The research program of Brian Robertson’s group is directed towards:
- magnetic and electronic thin films, nanoscale wires and devices
- electron probe-based characterization and fabrication for materials research and processing
Electron beam-induced deposition in a field-emission scanning transmission electron microscope (STEM) has been used to create wires under 4 nm wide. With a newly designed system to deliver molecules of source compounds to substrates with much greater control than previously, we are now studying how precisely the elemental composition can be chosen and what limits exist for nanofabrication using electrons. Conducting all phases of part of this research in the STEM allows comprehensive fabrication, microstructural characterization and performance evaluation without atmospheric contamination. This work is being applied in making nanowires for wiring up nano-objects, for exploring electromigration in nano-interconnects in situ, and for making novel dielectric barriers, especially high-resistivity boron carbide, for spintronic tunnel junction research.
Plasma-enhanced chemical vapor deposition (PECVD) is being used to coat substrates up to 3” wafer size with semiconducting boron carbide (of approximate composition B5C and quite distinct from traditional B4C) and related materials. Recent success includes the invention and proof of success of a new class of novel, very efficient, solid-state, neutron detectors, in collaboration with Professors Dowben and Adenwalla, that have many, broad ranging applications. Semiconducting boron carbide has important attributes for robust neutron detectors: large thermal neutron capture cross-section (effective target area for capture); low gamma ray sensitivity because of its low atomic number; and energetic neutron capture products that lose their energy within 5 micrometers and generate > 2 x 105 electron-hole pairs for each captured neutron.
The collaboration of Profs. Paul Blum (microbiologist, UNL School of Biological Sciences) and Shireen Adenwalla (solid-state and neutron physicist, UNL Physics and Astronomy) is working on fabricating novel arrays of magnetic and other structures by a novel route that involves deposition of material through the pores of self-assembled templates formed by microbiologically-derived macromolecules.
STEM methods are being developed to obtain microstructural / micromagnetic correlations in magnetic materials – by a novel differential phase contrast form of Lorentz electron microscopy and by spin polarized low energy electrons at the < 10 nm scale. New development of high-stability electron energy loss spectroscopy will complement these methods at closer to the atomic scale.
Integral to these research areas is intensive use of electron microscopes for microstructural characterization in the NCMN Central Facility for Electron Microscopy (http://www.unl.edu/ncmn/cfem/ ), which Brian Robertson established and now guides and which is a core NCMN research facility.
Robertson’s research is funded mostly by grants from the National Science Foundation, the Office of Naval Research, and the Nebraska Research Initiative.
Saenger, MF (Saenger, M. F.); Hoing, T (Hoeing, T.); Robertson, BW (Robertson, B. W.); Billa, RB (Billa, R. B.); Hofmann, T (Hofmann, T.); Schubert, E (Schubert, E.); Schubert, M (Schubert, M.), Polaron and phonon properties in proton intercalated amorphous tungsten oxide thin films, PHYSICAL REVIEW B, 78 (24): Art. No. 245205 Dec 2008
Harken, AD (Harken, A. D.); Robertson, BW (Robertson, B. W.), Comparative modelling of performance limits of solid-state neutron detectors based on planar B-rich capture layers, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 39 (23): 4961-4968 Dec 7 2006
Caruso, AN (Caruso, A. N.); Dowben, PA (Dowben, P. A.); Balkir, S (Balkir, S.); Schemm, N (Schemm, Nathan); Osberg, K (Osberg, Kevin); Fairchild, RW (Fairchild, R. W.); Flores, OB (Flores, Oscar Barrios); Balaz, S (Balaz, Snjezana); Harken, AD (Harken, A. D.); Robertson, BW (Robertson, B. W.); Brand, JI (Brand, J. I.), The all boron carbide diode neutron detector: Comparison with theory, MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 135 (2):129-133 Nov 25 2006
Lundstedt, C; Harken, A; Day, E; Robertson, BW; Adenwalla, S, Modeling solid-state boron carbide low energy neutron detectors, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 562 (1): 380-388 Jun 15 2006
L. Bernard, J. Monson, A. Sokolov, Zong-Yuan Liu, C.-S. Yang, P. A. Dowben, B. Doudin, A. Harken, P. Welsch, and B. W. Robertson, “Magnetoresistance in Boron Carbide Junctions”, Appl. Phys. Lett. 83, 3743-5 (2003).
Qiangmin Wei, Brian W. Robertson, “Thermodynamic Determination of the Cation Distribution in NixMn1-g-xFe2+gO4 Ferrites”, J. Solid State Chemistry 176, 279-283 (2003).
B. W. Robertson, S. Adenwalla, A. Harken, P. Welsch, J. I. Brand, P .A. Dowben and J. P. Claassen, “A Class of Boron-Rich Solid-State Neutron Detectors”, Appl. Phys. Lett. 80, 3644-6 (2002).
S. Adenwalla, P. Welsch, A. Harken, J. I. Brand, A. Sezer, and B. W. Robertson, “High Temperature Boron Carbide / n-Silicon Carbide Heterojunction Diodes”, Appl. Phys. Lett. 79, 4357-9 (2001).
H. Jiang, C.N. Borca, Bo Xu, and B. W. Robertson, “Fabrication of 2- and 3-Dimensional Nanostructures”, Int. J. Mod. Phys. B 15 (24 & 25), 3207-3213 (2001).