Dear Lata: Both method are suitable for nanomechanical characterization.

Of course the nature of the sample, the size of the sample, the size of the phases and the depth of the volume to be analyzed should be taken in account to decide which method is the best for that particular material.

For my experience applying the Nanoindentation is easier to obtain quantitative results, but limitations must be assumed, as to the sizes of areas to be analyzed, if they are very small (below the micron range) is difficult, the optical system the nanoindenter, allows you to locate and position yourself correctly on the areas of interest. If seccción is very thin may not be applicable technique.

In the case of AFM, also, it is possible to obtain satisfactory results but obtaining quantitative results is more difficult. Furthermore, if the sample is large can also be a limitation. However, the AFM technique has many advantages when analyzing areas are very small, when you are analyzing a soft material, or delicated material or simply when the material is extremely thin (few nanometers).

If you already have images of scanning electron microscopy, or other microscopy of the surface of the sample can assess the size of the grains, determine the size of the sample and whether or not susceptible to cut, determine the section thickness of the piece of material you will analyze.

All this information can help you decide which technique is most appropriate or possible to implement in your sample. If you already have the characteristics of your sample, I could try to help you assess what would be the most appropriate technique.

Nanoindentation a method for evaluation of nanomechanical properties, and AFM is mainly for imaging. I recommend you the NI. But is necessary that you define which properties and the scale (nanomechanics?)

AFAM technique may be useful to determine the elasticity moduli of different phases

Nanoindentation method may be useful when someone try to have hardness and Young's modulus in the nano scale (based on the Oliver&Phare method). This method can be used, for example, in the case of laser welding, to verify if the mechanical properties changed in the Heat affected Zone near to the welding point.

The results depend on the Poisson ratio (input), and also on the indentation position (e.g. in the case of dual phase material).

Dear Lata: Both method are suitable for nanomechanical characterization.

Of course the nature of the sample, the size of the sample, the size of the phases and the depth of the volume to be analyzed should be taken in account to decide which method is the best for that particular material.

For my experience applying the Nanoindentation is easier to obtain quantitative results, but limitations must be assumed, as to the sizes of areas to be analyzed, if they are very small (below the micron range) is difficult, the optical system the nanoindenter, allows you to locate and position yourself correctly on the areas of interest. If seccción is very thin may not be applicable technique.

In the case of AFM, also, it is possible to obtain satisfactory results but obtaining quantitative results is more difficult. Furthermore, if the sample is large can also be a limitation. However, the AFM technique has many advantages when analyzing areas are very small, when you are analyzing a soft material, or delicated material or simply when the material is extremely thin (few nanometers).

If you already have images of scanning electron microscopy, or other microscopy of the surface of the sample can assess the size of the grains, determine the size of the sample and whether or not susceptible to cut, determine the section thickness of the piece of material you will analyze.

All this information can help you decide which technique is most appropriate or possible to implement in your sample. If you already have the characteristics of your sample, I could try to help you assess what would be the most appropriate technique.

As you are interested to measure the mechanical properties of the composite at the surface.

As composites made of two different materials.

these two materials have different properties ( shapes, morphology, hardness, sizes etc.). As like MMC (Metal matrix composite), CMC (Ceramic matrix composite) PMC (polymer matrix composite) etc.

Now come to nano-indentation ..first of all nano-indentation is useful for nano-scale. In case of thin film the indenter depth will be 1/10 of the film thickness. If you have two different materials.. for example take MMC in which matrix is metal and dispersoids are some ceramics.

Now your dispersoid (reinforced) phase will be very different hardness than the metal(matrix phase). even the size of dispersoids is in nano scale the indenter will only cover single particle.

you will get two different mechanical properties one for matrix and other for reinforced phase. but not the composite mechanical property.

so in this case better you go for micro indentation... in which the indenter covers at least few particles (reinforced phase) with the matrix. So that you will get the mechanical property of the composite.rather than the individual phases.The depth is also few microns (depending on the applied load).But in this case you will end up with hardness only.

AFM is not use for mechanical properties It can be used for surface roughness, and imaging purpose.

Thank you all for your very interesting answers. But, what about sample preparation ? I heard for the AFM technic, that the sample should be finely polished to have a very smooth, flat and clean surface. Is it needed too for the nanoindentation ? I guess that the answer is Yes, but should the polishing be as fine as for AFM ? Actually, my materials are composites with a polymer matrix (PP) and vegetal fibres.

Dear Lata,

it will be a pleasure to help you for AFM and nanoindentation at IUT St denis and LSPM. The sample preparation depend also on the size of your fiber you use.

One of the major difference between the Nanoindentation and AFM is travel of Indenter. In case of Nanoindentation, the indenter travels vertically down for hardness and modulus evaluations and you can obtain the absolute values for the surface mechanical properties whereas in case of AFM the indenter penetrates slightly tangential to the surface therefore, the properties measured using AFM are more of including factor from the tangential/slanting penetration that makes it relative property for comparison purposes compared to absolute values.

For your concern regarding Surface Preparation. The nanoindentation got better as well as high probability of going ahead if your surface finish is better. Since Nanoindentation measures absolute properties of material surfaces its better to perform the indentation on finally prepared polymeric composites. In this way you might get few of the indentation experiments may fail but on the overall the actual property measurement.

Advantages of afm:

High load and depth resolution compared to nanoindentation. 

AFM is suitable for ultra-soft materials like hydrogels. Nanoindentation is suitable for hard materials. That is Youngs modulus (E) value is greater than 2 GPa. 

Image resolution is good in nanoindentation compared to that of afm.