We demonstrate depth profiling of polymer materials by using large argon (Ar) cluster ion beams. In general, depth profiling with secondary ion mass spectrometry (SIMS) presents serious problems in organic materials, because the primary keV atomic ion beams often damage them and the molecular ion yields decrease with increasing incident ion fluence. Recently, we have found reduced damage of organic materials during sputtering with large gas cluster ions, and reported on the unique secondary ion emission of organic materials. Secondary ions from the polymer films were measured with a linear type time-of-flight (TOF) technique; the films were also etched with large Ar cluster ion beams. The mean cluster size of the primary ion beams was Ar(700) and incident energy was 5.5 keV. Although the primary ion fluence exceeded the static SIMS limit, the molecular ion intensities from the polymer films remained constant, indicating that irradiation with large Ar cluster ion beams rarely leads to damage accumulation on the surface of the films, and this characteristic is excellently suitable for SIMS depth profiling of organic materials.

Cluster ion beams have revolutionized the analysis of organic surfaces in time-of-flight secondary ion mass spectrometry and opened up new capabilities for organic depth profiling. Much effort has been devoted to understanding the capabilities and improving the performance of SF(5)(+) and C(60)(n+), which are successful for many, but not all, organic materials. Here, we explore the potential of organic depth profiling using novel argon cluster ions, Ar(500)(+) to Ar(1000)(+). We present results for an organic delta layer reference sample, consisting of ultrathin "delta" layers of Irganox 3114 (approximately 2.4 nm) embedded between thick layers of Irganox 1010 (approximately 46 or 91 nm). This indicates that, for the reference material, major benefits can be obtained with Ar cluster ions, including a constant high sputtering yield throughout a depth of approximately 390 nm, and an extremely low sputter-induced roughness of <5 nm. Although the depth resolution is currently limited by an instrumental artifact, and may not be the best attainable, these initial results strongly indicate the potential to achieve high depth resolution and suggest that Ar cluster ions may have a major role to play in the depth profiling of organic materials.

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In this study, we present molecular depth profiling of multilayer structures composed of organic semiconductor materials such as tris(8-hydroxyquinoline)aluminum (Alq3) and 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPD). Molecular ions produced from Alq3 and NPD were measured by linear-type time-of-flight (TOF) mass spectrometry under 5.5 keV Ar70) ion bombardment. The organic multilayer films were analyzed and etched with large Ar cluster ion beams, and the interfaces between the organic layers were clearly distinguished. The effect of temperature on the diffusion of these materials was also investigated by the depth profiling analysis with Ar cluster ion beams. The thermal diffusion behavior was found to depend on the specific materials, and the diffusion of Alq3 molecules was observed to start at a lower temperature than that of NPD molecules. These results prove the great potential of large gas cluster ion beams for molecular depth profiling of organic multilayer samples.

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This is the first description of the production of a stable vacuum electrospray of volatile liquids such as water. This vacuum electrospray technique can be expected to produce a novel high-brightness large cluster ion beam source.

To perform remote and direct sampling for mass spectrometry, solid probe assisted nanoelectrospray ionization (SPA-nanoESI) has been newly developed. After capturing the sample on the tip of the needle by sticking it to the biological tissue, the needle was inserted into the solvent-preloaded nanoESI capillary from the backside. NanoESI gave abundant ion signals for human kidney tissues and the liver of a living mouse. The method is easy to operate and versatile because any biological specimen could be sampled away from the mass spectrometer. Minimal invasiveness is another merit of this method.