You don't explain what the samples are, or the imaging mode of the SEM.

The SEM is probably detecting secondary electrons from the surface of the sample, so what you see will be dominated by surface topology and texture..  Assuming the 100 um refers to the full length of the scale bar, the image field is roughly 0.25 mm across.

The TEM image field is 0.0005 mm across (500 nm), and presumably represents electrons transmitted though the thickness of the sample.  This will be sensitive to any variations in thickness or inhomogeneity within the sample.

So image D is a transmission image covering an area roughly 2.5 pixels wide by 2 pixels high in image A.  Are they are of the same sample?  If so which part of image A is image D taken from?  Do you expect images A and D to apear similar?

Image B is too unclear to make sense (is it a part from A?)

Image A resembles crystals formed by evaporation or by oxidation of gases on a surface. I have seen something relatively similar on agar gel surfaces in the presence of an atmosphere containing H2S. In that case the crystals were gamma-zerovalent sulfur (gSo). You have to test them for elemental composition to verify that they are 100% S). Sometimes microcrystals of sulfur form and then are partly corroded in an atmosphere containing a volatile (such as carbon disulfide)

Nabil:

Nothing can be resolved in TEM Image D.  SEM image A displays chaotic array of angular/flaky material to be determined by EDX analysis. It would have been better to know the source of material.

Best

Syed