The advantages of AFM for nanoparticle research

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Atomic Force Microscopy (AFM) is an advanced microscopy technique that allows researchers to characterize the surface characteristics of nanoparticles as small as 6 nm in diameter.

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Although it can be used as the only experimental technique for nanoparticle research, AFM is often combined with other approaches.

What is AFM?

AFM is used to create 3D images at high magnification levels down to a few nanometers. The technique was developed by IBM researchers Gerard Binning and Heinrich Rohrer in 1986.

AFM measures the interaction forces between the sample surface and an ultra-sharp probe. The probe is attached to a cantilever, which is attached to a laser sensor. The imaging software translates the sensor data into high magnification images.

The AFM can be contact (where the probe touches the sample), non-contact (the probe is held just above the surface of the sample), or oscillating (the probe is made to resonate and it kicks in. contact with the surface at regular intervals). Due to its higher sensitivity, Oscillating AFM is typically used for nanoparticle research.

Benefits of AFM for nanoparticle research

AFM is advantageous in nanoparticle research because no surface modification or coating is required for imaging. This allowed scientists to perform topological analyzes of small nanoparticles smaller than 6nm, such as ion-doped yttrium oxide (Y2oh3), without any prior processing.

Electron microscopy generally cannot characterize low density nanomaterials due to the low contrast they exhibit. However, AFM can also provide topological analyzes of these.

AFM has been used to characterize nanoparticle-based metal substrates used in sensors for Surface Enhanced Raman Spectroscopy (SERS).

The use of AFM led to a detection limit of just one molecule, allowing researchers to correlate the size, shape and surface properties of different nanoparticles with improved SERS performance.

The main advantage of AFM for nanoparticle research is its ability to do 3D image scans. Other techniques are often unable to characterize the height or the z-axis of nanoparticles.

The technique is also considerably less expensive and the devices take up less laboratory space than scanning electron microscopy (SEM) or transmission electron microscopy (TEM). However, AFM has slower scan times than any type of electron microscopy.

AFM at its best in combination with other techniques

In many cases, nanoparticle researchers combine several advanced characterization and analysis techniques to study multifaceted structures and events at the nanoscale.

Nanoscale materials exhibit unexpected properties due to their extraordinarily high surface area to volume ratio and the high molecular reactivity that accompanies them.

A wide range of metrological techniques are used to discover the unexpected electronic, optical, chemical and mechanical properties of these new materials.

AFM has been combined with high-resolution TEM to fill long-standing gaps in nanotechnology research, for example, to characterize the role of the dendrimer model in the growth of platinum nanoparticles. This combination also made it possible to characterize the catalytic activity of rhodium nanoparticles in the polymerization of phenylacetylene.

Kelvin Probe Force Microscopy (KPFM) is a suitable form of non-contact AFM used to determine the work-out of the surface of a sample. Work out is a property of a material’s surface nanostructure and relates to the loss of electrons.

AFM and KPFM were combined to create 3D maps of potential nanoparticle surface distributions, characterizing rust on steel and iron nanoparticles.

X-ray diffraction (XRD) is a technique commonly used for the characterization of nanoparticles. XRD is used to discover the crystal structures of nanoparticles, phase information, lattice parameters and crystal grain size.

Together, XRD and AFM have been used to characterize thin films of silver nanoparticles. Both techniques provide complementary information, in particular the grain size and nanoparticle coverage data that AFM can provide, combined with the ability of XRD to identify the preferred direction of nanoparticle growth.

Another method that relies on x-ray technology is small angle x-ray scattering (SAXS). SAXS is used to know the size of nanoparticles, their size distribution in the sample and their shape.

Grazing Incidence SAXS (GISAXS) is a unique technique that detects the intensity of scattered X-rays from nanoscale objects and uses it to obtain information about nanoparticles.

AFM and GISAXS also complement each other, with GISAXS providing localized morphological images of the surface and AFM supporting them with 3D topographic data. Both methods were used to study silicon dots produced by ion bombardment, as well as self-assembled iron oxide nanoparticles.

Using AFM to design new nanoparticles

The researchers also used AFM to help design new carbon-based nanocomposites.

AFM has been used to identify the structure-property relationship in a new compound. This type of analysis is important in the development of new nanomaterials, as well as drugs and pharmaceuticals.

AFM can provide information on the dispersion and morphological and topographic characteristics of resins loaded with various nanoparticles, including the carbon nanostructured doping agents studied in this research.

The technique is adopted for its non-destructive and non-contact capabilities, which have minimal effect on the structure-property relationship of new nanoparticles and other materials.

Continue Reading: Park FX40: The Story Behind The Design Of A New Class Of Automatic Atomic Force Microscope (AFM).

References and further reading

Mourdikoudis, S., RM Pallares and NTK Thanh (2018) Nanoparticle characterization techniques: comparison and complementarity on the study of nanoparticle properties. Nanoscale. Available at:https://pubs.rsc.org/en/content/articlelanding/2018/NR/C8NR02278J

Raimondo, R. et al. (2019) Aeronautical carbon-based epoxy nanocomposites: efficiency of atomic force microscopy (AFM) in the study of the dispersion of different carbon nanoparticles. Polymers. Available at: https://www.mdpi.com/2073-4360/11/5/832

Disclaimer: The opinions expressed here are those of the author, expressed in a private capacity and do not necessarily represent the views of AZoM.com Limited T / A AZoNetwork, the owner and operator of this website. This disclaimer is part of the terms and conditions of use of this website.

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