Think about electrode contact and pressure while mounting your sample within two electrodes?
Dear Madhusudan,
I think your doubt is about preparing the powder sample in a form suitable for dielectric measurements. In that case you can pelletize the sample as a thin disc, vacuum deposit ohmic contacts on both sides and do capacitance measurements.
Dear Kumar,
Some times it may so happen that the powder sample can't be pelletized. They appear to be brittle. In our case we are facing this problem too.
Perhaps you could use ellipsometry? Make a thin film of the material, make an ellipsometric measurement, and fit the data with software. It can give you film thickness, porosity, and complex refractive index which you can conver to dielectric constant. However you would need an idea of the porosity because the fitting model often accounts for porosity by reducing the refractive index.
Dear Schnabel,
Thank you for your input. If the sample is in powder form, making thin out of it could be another problem. One possibility: we need to know its right solvent. But we may not find solvent for specially metallorganic samples.
Well, I don't know about what range you're trying to measure the dielectric constant, but if you wanted to do ellipsometry there are a few drawbacks that have already been listed such as needing to know the porosity, not having significant optical penetration depth for thick samples, etc.
However, I reinvented a device in 2012 called "Total Internal Reflection Photoacoustic Spectroscopy" that uses the photoacoustic effect to determine refractive index (and thus dielectric constant). The most recent publication is called "Photoacoustic measurement of refractive index of dye solutions and myoglobin for biosensing applications" and was published recently in Biomedical Optics Express.
Essentially, all you need is a high index prism (higher than the powder's hypothetical refractive index at whatever wavelength of light you're using), a rotational stage (such as the one I use from Sherline in the paper that is driven by Labview and a stepper motor driver), a pulsed laser (doesn't necessarily have to be nanosecond like mine, but it helps with sensitivity), and an ultrasonic transducer.
From that, you should be able to measure the refractive index of most materials including powders (though the acoustic properties of the powder may need to be tested in order to get appropriate coupling, etc. but this is simple enough using normal incidence photoacoustics). In order to find the porosity to get the true refractive index of the material minus the "holes" if you will, just take two scans. One scan of the dry material, record the refractive index n1. Then add any liquid of known refractive index to it and immerse for several hours to fill the pores and remeasure the refractive index to be n2. Once you know n1 and n2 you can find out refractive index of just the material since you have two equations and two unknowns (porosity and refractive index of the material by itself).
If you'd like to collaborate on this let me know at [email protected].
Dear Dr. Goldschmidt
Thank you very much for your answer. I'll be writing you separately using your mail ID.
Kind regards,
Madhusudan Roy
Hello Madhusudan,
Have you figured out yet how to measure dielectric constant of the powder? I am very eager to know your expertise.
Thanks and regards,
Srinivas
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