Purushottam Chakraborty

Title : Alkali based molecular-ion sims: An innovative chemical approach for the exact composition analysis of quantum structures

Abstract:

If alkali metals such as Li, Rb, K, Na, Cs, …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. The formation of these (MA)⁺ molecular ions has strong correlation with 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-ion 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 been found to play a significant role in the emission of these molecular ions. Although these MA_n⁺ 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 MA_n⁺- SIMS approach, has been employed for the accurate germanium quantification in Molecular Beam Epitaxy (MBE)-grown Si_1−xGe_x 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 films, multilayer structures and quantum structures without the need of calibration standards. Recent SIMS study on various ZnO-based nanostructures has successfully been correlated to their photo-catalysis and photoemission responses. The talk will address the basics of SIMS, complex formation mechanisms of (MA_n)⁺ molecular ions and potential applications of the MA_n⁺-SIMS approach in chemical analysis of low-dimensional materials.

Audience take-away:

• My talk will address on the fundamentals of quantum structures, theoretical understandings of their “density of states” and their structural/compositional characterizations using state-of-the-art ion-beam methods.
• The audience will be acquainted with the basics of low-dimensional structures (nanomaterials) and an innovative methodology for direct quantitative analysis of smart materials.  
• The talk will be pedagogical and motivational which will help the audience know the intricacies and wonders of smart materials and their applications in diverse fields of materials science.
• The researchers will be highly benefited to gain knowledge so that they can initiate experimental research in this challenging area. They can expand the scope of their expertise in teaching and guiding the students and researchers.
• The experimental physicists/chemists with their basic background, knowledge and training will be greatly enriched with the comprehensiveness in novelties and complexities of analytical methods to characterize low-dimensional materials.

Biography:

Purushottam Chakraborty, a Former Senior Professor of Physics, Saha Institute of Nuclear Physics, Kolkata, India and a Former Adjunct Professor of Physics, University of Pretoria, South Africa is considered as one of the leading experts in Materials Science and Materials Analysis using Ion Beams. He was awarded the “Most Eminent Mass Spectrometrist of India” and conferred the “Gold Medal” by the Department of Atomic Energy (DAE), Government of India for his outstanding contributions in Secondary Ion Mass Spectrometry (SIMS). He received “Premchand Roychand Scholarship (PRS)” and “Mouat Medal” of Calcutta University. Prof Chakraborty’s research areas include: Atomic Collisions in Solids, Ion-Beam Modifications and Analysis, Secondary Ion Mass Spectrometry (SIMS), Low-dimensional Materials, X-UV optics, Nonlinear Optics, Photonics, Plasmonics, etc.

Prof Chakraborty indigenously fabricated an RF-Quadrupole Mass Spectrometer for the first time in India for working on Atomic Collisions in Solids. His “MCs_n⁺ molecular-ion based SIMS” is considered to be innovative for compositional analysis of nanostructured materials. His work on the fabrication of ‘layered Synthetic Microstructures (LSM)’ is recognized as a pioneering contribution in the “Realization of Optical Devices for the Extreme Ultraviolet to Soft X-rays”. His works on “Metal-Glass Nanocomposites” have led to the remarkable achievements in the development of novel photonic materials.

Prof Chakraborty worked at FOM-Institute in Netherlands, ICTP and Padova University in Italy, Laval University in Canada, Osaka Electro-Communication University in Japan, University of Pretoria in South Africa, Pontifical Catholic University of Rio de Janeiro in Brazil, etc. He delivered lectures at Imperial College in London; Maria Curie-Skłodowska University and Polish Academy of Sciences in Poland; Vanderbilt University, IBM T J Watson Research Centre, Rutgers University, Jackson State University, Furman University, Yale University in USA; Bielefeld University, Friedrich Schillar University, Kaiserslautern University in Germany; University of Western Australia, Newcastle University Australia; Osaka Electrocommunication University, Kyoto University, SPring-8, Nagoya Institute of Technology in Japan; National Taiwan University in Taiwan; Witwatersrand University, i-Themba Labs for Accelerator Sciences, Nelson Mandela University in South Africa;  Asian Institute of Technology in Thailand, TIFR, IISc, IITs, Tezpur University, in India, etc. Prof Chakraborty has delivered invited lectures at more than 140 international conferences across the globe and published more than 130 scientific papers including review articles, book chapters, etc. Prof Chakraborty edited a book on “Ion-beam Analysis of Surfaces and Interfaces of Condensed Matter Systems” (Nova Science Publishers, New York, USA) and Journal of Physics – Conference Series (UK). He is the Editor of “Photonic Materials”, as a Section of the “Encyclopedia of Materials: Electronics” (To be published by Elsevier Science). He is editing a book “Nanomaterials for Sensing and Labelling Applications” (Springer, Germany). Prof Chakraborty is a Fellow of the Indian Chemical Society and West Bengal Academy of Science and Technology.