Sub-micrometer-scale chemical analysis by nanosecond-laser-induced tip-enhanced ablation and ionization time-of-flight mass spectrometry

The tip-enhanced near-field technique has drawn great attention recently because it is a promising technique for nanoscale chemical analysis when combined with other spectroscopic methods. Furthermore, this integration can improve the spatial resolution of mass spectrometry. In this study, a nanosecond-laser (ns-laser)-induced tip-enhanced ablation and ionization source was coupled to an in-house-built laser ionization time-of-flight mass spectrometer. Sub-micrometer-sized craters (with diameters of 200–300 nm) were observed on titanium (Ti) film coated onto a gold (Au) substrate. The corresponding mass spectra were acquired, which verified that sub-micrometer-sized ablation (and subsequently ionization) could be achieved by the ns-laser-induced tip-enhanced electromagnetic field. In addition, formation of the crater was studied with an increased number of laser pulses. Furthermore, a mass spectrometry imaging (MSI) experiment was performed with potassium chloride (KCl) residue dropped onto nano-patterned gold pillars, achieving 80-nm lateral resolution.