Possibility of nano-local element analysis by near-field laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS): New experimental arrangement and first application

A near-field laser ablation inductively coupled plasma mass spectrometric (NF-LA-ICP-MS) procedure was created for element analysis in the nm resolution range. The method utilizes a well-known near-field effect in order to enhance the incident light energy on the thin tip of a Ag needle during the laser ablation process. A robust needle etching procedure was developed to produce the thin needles with a tip diameter in the range of hundreds of nm. An experimental arrangement was constructed to control the “sample-to-tip” distance via the measurements of tunnel current between the needle and sample surface. The NF-LA-ICP-MS technique thus developed was applied to analyze thin Au films deposited onto a Si substrate. The observed craters ranged from 500 nm to about 1 μm in diameter and were dependent on the needle used as well as on the “sample-to-tip” distance. These results were also confirmed by mass spectrometric measurements of the Au sample. Theoretical calculations performed showed that using the developed NF-LA-ICP-MS arrangement a detection efficiency of 2.7 × 10−5 cps per ablated Au atom can be achieved.