Case Study: Quantitative AFM could provide food industries with more conclusive quality checking method

Customer: Charles Clifford, Zeinab Al-Rekabi & Suzanne L. Davies, National Physical Laboratory, UK  

Highlighted publication: Nanomechanical properties of potato flakes using atomic force microscopy, Charles Clifford et al. (2021) Journal of Food Engineering 307 110646  

Instrument: Asylum Cypher S

Probes: SCOUT 350 RAl

Imaging modes: Tapping, Contact

Keywords: Food Industry, AFM, Atomic Force Microscopy, AFM Probes, Microscopy, Quality Assessment, Quality, Quantitative, Manufacturing, Characterisation

Potato flakes are a key base ingredient in many processed foods and snacks, and offer a longer-life alternative to raw potatoes. Flakes are industrially manufactured through a carefully controlled process where raw potatoes are selected by their suitability based on size, variety, reducing sugar, starch, and water content.

The quality of potato flakes can cause problems in the manufacturing process, for example in the production of crisps. Large blisters can form on the surface of the chip post-frying, causing issues during production and on final product quality.

The National Physics Laboratory (NPL) was tasked with identifying whether AFM screening of potato flakes at the point of selection could distinguish between flakes that would perform well right the way through to the finished product. This is something current quality checks are unable to do conclusively.

In the study, NPL used an Asylum Research Cypher S AFM and NuNano SCOUT 350 RAl probes to investigate the nanomechanical properties of four different types of low-leach potato flake samples provided by two suppliers from the initial screening process to determine suitability for snack manufacture.

By applying tapping mode to examine the topographies (Fig 1 of paper) of sub-optimal and optimal potato flake samples and force-volume mode to generate maps of force-displacement curves of the same samples, the study was able to show that there was a quantitative difference between the optimal and sub-optimal potato flakes.

The optimal samples had more granule-like structures than the sub-optimal ones (Fig 2 in original paper) and the optimal potato granule samples appeared stiffer (shown by the orange and yellow areas Fig 3. A and B) compared to the sub-optimal samples which appeared more compliant (as seen by the brown and red regions Fig 3C and D).

Conclusions 

By employing both amplitude-modulation and force-modulation AFM, NPL demonstrated that sub-optimal potato starch flakes appeared more compliant than the optimal samples.

These results offer a compelling rationale for future experimentation to aid food industries in adopting quantitative AFM measurements to provide food industries with a differential assessment between different food samples.

Other publications using NuNano probes and Asylum Research instruments: 

Characterizing the nanomechanical properties of microcomedones after treatment with sodium salicylate ex vivo using atomic force microscopy Al-Rekabi, Z., Rawlings, A. V., Lucas, R. A., Raj, N., & Clifford, C. A. (2021) International Journal of Cosmetic Science 43(5), 610-618. https://doi.org/10.1111/ics.12729

Case Study: Characterisation of graphene nanoribbons growth in the hunt for a new generation of nanoscale electronic materials

Customer: Peter Beton, Jonathan Bradford et al., Department of Physics, University of Nottingham, UK

Highlighted publication: Graphene nanoribbons with hBN passivated edges grown by high-temperature molecular beam epitaxy, Jonathan Bradford et al. (2023) 2D Mater. 10 035035, DOI 10.1088/2053-1583/acdefc

Instrument: Asylum Cypher S

Probes: SCOUT 70 RAl, SPARK 70 Pt

Imaging modes: Tapping, contact, conductive

Keywords: Electronics, semi-conductors, AFM, Atomic Force Microscopy, AFM Probes, Microscopy, Graphene, Materials, Characterisation

The global demand for faster, smaller and cheaper electronic devices is unrelenting. Limitations on existing semiconductor fabrication materials and processes demands that considerable effort is spent identifying new materials, characterising their properties and creating new processes to aid their transformation into devices.

Graphene and hexagonal boron nitride (hBN) are two such materials of interest, especially in combination as a conductor and dielectric, respectively.  Recent research by Professor Peter Beton and his team at the University of Nottingham has focused on the formation of graphene nanoribbons (GNRs) along hBN trenches to form nanoscale circuitry.

The method for growing GNRs on hBN required nickel nanoparticles to be deposited on hBN flakes by thermal evaporation, which were subsequently annealed in a mixture of hydrogen and argon. This caused the nanoparticles to migrate along the crystal’s zigzag lattice directions and etch oriented trenches in the top layer of the hBN flake. After removing the nanoparticles with a wet chemical etch a high-temperature molecular beam epitaxy (HT-MBE) process was used to grow the GNRs, with the hBN trenches acting as a blueprint for their growth. Atomic force microscopy was used extensively to characterise the samples at each stage of preparation and growth.

Using NuNano’s silicon AFM probes (Scout 70 RAI) with an Asylum Research Cypher S instrument the Nottingham team were able to study the early growth stages of the GNRs. They were able to show that at high growth temperatures the GNR growth rate affected whether the templating hBN step is terminated with boron (B) or nitrogen (N) atoms.

“My group has been using NuNano’s Scout 70 RAl AFM probes in combination with our Asylum Research Cypher AFM for the last 7 years. This has been a highly reliable combination, allowing us to readily achieve lattice resolution on hexagonal boron nitride and other 2D materials that we work with””

— Professor Peter Beton

Professor Peter Beton, University of Nottingham, UK

In Figure 1, you can see a close-up view of these etch tracks after the removal of the Ni particles using a wet chemical process. The tracks include both very shallow ones (0.36 nm, which is roughly one atomic layer) and deeper ones (1.1 nm, approximately three atomic layers). Most of the tracks are only one atomic layer deep.  In figure 2 the lattice of the hBN flake is resolved with sub-nanometre imaging resolution.

Figure 1

Figure 2

Using NuNano’s conductive AFM probes (Spark 70 Pt) to undertake conductive AFM (cAFM) Nottingham were able to study the electrical performance of the fully grown GNRs. They observed the creation of a conductive network within the hBN surface and noticed signs of electrons moving between different sublattices at the interface between graphene and hBN, a phenomenon known as intervalley scattering.

“”[Using] SPARK probes for conductive AFM [we have achieved]  lattice resolution in cAFM mode, despite some challenging sample conditions””

— Research Fellow, Dr Jonathan Bradford

Conclusions

Atomic force microscopy has enabled Professor Beton’s group to study the topological and electrical properties of the graphene nanoribbons at the nanoscale and enhanced their understanding not only of how the hBN and graphene interface is formed but also how this material holds great potential for use in extremely thin electronic devices and circuits.

Read the full paper here:

Graphene nanoribbons with hBN passivated edges grown by high-temperature molecular beam epitaxy, J. Bradford, T. S. Cheng, T. S. S. James, A. N. Khlobystov, C. J. Mellor, K. Watanabe, T. Taniguchi, S. V. Novikov & P. H. Beton (2023) 2D Materials, 10 035035 DOI 10.1088/2053-1583/acdefc 

Related publications:

Epitaxy of boron nitride monolayers for graphene-based lateral heterostructures J. Wrigley, J. Bradford, T. James, T. S Cheng, J. Thomas, C. J. Mellor, A. N. Khlobystov, L. Eaves, C. T. Foxon & S. V. Novikov (2021) 2D Materials, 8, 3 DOI 10.1088/2053-1583/abea66

Step-flow growth of graphene-boron nitride lateral heterostructures by molecular beam epitaxy J. Bradford, T. S. Cheng, T. S. S. James, A. N. Khlobystov, C. J. Mellor, K. Watanabe, T. Taniguchi, S. V. Novikov & P. H. Beton (2023) 2D Materials, 10 035035 DOI 10.1088/2053-1583/ab89e7