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,... 

Atomic force microscopy (AFM) is a variant of STM and was introduced in 1986 by Binnig et al. (11). AFM belongs to a family of near-field microscopies and is capable of imaging a wide variety of specimens surface down to an atomic scale. The technique employs a probe (pyramidal tip) mounted at the end of a sensitive but rigid cantilever (see Fig. 2). The probe is drawn across the specimen under very light mechanical loading (1). Measurements of the probe s interaction with the sample s surface are accomplished with a laser beam reflected from the cantilever. 

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Current instruments differ little, in principle, front the first AFM developed over I0 years ago. The biggest changes have come in the methods used to detect the deflection of the cantilever spring, as mentioned above, and the development of microfabricated silicon nitride cantilevers with integrated pyramidal tips. 

Several chip-shaped LEDs have been commercialized including the pedestalshaped chip shown in Figs. 1.16(a) and (b) and the truncated inverted pyramid (TIP) chip shown in Figs. 1.16(c) and (d) [52], The ray traces indicated in the fig-... 

Fig. 1.16 Die-shaped devices (a) Blue GalnN emitter on SiC substrate with trade name Aton . (b) Schematic ray traces illustrating enhanced light extraction, (c) Micrograph of truncated inverted pyramid (TIP) AIGalnP/GaP LED. (d) Schematic diagram illustrating enhanced extraction (after Osram, 2001 ref. [52]).

Figure 1. Height (top) and Amplitude (bottom) TMAFM images of HPY (needles) formed upon reaction of [Pbaq]i = 100 mg L with HAP. Pc membrane appears in lower right-hand corner. Triangular pyramidal tip-sample interaction artifacts can be seen just to left of center. Maximum z-range (white to black) on Height image = 500 nm. Both images 2.3 pm on a side. Scales in pm.

The aspect ratio (or cone angle) of a particular tip is crucial when imaging steep sloped features. Electron-beam-deposited tips have been used to image steep-walled features far more faithfully than can be achieved with the common pyramidal tips. 

AFM has become the method of choice for measuring cellular elasticity. Harris and Charras et al. [8] have shown that in AFM elasticity measurements, experimental force-indentation curves are analyzed using contact mechanics models that infer the tip-cell contact area from the tip geometry and indentation depth. However, values of cellular elasticity reported in AFM measurements are large compared to those reported by other methods, and measurements affected using spherical tips give significantly lower elasticity than pyramidal tips [8]. 

ATM imaging in the contact mode and in the friction mode was done with a Nanoscope 111 A from Digital Instruments (Santa Barbara, USA) using a 100 xm piezoelectric scanner. The cantilevers used were characterized by a spring constant of 0.16Nm". A standard pyramidal tip of silicon nitride was used. The measurements were carried out in air and at a constant force in the 10 to 10 N range. 

Dendritic growth occurs at screw dislocations. Sword-like dendrites with pyramidal tips are formed by this process [3, 16],... 

Fig. 6.13 A broad tip in a STM (A) may change the position where the localized current flows as it moves across a rough surface. The result is to smooth out the apparent surface. A sharp pyramidal tip (B) follows the surface much more accurately. (From Nishikawa et al [137] reproduced with permission.)...

Figure 7.5. Diagrams illustrating effects of shape of probe tip on spatial resolution (a) Wollaston wire (b) low-aspect-ratio pyramidal tip (c) high-aspect-ratio pyramidal tip.

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