VS-SKP Scanning Kelvin Probe Microscope

• Uses a relative work function measurement, typically in atmospheric conditions, to map the anodic and cathodic nature of samples
• Superior probe design and signal measurement capability provide high resolution measurements

The VersaSCAN Scanning Electrochemical Workstation is a single platform capable of providing spatial resolution to both electrochemical and materials-based measurements.  This system integrates a positioning system, measurement instrumentation and probe to provide local information.  Traditional electrochemical experiments measure an average response over the entire electrode, electrolyte interface.  Rarely is a sample homogenous.  Samples often consist of local sites of passivate or active nature and sites of anodic or cathodic character.  This need to investigate localized phenomenon led to the emergence of scanning probe electrochemistry.

Positioning System:

• VersaSCAN is unique in the use of piezoelectric motors to drive the stages on all axes.
• Piezos are materials that move with very high precision, accuracy, repeatability but over small distances.  We use them to drive stages; therefore we reach a combination of scan area and scan resolution that is unmatched.
• AFMs do not move with the same scan range (usually piezo-element only; without the stage)
• Alternative positioning system designs use step motors, exclusive or as a basis for a hybrid system, and cannot move with the same resolution.

System Installation and Training:

This is full ‘white-glove’ service. An experienced team member arrives on site – unpacked the instrumentation, assembles, levels the system.  A developed checkout procedure is executed on a test sample to verify the system (installation).  The fundamentals of the technique are covered.  The users are trained to execute the same test (training).

Multi-Technique platform:

The VersaSCAN platform offers the ability to leverage the positioning system and software as common components for other scanning probe techniques.  The best-in-class measurement characteristics of AMETEK equipment combines with this unique positioning system for high-resolution measurements even at large areas.

The Kelvin Probe experiment uses a nondestructive method to determine the relative work function difference between the probe and the sample. Work function describes the energy required to liberate an electron from the surface of a conductor; electrochemists often interpret this as the difference from an electrode’s Fermi Level, average energy of electrons, and that of vacuum.

A metal microprobe is positioned close to the surface of the sample (on the order of 100-microns). If the microprobe and sample are of different metals, there is an energy difference between their electrons. The microprobe is then electrically shorted to the sample, through internal electronics of the system. As a consequence, one metal forms a positive charge on its surface and the other metal forms a negative charge on its surface. The probe and sample are separated by a dielectric (air), so a capacitor is formed. The probe is then vibrated and "backing potential" or "nulling potential" is then applied sufficient to minimize this capacitance. At the applied voltage that causes the capacitance to go to zero, the original state is achieved. This value is recorded and charted.

Experiments are typically performed in ambient gaseous conditions, but several published examples use humidified environments. The underlying conducting sample can have an organic coating or paint applied.

This relative work function can also be correlated to an Ecorr value.

Our SKP is also capable of functioning in Topography Mode. Without changing connections or probe, a reference voltage is applied to the sample. This reference voltage makes the surface of the sample uniform. Change in capacitance is then from a changing plate separation (via equation of a capacitor).

This information can be used in 2 ways: Position the probe a known distance from the sample, using a Calibration Coefficient.

Map topography for further use in Constant-Distance Mode SKP. This is particularly useful in studying welds or other samples of complex topography. 

• Measures relative work function between probe and sample.
• Can correlate Work Function to Corrosion potential (Ecorr). 
• Capable of Topography Mode experiments to measure and set probe-to-sample distance
• Can perform Constant-Distance operation in conjunction with the Topography Mode experiments, using the same probe.

 

VersaSCAN Positioning System

Specifications	VersaSCAN Base (VS-BASE)
Positioning System Range	X-axis:  100 mm Y-axis:  100 mm  Z-axis:  100 mm
Positioning Motor Technology	X-axis:  Piezoelectric motors,            no stepper-motor Y-axis:  Piezoelectric motors,            no stepper-motor Z-axis:  Piezoelectric motors,            no stepper-motor

SKP Measurement Technology

Specifications
Electrometer Range	± 10 Volts
Electrometer Gains	1x to 10,000x in decades
Piezo Vibration Unit	0 - 30 µm perpendicular to sample
SR 7230 Lock-in Amplifier
DSP Stability (not analog-based, impervious to temperature drift)
High Stability (no fan for failure)
Radically better Noise Sensitivity (13 fA/√Hz)