PeakForce Scanning Electrochemical Microscopy: AFM-SECM ...

PeakForce Scanning Electrochemical Microscopy: AFM-SECM with PeakForce Tapping

Teddy Huang, PhD Sr. Applications Scientist, Bruker Nano Surfaces, [email protected]

SiO2 Au

Outline

• Motivation

• PeakForce SECM equipment

• PeakForce SECM applications

• Nanoelectric measurements in liquid

9/7/2016 2 Bruker Confidential

Why PeakForce SECM?

• Energy driven research • Batteries

• Photovoltaics

• Fuel cells

• Solar fuels

• Biology and biosensors • Enzyme activity

• Membranes permeability

• Respiratory activity

• Neurotransmitter detection

• Materials and corrosion

• Electrolysis

• Synthesis

• Surface etching/coatings

• Anti-corrosion coatings


1.65 nA

1.25 nA

SEI evolution during battery cycling

Catalyst nanoparticles with different EC activities

• In situ study

• Localized approach

• High resolution

• Surface topography

• Mechanical failure

• Electrical performance

• EC behaviors

Scanning Electrochemical Microscopy

• Conduct electrochemical measurements on the scale defined by the tip dimension.

• The nature and properties of the substrate perturb electrochemical processes on the tip.


R O

M

M

M M

M

M

M

M M M

M

e

SECM for Local Electrochemistry


Unwin, Physiol. Meas. 2006, 27, R63

• Current response changes upon imaging certain features

Conductor

Insulator i

SECM for Local Electrochemistry


• Approach curves for quantifying interfacial charge transfer dynamics

Bard & Mirkin, SECM (2nd Ed), CPC Press, Boca Raton, 2012

i

Charge transfer rate, k (cm/s):

a. 1, conductor

b. 0.5

c. 0.1

d. 0.025

e. 0.015

f. 0.01

g. 0.005

h. 0.002

i. 0.0001, insulator

Conductor

Insulator

Hynek et. al. InTech, 2014, DOI: 10.5772/57203

• Typically, µm-sized disc electrode: intrinsic “low” resolution

• Typical imaging modes: convoluted topographic & EC information

Classic SECM and Its Limitations


Constant height Constant current

AFM Based SECM

• True nanoelectrodes = true nanoscale resolution

• Precise position control: e.g. the lift height in interleaved scan mode

• Can be combined with most advanced imaging mode: PeakForce Tapping


Lift height

Topography and other properties

Electrochemistry

PeakForce Tapping


Probe is sinusoidally modulated at 1~2 kHz:

• Ultralow imaging force, < 50 pN.

• Stable force control.

• High resolution imaging.

• Ease-of-use:

• No cantilever tuning required.

• Automatic image optimization.

• PeakForce Quantitative NanoMechanics.

• Simultaneous nanoelectric measurement.

Time Z position Separation

Electric

Time

Double-helix corrugation and height of a DNA plasmid imaged at a peak force of 49 pN.

Pyne et. al., Small, 2014, 10, 3257

PeakForce EC-AFM


Probe Holder

EC Cell

Closed Cell

When Engaged

• PeakForce imaging on a working electrochemical system.

• A built-in heater and temp control system (ambient ~ 65o).

• Electrochemical cell designed to be compatible with a wide range of electrochemistry.

• It closes up on tip engage for volatile solvents or additives.

PeakForce EC-AFM in Glovebox


PeakForce EC-AFM in Glovebox


Cycle 1 Cycle 2

PeakForce EC-AFM vs. PeakForce SECM


AFM Probe

Counter

Reference

Sample

PeakForce Tapping Force Control

• PeakForce EC-AFM:

• PeakForce imaging during electrochemical reactions for topography and mechanics.

• PeakForce SECM:

• The probe is a nanoelectorde and part of the electrochemical system.

• Simultaneously capture multidimensional correlated information:

Topography, mechanics, conductivity, electrochemistry, etc.

PeakForce EC-AFM PeakForce SECM

Sample

E vs Ref

E + ΔV vs Ref

O + e R

R O + e

SECM Probe

• Probe

• Bruker batch manufactured

• Exposed tip height: ~ 200 nm

• End tip diameter: ~ 50nm

• Exposed tip material: Platinum

• Passivation: silicon dioxide

• Package

• Fully isolated

• Encapsulated in two parts glass

• Easy to handle package

• Chemical resistant epoxy


100 µm

• Current flow only through the tip apex - no leakage elsewhere through tip or tip mount

SECM Probe: Nanoelectrode

• Robust for handling and electrochemistry:

4 rinse-and-dry cycles, 5 min amperometry, and 29 CV cycles


10 pA

High-quality insulating coating

Scan rate: 20 mV/s; 2.5 mM [Ru(NH3)6]3+; 0.1 M KNO3.

pA 2000 i



t

i

Cyclic voltage: -0.5 V to +0.1 V

Scan rate: 300 mV/s

• 50 CVs plotted in the i-t fashion


• Highly localized diffusion layer

• 60% recovered at 50 nm away from the tip surface


0

5

10 mM

Image courtesy of C. Xiang and Y. Chen, JCAP, Caltech

[Ru(NH3)6]3+ [Ru(NH3)6]

2+

e

COMSOL simulation of [Ru(NH3)6]3+ concentration profile

PeakForce SECM Setup


Insert the probe

Complete PeakForce SECM Solution

Packaged probe SECM tip holder Assembled probe, tip holder and EC boot

Bipotentiostat Use EC option

PeakForce SECM Software


Integration of EC with AFM data

V-t plot

i-t plot

Topography, mechanics, conductivity, and electrochemistry

Adhesion Height Sensor

Current (lift) Current (main)

EC panel

AFM panel

Force display

PeakForce SECM: Approach Curves

• > 20% negative/positive feedback current

• Changes mostly occur within 150 nm

• Stable and reproducible approach curves

• Stable for EC and mechanical robustness


Conductor

Insulator

Contact current

10 mM [Ru(NH3)6]3+, 0.1 M KCl, Ag/AgCl reference

Tip: -0.4 V; Sample: -0.1 V or N/A

COMSOL simulation

Image courtesy of C. Xiang and Y. Chen, JCAP, Caltech

How does PF-SECM work?


Current (main)

0.5

15 nA

Si3N4

55 nm

Au 7 nm Height

Au 0 nm

2 µm 500 nm

Current (lift)

0.55

0.7 nA

Au

Si3N4

Approach Curves

Location (m)0 5 10 15 20

Curr

ent

(pA

)

575

600

625

650

675

Hei

ght

(nm

)

0

15

30

45

60

Au

Si3N4

Cross-Sectional Profiles

• Clearly differentiate Au and nitride features on sub-µm scale through topography, conductivity and electrochemistry

10 mM [Ru(NH3)6]3+; Tip: -0.4 V; Sample: -0.1 V

Δi

Image courtesy of C. Xiang and Y. Chen, Caltech

Outline

• Motivation



• Nanoelectrode probe

• Nanomesh electrode

• 3D electrochemistry

• Nanoelectrode array

• Interfacial charge transfer dynamics

• Self-assembled monolayer (SAM)

• Surface defect on highly-oriented poly graphite (HOPG)

• Nanoparticle catalysis


• HOPG: anisotropic conduction in liquid

• Semiconductor/metal junction in liquid


Applications: Nanoelectrodes


• General electrochemical applications

• Diffusion, electrode potential, reversibility, etc.

• High rate of mass transport

• Interfacial reaction kinetics

• Low current electrochemistry

• Resistive media

• Two-electrode configuration

• Steady-state electrochemical current

• Fast electrochemistry

• Rapid detection

• Rapid response

• Low characteristic dimension

• Small volume detection: single cell

• Singe particle electrochemistry

• Localized signal

• High S/N

• Electricity in liquid

10 pA

Sample

Sample chuck

DC bias

Amplifier, filter and gain stage

to A/D

AC bias

“Nanoelectrodes: Applications in electrocatalysis, single-cell analysis and high-resolution electrochemical imaging” Clausmeyer & Schuhmann, Trends Anal. Chem., 2016, 79, 46








• Resistive media




• Rapid detection

• Rapid response





• High S/N


10 pA

Sample

Sample chuck

DC bias


to A/D

AC bias









• Resistive media




• Rapid detection

• Rapid response





• High S/N


10 pA

Sample

Sample chuck

DC bias


to A/D

AC bias


Nanomesh Electrode (Au-SiO2)


SiO2

Au

Sample courtesy: C. Stelling, M. Retsch, Physical Chemistry, University of Bayreuth Image courtesy: A. Mark, S. Gödrich, G. Papastavrou, Physical Chemistry, University of Bayreuth

• Stretchable, foldable, and transparent conducting electrodes.[1]

• Preparation by nanosphere lithography.[2]

• Crucial components for optoelectronic and photoelectrochemical devices.

[1] Jang & Park et. al. Chem Mater 2013, 25, 3535; [2] Stelling, Mark, Papastavrou, & Retsch, et al. Nanoscale, 2016, 8, 14556

Nanomesh Electrode (Au-SiO2)


SiO2

Au

SiO2

Au

Current (lift)

Location (m)

0 1 2 3 4 5

Hei

ght

(nm

)

0

20

40

60

80

100

120

Tip

curr

ent

(pA

)

70

75

80

85

90

95

100Height

Current


• Increased current over Au areas

• Tracking of the current over the sample profile: < 100 nm resolution

Δi

, d

d

Nanomesh Electrode -- 3D Electrochemistry



Lindner, Anal. Chem. 2009, 81, 130

Location (m)

-0.2 0.0 0.2 0.4 0.6 0.8 1.0

Cu

rren

t (p

A)

230

240

250

260

Hei

gh

t (n

m)

0

50

100

150

200

25050 nm

75 nm

100 nm

150 nm

200 nm

400 nm

Height

Nanomesh Electrode -- 3D Electrochemistry



50 nm

75 nm

100 nm

150 nm

200 nm

400 nm

200 nm

150 nm

100 nm

75 nm

Current (lift)

Au SiO2 Au Au SiO2 Au

Nanoelectrode Array


• Integrated sensor systems

• Advantages from nanoelectrode

• Enhanced S/N

• Bioelectroanalysis


O’Riordan et. al. Faraday Discuss., 2013, 164, 377

Sample courtesy of M. Nellist and Prof. S. Boettcher, Univ. Oregon

Nanoelectrode Array


• < 100 nm EC resolution

• Inhomogeneous interface conductivity

• Inhomogeneous EC activities

Current (main)

Current (lift)

Hot spot of conductivity, > 1nA

Hot area of EC activity

Location (nm)

0 200 400 600 800

Hei

gh

t (n

m)

0

20

40

60

80

Rel

ativ

e C

urr

ent

(pA

)

-6

-4

-2

0

2

4

6

8

10

70 nm


Charge Transfer Dynamics


3 µm

3 µm

3 µm

Si3N4

Pt

• Inhomogeneous conductivity

• Inhomogeneous electrochemical activity

• Approach curves of distinct characteristics

• Applications:

• Etch resists

• Barriers to charge transfer

• Platforms for biological surfaces

• Sensors, etc.

Self-Assembled Monolayers (SAMs)


5 µm

Zhao et. al., Phys. Chem. Chem. Phys., 2006, 8, 5653.

• Desired properties:

• Topographic homogeneity

• Controlled conductivity

• Chemical stability

• Tailorable electrochemistry

• Topography variation: ~ 1 nm

• Quantitative adhesion: clear differentiation of SAM from Au regions

• Electrochemistry: SAM results in reduced tip faradaic current

Self-Assembled Monolayers


Image courtesy: A. Mark, S. Gödrich, G. Papastavrou, Physical Chemistry, University of Bayreuth

5 µm

Au

Thiol SAM

Au

Highly Oriented Poly Graphite (HOPG)


• Numerous applications

• Functionalized interfaces.

• Electrochemical sensors.

• Electrocatalysis.

• Nanoscale electrochemistry

• Basal planes

• Edge sites

• Surface defects.

Surface Defect on HOPG


Location (m)

0.0 0.4 0.8 1.2 1.6H

eig

ht

(nm

)

-6

-4

-2

0

Tip

cu

rren

t (p

A)

480

495

510

525

5400.4 nm step

55 pA difference

4 nN difference

800 nm

800 nm

800 nm

900 nm x 600 nm

2~5 pA higher

Catalytic Nanoparticles on Electrode


• Chemical manufacturing, energy-related applications and environmental remediation.

• Compositions, sizes, shapes, structures, patterns and interfacings with the substrates.

• Impacts from the electrolyte or surrounding media.

Freund et. al. Accounts Chem Res 46, 1673 (2013)

Catalytic Nanoparticles on Electrode


1 2

3 (> 4 nA) 4

1 2

3 4

Current (main)

Current (lift)

1.3 nA

1.7 nA

1 2

3 4

Height

-25 nm

125 nm

Peak force: 400 pN; Scan size: 750 nm; Scan rate: 0.2 Hz; Lift height: 75 nm;

Sample courtesy of J. Jiang, Caltech

Outline

• Motivation



• Nanoelectrode probe

• Nanomesh electrode

• 3D electrochemistry

• Nanoelectrode array

• Interfacial charge transfer dynamics

• Self-assembled monolayer (SAM)

• Surface defect on highly-oriented poly graphite (HOPG)



• HOPG: anisotropic conduction in liquid

• Semiconductor/metal junction in liquid


Nanoelectric Measurement in Liquid

• Insulating probe with only the tip apex exposed

• Combined with PeakForce mode


Electrical

PeakForce Tunneling AFM

(PF-TUNA)

C: Peak current

B-D: Contact current

A-E: TUNA current

PF-TUNA in Liquid: HOPG in di-H2O


• Generally,

• Local contact current depends on local configurations.

40//

Armchair

Zigzag

• Negligible stray current.

Banerjee et. al. Phys Rev B, 2005, 72, 075418

Contact

current

TUNA

current

• Anisotropic conduction. • ≥0.5 µA tip current.

Semiconductor/Metal Junction in Liquid


• Semiconductor/metal catalyst photoelectrodes:

Solar-driven pollutant decomposition, water purification, and artificial photosynthesis.

• Electrolyte solution impacts interfacial energetics.

Boettcher, et. el. Accounts Chem Res, 2016, 49, 733

Semiconductor/Metal Junction in Liquid

• Minimized background current from the contact current.

• Sample shows diode behavior in air

• I-V characteristics in H2O totally changes



air

Liquid

Liquid on SiO2

Bias: 0.3V

Conclusion

• Bruker’s new AFM-SECM probe technology improves SECM lateral resolution by orders of magnitude and opens the door to new measurements on individual nanoparticles, -phases, and –pores

• PeakForce SECM enables the highest spatial resolution on soft and fragile samples

• PeakForce SECM simultaneously images correlated topographic, mechanic, electrochemical and conductivity information

• PeakForce nanoelectrical measurements in liquid provide new capabilities for visualization of electrical processes in solution


5 µm

Au

Thiol SAM

Au

Acknowledgements


Sebastian Gödrich Andreas Mark Prof. Georg Papastavrou Christian Stelling Prof. Markus Retsch

• Universität Bayreuth

• Joint Center for Artificial Photosynthesis (Caltech); CCI Solar (Caltech)

Dr. Chengxiang (CX) Xiang Dr. Bruce Brunschwig Yikai (Katie) Chen Jingjing (Jessica) Jiang

• University of Oregon

Prof. Shannon Boettcher Michael Nellist

• University of Leeds

Prof. Christoph Wälti Dr. Andrew Lee Dr. William Morton

Ravi Kumar Prof. Brian Sheldon Dr. Anton Tokranov

• Brown University

Dr. Xingcheng Xiao

• General Motors R&D

© Copyright Bruker Corporation. All rights reserved.

www.bruker.com

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