Tathagata De

Sample-profile estimate for fast atomic force microscopy

In this letter, 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. In this design scheme, the objective of maintaining a constant tip-sample force while scanning at high bandwidth does not impose limitations on the reconstruction of the sample topography. 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. Comparison with the existing methods of using the control signal as the image is provided. The experimental results corroborate the theoretical development.

Construction and Experimental Implementation of a Model-Based Inverse Filter to Attenuate Hysteresis in Ferroelectric Transducers

Hysteresis and constitutive nonlinearities are inherent properties of ferroelectric transducer materials due to the noncentrosymmetric nature of the compounds. In certain regimes, these effects can be mitigated through restricted input fields, charge- or current-controlled amplifiers, or feedback designs. For general operating conditions, however, these properties must be accommodated in models, transducer designs, and model-based control algorithms to achieve the novel capabilities provided by the compounds. In this paper, we illustrate the construction of inverse filters, based on homogenized energy models, which can be used to approximately linearize the piezoceramic transducer behavior for linear design and control implementation. Attributes of the inverse filters are illustrated through numerical examples and experimental open loop control implementation for an atomic force microscope stage

Model development and inverse compensator design for high speed nanopositioning

This paper focuses on the development of constitutive models, commensurate system models, and inverse compensator construction for high speed nanopositioning in atomic force microscopes (AFM). All current AFM employ either stacked or cylindrical piezoceramic actuators for both longitudinal and transverse positioning of the sample. An inherent property of these materials is the presence of hysteresis and constitutive nonlinearities, even at the low drive levels employed for angstrom-level resolution. At low frequencies, standard feedback mechanisms effectively attenuate the hysteresis, whereas noise at high frequencies diminishes the efficacy of feedback and leads to unacceptable accuracy. In this paper, we discuss modeling techniques which provide a first step toward high speed nanopositioning for applications ranging from macroscopic product evaluation to real-time imaging of biological processes.

Model development for atomic force microscope stage mechanisms

In this paper, we develop nonlinear constitutive equations and resulting system models quantifying the nonlinear and hysteretic field‐displacement relations inherent to lead zirconate titanate (PZT) devices employed in atomic force microscope stage mechanisms. We focus specifically on PZT rods utilizing

Real-time detection of probe loss in atomic force microscopy

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Immobilization method of yeast cells for intermittent contact mode imaging using the atomic force microscope

motion and PZT shells driven in

Model development and control design for high speed atomic force microscopy

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Model development for piezoceramic nanopositioners

regimes, but the modeling framework is sufficiently general to accommodate a variety of drive geometries. In the first step of the model development, lattice‐level energy relations are combined with stochastic homogenization techniques to construct nonlinear constitutive relations which accommodate the hysteresis inherent to ferroelectric compounds. Second, these constitutive relations are employed in classical rod and shell relations to construct system models appropriate for presently employed nanopositioner designs. The capability of the models for quantifying the frequency‐dependent hysteresis inherent to the PZT stages is illustrated through comparison...

Experimental implementation of a model-based inverse filter to attenuate hysteresis in an atomic force microscope

In this letter, a real-time methodology is developed to determine regions of dynamic atomic force microscopy based image where the cantilever fails to be an effective probe of the sample. Conventional imaging signals such as the amplitude signal and the vertical piezoactuation signal cannot identify the areas 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.

Micro-manipulation using combined Optical Tweezers and Atomic Force Microscope

The atomic force microscope (AFM) is widely used for studying the surface morphology and growth of live cells. There are relatively fewer reports on the AFM imaging of yeast cells [1] (Kasas and Ikai, 1995), [2] (Gad and Ikai, 1995). Yeasts have thick and mechanically strong cell walls and are therefore difficult to attach to a solid substrate. In this report, a new immobilization technique for the height mode imaging of living yeast cells in solid media using AFM is presented. The proposed technique allows the cell surface to be almost completely exposed to the environment and studied using AFM. Apart from the new immobilization protocol, for the first time, height mode imaging of live yeast cell surface in intermittent contact mode is presented in this report. Stable and reproducible imaging over a 10-h time span is observed. A significant improvement in operational stability will facilitate the investigation of growth patterns and surface patterns of yeast cells.