铜合金表面元素的飞行时间二次离子质谱微区原位分析

Copper Alloy Surface Elements in situ Analysis Using Time of Flight Secondary Ion Mass Spectrometry

铜合金中含有Pb、Sn、Zn、Ni等元素,其分布和相对含量对铜合金的性能具有重要影响。本工作采用飞行时间二次离子质谱(TOF-SIMS)法对铜合金标准样品GBW02137和GBW02140的表面进行了微区原位分析;采用束斑直径约5μm的一次离子束轰击500μm×500μm区域内的混合固体合金样品,实现了Cu、Pb、Ni、Sn和Zn元素的表面成像,并测量了各元素在铜合金样品表面的分布情况;利用标样校准法对GBW02137、GBW02140中的^(64)Zn/^(120)Sn、^(208)Pb/^(120)Sn值进行相对含量分析。实验结果表明:TOF-SIMS法可用于铜合金中Cu、Pb、Ni、Sn和Zn等元素的表面成像和相对含量测定;采用标样校准法进行相对含量分析时,测得的^(64)Zn/^(120)Sn相对误差小于5.1%,RSD优于2.5%,^(208)Pb/^(120)Sn的测量相对误差较大,接近27%,但其RSD仍低于5%。

Copper alloy contains Pb, Sn, Zn, Ni and other elements, whose distribution and concentration on the surface have important influence on its behavior. As an ad vanced method for surface analysis of solid samples, time of flight mass spectrometry （TOF-SIMS） has remarkable characteristics of high spatial and mass resolution, and high sensitivity in elemental and isotopic measurements over a wide mass range. In situ analysis of copper alloy surface elements of GBW02137 and GBW02140 samples was im- plemented by TOF-SIMS, including surface elemental mapping and relative concentra- tion measurement. A pulsed primary ion beam with 5 μm spot size and 30 keV energy was used to bombard the mixed solid alloy samples within a 500μm×500μm region, so as to provide complete surface elemental mapping of Cu, Pb, Ni, Sn and Zn elements on copper alloy surface. After being fixed by epoxy resin, the samples were polished and gilded on its surface in order to achieve a surface roughness smaller than 1 μm. After being extracted and focused, the secondary ions got into the time of flight mass analyzer and were recorded by the detector to form spectral peaks. In order to reduce influence of target surface charge accumulation on the secondary ion extraction field, an electron gun was used to inject electrons towards the target surface to achieve the purpose of charge neutralization. While mapping the elements, a color bar was used to indicate individual content. A deeper color showed a smaller content, and vice versa. Finally, by standard sample calibration method, the calibration curve was established, and the relative con- centrations of ^64Zn/^120Sn and ^208pb/^120Sn in GBW02137 and GBW02140 were measured. Considering the difficulty in direct measurement of content by TOF-SIMS because of matrix effect and mass fraetionation, calibration of instrument error was needed by using standard samples. Obvious difference of element content exists in the crack and on the alloy surface spot, especially enrichment for Pb element than others. By the stand- ard sample calibration method to measure the content, for ^64Zn/^120 Sn, a result of rela- tive error value less than 5.1% and RSD better than 2.5% is achieved; For ^208pb/^120Sn, although relative error is nearly 27%, a result of RSD better than 5~ is also achieved. The reason why relative error of ^208Pb/^120 Sn is obviously greater is that there exist incomplete calibration curve and ion productive rate difference between Sn and Pb elements. If a precision, complete calibration curve is established, the accuracy of meas- urement will be improved accordingly.