High Lateral Resolution Auger Electron Spectroscopic (AES) Measurements for Sn Whiskers on Brass

We report high lateral resolution Auger electron spectroscopic (AES) measurements on high aspect ratio Sn whiskers. The whiskers were grown from compressively stressed thin films (~ 6000 Å) of Sn on brass using a magnetron sputtering system. The Auger spectra show that, after sputter cleaning, the whisker is nearly 100% Sn at all locations along the whisker shaft, at the growing blunt end of the shaft, and with depth (~ 1000 Å) into the side of the whisker. The “as received” Sn whisker surface shows the expected ~ 200 Å of native Sn oxide at all locations and the O signal nearly disappeared (~ 3 atom%) after 200 Å of sputter cleaning. There was no evidence of high amounts of oxygen within the bulk of the whisker. That brass is not observed in the whisker shaft supports the notion that whisker formation is accompanied by material mass transport through interfaces and grain boundaries which causes stress (usually compressive) relief. This is supported by the most remarkable aspect of the whisker growth; namely, that high aspect ratio Sn whiskers ~ 100-500 μm in length containing no brass can be grown from a ~ 0.6 μm thin film of Sn.