Torsional Ressonance Tunneling (TR TUNA) AN107

® The implementation of a torsional drive TUNA can be applied to many research cycle in a regime having no near-fi eld system for use with AFMs from Veeco or manufacturing areas on a wide interaction with the surface, fi gure 2. Instruments is a simple modifi cation range of materials. However, the use of This is advantageous for eliminating to the cantilever holder found on all Contact Mode for topographic feedback tip wear and sample damage, but is ® Tapping Modeis a limiting factor. For samples that problematic for the measurement of enabled AFMs. The require low imaging forces, in either or properties that demand near-fi eld holder employs two parallel actuators, ® both the vertical or lateral directions, interactions - such as TUNA marked as piezos 1 and 2 in fi gure 3. . Contact Mode may not be applicable. It To excite the torsional resonance, drive It is known however, that AFM ® is therefore diffi cult to extend TUNA signals of opposite phase are applied to cantilevers can oscillate at many imaging to the study conductive 1-10 these two piezos. Due to the asymmetry different modes , including higher polymers, organics or other soft of the tip mass about the rotation axis order fl exural and torsional or twisting conducting materials or loosely bound this actuation will create a rotation of modes. These extended modes enable samples such as nanowires. the cantilever substrate about its center the study of widely differing tip-surface point. Since the tip is far away from interactions. Consider the case of TORSIONAL RESONANCE MODE the center, the trajectory of the tip is imaging with the cantilever oscillating Atomic force microscopy has achieved almost horizontal. As with conventional in the fi rst torsional resonance mode.tremendous benefi ts from a variety of ® Tapping Modeoscillating tip modes of operation, most the torsional cantilever In this mode, lateral forces that act on ® notably Tapping Mode defl ection is detected using a four-. During Tapping the tip cause a change in the torsional ® segment photodetector.Mode the AFM cantilever is oscillated resonant frequency, amplitude, and/ at its fundamental fl exural resonance. 11 or phase of the cantilever AFM uses the angular displacement of . AFM This has the advantage of largely the cantilever and the resulting change measurements at torsional resonances eliminating lateral forces that tend to in the refl ected laser beam angle at the have many advantages but the key damage the tip and/or sample when ® advantage for TUNA is the ability to imaging in contact mode. The vertical achieve low-force scanning whilst interaction force is also substantially maintaining the tip in the near-fi eld. reduced due to high mechanical Q of the cantilever, permitting imaging of With the ability to maintain the probe delicate soft samples. tip in the near-fi eld (at the boundary between direct contact and the long-® When imaging in Tapping Mode , the range force regime), we are once again AFM tip position varies relative to the