SKP Scanning Kelvin Probe Microscopy

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. 
  • Documents +

  • Specifications +


    Lock-in Amplifier:
    Noise Sensitivity 13fA per second
    Frequency Range 1mHz up to 250 kHz
    Full Scale Sensitivity from 10nV to 1V
    DSP Stability Impervious to temperature drift
    High Mechanical Stability No fan for failure
    Piezo: Up to 30-microns vibration perpendicular to sample surface
    Electrometer:
    Gain from 1x to 10,000x in decades
    Probes:
    Material Tungsten
    Dimensions 500-micron and 250-micron diameter probes are available
    Backing Potential Controller:
    Range ±10V
  • Options +


    L-Cell VersaSCAN L-Cell
    • Screws into optical table of VersaSCAN
    • Approximately 1 Liter in volume
    • Level adjustment mechanism
    • Accepts large flat samples and 32-mm diameter mounted samples
    • Recommended for all techniques, particularly LEIS, SVET, SKP, SDC, OSP
    mL-Cell VersaSCAN mL-Cell
    • Screws into optical base of VersaSCAN
    • Approximately 7 mL in volume
    • Level adjustment mechanism
    • Accepts a range of samples including 32-mm diameter mounted samples and non-standard samples
    • Specifically engineered for low-volume SECM applications
    VersaCAM VersaCAM
    Long Working Distance Video Microscope
    • Camera:
      • Color
      • Number of pixels: 795 (H) x 596 (V)
      • Minimum illumination 0.02 lx. F1.2
      • Power: 12V DC ±10%
      • CS-mounted or C-mount with provided adapter
    • Lens:
      • C-Mount
      • Manual focus
    • Display:
      • 8 inch color TFT display
      • PAL & NTSC auto selection
      • 640x480 (307,200 pixels) screen resolution
  • Video +

    Watch video demonstrations of the SKP Scanning Kelvin Probe Microscopy

  • Experiments +


    Line Scan Scanning Kelvin Probe (SKP) measures the relative work function difference between the probe and sample. The probe is scanned in the XY plane above the sample, generating a map of the response. The probe can be maintained at a constant-height or a constant-distance (if a topographic background scan is acquired first). Step-scan data acquisition is recommended for oversampling and averaging of the data, also this gives the logic time to determine the appropriate nulling voltage.
    Area Scan Capacitive Height Measurement (CHM) applies a voltage to the sample. A calibration constant is determined to relate the measured probe response to a distance…over a relatively small change in distance. The same SKP probe is scanned across the XY plane above the sample and the response is reported as a probe-to-sample distance (mountains are low-values and valleys are large-values). These data could then be used as a background to run an additional SKP experiment in constant-distance mode.
    CTM Area Scan CHM applies a voltage to the sample. A calibration constant is determined to relate the measured probe response to a distance…over a relatively small change in distance. The same SKP probe is scanned across the XY plane above the sample and the response is reported as a probe-to-sample distance (mountains are low-values and valleys are large-values). These data could then be used as a background to run an additional SKP experiment in constant-distance mode.