UV laser-induced desorption mechanism analyzed through two-layer alkali halide samples.
Time of flight-mass spectrometry (TOF-MS) is used to analyze positive and negative desorbed ions generated by UV laser ablation of several alkali (X) halide (Y) salts. Most of the observed desorbed cluster ions have the structure (XY)(n)X(+) or (XY)(n)Y(-). Their desorption yields decrease as exp(-kn), where k approximately 2 for both series, suggesting that the neutral component (XY)(n) plays the dominant role in the desorption process. Mass spectrum measurements were performed for compound samples in which two salts (out of CsI, RbI, KBr, KCl and KI) are homogeneously mixed or disposed in two superposed layers. The detection of small new ion species and large cluster ions of the original salts supports the scenario that the uppermost layers are completely atomized while deep layers are emitted colder and fragmented: It is proposed that ns-pulsed laser induced desorption of ionic salts occurs via two sequential mechanisms: (1) ejection of cations and anions in the hot plume, followed by recombination into new cluster ions and (2) ejection of relatively cold preformed species originated from deep layers or from periphery of the irradiated region.
Fernández-Lima
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FA
Instituto Superior de Tecnologias y Ciencias Aplicadas, Havana, Cuba.
Ponciano
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CR
da Silveira
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EF