Nanoscale Engineering Science & Technology

Publications related to nano-science and nano-technology published by University of Dayton faculty and University of Dayton Research Institute staff members that have used NEST lab facilities are listed in this secton. As an additional reference, an extensive number of polymer nanocomposite analysis papers have been reviewed by Dr. Alex Morgan.

"Functionalization of carbon nanofibers through electron beam irradiation", Carbon 48, 2037-2046 (2010). M. C. Evora, D. Klosterman, K. Lafdi, L. Li, and J.L Abot

Abstract: Carbon nanofibers were oxidized in air at 350 °C under the influence of a 3 MeV electron beam at doses of 1000 and 3500 kGy. XPS analysis showed that oxygen was readily incorporated on the surface: the O 1s/C 1s increased apporimately by a factor of three when the carbon nanofibers were irradiated at 3500 kGy. The oxidized nanofibers exhibited better dispersion than as-received nanofibers when mixed with water/methanol (50% v/v). Raman spectroscopy revealed that the ID/IG ratios were statistically unchanged for all samples because the damage on the nanofiber surface was highly localized and did not lead to modifications on the bulk carbon nanofiber structure. On the other hand, SEM, TEM and AFM images illustrated that cutting, welding, and collapse may occur on the structure of irradiated nanofibers. BET analysis showed that the surface area of irradiated samples did not significantly increase, probably because the radiation process may lead to micro-porosity formation. The temperature during irradiation had no effect on the nanofibers' surface and the thermal stability of the irradiated samples was determined to be lower.

"Sonochemically Assisted Thermal Decomposition of Alane N,N-Dimethylethylamine with Titanium (IV) Isopropoxide in the Presence of Oleic Acid to Yield Air-Stable and Size-Selective Aluminum Core-Shell Nanoparticles", J. Phys. Chem. Lett.C 113, 500-503 (2009). K. A. Shiral Fernando, Marcus J. Smith, Barbara A. Harruff, William K. Lewis, Elena A. Guliants, and Christopher E. Bunker.

Abstract: Using sonochemistry to provide the thermal energy and mixing, we demonstrate the ability to synthesize air-stable aluminum nanoparticles of two different size distributions from the titanium-catalyzed thermal decomposition of alane. Characterization data indicate the presence of spherical face-centered-cubic aluminum nanoparticles with average sizes of either 5 or 30 nm that are capped with an organic shell. The average size of the nanoparticles correlates with the concentration of the passivation agent oleic acid, where a higher concentration results in smaller particles. Thermal analysis data demonstrates that at elevated temperatures (>550°C), these particles react via a typical aluminum oxidation mechanism, whereas at low temperatures (<550°C), the behavior of these particles is unique and directly related to the presence of the organic shell.

"Generalized ellipsometry for monoclinic absorbing materials: determination of optical constants of Cr columnar thin films", Optics Letters 34, 992 - 994 (2009). D. Schmidt, B. Booso, T. Hofmann, E. Schubert, A. Sarangan and M. Schubert.

Abstract: Generalized spectroscopic ellipsometry is used to determine the form-induced biregringence and monoclinic optical constants of chromium columnar thin films. The slanted nanocolumns were deposited by glancing angle deposition under 85° incidence and are tilted from the surface normal. Dichroism measured for wavelengths from 400 to 1000 nm renders the Cr nanocolumns monoclinic absorbing crystals with c axis along the nanocolumns axis, b axis parallel to the film interface, and 74.8° monoclinic angle between a and c axes. the columnar thin film reveals anomalous optical dispersion, extreme berefringence, and strong dichroism and differs entirely from bulk chromium.

"Structural analysis and electronic properties of a homodinuclear erbium(III) complex bridged by the polyazine ligand 2,2'-bipyrimidine", Inorg. Chem. Comm. 12, 509-510 (2009). Albert Fratini and Shawn Swavey.

Abstract: Structural analysis of the previously reported homodinuclear complex [Er (tfa)₃]₂ (where tfa = 4,4,4-trifluoro-1-(2 furyl)-1,3-butanedione and bpm = 2,2'-bipyrimidine) synthesized by reaction of two equivalents of ErCl₃ with six equivalents of tfa and one equivalent of bpm in a basic ethanol solution is presented. X-ray quality crystals were grown by slow evaporations of concentrated methanol solution containing the complex. The complex crystallizes in the monoclinic space group P2₁/n, with a planar bpm ligand. The erbium-erbium distance is 6.715 A. Each erbium center is eight coordinate from six tfa oxygens and two bpm nitrogens. Electronic transitions of concentrated solutions of the complex reveal three sharp lines corresponding to the 4f - 4f^*transitions at 486 nm, 520 nm and 657 nm with the lowest energy transition corresponding to ⁴I_15/2--> ⁴F_9/2. Journal homepage: www.elsevier.com/locate/inoche.

Abstract: Femtosecond lasers have a unique ability of processing bulk transparent materials for various applications such as micromachining, waveguide manufacturing, and photonic bandgap structures just to name a few. These applications depend on the formation of micron or submicron size features that are known to be index modifications to the bulk substrate [H. Guo, H. Jiang, Y. Fang, C. Peng, H. Yang, Y. Li, Q. Gong, J. Opt. A: Pure Appl Opt. 6 (2004) 787]. To the best of our knowledge the physical understanding of how these index-modified features are formed is still unknown, but many good theories exist such as Petite et al. [G. Petite, P. Daguzan, S. Guizard, P. Martin, in: IEEE Annual Report Conference on Electrical Insulation and Dielectric Phenomena, vol. 15, IEEE, 1995, pp. 40-44] of Tien et al [A. Tien, S. Backus, H. Kapteyn, M. Murnane, G. Mourou, Phys. Rev. Lett. 83 (1999) 3883]. In this letter the question on the physical cause for index changes is investigated by the combined efforts between Wright-Patterson AFB and the University of Dayton using numerous imaging equipment such as TEM, AFM, MSOM, Nomarski microscopy, X-ray crystallography, Raman spectroscopy, and even diffraction efficiency experiments. With all the combined imaging equipment this research is able to present valuable data and to deduce plausible theories of the physics of the index modification mechanism. Journal homepage: www.elsevier.com/locate/pla.

Abstract: The large-scale practical application of fuel cells will be difficult to realize if the expensive platinum-based electrocatalysts for oxygen reduction reactions (ORRs) cannot be replaced by other efficient, low-cost, and stable electrodes. Here, we report that vertically aligned nitrogen-containing carbon nanotubes (VA-CNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells. In air-saturated 0.1 molar potassium hydroxide, we observed a steady-state output potential of -80 millivolts and a current density of 4.1 milliamps per square centimeter at -0.22 volts, compared with -85 millivolts and 1.1 milliamps per square centimeter at -0.20 volts for a platinum-carbon electrode. The incorporation of electron-accepting nitrogen atoms in the conjugated nanotube carbon plane appears to impart a relatively high positive charge density on adjacent carbon atoms. This effect, coupled with aligning the NCNTs, provides a four-electron pathway for the ORR on VA-CNTs with a superb performance. Journal homepage: www.sciencemag.org.

Abstract: Well dispersed Ag nanoparticles have been formed by a process denoted Through Film Ablation. The nanoparticles were deposited on room temperature substrates, had a most probable size of 1 nm, and were not agglomerated. The nanoparticle deposit produced by this process showed no evidence of the larger particles commonly observed from conventional pulsed laser ablation that uses a bulk target. Synthesis of nanoparticles by Through Thin Film Ablation should be possible for any material that can be made as a thin film target and may enable the unique properties of isolated, non-agglomerated nanoparticles to be exploited more fully. Journal homepage: www.elsevier.com/locate/matlet.

Abstract: We report the optical characterization of a metal wiregrid micropolarizer array for IR imaging polarimetry. The micropolarizers are designed for operation in the 1.5 - 5.0 micron band with a specially designed thin SiO₂ layer between the silicon substrate and the wiregrids to improve the performance at the shorter wavelengths. Deep-UV projection lithography is used to fabricate 140-nm-deep wiregrids with a 400 nm period. The extinction ratio and the transmission coefficient are measured with a tunable IR laser. A TM transmission coefficient greater than 70% with an extinction ratio greater than 10⁴ is achieved for the midwave-IR region while maintaining an extinction ratio better than 10² for the near-IR region above 1.5 microns.

"Are Diamond Nanoparticles Cytotoxic?", J. Phys. Chem. B Condens. Matter Mater. Surf. Interfaces Biophys. 2007 Jan 11; 111 (1): 2-7. Amanda M. Schrand, Houjin Huang, Cataleya Carlson, John J. Schlager, Eiji Oh sawa, Saber M. Hussain, and Liming Dai.

Abstract: Finely divided carbon particles, including charcoal, lampblack, and diamond particles, have been used for ornamental and official tattoos since ancient times. With the recent development in nanoscience and nanotechnology, carbon-based nanomaterials (e.g., fullerenes, nanotubes, nanodiamonds) attract a great deal of interest. Owing to their low chemical reactivity and unique physical properties, nanodiamonds could be useful in a variety of biological applications such as carriers for drugs, genes, or proteins; novel imaging techniques; coatings for implantable materials; and biosensors and biomedical nanorobots. Therefore, it is essential to ascertain the possible hazards of nanodiamonds to humans and other biological systems. We have, for the first time, assessed the cytotoxicity of nanodiamonds ranging in size from 2 to 10 nm. Assays of cell viability such as mitochondrial function (MTT) and luminescent ATP production showed that nanodiamonds were not toxic to a variety of cell types. Furthermore, nanodiamonds did not produce significant reactive oxygen species. Cells can grow on nanodiamond-coated substrates without morphological changes compared to controls. These results suggest that nanodiamonds could be ideal for many biological applications in a diverse range of cell types. For the full text of this article see http://pubs.acs.org/cgi-bin/sample.cgi/jpcbfk/asap/pdf/jp066387v.pdf