How can we measure work function of a polymer? As it has an important role for charge generation when the material comes in contact with metal/non-metal/polymer. So if anyone suggest me how to measure it will be helpful to me.
Kelvin Probe microscopy is suitable technique for the calculation of work function.
The most direct method of measuring the work function of materials in general, is Ultraviolet photoemission spectroscopy (UPS).
A sample is irradiated with UV photons from a gas discharge lamp to towards the sample in Ultrahigh vacuum (UHV) conditions. This leads to the electrons leaving the samples with a Kinetic energy which depends on the energy of incident photons (typically 21.2 eV for He I line) and the binding energy of the electrons in the material. The resulting spectrum with X-axis as Kinetic energy and Y-axis as intensity of electrons generally represents -to a first approximation- the density of states of the valence band. Electrons lying at the Fermi level will have the highest Kinetic energy since they are weakly bound to the material. Electrons coming from levels below the Fermi level gets inelastically scattered and they lose energy along the way towards leaving the sample surface, and thus result in increased intensity in the UPS spectrum towards lower Kinetic energies with a sharp cut-off where electrons are no longer able to leave the surface of the sample. This is called the secondary electron cut-off (SECO) which occurs at the minimum energy required to take an electron out of the material and place it at rest at the vacuum level. This is the definition of the work function.
An important aspect of the method with respect to polymers and organic materials in general, is the fact that such materials undergo degradation under the high photon flux of the incident photons. Meaning that your work function will change with subsequent measurements or for example if you run XPS before UPS. For that purpose attenuation filters (metal foils) for the UV photon flux from the discharge lamp is typically used to decrease the flux of the photons before reaching the sample.
Hi Muhammad, it is actually very challenging to measure the workfunction of a material as it is critically dependent on the surface. Any surface contamination, texturing... and even the atmospheric conditions at the time can drastically change the measured results. You may be able to make inferences about the workfuction looking at the photo-conductivity of the material as a function of wavelength. These will however also contain effects of charge traps in your material.
- Badges
- Science topic