Prolog
A bit tired of the usual lists, I tried to put my favorite scientific projects in prose.
If you prefer to have it all at a glance, the usual publication list and cv is only a click away!
In the small romantic city of Göttingen, nowadays right in the heart of Germany, I took my first fledgeling steps in science, studying physics and maths at the Georgia Augusta. The Georgia Augusta is a moderately young university founded in the mid 1700's by a king of Hannover of same name. Unusual at the time was the strong focus on the hard sciences and the university of Göttingen has seen such eminent mathematicians and physicists as Carl-Friedrich Gauß, Felix Klein, David Hilbert, Richard Courant, and Emmy Noether, as well as Wilhelm Weber, James Franck, and Max Born in the past two hundred years. Nowadays the university is a public school (no tuition!) with 35,000 students. Student life in Göttingen is famous for the numerous student pubs, many of them located in historic old basements like Blue Note, Trou, Theaterkeller, to name a few of my old favorite hang-outs.
For my undergraduate and graduate thesis projects I joined the group of J. Peter Toennies at the Max-Planck-Institut für Strömungsforschung, right across the street from the Physics Institute. Working in Ekkehard Hulpke’s lab, I learned to deal with ultra-high vacuum equipment and surface preparation. The ultimate research tool in the Toennies Group were ultrasonic beams of thermal helium atoms that can be scattered from molecules, surfaces, and atom clusters. I used helium scattering to measure atom diffraction patterns and surface phonons. My thesis project was to study the structure and dynamics of the reconstruction of the clean molybdenum(001) surface. In the course of my studies I could show that the molly surface reconstruction was correlated with the softening of a surface phonon [1], [2], and that the reconstruction was high-order commensurate [3]. Due to the high reactivity of the molly surface, especially with regard to hydrogen, such studies are a major tour de force in vacuum science.
Still curious about the molly reconstruction, I joined Ian Robinson at AT&T Bell Labs, in order to learn about surface x-ray diffraction, which has been my field of study ever since. Working with Ian and Peter Eng at beamline X16A at the National Synchrotron Light Source, it took two blood-sweat-and-tears experiments to finally observe the molly reconstruction. We found that Mo(001) features the peculiar zig-zag reconstruction known from W(001), however, the zig-zag chains are interspersed with periodic anti-phase domain boundaries [4] yielding the high-order commensurate structure. The greatest things about living in Eastern Long Island were the ocean beaches, hiking on the Forks, and contra-dancing at Smithtown. And there I met Melanie ...
The first successes got me hooked to synchrotron radiation and decided to extend my stay. I found a follow-up postdoc position at Rutgers with Jane Hinch. Here we had two projects: building a new helium atom beam spectrometer at Rutgers and studying the etching of silicon surfaces with HF and buffered HF solutions in-situ exploiting surface x-ray diffraction at Brookhaven.
After Rutgers I accepted a postdoctoral position with Robert Feidenhans’l and Mourits Nielsen at Risø National Lab in Denmark. I joined the group at a very productive phase with multiple collaborations and a large diversity of research projects, for instance surfaces of organic crystals [5], electrochemistry [6] and studies of laser-deposited thin films of high-Tc superconductors [7]. Apart from these projects that were covering new grounds in the Risø group at the time, structure determination of so-called deep reconstructions on semiconductor surfaces was the main research effort. In such systems, the reconstruction at the surface, either by itself or induced by adsorbtion of a metal atom, results in distortions of the semiconductor lattice over several successive layers. A nice example - and a very hard nut to crack - presented the c(2x8) reconstruction of the InSb(001) surface [8]. So every couple of weeks we packed up our stationwagon and took the 5-hour trip to the Risø diffractometer at HASYLAB's BW2 beamline, to take another data set on samples expertly prepared by Robert Johnson and his students at HASYLAB.
During this time, a project very dear to my heart was in-situ sputtering of a germanium(001) surface [9]. The non-equilibrium roughening dynamics of this surface features a dramatic change in surface signal at a sharp transition temperature. The project was a collaboration with my fellow-postdocs Peter Eng (AT&T) and Erik Landemark (Risø) as well as Mourits Nielsen and we were among the first users of the Surface Diffraction Beamline (ID3) of the ESRF.
The greatest Danish achievement of all, for Melanie and me, was the birth of our son Max. Right at the beginning of the hot summer of 1995, the summer of the red poppy fields, just after sunrise ... If you ever think, you are a tough synchrotron scientist, and can run night shifts without end, wait until your first baby is born ...
The European Mecca of synchrotron radiation science, the ESRF, should become my next employer: I got hired as a beamline scientist in the Troïka-Group (ID10), to build the second branch of Troïka. Gerhard Grübel, Andreas Freund, and Jens Als-Nielsen had pioneered the idea of utilizing an x-ray transparent single crystal of diamond as a beam splitter, in order to multiplex an undulator beamline into multiple independent stations. The Troika II station was to be a multi-purpose x-ray scattering beamline for the study of liquid and solid surfaces.
Inspired by the Troika II misson, I shifted my own field of interest to organic thin films, when the beamline first became operative. Organic thin films is a rapidly developing interdisciplinary field with applications in physics, materials science, and chemistry, and reaching into biology and medicine. The in-house research program at ID10B was carried by me and three postdocs, Nathalie Boudet, Bernd Struth, and Oleg Konovalov. As my first steps into this new field I started out with something that felt somewhat familiar to me with my solid state background: thin crystalline films of electroluminescent molecules, as are of interest in molecular electronics applications such as organic light-emitting diodes or lasers and organic transistors. I developed grazing-incidence diffraction techniques to study the microstructure of such films which feature 3D growth and are charactrized by small crystallites with preferential orientations [10, 11].
Becoming more adventurous, I started looking into nanoparticles on glass and on the water surface as well as into monolayers on GaAs and silver films. A special challenge was the development of the high-resolution grazing-incidence small-angle scattering (GISAXS) technique which yielded very nice first results on properties of ultrathin polymer films, extending my point of view from the Ångstrøm scale to mesoscopic scales of several 100 nm [12, 13]. The initial Troika II research program featured a close interaction of instrument development and scientific applications and evolved in close collaboration with the beamline postdocs, collaborators, and the ID10B User Community within two very intense and exciting years. I am indebted to all persons involved. An account of experimental achievements at ID10B was given in various contributions at the workshop “Surface Science 2000: Self-Organization at Interfaces and in Thin Films” at ESRF in February 2000 [14] and later summarized in an instrumentation paper [14a].
With one year left on my ESRF contract, I started looking into new options. I chose to accept an offer to work as a senior staff scientist on constructing G-line with Joel Brock and Alan Pauling at Cornell University. G-line features a new 50 pole wiggler at Cornell’s CESR storage ring, supplying three experimental hutches simultaneously with intense x-ray beams. G-line was built on an NSF grant by a group of researchers from within Cornell faculty and supplies primarily beamtime to these groups. The first batch of Cornell students received hands-on training in designing and building beamline components and instrumentation needed for their research. A first comprehensive overview of current research projects was presented recently at the workshop “Science at Cornell’s G-line" in November 2000 [15]. Essential for this ambitious research program was the development of the high-flux beamline optics based on fucosed multilayer beams, as pioneered by Randy Headrick and coworkers at CHESS A2.
My own research efforts on the microstructure characterization of organic thin films continued at various CHESS beamlines. A break-through GISAXS study revealed detailed insights in lamellar thin films of diblock copolymers [15a]. I also continued my collaboration with Ed Kintzel to study the adsorption of phenylenes on alkali halide surfaces, a continuation of studies I had started at ESRF. At G2 station chemistry student Daniel Blasini and I built a grazing-incidence reciprocal space mapping set-up, in its latest incarnation comprising a psi-circle kappa diffractometer and a 100 mm gas detector with matching Soller collimator [16]. We have been able to characterize a variety of different types of "real" surfaces such as 3D powders of device-grade amorphous organic semicondutors [17], polycrystalline materials on fuel cell electrode surfaces [18], 2D powders in organic crystals and Langmuir-Blodgett films [16], and single crystalline samples of small molecules on alkali halide surfaces [19].
In 2004, after installation of the G-line main optics, I accepted to switch over to CHESS D-line. After 4 years of beamline construction, and adopting baby Mauro with my wife in 2003, I was ready for less operations responsibilities and more research. Nonetheless, under my lead D-line was gradually completely renovated - motion control system, hutch instrumentation (2nd optical table, ISO-100 modular flight path), cabling, and control area - while maintaining a full user load. I managed to develop the CHESS GISAXS user community [20-24] and have gotten recently into GIWAXS, which nicely complements the GID system at G2 - less resolution, but quicker data acquisition. The latest facet of D-line developments is scattering of microbeams making use of the in-house x-ray capillaries developed by Don Bilderback's group [25]. This project was started to gain experience with future scattering technologies, as required for the Cornell Energy-Recovery Linac project (ERL).
References
[1] E. Hulpke and D.-M. Smilgies, Phys. Rev. B 40, 1338 (1989).
[2] E. Hulpke and D.-M. Smilgies, Phys. Rev. B42, 9203 (1990).
[3] E. Hulpke and D.-M. Smilgies, Phys. Rev. B43, 1260 (1991).
[4] D.-M. Smilgies, P.J. Eng, and I.K. Robinson, Phys. Rev. Lett. 70, 1291 (1993).
[5] D. Gidalevitz et al., Angew. Chem. Int. Ed. Engl. 36, 955 (1997);
Surface Review and Letters 4, 721 (1997).
[6] D.-M. Smilgies et al., Surf. Sci. 367, 40 (1996).
[7] Q.D. Jiang et al., Solid State Comm. 98, 157 (1996).
[8] C. Kumpf et al., Physical Review Letters 86, 3586 (2001).
[9] D.-M. Smilgies et al., Europhys. Lett. 38, 447 (1997).
[10] D.-M. Smilgies et al., J. Cryst. Growth 220, 88-95 (2000).
[11] E.J. Kintzel et al., J. Vac. Sci. Technol. A 19, 1270 (2001).
[12] J.S. Gutmann et al., Physica B 283, 40 (2000).
[13] Peter Müller-Buschbaum et al., Macromolecules 34, 1369 (2001).
[14] Surf 2000 Workshop, Program Announcement on the Web
[14a] D.-M. Smilgies et al, J. Synch. Rad., 2005.
[15] Workshop "Science at Cornell's G-line", Program
[16] D.E. Nowak et al., Rev. Sci. Instrum. 2006
[17] D.R. Blasini et al., J. Mat. Chem. Hot Paper2007
[18] D.R. Blasini et al., to be published
[19] D.-M. Smilgies et al., J. Synch. Rad. 2005
[20] C. Tang et al., JACS Communication, 2005.
[21] R. Zhang et al., JACS Communication, 2005.
[22] A. Saunders et al., Nanoletters, 2006.
[23] P. Busch et al., Macromolecules, 2006.
[24] P. Busch et al., Macromolecules, 2007.
[25] J. Lamb et al., J. Appl. Cryst., 2006.
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