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Prototype SI-Traceable Reference Cantilevers for Calibrating AFM Cantilever Spring Constants Many researchers use atomic force microscopy (AFM) to measure forces responsible for adhesion, friction, and deformation at the nanoNewton scale. The combination of large variations in cantilever spring constant from manufacturing batches (sometimes as high at ±200 percent), coupled with the lack of accurate (SI-traceable) methods for calibrating individual cantilevers, limits the absolute accuracy of such research. The Ceramics Division, MSEL, has developed prototype reference cantilevers made from single crystal silicon that can be used to calibrate AFM cantilevers. Using e-beam lithography and a combination of microfabrication processes on silicon-on-insulator wafers, batches of extremely uniform cantilevers were created. Variations in cantilevers, measured using resonance frequency, were less than ± 1 percent (1 σ). Working with the Manufacturing Metrology Division, MEL, the spring constants of the cantilevers were measured (as low as 26 pN/nm) using an electrostatic force balance (EFB), which is traceable to the SI, with a standard uncertainty of ± 2 percent. The results confirm the feasibility of microfabricating a batch of uniform cantilevers, measuring the uniformity of the batch using resonance frequency, and calibrating the spring constant of a statistical subset using EFB. These results establish the basis for producing SI-traceable reference cantilevers that will be made available to the AFM community as an SRM to assist in calibrating test cantilevers to achieve accurate research measurements. For more information contact: Dr. Richard Gates.
Updated SRM for Quantitative Analysis by X-Ray Powder Diffraction NIST researchers in the MSEL Ceramics Division have established a new version of the x-ray powder diffraction intensity standard (SRM 674b) consisting of four oxide powders intended primarily for use as internal standards for quantitative x-ray diffraction analysis. The new version is certified with respect to amorphous content which permits absolute quantification of the unknowns. The powders are ZnO (wurtzite structure), TiO2 (rutile structure), Cr2O3 (corundum structure), and CeO2 (fluorite structure). These four oxides offer a range of linear attenuations for Cu-Kα radiation: 279 cm-1, 536 cm-1, 912 cm-1, and 2203 cm-1, respectively. This range allows the user to nominally match the attenuation of the standard to the attenuation of the unknown in order to minimize the effects of microabsorption. A unit of SRM 674b consists of approximately 10 g of each powder bottled in an argon atmosphere. SRM 674b may be ordered online from the NIST SRM Home Page. For further technical information contact: Dr. James Cline.
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