A light sensitive thin film was coated onto a PET substrate. In order to measure its photoconductivity, what kind of probe station (type of probe tip) is suitable? I have two different probe tips (gold and tungsten), which one is suitable?
I think gold one is better. In photoconductivity measurement, a relative large amount charges are deposited on the surface layer of the photoreceptor. Upon illuminating with proper light, the surfacial charges are neutralized by the photogenerated electrons/holes, and the opposite charges drain from the bottom electrode/substrate. Gold is one of the best conductors and thermal transportors, thus a gold tip leads to smaller charge accumulation on the tip and to better heat dissipation. As a result, the signals are more convincing.
I have used tungsten tips and berillium bronze tips. But my surface was silicon.
tungsten probe tips was much better - because it was hard enough to reliably scratch through passivation layer and produce reproducible results.
If you even suspect in your case non-conductive coating may exist, please use tungsten. Otherwise, both gold and tungsten will work. For measurement only, resistance of probe tip is negligible (you will be feeding like ~10nA current). I do not recommend to feed more current because your photo-conductive layer may self-heat and produce distorted results. Anyway, gold thermal conductivity will not help much because of probe geometry (probe is small compared to substrate). Also, most of the "gold" probes are steel or bronze with few um gold coating (for mechanical reasons). These have thermal conductivity no better than tungsten probes.
Thank you so much for the constructive comments. I have another question.
Please see the attached the design of the gold electrode coated onto the photoresponsive thin film (by using a photomask).
I always get confused with the transistor-type photodetector (source, drain and gate) and photodetector that uses only two electrodes (source and drain). Which electrode configuration is suitable for the measurement of photocurrent?
Thanks in advance.
Your 2-electrode design works well if contact resistance is low.
If you have significant contact resistance, use 4-contact setup
(feed current on outer stripes and measure voltage between inner stripes)
Since gold nanoparticles are known for their plasmonic effect when irradiated with light, would these gold electrodes affect the photoconductivity measurement? How do I justify the enhanced photocurrents are not from the plasmonic effect of gold nanoparticles?
You messing something up. (surface) plasmons do exist for any metal electrode. If you are concerned with precise polymer only conductivity measurement:
1) Make electrodes thick >=1um to shadow area beneath them
2) Use collimated light source not illuminating electrodes
In fact, inorganic nanoparticles were embedded in the polymeric thin film and I am interested to study the plasmonic effect upon irradiation with light. I agree with you that I should avoid irradiating on the electrode. Is there a proper measurement protocol/established method detailing the design of electrode (electrode thickness, width between source and drain), diameter of light source (laser spot), temperature-controlled environment, etc. for a precise measurement of photocurrent? Appreciate if you could provide some references pertaining the abovementioned. Thank you.
http://shodhganga.inflibnet.ac.in/bitstream/10603/3103/7/07_chapter%202.pdf
It mention what exact geometry is sample-specific and provide basic photoconductivity measurement guidelines.
Dear Oleg Nizhnik and Jingzhi Sun,
I have bought several books on plasmonic nanoparticles:
a) Nanoparticles: Building Blocks for Nanotechnology (Springer)
b) The Supramolecular Chemistry of Organic–Inorganic Hybrid Materials (Wiley)
Do you happen to know any good books especially on plasmonic nanoparticles?
Thanks in advance.
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