Nanoelectrical SPM in Liquid Teddy Huang, PhD Staff Applications Scientist, Bruker Nano Surfaces

Outline

• AFM Nanoelectrical Measurements

• Nanoelectrical Measurements in Liquids

• Nonpolar Liquids

• Polar Liquids

• Conclusion

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Pt

SiO2

r ~ 25 nm

h ~ 250 nm

AFM Nanoelectrical Measurements

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• Bruker provides a versatile array of nanoelectrical techniques for a multitude of applications.

PeakForce Nanoelectrical Measurements

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• For previously AFM-inaccessible, delicate samples and adds correlated nanomechanical data

• Improve tip lifetime with hard samples

• Decrease sample wear with soft samples

• Improve resolution due to sharper tips & less sample damage

Electrics

Time

PeakForce TUNA (A) topography, (B) current, and (C) adhesion maps

reveal the influence of an embedded nanotube on P3HT lamellar ordering

and current pathways. Image size 500 nm.

Leclere et al. Nanoscale, 2012, 4, 2705

DataCubes: Nanoelectrics with Fast Force Volume

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• Fast Force Volume imaging: a force-distance spectrum in every pixel

• Insert a ‘hold segment’ (= ‘dwell time’) and perform an electrical measurement during the hold segment: electrical spectrum in every pixel

• Retain advantages of Peak Force nanoelectrics

• Big data & deep data characterization

PFM phase vs Bias

• Previous webinar by Dr. Peter De Wolf: https://www.bruker.com/service/education-training/webinars/afm/using-nanoelectrical-solutions-to-expand-the-capability-of-afm.html

Nanoelectrical SPM in Nonpolar Liquids

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Non-polar liquid

• Clean surface: Mimicking vacuum for fundamental studies

• Free from capillary force: Low force imaging

• High-resolution mapping

• Generally, no need for special probes

Contact Mode in FluidContact Mode in Fluid

Contact Mode in Air Contact Mode in Fluid

KPFM in Nonpolar Liquids

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Air

Decane HDT-Au

Berger, Langmuir 2012, 28, 13892

Decane: non-polar liquid

• Alkanethiols on SAMs tune the work function of the underlying metal, which is attractive for optoelectronics.

• Obtaining reliable CPD requires clean surface. Different from UHV, KPFM in nonpolar liquids is much less technically demanding.

• Results are in excellent agreement with UPS.

UPS: -1.35 eV

Closed Loop-AM-KPFM, regular Pt/Ir coated probe

HDT: hexadecanethiol

PFM in Nonpolar Liquids: High Resolution Electromechanical Imaging

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A

B

A

B

• SCM-PIT probe

• Free from capillary force

• Resolution is only limited by the tip radius

• Domain wall, ~ 10 nm

Unpublished results. Paper under review.

Contact Resonance - PFM in Nonpolar Liquids

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A

B

A

B

A B

A

B

• Drive near or coincide with the contact resonance (CR) for signal enhancement.

• Single frequency measurement is insufficient.

• DCUBE-CR-PFM: frequency sweep on every image pixel for resonance tracking

• Phase at contact resonance is robust to differentiate domains of different polarizations

Unpublished results. Paper under review.

DCUBE-CR-PFM: PPLN in Decane

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• High Volume, High Throughput:

260 image / channel x 4 channels = 1040 images

• High Spectra Resolution: 0.67 kHz / image

• Correlated Images and Channels

• All QNM images

Unpublished results. Paper in review

Unpublished results. Paper under review.

DCUBE-CR-PFM: PPLN in Decane Dynamic Electromechanical Properties

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Along frequency direction Along X direction Along Y direction

Fre

qu

en

cy (

kH

z)

Fre

qu

en

cy (

kH

z)

• PFM amplitude channel

• Dynamic electromechanical properties along drive frequency

• Spatial dynamic changes along X and Y directions

Unpublished results. Paper under review.

DCUBE-CR-PFM: PPLN in Decane Statistical Analysis

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Unpublished results. Paper under review.

• Correlation of amplitude channel with phase channel

• Density plots show which PFM responses are most commonly present

• Two distinct PFM domains are differentiated by the two density plots

A

B

A

B

A

B

A

B

A

B

A

B

DCUBE-CR-PFM: PPLN in Decane Quantitative Analysis

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pm

pm

Unpublished results. Paper under review.

DCUBE-CR-PFM: PPLN in Decane Phase at Contact Resonance

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• DCUBE enables the generation of a map of PFM phase at contact resonance.

Unpublished results. Paper under review.

Nanoelectrical SPM in Polar Liquids

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Battery • Applications

• Energy research

• Bio-electricity

• Electromechanics

• Catalysis

• Sensor

Energy/Catalysis

Lee et al. Adv. Mater. 2014, 26, 4880

Bio-electricity

Kumar et al. ACS Appl. Mater. Interfaces, 2017, 9, 28406

Jiang et al. ChemSusChem, 2017, 10, 4657

Nanoelectrical SPM in Polar Liquids

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• Challenges

• Compatibility:

Environment & chemicals

• Parasitic EC reactions: Background signal

• Stray capacitance Background signal & slow response

• Conductive liquid: De-localized electric field

Nanoelectrical Liquid Imaging

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• Bruker Solution

• Isolated, leakage-free nanoelectrode

• Optimized, special tip holders, container (EC cells)

• Good implementation of electrical modes (existing from air)

PFM in Biomimetic Environment

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Bruker Nanoelectrode • Physiological environment: ~ 150 mM, pH ~ 7.0.

• Bio-compatible ferroelectric crystal in NaCl electrolytes.

• Insulated probe for enhanced resolution.

• < 0.5 M, OP domain wall can be recognized clearly.

In collaboration with Dr. Anyang Cui from East China Normal University. Paper under review.

Air- CR H2O – fair, non-CR H2O - CR 0.01 M NaCl 0.1 M NaCl

0.5 M NaCl 1 M NaCl

PFM in Biomimetic Environment

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• High-resolution PFM in liquid: domain wall ~ 30 nm, superior to non - insulated probe

SECM Probe

w = 35 nm

In collaboration with Dr. Anyang Cui from East China Normal University. Paper under review.

KPFM in Polar Liquids

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Pt

Pt

Si3N4

Si3N4

• PF-KPFM: DMC, H2O, dilute NaCl solution

Honbo K, et al. Acs Nano, 2016, 10, 2575

• KPFM for research in battery, corrosion etc.

• Corrosion behaviors of Cu and stainless steel. • Areas of higher potential correspond to corrosion sites.

• Challenges: only work for low concentration electrolyte

• Alternatives: SECPM or tech by Boettcher’s group

PeakForce TUNA in Liquid Interfacial Energetics on a Photoelectrode

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Air

Liquid

Liquid on SiO2

-250 pA

100 pA

120 nm

120 nm

Sample bias: 0.3 V

Huang et al. Microscopy Today 2016, 24, 18

• Semiconductor/metal catalyst photoelectrodes.

• Electrolyte solution impacts interfacial energetics.

• Sample shows diode behavior in air.

• I-V characteristics in H2O totally changes. Nellist et. el. Accounts Chem Res, 2016, 49, 733

Surface Layer or SEI for Li Batteries

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Surface layer or solid electrolyte interface (SEI)

• Ionically conductive, electrically insulating, and mechanically elastic and robust.

• Essential for good power cyclability, cycle life and cell safety

• Dynamic phase during voltage cycling

LiNi0.5Mn1.5O4 Cathode: Facet Effect, in situ study

Liu et. al. Chem. Commun. 2014, 50, 15756

• Facet-dependent SEI formation during the first charge–discharge process.

• The surface film with a thickness of 4–5 nm was formed on the (111) surface.

• Not detectable change for (100)

LiCoO2 Cathode in Glovebox 1 M LiPF6:EC:DMC (1:1 in volume) 300 mV sample bias

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Before any charging After stabling at 4.2 V

(de-lithiation)

Featureless low current

Iave: 180 pA

Saturated

Voltage pattern

Courtesy: Prof. Zhigao Huang, Prof. Yingbin Lin, and Dr. Yue Chen, Fujian Normal University, China

• In Situ imaging of topography, mechanics, conductivity change of the surface layer

• Edges of particles smoothen out

• Some boundaries shows conductivity

Conclusion

• Brukeroffers a set of unique solutions that enables nanoelectrical studies in liquids

• Using isolated nanoelectrode tips, one can carry out high-performance electrical measurements in polar liquids in multiple modes for a variety of applications

• TUNA & PeakForce TUNA

• KPFM & PeakForce KPFM

• PFM

• DCUBE

• Nanoelectrical SPM enables new research areas

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Pt

SiO2

r ~ 25 nm

h ~ 250 nm

SECM Probe

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25 Bruker Confidential