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Modeling Thermal Interaction between Laser Light and AFM
A computational model for the thermal interaction between laser light and an atomic force microscope (AFM) cantilever.
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A computational model for the thermal interaction between laser light and an atomic force microscope (AFM) cantilever. Design parameters in our model include laser power, laser spot positions, as well as geometric and material properties of the AFM cantilever. In the area of nanotechnology, the laser beam deflection method has been widely used in AFMs in detecting the cantilever’s deflection and resonance frequency. The laser deflection method consists of reflecting a laser beam off of an AFM cantilever to a photo diode,which is converted to a voltage signal. Deflection of the cantilever results in a change laser reflection angle and a change in voltage signal. The mechanical properties of the cantilever affect the amount of deflection. Although much work has been done on increasing the sensitivity of the AFM, little work has been done on investigating the thermal effect of the laser-cantilever interaction. We find that a small change in the size of the AFM cantilever caused by thermal expansion from the laser is measureable. Our simulated results suggest that both the laser power and spot positions significantly change the resonant response of the cantilevers. AFM cantilevers are resonated during the tapping mode. In considering various laser powers, we observe that as we increase the power, the average temperature of the beam increases, which causes a decrease in resonance frequency. In considering various laser reflection spot positions, as the laser spot moves away from the clamped end of the cantilever, the dissipation to the substrate decreases, causing an increase in temperature but decrease in material softening. The results of our investigations suggest significant effects that are large enough to be measureable.
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