My personal chemical biography

Who would have thought that I would end up working up close with so many elements? Not me. What follows is my own personal chemical biography. Not two of them are the same.

It all began with argon. Before that, it was all points, ideal particles and fields for me. For four years I got to know argon inside out: its electronic structure, its excited levels and emission spectrum, and its so called plasma chemistry, its electron impact cross sections and the excitation exchanges between atoms. In contrast helium is like Ar’s little brother, but without the Ramsauer minimum in the momentum transfer cross section that is characteristic for the rest of noble gases.

Hydrogen, oxygen, and nitrogen are also from my plasma days, with hydrogen always occupying an special place, since knowing the plasma chemistry of hydrogen means that you know about more than 90% of the visible matter in the universe. Think of an hour long lecture about the plasma chemistry of hydrogen: the chemistry of the universe. While carbon is nowadays mainly associated with graphene, for me carbon will always be linked to the emission spectra of molecules such as C2, CH and CN, kind of like watching mostly silent films in the era of 3D movies.

Silicon was the other element of my PhD, in the shape of tetramethylsilane, SiO2 and silicones that I deposited by plasma enhanced CVD, while I also got my first brushes with titanium and copper when I did some characterization of TiO2 and Cu during my short stay at Cambridge.

Elementwise, Bochum introduced me to fluorine, mostly through the growth of teflon from fluorocarbon precursors like C3F8, though during my PhD I also had a brush with HF before I even knew what it could do to you. But as I became the resident chemist in a group of physicists (let’s ignore for a second the fact that I have an unlikely background in theoretical physics), I also worked with aluminum, sodium, and potassium, in the context of a makeshift aluminum anodising reactor to insulate parts of our microplasma discharges.

When I moved to Urbana my chemical universe expanded once more to incorporate boron to my personal periodic table, in the shape of different metal diborides, mostly HfB2 and TiB2 and the single source precursors. That way hafnium also made it into the list. Magnesium, erbium, and again titanium also featured strongly in the context of the synthesis of MgO, Er2O3, and TiO2 by CVD. While I did not work directly with them for CVD purposes, my awareness of copper and ruthenium also increased during that time. Instead, I worked with copper, gold, and silver in the context of evaporation and/or sputtering. Copper, tungsten, gallium, and arsenic also gain a small mention in the theory section in the context of CVD and ellipsometry.

And then I got to Argonne and things exploded: aluminum, zinc as the oxides and the Al:ZnO, chlorine from TiCl4, indium and tin for transparent conducting oxides ITO and In2O3, yttrium for Y2O3, europium and erbium as dopant and rare earth oxides, zirconium and again hafnium for the gate dielectrics ZrO2 and HfO2. I became very good at growing NiO, which added nickel to my list, worked with Nb for Nb:TiO2, revisited by old friend magnesium for MgO, and the noble metals Ir and Pt also in the context of Atomic Layer Deposition. My work in dye sensitized solar cells expanded my range to iodine, and also ruthenium from the bipyridyl dyes, and lithium in the shape of some additives for my home-made liquid electrolytes. Chlorine crept back as a catalyst for sol-gel synthesis. Other elements like antimony, iron, molybdenum, and manganese were also added to my collection as minor additions as the main components of materials that I’ve characterized at some point and, although I didn’t synthesize them, I’ve worked with Sb:SnO2 nanoparticles and one picture of them is actually featured in Argonne’s collection. Molybdenum and manganese have featured strongly in my experiments at the Advanced Photon Source.

More recently, gallium is playing an important role in the shape of GaN, and silicon and carbon are back again for SiC in the context of my wide bandgap semiconductor research projects: theory section. Other projects have led me to add iron, sulfur, samarium, and cobalt to my belt, in the context of magnetic materials. Finally, helium is back and it is helping me measure the work function and ionization potential of some of the materials I’ve grown.

In addition to these elements, as you share many hours with other people their elements become also a little bit yours. For me cerium is always linked to cerium oxide films deposited by e-beam evaporation, palladium to the coupling of aryl halides with thiols, ruthenium in the context of metal deposition by CVD.

When I look back at the list of all the elements I have worked with I cannot help looking at the gaps. What could I do to widen my list of transition metals? Which future projects will allow me to move across the lanthanide series? Will I be able to distinguish them as vividly as I distinguish other elements like Ti, Zr, Hf, each coming with its own project and background? It may well be that I end up working with elements that I have already worked with, bringing more nuance and complexity to the way I see them. In any event, my perception of the elements is irreversibly linked to my research, much like the way I see particles, equations, and fields.