92 research outputs found
Dynamic Calibration of Higher Eigenmode Parameters of a Cantilever in Atomic Force Microscopy Using Tip-Surface Interactions
We present a theoretical framework for the dynamic calibration of the higher
eigenmode parameters (stiffness and optical lever responsivity) of a
cantilever. The method is based on the tip-surface force reconstruction
technique and does not require any prior knowledge of the eigenmode shape or
the particular form of the tip-surface interaction. The calibration method
proposed requires a single-point force measurement using a multimodal drive and
its accuracy is independent of the unknown physical amplitude of a higher
eigenmode.Comment: 4 pages, 4 figure
Interpreting motion and force for narrow-band intermodulation atomic force microscopy
Intermodulation atomic force microscopy (ImAFM) is a mode of dynamic atomic
force microscopy that probes the nonlinear tip-surface force by measurement of
the mixing of multiple tones in a frequency comb. A high cantilever
resonance and a suitable drive comb will result in tip motion described by a
narrow-band frequency comb. We show by a separation of time scales, that such
motion is equivalent to rapid oscillations at the cantilever resonance with a
slow amplitude and phase or frequency modulation. With this time domain
perspective we analyze single oscillation cycles in ImAFM to extract the
Fourier components of the tip-surface force that are in-phase with tip motion
() and quadrature to the motion (). Traditionally, these force
components have been considered as a function of the static probe height only.
Here we show that and actually depend on both static probe height
and oscillation amplitude. We demonstrate on simulated data how to reconstruct
the amplitude dependence of and from a single ImAFM measurement.
Furthermore, we introduce ImAFM approach measurements with which we reconstruct
the full amplitude and probe height dependence of the force components
and , providing deeper insight into the tip-surface interaction. We
demonstrate the capabilities of ImAFM approach measurements on a polystyrene
polymer surface.Comment: 12 pages, 7 figure
Quantum Phase Slips in one-dimensional Josephson Junction Chains
We have studied quantum phase-slip (QPS) phenomena in long one-dimensional
Josephson junction series arrays with tunable Josephson coupling. These chains
were fabricated with as many as 2888 junctions, where one sample had a tunable
weak link in the middle. Measurements were made of the zero-bias resistance,
, as well as current-voltage characteristics (IVC). The finite is
explained by QPS and shows an exponential dependence on with a
distinct change in the exponent at . When the IVC
clearly shows a remnant of the Coulomb blockade, which evolves to a
zero-current state with a sharp critical voltage as is tuned to a smaller
value. The zero-current state below the critical voltage is due to coherent QPS
and we show that these are enhanced at the central weak link. Above the
critical voltage a negative differential resistance is observed which nearly
restores the zero-current state
Coulomb Blockade and Coherent Single-Cooper-Pair Tunneling in Single Josephson Junctions
We have measured the current-voltage characteristics of small-capacitance
single Josephson junctions at low temperatures (T < 0.04 K), where the strength
of the coupling between the single junction and the electromagnetic environment
was controlled with one-dimensional arrays of dc SQUIDs. We have clearly
observed Coulomb blockade of Cooper-pair tunneling and even a region of
negative differential resistance, when the zero-bias resistance of the SQUID
arrays is much higher than the quantum resistance h/e^2 = 26 kohm. The negative
differential resistance is evidence of coherent single-Cooper-pair tunneling in
the single Josephson junction.Comment: RevTeX, 4 pages with 6 embedded figure
Imaging high-speed friction at the nanometer scale
Friction is a complicated phenomenon involving nonlinear dynamics at
different length and time scales[1, 2]. The microscopic origin of friction is
poorly understood, due in part to a lack of methods for measuring the force on
a nanometer-scale asperity sliding at velocity of the order of cm/s.[3, 4]
Despite enormous advance in experimental techniques[5], this combination of
small length scale and high velocity remained illusive. Here we present a
technique for rapidly measuring the frictional forces on a single asperity (an
AFM tip) over a velocity range from zero to several cm/s. At each image pixel
we obtain the velocity dependence of both conservative and dissipative forces,
revealing the transition from stick-slip to a smooth sliding friction[1, 6]. We
explain measurements on graphite using a modified Prandtl-Tomlinson model that
takes into account the damped elastic deformation of the asperity. With its
greatly improved force sensitivity and very small sliding amplitude, our method
enables rapid and detailed surface mapping of the full velocity-dependence of
frictional forces with less than 10~nm spatial resolution.Comment: 7 pages, 4 figure
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