Kelvin Probe Features:
The Digital Kelvin Probe System is a vibrating capacitor technique used to measure the change in work function of metals, semiconductors and liquids.
The Kelvin method has extremely high surface sensitivity (<0.1 meV, typically corresponding to 10-3 of an adsorbate layer) and is completely non-damaging, even to the most sensitive adsorbates. It enjoys wide ranging applications in physics, bio-chemistry, engineering and, most recently, as a UHV surface analysis technique.
The Kelvin Probe design is 100% UHV compatible. It features a completely shielded driver, vastly improved signal detection methods and optional computer-controlled probe positioning. These innovations, combined with the non-contact, non-destructive nature of its measurement, make the Kelvin Probe system an ideal tool in the study of thin films, adsorption kinetics, work function topographies, surface photo-voltage spectroscopy, phase transitions, surface stress and similar phenomena.
How it Works
The Kelvin Probe consists of a vibrating reference electrode in plane-parallel orientation to the sample, creating a capacitor. The sample and probe are connected via a voltage source called the "backing potential" (Vb). When Vb is set to zero, a contact potential difference (Vcpd) equal to the difference in the probe and sample work functions appears across the probe/sample faces.
The change in work functions is detectable because Δwf = eΔVcpd where e is the electronic charge. At the unique point where Vb= -Vcpd the circuit is balanced, and the electric field between the plates vanishes resulting in a null output signal. This null condition, and deviations from it, can be detected with high precision, thereby directly measuring the changing sample work function.
Dependability and Versatility
The Kelvin Probe System measures work function changes in electron volts and needs no calibration. The Kelvin Probe does not run the risk of desorbing weakly bound adsorbates. This method provides a mean work function value of the sample and is not biased towards low work function patches as is the case in thermionic emission, photoemission and field emission.
In addition to UHV use, the Kelvin Probe System can operate in air, gas and even some liquid environments. This allows in situ measurements under real-world conditions as well as the laboratory environment.
Increased Signal-to-Noise Ratio
The Kelvin Probe System measures work function changes in electron volts and needs no calibration. The Kelvin Probe does not run the risk of desorbing weakly bound adsorbates. This method provides a mean work function value of the sample and is not biased towards low work function patches as is the case in thermionic emission, photoemission and field emission.
In addition to UHV use, the Kelvin Probe System can operate in air, gas and even some liquid environments. This allows in situ measurements under real-world conditions as well as the laboratory environment.
No Lock-In!
Historically, many problems have arisen when the null condition is detected using a lock-in amplifier. The Kelvin Probe System uses a digital oscillator and digital trigger which eliminate the need for a lock-in amplifier. This allows data to be recorded at a variety of frequencies and amplitudes. This ability to acquire data off resonance eliminates the subtle, but significant, resonant frequency shifts that plague other probes. These features are unique to the Kelvin Probes from this company.
Completely integrated software is included with the system. The MS Windows-based (Win XP, Vista, Win 7) measuring and analysis program allows the operator to find the optimum signal-to-noise ratio by complete, independent control of amplitude, frequency of operation and probe-to-sample distance.
The automatic tracking system senses and compensates for sample position variations due to thermal drift or mechanical disturbances.
The rack-mounted electronics include three additional user-assignable input channels which can be used to monitor other processes such as pressure and temperature either in conjunction with, or independently from work function measurements.
The KP FAQ page
Yeah, we all know what FAQ pages are like. They never seem to answer our 'real' questions. Well, this one is a bit different. This doesn't have things like, "How do I copy a file?" It has FAQs for new and potential KP users who are looking for more in-depth coverage of some of the key points of CPD measurement. It really is worthwhile reading.
Additional Information
A handy stand for performing KP tests in atmosphere.
A simple procedure for adjusting the balance in the KP preamplifier.
For further information, visit the reference section.
Lord Kelvin's Original Apparatus
The Kelvin method was first postulated by the renowned Scottish scientist William Thompson, Lord Kelvin, in 1898.Using a Zn and a Cu plate, isolated by rubber handles, using a gold-leaf electroscope, he observed a charge appeared after the two plates were shorted (touched) together and then moved apart.
In addition to our broad line of standard scientific products, we know that today's scientist needs choices and options to fulfill the ever-changing demands of the research community. For more than thirty years we have been providing those options. Please do not hesitate to contact us with your requirements or if you have any questions, comments or suggestions.