantilever while its effect on
the first three resonance modes is detected via a low-power readout laser (1
{\mu}W) positioned at the cantilever tip. We find that the measured effect of
back-action is not only dependent on position but also the shape of the
resonance mode. Relevant silicon nitride material parameters are extracted by
fitting the temperature-dependent frequency response of the first three modes
to finite element (FE) simulations. In a second round of simulations, using the
extracted parameters, we successfully fit the FEM results with the measured
mode and position dependent back-action. Finally, different routes for
minimizing the effect of this optical detection back-action are described,
allowing further improvements of cantilever-based sensing in general
Stress-Induced Variations in the Stiffness of Micro- and Nanocantilever Beams
The effect of surface stress on the stiffness of cantilever beams remains an outstanding problem in the physical sciences. While numerous experimental studies report significant stiffness change due to surface stress, theoretical predictions are unable to rigorously and quantitatively reconcile these observations. In
this Letter, we present the first controlled measurements of stress-induced change in cantilever stiffness with commensurate theoretical quantification. Simultaneous measurements are also performed on equivalent clamped-clamped beams. All experimental results are quantitatively and accurately predicted using elasticity theory. We also present conclusive experimental evidence for invalidity of the longstanding and unphysical axial force model, which has been widely applied to interpret measurements using cantilever beams. Our findings will be of value in the development of micro- and nanoscale resonant mechanical sensors
Antimicrobial Activity of Daptomycin and Comparator Agents Tested Against Gram-positive Organisms from Hong Kong, Indonesia, Philippines, Singapore and Thailand
The Role of Nonlinear Dynamics in Quantitative Atomic Force Microscopy
Various methods of force measurement with the Atomic Force Microscope (AFM)
are compared for their ability to accurately determine the tip-surface force
from analysis of the nonlinear cantilever motion. It is explained how
intermodulation, or the frequency mixing of multiple drive tones by the
nonlinear tip-surface force, can be used to concentrate the nonlinear motion in
a narrow band of frequency near the cantilevers fundamental resonance, where
accuracy and sensitivity of force measurement are greatest. Two different
methods for reconstructing tip-surface forces from intermodulation spectra are
explained. The reconstruction of both conservative and dissipative tip-surface
interactions from intermodulation spectra are demonstrated on simulated data.Comment: 25 pages (preprint, double space) 7 figure
Mechano-chemical manipulation of Sn chains on Si(1 0 0) by NC-AFM
We investigate the atomic structure of Sn dimer chains grown on the Si(1 0 0) surface using non-contact atomic force microscopy (NC-AFM) at cryogenic temperatures. We find that similar to the native Si(1 0 0) dimer structure, the ground state of the Sn dimer structure is buckled at low temperature. At 5 K we show that the buckling state of the Sn dimers may be controllably, and reversibly, manipulated with atomic precision by close approach of the tip, without modification of the underlying substrate buckling structure. At intermediate cryogenic temperatures we observe changes in the configuration of the dimer chains in the region where the tip-sample interaction is very weak, suggesting that the energy barrier to transit between configurations is sufficiently small to be surmounted at 78 K
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