SEM gives u the surface structure while TEM tells u the transverse image and EDX tells u the elements and their concentration alone as well as their compound form

Heba Y. Elbasiouny

It's all about what you want to determine but the sample needs to be representative of the whole or it's effectively random and meaningless.

I have a totally different opinion. Soils are all about 'big' whereas the techniques you mention are all about 'small' (especially tiny samples). I would argue that manual microscopy is of far more value than electron microscopy for most soil and sediment applications. Calculate the minimum mass required based on the top end size for a required or specified standard error. I suspect you'll need kilograms and you'll never measure all of this with electron microscopy. See (registration required):

Keys for Successful Analysis – Representative Sampling & Estimation of Standard Error Calculation

https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190613KeysLD

Thanks so much @Alan F Rawle for you clarification, but I need more information abut the use of each one and if one if them is alternative to other

Heba Y. Elbasiouny All techniques are complementary, not competitive, in the general scenario.

Heba Y. Elbasiouny SEM is used mainly to characterize surface topography and morphology. You can get "3D" images. In the SEM the electrons that you are interested in are the ones of the bean that are backscattered by the sample of the secondary electrons that are expelled from the sample. The important thing here is that the sample has to be conductive. Whereas for the TEM the important electrons are the ones that pass through the sample, therefore the sample does not have to be conductive. With TEM you can reach a higher resolution but the "3D" structure of the sample is kind of lost. Also, TEM is pretty good to analyze sample composition, depending on the molecular weight of the element the sample is going to be darker or more clear, as higher the Mw as darker the sample. You can use wither of them depending on what you want to observe of course they can be complementary. In the case of FTIR is related to the vibration frequency of the moieties present in your sample. You will make a wavelength scan and once the wavelength matches the vibration frequency of a certain part of the molecules the light will be absorbed and that is reflected in the spectrum as a band. FTIR is mostly used for organic compounds and biomolecules, but it can be also used for inorganic compounds and coordination complexes. The question is , could you detect changes in your sample after the interaction with a nanomaterial?, Well usually yes but that depends entirely on your sample and the moieties that are affected after the interaction. FTIR can be used to quantify but is hard and time-consuming. Finally, in EDX the electron bean ejects electrons from the sample, those vacancies are occupied by electrons that are in a different energy level. The movement of the electrons from one level to another produces an x-ray that is detected. The difference in energy is particular for each element, therefore you can determine the composition @of the sample, in percentage. This technique is always nice if you are modifying substrates and want to know the real amount of the substrate incorporated to the sample. I will say that work better for inorganic compounds.

Eduardo González-Martínez

You state 'TEM is pretty good to analyze sample composition'. That assumes that the measured specimen (definitely not a sample) is representative of the whole and soils are notoriously heterogeneous.... Sample preparation (thinning) has a major impact on the results. See the attached.

How are aggregates and agglomerates distinguished from primary particles?

Alan F Rawle I was just referring in a general way. I was not talking specifically about soils, which I have not work with. I have use TEM to study the composition of core-shell nanoparticles for example, where you can state who is the core and who is the shell using the TEM images. Of course to obtain a precise composition analysis EDX, X-Ray fluorescence etc are best than TEM. But for example, if you introduce a metallic nanomaterial to a plant extract it should possible to observe the presence of the nanometal in the matrix using the TEM images.

It depends on your objective of the study.

Thanks so much Dr. Alan F Rawle for your useful information