Using Nanomechanical Mode and AFM to Defect Surface Recognition on Coating Layer

In numerous fields and industries, including automobile,1 aerospace,2 construction materials,3 and mobile and precision,4 surface treatment is regarded as an important component.

A coating process is generally involved in surface coating treatment methods, and this process is extensively used at the industrial level to prevent abrasion and corrosion of surfaces. The potential to impart unique characteristics to coating materials, like anti-static,5 antibacterial,6 and electromagnetic wave shielding,7 has been developed more recently. During the 1990s, digital devices became extremely popular, which spurred rapid advancements in industrial coating technologies. Such technologies helped in developing device protection in several ways, such as UV protection, chemical resistance, anti-fingerprint, and scratch resistance.8 Atomic force microscopy, or AFM, is extensively used in the domain of material surface research and is also widely used on coated surfaces.9

Analysis of AFM images enables deriving the coating’s thickness from the morphology of the sample surface, whereas surface roughness aids in providing information about the evenness of a coating after it is applied. In addition, AFM images enable inspection and review of quality control for potential defects. AFM determines both mechanical properties and surface morphology. Mechanical characteristics like modulus, adhesion, and stiffness, can be measured using force-distance curves on the coated surface.10

This article comprehensively describes an innovative technique devised by Park Systems. Named “PinPoint™ nanomechanical mode,” the method explores the mechanical characteristics of a surface. The article also demonstrates how this technique can be used for analyzing the stages at which defects are created at the time of material surface processing, particularly during the coating process.

Generally, AFM images can reveal the defects present on the surface of a sample, but a mere observation of surface morphology does not make it easy to establish when exactly the defect was produced (at the time of production). This problem is resolved by PinPoint™ nanomechanical mode — it collects mechanical data about the coated surface and establishes whether defects were produced before or after the coating at the time of production.

Materials and Methods

PinPoint Nanomechanical Mode

PinPoint™ nanomechanical mode gathers high-resolution topographical data and, at the same time, obtains force-distance data for every pixel of the scan area.11 This enables measuring the morphology of the sample surface while concurrently obtaining quantitative nanomechanical characteristics such as energy dissipation, stiffness, deformation, adhesion, and modulus.

Experimental Setup

To determine the sample’s mechanical properties, the PinPoint™ nanomechanical mode was used on Park NX10 AFM from Park Systems combined with an NSC36 cantilever, obtained from MikroMasch. The spring constant (k = 2 N/m) and resonant frequency (f = 130 kHz) of the cantilever enable sufficient deformation of a sample and, at the same time, maintain the sufficient deflection of a cantilever. The outcomes were examined with the Park XEI data processing software, which enables the characterization of the surface material, allows comparison of mechanical property values, and offers quantitative data from the images.

Testing Samples

The samples were prepared in two ways, to test the potential of the PinPoint™ nanomechanical mode in differentiating defects produced both before and after the application of the coating. The first test included a scratch created over the surface of a coated glass substrate, while the second test involved a scratched glass substrate whose surface was again coated later. The variation between the creation times of the defect can be established from whether the glass material was subjected to the scratch site. The glass will not be exposed if the scratch was produced before coating, since the coating is applied over the scratch. However, the coating will peel off and easily expose the glass material if the scratch was produced after coating.

When the site is imaged using PinPoint™ nanomechanical mode, surface mechanical characteristics, like modulus and adhesion, display an evident contrast when the tip of the AFM probes varied materials (coating and glass). This data cannot be established from the topography alone, and this is clearly shown in Figure 1.

Illustration of a defect created before and after coating. The difference between the materials cannot be seen through the depth of the scratch alone but through the mechanical properties of the material.

Figure 1. Illustration of a defect created before and after coating. The difference between the materials cannot be seen through the depth of the scratch alone but through the mechanical properties of the material.

Results

PinPoint™ nanomechanical mode was used to obtain modulus, adhesion energy, and topography images from a couple of samples with defects produced before and after coating. In both cases, the topography images demonstrated the scratch behind a trench (see Figure 2a and 3a). Images from this site emphasize the differences in mechanical property between the unaffected area and the scratch area.

PinPoint™ nanomechanical mode images of a glass substrate when the scratch was created before the coating was applied. No contrast was observed between the coated area and the scratched area, in both adhesion energy and modulus images.

Figure 2. PinPoint™ nanomechanical mode images of a glass substrate when the scratch was created before the coating was applied. No contrast was observed between the coated area and the scratched area, in both adhesion energy and modulus images.

Analysis of the modulus and adhesion energy images of the scratch prior to coating (Figure 2b and 2c) did not show any visible variation in the mechanical characteristics between the coating area and the scratch area. Figures 3b and 3c show the glass substrate that is scratched post the coating, demonstrating an extremely clear contrast between the scratch surface and the neighboring surface.

PinPoint™ nanomechanical mode images of a glass substrate when the scratch was created after a coating was applied. The contrast between the coating area and the scratched area is clearly visible in both adhesion energy and modulus images.

Figure 3. PinPoint™ nanomechanical mode images of a glass substrate when the scratch was created after a coating was applied. The contrast between the coating area and the scratched area is clearly visible in both adhesion energy and modulus images.

Comparison of the surfaces’ mean adhesion energy and modulus values both before and after scratching evidently differentiates the two varied surfaces. The Park XEI data processing software helps in choosing different regions of the same image, that is, the coating area and the scratch area (see Figure 4).

Region selection applied in Park XEI software, to calculate mean adhesion and modulus values of each distinct area.

Figure 4. Region selection applied in Park XEI software, to calculate mean adhesion and modulus values of each distinct area.

The mean value of each mechanical trait was computed for each region; for comparison purposes, those values are shown in Table 1.

Adhesion Energy Modulus
Scratch Before Coating After Coating Before Coating After Coating
Figure 4a (Full Area) 4b (Red) 4b (Green) 4c (Full Area) 4d (Red) 4d (Green)
Average 1.22 fj 1.15 fj 2.47 fj 3.15 GPa 3.08 GPa 1.79 GPa

In Figure 4a, the selected coating area can be seen, which created a measured mean value of 1.22 fJ. In Figure 4b, the coating area and the underlying exposed material were chosen separately. The coating’s adhesion energy value (1.15 fJ) was observed to coincide with the earlier value, whereas the adhesion energy of the underlying glass substrate displayed a higher value of 2.47 fJ). Moreover, during the comparison of the modulus values, the coating from Figure 4c provided a measured value of 3.15 GPa, akin to the coating’s modulus value from Figure 4d. (3.08 GPa). Contrary to the adhesion energy values, the modulus of the underlying scratched glass substrate exhibited a lower value of 1.79 GPa.

Conclusion

This article has shown how the Park Systems’ PinPoint™ nanomechanical mode can be used for examining the mechanical characteristics of defects to find out whether a surface defect was produced before or after the application of the coating process. The initial time of formation of the defect was effectively identified by determining the modulus and adhesion energy variations between glass and coating materials.

AFM can be employed for a host of applications in the coating sector due to its potential to closely inspect the samples’ surface properties — properties that otherwise cannot be observed by inspecting morphology alone. The PinPoint™ nanomechanical mode allows users to study mechanical characteristic at the nanoscale and also to examine the variations between different coating methods and coating materials. Advantages like these will increase the utility of AFM as an essential tool in the coating sector.

References

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  2. Benavides, S. (Ed.). (2009). Corrosion control in the aerospace industry. Elsevier.
  3. Lee, J., Mahendra, S., & Alvarez, P. J. (2010). Nanomaterials in the construction industry: a review of their applications and environmental health and safety considerations. ACS Nano, 4(7), 3580–3590.
  4. Leopold, J., Neugebauer, R., Löffler, M., Schwenck, M., & Hänle, P. (2006). Influence of coating-substrate systems on chip and burr formation in precision manufacturing. Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 220(4), 499–506.
  5. Qiu, C., Wang, J., Mao, S., Guo, W., Cheng, S., & Wang, Y. (2010). Preparation of poly (3, 4-ethylenedioxythiophene)/poly (styrene sulfonate) (PEDT/PSS) composite and its applications in anti-static coating. Polymers for Advanced Technologies, 21(9), 651–655.
  6. Ciacotich, N., Din, R. U., Sloth, J. J., Møller, P., & Gram, L. (2018). An electroplated copper-silver alloy as antibacterial coating on stainless steel. Surface and Coatings Technology, 345, 96–104.
  7. Kim, C. G., Nam, Y. W., & Choi, J. H. (2018). U.S. Patent Application No. 15/809,345.
  8. Future Markets. “Automotive.” Nanocoatings. Nov. 2013.
  9. Carpick, R. W., & Salmeron, M. (1997). Scratching the surface: fundamental investigations of tribology with atomic force microscopy. Chemical reviews, 97(4), 1163–1194.
  10. Butt, H. J., Cappella, B., & Kappl, M. (2005). Force measurements with the atomic force microscope: Technique, interpretation and applications. Surface science reports, 59(1–6), 1–152.
  11. John Paul Pineda, Gerald Pascual, Byong Kim, and Keibock Lee (2017). Using AFM PinPoint™ Nanomechanical Mode for Quantification of Elastic Modulus in Materials Two Orders of Magnitude Faster than Force Volume Spectroscopy, Park Systems Application note #26.

This information has been sourced, reviewed and adapted from materials provided by Park Systems.

For more information on this source, please visit Park Systems.

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