Feasibility of wear reduction for soft nanostructured thin film through enhanced elastic recoverability and contact stress relief

Over several decades many studies on the reduction of wear of mechanical systems have been conducted.
Methods to reduce wear are generally divided into the following categories: applying lubrication, coating with high-hardness materials, and surface texturing. *

Several studies have reported that coatings with higher hardness show more wear than those with lower hardness. From these reports, it is apparent that wear does not depend solely on the hardness of the surface.  Hence, there is a strong motivation for utilizing additional strategies for designing wear-resistive surfaces rather than only enhancing the hardness of the coating. *

In the article “Feasibility of wear reduction for soft nanostructured thin film through enhanced elastic recoverability and contact stress relief” Kuk-Jin Seo, Hyun-Joon Kim and Dae-Eun Kim show, that a soft, thin film comprising randomly aligned carbon nanotubes (CNTs) can reduce surface wear more effectively than a homogeneous thin film because of enhanced elastic recoverability and contact stress relief originating from its mesh structure. *

To investigate the wear characteristics of the mesh structure compared to those of the homogeneous thin film, multi-walled CNTs (MWCNTs) and diamond-like carbon (DLC) thin films were prepared to conduct nanoscale tribological experiments using atomic force microscopy (AFM). The MWCNT thin film showed unmeasurably low wear compared with the DLC thin film under a certain range of normal load. *

To demonstrate the wear reduction mechanism of the MWCNT thin film, its indentation and frictional behaviors were assessed. The indentation behavior of the MWCNT thin film revealed repetitive elastic deformation with a wide strain range and a significantly lower elastic modulus than that of the DLC thin film. The permanent deformation of the MWCNT thin film was observed through frictional experiments under relatively high normal load conditions. *

The presented results are expected to provide insights into the design of highly wear-resistant surfaces using nanostructures. *

The thickness and surface roughness of the MWCNT and DL thin films were measured using Atomic Force Microscopy. *

The force-displacement (F-D) curves were measured on the MWCNT thin film using the AFM to verify the mechanical behavior when indented by the zirconia microspheres that were used for wear and friction experiments. *

The adhesion forces between the thin films and zirconia microspheres were measured by observing the pull-off force of the F-D curve with the AFM. *

The adhesion force was measured using a colloidal AFM probe to aid the analysis of the tribological characteristics of the thin film. *

The pull-off forces for the DL specimens were obtained at 35 different locations with displacements of 50-200 nm. *

Diamond-coated AFM probes (NanoWorld Pointprobe® DT-NCHR ) were used for scanning, while non-coated silicon AFM probes with relatively high and low spring constants (NanoWorld Pointprobe® NCHR and CONTR) were used for the tribological experiments and specimen characterizations. *

Diamond-coated AFM probes (NanoWorld Pointprobe® DT-NCHR ) were used for scanning, while non-coated silicon AFM probes with relatively high and low spring constants (NanoWorld Pointprobe® NCHR and CONTR) were used for the tribological experiments and specimen characterizations.
Figure 6 from “Feasibility of wear reduction for soft nanostructured thin film through enhanced elastic recoverability and contact stress relief” by Kuk-Jin Seo et al.:
AFM images of wear tracks on the MWCNT thin film under test conditions of (a) 2,000 nN and 20,000 cycles, (b) 6,000 nN and 30,000 cycles, (c) 7,000 nN and 30,000 cycles, (d) 9,200 nN and 30,000 cycles, (e) 13,500 nN and 30,000 cycles, and (f) 28,000 nN and 30,000 cycles. Post-processed AFM images that subtracted the original image before each wear test under conditions of (g) 6,000 nN and 30,000 cycles, (h) 7,000 nN and 30,000 cycles, and (i) 28,000 nN and 30,000 cycles

*Kuk-Jin Seo, Hyun-Joon Kim and Dae-Eun Kim
Feasibility of wear reduction for soft nanostructured thin film through enhanced elastic recoverability and contact stress relief
Friction 11(7): 1292-1306 (2023)
DOI: https://doi.org/10.1007/s40544-022-0669-7

Please follow this external link to read the full article: https://rdcu.be/dejTa

The article “Feasibility of wear reduction for soft nanostructured thin film through enhanced elastic recoverability and contact stress relief” by Kuk-Jin Seo, Hyun-Joon Kim and Dae-Eun Kim is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third-party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.

Electrochromic switching of tungsten oxide films grown by reactive ion-beam sputter deposition

Because of the global climate change, energy-saving and sustainable technologies are becoming more and more important. Therefore, the demands on technologies for the conversion, storage and use of renewable energies are constantly growing. *

The building sector plays an important role in terms of energy saving potential. *

In particular, the class of so-called smart windows offers an approach to save energy in the building sector by efficiently regulating incident light. *

Chromogenic thin films are crucial building blocks in smart windows to modulate the flux of visible light and heat radiation into buildings. *

Due to their diversity in composition and structure as well as their superior performance, electrochromism based on thin film transition metal oxides has become increasingly important in the last decade. *

Electrochromic materials such as tungsten oxide are well established in those devices. Sputter deposition offers a well-suited method for the production of such layers, which can also be used on an industrial scale. *

The EC properties of tungsten oxide layers depend on the composition, the crystal structure and the morphology. *

The film characteristics are strongly dependent on the growth technique. *

In the article “Electrochromic switching of tungsten oxide films grown by reactive ion-beam sputter deposition” Mario Gies, Fabian Michel, Christian Lupó, Derck Schlettwein, Martin Becker and Angelika Polity describe how Tungsten oxide thin films were grown by ion-beam sputter deposition (IBSD), a less common sputtering variant. *

They then show the possibility of influencing technologically relevant samples characteristics by using different preparation parameters (e.g., gas mixture or growth temperature). This allows to tune the elemental composition, optical properties or to influence the structure and the degree of crystallization in the resulting thin films. *

The high reproducibility as well as the high purity of IBSD-grown layers render ion-beam sputter deposition a suitable candidate for growth of tungsten oxide and, most likely, other chromogenic materials. *

Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were conducted to analyze the crystallite surface structure.

For the AFM investigations in air NanoWorld® Pointprobe® SEIHR AFM probes designed for soft non-contact mode imaging were used. (typical resonance frequency 130 kHz, typical force constant 15 N/m ). *

Figure 2 g, h and i from "Electrochromic switching of tungsten oxide films grown by reactive ion-beam sputter deposition" by Miario Gies et al. In Fig. 2 g, the surface of a sample deposited at RT and a moderate O2 flux of 5.15 sccm is shown as analyzed by Atomic Force Microscopy ( AFM ). Individual grains of about 0.2 μm size appear interconnected without sharply defined grain boundaries. The root-mean-square surface roughness was determined to be around 9 nm. In comparison, Fig. 2h shows the morphology of a sample synthesized at RT under oxygen-poor conditions. Again, no sharply defined grains are recognizable. However, the grains seem to be a bit more extended. The determined roughness of the surface is approximately 7 nm. At an increased deposition temperature of 400 ∘C, larger round-shaped grains of about 0.5 μm lateral expansion were obtained, cf. Fig. 2i, leading to an increased roughness of around 20 nm, much higher than for the unheated samples. NanoWorld Pointprobe SEIHR AFM probes were used.
Figure 2 g, h and i from “Electrochromic switching of tungsten oxide films grown by reactive ion-beam sputter deposition” by Mario Gies et al.:
AFM images of samples, deposited at room temperature under a moderate O2 flux of 5.15 sccm (g) and under oxygen-poor conditions (h). Compared to the surface of a sample grown at 400 ∘C (i), the surface roughness is significantly smoother. For the full figure please refer to the full article: https://link.springer.com/article/10.1007/s10853-020-05321-y

*Mario Gies, Fabian Michel, Christian Lupó, Derck Schlettwein, Martin Becker and Angelika Polity
Electrochromic switching of tungsten oxide films grown by reactive ion-beam sputter deposition
Journal of Materials Science (2020)
DOI: https://doi.org/10.1007/s10853-020-05321-y

Please follow this external link to read the full article: https://link.springer.com/article/10.1007/s10853-020-05321-y

Open Access : The article “Electrochromic switching of tungsten oxide films grown by reactive ion-beam sputter deposition” by Mario Gies, Fabian Michel, Christian Lupó, Derck Schlettwein, Martin Becker and Angelika Polity is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.

Photoresponsive Photoacid-Macroion Nano-Assemblies

In mother nature, the concept of self-assembly is vital for life, as it generates much of the functionality of living cells. It also bears great synthetic potential for the formation of versatile, switchable, and functional nanostructures.*

Noncovalent interactions can be triggered by external influences, such as the change of pH, light irradiation, thermal activation, introduction of a magnetic field, moisture, or redox response. Of high interest are light-responsive systems, for example in the fields of sensors or therapy, and, thus, it is desirable to explore novel concepts toward light-triggerable self-assembly.*

In the article “Photoresponsive Photoacid-Macroion Nano-Assemblies” Alexander Zika, Sarah Bernhardt and Franziska Gröhn present light-responsive nano-assemblies with light-switchable size based on photoacids.*

Anionic disulfonated napthol derivates and cationic dendrimer macroions are used as building blocks for electrostatic self-assembly. Nanoparticles are already formed under the exclusion of light as a result of electrostatic interactions. Upon photoexcitation, an excited-state dissociation of the photoacidic hydroxyl group takes place, which leads to a more highly charged linker molecule and, subsequently, to a change in size and structure of the nano-assemblies. The effects of the charge ratio and the concentration on the stability have been examined with absorption spectroscopy and -potential measurements.*

The influence of the chemical structure of three isomeric photoacids on the size and shape of the nanoscale aggregates has been studied by dynamic light scattering and atomic force microscopy, revealing a direct correlation of the strength of the photoacid with the changes of the assemblies upon irradiation.*

NanoWorld Ultra-Short AFM Cantilevers of the USC-F0.3-k0.3 type ( typical force constant 0.3 N/m ) were operated in tapping mode for the Atomic Force Microscopy (AFM) images presented in the article.*

Figure 1 a from “Photoresponsive Photoacid-Macroion Nano-Assemblies” by Alexander Zika  et al:
Assembly formation and photoresponse of the dendrimer–photoacid system at a charge ratio of r = 0.25: (a) AFM height images before (right) and after (left) irradiation.  Figure 1 a from “Photoresponsive Photoacid-Macroion Nano-Assemblies” by Alexander Zika  et al:
Assembly formation and photoresponse of the dendrimer–photoacid system at a charge ratio of r = 0.25: (a) AFM height images before (right) and after (left) irradiation.
Figure 1 a from “Photoresponsive Photoacid-Macroion Nano-Assemblies” by Alexander Zika  et al:
Assembly formation and photoresponse of the dendrimer–photoacid system at a charge ratio of r = 0.25: (a) AFM height images before (right) and after (left) irradiation. Please refer to the full article for the full figure https://www.mdpi.com/2073-4360/12/8/1746

*Alexander Zika, Sarah Bernhardt and Franziska Gröhn
Photoresponsive Photoacid-Macroion Nano-Assemblies
Polymers 2020, 12, 1746
DOI: 10.3390/polym12081746

Please follow this external link to read the full article: https://www.mdpi.com/2073-4360/12/8/1746

Open Access : The article “Photoresponsive Photoacid-Macroion Nano-Assemblies” by Alexander Zika, Sarah Bernhardt and Franziska Gröhn is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.