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I'd like to make a museum exhibit for the photo-electric effect. The classical demo, demands that a piece of Zinc be placed on the electroscope , then the electroscope is charged negatively then we see the electroscope loose charge under UV light.

I've also seen this performed with aluminium instead of Zinc, but in both cases the metals have to be scrubbed before the demo to remove the oxide layer. The scrubbing is inconvenient for a permanent exhibit. My question is, are there metals for which no scrubbing would be required ? Would it work if, instead of zinc, the electroscope input was plated with a noble metal (gold etc..)?

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Yes, you can use gold, but you will need to use higher frequency UV, because gold has a significantly higher work function (5.10 - 5.47 eV) than aluminium (4.06 - 4.26 eV) or zinc (3.63 - 4.9 eV).

Generally, if it's easy to remove electrons from the metal surface, then the surface will be reactive. Eg, alkali metals like sodium & potassium have much smaller work functions than zinc. You can see a small table of work functions of various metals in the Wikipedia article.

One way around this is to use zinc, etc, but enclose your demo in an inert atmosphere, eg argon.

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    $\begingroup$ Or one uses a vacuum photocell, with light entering from the outside. $\endgroup$
    – user137289
    Commented Jan 4, 2020 at 21:07
  • $\begingroup$ @Pieter True, but that's probably not so practical for this museum exhibit that Manu wants to build. $\endgroup$
    – PM 2Ring
    Commented Jan 4, 2020 at 21:14
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    $\begingroup$ It is not an easy display to design, and it is not going to be spectacular. Maybe more fun with Hertzian sparks in UV light? $\endgroup$
    – user137289
    Commented Jan 4, 2020 at 21:25
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    $\begingroup$ @Manu Graphite has a fairly high work function of 4.62 eV, but tungsten carbide looks better, at 3.73 eV. Tungsten carbide is more resistant to oxidation than pure tungsten, especially at low temperatures (& has a lower work function), but it will form a tungsten oxide layer. See sciencedirect.com/science/article/abs/pii/S0263436896000273 $\endgroup$
    – PM 2Ring
    Commented Jan 5, 2020 at 12:34
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    $\begingroup$ @Manu Using the Google calculator, h *c / (360 nm) in eV is only 3.444 eV. You need to use a shorter wavelength. $\endgroup$
    – PM 2Ring
    Commented Jan 5, 2020 at 14:15

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