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In order to learn about in situ structural changes in materials at subseconds time scale, we have further refined the techniques of quick extended x-ray absorption fine structure (QEXAFS) and quick x-ray absorption near edge structure (XANES) spectroscopies at beamline X18B at the National Synchrotron Light Source. The channel cut Si (111) monochromator oscillation is driven through a tangential arm at 5 Hz, using a cam, dc motor, pulley, and belt system. The rubber belt between the motor and the cam damps the mechanical noise. EXAFS scan taken in 100 ms is comparable to standard data. The angle and the angular range of the monochromator can be changed to collect a full EXAFS or XANES spectrum in the energy range 4.7-40.0 KeV. The data are recorded in ascending and descending order of energy, on the fly, without any loss of beam time. The QEXAFS mechanical system is outside the vacuum system, and therefore changing the mode of operation from conventional to QEXAFS takes only a few minutes. This instrument allows the acquisition of time resolved data in a variety of systems relevant to electrochemical, photochemical, catalytic, materials, and environmental sciences.

We investigated the alomic-scale stick-slip motion between MJSCOVke mica and the Si3Nd tip apex of a cantilever using an atomic-force mkroscope combined with a lateral-force m:croscope (AFMILFM). As a resuit, we found a square-wave behavior d the cantilever maion across the scan direction, in addtion io the well known sawtooth behavior along the scan 0irect:on. We also founo that the square-wave behavior was synchronized with the sawtooth behavior. To explain these phenomena, we proposed the two-d:mensional stick-slip model, where the stick-points have the same p%r:odicity as the lattice structure of the mica surface, so that the tip shows a zigzag walk along the scan. This new model seems to explain not only the one-dimensional line-scan profile, bLt also the contrast mechanism of the two-dimensional image.

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A mode-locked laser is employed as the light source of a laser autocollimator, instead of the conventionally employed single-wavelength laser, for an expanded range of tilt angle measurement. A group of the spatially separated diffracted beams from a diffraction grating are focused by a collimator objective to form an array of light spots on the focal plane of the collimator objective where a light position-sensing photodiode is located for detecting the linear displacement of the light spot array corresponding to the tilt angle of the reflector. A prototype mode-locked femtosecond laser autocollimator is designed and constructed for achieving a measurement range of 11000 arc-seconds.

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