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Keysight Technologies
In Situ Electrochemical Measurements
Using Keysight 7500 AFM
Application Brief
Introduction control both the potential of the sample and the
potential of the probe versus the same refer-
EC-SPM essentially combines two valuable, ence electrode. As with usual STM imaging, the
independent techniques: electrochemistry (EC) tunneling current between the tip and the sample
and scanning probe microscopy (SPM). The depends on the potential difference as well as
electrochemical unit includes a potentiostat and the distance between the two, and is used as
a three-electrode cell that controls the electro- the control signal for STM image formation. In
chemical state of the working electrode, usually EC-STM, the morphological information about
the sample. The scanning probe microscope the electrode surface under potential control can
characterizes the surface of the solid electrode be imaged in constant-current mode, and the
with either a passive or an active probe. changes in the localized electronic state of the
electrode surface with electrochemical poten-
With a passive probe like that utilized in EC- tial can be studied using "current vs. voltage"
AFM, the potential of the probe is not controlled. spectroscopy.
Thus, the AFM cantilever acts as an inert probe
that monitors the topographic changes of the EC-SPM can deliver nanometer-scale resolution
electrode surface caused by electrochemical of the electrode surface in liquid. The true merit
processes (using standard AFM imaging modes). of EC-SPM, however, is the capability to control
the experimental conditions (e.g., temperature
On the other hand, with an active probe like that and humidity) and mimic the real-world environ-
utilized in EC-STM, a bipotentiostat is used to ment of the sample under test. This is particularly
important for energy and corrosion research.
02 | Keysight | In Situ Electrochemical Measurements Using Keysight 7500 AFM - Application Brief
Instrumentation The Keysight 7500 can also be equipped
with an optional bipotentiostat that
The Keysight Technologies, Inc. 7500 AFM/ enables stable electrochemistry control
SPM microscope is a high-performance in either EC-AFM or EC-STM mode. The
instrument that delivers high-resolution bipotentiostat offers a series of different
sensitivity settings (10nA/V, 100nA/V,
imaging with integrated environmental
1A/V, 100 A/V, and 1mA/V) covering
control functions. The standard Keysight
four orders of magnitude of currents from
7500 includes contact mode, acoustic
10 pA to 10mA. Coupled with a specially
AC mode, and phase imaging. It comes
designed liquid cell that allows the use
with a universal scanner that is capable of
of a mini-reference (Ag/AgCl) electrode
operating in both open-loop and closed-
for true potential control, instead of a
loop mode. Switching imaging modes
quasi Ag wire reference as other EC-SPM
with the 7500 AFM/SPM microscope is
systems do, the Keysight 7500 provides an
quick and simple, a result of the scanner's
outstanding imaging system for electro-
interchangeable, easy-to-load nose cones.
chemistry research.
Every 7500 AFM/SPM microscope utilizes
the industry's lowest-noise closed-loop
scanner to provide the ultimate conve-
Examples of EC-SPM
nience and performance in imaging, with- Measurement
out sacriicing resolution or image quality. Electrochemical SPM has been applied to
study a wide range of systems, including
An optional EC glove box designed spe- surface adsorption, ilm growth and dis-
ciically for use with the 7500 features a solution, membrane ion transport, battery,
dual-chamber design that allows samples fuel cell, photovoltaic, and catalysis. The
to be prepared under environmental con- examples below highlight only the basic Microscope on glove box. Inset: sample plate
with the mini reference electrode (Ag/AgCl).
trol (e.g., humidity, temperature, oxygen EC-SPM capabilities of the Keysight 7500.
levels, reactive gases) in one area and
then moved to an inner chamber directly
Oxygen-Free and Controlled
underneath the microscope's head/scan-
ner. An optional mini reference electrode
Environments
(Ag/AgCl) provides a true reference and Environmental control is critical for many
controls sample potential. The 7500 head EC-SPM experiments. For example, it has
on the glove box can be placed inside the long been recognized that electrochemi-
Keysight Pico IC isolation chamber. cal processes are signiicantly affected by
Current (mA)
Voltage (V)
Figure 1. Oxygen level control by glove box. CV of Au in 0.1M H2SO 4 recorded after 1 hr in N2 (red) and 30 min
after exposure to air (blue).
03 | Keysight | In Situ Electrochemical Measurements Using Keysight 7500 AFM - Application Brief
the amount of oxygen existing in the experimental environment. Therefore, the elec-
trolyte and the cell in regular electrochemical experiments are often deoxygenated by
purging inert gases such as N2 and Ar before or during the experiment. The integrated
environmental control system for the 7500 is capable of temperature control, humidity
control, liquid exchange, and more (see Figure 1). This control is particularly useful for
the sample preparation and transportation often required for battery studies. With the
help of the 7500's environmental control system, clean and "oxygen-free" conditions
can be achieved to ensure proper electrochemical experiments. The oxygen level can -0.4V
be reduced from ambient (~21%) to less than 1% in about 5 minutes by N2 purging. -0.3V
-0.2V
Copper Electrodeposition on Au
-0.1V
Electrodeposited copper is used extensively in microelectronics and microelectro-
mechanical systems (MEMS), particularly in chip metallization such as contacts and Figure 2. Three-dimensional EC-AFM topog-
interconnects and the illing of vias. As these processes and devices are continually raphy image of Cu ilms deposited at different
overpotentials.
driven toward the nanoscale, the need for more research into conditions affecting the
electrochemical plating process arises. Electrochemical SPM techniques have been ex-
tremely beneicial in understanding the dynamics of nucleation and growth processes,
and how additives and adsorption can inhibit or enhance these processes.
The simple experiment presented here examines the effect of overpotential on the
kinetics and ilm properties of Cu deposition on epitaxial Au(111)/mica surface. The
electrolyte used was 15mM CuSO4 in 0.1M H2SO4 and the potential was controlled
against a quasi-reference electrode (Cu/Cu2+). The electrode potential was pulsed for
2 sec to -0.1, -0.2, -0.3, and -0.4V sequentially. After each pulse, the electrodeposited
Cu ilm was kept at 0.0 V for imaging by AFM for about 2 minutes, then stripped off at
0.4V before the next pulse. Figure 2 shows the ilms deposited at each of the different
overpotential values, and imaged by contact AFM.
Since the rate of Cu deposition is highly dependent on the overpotential applied, which
in turn affects surface properties such as the roughness of the ilm, the kinetics and
surface roughness for ilm growth can be evaluated by EC-SPM. For example, the
thickness of the Cu ilms deposited during the pulse experiment can be measured from
the averaged line proile shown in Figure 3(A). The estimated thickness and surface
roughness of each ilm are presented in Figure 3(B).
A
Voltage 0.4 V -0.1 V -0.2 V -0.3 V -0.4 V
Cu/Au
Thickness (nm) 0 10.4 53.0 77.2 84.2
Roughness (nm) 2.78 3.29 3.81 5.79 10.3
B
Figure 3. (A) Averaged topography line proile from the AFM image. (B) The estimated thickness and
surface roughness of the Cu ilms deposited at different overpotentials.
04 | Keysight | In Situ Electrochemical Measurements Using Keysight 7500 AFM - Application Brief
For more information on Keysight
Summary AFM Instrumentation from Technologies' products, applications or
EC-SPM has been proven to be an indis-
Keysight Technologies services, please contact your local Keysight
office. The complete list is available at:
pensable tool for direct, high-resolution www.keysight.com/find/contactus
Keysight Technologies offers high-preci-
studies of physicochemical processes,
sion, modular AFM solutions for research,
providing an atomic and molecular Americas
industry, and education. Exceptional
basis for understanding the kinetics and Canada (877) 894 4414
worldwide support is provided by experi-
thermodynamics of electriied interfaces. Brazil 55 11 3351 7010
enced application scientists and technical Mexico 001 800 254 2440
Application of electrochemical SPM will
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continue to impact and drive research in
R&D laboratories are dedicated to the time-
diverse disciplines, including energy, cor-
ly introduction and optimization of innova- Asia Paciic
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