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9th World Congress on Spectroscopy & Analytical Techniques

Paris, France

Purushottam Chakraborty

Purushottam Chakraborty

Saha Institute of Nuclear Physics, India

Title: Alkali - containing molecular-ion secondary ion mass spectrometry for complete compensation of matrix effect


Biography: Purushottam Chakraborty


If alkali metals such as Li, Rb, K, Na, etc. (referred to as A in general) are present in the neighborhood of the probing element (M) on a sample surface, quasi-molecular ions can be formed by the attachment of these alkali ions [(MA)+ formation] in the secondary ion mass spectrometry (SIMS) process. Formation of these MA+ molecular ions has a strong correlation to the atomic polarizability of the element M. The emission process for the re-sputtered species M0 is decoupled from the MA+ ion formation process, in analogy with the ion formation in secondary neutral mass spectrometry (SNMS), resulting in a drastic decrease in the conventional ‘matrix effect’ in secondary ion mass spectrometry (SIMS). Although the detection of MA+ molecular ions in SIMS has found its applicability in direct materials quantification, it generally suffers from a low useful yield. In such cases, detection of (MA)n + [n=2, 3……] molecular ions offers a better sensitivity (even by several orders of magnitude), as the yields of such molecular-ion complexes have often been found to be much higher than that of MA+ ions. The recombination coefficient of MA+ or MA2+ molecular species depends on the electro-positivity or electro-negativity of the element M, respectively. Apart from the surface binding energy of the respective uppermost monolayer, the changes in local surface work-function have often been found to play a significant role in the emission of these molecular ions. Although these MAn+  molecular-ion based SIMS has great relevance in the analysis of materials, a complete understanding on the formation mechanisms of these ion-complexes is still lacking. A procedure, based on MAn+-SIMS approach, has been proposed for the accurate germanium quantification in Molecular Beam Epitaxy (MBE)-grown Si1-xGex alloys. The ‘matrix effect’ has been shown to be completely suppressed for all Ge concentrations irrespective of impact Cs+ ion energies. The methodology has successfully been applied for direct quantitative composition analysis of various thin film and multilayer structures. Recent study on various ZnO-based nanostructures has successfully been correlated to their photocatalysis and photoemission responses. The talk will address the complex formation mechanisms of MAn+ molecular ions and potential applications of the MAn+-SIMS approach in chemical analysis of low-dimensional materials.