Deflection detection device

Deflection detection devices. To measure the force between the tip and the sample the deflection of the cantilever must be determined. Normally, the silicon cantilevers need additional equipment for detecting the deflection of the cantilever. Several deflection detection devices have emerged over the two decades in the development of AFM. As an example, Fig. 7 shows two commonly used techniques for measuring the deflection of a silicon cantilever under different conditions. 

In the mass spectrometer the ions so produced are accelerated by an electric field, and the beam iS passed through a transverse magnetic field. The deflected beam is focused in such a way that ions of the same e/m ratio arrive together at the detecting device. 

Nakabeppu et al. [58] describe the use of composite cantilevers made from tin or gold deposited on conventional silicon nitride AFM probes to detect spatial variations in temperature across an indium/tin oxide heater. Differential thermal expansion of the bimetallic elements causes the beam to bend. This movement is monitored using the AFM optical lever deflection detection system. In order to separate thermal deflection of the beam from displacement of the cantilever caused by the sample topography, an intermittent contact mode of operation is employed. Measurements were made under vacuum so as to minimize heat loss. A more practical use of this technology is in the form of miniature chemical and thermal sensors [59]. This approach has been used to perform thermal analysis on picolitre volumes of materisd deposited on the end of a bimetallic cantilever [60]. Arrays of such devices have applications as highly sensitive electronic noses . 

FTC measurements were conducted 90 seconds after demoulding. The foam pad was removed from the mould, weighed and placed in the FTC apparatus (Instron 4502). The force detection device is equipped with a 5.0 kN capacity pressure transducer. The actual force is shown on a digital display. This device mimics the ASTM D3574, Indentation Force Deflection Test and provides a numerical value of freshly demoulded foams initial hardness or softness. The pad was compressed to 70 percent of its original thickness at a cross head velocity of 380 mm per minute with the force necessary to achieve the highest compression cycle recorded in Newtons. Values are reported as the FTC value for the foam based on the assumption that the lower the FTC values the better the dimensional stability of the foam. 

Fig. 6.9. Illustrating the principle of the alpha-particle deflection (scattering) experiments. Positively charged helium atoms are directed at a metal film, and its eWecf on the particles observed with detecting devices placed at various angles. The angle () is a measure of the deflection.

In the nanosecond (ns) time-scale the use of kinetic detection (one absorption or emission wavelength at all times) is much more convenient than spectrographic detection, but the opposite is true for ps flash photolysis because of the response time of electronic detectors. Luminescence kinetics can however be measured by means of a special device known as the streak camera (Figure 8.2). This is somewhat similar to the cathode ray tube of an oscilloscope, but the electron gun is replaced by a transparent photocathode. The electron beam emitted by this photocathode depends on the incident light intensity I(hv). It is accelerated and deflected by the plates d which provide the time-base. The electron beam falls on the phosphor screen where the trace appears like an oscillogram in one dimension, since there is no jy deflection. The thickness of the trace is the measurement of light intensity. 

The apparatuses described thus far were all designed to detect the ionic products from ion-neutral interactions, whereas the TOF apparatus described by Moran and co-workers9911,146,147 has been employed to detect the neutral products from these processes. In the latter device the ions formed by electron impact are accelerated out of the source by an extraction pulse and are further accelerated by a series of grids. The primary beam is then focused by deflection and enters the drift region or flight tube, where mass separation of the different velocity groups occurs. 

There exist a number of readout techniques based on optical beam deflection, variation in capacitance, piezoresistance, and piezoelectricity. Piezoelectricity is more suited for a detection method based on resonance frequency than the method based on cantilever bending. The capacitive method is not suitable for liquid-based applications. The piezoresistive readout has many advantages, and it is ideally suited for handheld devices. 

Much ingenuity has liocn cx H>nded in devices for detecting deflection or faults in gun-banels, and for straight< ning them when unevenncs.s is detected. 

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