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Friction characteristics of Cd-rich carbonate films on calcite surfaces: implications for compositional differentiation at the nanometer scale.

Cubillas P, Higgins SR - Geochem. Trans. (2009)

Bottom Line: Lateral Force Microscopy (LFM) studies were carried out on cleaved calcite sections in contact with solutions supersaturated with respect to otavite (CdCO3) or calcite-otavite solid solutions (SS) as a means to examine the potential for future application of LFM as a nanometer-scale mineral surface composition mapping technique.Layer-by-layer growth of surface films took place either by step advancement or by a surface nucleation and step advancement mechanisms.In most experiments at fixed load, the film showed higher friction than the calcite surface, but the friction-load dependence for the different surfaces revealed that at low loads (0-40 nN), a calcian otavite film has lower friction than calcite; a result that is contrary to earlier LFM reports of the same system.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemistry, Wright State University, 3640 Col, Glenn Hwy, Dayton, Ohio 45435, USA. pablo.cubillas-gonzales@manchester.ac.uk

ABSTRACT
Lateral Force Microscopy (LFM) studies were carried out on cleaved calcite sections in contact with solutions supersaturated with respect to otavite (CdCO3) or calcite-otavite solid solutions (SS) as a means to examine the potential for future application of LFM as a nanometer-scale mineral surface composition mapping technique. Layer-by-layer growth of surface films took place either by step advancement or by a surface nucleation and step advancement mechanisms. Friction vs. applied load data acquired on the films and the calcite substrate were successfully fitted to the Johnson Kendall Roberts (JKR) model for single asperity contacts. Following this model, friction differences between film and substrate at low loads were dictated by differences in adhesion, whereas at higher load they reflect differences in contact shear strength. In most experiments at fixed load, the film showed higher friction than the calcite surface, but the friction-load dependence for the different surfaces revealed that at low loads (0-40 nN), a calcian otavite film has lower friction than calcite; a result that is contrary to earlier LFM reports of the same system. Multilayer films of calcian-otavite displayed increasing friction with film thickness, consistent with the expectation that the film surface composition will become increasingly Cd-rich with increasing thickness. Both load- and thickness-dependence trends support the hypothesis that the contact shear strength correlates with the hydration enthalpy of the surface ions, thereby imparting friction sensitivity in the LFM to mineral-water interface composition.

No MeSH data available.


Related in: MedlinePlus

Simplified diagram of the photodetector set-up and laser path. The diagram shows the lateral view (a) and front view (b) of the laser path and photodector set up. The original angle formed by the reflected beam on the cantilever (2θ) changes to 2θ' from refraction by the sapphire window (2θ' = 2θ/1.33).
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Figure 1: Simplified diagram of the photodetector set-up and laser path. The diagram shows the lateral view (a) and front view (b) of the laser path and photodector set up. The original angle formed by the reflected beam on the cantilever (2θ) changes to 2θ' from refraction by the sapphire window (2θ' = 2θ/1.33).

Mentions: An Atomic Force Microscope measures the forces between a sharp tip (with a typical radius of 10–100 nm) and a sample surface. Most commonly, the tip is mounted on the end of a cantilever that serves as a force sensor. Variations in the sample-tip force results in the deflection of the cantilever, which can be monitored by the change in position of a laser beam reflected from the cantilever surface into a four-quadrant photodiode. During the scanning process the cantilever will bend due to forces acting normal to the sample surface. In addition, the cantilever will twist due to lateral (friction) forces between the tip and the substrate that opposes relative movement between the two. This twisting is detected by the photodiode mechanism as a change in the "lateral" position of the laser spot (Fig. 1). In the monitoring of these "lateral forces" by an AFM, in the daughter method of LFM, the lateral force signal measured for forward or backward scans will have opposite sign since the cantilever will twist in opposite directions. A plotting of the lateral force signal vs. lateral displacement for both scans defines the so-called friction loop. Friction force, then, is defined as the half of the difference between the two signals measured in the opposing scanning directions [44,45].


Friction characteristics of Cd-rich carbonate films on calcite surfaces: implications for compositional differentiation at the nanometer scale.

Cubillas P, Higgins SR - Geochem. Trans. (2009)

Simplified diagram of the photodetector set-up and laser path. The diagram shows the lateral view (a) and front view (b) of the laser path and photodector set up. The original angle formed by the reflected beam on the cantilever (2θ) changes to 2θ' from refraction by the sapphire window (2θ' = 2θ/1.33).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2719640&req=5

Figure 1: Simplified diagram of the photodetector set-up and laser path. The diagram shows the lateral view (a) and front view (b) of the laser path and photodector set up. The original angle formed by the reflected beam on the cantilever (2θ) changes to 2θ' from refraction by the sapphire window (2θ' = 2θ/1.33).
Mentions: An Atomic Force Microscope measures the forces between a sharp tip (with a typical radius of 10–100 nm) and a sample surface. Most commonly, the tip is mounted on the end of a cantilever that serves as a force sensor. Variations in the sample-tip force results in the deflection of the cantilever, which can be monitored by the change in position of a laser beam reflected from the cantilever surface into a four-quadrant photodiode. During the scanning process the cantilever will bend due to forces acting normal to the sample surface. In addition, the cantilever will twist due to lateral (friction) forces between the tip and the substrate that opposes relative movement between the two. This twisting is detected by the photodiode mechanism as a change in the "lateral" position of the laser spot (Fig. 1). In the monitoring of these "lateral forces" by an AFM, in the daughter method of LFM, the lateral force signal measured for forward or backward scans will have opposite sign since the cantilever will twist in opposite directions. A plotting of the lateral force signal vs. lateral displacement for both scans defines the so-called friction loop. Friction force, then, is defined as the half of the difference between the two signals measured in the opposing scanning directions [44,45].

Bottom Line: Lateral Force Microscopy (LFM) studies were carried out on cleaved calcite sections in contact with solutions supersaturated with respect to otavite (CdCO3) or calcite-otavite solid solutions (SS) as a means to examine the potential for future application of LFM as a nanometer-scale mineral surface composition mapping technique.Layer-by-layer growth of surface films took place either by step advancement or by a surface nucleation and step advancement mechanisms.In most experiments at fixed load, the film showed higher friction than the calcite surface, but the friction-load dependence for the different surfaces revealed that at low loads (0-40 nN), a calcian otavite film has lower friction than calcite; a result that is contrary to earlier LFM reports of the same system.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemistry, Wright State University, 3640 Col, Glenn Hwy, Dayton, Ohio 45435, USA. pablo.cubillas-gonzales@manchester.ac.uk

ABSTRACT
Lateral Force Microscopy (LFM) studies were carried out on cleaved calcite sections in contact with solutions supersaturated with respect to otavite (CdCO3) or calcite-otavite solid solutions (SS) as a means to examine the potential for future application of LFM as a nanometer-scale mineral surface composition mapping technique. Layer-by-layer growth of surface films took place either by step advancement or by a surface nucleation and step advancement mechanisms. Friction vs. applied load data acquired on the films and the calcite substrate were successfully fitted to the Johnson Kendall Roberts (JKR) model for single asperity contacts. Following this model, friction differences between film and substrate at low loads were dictated by differences in adhesion, whereas at higher load they reflect differences in contact shear strength. In most experiments at fixed load, the film showed higher friction than the calcite surface, but the friction-load dependence for the different surfaces revealed that at low loads (0-40 nN), a calcian otavite film has lower friction than calcite; a result that is contrary to earlier LFM reports of the same system. Multilayer films of calcian-otavite displayed increasing friction with film thickness, consistent with the expectation that the film surface composition will become increasingly Cd-rich with increasing thickness. Both load- and thickness-dependence trends support the hypothesis that the contact shear strength correlates with the hydration enthalpy of the surface ions, thereby imparting friction sensitivity in the LFM to mineral-water interface composition.

No MeSH data available.


Related in: MedlinePlus