Si3N4 pyramidal tips

Figure 3 shows an SEM micrograph of a typical SFM cantilever. The cantilevers are 100—200 pm long and 0.6 pm thick, microfabricated from low-stress Si3N4 with an integrated, pyramidal tip. Despite a minimal tip radius of about 400 A,... 

At present, all commercial SFM tips are square pyramids, formed by CVD deposition of Si3N4 on an etch pit in (100) Si. The etch pit is bounded by (111) faces, which means that the resulting tip has an included angle of about 55°. Therefore the edge profiles of all features with sides steeper than 55° will be dominated by the profile of the tip. 

SFM was performed on a Nanoscope IV Bioscope (Veeco). The microscope was vibration- and acoustic-damped (Brunhild II, Veeco). Commercially available pyramidal Si3N4 tips (Veeco) on a V-cantilever (length 125 pm) were used for the force measurements. For the force measurements with attached ECs, the tip was removed mechanically from the cantilever. The measurements were done in contact mode with PBS (pH 7.4) medium. The force constants of the cantilevers were determined according to Florin et al. [37] and were in the range... 

We used commercially available pyramidal Si3N4 tips (NCH-W, Digital Instruments, Santa Barbara, CA) in tapping mode with a scan frequency between... 

Using a sharp AFM tip that generates relatively large local pressures, AFM can be used to observe the adsorbed layer and study some of its properties. A typical force plot with a sharp pyramidal Si3N4 tip is shown in Fig. 3.4. At large separations there is no detectable force, whereas at a separation of 10-20 nm, a weak attractive force suddenly appears. Then, at a separation of several nm, the tip touches a relatively soft layer, that is elastically deformed by increasing the force load. At a certain force load, the layer cannot resist any more and ruptures. 

---