Laser-beam deflection signal

Figure 5. Relative amplitude at 1 MHz of laser beam deflection signal as a function of Al film thickness for a series of Al-on-Si and Al-on-Si02-on-Si films. Circles are experimental data, and curves are from the extended Opsal-Rosencwaig model.

Instrumentation. A cantilever with a sharp tip interacting with the surface under investigation is used. The actual bending of the cantilever is measured with a laser beam deflected from a mirror-like surface spot on the back of the cantilever towards a position-sensitive photodetector. The measured signal is used to control the piezo actuators. A constant force mode in which the cantilever-surface distance is kept at a preset interaction force and a constant height mode of scanning operation are possible. The principle of operation is schematically outlined in Fig. 7.9. 

In the EBES electron beam mask-maker, the beam is electronically scanned in one direction only, and the sample continuously moved in the other direction (55). Chips are written strip by strip, the same strip on every chip being written before proceeding to the next strip. The position of the beam is checked initially with a direct beam to sample measurement, but after this a laser interferometer keeps track of the sample. Errors in position are corrected by feeding signals to the electron beam deflection coils. 

Atomic force microscopes have been built in many different versions, with at least six different ways of measuring the deflection of the cantilever [36, 37, 40-42], The commercially available AFM systems use the double photo detector system shown in Figure 7.17 and described by Meyer and Amer [44], Here, a lens focuses a laser beam on the end of the cantilever, which reflects the beam onto two photo detectors which measure intensities T and f2. When the cantilever bends towards the surface, detector 2 receives more light and the difference (h — h) becomes larger. If the tip is scanned over the sample by means of the x- and y-components of the piezo crystal, the difference signal (T — h)/(h + h)... 

Chronodeflectogram — A deflection signal where the deviation angle (6) of a probe laser beam is plotted as a function of time. It is also called chronodeflectomet-ric profile or PBD transient and is usually characterized by the presence of the - PBD maximum (or minimum) during the time evolution of the deflection signal [i]. See also - chronodeflectometry. 

There is a convention used to describe the refraction of a probe laser beam that considers the deflection as negative if the beam deviates towards the electrode surface and positive when the opposite deviation occurs. The former corresponds to the generation (or releasing) of soluble species, while the latter is related to the consumption (or inclusion) of reactants during the electrochemical experiment. The deflection signal has the same sign than the refractive index gradient developed from the electrode surface to the solution [iv]. 

Fig. 3.52 A centrifugal-force viscometer. The —50 xm diameter nickel ball is driven along the horizontal diamond surface by centrifugal force. The rotation of a mirror on the shaft of the rotor deflects a laser beam across a detector to produce a signal whose frequency gives the speed of the rotor. Our current centrifuge is able to generate an acceleration of 17000 m s (Reprinted with permission from J. Phys. Chem. 1993, 97, 2355. Copyright 1993. American Chemical Society.

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