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FAQ



What is the Surface Photovoltage option for and how is it different from your base, system & scanning packages?


We offer several forms of SPV, essentially they are the same across our product range, however the physical implementation may differ, for example in Ambient and Ultra High Vacuum environments. Firstly there is the simple programmed DC-SPV (SPV010) of a light source being switched on and off, synchronised with surface potential (SP) measurements to produce delta (SPV) = SP (Illuminated) - SP(Dark). One can also manually switch the light source on and off and watch the SP transient (approx 1000 measurements/min). Most devices have decay times in the seconds to minutes range. Results over longer periods are not well known as probably the only way of measuring the SP on longer timeshares is with the Kelvin probe.

The light source can be either high intensity LEDs (which work very well) or QTH lamp. The QTH lamp is useful both by itself and for a source of wavelength specific SPS.

The next SPV system SPV020 is of most interest to general customers, in this case all the features of SPV010 apply but in addition the light source intensity is controllable, thus a plot of SPV versus light flux is produced. This can be useful for scoping out the whole response: in the cells I have measured to date both Voc is variable (say from 250 to 450 mV) as is the light sensitivity curve. There is certainly interesting data there and if the light source output was independently calibrated perhaps a rough guide to Air Mass would result.

We can offer the above systems with or without a light enclosure, secondly we can offer a variant of SPV020 with an optical chopper resulting in AC-SPV.

Lastly we offer either motorised linear variable filter (SPS030) or motorised monochromator (SPS040) systems to probe the specific wavelength dependency of SPV from 400-700 and 400 - 800 nm respectively. The LVF produces perhaps a higher light intensity than the monochromator system, however the pass band is obviously somewhat larger. We can optionally additionally populate the system with infra-red LEDS to cover higher wavelengths than can be easily obtained with either filter or monochromator system.

The base, system and SKP packages do not offer automatic SPV however obviously one can implement one's own light source and switch it on and off to measure SP. Having used both ways in the past we know that it is much more efficient researching photosensitive behaviour with SPV/SPS using the automated systems. It allows the possibility to specify the experimental protocol so that a non-specialist can undertake the measurements and they will be comparable.

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KP Technology
Burn Street, Wick, Caithness, KW1 5EH, Scotland

Telephone: +44 (0)1955 602 777
Fax: +44 (0)1955 602 555
Email: sales@kelvinprobe.com

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