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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2928-2936 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Increasing the imaging speed of tapping mode atomic force microscopy (AFM) has important practical and scientific applications. The scan speed of tapping-mode AFMs is limited by the speed of the feedback loop that maintains a constant tapping amplitude. This article seeks to illuminate these limits to scanning speed. The limits to the feedback loop are: (1) slow transient response of probe; (2) instability limitations of high-quality factor (Q) systems; (3) feedback actuator bandwidth; (4) error signal saturation; and the (5) rms-to-dc converter. The article will also suggest solutions to mitigate these limitations. These limitations can be addressed through integrating a faster feedback actuator as well as active control of the dynamics of the cantilever. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 7491-7496 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method to calculate the contact stiffness between a layered material and an ultrasonic atomic force microscope (UAFM) tip is proposed. The radiation impedance method is used to determine the ratio of the applied force to the average displacement within the contact area. This information is used in an iterative algorithm based on Hertzian theory to obtain the contact stiffness. The algorithm converges into a couple of iterations and does not suffer from numerical convergence difficulties as does finite element analysis (FEA). In the ultrasonic frequency range, comparisons with Hertzian theory and FEA show the validity of the results in a quasistatic case. Definitions of the minimum detectable layer thickness and the penetration depth of the UAFM are given and evaluated for several thin film–substrate pairs. These results also show the potential of the method for modeling defects and power loss due to radiation in layered materials. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Random fluctuations of displacement or velocity in mechanical systems can be calculated by using the analogy between electrical circuits and mechanical systems. The fluctuation-dissipation theorem expresses the relation between the generalized mechanical admittance and the noise in velocity. Similarly, correlation of mechanical noise can be calculated by using the generalized Nyquist theorem which states that the current noise correlation between two ports in an electrical circuit is dictated by the real part of the transadmittance. In this article, we will present the determination of the mechanical transadmittance and we will use the mechanical transadmittance to calculate the noise correlation on geometrically complex structures where it is not possible to approximate the noise by using the simple harmonic oscillator model. We will apply our method to atomic force microscope cantilevers by means of finite element method tools. The application of the noise correlation calculation method to rectangular cantilever beams shows some interesting results. We found that on the resonance frequencies, the correlation coefficient takes values 1 (full correlation) and −1 (anti-correlation) along the cantilever axis depending on the mode shapes of the structure. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1787-1789 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed an atomic force microscope that uses interferometry for parallel readout of a cantilever array. Each cantilever contains a phase sensitive diffraction grating consisting of a reference and movable set of interdigitated fingers. As a force is applied to the tip, the movable set is displaced and the intensity of the diffracted orders is altered. The order intensity from each cantilever is measured with a custom array of silicon photodiodes with integrated complementary metal–oxide–semiconductor amplifiers. We present images from five cantilevers acquired in the constant height mode that reveal surface features 2 nm in height. The interdigital method for cantilever array readout is scalable, provides angstrom resolution, and is potentially simpler to implement than other methods. © 2001 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 111-113 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lamb wave devices based on capacitive micromachined ultrasonic transducers (CMUTs) have been built on 500-μm-thick silicon wafers for frequencies in the vicinity of 1 MHz. CMUTs have been used to both excite and detect Lamb waves in the substrate. This configuration eliminates the need for piezoelectric materials, which are not compatible with the existing integrated circuit (IC) fabrication techniques, and allows easy integration of Lamb wave devices and electronics on the same wafer. Finite element analysis of the devices shows that the lowest order antisymmetric Lamb wave (A0) is the dominant mode in the substrate in this frequency range. This result is also confirmed by demonstration experiments. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a technique in which atomic force microscopy at ultrasonic frequencies is used to determine the thickness of thin films. In this technique, the resonance frequency of a flexural mode of an atomic force microscope cantilever is used to determine the tip-sample contact stiffness. This allows the film thickness to be determined, provided that the tip and sample elastic moduli and radii of curvature are known. We report experimental results for thin metal and polymer films deposited on silicon substrates and compare them with the predictions of a theoretical model. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The speed of tapping mode imaging with the atomic force microscope (AFM) has been increased by over an order of magnitude. The enhanced operation is achieved by (1) increasing the instrument's mechanical bandwidth and (2) actively controlling the cantilever's dynamics. The instrument's mechanical bandwidth is increased by an order of magnitude by replacing the piezotube z-axis actuator with an integrated zinc oxide (ZnO) piezoelectric cantilever. The cantilever's dynamics are optimized for high-speed operation by actively damping the quality factor (Q) of the cantilever. Active damping allows the amplitude of the oscillating cantilever to respond to topography changes more quickly. With these two advancements, 80μm×80 μm high-speed tapping mode images have been obtained with a scan frequency of 15 Hz. This corresponds to a tip velocity of 2.4 mm/s. © 2000 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7405-7415 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interdigital (ID) cantilever with two sets of interleaving fingers is an alternative to the conventional cantilever used in the atomic force microscope (AFM). In this paper we present a detailed analysis of the interdigital cantilever and its use as a sensor for the AFM. In this study, we combine finite element analysis with diffraction theory to simulate the mechanically induced optical response of the ID. This model is used to compare this system with the optical lever detector as used in conventional instruments by analyzing the ratio of signal to noise and overall performance. We find that optical detection of the cantilever motion with interdigital fingers has two advantages. When used in conjunction with arrays of cantilevers it is far easier to align. More importantly, it is immune to laser pointing noise and thermally excited mechanical vibrations and this improves the sensitivity as compared to the optical lever. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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