Many people use both side adhesive conducting carbon tape as conducting electrode especially in PVDF based flexible nanogenerators. This tape is also extensively used in SEM, EDS, XPS etc. We tried to check (by using multimeter) whether the two sides of this tape conducts or not and found no conducting nature. We also tried to check this thing by affixing two aluminium foil on the two sides of the both side adhesive carbon tape. But in this case also, we found no conducting nature between the two aluminium foil. We also applied pressure and electric field (~ 100 V) across this system during checking the conducting nature through multimeter. But, in this case also same result appeared. Why is it happening? How is it useful for the purpose mentioned above?
Hello,
those tapes and tabs used for SEM are not perfect conductors.
If you look here:
https://www.tedpella.com/adhesive_html/conductive-tapes-comparison.htm
the last column shows typical resistance in Z direction in [Ohms/in^2] and it ranges from values close to 0 (perfect conductor) to hundreds of thousands Ohms/in2. It is hard for me to tell you what is going on with your tape (I do not know any details, manufacturer, parameters, etc.), but the span of possible resistances suggests that you have one with higher values. They are used for various things and various conditions (in SEM for example). The amount of charge in SEM deposited by the e-beam on the sample is small, so even the tape with higher resistance per area will do the job. I hope this helps.
The main purpose of using carbon tape is to avoid the charging effect that occurs due to the high energy electron beam strike to the sample. In the case of metallic samples, electrons get easily grounded to the sample holder, which is not in the case of the insulating samples such as oxides, silicon-germanium alloys, and other ceramics. Using the normal multimeter you are measuring the resistance, not the resistivity. These tapes have a small thickness of about 0.1 - 0.3 mm. Also by hand pressing, you can not make good ohmic contact in order to determine the electrical conductivity of the adhesive carbon tape. I suggest you calculate the resistivity by taking the dimensional factor and resistance measured using I-V curve. Conductivity i.e. inverse of electrical resistivity can be estimated from it to get an idea.
Typically the energy of the beam source used in SEM EDX, XPS, TEM etc is in the range of 1 - 40 keV. If the sample is insulating in nature, the surface has the charging effect due to the accumulation of electrons at the sample surface. If we do not ground such a high energy electron beam, it can damage the microstructure and can affect the chemical compositions especially when we used phosphorus or some other volatile elements. The electrical conductivity of adhesive carbon tape is good enough to act as conducting path for grounding the high energy electrons falling on the sample. If the sample with a high energy electron beam is exposed for a longer duration (which is required to take good quality SEM images, mapping and several different scans i.e. line scan area scan etc..), a shadow of burn kind of nature can be seen. Of course, other solutions are available such as making the thin gold coating on the sample surface, using conducting paste at the bottom side, use of another tape like copper tape etc. Out of these carbon tape is found to be easy, cheap, quick mounting the sample and easy to detach from the sample and reuse the sample for other measurements. Therefore, most of the places and time people use carbon tape. If you understand the basic purpose, you can use anything you like depending on the availability. Due to its adhesive nature, the entire bottom surface gets fixed uniformly to the sample (bulk sample, thin films on substrate) stage without any trouble. To see the importance of the carbon tape, it is suggested to make an experiment with a 10 mm pellet of insulating sample loaded on the sample holder with 1 mm by 2 mm size of carbon tape at the bottom, and expose the 10 - 20 keV electron beam on the sample surface for 5 to 10 minute. You can easily convince yourself by taking look at the burnt area. Then reduce the sample dimension to about 1 mm by 2 mm and use a large size (5 times larger than sample area) of carbon tape at the bottom side, and repeat the experiment. Now let me discuss the case of XPS. Typically in XPS machines people use a copper sample holder where a sample is fixed on it using conducting silver paste, so good grounding is found when the sample is exposed to a high energy X-ray source. For pictures you can directly message me, I can provide the sample holder and sample mounting for XPS, SEM, EPMA, ARPES, to get a better idea. Good luck.
Personally, I support Saurabh Singh has very well explained the impact w.r.t. the examination intended of samples.
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