Application Note

#157

Webinar Recap:
A Guided Tour of AFM Modes forMaterials Characterization
The hundreds of modes + probes combinations available today provide endless
opportunities for AFM studies in materials research. In this webinar, Bruker
AFM experts reviewed modes ranging from the foundational to the specialized.
They presented case studies for four different application spaces: polymers,
semiconductors, battery technology, and 2D materials.

Modes 101
At the hub of the AFM modes “wheel” – as Application Manager Ian Armstrong
calls it – are the primary topographical modes. These include contact mode,TappingMode™, Fast Scanning, as well as Bruker’s exclusive PeakForceTapping®. Extending beyond topographical imaging are the spokes of thewheel, the secondary or derivative modes. While many secondary modes exist,
they all generally fall into the categories of: electrical, mechanical, thermal,
electrochemical, chemical, and fabrication. As a bonus, all these modes can be
performed in a variety of environmental conditions: in a glove box, heated orcooled, with controlled humidity, or in a controlled atmosphere.

Webinar Presenters:
Ian Armstrong, Ph.D.
Peter De Wolf, Ph.D.
John Thornton, Ph.D.
Ravi Chintala, Ph.D.
Senli Guo, Ph.D.

In this webinar, our webinar hosts gave 22 specific case study examples of AFM
modes used in several important applications in materials research and industry.

FIGURE 1.
Collection of AFM application andprobe tip images.

Polymers
Dr. Thornton presented four different polymer
case studies:
1.

Nanomechanical and nanochemical characterization of impact
modified copolymers
PeakForce QNM®, AFM-nDMA, and AFM-IR were used to conduct
nanoscale property mapping on impact modified copolymers [1,2].
These modes provide insights into the distribution of individual
copolymer components and provide quantitative measurements of
the resulting elastic, viscoelastic, and chemical properties.

2. Temperature studies of PHB/V crystallization
Fast scanning was used to directly observe in situ crystallization ofPoly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/V) in real-time.
Varying the temperature of the sample resulted in changes to boththe crystal structure and growth dynamics. Related publications
can be found at [3,4].
3. Thermal analysis of multilayer packaging material
Using the AFM tip to induce localized heating, nanoscale thermal
analysis (nanoTA) was conducted on a cross-sectioned multilayer
packaging material, seen in Figure 2. At each location, melting
temperature of the component of interest was determinedby identifying when the tip deflected into the sample, without
needing to heat the bulk of the sample.
4. Electrical measurements on P3HT thin films with
conductive fibers
PeakForce TUNA™ was a key technique used to relate chargetransport in Poly(3-Hexylthiophene) (P3HT) directly to its multiscaleordered structure [5].

MODES
Terminology
PeakForce QNM– PeakForce Quantitative
Nanomechanical Mapping

AFM-nDMA– AFM Nanoscale Dynamic
Mechanical Analysis

AFM-IR– Atomic Force MicroscopyBased Infrared Spectroscopy

nanoTA– Nanoscale Thermal Analysis

TUNA– Tunneling AFM

C-AFM– Conductive AFM

SCM– Scanning CapacitanceMicroscopy

KPFM– Kelvin Probe ForceMicroscopysMIM– Scanning Microwave
Impedance Microscopy

FIGURE 2.
Polymer multilayer packaging material, analyzed
using nanoTA to determine local melting
temperature of layers and interfaces.

2

Semiconductors
Dr. Chintala presented how various
nanoelectrical AFM modes are used
to study semiconductor materials anddevices.
1.

Organic photovoltaic material
Variations in local conductivity measured
by C-AFM™ revealed phase separationof the components within the material.
Current maps (e.g., Figure 3, right) are an
indirect indicator of the chemical nature of
the sample.

After these images obtained throughconstant external bias (or constantcurrent), Dr. Chintala expanded his
examples to those that included
another measurement element:
5. DataCube SCM on PNP transistors
To obtain a 3D cube of data (capacitanceas a function of voltage at each locationin the sample), the voltage is ramped
at each point while the capacitance ismeasured. That data is stored in an array
which can be resliced and analyzed forany relevant axis value. In this case, thedata (from N. Chevalier and D. Mariolle ofUni. Grenoble Alpes, CEA, LETI, France)
notably showed a defect only at certain
applied voltages in PNP transistors.
– Note: You can learn more about DataCube
modes from our free E-Book that can be
downloaded here.

FIGURE 3.
Conductive AFM enables high-resolution current
mapping that directly correlates to topgraphicaldata in this organic photovoltaic material.

2. Device failure analysis
Deposited metal contacts on a device
surface were imaged by C-AFM. The
resulting conductivity map revealed
differences in the quality/consistencyof the contacts. I-V spectra werethen collected on individual contacts
which provided localized, quantitative
measurements of their conductivity.
3. Defect characterization
Defects in the SiO² layer of a siliconbased device were imaged using TUNA
mode in constant current mode (where
the feedback loop maintains a constantcurrent by adjusting the applied voltage).
Areas of lower voltage indicate thepresence of a defect in the oxide layer.
Supplemental TEM imaging showedthat this defect was the result of oxidethinning.
4. Dopant carrier profiling
Using scanning capacitance microscopy(SCM), the carrier type and concentration
were assessed through the cross sectionof a 70 nm dopant layer of a silicon
device. Mapping phase and amplitude
information from the capacitance (dC/dV) signal identified locations of p- and ntype carriers and lossy regions as well as
concentration of carriers at each point.

6. C-AFM tomography of a conductive
filament
In AFM tomography, a very hard(e.g., diamond) probe is used to remove
material from the surface with a larger
force, then imaging on the newly-exposed
surface occurs at a lower force. Repeating
this removal-then-imaging cycle, a set of
known-depth image slices are generated.
Stacking of these image slices creates a
tomographic dataset, as in the example
shown of a conductive filament [6].
7.

Photo-KPFM on organic materials
Though the height and adhesion channels
did not show a difference between the“light on” and “light off” conditions of anorganic photovoltaic (sample courtesyof P. Leclère, University of Mons), thepotential channel using Kelvin probe force
microscopy (KPFM) did. When the light
was switched on, the surface charged andthe work function changed.

8. Dopant carrier profile forprocess monitoring
A bonded device was cross sectioned,
so that two samples could be scannedside by side. Dopant concentration wasmeasured using scanning microwave
impedance microscopy (sMIM) acrossthe two samples. The plot of dopant
concentration (data from PrimeNano
Inc.) clearly showed different regions
and made it straightforward to spot
differences between the two samples.

3

Battery Technology
Dr. Guo presented several case studies looking into theindividual components of lithium-ion batteries (LIB). He
noted that since LIB are so well-developed and AFM
is so versatile, there has been battery research doneusing a wide variety of AFM modes. Importantly, thesemeasurements often take advantage of the adaptability ofenvironmental conditions: in a glove box, in liquid, or atvarious temperatures.
1.

Cathode electrical and mechanical property mapping
DataCube tunneling AFM (TUNA) was used to test conductivityof a cathode sample under different voltages. Looking at different
signal channels, the sample was mapped according to height,
stiffness, modulus, and current. With the DataCube capability
added in, an image could be extracted for discrete values within
the voltage sweep (along the I-V curve).

2. SEI layers on graphitic electrodes
In-situ solid electrolyte interface (SEI) layer growth was compared
between two different graphitic materials using C-AFM [7]. The
layer could be seen to grow during charging until reaching a
relatively homogeneous state for the highly ordered pyroltic
graphite. In contrast, the disordered graphite had preferential
growth at the edges and less uniform defect shapes.
3. Microfabricated amorphous silicon anode
Anodes are typically C-based, but an alternative with highcapacitance is microfabricated Si-based anodes. This case study
for C-AFM layered aluminum oxide (Al²O³) onto a Si-based anodeand tracked topography and performance over several charging
cycles [8]. Without the Al²O³ protective layer, there were significant
changes in the topography and conductivity of the anode.
4. Ion and electron migration in composite solid-state electrolyte
AFM was used to examine the mechanisms of ion and electron
migration in a composite solid-state electrolyte at different
temperatures and with varying amounts of Lithium lanthanum
zirconium oxide (LLZO) [9]. With increasing temperature, modulus
decreased and adhesion increased. At higher temperatures,
the Poly(ethylene oxide) (PEO) deviated from its crystalline
form (seen through topographical imaging). Conductivity
measurements indicated that the PEO was only conductivein the high-temperature amorphous phase, and not in thelower-temperature crystalline phase.

FIGURE 4.
This sample is a metal oxide cathode measured with
DataCube TUNA. Property maps shown are (left to right):
height, modulus, and conductivity.

4

2D Materials
Dr. De Wolf presented the final six case studies,on the topic of 2D materials:
1.

Epitaxial graphene on SiC
A silicon carbide (SiC) sample was partially covered in graphene,
with preferential coverage at the edges of the SiC steps (sample
courtesy of R. Elmquist, NIST). Topography alone does not clearlyshow the location of graphene coverage, but it can be seen using
adhesion, DMT modulus, surface potential, or phase mapping.

2. Suspended graphene membranes
PeakForce Tapping was used to nondestructively image fragile
suspended graphene membranes [10]. The very low imaging
forces available in PeakForce Tapping mode made this imaging
possible, where TappingMode was unsuccessful.
3. Programmable graphene nanobubbles
A voltage was applied between tip and sample to desorb
hydrogen on a germanium (Ge) substrate and form hydrogen gas
nanobubbles [11]. This method can produce localized nanobubbles
with incredible resolution and control.
4. Co-localized Raman and KPFM on graphene
Topographical and KPFM imaging were performed on a multilayer
graphene sample. Raman microscopy was carried out at the same
location as the topographical and KPFM imaging (co-localized
imaging). From the resulting correlated datasets, it was possible
to distinguish each of the graphene layers and the properties ofeach successive layering.
5. Moiré pattern graphene on hBN
Overlaid graphene and hexagonal boron nitride (hBN) withdifferent respective orientations combine to produce different
moiré patterns. The moiré pattern in different zones of the sample(corresponding to different orientations) was observed with sMIM
(data provided by PrimeNano Inc.), and periodicity was measured,
down to several nanometers.
6. Nanoscale redox mapping at the MoS²-liquid interface
In this study, single- and multilayer molybdenum disulfide (MoS²)
were placed in an electrochemical environment and measured
using scanning electrochemical microscopy (SECM) and
KPFM [12]. The resulting data showed that electrochemical activity
scaled with layer thickness.

FIGURE 5.
Graphene grown epitaxially on SiC, mapped using
PeakForce QNM, PeakForce KPFM™,
and PeakForce TUNA.

FIGURE 6.
Co-localized mappingof graphene: height,
Raman G-band, andRaman 2D-band (topto bottom).

5

Further Information[1] Pittenger, B., Osechinskiy, S., Yablon,D., and Mueller, T. (2019). Nanoscale DMA
with the Atomic Force Microscope: A New
Method for Measuring Viscoelastic Propertiesof Nanostructured Polymer Materials. JOM,
71(10), 3390–3398. https://doi.org/10.1007/
s11837-019-03698-z[2] Tang, F., Bao, P., Roy, A., Wang, Y., and Su,
Z. (2018). In-situ spectroscopic and thermal
analyses of phase domains in high-impact
polypropylene. Polymer, 142, 155–163.
https://doi.org/10.1016/j.polymer.2018.03.037[3] Farrance, O. E., Jones, R. A. L., andHobbs, J. K. (2009). The observation of rapid
surface growth during the crystallizationof polyhydroxybutyrate. Polymer, 50(15),3730–3738. https://doi.org/10.1016/j.
polymer.2009.05.061[4] Hobbs, J. K., Farrance, O. E., and Kailas,
L. (2009). How atomic force microscopy has
contributed to our understanding of polymer
crystallization. In Polymer (Vol. 50, Issue
18, pp. 4281–4292). Elsevier BV. https://doi.
org/10.1016/j.polymer.2009.06.021[5] Wang, B., Chen, J., Shen, C., Reiter, G.,
and Zhang, B. (2019). Relation Between
Charge Transport and the Numberof Interconnected Lamellar Poly(3Hexylthiophene) Crystals. Macromolecules,
52(16), 6088–6096. https://doi.org/10.1021/
acs.macromol.9b01146[6] Celano, U., Goux, L., Belmonte, A.,
Opsomer, K., Franquet, A., Schulze, A.,
Detavernier, C., Richard, O., Bender, H.,
Jurczak, M., and Vandervorst, W. (2014).
Three-Dimensional Observation of theConductive Filament in Nanoscaled Resistive
Memory Devices. Nano Letters, 14(5), 2401–
2406. https://doi.org/10.1021/nl500049g[8] Becker, C. R., Prokes, S. M., and Love, C.
T. (2016). Enhanced Lithiation Cycle Stabilityof ALD-Coated Confined a-Si Microstructures
Determined Using In Situ AFM. ACS Applied
Materials and Interfaces, 8(1), 530–537.
https://doi.org/10.1021/acsami.5b09544[9] Shen, C., Huang, Y., Yang, J., Chen,
M., and Liu, Z. (2021). Unraveling themechanism of ion and electron migrationin composite solid-state electrolyte using
conductive atomic force microscopy. Energy
Storage Materials, 39, 271–277. https://doi.
org/10.1016/j.ensm.2021.04.028[10] Clark, N., Oikonomou, A., andVijayaraghavan, A. (2013). Ultrafast
quantitative nanomechanical mappingof suspended graphene. Physica Status
Solidi (b), 250(12), 2672–2677. https://doi.
org/10.1002/pssb.201300137[11] Jia, P., Chen, W., Qiao, J., Zhang, M.,
Zheng, X., Xue, Z., Liang, R., Tian, C., He, L.,
Di, Z., and Wang, X. (2019). Programmablegraphene nanobubbles with three-foldsymmetric pseudo-magnetic fields. Nature
Communications, 10(1), 3127. https://doi.
org/10.1038/s41467-019-11038-7[12] Du, H.Y., Huang, Y.F., Wong, D., Tseng,M.F., Lee, Y.H., Wang, C.H., Lin, C.L.,
Hoffmann, G., Chen, K.H., and Chen, L.C.
(2021). Nanoscale redox mapping at the
MoS²-liquid interface. Nature Communications,12(1), 1321. https://doi.org/10.1038/s41467021-21660-z

Bruker Nano Surfaces and Metrology
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www.bruker.com/AFMmodes

are trademarks of Bruker. All other trademarks are the property of their respective companies. All rights reserved. AN157, Rev. A0.

References[7] Zhu, H., Russell, J. A., Fang, Z., Barnes,
P., Li, L., Efaw, Corey, M., Muenzer, A., May,J., Hamal, K., Cheng, I. F., Davis, P. H., Dufek,
Eric, J., and Xiong, H. (2021). A Comparisonof Solid Electrolyte Interphase Formation and
Evolution on Highly Oriented Pyrolytic andDisordered Graphite Negative Electrodes in
Lithium-Ion Batteries. Small, 17(52), 2105292.
https://doi.org/10.1002/smll.202105292©2023 Bruker Corporation. C-AFM, PeakForce KPFM, PeakForce QNM, PeakForce Tapping, PeakForce TUNA, and TappingModeIf you would like more information after
watching the webinar, you can visit our
website page describing the modes, orfind probes to match your application. You canlearn more about DataCube modes from ourfree E-Book that can be downloaded here.