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Complete Kelvin Probe Removes measured CPD ambiguity

Dedicated to measure Contact Potential Difference of the sample and the tip, separately.

Description

Complete Kelvin Probe is an invention of Instytut Fotonowy that solves the 150 years old problem with Kelvin Probes: If you observe a CPD change, you don’t know whether it is a change of the sample’s Work Function or the change of the WF of the tip.
Complete Kelvin Probe is an ultimate Contact Potential Difference (CPD) measuring device. It can do whatever other Kelvin Probes can do but it also can measure

  • CPD of a sample with respect to the ground,
  • CPD of the tip with respect to the ground.

That lets the user clearly see what contribution to the sample-tip CPD comes from the sample and what from the tip.

 

Complete Kelvin Probe at work

Sample-Tip CPD

Sample-Tip Contact Potential Difference (blue) with recorded ambient air temperature (green) and relative humidity (orange):

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Sample-ground CPD

Sample-ground Contact Potential Difference (red) with recorded ambient air temperature (green) and relative humidity (orange). It represents only small fraction of the sample-tip variation:

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Tip-ground CPD

Tip-ground Contact Potential Difference (gold) with recorded ambient air temperature (green) and relative humidity (orange). It shows that most of the CPD change is due to the change on the tips surface:

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kelvin probe modules

The Kelvin Probe set consists of:

  • Controller unit,
  • Kelvin Probe instrument with the Probe Tip,
  • Faraday Cage.
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The Kelvin Probe instrument is equipped with:

  • Protective bay to park the Probe Tip after experiment,
  • Laser pointer to indicate the area directly,
  • Light source that helps to handle the sample when the instrument is covered with the Faraday Cage,
  • Laser barrier to precisely detect the Probe Tip distance to the sample,
  • Golden Probe Tip,
  • Sample holder,
  • Motorized XY Table.
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Probe Tip

The most important part of the Kelvin Probe instrument is the Probe Tip.  The reference electrode is made of Au mesh of 2.5 mm in diameter. It provides high signal to noise ratio, even from a distance of 0.5 mm above the sample. Thus, it does not matter if the examined sample surface is rough or polished. The tip oscillations are generated with an electromagnet.

The Probe Tip is the component fully designed and manufactured by Instytut Fotonowy Sp. z o.o.

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Sample holders

The standard Kelvin Probe Set includes two types of sample stands:

  • Bottom contact stand for samples on conducting substrates,

  • Top contact stand for non-conducting substrates,

Faraday Cage

The entire instrument is covered with the Faraday Cage, shielding the setup from the ambient light and electromagentic fields.

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Gas-tight Faraday Cage with inert gas flow system

Scince measurements of the CPD is often sensitive to environmental factors such as temperature, humidity, dust and chemical contaminants, Kelvin Probe may be placed inside the hermetic version of the Faraday Cage with the inert gas flow system.

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Laser barrier

The Kelvin Probe is equipped with the Laser barrier system. The system automatically detects the sample substrate. Each time the probe approaches the sample being examined, an accurate distance between the sample surface and the Probe Tip is measured with 20 µm precision.

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Sample illumination

The sample may be illuminated during the measurements from the optical fiber situated above the Probe Tip. The Probe Tip lets the light through. The light at optical fiber input may be provided by the LED Revolver, Xenon Lamp combined with the Monochromator or any other type of the light source desired.

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Specifications

General:

  • Weight: 10 kg,
  • Size: 40x40x45 cm,
  • PC connectivity: USB 2.0,
  • Power supply: 230 V, 50 Hz or 115 V, 60 Hz,
  • Measurement technique: 2-channel lock-in-amplifier,
  • Laser barrier to automatically detect the substrate and prevent the tip from running into the sample,
  • Auxiliary sensors: humidity, temperature,
  • Small lamp,
  • Laser pointer for examined point of the surface indication,
  • Sample holders:
    – Freely shaped solid state with top contact holder,
    – Bottom contact holder,
    – Electrochemical holder,

Faraday Cage:

  • Standard / gas-tight with inert gas flow system,

Measurement unit:

  • Bias voltage range: -5 ÷ 5 V,
  • Voltage measurement resolution: 0.15 mV,
  • Current ranges: 300 nA, 30 nA, 3 nA, 300 pA,

Probe Tip:

  • Probe Tip type: Au mesh, 2.5 mm in diameter,
  • Tip positioning resolution in vertical axis: 20 µm,
  • Automated resonance frequency scanning,
  • Adjustable oscillation amplitude,
  • Automated removal of the parasitic current of the tip,
  • Partial transparency for the light,
  • Typical CPD measurement distance: 0.2 – 1 mm,

XY Table:

  • Motorized, controlled via software,
  • Size: 50 x 50 mm,
  • Movement range: 50 x 50 mm,

 

Exemplary results

Aluminium surface

Distribution of the electric potential on the sample surface:

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Ambient temperature during measurement:

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Air humidity during measurement:

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Metal surface sample with periodic holes

Evaluated CPD values on surface:

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Preview during ongoing measurement

Distribution of the electric potential on the sample surface:

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Ambient temperature during ongoing measurement:

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Air humidity during ongoing measurement:

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Charge distribution on the dielectric surface

PTFE on alluminium foil – Electric potential from the surface charge of the sample

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ACCESSORIES The following accessories are compatible with the product
LED revolver
Photoelectric Spectrometer
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