Ambient

Ambient Kelvin Probes use a non-invasive, non-contact vibrating capacitor technique, which measures to mV resolution the voltage between a vibrating micro-electrode and a conducting or semiconducting sample. The surface potential maps contain information on the sample's work function (which can be used to indicate chemical composition) but more importantly how the surface responds to treatment: such as deposited thin films, oxidation, illumination.
Applications include the fundamental study of corrosion, surface passivation, general of low and high work function surfaces for ion and electron emission, fundamental surface adsorption studies, semiconductor oxide quality, etc.
This system has also been utilised to provide surface charge imaging of non-conductors such as ptfe, platinium-pfte mixtures and charges deposited on top of silicon oxide.
The vibrating tip (amplitude of vibration can be digitally changes from a few microns to 1-2 mm) moves in a plane-parallel fashion with respect to the sample. The mean tip-to-sample spacing is usually in the 0.3 - 1.0 mm range, although measurement can be made with larger tips with an off set of 2-5 mm. The tip actuator is voice-coil driven, powered from a computer controller digital oscillator with a 0.2 - 0.3 Hz frequency resolution. Some of our smaller tips (diameter < 200 um) are shielded using a thin guard electrode. An automatic measurement procedure controls the (x,y,z) micro-translator (0.4 um resolution), amplitude and frequency of oscillation, tip and shield bias. We utilise an 'off-null' measurement procedure featuring a tracking routine to maintain an average tip to sample spacing to within approximately 1 micron, to avoid spurious work function changes associated with spacing changes.
The voltage gradient above most samples is considerable and without the tracking routine measurements, made at different heights will, often not correlate well.
The general-purpose system also includes a peeltier stage to allow sample heating and cooling and an optical illumination source to allow surface photovoltage and surface photovoltage spectroscopy measurements. The Kelvin Probe provides the relative work function between the tip and sample. The work function is highly sensitive to surface conditions: surface processing, roughness, chemical composition, charge and contamination will all produce measurable changes in metal or semiconductor work functions.