Figure 17.1: Evolution from MEMS to NEMS to molecular structures. Nanostructures may have a total mass of only a few femtograms. In the nanomechanical regime, it is possible to attain extremely high fundamental frequencies approaching those of vibrational molecular modes.

Figure 17.2: Different transduction mechanisms for a cantilever that can provide conversion of input stimuli into output signals. Depending on the measured parameter – structural deformations or resonance frequency changes - the mode of sensor operation can be refereed to as either static or resonant. Each of these modes, in turn, can be associated with different input stimuli and transduction scenarios.

Figure 17.3: Schematic depiction of chemisorption of straight-chain thiol molecules on a gold coated cantilever. Spontaneous adsorption processes are driven by an excess of the interfacial free energy, and accompanied by reduction of the interfacial stress.

Figure 17.4: Schematic depiction of the case for analyte-induced stresses when the cantilever surface is modified with a much than a monolayer analyte-permeable coating. Interactions of the analyte molecules with the bulk of the responsive phase lead to coating swelling and can be quantified using approaches employed in colloidal and polymer Science.

Figure 17.5: Schematic depiction of the case for structured phases (molecular sponges). Analyte-induced deflections of cantilevers with structured phases combine mechanisms of bulk, surface, and inter-surface interactions.

Figure 17.6: Examples of typical triangular cantilevers used as standard AFM probes.

Figure 17.7: Illustration of the steps in a process flow used for fabrication of silicon nitride membranes, bridges and cantilevers. The process begins with deposition of a structural silicon nitride layer on a single-crystal silicon wafer. The cantilever shapes can be defined by patterning the silicon nitride film on the top surface using photolithography followed by reactive ion etching (RIE).

Figure 17.8: Optical lever readout commonly used to measure deflections of microfabricated cantilever probes in AFM.

Figure 17.9: Ultrasensitive cantilevers for magnetic resonance microscopy. The cantilevers are about 200 microns long and 65 nm thick. Interferometric readout was used to measure their deflections. At liquid helium temperatures, these cantilevers permitted detection of forces as small as 3 attonewtons (3 x N) in a 1 Hz bandwidth. (Reproduced with kind permission of T. Kenny and T. Stowe.)

Figure 17.10: The “quantum bell” fabricated and studied by Blick et al. This NEMS operates at about 30 MHz and provides signal transduction in the electron shuttle regime. (From Ref. [60] by permission of Elsevier Science.)