No, surface concentration doesn't necessarily equal bulk concentration (presumably you mean the bulk composition of the film?). It can, but you don't have enough information yet. You need to be aware of the interaction volume, given your excitation energy and the density of your material, and the thickness of your deposited thin film. When you know these then you will have a better understanding of whether your surface=bulk.

So, what is your film? Elements, density, accelerating voltage and thickness? What is the substrate?

Basanta.

The surface composition of a deposited film should be similar to its bulk if we say about quite a thick film: the thickness more than 0.5micron.

As for analysis of the film, you should define for yourself first: what is the surface? People say “surface” when describe the first several mono-atomic layers. This is 1-2nm of depth, only. The analytical depth of EDX method is around one micron (for 10keV electron beam), so you cannot analyze the surface composition by this method; you obtain an average concentration of your film up to around 1micron of depth (this analyzed depth is a function of the electron energy).

If you need compare the surface and volume concentrations you need XPS, AES or SIMS methods (the so-called depth profiling analysis).

You can estimate roughly the composition gradient in your film by EDX with variable electron energy EDX: you should measure EDX spectrum with energies from 3keV up to 30 keV and compare results after de-convolution. There are free program for electron - solid interaction; you can calculate the depth of penetration (analyzing depth) of electron before EDX analysis.

Ian Slipper sir,

Thank you for your information, I have deposited Cobalt At different watt (5-25) and silicon at 100 Watt.

Voltages are silent in the power operating system in My DC and RF sputtering type gun.

Thickness approx. 1 micron.

Basanta, thanks for that.

Just to clarify - your materal is a compound of Co and Si at ~1um thickness.

Can you tell me what accelerating voltage you used for the SEM/EDS analysis?

What is your substrate?

Basanta

As Ian and Yuriy have pointed out, it all depends on the interaction volume. If your film is really 1 micron thick, and is not too porous, you should be able to measure the composition if you drop the acceleration voltage to 5kV, as then the interaction volume for the materials you have given will be well below 1 micron. Conventionally, EDS software always assumes the composition to be homogeneous within the interaction volume and if that is not the case (i.e. if your film thickness is smaller than the interaction volume), your results will not be correct.

A better way to measure film composition (and thickness) with EDS is to use a software where you can treat the film and the substrate separately. Oxford Instruments have a software for the AZtec Platform called LayerProbe that can treat films separately from the substrate and therefore accurately give you the film composition. I have put in a link below.

http://www.oxford-instruments.com/products/microanalysis/solutions/layerprobe