curve is recorded utilizing the DC
displacement of the cantilever versus
the extension of the scanner. Many
indentations may be made using
various forces, rates, etc. Upon exiting
indentation mode, TappingMode AFM
is turned back on and the instrument
returns to imaging mode; theindentations made on the surface maythen be imaged.
Scratching is done in a similar manner.
First, engage on the surface with anindentation cantilever and image thesurface to locate the desired position
for the scratch. Next, select Scratch
Mode where, once again, the lateralscanning halts and the tip is liftedslightly off the surface. Then, set thescratch parameters, such as force,
rate, scratch length and direction, andthe scratch is executed. During thescratching, the cantilever oscillation isturned off, the tip is forced into thesurface until the specified cantileverdeflection is reached, and the tip isthen moved laterally according to thepreset length, rate, and direction.
Multiple scratches may be made using
various forces, lengths, rates, anddirections. Upon exiting Scratch
Mode, TappingMode AFM is turnedback on, and the instrument is readyto image the scratches made on thesurface of the sample.

1-100µN with resolution better than
0.5µN. Larger forces up to about
300µN can be accommodated
using custom cantilevers with higher
spring constants.

Figure 2. Indentations on a 1µm gold
ruling at various forces used for testing thesharpness and orientation of the diamondtips mounted on the indentation cantilevers.
3µm scan.

size of the diamond. For comparison,
the resonant frequency for standard
TappingMode AFM cantilevers is
usually about 300kHz.
A typical indentation cantilever has
a spring constant of 150N/m;
length, width, and thickness of about
350, 100, and 13µm, respectively(Figure 1); and a resonant frequencyof 50kHz. Veeco Probes measures andsupplies the customer with the spring
constant of each cantilever purchased.
The typical indentation force range
available with our instruments is

The diamond tip mounted to the endof the cantilever has a tip radius thatis less than 25nm to assure good
imaging resolution and nanometerscale indents and scratches. The
diamond tip is the apex of three sides
of a four-sided pyramid with an apex
angle of about 90 degrees. Toprovide symmetric indents, thediamond is mounted such that thevertical axis of the pyramid isapproximately normal to the sample
surface when mounted on
the microscope.
Unlike contact mode, our patented
TappingMode technique allows useof the high spring-constant cantilevers
required for nanoindentation, whilestill imaging the surface with minimal
damage. This is illustrated by theindentations made in the 1µm gold
ruling shown in Figure 2. The
indentation cantilever that was used toindent and image the surface has aparticularly large spring constant of
about 400N/m. If this cantilever wereused to image the gold in contact

Indentation Cantilevers
Indentation cantilevers are thicker,wider, and longer than standard AFM
cantilevers, and are composed ofstainless steel. The typical range forspring constants of contact mode,TappingMode, and indentationcantilevers are 0.01-1.0N/m,20-100N/m, and 100-300N/m
respectively. The fundamental
resonance frequency for indentationcantilevers is in the range of
35-60kHz, depending on thedimensions of the cantilever and the2a.

b.
Figure 3. (a) Indentations on a 15nm thick diamond-like carbon (dlc) thin film using three forcesof about 15, 20, and 25µN respectively. All indentations are less than 10nm deep. The smallest
indentations are approximately 3nm deep as seen in the section view (b). 800nm scan.

mode, it would have damaged thesurface sufficiently to prevent
meaningful imaging of either theindentations or the rulings. Veeco
Probes also provides an image of agold ruling, similar to Figure 2, foreach indentation cantilever sold. The
indents and the image are captured
with the same cantilever that is sold tothe customer.
Figure 4. Indentations on two different diamond-like carbon thin films
using three different forces (23, 34, and 45µN) with four indents made ateach force. Each film was indented using the same forces and cantilever inorder to compare hardness. 500nm scans.

ExamplesNanoindentation with an AFM
cantilever is useful for investigating
the hardness of films as thin as 5nm.
Since the macroscopic properties ofthin films of a material may be different
from the microscopic properties, theability to perform tests at thenanometer level is of great importancein many processes. The 15nm thickdiamond-like carbon (dlc) film in
Figure 3a was indented five times
with three different forces: about 15,20, and 25µN, respectively. The
indentations were then imaged withthe same tip, which did the indenting.
In the cross-section image (Figure 3b),the depth of the 15µN indentations(measured after any elastic recoveryof the film has occurred) is only about
3nm. The projected area of theseindentations is approximately
1,600nm2. The 20 and 25µN
indentations have depths of about
5nm and 7nm and projected areasof about 2,000 and 2,500nm2,respectively. Given the small size ofthese indentations, the ability to image
immediately with the same instrument
and tip is a major benefit.
Using indentation cantilevers, it ispossible to indent various samples withthe same force in order to compare
hardness. Figure 4 shows two different
dlc thin films that were indented fourtimes with three different forces of 23,
34, and 45µN. The same forces wereused for both films by using the same3b.

a.

c.

d.

Figure 5. Array of scratches performed on four different 10nm thick diamond-like carbon
thin films, all using the same force and cantilever in order to compare film adhesion anddurability. The scratches are 1µm long and less than 10nm deep. 2µm scans.

indentation cantilever under the sameconditions. The indentations on the left
film are smaller than the ones on theright film. For the film on the left, theaverage indentation depth for each of
the forces used is about 1.5, 3, and6nm, respectively. For the film on theright, the indentations are about twice
as deep: 3, 7, and 13nm. The
images of the two films also show adifference in the way that the material
has piled up around the indentations.

Properties such as film adhesion anddurability can also be studied using
indentation cantilevers. Figure 5 shows
four different 10nm thick dlc films(coated on computer hard disks) on
which a series of scratches were madeat a force of 15µN. The average
depth of the scratches for each film is
3, 6, 6, and 3nm for Figures 5a to5d, respectively. The material deposits,
which have piled up near thescratches are likely peels or shavings

of the film, which were scratchedaway from the surface. The films may
also have delaminated from thesubstrates causing taller features(brighter colors) in the images.

b.

a.

c.

d.

Figure 6. Worn areas on four different 10nm thick diamond-like carbon thin films
generated using the same force and cantilever in order to compare film adhesion anddurability. The worn areas are 5µm square. 9µm scans.

Figure 7. Worn area on adiamond-like carbon thin film inwhich the film delaminated from thesubstrate. The worn area is 2µmsquare. 3µm scan.
Figure 8. Digital Instruments logo
indented on a 15nm thickdiamond-like carbon thin film. The
small indents are 1nm deep and thelarge indent is about 2.5nm deep. Theforces used for the indentations wereabout 5µN and 10µN respectively.
250nm scan.

4The cantilevers used fornanoindentation and scratching canalso be used for wear testing. Figure 6
shows four different dlc films (coatedon computer hard disks) on which anarea was worn by scanning thesurface – in this case using contact
mode – at a preset force using a rasterscan pattern. The worn areas result
from only a single pass (scan) from
top to bottom over the square area.
Using this type of testing, the durabilityof materials can be compared. InFigure 6a, the film has been
completely worn away from thesubstrate, whereas the films inFigures 6c and 6d appear to haveworn only slightly with small amountsof debris shown at the edges of thescan. The film in Figure 6b exhibits
wear similar to the topmost portion ofFigure 6a; however the film did not failentirely. The image shows that films 6cand 6d are tougher than films 6a and6b. Figure 7 shows a dlc film, whichappears to have delaminated from thesubstrate of the hard disk during thewear test.
The image shown in Figure 8 is agood illustration of the indent size
and image resolution possible withthe indentation cantilevers. TheDigital Instruments logo was indented
on dlc film using the indenting
software/hardware and then imaged
with the same tip. The scan size isabout 250nm and the z-range (or fullheight range) is 4nm. The indentation
depth, measured from the image, isabout 1nm for the small indents andabout 2.5nm for the indent used to dot
the “i”. For the small indentations, theprojected area is approximately
400nm2, with spacing of 25-30nm

and indent width of about 20-25nm.
The force applied during the indent
was about 5µN for the small indents
and 10µN for the large indent.
Figure 9 shows an array ofindentations, which were performed on
two polymer films using five different
forces. Figure 9a is PMDA-ODA
polyimide and Figure 9b is BPDA-PDA
polyimide. The smallest indents areabout 20nm deep and the largest
about 200nm deep for both samples.
The average depth of the indentations
on the polymer in Figure 9b is about
85% of the depth for the polymer inFigure 9a, suggesting that the BPDAPDA polyimide is harder than thePMDA-ODA. This is consistent withthe chemical structures of the twopolyimides, which indicate that theBPDA-PDA has stronger bonding than
the PMDA-ODA. There is also an
obvious difference in the amount ofmaterial, which has piled up at theedges of the indents for each of thepolymers. The PMDA-ODA polyimide,
which has deeper indentations, hasless accumulated material thanthe BPDA-PDA.
The bovine and human sperm nuclei,
shown in Figure 10, were indented
using the same forces in order tocompare the hardness of each. Bothsamples were indented using forces ofabout 8 and 16µN, and then imaged
in air using the same indentationcantilever. The hardness of the bovine
and human sperm was calculated as
0.9 and 0.5GPa, indicating thatbovine sperm is about twice as hard
as human sperm. This result is
consistent with what is known about
the different proteins, which compact
the DNA in bovine and humansperm. Figure 10c and 10d show
full size images of the sperm nuclei,
which were imaged using theindentation cantilever.

5b.

a.

Figure 9. Indentations on two different polymers using the sameforces to compare hardness. Each sample was indented four times
using each of five forces. The first sample (a) is a PMDA-ODA
polyimide, and the second sample (b) is a BPDA-PDA polyimide.
The indentation depths vary from about 20-200nm and are deeper
for the softer PMDA-ODA polyimide. 3µm scans.

b.

a.

c.

d.

Figure 10. Indentations on bovine (a) and human (b) sperm nuclei, imaged in air andindented at forces of about 8 and 16µN. 1µm x 0.25µm scans. The hardness for thebovine and human sperm were calculated at about 0.9 and 0.5GPa, respectively. Fullsize images of bovine (c) and human (d) sperm nuclei were also imaged with theindentation cantilever. 10µm scans.