Non Contact Atomic Force Microscopy

• Non-Contact Atomic Force Microscopy (NC-AFM) | Zurich Instruments
• Non contact atomic force microscopy applications

Laser beam deflection for atomic force microscopes Measuring Forces Because the Atomic Force Microscope relies on the forces between the tip and sample, these forces impact AFM imaging. The force is not measured directly, but calculated by measuring the deflection of the lever, knowing the stiffness of the cantilever. Hooke's law gives: F = -kz where F is the force, k is the stiffness of the lever, and z is the distance the lever is bent. Force-distance curve for Atomic Force Microscopes Feedback Loop for Atomic Force Microscopy Atomic Force Microscopy has a feedback loop using the laser deflection to control the force and tip position. As shown, a laser is reflected from the back of a cantilever that includes the AFM tip. As the tip interacts with the surface, the laser position on the photodetector is used in the feedback loop to track the surface for imaging and measuring. Schematic for contact mode Atomic Force Microscopy

Non-Contact Atomic Force Microscopy (NC-AFM) | Zurich Instruments

When normalized to a unit length, these forces are the interface tensions between the three phases (S/L/G). By projecting the equilibrium forces on the solid plane, one obtains the Young' relation. γ sl - γ s + γ lv θ = 0 or cos θ = (γ s - γ sl)/ γ lv It is evident that θ can be defined only if the spreading parameter is negative. θ increases when the liquid is non-wetting. 2) The second method relies on calculating the work done by moving the line of contact by a distance dx: dW = γ sl - γ s + γ lv θ At equilibrium, dW/dA = 0, which leads to the same equation as above. For information about measurement of contact angle, click here. (v) Contact angle hysteresis: advancing Vs receding contact angle Contact angle measured for a liquid advancing across a surface exceeds that of one receding from the surface. Contact angle is generally attributed to surface roughness, surface heterogeneity, solution impurities adsorbing on the surface, or swelling. Advancing contact angle (θ A < θ R) is always larger than or equal to the receding contact angle.

Non contact atomic force microscopy applications

Other Modes of Operation Apart from the scanning modes described, new ones have been developed that actually take advantage of and measure for example, frictional forces and the twist of the cantilever instead of its deflection (Lateral Force Microscopy). Other examples include the oscillation of the cantilever in a very high frequency compared to its resonant frequency (Force Modulation). The versatility of AFM operation makes it a great research tool and worthy competitor among other microscopy techniques. Samples of the AFM Imaging Sources:: Atomic Force Microscopy: The Common AFM Modes "Atomic Force Microscopy: A Guide to Understanding and Using the AFM", Galloway Group, 2004

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Unlike Scanning Tunneling Microscopes, the Atomic Force Microscope does not need a conducting sample. Instead of using the quantum mechanical effect of tunneling, atomic forces are used to map the tip-sample interaction. Often referred to as scanning probe microscopy (SPM), there are Atomic Force Microscopy techniques for almost any measurable force interaction – van der Waals, electrical, magnetic, thermal. For some of the more specialized techniques, modified tips and software adjustments are needed. In addition to Angstrom-level positioning and feedback loop control, there are 2 components typically included in Atomic Force Microscopy: Deflection and Force Measurement. AFM Probe Deflection Traditionally, most Atomic Force Microscopes use a laser beam deflection system where a laser is reflected from the back of the reflective AFM lever and onto a position-sensitive detector. AFM tips and cantilevers are typically micro-fabricated from Si or Si 3 N 4. Typical tip radius is from a few to 10s of nm.

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