9,544 research outputs found
Systems approach based solution to fundamental limitations in unraveling spatial and temporal regimes in nano-interrogation and nano-positioning
A design scheme that achieves an optimal tip-sample force regulation with an ideal topography image reconstruction is presented. It addresses the problem of obtaining accurate sample profiles when scanning at high bandwidth while maintaining a constant cantilever-tip sample force in atomic force microscopes. It is shown that the proposed scheme provides a faithful replica of the sample at all relevant scanning speeds limited only by the inaccuracy in the model for the atomic force microscope. This provides an improvement over existing designs where the sample profile reconstruction is typically bandwidth limited. The experimental results corroborate the theoretical development.;Conventional imaging signals such as the amplitude signal and the vertical piezoactuation signal cannot identify the areas of probe loss, where dynamic atomic force microscopy based image where the cantilever fails to be an effective probe of the sample. A real-time methodology is developed to determine regions of probe loss. It is experimentally demonstrated that probe-loss affected portion of the image can be unambiguously identified by a real-time signal called reliability index. Reliability index, apart from indicating the probe-loss affected regions, can be used to minimize probe-loss affected regions of the image, thus aiding high speed AFM applications.;A new immobilization technique for quantitative imaging and topographic characterization of living yeast cells in solid media using Atomic force microscope (AFM) is presented. Unlike previous techniques, proposed technique allows almost complete cell surface to be exposed to environment and studied using AFM. Apart from the new immobilization protocol, in this report, for the first time, high resolution height imaging of live yeast cell surface in intermittent contact mode is presented. High resolution imaging and significant improvement in operational stability facilitated investigation of growth patterns and evolution of surface morphology in quantitative terms. Growth rate of mother cell and budding cell showed distinct patterns over the imaging time
Interaction imaging with amplitude-dependence force spectroscopy
Knowledge of surface forces is the key to understanding a large number of
processes in fields ranging from physics to material science and biology. The
most common method to study surfaces is dynamic atomic force microscopy (AFM).
Dynamic AFM has been enormously successful in imaging surface topography, even
to atomic resolution, but the force between the AFM tip and the surface remains
unknown during imaging. Here, we present a new approach that combines high
accuracy force measurements and high resolution scanning. The method, called
amplitude-dependence force spectroscopy (ADFS) is based on the
amplitude-dependence of the cantilever's response near resonance and allows for
separate determination of both conservative and dissipative tip-surface
interactions. We use ADFS to quantitatively study and map the nano-mechanical
interaction between the AFM tip and heterogeneous polymer surfaces. ADFS is
compatible with commercial atomic force microscopes and we anticipate its
wide-spread use in taking AFM toward quantitative microscopy
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Array atomic force microscopy for real-time multiparametric analysis.
Nanoscale multipoint structure-function analysis is essential for deciphering the complexity of multiscale biological and physical systems. Atomic force microscopy (AFM) allows nanoscale structure-function imaging in various operating environments and can be integrated seamlessly with disparate probe-based sensing and manipulation technologies. Conventional AFMs only permit sequential single-point analysis; widespread adoption of array AFMs for simultaneous multipoint study is challenging owing to the intrinsic limitations of existing technological approaches. Here, we describe a prototype dispersive optics-based array AFM capable of simultaneously monitoring multiple probe-sample interactions. A single supercontinuum laser beam is utilized to spatially and spectrally map multiple cantilevers, to isolate and record beam deflection from individual cantilevers using distinct wavelength selection. This design provides a remarkably simplified yet effective solution to overcome the optical cross-talk while maintaining subnanometer sensitivity and compatibility with probe-based sensors. We demonstrate the versatility and robustness of our system on parallel multiparametric imaging at multiscale levels ranging from surface morphology to hydrophobicity and electric potential mapping in both air and liquid, mechanical wave propagation in polymeric films, and the dynamics of living cells. This multiparametric, multiscale approach provides opportunities for studying the emergent properties of atomic-scale mechanical and physicochemical interactions in a wide range of physical and biological networks
Phase imaging with intermodulation atomic force microscopy
Intermodulation atomic force microscopy (IMAFM) is a dynamic mode of atomic
force microscopy (AFM) with two-tone excitation. The oscillating AFM cantilever
in close proximity to a surface experiences the nonlinear tip-sample force
which mixes the drive tones and generates new frequency components in the
cantilever response known as intermodulation products (IMPs). We present a
procedure for extracting the phase at each IMP and demonstrate phase images
made by recording this phase while scanning. Amplitude and phase images at
intermodulation frequencies exhibit enhanced topographic and material contrast.Comment: 6 pages, 6 page
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
Numerical Simulation of Nano Scanning in Intermittent-Contact Mode AFM under Q control
We investigate nano scanning in tapping mode atomic force microscopy (AFM)
under quality (Q) control via numerical simulations performed in SIMULINK. We
focus on the simulation of whole scan process rather than the simulation of
cantilever dynamics and the force interactions between the probe tip and the
surface alone, as in most of the earlier numerical studies. This enables us to
quantify the scan performance under Q control for different scan settings.
Using the numerical simulations, we first investigate the effect of elastic
modulus of sample (relative to the substrate surface) and probe stiffness on
the scan results. Our numerical simulations show that scanning in attractive
regime using soft cantilevers with high Qeff results in a better image quality.
We, then demonstrate the trade-off in setting the effective Q factor (Qeff) of
the probe in Q control: low values of Qeff cause an increase in tapping forces
while higher ones limit the maximum achievable scan speed due to the slow
response of the cantilever to the rapid changes in surface profile. Finally, we
show that it is possible to achieve higher scan speeds without causing an
increase in the tapping forces using adaptive Q control (AQC), in which the Q
factor of the probe is changed instantaneously depending on the magnitude of
the error signal in oscillation amplitude. The scan performance of AQC is
quantitatively compared to that of standard Q control using iso-error curves
obtained from numerical simulations first and then the results are validated
through scan experiments performed using a physical set-up
Piezo-generated charge mapping revealed through Direct Piezoelectric Force Microscopy
While piezoelectrics and ferroelectrics are playing a key role in many
everyday applications, there are still a number of open questions related to
the physics of those materials. In order to foster the understanding of
piezoelectrics and ferroelectric and pave the way to future applications, the
nanoscale characterization of these materials is essential. In this light, we
have developed a novel AFM based mode that obtains a direct quantitative
analysis of the piezoelectric coefficient d33. This nanoscale tool is capable
of detecting and reveal piezo-charge generation through the direct
piezoelectric effect at the surface of the piezoelectric and ferroelectric
materials. We report the first nanoscale images of the charge generated in a
thick single crystal of Periodically Poled Lithium Niobate (PPLN) and a Bismuth
Ferrite (BiFO3) thin film by applying a force and recording the current
produced by the materials. The quantification of both d33 coefficients for PPLN
and BFO are 13 +- 2 pC/N and 46 +- 7 pC/N respectively, in agreement with the
values reported in the literature. This new mode can operate simultaneously
with PFM mode providing a powerful tool for the electromechanical and
piezo-charge generation characterization of ferroelectric and piezoelectric
materials
Hardware for digitally controlled scanned probe microscopes
The design and implementation of a flexible and modular digital control and data acquisition system for scanned probe microscopes (SPMs) is presented. The measured performance of the system shows it to be capable of 14-bit data acquisition at a 100-kHz rate and a full 18-bit output resolution resulting in less than 0.02-Å rms position noise while maintaining a scan range in excess of 1 µm in both the X and Y dimensions. This level of performance achieves the goal of making the noise of the microscope control system an insignificant factor for most experiments. The adaptation of the system to various types of SPM experiments is discussed. Advances in audio electronics and digital signal processors have made the construction of such high performance systems possible at low cost
Optomechanical transduction of an integrated silicon cantilever probe using a microdisk resonator
Sensitive transduction of the motion of a microscale cantilever is central to
many applications in mass, force, magnetic resonance, and displacement sensing.
Reducing cantilever size to nanoscale dimensions can improve the bandwidth and
sensitivity of techniques like atomic force microscopy, but current optical
transduction methods suffer when the cantilever is small compared to the
achievable spot size. Here, we demonstrate sensitive optical transduction in a
monolithic cavity-optomechanical system in which a sub-picogram silicon
cantilever with a sharp probe tip is separated from a microdisk optical
resonator by a nanoscale gap. High quality factor (Q ~ 10^5) microdisk optical
modes transduce the cantilever's MHz frequency thermally-driven vibrations with
a displacement sensitivity of ~ 4.4x10^-16 m\sqrt[2]{Hz} and bandwidth > 1 GHz,
and a dynamic range > 10^6 is estimated for a 1 s measurement.
Optically-induced stiffening due to the strong optomechanical interaction is
observed, and engineering of probe dynamics through cantilever design and
electrostatic actuation is illustrated
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