Laser beam deflection method

J.Y. (2005) An investigation of intercalation-induced stresses generated during lithium transport through sol-gel derived LixMn204 film electrode using a laser beam deflection method. Electrochim. Acta, 51 (3), 441-449. 

Fig. 5. a Schematic representation of the SFM set-up using the optical beam deflection method, b When the tip interacts with the sample surface, the cantilever exhibits deflection perpendicular to the surface as well as torsion parallel to the surface plane. The normal force Fn and the lateral force FL corresponds to the force components which cause the deflection and torsion, respectively. Both responses are monitored simultaneously by the laser beam which is focused on the back side of the cantilever and reflected into a four-quadrant position sensitive detector (PSD)... 

Bending beam method — The principles of the bending beam ( bending cantilever , laser beam deflection wafer curvature ) method were first stated by Stoney [i], who derived an equation relating the stress in the film to the radius of curvature of the beam. The bending beam method can be effectively used in electrochemical experiments, since the changes of the surface stress... 

We have developed a laser beam deflection technique which, although similar to the method employed by Amer s group, differs in several important respects. U4-15) In particular, our method employs highly focused heating and probe laser beams, both incident normal to the sample surface, and the experiments are performed at high modulation frequencies of up to 10 MHz. 

Shock tube studies of the decomposition of Oj have revealed the presence of an incubation period which precedes the observation of a steady rate of dissociation [11, 13, 58]. The length of the incubation period at a particular temperature was related to the vibrational relaxation time for oxygen at that temperature using previously measured relaxation data [59, 60]. The decomposition has been observed in a variety of inert diluents (He, Ar, Kr and Xe) in a wide range of oxygen concentrations (1—50%) over an extensive temperature range (2850—8500°K) by several different analytical methods including ARAS [13] and the laser-beam deflection technique [11]. 

Laser beam deflection offers a convenient and sensitive method of measuring cantilever deflection. In the non-contact mode, the AFM derives topographic images from measurements of attractive forces the tip does not touch the sample. On the other hand, in the contact mode, repulsion forces between the tip and the sample produce topographic images. 

Instrumentation. Commercial atomic force microscopes Explorer from Topometrix Inc., Nanoscope Illa Digital Instruments Co. Ltd.) which are based on the laser beam deflection detection scheme were used in conjunction with digital oscilloscopes of very stable low frequency (1-20 Hz) trigger system for lateral force (friction) measurements, and dual-phase lock-in amplifiers and function generators for force modulation measurements. Various triangular silicon nitride cantilevers were used. The lateral spring constants were determined with the "blind torsional calibration method discussed in more detail in the Appendix. 

Bulk analytical methods, including laser beam deflection and X-ray or neutron diffraction techniques, have been used to measure lattice strains and stresses. These methods, however, are limited to measuring lattice volume expansion due to li-ion intercalation on the molecular scale. They cannot detect extended defects, cracks, or microfractures, and thus cannot be directly used for mechanics analysis of particles or porous particle networks. Even with this limitation, diffraction or deflection techniques can stiU provide valuable information on lattice structural... 

Detection of cantilever displacement is another important issue in force microscope design. The first AFM instrument used an STM to monitor the movement of the cantilever—an extremely sensitive method. STM detection suffers from the disadvantage, however, that tip or cantilever contamination can affect the instrument s sensitivity, and that the topography of the cantilever may be incorporated into the data. The most coimnon methods in use today are optical, and are based either on the deflection of a laser beam [80], which has been bounced off the rear of the cantilever onto a position-sensitive detector (figme B 1.19.18), or on an interferometric principle [81]. 

For SFM, maintaining a constant separation between the tip and the sample means that the deflection of the cantilever must be measured accurately. The first SFM used an STM tip to tunnel to the back of the cantilever to measure its vertical deflection. However, this technique was sensitive to contaminants on the cantilever." Optical methods proved more reliable. The most common method for monitoring the defection is with an optical-lever or beam-bounce detection system. In this scheme, light from a laser diode is reflected from the back of the cantilever into a position-sensitive photodiode. A given cantilever deflection will then correspond to a specific position of the laser beam on the position-sensitive photodiode. Because the position-sensitive photodiode is very sensitive (about 0.1 A), the vertical resolution of SFM is sub-A. 

This temperature rise can be detected directly (laser calorimetry and optical calorimetry), or indirectly by measuring the change in either the refractive index (thermal lensing, beam deflection or refraction and thermal grating) or the volume (photo- or optoacoustic methods). This review will focus primarily on photoacoustic methods because they have been the most widely used to obtain thermodynamic and kinetic information about reactive intermediates. Other calorimetric methods are discussed in more detail in a recent review.7... 

Another method, based on an old idea about radiation pressure, uses the local separation of different isotopes in atomic or molecular beams. If the laser beam which crosses the molecular beam at right angles is tuned to an absorption line of a defined isotope in a molecular beam containing an isotopic mixture, the recoil from the absorption of the laser photons results in a small additional transverse velocity component. This leads to a beam deflection for the absorbing molecules which enables the desired isotope to be collected in a separate collector 154g)... 

Many factors and considerations are germane to future research in this area. On the technical side, achieving cluster size selection stands as one of the most important and sought-after goals. It would be most desirable to achieve this while maintaining sufficiently high densities for studies of photoinitiated reactions to be carried out with product state resolution and/or ultrafast time resolution. The two methods that, in our opinion, are most viable are molecular beam deflection, as pioneered by Buck (1994) and coworkers, and laser-based double-resonance methods. Less direct approaches are deemed inferior. 

The relatively novel method of atomic force microscopy can be used both ex situ and in situ for the study of the surface morphology of electrodes. It is based on a thin and sensitive cantilever to which a sharp microscopic tip is attached. The tip is raster-scanned along the studied surface, changing its deflection as a result of topographic changes. The deflection is measured by a laser beam which is reflected from the back of the cantilever to a detector that measures the position... 

Where R is the reflectivity and d is the thickness. Very accurate values of R and T are needed when the absorptance, (id, is small. The technique of photothermal deflection spectroscopy (PDS) overcomes this problem by measuring the heat absorbed in the film, which is proportional to ad when ad 1. A laser beam passing just above the surface is deflected by the thermal change in refractive index of a liquid in which the sample is immersed. Another sensitive measurement of ad is from the speetral dependence of the photoconductivity. The constant photocurrent method (CPM) uses a background illumination to ensure that the recombination lifetime does not depend on the photon energy and intensity of the illumination. Both techniques are capable of measuring ad down to values of about 10 and provide a very sensitive measure of the absorption coefficient of thin films. 

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