To investigate nanoscale mechanical behavior, new approaches using dynamic modes of the atomic force microscope cantilever are being developed. One method, atomic force acoustic microscopy (AFAM), measures cantilever resonances in the acoustic frequency range to obtain elastic-property information. We describe quantitative AFAM measurements and compare them to results from techniques like surface acoustic waves and instrumented indentation. With AFAM we examined a niobium film using two separate calibration samples and two cantilever geometries. Depending on the cantilever type we found M=105-114 GPa, in good agreement with literature values of M=116-133 GPa for bulk niobium and M=120 GPa obtained with surface acoustic waves. We also obtained AFAM values of M=54-81 GPa for the indentation modulus of an aluminum film. In comparison, literature values for bulk aluminum are M=76-81 GPa, while other results on the same film yielded M=78-85 GPa. To understand the results more thoroughly, we compare two methods of AFAM spectrum analysis. The analytical approach assumes a cantilever of uniform rectangular cross-section while the finite-element model accounts for spatial variations in cantilever dimensions. The same data are interpreted with the two approaches to better understand measurement uncertainty and accuracy.
The remarkable sensitivity of depleted silicon to ionizing radiation is a nuisance to astronomers. 'Cosmic rays' degrade images because of struck pixels, leading to modified observing strategies and the development of algorithms to remove the unwanted artifacts. In the new-generation CCD's with thick sensitive regions, cosmic-ray muons make recognizable straight tracks and there is enhanced sensitivity to ambient gamma radiation via Compton-scattered electrons ('worms'). Beta emitters inside the dewar, for example high-potassium glasses such as BK7 , also produce worm-like tracks. The cosmic-ray muon rate is irreducible and increases with altitude. The gamma rays are mostly by- products of <SUP>40</SUP>K decay and the U and Th decay chains; these elements commonly appear as traces in concrete and other materials. The Compton recoil event rate can be reduced significantly by the choice of materials in the environment and dewar and by careful shielding. Telescope domes appear to have significantly lower rates than basement laboratories and Coude spectrograph rooms. Radiation sources inside the dewar can be eliminated by judicious choice of materials. Cosmogenic activation during high-altitude fights does not appear to be a problem. Our conclusion are supported by tests at the Lawrence Berkeley National Laboratory low-level counting facilities in Berkeley and at Oroville, California (180 m underground).
Conference Committee Involvement (4)
Testing, Reliability, and Application of Micro- and Nano-Material Systems IV
1 March 2006 | San Diego, CA, United States
Testing, Reliability, and Application of Micro- and Nano-Material Systems III
9 March 2005 | San Diego, CA, United States
Testing, Reliability, and Application of Micro-and Nano-Material Systems II
15 March 2004 | San Diego, CA, United States
Testing, Reliability, and Application of Micro- and Nano-Material Systems
3 March 2003 | San Diego, California, United States