phase imaging is comparable to thefull resolution of TappingMode AFM.
Phase imaging can also act as areal-time contrast enhancement
technique. Because phase imaging
highlights edges and is not affectedby large-scale height differences,it provides for clearer observationof fine features, such as grainedges, which can be obscured byrough topography.

Figure 2. Phase (top) and TappingMode(bottom) images of wood pulp fiber. The
phase image highlights cellulose microfibrils.
In addition, a lignin component appears aslight areas in the phase image, but is notapparent in the topography image. 3µm scan
by Don Chernoff, Advanced Surface
Microscopy; sample provided by Dr. Damaris
E. Doro Pereira, Aracruz Celulose.

ExamplesPhase imaging is useful fordifferentiating between component
phases of composite materials. The
bulk of the wood pulp shown in
Figure 2 consists of cellulose
microfibrils that are highlighted byphase imaging. In addition, a lignin
component, not apparent in thetopography, appears as areas of lightcontrast atop the cellulose component.
Similarly, the two-phase structure of
the polymer blend in Figure 3 isshown clearly by the high resolutionof phase imaging, even as
TappingMode tracks relatively large(~1µm) topographical variations.
Phase imaging can also identify
surface contaminants and evaluate
processing steps. The integrated
circuit bond pad in Figure 4 iscovered with remnant spots ofpolyimide that an etching process
failed to remove. Note that thepolyimide is barely visible in the
topographic image, but produces
sizeable contrast in the phase image.
In Figure 5, the phase image of ahuman hair shows endocuticle debris(dark region) left behind by theerosion of the overlying cuticle in thelower left. Such information may help
compare the effectiveness of various
cosmetic treatments. Figure 6 shows
topography and phase images of a
SiO2 crucible in which boules ofcrystalline Silicon were grown at
1450° C. The imaged area
corresponds to a region ofcharacteristic Si contamination, visible
as brown rings to the naked eye,which prevents re-use of thesecrucibles. Although no phase contrast
was anticipated in this case, thephase image shows a complex multicomponent structure which may serve
as a signature of the contaminationand give clues as to the nature of thecontamination process.
A combination of these applications isshown by the images of a composite
magnetic recording head in Figure 7.
These heads typically have twomagnetic pole pieces separated by aFigure 3. TappingMode (top) and phase(bottom) images of a composite polymer
embedded in a uniform matrix. The highresolution of the phase contrast image
highlights the two-component structure of
the composite regions. Sample courtesyof Raj Michael.

narrow diamagnetic gap. The central
phase shows a section of a polepiece and the gap, with the gap
appearing as a light band across thetop. This distinction is not apparent in
the topography. Note also the verticalstring of contaminants in the first twoimages, shown in close-up by theright phase image. The phase contrastof the contaminants matches that of
the gap material, suggesting that thismaterial comprises the contaminants.
For comparison, contact LFM
produced no useful contrast, and thecontaminants were swept away
during imaging.
What information does phaseimaging give about a sample? TheMoO3 crystallites in Figure 8 produce
a vast contrast in the phase image
relative to the MoS 2 background. TheLFM image of the same area showsthat the crystallites have relatively
strong surface friction and adhesion,1suggesting that phase imaging issensitive to these properties. Also,
the advantages of TappingMode for
imaging delicate samples allow
phase imaging to be done in the
many cases where the lateral forcesof LFM can cause sample damage
and produce poor resolution.
Differences in surface modulus andviscoelasticity also appear to produce
phase contrast. For example, force
modulation indicates that the polymer
composites in Figure 3 have greater
elasticity than the matrix in which they
are embedded. Other tip-sample
interactions may also affect the phasesignal. Although there is currently nosimple correlation between phase
contrast and a single material
property, the examples shown here
demonstrate that phase imaging gives
valuable information for a wide range
of applications, in some cases giving
contrast where none was anticipatedfrom the material properties.

Figure 4. Bond pad on an integrated circuit imaged by TappingMode (left) and phase(right). Areas of the pad contaminated with polyimide produce light contrast with phaseshifts of over 120 deg. 1.5µm scan.

Figure 5. TappingMode (left) and phase (right) images of human hair cuticles. The phase
image shows remnants of endocuticle (dark region) left behind as the upper cuticle (lower left)
flaked away. Sample courtesy of JoAnne Crudele, Helene Curtis. 10µm scan.

Figure 6. 2.5µm images of a quartz crucible used to grow crystalline silicon at hightemperature. The multi-component structure in the phase image (right) is likely caused by Si
contamination of the crucible that prevents its re-use. Sample provided by Dr. Robert Fisher,
University of Washington.