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Jun 2000

Volume 71, Issue 6, pp. 2263-2611

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back to top MICROSCOPY and IMAGING

Characterization of a microfocused circularly polarized x-ray probe

J. Pollmann, G. Srajer, J. Maser, J. C. Lang, C. S. Nelson, C. T. Venkataraman, and E. D. Isaacs

Rev. Sci. Instrum. 71, 2386 (2000); http://dx.doi.org/10.1063/1.1150625 (5 pages) | Cited 4 times

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We report on the development of a circularly polarized x-ray microprobe in the intermediate energy range from 5 to 10 keV. In this experiment linearly polarized synchrotron radiation was circularly polarized by means of a Bragg-diffracting diamond phase retarder and subsequently focused down to a spot size of about 4×2 μm2 by a Fresnel zone plate. The properties of the microprobe were characterized, and the technique was applied to the two-dimensional mapping of magnetic domains in HoFe2. © 2000 American Institute of Physics.
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07.85.Qe Synchrotron radiation instrumentation
07.85.Jy Diffractometers
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
75.60.Ch Domain walls and domain structure

Quantitative measurement of sliding friction dynamics at mesoscopic scales: The lateral force apparatus

C. P. Hendriks and W. P. Vellinga

Rev. Sci. Instrum. 71, 2391 (2000); http://dx.doi.org/10.1063/1.1150626 (12 pages) | Cited 5 times

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We describe an apparatus designed to quantitatively measure friction dynamics at the mesoscopic scale. This lateral force apparatus, LFA, uses double parallel leaf springs in leaf-spring units as force transducers and two focus error detection optical heads, optical heads, to measure deflections. The design of the leaf-spring units is new. Normal spring constants are in the range of 20–4000 N/m, and lateral spring constants are 7–1000 N/m. The optical heads combine a 10 nm sensitivity with a useful range of about 100 μm. The proven range of normal forces is 400 nN–150 mN. The leaf-spring units transduce friction and normal forces independently. Absolute values of normal and friction forces are calibrated. Typical errors are less than 10%. The calibration is partly in situ, for the sensitivity of the optical heads, and partly ex situ for the normal and lateral spring constants of the leaf-spring units. There is minimal coupling between the deflection measurements in the lateral and normal directions. This coupling is also calibrated in situ. It is typically 1% and can be as low as 0.25%. This means that the displacements of the tip can be measured accurately in the sliding direction and normal to the surface. Together, these characteristics make the LFA, well suited for quantitative study of friction dynamics at mesoscopic scales. Furthermore the design of the leaf-spring unit allows exchange of tips which may be fabricated (e.g., etched) from wire material (d ≈ 0.4 mm) and can have customized shapes, e.g., polished flat squares. The ability of the LFA to study friction dynamics is briefly illustrated by results of stick-slip measurements on soft polymer surfaces. © 2000 American Institute of Physics.
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07.79.Lh Atomic force microscopes
07.10.Pz Instruments for strain, force, and torque
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear

Nanoscale elasticity measurement with in situ tip shape estimation in atomic force microscopy

Kazushi Yamanaka, Toshihiro Tsuji, Atsushi Noguchi, Takayuki Koike, and Tsuyoshi Mihara

Rev. Sci. Instrum. 71, 2403 (2000); http://dx.doi.org/10.1063/1.1150627 (6 pages) | Cited 18 times

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For a quantitative evaluation of nanoscale elasticity, atomic force microscopy, and related methods measure the contact stiffness (or force gradient) between the tip and sample surface. In these methods the key parameter is the contact radius, since the contact stiffness is changed not only by the elasticity of the sample but also by the contact radius. However, the contact radius is very uncertain and it makes the precision of measurements questionable. In this work, we propose a novel in situ method to estimate the tip shape and the contact radius at the nanoscale contact of the tip and sample. Because the measured resonance frequency sometimes does not depend so sensitively on the contact force as expected from the parabolic tip model, we introduced a more general model of an axial symmetric body and derived an equation for the contact stiffness. Then, the parameters in the model are unambiguously determined from a contact force dependence of the cantilever resonance frequency. We verified that this method is able to provide an accurate prediction of the cantilever thickness, the tip shape, and the effective elasticity of soft and rigid samples. © 2000 American Institute of Physics.
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07.79.Lh Atomic force microscopes
68.35.B- Structure of clean surfaces (and surface reconstruction)
62.20.D- Elasticity
46.80.+j Measurement methods and techniques in continuum mechanics of solids
81.70.Bt Mechanical testing, impact tests, static and dynamic loads

Controlled-atmosphere chamber for atomic force microscopy investigations

Marco Sartore, Raffaele Pace, Paolo Faraci, Daniele Nardelli, Manuela Adami, Manoj K. Ram, and Claudio Nicolini

Rev. Sci. Instrum. 71, 2409 (2000); http://dx.doi.org/10.1063/1.1150628 (5 pages) | Cited 6 times

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The present work describes a simple chamber suitable for morphological investigations by implementing the atomic force microscopy (AFM) in controlled experiments. The novelty of our application stems from proposing an open system located in between the expensive, ultra-high-vacuum instruments and those working in air conditions, both available on the market. The former are in fact designed to obtain a detailed inspection of the samples and to develop particular geometries on them, by means of nanolithography or nanomanipulation, while the latter are designed for and used in all the situations in which the environmental conditions do not cause artifacts, problems, or formation of spurious particles on the samples during imaging. We have developed an ad hoc system based on a high-vacuum chamber (up to 10−6 Torr), which allows us to work under controlled-atmosphere conditions. The system, therefore, can be used with most of the samples which suffer from higher pressures, and exploits all the benefits arising from a controlled environment. We have equipped the chamber with an AFM and a sample-holder/mover. An external X–Y–Z motion controller, completely automated, allows the easy positioning of the sample under the sensing cantilever and the consequent relative approach. Experiments with the proposed system are presented, in which the control of environmental conditions during AFM measurements has been investigated with satisfactory results. © 2000 American Institute of Physics.
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07.79.Lh Atomic force microscopes
07.30.Kf Vacuum chambers, auxiliary apparatus, and materials
07.07.Tw Servo and control equipment; robots
06.60.Sx Positioning and alignment; manipulating, remote handling
06.60.Ei Sample preparation (including design of sample holders)

Tip–sample distance feedback control in a scanning evanescent microwave probe for nonlinear dielectric imaging

Fred Duewer, C. Gao, and X.-D. Xiang

Rev. Sci. Instrum. 71, 2414 (2000); http://dx.doi.org/10.1063/1.1150629 (4 pages) | Cited 7 times

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We implemented tip–sample distance control in a scanning evanescent microwave probe for nonlinear dielectric microscopy. With the analytic expression of the tip–sample capacitance as a function of tip–sample distance, we can quantitatively regulate the tip–sample separation and independently measure the dielectric nonlinearity by application of an ac bias voltage. Simultaneous imaging of topography and ferroelectric domains has been demonstrated on periodically poled LiNbO3 single crystals. © 2000 American Institute of Physics.
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07.05.Dz Control systems
62.20.F- Deformation and plasticity
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Infrared imaging of defects heated by a sonic pulse

L. D. Favro, Xiaoyan Han, Zhong Ouyang, Gang Sun, Hua Sui, and R. L. Thomas

Rev. Sci. Instrum. 71, 2418 (2000); http://dx.doi.org/10.1063/1.1150630 (4 pages) | Cited 39 times

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High-frequency pulsed sonic excitation is combined with an infrared camera to image surface and subsurface defects. Irreversible temperature increases on the surface of the object, resulting from localized heating in the vicinity of cracks, disbonds, or delaminations, are imaged as a function of time prior to, during, and following the application of a short pulse of sound. Pulse durations of 50 ms are sufficient to image such defects, and result in surface temperatures variations of ∼2 °C above the defect. As an example, sonic infrared images are presented for two fatigue cracks in Al and of interply delamination impact damage in a graphite–fiber-reinforced polymer composite. The shorter of the two fatigue cracks is ∼0.7 mm in length, and is tightly closed. Thus, this new technique is sensitive, and capable of rapid imaging of defects under wide surface areas of an object. © 2000 American Institute of Physics.
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81.70.Fy Nondestructive testing: optical methods
42.79.Pw Imaging detectors and sensors
43.35.Ty Other physical effects of sound
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