Scanning Photoelectron Spectromicroscopy (SPES): Topography and Chemistry of Natural Specimens with 1 nm Resolution
Pupa Gilbert1 (née Gelsomina De Stasio), John C. H. Spence2, and Ernst Bauer2
1Department of Physics,
University of Wisconsin-Madison
2Department of Physics and
Astronomy, Arizona State University-Tempe
The possibility of using 1-nm diameter photon beams with tunable energy between 100 and 4000 eV is extremely exciting and will revolutionize the present modes to analyze proteins, minerals and biominerals. The current scanning electron microscope (SEM) gives excellent topographic images but has very limited spectroscopic capability. Photoelectron emission spectromicroscopy (X-PEEM) (1) has excellent x-ray absorption near-edge structure (XANES) spectroscopy performance, due to the tunability of synchrotron photon sources. PEEM, however, has very limited depth of field, and samples must be flat (or polished) to be imaged with this approach. Combining the advantages of the SEM and PEEM has been thus far only a dream, but with the advent of the energy recovery linac (ERL) at Cornell it may become a reality.
With the 1-nm diameter x-ray beam expected from the ERL we can now think of doing Scanning PhotoElectron Spectromicroscopy (SPES) with 10 times better resolution than in the past (2), that is, scan the sample position (or the beam position using a rastering plane mirror) and detect photoelectrons with a large acceptance angle detector. It is also possible to add a parallelizer magnetic lens (3,4) to increase the collection angle for secondary electron imaging, and therefore increase the detection efficiency. This microscope will produce “seemingly” 3D images of the sample surface topography, much like the SEM, but will also have chemical resolution, much like the PEEM, because the photon energy is tunable, enabling XANES and EXAFS with 1-nm resolution.
SPES will not only be a high resolution, high-sensitivity instrument, but will also enable by XANES the organic and inorganic molecular structure (5,6). Minerals, biominerals, cells and tissues will be analyzed in their natural appearance, without the need of embedding and polishing them. Biominerals, including biofilms (7,8), bone, teeth, shells (9), as well as cells and tissues (10,11) will be imaged and analyzed in their 3-dimensional natural form.
References:
1. Frazer, Girasole, Wiese, Franz, and De Stasio; Ultramicroscopy 99, 87-94 (2004)
2. Gunther, Kaulich, Gregoratti, and Kiskinova; Progr. In Surf. Sci. 70, 187-260 (2002)
3. Kruit and Venables; Ultramicroscopy 25, 183-194 (1988)
4. Hembree and Venables; Ultramicroscopy 47, 109-120 (1992)
5. Johnson, Olabisi, Metzler, Gilbert, Frazer, McKenzie, Aiken, and Gilbert. Submitted 2006
6. Metzler, Abrecht, Olabisi, Ariosa, Johnson, Frazer, Coppersmith, and Gilbert. Submitted 2006
7. Labrenz, Druschel, Thomsen-Ebert, Gilbert, Welch, Kemner, Logan, Summons, De Stasio, Bond, Lai, Kelly, and Banfield; Science 290, 1744-47 (2000)
8. Chan*, De Stasio*, Welch, Girasole, Frazer, Nesterova, Fakra, and Banfield; Science 303, 1656-1658 (2004)
9. Gilbert and Frazer, Abrecht; The Organic-mineral Interface in Biominerals. Reviews in Mineralogy and Geochemistry. In: Molecular Geomicrobiology. Vol 59. JF Banfield, KH Nealson, J. Cervini-Silva (eds), Mineralogical Society of America, Washington DC, p 157-185 (2005)
10. De Stasio, Casalbore, Pallini, Gilbert, Sanita’, Ciotti, Rosi, Festinesi, Larocca, Rinelli, Perret, Mogk, Perfetti, Mehta, and Mercanti; Cancer Research 61, 4272-4277 (2001)
11. De Stasio, Rajesh, Ford, Daniels, Erhardt, Frazer, Tyliszczak, Gilles, Conhaim, Howard, Fowler, Estève, and Mehta;. Clinical Cancer Research 12, 206-213 (2006)
