Nanoscale Engineering Science & Technology

In this section of the site, you will find summaries of nanoscale research either being undertaken at the NEST Laboratory itself and/or conducted by researchers locally, nationally, and internationally. An extensive list of polymer nanocomposite analysis papers have been reviewed by Dr. Alex Morgan. Recent articles related to nano-science and nano-technology published by University of Dayton faculty and University of Dayton Research Institute staff members are listed below.

"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.

"Polymer and aligned carbon nanotube nanocomposites and nanodevices", SAMPE Journal 43 (6), 38-46 (2007). Liangti Qu, Wei Chen, Liming Dai, Ajit Roy and Tia Benson Tolle.

Abstract: We have previously develope a simple pyrolytic method for large-scale production of aligned carbon nanotube arrays perpendicular to the substrate. These aligned carbon nanotube arrays can be transferred onto various substrates of particular interes in either a patterned or non-patterned fashion. The well-aligned structure provides additional advantages for not only an efficient device construction but also surface functionalization (both the inner and outer wall). The surface functionalization of aligned carbon nanotubes is particularly attractive, as it allows surface characteristics of the aligned carbon nanotubes to be tuned to meet specific requirements for particular applications while their alignment structure can be largely retained. These aligned carbon nanotubes with tunable surface characteristics are of great significance to various practical applications, included nanotube sensors and optoelectronics. For instance, we have previously immobilized glucose oxidase (GOX) onto the aligned multi-wall carbon nanotube arrays by electropolymerization of pyrrole in the presence of GOX. The resultant GOX-containing polypyrrole-carbon nanotube coaxial nanowires were shown to be promising new sensing active materials for making advanced glucose sensors with a high sensitivity. Also, single-strand DNA chains have recently been chemically grafted onto aligned carbon nanotube electrodes, leading to novel aligned carbon nanotube-DNA sensors of a high sensitivity and selectivity for probing complementaary DNA and target DNA chains of specific sequences. More recently, we have also developed a rational approach to partially coat perpendicularly-aligned carbon nanotube arrays with an appropriate polymer thin film along their tube length to create synergetic effects, which provide the basis for developing novel sensors for the detection of chemical vapors, thermal and mechanical stimuli with a high sensitivity, good selectivity, excellent environmental stability, and low power consumption. In this talk, we will summarize our work on the preparation of polymer and aligned carbon nanotube nanocomposites and nanodevices. Potential applications of polymer and aligned carbon nanotube nanocomposites in other areas will also be discussed.

"Electrophoresis coating of titanium dioxide on aligned carbon nanotubes for controlled syntheses of photoelectronic nanomaterials", Advanced Materials 19 (9), 1239 (2007). Yaodong Yang, Liangti Qu, Liming Dai, Tae-Sik Kang and Michael Durstock.

Abstract: Using electrophoresis for TiO2 coating and photoexcited electrons for metal-nanoparticle deposition, a facile method for the development of aligned coaxial nanowires of carbon nanotubes sheathed with TiO2, and well-defined TiO2 nanomembranes decorated with and without metal nanoparticles, is developed. The TiO2-based nanostructures show fast photocurrent responses and possess unique photo-induced electron-transfer properties.

"A facile synthesis of aliphatic thio surfactant with tunable length as a stabilizer of gold nanoparticles in organic solvents", J. Colloid and Interface Sci. 308, 381-384 (2007). Xiaoli Zhou, Jouliana M. El Khoury, Liangti Qu, Liming Dai and Quan Li.

Abstract: Three new aliphatic thiol surfactants were synthesized by reacting alkyl bromide with hexamethyldisilathiane under a mild condition. This approach provides an easy access for the direct synthesis of various different length thiol surfactants which play a crucial role in tuning the properties of gold nanoparticles. Gold nanoparticles encapsulated with one of our synthetic thiols were prepared and well-characterized by H-NMR, UV-vis, FTIR and TEM. The hybrid nanoparticles are very stable in both organic solvents and the solid state.

"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