Surface roughness (as the name itself suggests) is the degree of unevenness of the film surface and provides a measure of how smooth (or rough) the surface of a film is. This can usually help to determine the quality of your deposition technique and assist in the tailoring of deposition conditions in order to achieve the desirable film smoothness for your application.
The surface of the film may deviate from the ideal plane on different scales in regular or random manner. Some of these scales may be relevant to a particular technology. In this case it is necessary to characterize these deviations (surface roughness). For example AFM is used for characterization of surface topography with resolution up to angstroms in height.
It is a measure of surface irregularity or unevenness along out of plane of a thin film. They play a key role in transport & optical properties like by inducing surface states, traps, scattering sites etc to name a few. There are two roughness widely reported for thin films, one is average roughness and other is rms roughness. They represents the deviation of hillocks and valleys (or pits) on the film surface from a reference plane. Avg. roughness is simply the avg of positive (hillocks deviation) and negative (valley deviation) values from the reference plane. Which is not truly reflect the surface deviation. What i mean is, from a scanned region let say we have values like +3, +5, -3, -4, -1 the avg is zero it does not make sense, because the values signifies the deviation. Whereas the rms is 3.46 says that from reference plane each of the grain hillock or pits are deviated on an average 3.46 either above or below.
It is the vertical deviation of surface points from an average plane and it is commonly defined as a root mean square deviation (rms). Depending on the application the roughness that matters can be at different lengthcales: nm, um, mm etc, depending on whether you are doing electrochemical, optical or tribological measurements. In thin film technology it is usually determined via AFM. Other possible methods are ellipsometry modelling of roughness and electrochemical determinations of the microscopic vs. geometrical areas, for instance via capacitance measurements.
Yes, AFM microscopy is a good tool for characterizing surface topography (surface roughness ). I worked with AFM, result is published in:
Study of the bed fouling problems in a biomass fired commercial CFB boiler; Tranvik, A.E., Sanati, M, Zethraeus, B, Lyberg, M; American Society of Mechanical Engineers, Fuels and Combustion Technologies Division (Publication) FACT, v 23-1, 1999, p 267-273
I add to another consideration: surface roughness only means the vertical derivation from the sandard surface; If you want to get the spatial frequency of the surface topography, you need to calculate the PSD (Power Spectrum Density) function.
Surface roughness term very frequently we get whenever we carry out study on polycrystalline material or material with variable grain boundary.
Homogenous Distribution of molecules and its nucleation may brings out regular surface but since all the process is self-directed so sometime more nucleation may happen so irregularity appear over the apparent surface this gives rise to surface roughness.
This surface roughness can be estimated by contact or non-contact mode mostly discussed by other friends above.
Thanks
Surface roughness determine the dielectric function of thin film with high surface roughness more than 10 nm peak to valley distance.
Part of the utility of atomic force microscopy as a metrological tool is its remarkable resolution in x, y, and z. The use of AFM (Atomic Force Microscopy) to examine the surface roughness and topology of complicated material systems is invaluable. AFM equipment produce high-quality surface maps with an Angstrom resolution to aid in the understanding, identification, and distribution of material within a sample.
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