We present herein a joint physical/physico-chemical study and, more specifically, the first application of Matrix Assisted Laser Desorption Ionization coupled with Time of Flight Mass Spectrometry (MALDI-TOF-MS) to analyze small-sized ZnO quantum dots (QDs) (2.8-3.1 nm diameter range) synthesized by sol-gel chemistry and stabilized through an aminosilane coating. A careful investigation of the stability of ZnO QDs was initiated once these dots were dispersed in different media (water, biological buffer) for a period up to 3 weeks. Positive ion mode mass spectra MALDI-TOF-MS combined with optical spectrometry was used to monitor the stability of ZnO QDs when aging. Such a unique combination of MALDI-TOF-MS and physico-chemical techniques is likely to bring new insights into the structure analysis, the stability and consequently the potential toxicity of QDs.

The surfaces of inorganic substrates containing hydroxyl groups can be adapted to a variety of physical and chemical requirements by reaction with cyclic azasilanes. The moderately-strained ring structure of cyclic azasilanes containing adjacent Si and N atoms, along with the high oxophilicity of silicon, enables the high reactivity towards available hydroxyl groups on all siliceous surfaces investigated, including amorphous silica and borosilicate glass. The reaction occurs quantitatively at room temperature, requires no catalyst and has no byproducts. This investigation looks specifically at the reaction kinetics by means of DRIFT spectroscopy and quantifies extent of reaction by TGA. The less sterically-hindered the Si–N bond, the faster the reaction occurs. In all cases, the reaction is essentially complete in less than one minute. This study provides the first confirmation that the rate and extent of reaction without catalysis or byproducts of cyclic azasilanes conforms to the Sharpless requirements for “click chemistry” and can be deemed “click chemistry for surfaces.”

CZT is a semiconductor material that promises to be a good candidate for uncooled gamma radiation detectors. However, to date, we are yet to overcome the technological difficulties in production of large size, defect-free CZT crystals. The most common problem is accumulation of Tellurium precipitates as microscopic inclusions. These inclusions influence the charge collection through charge trapping and electric field distortion. We employed high energy transmission X-ray diffraction techniques to study the quality of the CdZnTe crystals grown by Bridgman Technique. Crystallinity and defects within two different growth set-ups, i.e. with and without choked seeding, were compared by imaging the crystal orientation topography with white beam X-ray diffraction topography (WBXDT). The X-ray diffraction topography results show high correlation with large-area infrared transmission images of the crystals. Grain boundaries that are highly decorated with Te inclusions are observed. Characteristic Te inclusion arrangements as a result of growth conditions are discussed. We also measured the electronic properties of the detectors fabricated from ingots grown using two Bridgman processes, and observed a reduction in electrical resistivity of choked-seeding-grown CdZnTe crystals. Our results show that although choked seeding technique holds a promise in the realization of high quality mono-crystalline CdZnTe, current growth parameters must be improved to obtain defect-free crystals. These results are helpful to attain optimal seeding process for Bridgman-growth of large single crystals of CdZnTe.

In this study a process analysis of the melting process of solid particles in a bath of same composition is performed using both experimental information and theoretical computations. An experimental setup was used to measure the thermal histories and to follow the evolution with time of the size of solid metallic spherical particles being melted in a metallic bath of same composition. For such a purpose, pure aluminum was used during the experiments for both solid particles and liquid bath. A mathematical model was also developed based on first principles of heat transfer to simulate the melting kinetics of a cold metallic spherical particle immersed in a hot liquid bath of same composition. The mathematical model was reasonably validated when compared against the experimental results obtained in this work. A process analysis of the melting process was performed to determine the effect of the initial temperature and size of the solid particle, the bath temperature and the convective heat transfer coefficient on the melting time and on the energy consumption.

The analysis showed that the variable presenting the most significant effect on both the melting time and the energy consumption is the convective heat transfer coefficient between the particle and the bath, since an increment in such a parameter accelerates the melting process and saves energy. Therefore, proper stirring of the bath is highly recommended to enhance the melting of metallic alloying additions in the metallic baths.

Differences on physicochemical properties of poly(pentadecanolide), PPDL, synthesized by enzymatic ring opening polymerization at two different temperatures, 70 C and 90 C, using Novozyme-430 were assessed. PPDL synthesized at 90°C presents lower molecular weight and crystallinity than the one prepared at 70°C. It was detected by FTIR that PPDL synthesized at 90°C presents a large amorphous phase with more terminal OH groups. A difference in the melting and crystallization behavior was detected by differential scanning calorimetry, DSC, where the melting of the PPDL synthesized at 90°C presents multiple melting and crystallization events at lower temperature than those exhibit by PPDL synthesized at 70°C which presents a well defined single melting and crystallization event. The differences in melting behavior are attributed to the presence of a larger amorphous phase in PPDL synthesized at 90°C due to increased number of terminal OH groups that disrupt the crystalline structure. Thermal stability is also higher in PPDL synthesized at 70°C since the onset of decomposition starts 50°C above that observed in PPDL obtained at 70°C.

In this report, we describe a process for achieving atomically smooth, few-layer thick, hexagonal boron nitride (h-BN) films on sapphire substrates by MOCVD, using Triethylboron (TEB) and NH3 as precursors. Two different growth modes have been observed depending on the V/III ratio. Three-dimensional (3D) island growth is dominant in the low V/III range; in this range growth rate decreases with increasing deposition temperature. This island growth mode transitions to a self-terminating growth mode when V/III > 2000, over the entire deposition temperature range studied (i.e. 1000-1080oC). Raman spectroscopy verifies the h-BN phase of these films, and atomic force microscopy measurements confirm that the surfaces are smooth and continuous, even over atomic steps on the surface of the substrate. Using X-ray reflectance measurements, the thickness of each film grown under a range of conditions and times was determined to consistently terminate at 1.6nm, with a variation of less than 0.2 nm. Thus we have identified a self-terminating growth mode that enables robust synthesis of h-BN with highly uniform and reliable thickness on non-metal catalyzed substrates. Furthermore, this self-terminating growth behavior has shown signs of transitioning to continuous growth as deposition temperature increases.

Tumors of the distal and proximal femur are treated by total femur resection. A hip disarticulation sometimes is a result of massive trauma with crush injuries to the lower extremity. This article discusses a system designed for patient rehabilitation with bilateral hip disarticulations. The prosthetics designed allowed a patient to attain natural gait suspended between parallel articulate crutches with the body weight supported between the crutches. The design is patent pending and it could be used in people with a simple ankle sprain, people with partial immobilizations in inferior members, or people with bilateral hip disarticulation. The final design system allows patients with bilateral hip replacement or partial immobilizations to attain mobility in a natural way.

Concerning a materials ability to convert heat to electrical energy, the electrical power factor S 2 /ρ as well as the thermal conductivity at elevated temperatures are of special interest. Since Flash experiments measure the thermal diffusivity and standard steady-state heat-flow experiments are inaccurate at elevated temperatures due to radiation errors inherent to this technique, direct and accurate thermal conductivity data on type-I clathrate single crystals at elevated temperatures are scarce in literature. Here we report 3ω thermal conductivity data on single crystalline Ba8Cu5.09Ge40.91 (BCG), La1.23Ba6.99Au5.91Si39.87, and Ce1.06Ba6.91Au5.56Si40.47 in the temperature range between 80 and 330 K, and specific heat data on BCG between 2 and 300 K. The comparison of our room temperature phonon thermal conductivity data (κ ph ) to results on transition metal (TM) free type-I clathrates in terms of the guest free space (R free) suggests a stronger dependence of κ ph on R free for the clathrates containing TM elements.

We report effective passivation of silicon surfaces by heating single crystalline silicon substrates in liquid water at 110°C for 1 h. High values of photo-induced effective minority carrier lifetime τeff in the range from 1.9x10-4 to 1.8x10-3 s were obtained for the n-type samples with resistivity in the range from 1.7 to 18.1 Ωcm. τeff ranged from 8.3x10-4 to 3.1x10-3 s and from 1.2x10-4 to 6.0x10-4 s over the area of 4 inch sized 17.0 Ωcm n- and 15.0 Ωcm p-type samples, respectively. The heat treatment in liquid water at 110°C for 1 h resulted in low surface recombination velocities ranging from 7 to 34 cm/s and from 49 to 250 cm/s for those 4 inch sized n- and p-type samples, respectively. The thickness of the passivation layer was estimated to be approximate only 0.7 nm. Metal-insulator-semiconductor type solar cell was demonstrated with Al and Au metal formation on the passivated surface. Rectified current voltage and solar cell characteristics were observed. Open circuit voltage of 0.47 V was obtained under AM 1.5 light illumination at 100 mW/cm2.

In this work, the structure and conductive structure of perfluorinated sulfonated ionomers were investigated by tapping mode, material sensitive atomic force microscopy (AFM). At cross section of membranes, large ordered lamellar-like areas were found. From adhesion force mappings, approximately 50 nm large water-rich areas could be identified by their low adhesion. These areas were interpreted as ionically conductive phase. They appeared circular and isolated before any forced current flow through the sample (activation). After activation, branched, long and flat ionically conductive phase structures in direction of applied voltage were found. They were interpreted as the formation of a continuous ionically conducting network formed by the current flow. In a second part, the material sensitive imaging was used to analyze the distribution of ionomer and platinum covered carbon particles in fuel cell electrodes. The analysis was based on the high adhesion of ionomers compared to the carbon supported catalyst particles.

This contribution presents a critical review about some materials used in dosimetry and the interest that has emerged on topaz recently. In addition, results about the feasibility for synthesizing topaz by the HYSY-CVD route using Na2SiF6 and Al2O3 are shown. Synthesis tests in nitrogen atmosphere were conducted varying temperature (700 and 750°C) and time (60 and 90 min) while maintaining constant the amounts of Al2O3 and Na2SiF6. The microstructural characterization by XRD, SEM and EDS revealed the succesful formation of topaz and aluminium fluoride.

The determination of the long-term stability and corrosion of vitrified nuclear waste is an important aspect of research for the U.S. Department of Energy (DOE). It is necessary to understand the rate and mechanisms of Nuclear Waste Glass (NWG) corrosion to determine whether or not the glassy matrix will be able to retain radionuclides for the required repository performance time period. Glass corrosion and the rate of glass corrosions is determined by both chemical and microscopy. Electron Microprobe Analysis (EPMA) is a common and powerful method utilized in the examination of the chemographic difference between corroded and uncorroded NGWs. In this work, two forms of quantitative and semi-quantitative EPMA methods are defined by optimizing the instruments counting statistics against a standard glass and NIST minerals that have compositions similar to the glasses under examination. Data collected on both the planar and cross-sectioned surfaces of an unaltered simulated NWG by Standard based Wavelength Dispersive Spectroscopy (WDS) was found to be comparable to the theoretical composition of the glass. Conventional standardless Energy Dispersive Spectroscopy (EDS) data collected on the same surfaces was not comparable. However, standard-based EDS analysis is shown to be able to discriminate between unaltered and corroded glass surfaces.

The necessity to a priori predict the durability of high level nuclear waste (HLW) glasses on extended time scales has led to a variety of modeling approaches based primarily on solution (leachate) concentrations. The glass composition and structure control the leachate and the gel compositions which in turn control what reaction products form: the leached layer is a hydrogel and reacts with the solution (leachate) to form secondary phases some of which cause accelerated glass dissolution which is undesirable. Glasses with molar excess alkali that is not bound to glass forming (Al,Fe,B)O4 structural groups in the glass resume accelerated leaching. The hydrogels of the glasses that resume accelerated leaching at long times contain excess alkali and the leachates contain excess strong base, [SB]ex. The [SB]ex further accelerates aluminosilicate gel aging into analcime with time. Glasses with no excess molar structural alkali do not resume accelerated leaching: the glass generates weak acids, [WA], in the leachate favoring hydrogel aging into clays. These data indicate that the gel layer transforms to secondary phases in situ in response to interactions with the chemistry of a continuously evolving leachate.

Calcium chlorosilicate (Ca3(SiO4)Cl2) is seen as a potential host phase for the immobilization of Cl-rich wastes arising from pyrochemical reprocessing, a waste stream often containing a mix of both di- and trivalent cations. Substitution of trivalent cations into the lattice requires some form of charge compensation to ensure the lattice remains charge neutral overall. Whilst previous work has only examined this through the formation of Ca vacancies, this study investigates the feasibility of charge-balancing via the substitution of a monovalent cation onto the Ca sites of the lattice. To that end, a series of static lattice calculations were performed to determine the site selectivity of monovalent cations of differing size when substituted onto the Ca sites of the calcium chlorosilicate lattice and the solution energies for the overall substitution processes compared with those for charge compensation via vacancy formation. In all cases the monovalent charge-balancing species shows a clear preference for substitution onto the Ca1 site in the calcium chlorosilicate lattice. The solution energy of the substitution process increases with the increasing ionic radii of both the mono- and trivalent species as the steric stresses associated with substitution of larger cations than the Ca2+ host increase. As such, only charge-balancing using Li+, Na+ or K+ is more favourable than via formation of a Ca vacancy.

LaNi(1-x)FexO3 (LNF) compounds, with 0.0 ≤ x ≤ 0.4, have interesting physical properties such as high ionic and electronic conductivity, good catalytic activity for oxygen reduction, and thermodynamic compatibility with the YSZ electrolyte, which makes them potential candidates for SOFCs (solid oxides fuel cells) cathodes. Order for these excellent properties are achieved, it is necessary to ensure the presence of the homogeneous phase LNF. The methods for preparing these compounds influence the formation and stabilization of the homogeneous phase and therefore the physical properties of these oxides. For this reason, this work deals with the synthesis of the family of compounds LNF and the correlation between the synthesis and the physical properties obtained. In this context, LNF compounds were synthesized by a modified Pechini method for production of powders. Two different synthetic routes were employed, changing the source of nickel: nickel acetate and nickel nitrate. In order to study the thermal evolution of the LNF phase in these compounds, thermal analysis (DTG) and X-ray diffraction (XRD) were performed. The XRD was verified that the series of compounds synthesized by nickel acetate originated monophasic samples different from those obtained with nickel nitrate. We studied the influence of time and sintering temperature on the superficial characteristics of the samples and it was observed the reduction in sintering time allowed obtaining powders of perovskite phase, with grain sizes and smaller clusters than what was observed in the compound -treated for 10 h. To characterize the particle size, the powders were characterized by curves absorption/desorption (BET). The results also show that heat treatment for shorter times resulted in decreased particle size as well as increase the surface area of the compounds.

We have demonstrated some facile ways to fabricate the large area polymer surfaces with varying roughness followed by studying their anti-reflective properties. One of the approaches is based on electrospun nanofibers deposited on a substrate in an uneven non-woven matrix. This electrospun fabric was used as a master template to fabricate the negative replica of the fibers by soft lithography generating the roughness in polydimethylsiloxane (PDMS) surfaces. The second approach is based on biomimicking of flower petals. Petals are used as a master template to transfer surface features with hierarchical roughness over PDMS surface using replica moulding. As fabricated polymer surfaces with varied roughness have then tested for their anti-reflective properties using UV-VIS spectroscopy over a wide range of wavelengths and angles of incidence of light. These measurements show near zero reflection of patterned PDMS surfaces as compared to planar PDMS. This omnidirectional broadband anti-reflection behaviour of polymer surfaces can be used in wide variety of engineering applications including in solar cells.

In this work we produce atomically thin carbon nanostructures which have a disk-like shape when deposited on a substrate. These nanostructures have intermediate characteristics between a graphene island and a molecular compound and have the potentiality to be used either as they are, or to become building blocks for functional materials or to be manipulated and engineered into composite layered structures.

The carbon nanostructures are produced in a premixed ethylene/air flame with a slight excess of fuel with respect to the stoichiometric value. The size distribution of the produced compounds in aerosol phase has been measured on line by means of a differential mobility analyzer (DMA) and topographic images of the structures deposited on mica disks were obtained by Atomic Force Microscopy. Raman spectroscopy and XPS have been used to characterize their structure and the electronic and optical properties were obtained combining on-line photoionization measurements with Cyclic Voltammetry, light absorption and photoluminescence.

When deposited on the mica substrate the carbon compounds assume the shape of an atomically thin disk with in plane diameter of about 20 nm. Carbon nano-disks consist of a network of small aromatic island with in plane length, La, of about 1 nm. Raman spectra evidence a significant amount of disorder which is in a large part due to the quantum confinement in the aromatic islands. Nano-disks contain small percentage of sp3 and the O/C ratio is lower than 6%. They furthermore present interesting UV and visible photoluminescence properties.