How do you define the compactness of thin films? 

As I understand, you analyzed two films with different thickness (600 nm and 715 nm) by using SIMS. If you know the total number of layer that you deposited for each film,you can then calculate the interlayer distance. In my sense, this distance is directly related to the compactness. 

You need most of all an  instrumental calibration of mass density per count (that is,  for example,  16O/cm^2 per 16O count).  This is complicated because the calibration can change dramatically as the material changes - it is not constant and can only be calibrated accurately through sample-matched standards.  Then you need to be sure that your depth scale is correct.  This is also complicated because the sputtering rate changes (sometimes dramatically) with material.  In your case you need to check the sputter rate in the SiOC film and in the Si substrate - these will be different!  I start off by not believing your depth scale!

If these calibrations are correct you will have a linear thickness (in nm) for a given mass per unit area:  the ratio directly gives you the material density.  Note that this is very easy to say and remarkably hard to do with any useful precision.  Especially with SIMS,  a notoriously unquantitative technique!

Mr Atilla, Mr Jeynes, first of all Thank you! Here i'm not trying to MESURE density or compactness of my SiC Mono-layer, i just try qualitatively to understand (and explain) the behaviour of the SIMS Profile 02 (Where signal is distorted compared to Profile 01 -planar signal) i suggested that this may be related to the volume structure which is not if you want a succession of several atomic monolayers, but plenty of structural defaults (pipes, dislocations etc.) ie Totally unhomogeneous !!!

The reason profile 02 looks noisy is because you have significant abouts of oxygen. Whenever you have a spike in Si,C you have a dip in O. Basically, looks like your second profile has plenty of inhomogeneously distributed oxygen in it.

In my opinion, the reason of signal inhomogeneity/distortion is charging of the sample.

From the high signal of O and Si, I conclude there is the SiO2 layer which is insulated.