Micromechanical cantilevers

X.L. Su and Y.B. D, Micromechanical cantilever array sensors for selective fungal immobilization and fast growth detection. Biosens. Bioelectron. 21, 840-856 (2005). 

Sensors for measurements of physical parameters such as pressure, rotation or acceleration are commonly based on elongation or vibration of membranes, cantilevers or other proof masses. The electrochemical processes used to achieve these micromechanical structures are commonly etch-stop techniques, as discussed in Section 4.5, or sacrificial layer techniques, discussed in Section 10.7. 

Other valuable extensions of contact-mode SFM probe micromechanical properties of the sample. Variation of the repulsive force or upward deflection of the cantilever are registered while a Z-modulation is applied either to the sample or the cantilever base (Fig. 6). The dZ/dZc signal contains information about the local stiffness dF/d.8 of the sample, where S=Zt-Zc is the indentation depth. Micromechanical applications will be discussed in Sect. 2.2. 

When the experimentalist set an ambitious objective to evaluate micromechanical properties quantitatively, he will predictably encounter a few fundamental problems. At first, the continuum description which is usually used in contact mechanics might be not applicable for contact areas as small as 1 -10 nm [116,117]. Secondly, since most of the polymers demonstrate a combination of elastic and viscous behaviour, an appropriate model is required to derive the contact area and the stress field upon indentation a viscoelastic and adhesive sample [116,120]. In this case, the duration of the contact and the scanning rate are not unimportant parameters. Moreover, bending of the cantilever results in a complicated motion of the tip including compression, shear and friction effects [131,132]. Third, plastic or inelastic deformation has to be taken into account in data interpretation. Concerning experimental conditions, the most important is to perform a set of calibrations procedures which includes the (x,y,z) calibration of the piezoelectric transducers, the determination of the spring constants of the cantilever, and the evaluation of the tip shape. The experimentalist has to eliminate surface contamination s and be certain about the chemical composition of the tip and the sample. 

Bashir R, Hilt JZ, Elibol O, Gupta A, Peppas NA (2002) Micromechanical cantilever as an ultrasensitive pH microsensor. Appl Phys Lett 81(16) 3091-3093 Benoit D, Chaplinski V, Braslau R, Hawker CJ (1999) Development of a universal alkoxyamine for "living" free radical polymerizations. J Am Chem Soc 121 3904-3920 Caykara T, Kiper S, Demirel G (2006) Thermosensitive poly(N-isopropylacrylamide-co-acryl-amide) hydrogels synthesis, swelling and interaction with ionic surfactants. Eur Polymer J 42 348-355... 

The use of polymer-coated cantilevers such as microfabricated beams of silicon is becoming more popular as the basis of nanomechanical sensors [11]. These devices detect physical and chemical interactions between the reactive layer on the surface and the environment [8]. When the polymer interacts with a gaseous species, it swells and causes the cantilever to bend as a result of surface stresses when used in the static mode. In the dynamic mode, the cantilever acts as a microbalance, which responds to changes in resonance frequency. Savran s group at Purdue University has been researching the micromechanical detection of proteins by use of aptamer-based receptor molecules [12]. 

Bashir R, Hilt J, Elihol O, Gupta A, Peppas N (2002) Micromechanical cantilever as an ultrasensitive pH microsensor. Appl Phys Lett 81 3091... 

Pellejero I, Agustt J, Urbiztondo MA, Ses J, Pina MP, Santamarta J, Abadal G. Nanoporous silicalite-only cantilevers as micromechanical sensors Fabrication, resonance response and VOCs sensing performance. Sens Actuators B 2012 171-712 822-831. 

Surface stress can be measured by a number of experiments, including piezoelectric elements [145], ribbon electrodes [146], and more recently developed micromechanical sensors [147-149]. It can be also measured with AFM and STM, as demonstrated by several groups [150,151]. The AFM and STM-based surface stress measurements usually detect the bending of a thin plate (cantilever) as a result of a surface stress change at one of the two surfaces. If the plate is isotropic and freely standing, the change in the surface stress can be calculated from the amount of bending by [152]... 

Tsukruk and co-workers evaluated different classic models of elastic contacts, including Sneddon s, Hertz, and JKR model, to probe the micromechanical properties of elastic polymeric materials (253). A close agreement between absolute values of elastic moduli and bulk data has been observed. With typically available cantilevers with stiffnesses in the range of 0.1-50 N/m, materials moduli... 

Keywords Atomic force microscopy Evaporation law Microdrop evaporation Micromechanical cantilevers Surface tension Vaporization heat Young s equation... 

R. Bashir, J. Hilt, O. Elibol, A. Gupta, N. Peppas, Micromechanical cantilever as an ultrasensitive pH microsensor. Applied Physics Letters 81 (2002) 3091-3093. 

A. Boisen, S. Dohn, S.S. Keller, S. Schmid, M. Tenje, Cantilever-Eke micromechanical sensors. Reports on Progress in Physics 74 (2011) 036101. 

Scanning force microscopy (SFM) was used for probing micromechanical properties of polymeric materials. Classic models of elastic contacts, Sneddon s, Hertzian, and JKR, were tested for polyisoprene rubbers, polyurethanes, polystyrene, and polyvinylchloride. Applicability of commercial cantilevers is analyzed and presented as a convenient plot for quick evaluation of optimal spring constants. We demonstrate that both Sneddon s and Hertzian elastic models gave consistent and reliable results, which are close to JKR solution. For all polymeric materials studied, correlation is observed between absolute values of elastic moduli determined by SFM and measured for bulk materials. For rubber, we obtained similar elastic modulus from tensile and compression SFM measurements. 

Micromechanical resonator has emerged as a promising component for rapidly developing telecommunication systems. These resonators also have a wide range of sensing applications. High-frequency resonators can use capacitive or piezoelectric transduction. To understand the importance of miniaturization, let us consider a cantilever beam. The natural frequency of the beam is given by the relation ... 

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