Jerome Workman, Jr.

Zeolites represent a cornerstone of today’s industry as the most-used catalyst by weight in the world. Zeolites are nanoporous, crystalline alumino-silicate materials with regular arrays of molecule-sized nanopores, which give rise to shape- and size-selective adsorption, diffusion, and reaction of adsorbed guest molecules. Synthetic zeolites can be fabricated as pure silica (SiO

) polymorphs, alumino-silicates, alumino-phosphates, or including other elements such as B, Ge, Sn, Ti, Zn, or Zr. A host of new, energy-relevant applications such as biomass conversion to biofuels, carbon capture, hydrogen purification, and energy-efficient separations could be realized with targeted zeolite architectures. Zeolite structure is often thought of in terms of the collection of rings that make up zeolite channels and cavities. Achieving the synthesis of tailor-made zeolites, with targeted rings and cavities, is greatly hampered by a poor understanding of   how zeolite crystals actually form in solution. Solving this problem by identifying critical structures that lead to zeolite crystals has presented a difficult analytical challenge. Recently, we spoke to Scott M. Auerbach a professor of chemistry and chemical engineering  at the University of Massachusetts Amherst, about his work in the use of Raman spectroscopy for zeolite structure characterization, which has focused on a collection of nine all-silica zeolites.

From both theory and experience it is understood that the precursors for zeolites are not sufficiently well characterized using infrared (IR), nuclear magnetic resonance (NMR) or X-ray diffraction (XRD). In researching the analysis of zeolites, you have recently recognized Raman spectroscopy as an analytical tool capable of understanding the formation of zeolites, especially their individual ring structures (1). Is it possible to assign Raman spectral features to individual ring structures or should assigned Raman spectral features be associated with other zeolite building units? 

	Since the pioneering work in the 1980s by Prabir Dutta and others, there is a history of assigning Raman spectra of zeolites to individual rings, especially for Raman bands in the 200–700 cm

 range. This is perhaps not surprising given that Raman spectroscopy can be sensitive to collective, non-polar vibrations such as those of silica-based rings. This zeolite Raman assignment approach arises from observed correlations between known rings in zeolites and the locations of Raman bands. For example, zeolites with so-called “four-membered rings” (four alternating pairs of ...-Si-O-... atoms in a ring) are known to exhibit a strong Raman band around 450–550 cm

, while zeolites with six membered rings show Raman bands around 300–350 cm

, and those with eight membered rings show Raman bands at even lower wavenumbers, around 200–250 cm

. The apparent anti-correlation between ring size and Raman wavenumber also makes sense, as frequency is expected to decrease with increasing wavelength, and ring size should be related to vibrational wavelength. So in the end, there is a certain logic to assigning Raman bands to rings. However, the problem is that these rings exist in environments of other rings, raising the question: How do nearby rings influence Raman excitations? We thought to ask this question because of zeolites like Linde Type A (LTA) and Chabazite framework (CHA), which have 4-rings, 6-rings, and 8-rings (in different arrangements) but exhibit different Raman spectra. We wondered why. Answering that question was the original reason for our study.

How is your Raman work on zeolite structural characterization different from what others have done previously to study these structures?

	The innovative aspect of our approach is that we engaged in an 

 synthesis, spectroscopy, and simulation study to address two big problems that exist in the previous literature. The first problem is the difficulty in comparing properties for different zeolites, which can exhibit distinct framework structures and contain different compositions such as different Si:Al ratios in alumino-silicate frameworks. As such, if Raman spectra for different zeolites were distinct, it’s not obvious why because we typically have to change two variables at a time, and in science, we’re not supposed to do that. The second problem is the difficulty in assigning Raman spectra, especially by first principles calculations, because of the large sizes of typical zeolite unit cells. We tackled both problems by identifying nine distinct zeolites all sharing the same properties: 1) they could be synthesized as all-silica materials, which removes ambiguities associated with locations of aluminum atoms in the zeolite framework, and locations of charge-compensating cations in zeolite pores; 2) they have unit cells small enough to be treated accurately with periodic density functional theory, including the calculation of Raman intensities; and 3) they all share a common structural feature–the zeolite four-membered ring-to determine if Raman bands associated with four-membered ring vibrations are sensitive to different local environments, or not. Studying this disparate collection of zeolites was made possible by our zeolite synthesis capabilities, allowing us to consider relatively novel zeolite materials that are not commercially available. In the end, our approach allowed us to make systematic comparisons among Raman spectra of different zeolite frameworks in ways that others have not.

You and your coworkers have approached the question of zeolite structure using such methods as integrated synthesis, Raman spectroscopy, and periodic density functional theory (DFT) modeling. How do these methods complement one another in understanding zeolite structures?

	Insights in materials chemistry often follow the central dogma that 

 means a given zeolite’s framework structure with its collections of interlocking rings and cages, which after synthesis is tested and confirmed by comparing measured XRD patterns to known standards. Then, 

 means the corresponding Raman spectra, which were collected with our colleagues at Worcester Polytechnic Institute. As mentioned above, using zeolite structure (rings) to explain properties (Raman band locations) has-in the past-required assumptions and lacked accurate, first principles theory. We have bridged that gap in our study by applying periodic density functional theory on zeolite unit cells in a three-step process: 1) optimizing atomic positions and lattice parameters; 2) computing normal mode frequencies and vibrational coordinates; and 3) computing dielectric susceptibilities which underlie the Raman intensities. As such, the theory provides both accurate Raman spectra and illustrative pictures of key vibrations-the normal modes-thus answering whether bands can indeed by assigned to individual rings.

What are the larger questions associated with the accuracy of the assignments of Raman spectra related to zeolite structure? What are the aspects of these spectral assignments that are not well understood?

	Zeolite structures consist of “secondary building units” such as four-membered rings, and “composite building units” such as small and large cages. The big question is whether Raman bands can be assigned to rings or cages or both, depending on the given zeolite. This is a burning question, because after all these years in zeolite science, we still don’t really understand how zeolites form small crystals that grow into larger ones. Discovering this could help us synthesize new zeolites for advanced applications in, for example, creating carbon-neutral biofuels and capturing carbon dioxide. That’s why we’re funded by the Department of Energy.

	Two diametrically opposed theories for how zeolites form are 1) random monomer addition, like a sand castle forming from random addition of grains of sand, and 2) hierarchical growth from populations of pre-formed rings and cages in solution, like a sand castle forming from pre-formed buckets of sand. The former seems rather unlikely, but we don’t really have evidence for the latter yet. Being able to assign Raman spectra to rings and cages could answer this grand challenge question in materials chemistry, important for the reasons stated above.

Using normal-mode analysis, you discovered that Raman bands can be assigned to tricyclic bridges (which are structures comprised of three zeolite rings that share common Si−O−Si bridges). You also found that the vibrational frequency of a given Raman band can be correlated to the smallest ring of its tricyclic bridge and not to the ring that is actually vibrating. Lastly, you have discovered a precise anticorrelation between Raman frequency and Si−O−Si angle. How do these discoveries reveal new ways to investigate structures like those found in zeolites?

	The new structural concept of the tricyclic bridge offers a new organizing principle for understanding Raman bands from different, though related materials. Tricyclic bridges are both building blocks for understanding zeolite structure, and objects that collectively vibrate during Raman scattering. Grouping normal modes by the smallest ring of the corresponding tricyclic bridge allows us to categorize and structurally correlate vibrations with similar but slightly different band locations, and also explain the reasons for outliers that don’t obey a given correlation. The angular correlation you mention allows us to identify specific molecular coordinates (the Si-O-Si angle) from Raman band locations. In the end, it’s like finding the key to unlock the treasure of zeolite structure, elucidated by Raman spectroscopy.

How do you properly sample a complex material like zeolites to understand their general structural properties?

	The key to accurate calculations on materials such as zeolites is optimizing both geometrical and electronic structures. The key to a good geometry is a good first guess, and that is furnished by previous experimental XRD studies on zeolite crystals. When we optimize atomic locations and unit cell parameters, we start from experimental data and make small tweaks consistent with quantum density functional theory (DFT). The Nobel Prize in Chemistry was given to Walter Kohn in 1998 for DFT, which has revolutionized computational materials chemistry. DFT is tractable for zeolites because of the use of “plane waves,” which are great mathematical functions for modeling valence electrons in crystals such as zeolites. The only problem with zeolites is their typically large unit cells, meaning many atoms, many valence electrons, and thus, many functions in the basis set. That’s why we had to focus on materials with smaller unit cells to make calculations tractable.

What were the key challenges you encountered during this research work?

	Each component of the project-synthesis, spectroscopy, and modeling-had its unique challenges. Synthesizing all-silica materials often requires an esoteric organic molecule to act as a sacrificial “structure directing agent” or SDA. Before our team could actually synthesize a given zeolite, we had to do the multistep organic synthesis of a certain SDA, and that could take weeks. The spectroscopy was challenging-to get good Raman signals, we needed to “hunt” for zeolite crystallites with an orientation that happens to give good backscattering (our WPI collaborator, Dr. Geoff Tompsett, has Jedi skills when it comes to backscattering), and good signal-to-noise requires plenty of time to collect and average over spectra. And finally, the quantum calculations of Raman intensities were, by far, the most computationally intensive aspect of our work. Our computations were performed on fast computers at the Massachusetts Green High Performance Computing Center in Holyoke, Massachusetts. In the end, the graduate students on this project, Tongkun Wang and Song Luo, showed heroic resilience and resourcefulness, leading to our breakthrough findings.

What do you consider to be the most useful contribution of your work?

	Actually I see two: one about science, and the other about scientists.

	The science contribution is about the discovery of a new “Platonic form,” in other words, a new fundamental shape, the tricylic bridge. which helps us understand zeolite structure. The trycyclic bride is an interesting shape, involving three rings that share one edge. I can’t help but wonder where else in nature we might find the tricyclic bridge. (A Star Wars Aside: Darth Vader’s shuttle craft actually has this form, with three triangular fins attached to the shuttle craft’s fuselage-the bridge. In our language, this is a 3-3-3 bridge, which interestingly does not show up in zeolite structures. Maybe it’s a Sith thing.)

	The contribution related to scientists is about how our integrated science approach made a real difference. By crossing disciplinary boundaries in our team, we taught one another about our respective fields, creating fertile ground for new ideas. I am the executive director of an integrated science program for science, technology, engineering, and math (STEM) undergraduates at UMass Amherst called the UMass iCons Program (

), which gave me a head start in launching and running a research program aimed at creating breakthroughs through “radical synergies.”

	We’d like to connect the dots between Raman spectra of perfect zeolites (our recent 

 paper [1]), to Raman spectra during zeolite formation, which can shed light on how zeolites form. To do this, we have to consider what’s in the soup that makes zeolites, the signature vibrations of each of these ingredients, and how interactions among these ingredients can be probed by Raman spectroscopy. Step by step, we will cross the chasm between zeolite structure to zeolite formation with the nexus among zeolite synthesis–Raman spectroscopy–quantum modeling.

		T. Wang, S. Luo, G.A. Tompsett, M.T. Timko, W. Fan, and S.M. Auerbach, Critical Role of Tricyclic Bridges Including Neighboring Rings for Understanding Raman Spectra of Zeolites. 

Dr. Scott Auerbach is professor of physical chemistry at the University of Massachusetts at Amherst (UMass Amherst). Professor Auerbach’s research focuses on modeling nanostructured materials such as zeolites, which are of importance to renewable energy technologies including biofuels and fuel cells, leading to 2 books and 120 articles. Auerbach graduated with a BS in Chemistry from Georgetown in 1988 and with a PhD in theoretical chemistry from UC Berkeley in 1993. After an NSF-funded postdoc at the University of California (UC) Santa Barbara, Auerbach began his career in 1995 at UMass, and was promoted to full professor in 2004. Auerbach won an NSF Career Award in 1998, a Sloan Fellowship in 1999, and a Camille Dreyfus Teacher-Scholar Award in 1999. Auerbach is the founding director of the Integrated Concentration in Science (iCons) Program at UMass, which challenges science and engineering students to design solutions for societal problems in renewable energy and biomedicine. Auerbach won the inaugural UMass Manning Prize for Teaching Excellence in 2016; and the UMass Distinguished Teaching Award in 2017.

Articles

Recently, we spoke to Scott M. Auerbach a professor of chemistry and chemical engineering  at the University of Massachusetts Amherst, about his work in the use of Raman spectroscopy for zeolite structure characterization, which has focused on a collection of nine all-silica zeolites.

Using Raman Spectroscopy for the Characterization of Zeolite Crystals

) nanopore sensors, when combined with specially tuned sensing conditions, can be used to analyze natural and synthetic oligosaccharides and polysaccharides like the anticoagulant drug heparin. The nanopore sensors enable reliable detection and differentiation of polysaccharides and enzymatic digestion products. These sensors are demonstrating the capability to not only characterize polysaccharide properties but also to provide an understanding of nanopore electrokinetics-mechanisms important for capillary electrophoresis with often outsized importance on the nanoscale. Recent foundational work in the use of nanopores for sensing is providing a platform for the development of new assays applicable to clinical heparin and other therapeutic molecules. Nanopore sensors can also be combined with spectroscopic techniques for a wide variety of analytical applications. Recently, we spoke to Jason R. Dwyer, of the University of Rhode Island (USA) and a FACSS Innovation Award winner from the 2019 SciX conference, regarding his work in this field. This interview is part of a series of interviews with the winners of awards that are presented at the SciX conference.

In a recent paper you discuss the complexities of therapeutic oligo- and polysaccharides (1). Characterizing polysaccharides is a daunting task for conventional chemical analysis, as details such as contamination, monomer composition, stereochemistry, polymer length, monomer sequence, polymer branching, and monomer linkage types are required to understand the structure and function of these molecules. In 2008 an undetected contamination in a heparin supply caused severe adverse clinical effects among patients within the United States, including approximately 100 deaths. Where did you have the initial idea to investigate nanopore sensors for polysaccharide characterization, rather than typical separation methods combined with mass spectrometry? How did you decide to investigate polysaccharides, and specifically heparin?

	When I started my independent academic career, the development of nanopore-based sequencing of DNA was in full swing and was being pushed by an intrepid few toward protein analysis. I remember reading about the heparin crisis and thinking that on some level (a very simplistic level, mind you), that the heparin molecule is just a charged biopolymer like DNA and that we might be able to apply the single-molecule sensing performance of nanopores to a pressing and important problem. What differentiates nanopores in this application compared to more sophisticated conventional chemical analysis tools is that they hold the promise of low-cost, high-performance sensing in a platform that relies on a very basic principle of operation. While simple in principle, it took a lot of development effort to bring the idea to fruition. Really talented students doing this hard work afforded me the luxury of considering what I wanted to do in the nanopore world. I had always been interested in turning nanopore sensors into sensors that were general and not restricted to only a particular class of analyte. At the same time, I reflected that my training as a chemist had helped me make unique contributions to my past research in ultrafast science-developing femtosecond electron diffraction and exploring the hydration dynamics of DNA by femtosecond infrared spectroscopy. It’s probably fair to say that if you can make a nanopore carbohydrate analyzer, you’re not too far away from a general chemical sensor platform. Given the importance of carbohydrate analysis, and the opportunities I saw from a chemistry and materials science perspective, it seemed like nanopore carbohydrate sensing was a very exciting and promising area on which to focus.

How is your work on nanopore sensing different from what others have done previously?

	The work for which we won the FACSS Innovation Award involved discovering and optimizing a way to chemically tune nanopore sensing performance. Early demonstrations in the field required special materials or significant expertise to surface coat nanopores. In our paper we functionalized more than 100 pores-I think more than had been reported functionalized in a decade of thin-film, solid-state nanopore literature. I can best summarize our approach as “bulletproof.” It opens up the palette of organic chemistry to nanopore science in a very straightforward way.

	In the domain of nanopore carbohydrate sensing we were the first to do two things: First, we used thin-film nanopores made with a material that is ubiquitous in consumer electronics. Using a conventional micro- and nanofabrication material means fewer barriers to commercialization of our discoveries. Second, getting reliable tools into the hands of end users is a focus of our work, and therefore, we performed a survey study of a range of carbohydrates exhibiting properties that both revealed key mechanisms to exploit and showed that nanopore sensing could be optimized to cope with the incredible diversity of carbohydrate properties. This carbohydrate sensing work underscored the importance of our work on chemically functionalizing nanopores; the native nanopore composition, alone, would be hard-pressed to cope with the chemical diversity of carbohydrates.

In your nanopore sensing device you use a voltage-driven passage of a sample molecule that can pass into, across, or through an electrolyte-filled nanopore. Would you explain for our readers how this device can be used for analyte detection and characterization? How specifically does the sensing or characterization of molecules take place?

	The passage of electrolyte ions, only, through the nanopore gives a steady “open pore” current whose magnitude is determined by the size and surface chemistry of the nanopore, the electrolyte composition, and the applied voltage. When an analyte passes into the nanopore (or near it), it displaces those electrolyte ions, giving rise to a current perturbation whose magnitude is dependent on those same parameters, plus size and charge distribution of the analyte. When the nanopore is small enough to force a biopolymer to pass linearly through a nanopore, each monomer constrained in the nanopore will contribute uniquely to the overall current perturbation. In the nanopore DNA sensing world, especially, considerable effort has gone into pulling out this sequence-specific information from the total signal.

Is the device and technology associated with nanopore sensors mostly applicable to spectroscopic applications, or could it also be used in conjunction with separation methods, such as chromatography or sample partitioning for mass spectrometry? Do you foresee nanopore devices being designed for specific assays and providing specific tests for low cost, yet accurate analysis of therapeutic molecules?

	I think that nanopores have a tremendous amount of potential in a stand-alone sense, especially when suitably chemically tuned to optimize sensitivity and selectivity for a particular analyte. They offer single-molecule sensing without the need for chemical labelling or spectroscopic readout, since the properties the nanopore is sensitive to-size and charge-are inherently their own labels. Of course nanopore sensing could be implemented after a chromatographic separation step, thereby increasing the selectivity. Nanopore sensing can also be used in conjunction with fluorescence detection, or with electron tunneling detection, for example. More broadly, nanopores can trap and manipulate single molecules in solution, and this capability can be exploited in a number of ways, and in combination with a number of other analysis tools. Nanopores already have a very strong foothold in DNA sequencing, and I can imagine that they will find application in a wide range of other sensing areas. We are really optimistic about their use for glycomics.

In another paper (2) you discuss nanofabricated thin-film platforms and their analytical applications using techniques such as visible or infrared spectroscopy, electron energy loss spectroscopy, X-ray photoelectron spectroscopy, and single molecule sensing. In this paper your focus was on the thin film structure being common across platforms, rather than the nanopore being a focal element. However, what are the required differences in the nanopore sensor device itself when applied to these different analytical methods? Would you explain how the nanopore devices can be extended for imaging applications?

	To specifically address your question, we craft well-defined, near molecular-sized channels through thin films of silicon nitride to create optimal nanopore sensors. Those channels can be used for nanopore-based sensing, to hold single molecules for study by other techniques, or as well-defined access ports to the contents of a sample cell bounded by the thin film. For conventional nanopore single-molecule sensing, the diameter of the nanopore should in general be not much larger than the dimensions of the conformation of interest of the given analyte. These same films that house the nanopores, when left intact, can serve as ~10–100 nm-thick windows for sample chambers that allow interrogation with a variety of techniques using optical and charged-particle beams. When even this sample wall thickness is too thick, well-defined access ports can be formed through the film-on the same scale or larger than the nanopores used for sensing-in order to permit access to the underlying sample.

What are the sampling limitations when using the nanopore sensing devices? Do all samples have to be suspended into a liquid phase or are there other options that might be applicable for solid surface or gas phase analysis?

	Broadly speaking, the nanopore sensor will detect every single molecule that passes through the pore. The trick is to make sure that the molecules of interest make it to the nanopore in a reasonable amount of time-an area benefiting from significant research effort. In nanopore DNA sequencing work, electrophoresis has been the easiest way to control the biopolymer motion. In our work on carbohydrates, the possibility of charge-neutral biopolymers has eliminated electrophoresis as a possibility, and we are relying on electroosmosis.

	Nanopore sensing is not limited to solution-phase samples, although that is how the majority of the studies are carried out. In leaving the solution phase behind, the role of the nanopore might well change to be a single-molecule orifice to inject sample into a different type of detector, for example. But even in the solution domain, it’s really interesting to think about what the insolubility of a sample might mean for a detector that simply relies on passage of a molecule through a channel.

What were the key challenges you encountered during the development of this device?

	We benefited enormously from the work of others in just being able to make nanopores that are <10 nm in diameter. In fact, our Innovation Award work making chemically tuned nanopores relies on pioneering work by the Tabard-Cossa group at the University of Ottawa as a first step.

	First, developing a reliable method to easily control the surface chemistry of a nanopore-allowing for molecular-level control over its sensing performance. Second, showing that nanopore sensors can cope with carbohydrate complexity and offer new mechanistic insights and functional tools for tailoring nanopores for this application.

	We are pushing onward in using chemically tuned nanopores to advance nanopore carbohydrate analysis-carrying out fundamental work and trying to develop applications.

	(1) B.I. Karawdeniya, Y.N.D. Bandara, J.W. Nichols, R.B. Chevalier, and J.R. Dwyer, Surveying silicon nitride nanopores for glycomics and heparin quality assurance. 

(1), 3278 (2018). doi: 10.1038/s41467-018-05751-y.

	(2) J.R. Dwyer, and M. Harb, Through a window, brightly: a review of selected nanofabricated thin-film platforms for spectroscopy, imaging, and detection. 

(9), 2051-2075 (2017). doi.org/10.1177%2F0003702817715496.

Jason Dwyer is an Associate Professor of Chemistry at the University of Rhode Island. His research is at the intersection of bioanalytical chemistry and nanofabrication, with a focus on developing enabling tools for discovery and application. Both are pursued in his research group. Molecular- and nanoscale-level tuning of nanopore single-molecule sensing platforms is used to support molecular-scale exploration of the natural world, and the resulting discoveries and nanofluidic tools are used to develop and support applications. A principal effort is focused on advancing nanopores from a tool primarily for sequencing DNA to one reaching also to glycomics. A number of materials science discoveries arising from this primary effort underpin a secondary research effort in technology development for surface-enhanced Raman spectroscopy (SERS).

	Dwyer was awarded an NSF CAREER award, and additional funding from NSF and NIH, in support of his research at URI. He has two patents arising from his nanofluidics research, and he has been active in technology commercialization. He has given over 60 invited lectures, including at Pittcon, Gordon Conferences, and at the International Symposium: Advanced Science and Technology for Single Molecular Analysis of DNA and Related Molecules in Kyoto. Dwyer has a strong interest in public science outreach and has been featured in a number of media sources, including the Discovery Channel.

	Dwyer received his Ph.D. in Physical Chemistry from the University of Toronto, with his thesis work featured on the front cover of 

 and proceeded to postdoctoral research in biophysics at the Max Born Institute in Berlin, earning Natural Sciences and Engineering Research Council of Canada (NSERC) fellowships at both stages. A switch to single-molecule sensing in applied bio-physics at the University of British Columbia followed, where he developed nanopore single-molecule sensors for genomics applications. Since 2009, Dwyer has worked as an analytical chemist at the University of Rhode Island. At the same time that he started his independent academic career, Jason co-founded a nanotechnology startup to commercialize a nanofluidic sample cell for transmission electron microscopy. Following his initial foundational work featured in 

, Jason directed the company’s research and development until leaving it in 2014.

Solid-state silicon nitride (SiNx) nanopore sensors can be used to analyze natural and synthetic oligosaccharides and polysaccharides like the anticoagulant drug heparin. These sensors are providing an understanding of nanopore electrokinetics-mechanisms important for capillary electrophoresis with often outsized importance on the nanoscale. Recent work in the use of nanopores is providing a platform for the development of new assays applicable to clinical analysis for a variety of therapeutic molecules. Nanopore sensors can be combined with spectroscopic techniques for multiple analytical applications. Recently, we spoke to Jason R. Dwyer, of the University of Rhode Island (USA) and a FACSS Innovation Award winner from the 2019 SciX conference, regarding his work in this field. This interview is part of a series of interviews with the winners of awards that are presented at the SciX conference.


Using Nanopore Sensors to Analyze and Characterize Heparin and Other Therapeutic Polysaccharides

Raman spectroscopy is a versatile tool to identify and characterize the chemical and physical properties of graphene-based materials (1–4), providing information on graphene structures for fundamental research and for practical device fabrication, as well as demonstrating the first- and second-order modes in intrinsic graphene, as well as the shear, layer-breathing, and the G and 2D modes of multilayer graphene. Professor Ping-Heng Tan from the State Key Laboratory of Superlattices and Microstructures at the Institute of Semiconductors at the Chinese Academy of Sciences is carrying out new research to advance the use of Raman analysis of these materials. We recently interviewed Tan about this work.

You have described Raman techniques to determine the number of graphene layers, to probe resonance Raman spectra of monolayer and multilayer graphenes, and to obtain Raman images of graphene-based materials. What are the greatest benefits of applying Raman spectroscopy to investigate graphenes? How does Raman compare to other methods for this application?

	Raman spectroscopy is a fast, nondestructive, and versatile tool for the characterization of the lattice structure and the electronic, optical, and phonon properties of graphene-based materials. Raman spectra of all graphene-based materials show a few prominent features (D, G and 2D modes), regardless of the final structure. However, the positions, line shapes, and intensities of these peaks give abundant useful information for the investigation of the structures and electronic properties of graphene-based materials. In comparison to other methods, Raman spectroscopy can give more information without the additional treatments or damage to the sample, and with much less time and cost.

Would you briefly explain the theory behind how Raman measurements provide detailed information for investigation of the fundamental properties of graphene, including the states, effects, and mechanisms of graphene?

	The first-order Raman scattering in a crystal is a three-step process, including the generation of the photo-excited electron and hole, scattering of the excited electron or hole by the phonon phenomena, and the recombination of the electron and hole. The phonons involved reflect the corresponding fundamental properties. For example, the single-axis strain of graphene can be revealing by the splitting of the E

phonon (G mode), and the frequency of the interlayer shear (C) mode, giving information on the number of graphene layers as well as the interlayer coupling strength. Moreover, it’s obvious that the intensities of the Raman modes are related to the optical properties of graphene. By obtaining the resonance Raman spectra, the optical transition probability of graphene-based materials can be obtained. For example, the twisted bilayer graphene has a twist-angle dependent Van Hove singularity in the joint density of state, which leads to twist-angle dependent optical transition energies, and can be investigated by multi-wavelength Raman spectroscopy. Moreover, due to the unique linear band structure, the second-order Raman scattering (involving two phonons, represented by the 2D mode) is easily observed in graphene-based materials, which is enhanced by a double resonance Raman scattering process. This excitation-wavelength dependent mode allows one to detect the phonon dispersion, electron-phonon coupling, and band structure of graphene-based materials.

Why are graphene-based materials important?

	Graphene is a truly two-dimensional system, consisting of sp

 carbon hexagonal networks with strong covalent bonds. Multilayer graphene can be stacked layer by layer in a Bernal or rhombohedral way through van der Waals coupling. High-quality monolayer graphene and multilayer graphene can be produced by several methods, such as micromechanical exfoliation, chemical vapor deposition, and epitaxial growth from the silicon carbide (SiC) surface. Other artificial fabrication routes for production, such as the reduction of a graphene oxide solution and organic synthesis, tend to introduce defects into the graphene, such as vacancies and dislocations, as well as exposing the graphene to oxidation, hydrogenation, fluorination, and other chemical functionalization. Graphene can also be decomposed into one-dimensional and zero-dimensional forms, such as graphene nanoribbons and nanographene. All these materials with various dimensions are derived from graphene, and can be termed 

	The remarkable properties of graphene and graphene-based materials, including their high carrier mobility (near ballistic transport), high thermal conductivity, unique optical and mechanical properties, and high specific surface area, make them promising materials for high-frequency nanoelectronics, micro- and nanomechanical systems, thin-film transistors, transparent and conductive composites and electrodes, batteries and supercapacitors with high charging speeds, highly sensitive chemical sensors, flexible and printable optoelectronics, and photonics.

	In addition, recent research studies have advanced to investigate vertical van der Waals heterostructures because they can be formed by vertically stacking various two-dimensional materials by van der Waals forces but without any constraints of lattice matching and fabrication compatibility, offering huge opportunities for the design of new functionalities. Graphene and multilayer graphene are the essential building blocks for van der Waals heterostructures as electrodes in various high-performance devices, such as field-effect tunneling transistors, logic transistors, photovoltaics, and memory devices.

What is the potential for Raman spectroscopy to be used routinely for characterizing graphene materials in a manufacturing or production environment?

	For the large-scale characterization of graphene materials in industry, Raman spectroscopy has several advantages, including short measurement time, low cost, lower training requirements compared to other techniques, and, very importantly, the nondestructive nature of the technique. The relatively simple features of the Raman spectra in graphene-based materials make them quite easy to interpret by an engineer with some limited training. The cost of the Raman measurement is becoming lower and lower with the development of Raman instrumentation, including portable systems. It just takes a few minutes to obtain a state-of-art Raman spectrum of graphene-based materials. And the Raman measurement would not affect the quality of the materials after measurement by gently controlling the incident laser power.

What recent advances in Raman instrumentation, software, or sampling methods have you been most active in over the recent past?

	Recently, I have been active in pushing the detection limit of the low frequency Raman modes in a single-monochromator Raman system. Our target is to probe the Raman modes with the frequency as low as possible. As we know, a well-aligned triple grating spectrometer can give a low frequency limit down to 5 cm

, but with a low detection efficiency. In our previous work, we obtained a frequency limit down to 2.0 cm

 by a single-monochromator Raman system coupled with volume-Bragg-grating-based notch filters (5), and achieved a frequency limit down to 10 cm

 by a single-monochromator Raman system with long pass edge filters (6). Those filter-based techniques to detect low frequency Raman modes are much higher in efficiency than a triple grating spectrometer. We have also developed a tunable single-monochromator Raman system based on the supercontinuum laser and tunable filters, showing its potential application for resonant Raman profile measurements (7). We also devote ourselves to updating a single grating spectrometer with our homemade micro-Raman module into a high-throughput confocal Raman system. The homemade micro-Raman module can connect two single grating spectrometers to obtain a very broad photoluminescence spectrum in a single capture and a Raman spectrum with high spectral resolution. You can see a demonstration of this on the website http://www.fergiespec.com/case-study/ping-heng-tan/.

What have been your greatest challenges in scientific discovery over your career? What is your general approach to problem solving in your scientific work?

	As a physicist studying Raman spectroscopy, the greatest challenge in scientific discovery is always how to obtain the intrinsic Raman spectra and how to understand them properly. That challenge arises frequently when you are exploring the fundamental properties of new materials by Raman spectroscopy. Fortunately, with the development of theoretical approaches, it’s becoming easier to understand the measured Raman results quickly and accurately. As an experimental physicist, I always benefit a lot by collaborating with many theoretical scientists.

What are some major gaps in knowledge for Raman technology that you would like to see more research and development time devoted to?

	I have been working on Raman spectroscopy for over 20 years. At the beginning, Raman technology was used as a tool by a few Raman experts in physics and chemistry to investigate the lattice and molecular dynamics of molecules and their other related properties. The Raman technique has developed exponentially in past 15 years, leading to many non-experts wishing to enter this field. Now, Raman spectroscopy has become a standard and routine technique to identify and characterize many materials, both at the laboratory and mass-production scale. However, some users may just know how to measure Raman spectra simply by using a commercial Raman system, but do not know the real physical meaning behind the spectra they measure. Thus, as a physicist of Raman spectroscopy, I would like to appeal to and help more researchers to put their sights on the depths of this area, which will be helpful for the development of this field.

What do you anticipate is your next major area of research or application in this field?

	We are really interested in characterizing the two-dimensional materials (especially graphene-based materials) and related van der Waals heterostructures in an operating device in situ. It would be helpful for us to understand the working mechanism of the device, and to reveal new physical phenomena of various materials and related devices.

For those having greater interest in this topic, what reference papers or books would you recommend they obtain to read or study?

	In the past decade, the attention to this field keeps growing. The following review papers or books can be recommended for non-experts wishing to enter the field:

		L.M. Malard, M.A.A. Pimenta, G. Dresselhaus, and M.S. Dresselhaus, “Raman Spectroscopy in Graphene,“ 

		A. Jorio, M.S. Dresselhaus, S. Riichiro, G. Dresselhaus, 

Raman Spectroscopy in Graphene Related Systems

		A.C. Ferrari and D.M. Basko, “Raman Spectroscopy as a Versatile Tool for Studying the Properties of Graphene,”

		J.B. Wu, M.L. Lin, X. Cong, H.N. Liu, and P.H. Tan, “Raman Spectroscopy of Graphene-Based Materials and its Applications in Related Devices,” 

Raman Spectroscopy of Two-Dimensional Materials

 (Springer Nature Singapore Pte Ltd., 2019). DOI: 10.1007/978-981-13-1828-3.

	The first three suggestions present the fundamental understanding of the use of Raman spectroscopy in graphene materials, and the last two give a more complete understanding and updates on newer progress in the analysis of graphene-based materials and other two-dimensional materials.

		J.B. Wu, M.L. Lin, X. Cong, H.N. Liu, and P.H. Tan, 

Raman Spectroscopy of Two-Dimensional Materials 

(Springer Nature Singapore Pte Ltd., 2019). DOI: 10.1007/978-981-13-1828-3.

Ultralow-Frequency Raman Spectroscopy of Two-dimensional Materials. In Raman Spectroscopy of Two-Dimensional Materials 

(Springer, Singapore, 2019), pp. 203–230.

		J.B. Wu, M.L. Lin, and P.H. Tan, “Raman Spectroscopy of Monolayer and Multilayer Graphenes,” in 

 (Springer, Singapore, 2019), pp. 1–27.

Ping-Heng Tan of the Chinese Academy of Sciences is advancing the use of Raman spectroscopy to characterize graphene-based materials.

Raman Spectroscopy of Graphene-Based Materials

This year’s Atomic Spectroscopy award recipient, Jake Shelley, focuses on the development of plasma-based tools for mass spectrometry, which enable rapid and sensitive detection and identification of a broad range of analytes from complex matrices.

	Jacob T. (“Jake”) Shelley is the Alan Paul Schulz Professor of Chemistry in the Department of Chemistry and Chemical Biology at Rensselaer Polytechnic Institute (RPI) in Troy, New York. He is the winner of the 2020 Emerging Leader in Atomic Spectroscopy Award, which will be presented by Spectroscopy at the Winter Conference on Plasma Spectrochemistry the week of January 12–18, 2020, in Tucson, Arizona.

	The Spectroscopy Emerging Leader in Atomic Spectroscopy Award recognizes the achievements and aspirations of a talented young atomic spectroscopist who has made strides early in his or her career toward the advancement of atomic spectroscopy techniques and applications. The winner must be within 10 years of receiving his or her highest academic degree in the year the award is granted.

	Shelley earned his undergraduate degree from Northern Arizona University, and received his PhD in 2011 from Indiana University under Professor Gary M. Hieftje. Following postdoctoral research at Purdue University (mentored by Prof. R. Graham Cooks), and the University of Münster (under Prof. Uwe Karst and Prof. Carsten Engelhard), he then became an assistant professor at Kent State University in 2014. In 2016, he was appointed the Alan Paul Schulz Career Development Professor of Chemistry at RPI.

	Shelley has published more than 41 peer-reviewed papers and one book chapter, holds five patents and patent applications, and has presented more than 60 papers and invited talks at scientific conferences. He has specialized in the development of atmospheric-pressure plasmas as ionization sources for atomic, molecular, and biological mass spectrometry.

	He has received multiple awards and scholarships, including the Gordon F. Kirkbright Bursary Award from the Association of British Spectroscopists; the Tagungsstipendium Analytische Chemie of the German Chemical Society (twice); a Humboldt Research Fellowship of the Alexander von Humboldt Foundation; and the Bunsen-Kirchhoff Award.

	With an impressive h-index of 23, Shelley’s research explores new and advanced desorption and ionization mechanisms of plasma-based sources for mass spectrometry applications and instrumentation. As a student at Indiana University and since, Shelley has published in such diverse and prestigious journals as Mutagenesis, Biometals, Analytical Chemistry, Microporous and Mesoporous Materials, The Journal of Analytical Atomic Spectrometry, Journal of the American Society for Mass Spectrometry, Analyst, and Rapid Communications in Mass Spectrometry.

	His volunteer activities are diverse. He was on the conference organizing committee for the 2017 Ionization Principles in Organic and Inorganic Mass Spectrometry conference in Menorca, Spain. He has acted as chair and organizer for five invited symposia at Pittcon (in 2012, 2013, 2015, 2017, and 2018) and for eleven invited sessions at the Federation of Analytical Chemistry and Spectroscopy Societies (FACSS) Conference/SciX Conference (2009–2019). He also acts as a referee for a number of journals, including Nature, Analytical Chemistry, Analyst, Rapid Communications in Mass Spectrometry, Journal of the American Society for Mass Spectrometry, Journal of Analytical Atomic Spectroscopy, Analytica Chimica Acta, and Spectrochimica Acta Part B: Atomic Spectroscopy.

	Karst, of the University of Münster, was a postgraduate mentor of Shelley’s. “Dr. Shelley’s record and achievements are outstanding,” he says. “He is among the top-notch young investigators in the field.”

	Hieftje, a Distinguished Professor Emeritus and the Mann Chair of Chemistry at Indiana University, who was Shelley’s PhD supervisor, said that Shelley and his group have already made a number of significant contributions to spectroscopy. “Among them, I would rank highest his exploration of the combination of a solution-cathode glow discharge (SCGD) with mass spectrometry (MS),” he said. He also said that Shelley is inquisitive, objective, and determined, which are important qualities for scientific inquiry.

	Cooks, the Henry Bohn Hass Distinguished Professor of Chemistry in the Aston Laboratory of Mass Spectrometry at Purdue University, is also impressed with Shelley. “What struck me most about Jake, when I started to collaborate with him a decade ago, was the speed with which he worked-and his broad knowledge of physics, plasmas, and instrumentation,” he said. “He has clearly emerged as a leader in atomic spectroscopy, and this is further testament to the quality of his training under Gary Hieftje at Indiana University, as well as his native ability.”.

	Since 2008, George Chan, a research scientist at Lawrence Berkeley National Laboratory, has worked closely with Shelley on plasma-based ambient desorption ionization mass spectrometry (ADI-MS); they have collaborated on six research articles. Chan also considers Shelley’s greatest contributions to be his work on coupling an SCGD source to MS. This development took a source initially developed for atomic emission and coupled it to a mass spectrometer. “Jake showed its vast potential, not only for elemental analysis, but also for high-precision isotopic-ratio analysis as well as for biochemical analysis (peptide fragmentation),” Chan said. Chan was impressed with the precision in isotope-ratio analysis that was achieved. Using a 5-min analysis time, Shelley’s SCGD-MS technique met the international target values (ITVs) set by the International Atomic Energy Agency (IAEA) for analytical precision used in assaying uranium enrichment, and was also able to detect trace amounts of 234-U and 236-U. “The very impressive example that Jake showed is the use of the SCGD-MS (again, a source that originally designed for atomic analysis) for peptide fragmentation,” he says. “Not only can the SCGD source fragment peptides, the spectral interpretation is generally simpler than those generated from other ion sources.” In some cases, Chan notes, the amino acid sequence can be read directly.

	Steven Ray, the Winkler Assistant Professor of Chemistry at the State University of New York at Buffalo, remarked on the value of Shelley’s work on plasmas. “Jake recognized very early on in the development of ambient ionization sources that understanding the fundamental mechanisms by which molecules are sampled, then ionized, was going to be critical to fruitful application,” he said. “He has a deep understanding of the mechanistics of gas-phase ion chemistry and the fundamentals of plasmas, and it is the ability to work in both fields that provides him with insights that others do not see.”

Fundamental Research in Understanding the Physics and Chemistry Underlying ADI-MS

	In 2010, Shelley and Hieftje published research focusing on the detailed chemical and physical properties of ADI-MS (1). Their work delved into the underlying science behind desorption and ionization phenomena, as well as the issues associated with sample matrix effects inherent in plasma-based sources. ADI-MS seeks to eliminate sample pretreatment and separation steps for mass spectrometry analysis. The challenge in applications of ADI-MS is dealing with matrix effects. This research evaluated three plasma-based ADI-MS sources: a low-temperature plasma (LTP) probe, a flowing atmospheric-pressure afterglow (FAPA) source, and a direct analysis in real time (DART) source. The main area of study involved ion-suppression events, which typically result in a decrease in analyte signal. It was discovered that the FAPA source was least affected by ion suppression when proton-transfer ionization occurs. The research demonstrated that understanding the fundamental issues of matrix effects is essential to accurately applying ADI-MS for both quantitative and qualitative analysis.

	Karst cites this work among Shelley’s most significant contributions to date. “Jake is a pioneer in the development of and applications with FAPA as a new ambient ionization source for pharmaceutical, forensics, and environmental applications of mass spectrometry,” he says.

In related research, Shelley and coworkers recognized the critical role of the helium dimer ion (He2+) in the formation of the afterglow of a helium-based dielectric-barrier discharge (2). They conducted studies to understand the reaction mechanisms in the afterglow and reagent-ion formation for plasma-based ionization sources used in ambient MS. This work on the dielectric-barrier discharge of the LTP probe determined the roles of the helium dimer ion (He2+). This ion carries energy from the plasma discharge into the afterglow region, and it promotes charge transfer between He2+ and atmospheric nitrogen to form N2+. The N2+ ion is the key reaction intermediate in the formation of other important reagent ions, particularly protonated water clusters. In this work, the charge-transfer reaction between He2+ and N2 was described in detail, as well as the origin of excited atomic helium in the afterglow region of the LTP.

	Shelley and his group then developed a handheld, wireless LTP source for MS (3). This device is based on a dielectric-barrier discharge. This ambient ionization source was demonstrated on a miniature mass spectrometer. The battery-powered (7.4-V Li-polymer battery) source uses mini-helium and air cylinders as its source of discharge gas. The work demonstrated that the handheld source was not only more efficient, and easier to set up, but also showed improved analytical performance over large-scale laboratory LTP sources. The battery power is capable of providing plasma for 2 h of continuous use, while meeting all other requirements for an LTP source.           

	The concept of a tunable FAPA plasma ionization source for MS was also devised by Shelley and coworkers (4). This specific work addressed new ways to control or adjust the ionization chemistry by changing the working conditions of the source. They found that gas flow rates and discharge currents could be adjusted to change the abundance of proton-transfer reagent ions. A nonpolar analyte, biphenyl, was used as a model compound, and was found to exhibit significant changes in its ionization pathway, depending on the operating parameter settings of the source. The tunable ionization modes for the FAPA source allowed detection of analytes that typically have poor sensitivity in applications of plasma-based ADI-MS. This tunable process increases the number of detectable analytes by improved sensitivity and reduced
	matrix effects.

	Engelhard, a professor of Analytical Chemistry at the University of Siegen, in Germany, notes that Shelley’s particular knowledge of electronics facilitates all his work on ambient ionization sources. “Even though mass spectrometers typically come with electrospray sources and are not ready to be used with custom-built ambient desorption/ionization sources, Jake can defeat any interlock in a heartbeat,” he said. “He can put a FAPA source virtually on any mass spectrometer.”

	In a recent review article on trends and developments in ADI-MS (5), Shelley noted that key research is focused on sample introduction and preparation strategies, removing matrix effects, and multimode ionization sources, as well as pursuing applications in quantitative mass spectrometry and imaging.

Extending the Reach of Ambient Sampling Mass Spectrometry

	Shelley’s research has also extended into modern “-omics”, such as metabolomics, proteomics, and glycomics, with a focus on electrospray ionization and tandem MS to identify the structures of target species (6). Rather than rely on specialized MS instrumentation, Shelley and coworkers developed a novel approach enabling ionization and controlled, tunable fragmentation of peptides at atmospheric pressure. The new source that he and his team developed uses a direct-current plasma, which is sustained between a tapered metal pole and a flowing sample solution. The liquid stream is placed in contact with an electrical discharge that is able to volatilize peptides in the sample, prior to being further ionized and fragmented in the plasma. When using high discharge currents of 70 mA or more, the spectra resemble those of electrospray techniques. Such spectra have the dominant features of singly and doubly protonated molecular ions; at lower currents, near 35 mA, the peptides are fragmented into fragment types not previously observed at atmospheric pressure. This technique and the theory behind it are still under exploration.

	Some of this work has also led to patent filings and issued patents. In an issued US patent, for example, Shelley and coworkers describe a method for determining counterfeit electronic components using surface analysis via ambient sampling mass spectrometry and chemometric analysis (7). The method desorbs and ionizes material from the surface of a test sample without pretreatment. The resultant ions are detected and compared to known standards. The final result yields a confidence number related to a true or counterfeit electronic component. In other work, representing a break from fundamental research in plasma-based ambient mass spectrometry, Shelley and colleagues described a novel use of metal–organic cages (MOCs) to encapsulate Pt-based anticancer agents forming drug-containing nanoparticles for improved drug delivery (8).

	In his most recent research, Shelley and his team have demonstrated rapid analysis of solid metal complexes by coupling a FAPA source with differential mobility spectrometry–mass spectrometry (DMS-MS) (9). Metal-ligand complexes are important for environmental, security, industrial, and biological applications. A hybrid system was constructed and shown to be able to perform quantitative analysis of nickel acetylacetonate. This analysis was performed following deposition of nickel acetylacetonate complexes on mesh substrates. It is essential that any analytical method for this type of application be capable of performing analyses in situ. This further requires the development of field screening devices based on portable mass spectrometry (MS). Thus, FAPA sources are of high interest as portable tools. However, a limitation of FAPA alone may be the matrix effects of ambient chemicals interfering with the analyte of interest, leading to false positives. To reduce interference, DMS was used to enable additional post-ionization separation. To provide the optimum design, a FAPA desorption/ionization source was coupled with DMS for metal-ion speciation. The coupled FAPA-DMS device was able to separate and detect cobalt and nickel complexes with acetylacetonate in standard mixtures. The results of this research suggest a method for in situ applications for inorganic complex analyses.

In further research on ambient MS, Shelley and his group applied cross-correlation data analysis for improved background removal and analyte-ion recognition (10). A cross-correlation–based approach was used to extract chemical information within time domain data to identify mass-spectral peaks within a single analysis dataset. Ions originating from background or ambient species were detected and removed from the mass spectra. The result of the chemometric process was to simplify the mass spectra by removing 70% of the complexity arising from background ions. The process not only removes background ions, but is able to differentiate and categorize analyte ions based on their time-domain profiles. In some cases, this mathematical process removed more than 98% of spurious mass-spectral complexity. The cross-correlation approach was tested for varying sample introduction systems, as well as for different ionization sources. The fully automated data processing approach, which was written inhouse, can be completed within a few seconds. This approach provides a powerful additional tool for analyte separation for single mass-spectrometric analysis runs.

	Engelhard cited this work among Shelley’s most important contributions so far. “Jake’s approach simplifies analyte identification in complex samples, especially in non-targeted analysis, and provides an additional dimension of analyte separation,” he says. “A brilliant study, and a great contribution to our field.”

	Shelley’s group has also extended the application of plasma-based ADI-MS for the analysis of liquid-crystal displays (LCDs), (11). LCDs are globally the most widely used display technology in use today. Because the precise chemical composition of LCDs is critical to their long-term performance, many analytical techniques have been employed for quality analysis of LCDs, including gas chromatography–mass spectrometry (GC–MS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), high-resolution microscopy, and high-performance liquid chromatography (HPLC). Shelley’s research has shown that ADI-MS can provide faster, accurate, and less expensive analysis.

	Many in the community also remarked on Shelley’s personal qualities, including his ability to bring scientists together. R. Kenneth (Ken) Marcus, the University Professor of Chemistry at Clemson University, says that Shelley has a unique ability to work with diverse teams of measurement scientists-atomic spectroscopists, mass spectrometrists, and metallomics researchers.

	Karst agrees. “Dr. Shelley is one of the rare persons who combine a very positive personality with an unusual capability of critical thinking and the ability to critique in a way which is understood by others as extremely helpful, stimulating, and encouraging, rather than offensive,” he said, adding that Shelley has “a love for science, a passion for teaching, and an enjoyable personality.”

	Shelley’s speaking skills have also won him praise. Karst called Shelley “a truly outstanding lecturer,” an impression that led Karst to invite him to give a plenary lecture at the European Winter Conference on Plasma Spectrochemistry in 2015, which was held at the University of Münster.

	Maria Montes Bayón, a professor of analytical chemistry at the University of Oviedo, in Spain, agrees. “Didactically, Jake is excellent,” she said. “And simultaneously, he is entertaining while going deep into the science he is explaining.”

	Englhard also raised this point. “Jake has the ability to explain what he does in the lab very efficiently, not only to his fellow scientists, but also to visitors that would come regularly to the lab at Indiana University,” he said, citing a time when they were both in the Hieftje laboratory. “Jake would ask visitors to hand him a U.S. dollar bill for a quick mass spectrometry experiment. He would use the FAPA-MS instrument to directly probe the bill and was almost always able to show that he could detect traces of cocaine on any of the U.S. dollar bills while a Euro bill (that was provided by me) did not show traces of cocaine.”

	Given Shelley’s excellent work to date, his colleagues look forward to the future developments of his career. Hieftje says that Shelley’s future includes, “more publications, outstanding students, additional awards, and a top international reputation.” Montes-Bayón believes Shelley’s knowledge of instrumentation physics will propel him forward in plasma spectroscopy. Ray’s vision focuses on MS, and teaching. “I expect Jake to continue to do great work in mass spectrometry, and to mentor the next generation of leaders in spectrometry,” he said, describing Shelley as dynamic, hard-working, and insightful.

	Engelhard anticipates Shelley’s expansion into other areas. “I think that we will see Jake blossom as he expands his research interest into other types of mass spectrometry, optical spectroscopy, instrumentation, and automated data processing,” he said. Marcus takes an even broader view, believing that Shelley’s career will lead to “putting together the varied experiences of his past, to produce totally-new measurement tools.” Cooks expects Shelley to continue in the proud tradition of Gary Hieftje and Indiana University. “I look forward to watching his future successes.”

	Chan, in turn, sees no bounds, “For Jake, the sky is the limit,” he said.

		G.C.Y. Chan, J.T. Shelley, J.S. Wiley, A.U. Jackson, C. Engelhard, R.G. Cooks, and G.M. Hieftje, 

		J.S. Wiley, J.T. Shelley, and R.G. Cooks, 

		S.P. Badal, S.D. Michalak, G.C-Y Chan, and J.T. Shelley, 

		J.T. Shelley, S.P. Badal, C. Engelhard, and H. Hayen, 

		A.J. Schwartz, J.T.  Shelley, C.L. Walton, K.L. Williams, and G.M. Hieftje,

		G.M. Hieftje, S.J. Ray, K.P. Pfeuffer, J.T. Shelley, and N.J. Caldwell, Indiana University Research and Technology Corp., Ambient sampling mass spectrometry and chemometric analysis for screening encapsulated electronic and electrical components for counterfeits. U.S. Patent 9,607,306 (2017).

		Z. Yue, H. Wang, D.J. Bowers, M. Gao, M. Stilgenbauer, F. Nielsen, J.T. Shelley, and Y.R. Zheng, 

		I. Ayodeji, T. Vazquez, L. Song, J. Donovan, T. Evans-Nguyen, S.P. Badal, G.M. MacLean, and J.T. Shelley, 

		C. Kuhlmann, J.T. Shelley, and C. Engelhard, 

 (2019). doi.org/10.1007/s13361-019-02280-w

 is the Senior Technical Editor of Spectroscopy. Direct correspondence to 

Author | Jerome Workman, Jr.

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