Materials Science

Peptidic coating for gold nanospheres multifunctionalizable with photostable and photolabile moieties

by Valerio Voliani

Journal of Materials Chemistry 2012 (RSC), doi: 10.1039/C2JM31782F

A single-step method to coat and trifunctionalize water-dispersed gold nanospheres (AuNss) with
carboxylic acids,... more A single-step method to coat and trifunctionalize water-dispersed gold nanospheres (AuNss) with
carboxylic acids, amines, and alkynes is reported. The coating is based on a mix of two hexa-peptides,
differing only in the C-terminal amino acid. The process yields AuNss that are non-cytotoxic, stable in
physiological environments, and which present three reactive surface groups allowing rapid, selective,
10 and modular conjugation (click- and peptide-reactions) to virtually any chosen biomolecule or
fluorophore. Conjugated nanostructures were analyzed in vitro and in living cells. Confocal imaging and
colocalization analyses demonstrate the presence and reactivity of three different types of covalent bonds
with payloads: two of these are photostable while one bond is photolabile and can be cleaved by *Wpower
irradiation with a 561-nm cw laser.

High Density Growth of Indium seeded Silicon Nanowires in the Vapor phase of a High Boiling Point Solvent

by Hugh Geaney

Mechanical and Microstructural Properties of Sheep Hydroxyapatite (SHA)-Niobium Oxide Composites

by Nermin Demirkol

Hydroxyapatite nano-barium-strontium-titaniumoxide composites

by Nermin Demirkol

Comparison of Mechanical Properties of Sheep Hydroxyapatite (SHA) and Commercial Synthetic Hydroxyapatite (CSHA) MgO Composites

by Nermin Demirkol

Single and Mixed Phase TiO2 Powders by Excess Hydrolysis of Titanium Alkoxide

by Material Science

To investigate excess-hydrolysis of titanium alkoxides, TiO2 powders were fabricated from titanium-tetra-isopropoxide... more To investigate excess-hydrolysis of titanium alkoxides, TiO2 powders were fabricated from titanium-tetra-isopropoxide using 6:1 and 100:1 H2O:Ti (r) ratios. Powders were dried and fired at a range of temperatures (≤800ºC). Hydroxylation and organic content in powders were characterised using ATR-FTIR, laser Raman microspectroscopy, and elemental microanalysis; surface area and pore size distribution were evaluated using N2 gas adsorption; phase composition was analysed using XRD and laser Raman microspectroscopy; and crystallite size was evaluated by XRD, TEM and SEM. Results showed near-complete hydrolysis in a predominantly aqueous medium (r = 100), resulting in precipitated crystalline powders exhibiting brookite and anatase, which begin to transform to rutile below 500°C. Powders precipitated in a predominantly organic medium (r = 6) underwent partial hydrolysis, were highly porous and exhibited an amorphous structure, with crystallisation of anatase occurring at ~300°C and transformation to rutile beginning at 500°-600°C.

Highly Rigid and Stable Porous Cu(I) Metal-Organic Framework with Reversible Single-Crystal-to-Single-Crystal Structural Transformation

by Sudip Mohapatra

Analytical Bond-Order Potential for the Cadmium Telluride Binary System

by Bryan Wong

Physical Review B, 85, 115206 (2012)

Experimental evaluation of ochre-containing mastic in the hafting of hunting armatures

by Andrew Zipkin

Andrew M. Zipkin1,2; Alison S. Brooks2,3

Hominid Paleobiology Doctoral Program, 2. Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, The George Washington University, 3. Human Origins Program, National Museum of Natural History, Smithsonian Institution

    The use of ochre by humans prior to the Upper Palaeolithic and Later Stone Age has often been cited in... more     The use of ochre by humans prior to the Upper Palaeolithic and Later Stone Age has often been cited in studies addressing the origins of symbolic behavior.  Ochreous minerals such as hematite, specularite, and goethite are functionally united by the unique and vibrantly colored streak produced by each.  Analyses of the Middle Stone Age (MSA) assemblage from Twin Rivers, Zambia dated to 270 – 170 kya have concluded that humans preferentially acquired specularite from more distant sources when other ochreous minerals were available locally.  Some researchers have interpreted this evidence as indicative of MSA humans following an ochre acquisition strategy mediated by visual properties and suggestive of a symbolic application. However, experimental archaeology and residue analysis of MSA points from Sibudu Cave, South Africa dated to 60- 26 kya indicates that ochre possessed utilitarian value during the MSA, specifically as a loading agent in mastic used for hafting composite tools.  Here we report on a study addressing the hypothesis that ochre was used primarily in a non-symbolic capacity and that such a role may explain the patterns observed in the Twin Rivers assemblage.                                                                     

    Specifically, our experiment evaluated the performance of hematite (red ochre), hematite and quartz (yellow ochre), specularite, and quartz sand (non-ochre control) as loading agents in Acacia senegal resin-based mastic.  Hardness testing of air-dried mastics after storage under either high or low humidity conditions indicated that yellow ochre mastic is particularly hygroscopic and susceptible to moisture-induced degradation.  In addition, 58 knapped triangular points were hafted onto cedar arrow shafts using the four mastic recipes.  Arrows were evaluated as hunting weapons through shooting into a goat carcass with a recurve bow.  Results indicate that no significant difference in successful target penetration exists among arrows hafted with the different mastics.  However, specularite-containing mastic proved significantly more durable than the other mastics tested with 58% of specularite-hafted arrows classified as immediately reusable after firing.  Besides its possible worth due to visual properties, specularite may have been a valued ingredient in the mastic of composite tools intended for reliable, repeated use.

Drawing graphene nanoribbons on SiC by ion implantation

by Sefaattin Tongay

Cover Image Feb13th Applied Physics Letters

The most downloaded article in Feb 2012 and 3rd downloaded article in March 2012

We describe a straightforward technique for selective graphene growth and nanoribbon production onto 4H- and 6H-SiC.... more We describe a straightforward technique for selective graphene growth and nanoribbon production onto 4H- and 6H-SiC. The technique presented is as easy as ion implanting regions where graphene layers are desired followed by annealing to 100 degrees C below the graphitization temperature (T-G) of SiC. We find that ion implantation of SiC lowers the T-G, allowing selective graphene growth at temperatures below the T-G of pristine SiC and above T-G of implanted SiC. This results in an approach for patterning device structures ranging from a couple tens of nanometers to microns in size without using conventional lithography and chemical processing. (C) 2012 American Institute of Physics. [doi:10.1063/1.3682479]

Extinction of ferromagnetism in highly ordered pyrolytic graphite by annealing

by Sefaattin Tongay

We report that the ferromagnetism of highly ordered pyrolytic graphite (HOPG) samples as measured by hysteretic... more We report that the ferromagnetism of highly ordered pyrolytic graphite (HOPG) samples as measured by hysteretic magnetization loops can be diminished and eventually extinguished with sufficiently long high vacuum anneals at temperatures on the order of 2300 °C. Concomitant with the extinction of ferromagnetism, we observe an anneal-induced increase in grain size (accompanied by possible edge reconstruction) confirmed by X-ray diffraction measurements and improved transport properties, including lower in-plane and out-of-plane resistivity, higher electron and hole mobility and improved charge compensation. The implied reduction of defects and vacancies by annealing suggests that the ferromagnetism of pristine HOPG is correlated with localized states located at zigzag edges, vacancies and related defects.

Effect of immersion in water partially alkali-activated materials obtained of tungsten mine waste mud

by Antonio Albuquerque

Silva I., Castro-Gomes J. & Albuquerque A.
Construction and Building Materials, V. 35, 117-124.

Alkali-activated binders can be obtained using several sources of alumino-silicate materials, from calcinatedmore Alkali-activated binders can be obtained using several sources of alumino-silicate materials, from calcinated
clays, like kaolin, to industrial by-products, such as fly ash and, more recently, to calcinated waste mud from mining activities. The technology to obtain alkali-activated binders, also designated as geopolymers, is gaining increasing interest, since, in some cases, the properties of geopolymeric materials
are superior to other existing cementitious systems. The research presented in this paper intends to deepen
the knowledge regarding the properties of geopolymeric materials obtained using tungsten mining waste mud, particularly to study its behaviour after being immersed in water. However, in the current work, focus is given to follow compressive strength results in partially alkali-activated samples immersed in water, during different curing periods of time. Energy Dispersive X-ray Spectroscopy (EDS), X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy analysis (FTIR) were also utilised to investigate changes in the microstructure at different conditions of water immersion. A significant decrease in compressive strength occurring after 24 h of immersion in water was found out, of specific partially alkali-activated materials, despite of its initial high compressive strength after 35 days curing, at different temperatures.

Evaluation of the stability of waste-based geopolymeric artificial aggregates for wastewater treatment processes under different curing conditions

by Antonio Albuquerque

I. Silva, J. Castro-Gomes, A. Albuquerque
Advances in Science and Technology, 2010, V. 69, 86-91.

Waste geopolymeric artificial aggregates (WGA) with different atomic ratios of mining waste mud/Na2SiO (4 to 5) and... more Waste geopolymeric artificial aggregates (WGA) with different atomic ratios of mining waste mud/Na2SiO (4 to 5) and Na2SiO/NaOH (1.25 to 5) were produced using curing temperatures of 20ºC and 130ºC and its structural stability and pH variation after immersion in water was observed during 3 months. Results showed that WGA with mud/Na2SiO and Na2SiO/NaOH of 5 and 4, respectively, cured at 20ºC presented good stability in water and pH decreased from 10 to 7
in 24 days. Compressive strength was determined in additional samples cured at 20ºC and 80ºC in dry conditions, for 13 curing ages and 15 water immersion periods (up to 14 weeks). Results of this second stage showed that increasing temperature to 80ºC accelerated compressive strength gain but
only during the first 3 weeks (up to 15.4 MPa). After 24 h in water compressive strength decreased to half of the initial values determined in dry conditions in all samples and, therefore, the increase of temperature did not bring benefits to WGA strength in water. Regardless the curing temperature and the dry curing age comprehensive strength stabilizes between 1 MPa and 2 MPa after 4 weeks immersion in water, which are values that makes WGA suitable to be used as bed material for wastewater treatment processes.

Potential for reuse of tungsten mining waste-rock in technical-artistic value added products

by Antonio Albuquerque

J. Castro-Gomes, A. Silva, R. Cano, J. Suarez, A. Albuquerque
Journal of Cleaner Production, 2012, V. 25, 34-41

Mining and quarrying activities in Europe generate approximately 55% of total industrial wastes, according to a recent... more Mining and quarrying activities in Europe generate approximately 55% of total industrial wastes, according to a recent Eurostat report. Most of these wastes are directly dumped on land or deposited in landfill sites. The first solution may lead to negative environmental impacts on land (removal of vegetation, deforestation, land slope changes and increased risk of erosion), water (pollutant transport through surface runoff, soil infiltration and contamination of water resources), may lead to the contamination of agricultural goods and may impose risks on human health. In Portugal, about 20% of industrial waste produced originates from mines and quarries, particularly from Panasqueira mining, one of the largest tungsten mines in the world. Currently, Panasqueira mining generates almost 100 tonnes of waste-rock, per day. Such waste-rock have accumulated over a number of years into very large heaps and it is desirable to seek new economic solutions that can contribute towards their reuse. In this context, this work discusses the potential for reuse of waste-rock piles of Panasqueira tungsten mine, which may be a case statement to be followed. The proposed solution described in this paper consists in developing innovative polymer-based composite materials, obtained from non-contaminated waste-rock tailings. Such materials must have suitable properties for technical-artistic value added applications, such as conservation, restoration and/or rehabilitation of historic monuments, sculptures, decorative and architectural intervention, or simply as materials for building revetments.

Mineral wastes geopolymeric artificial aggregates as alternative materials for wastewater-treatment processes - Study of structural stability and pH variation in water

by Antonio Albuquerque

Silva I., Castro-Gomes J. & Albuquerque A.
Journal of Materials in Civil Engineering, V. 24, Nº 6, 1-6.

Artificial aggregates produced from mine waste geopolymeric binders were studied as a potential substrate for... more Artificial aggregates produced from mine waste geopolymeric binders were studied as a potential substrate for fixed-film
wastewater-treatment processes (biofilm reactors). Waste geopolymeric artificial aggregates (WGA) of 2–3 cm in size were produced using geopolymeric mine waste mud as a precursor and both sodium silicate and sodium hydroxide as alkaline activators. Seven mixtures were produced with different atomic ratios of sodium silicate to sodium hydroxide (S/H) and of precursor (waste mud) to sodium silicate (P/S), using curing temperatures of 20°C and 130°C, for a total of 112 samples. Structural stability and pH variation after immersion in water were observed over an 18-week period. The results showed that the initial water pH decreased with the increase of the curing time, taking between 17 and 42 days to reach pH 8. The mixture cured at 20°C for 28 days appears to be suitable for use as a substrate for biofilm reactors because the initial water pH was one of the lowest (approximately pH 10), and the time necessary to stabilize it to approximately pH 8 was only 17 days.

Microstructural Design of Multiphase Advanced High Strength Steels

by Alison Mark

A.F. Mark, D. Boyd, J. McDermid, D. Embury, Recent Developments in Advanced High Strength Steels Processing, COM’08 (keynote presentation), Winnipeg, MB, Canada (2008) 45-56.

Thickness Evolution of the Microstructural and Optical Properties of Si:H Films in the Amorphous-to-Microcrystalline Phase Transition Region

by Joshua Pearce

A. S. Ferlauto, G.M. Ferreira, R.J. Koval, J.M. Pearce, C.R. Wronski, R. W. Collins, M.M. Al-Jassim, and K.M. Jones, "Thickness Evolution of the Microstructural and Optical Properties of Si:H Films in the Amorphous-to-Microcrystalline Phase Transition Region" 29th IEEE Photovoltaic Specialists Conf. Proc., (IEEE, 2002) pp. 1076-1081, 2002.

The ability to characterize the phase of the intrinsic (i) layers incorporated into amorphous silicon [a-Si:H] and... more The ability to characterize the phase of the intrinsic (i) layers incorporated into amorphous silicon [a-Si:H] and microcrystalline silicon [μc-Si:H] thin film solar cells is critically important for cell optimization. In this research, a new method has been developed to extract the thickness evolution of the μc-Si:H volume fraction in mixed phase amorphous + microcrystalline silicon [(a+μc)-Si:H] i-layers. This method is based on real time spectroscopic ellipsometry measurements performed during plasma enhanced chemical vapor deposition of the films. In the analysis, the thickness at which crystallites first nucleate from the a-Si:H phase can be estimated, as well as the nucleation density and microcrystallite cone angle. The results show very good correlations with structural and electronic device measurements.

Effects on Amorphous Silicon Photovoltaic Performance from High-temperature Annealing Pulses in Photovoltaic Thermal Hybrid Devices

by Joshua Pearce

M.J.M. Pathak, J.M. Pearce and, S.J. Harrison, “Effects on Amorphous Silicon Photovoltaic Performance from High-temperature Annealing Pulses in Photovoltaic Thermal Hybrid Devices” Solar Energy Materials and Solar Cells, 100, pp. 199-203 (2012). http://dx.doi.org/10.1016/j.solmat.2012.01.015

There is a renewed interest in photovoltaic solar thermal (PVT) hybrid systems, which harvest solar energy for heat... more There is a renewed interest in photovoltaic solar thermal (PVT) hybrid systems, which harvest solar energy for heat and electricity. Typically, a main focus of a PVT system is to cool the photovoltaic (PV) cells to improve the electrical performance, however, this causes the thermal component to under-perform compared to a solar thermal collector. The low temperature coefficients of amorphous silicon (a-Si:H) allow for the PV cells to be operated at higher temperatures and are a potential candidate for a more symbiotic PVT system. The fundamental challenge of a-Si:H PV is light-induced degradation known as the Staebler-Wronski effect (SWE). Fortunately, SWE is reversible and the a-Si:H PV efficiency can be returned to its initial state if the cell is annealed. Thus an opportunity exists to deposit a-Si:H directly on the solar thermal absorber plate where the cells could reach the high temperatures required for annealing.

In this study, this opportunity is explored experimentally. First a-Si:H PV cells were annealed for 1 hour at 100\degreeC on a 12 hour cycle and for the remaining time the cells were degraded at 50\degreeC in order to simulate stagnation of a PVT system for 1 hour once a day. It was found that, when comparing the cells after stabilization at normal 50\degreeC degradation, this annealing sequence resulted in a 10.6% energy gain when compared to a cell that was only degraded at 50\degreeC.

Analytical Model for the Optical Functions of Indium Gallium Nitride with Application to Thin Film Solar Photovoltaic Cells

by Joshua Pearce

Dirk V. P. McLaughlin and J.M. Pearce, “Analytical Model for the Optical Functions of Indium Gallium Nitride with Application to Thin Film Solar Photovoltaic Cells”, Materials Science and Engineering: B, 177, 239-244 (2012).

This paper presents the preliminary results of optical characterization using spectroscopic ellipsometry of wurtzite... more This paper presents the preliminary results of optical characterization using spectroscopic ellipsometry of wurtzite indium gallium nitride (InxGa1-xN) thin films with medium indium content (0.38<x<0.68) that were deposited on silicon dioxide using plasma-enhanced evaporation. A Kramers-Kronig consistent parametric analytical model using Gaussian oscillators to describe the absorption spectra has been developed to extract the real and imaginary components of the dielectric function ({\epsilon}1, {\epsilon}2) of InxGa1-xN films. Scanning electron microscope (SEM) images are presented to examine film microstructure and verify film thicknesses determined from ellipsometry modelling. This fitting procedure, model, and parameters can be employed in the future to extract physical parameters from ellipsometric data from other InxGa1-xN films.

Thermochemistry of Alane Complexes for Hydrogen Storage: A Theoretical and Experimental Comparison

by Bryan Wong

Journal of Physical Chemistry C, 115, 7778 (2011)