e-book

Acoustic Microscopy

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This new edition follows growing demand for copies of Acoustic microscopy,
the original print run having become exhausted. Almost all of the original
edition is reproduced without change, except for a small number of corrections
and some minor additions. Of the errors in the first edition, the most
mysterious was the renumbering of Newton’s laws on their transmission from
Cambridge to Oxford: Newton’s second law is now restored to its correct place
in the sequence. Most of what was originally described remains valid. The
dominant role of Rayleigh waves in the contrast from high stiffness materials
had been previously identified in An introduction to scanning acoustic
microscopy (Briggs 1985)) and the theory and application to layered structures,
anisotropic materials, and surface cracks have stood the test of time.

There was, however, one topic which was not included in the first edition,
which has undergone substantial development in the intervening years.
It could have been foreseen: in 1986 a paper was presented at the IEEE
Ultrasonics Symposium entitled ‘Ultrasonic pin scanning microscope: a new
approach to ultrasonic microscopy’ (Zieniuk and Latuszek 1986, 1987). With
the advent of atomic force microscopy, it proved possible to combine the
nanometre-scale spatial resolution of scanning probe microscopy with the
sensitivity to mechanical properties of acoustic microscopy. The technique
became known as ultrasonic force microscopy, and has been joined by cognate
techniques such as atomic force acoustic microscopy, scanning localacceleration
microscopy, and heterodyne force microscopy.

The principle of ultrasonic force microscopy (UFM) can be likened to
a mechanical version of your great-grandfather’s crystal radio. The contact
between a tip and a surface works as a spring whose stiffness is not constant:
it generally increases when you push and decreases or vanishes when you
pull. It can therefore rectify an oscillating force that is applied, rather as an
electrical diode rectifies a radio signal. Thus if ultrasonic excitation is applied
to the sample in an atomic force microscope operating in the normal contact
mode, the cantilever average position will be displaced away from the sample.
Continuous ultrasonic excitation would not be very useful, because it would
be impossible to separate the rectified displacement from topography. Here
comes the clever bit. If you modulate the ultrasonic excitation faster than the
microscope feedback can respond, then the cantilever will exhibit deflections
at the modulation frequency. These can be detected with a lock-in amplifier,
and used to modulate the brightness of an image.

There might seem to be a trade-off in sensitivity. For atomic force
microscopy you want a cantilever that is not too stiff;t ypically about 1 N m-l
(or perhaps more appropriately 1 nN nm-1) is about right. But the stiffness of
the contact between a tip and most materials is far greater than this. At first
glance, such a soft cantilever would just follow the sample oscillations and
almost any material would be equally stiff for the tip. If that were the whole
story then the UFM would be insensitive to material stiffness, rather as the
tapping mode is (Burnham et al. 1997). But this would be to neglect the effect
of inertia. To the stiffness of the cantilever supporting the tip must be added
the effect of their combined mass multiplied by the frequency squared. By
appropriate choice of frequency the inertial stiffness can be made comparable
with or can even exceed the stiffness of the contact between the sample and
the tip, thus giving sensitivity to variations in the sample stiffness and discontinuities
such as cracks and delaminations. Ultrasonic modulation of the tipsurface
contact also offers almost complete elimination of the friction between
tip and surface and is thus, like traditional acoustic microscopy, largely nondestructive.

The crystal radio has long since been replaced by highly sensitive heterodyne
radios, which mix a weak signal from the antenna with a strong
signal of a slightly different frequency from a local oscillator, and amplify the
resulting low-frequency beats. This low-frequency signal carries all the phase
and amplitude information of the high-frequency signal, allowing frequencymodulated
radios, radar systems, multi-band cell phones, and other communication
systems to be built. The ultrasonic vibration of the tip can be put to
work to convert nanoscale high-frequency phenomena such as sample expansion
due to the heat from a pulsed laser to low-frequency displacements which
can be directly measured. The invention of heterodyne force microscopy
was announced at Ultrasonics International in 1997, and opened up highfrequency
microscopy using optically excited thermal waves for applications
such as polymer relaxation and subsurface imaging.

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Ketersediaan

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Informasi Detail

Judul Seri

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No. Panggil

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Penerbit

New York : Oxford University Press Inc.., 2010

Deskripsi Fisik

TA417.23.B74 - 620.1’1299-dc22

Bahasa

English

ISBN/ISSN

9780199232734

Klasifikasi

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Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

2nd ed.

Subjek

FISIKA

Info Detail Spesifik

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Pernyataan Tanggungjawab

gusut

Versi lain/terkait

Lampiran Berkas

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