Trivalent rare earth ions in crystalline or fiber hosts are among the most successful of laser materials, but new dopant-host combinations and more detailed understanding of existing materials continue to be needed. This paper presents a few examples from the work of our team at the Army Research Laboratory, highlighting the interrelation between spectroscopic properties and laser behavior. It focuses on bulk solids, though rare-earth-doped fiber lasers are also extremely important. One system discussed is Nd:YAG, particularly concentration quenching in heavily doped ceramic YAG. Spectroscopic properties of Yb:Y2O3 and Yb:Sc2O3 help to elucidate their laser performance. Spectra indicate that Er:YAG is more promising than Er:Sc2O3 for room temperature laser operation, but that the reverse is true for operation at and somewhat above liquid nitrogen temperature.

GaZnO and GaZnON thin films were deposited on both Si (100) and c-axis oriented sapphire substratesby RF co-sputtering of ZnO target and Ga2O3tablets in Ar/O2 and Ar/N2, respectively, by changing the number of Ga2O3tablets (NGa2O3) placed on the ZnO target in the range of 0 to 16.They were subsequently annealed in N2 at 800 °C and then, some of the samples formed by Ar/O2-sputtering were subjected to NH3 treatment at 650 °C for nitridation. XRD measurements revealed that the c-axis lattice parameter calculated from the ZnO (002) peak for GaZnON film son Si (100) was remarkably larger than for GaZnO films on Si (100). Moreover, ZnO (002) was observed up to NGa2O3=16 for GaZnON films formed on sapphire, while no XRD peaks were observed above NGa2O3=8 for GaZnON films on Si(100). Optical band-gap ofGaZnO and GaZnON films became wider from 3.34to 3.67 eVand from 3.21to 3.40 eV, respectively, with increasing NGa2O3 from 0 to 16. Photoluminescence spectra of GaZnO films showed band-to-band emission at 380nm, while those of GaZnON films exhibited broad and weak peaks centered at 550 nm and 647nm.

The equilibrium geometry and electronic structure of graphene deposited on a multilayer hexagonal boron nitride (h-BN) substrate has been investigated using the density functional and pseudopotential theories. We found that the energy band gap for the interface between a monolayer graphene (MLG) and a monolayer BN (MLBN) lies between 47 and 62 meV, depending on the relative orientations of the layers. In the most energetically stable configuration the binding energy is found to be approximately 40 meV per C atom. Slightly away from the Dirac point, the dispersion curve is linear, with the electron speed almost identical to that for isolated graphene. The dispersion relation becomes reasonably quadratic for the interface between MLG and 4-layer-BN, with a relative effective mass of 0.0047. While the MLG/MLBN superlattice is metallic, the thinnest armchair nanoribbon of MLG/MLBN interface is semiconducting with a gap of 1.84 eV.

In order to develop a novel proton conductive membrane for proton exchange membrane fuel cell (PEMFC), a poly(vinyl di-fluoride) (PVDF) matrix was irradiated with swift heavy ions (SHI) to obtain radically active cylindrical latent tracks in the polymer film. Styrene was then radiografted and further sulfonated into these irradiated cylindrical regions, leading to sulfonated polystyrene (PVDF-g-PSSA) domains within PVDF. The role of the grafting degree and fluence of irradiation of the PVDF matrix on PVDF-g-PSSA membranes properties (chemical composition, ion exchange capacity) was investigated. Then, a membrane-electrode assembly (MEA) was prepared and fuel cell tests have been performed. Our results clearly show that PVDF-g-PSSA membranes with a grafting degree of about 140%, obtained after irradiation at a fluence of 1010 ions/cm2, exhibit good conductivity values but their durability is limited to about 70 h. Decreasing the fluence leads to membranes with lower grafting yield but with fuel cell performances closer to those of 140% grafted PVDF-g-PSSA membrane and improved mechanical properties. Then, ion track grafting technique is a promising technique to obtain PEM with a good trade-off between proton conductivity and mechanical properties.

Pb(Zr0.53Ti0.47)O3 (PZT) films have been fabricated on stainless steel substrates by a Polyvinylpirrolidone (PVP) modified sol-gel route. The single layer of about 0.26 μm was achieved by using the PVP-modified PZT sol, and Crack-free PZT films with thickness of up to 2.37 μm were fabricated by repeating the deposition process. The variations in crystallite orientation, microstructure, dielectric and ferroelectric properties of PZT films were investigated as a function of film thickness. Our results indicate that PZT films prepared on stainless steel substrates maintain good dielectric and ferroelectric properties.

Transport properties of polymer nanocomposites become increasingly important for range applications with many outstanding questions remaining. Thermal conductivity is especially important in applications like temperature sensing and packaging. We chose isotactic PolyPropylene (iPP) as one of the most widely used polymers and created nano-colloidal dispersions at different weight percent concentration of carbon nanotubes (CNTs). We oriented the thin-film samples using melt-shear at 200°C and 1Hz in a Linkam microscope shearing hot stage. Thermal conductivity measurements were performed at room temperature on two iPP/CNT sheared thin-film samples (1% and 5% CNT content) both parallel and perpendicular to the shear direction as well as a pure iPP sheared thin-film, prepared using the same process. Our findings indicate that the CNTs enhance kappa by 12% for the 1% CNT sample and 35% by the 5% CNT sample compared to that measured for pure iPP. Additionally, the CNTs under shear induce a novel anisotropy to the thermal conductivity in iPP/CNTs nano-composites. We introduce an approach to extract the shear induced orientational order of thermal conductivity by the dispersed CNTs.

We report on a multiplexed, ratiometric method that can confidently distinguish between cancerous and non-cancerous epithelial prostate cells in vitro, as demonstrated by a double blind experiment. The technique is based on bright SERRS biotags (SBTs) infused with unique Raman reporter molecules, and carrying cell-specific peptides. Two sets of SERRS biotags were used. One targets the neuropilin-1 (NRP) receptors of cancer cells through the RPARPAR peptide. The other functions as a positive control (PC) and binds to both non-cancerous and cancer cells through the HIV derived TAT peptide. Averaging the SERRS signal over a given cell yielded an NRP/PC ratio from which a robust quantitative measure of the overexpression of the NRP-1 by the cancer cell line was extracted. The use of a local, on-cell reference produces quantitative, statistically robust measures of overexpression independent of such sources of uncertainty such as variations in the location of the focal plane, the local cell concentration and turbidity.

Magnetically separable and reusable core-shell CoFe2O4-ZnO photocatalyst nanospheres were prepared via hydrothermal synthesis technique using glucose derived carbon nanospheres as template. The morphology and phase of core-shell hybrid structure of CoFe2O4-ZnO was assessed via TEM, and XRD. The UV-vis photocatalytic activity of the composite was assessed via measuring the degradation rate of modeled pollutant methylene blue in water. The magnetic composite showed high UV photocatalytic activity for the degradation of methylene blue. The photocatalytic activity was found to be ZnO shell thickness dependent. Thicker ZnO shells lead to higher rate of photocatalytic activity. Hybrid nanospheres recovered using external magnetic field demonstrated good repeatability of photocatalytic activity. These results promise the reusability of hybrid nanospheres for photocatalytic activity.

We have developed a cluster-eliminating filter which reduces amount of amorphous silicon nanoparticles (clusters) incorporated into a-Si:H films. We have applied the filter to fabricate a-Si:H Schottky solar cells. The cells show a high initial fill factor FF=0.563 and a high stabilized value after light soaking FF=0.552 which light-induced degradation was quite low value of 1.95 %.

To date, there are a strikingly growing number of patients who need variousorthopedic implants. However, traditional orthopedic implants face manycomplications such as infection and implant loosening which may lead toimplant failures. Conventional metal implants such as titanium were chosenfor orthopedic applications mainly based on their excellent mechanicalproperties and biological inertness. Since natural bone matrix is nanometerin dimension, it is desirable to design a biologically inspirednanostructured coating that can turn conventional inert titanium surfacesinto biomimetic active interfaces, thus enhance bone cell adhesion andosseointegration. For this purpose, we designed a biomimetic nanostructuredcoating based on nanocrystalline hydroxyapatites (nHA) and single wallcarbon nanotubes (SWCNTs). Specifically, nHA with good crystallinity andbiomimetic dimensions were prepared via a wet chemistry method andhydrothermal treatment; and the SWCNTs were synthesized via an arc plasmamethod with or without magnetic fields. TEM images showed that thehydrothermally treated nHA possessed regular rod-like nanocrystals andbiomimetic nanostructure. In addition, the length of SWCNTs can besignificantly increased under external magnetic fields when compared tonanotubes produced without magnetic fields. More importantly, our resultsshowed that the above nHA and SWCNTs nanomaterials can greatly promoteosteoblast (bone-forming cell) adhesion on titanium in vitro, thus holding great promise to improve osseointegrationand lengthen the lifetime of current orthopedic implants.

Solid-electrolyte interphase (SEI) regions play a critical role in stabilizing lithium batteries, but little is known about the detailed mechanism of growth and formation. We have developed a novel method for in situ study of the interfacial regions of SEI layers, using an interface-selective nonlinear vibrational spectroscopy method termed femtosecond broadband multiplex vibrational sum-frequency generation spectroscopy (SFG) and a lithium battery electrochemical cell with optical access. SFG has high sensitivity and high selectivity needed to study vibrational transitions of molecular species during the SEI growth. SFG is most sensitive to interfacial regions, so with SFG we ignore the bulk electrolyte and focus on interface regions just a few molecules thick. During SEI growth there are two such interfaces, the electrode-SEI interface and the electrolyte SEI interface. We will present results obtained using a lithium battery and model materials relevant to Li batteries, where during successive cycles of charge and discharge we selectively probe the structural evolution of these two interfaces on Au, Cu and carbon.

We report the fabrication and characterisation of the first graphene ring micro electrodes, formed by dip coating fibre optics with subsequently reduced graphite oxide. The behaviour of the so-formed Graphene RIng Micro Electrodes (GRIMEs) is studied using the ferricyanide probe redox system while electrode thicknesses is assessed using established electrochemical methods. A ring electrode of ∼73 nm thickness is produced on 220 μm diameter fibre optics, corresponding to an inner to outer radius ratio of >0.999, so allowing for use of extant analytical descriptions of very thin ring micro electrodes in data analysis. GRIMEs are highly reliable (current response invariant over >3000 scans) with the microring design allowing for efficient use of electrochemically active graphene edge sites. Further, the associated nA scale currents neatly obviate issues relating to the high resistivity of undoped graphene. Thus, the use of graphene in ring micro electrodes improves the reliability of existing micro electrode designs and expands the range of use of graphene-based electrochemical devices.

Intermetallic compounds containing actinide ions exhibit a broad spectrum of different physical phenomena at low temperatures. The latter include heavy quasiparticles, unconventional superconductivity and various forms of magnetic ordering. The complex and sometimes enigmatic properties of these compounds derive from the strong correlations among the 5f electrons. Previous model calculations suggested that the intra-atomic Hund’s rule-type correlations may lead to partial localization which is reflected e. g. in the co-existence of itinerant 5f-derived heavy quasiparticles and local magnetic excitations. The conjectured "dual nature" of 5f electrons which is closely related to the question of the 5f valence of the actinide ions is not directly probed by ground state properties and the low-energy excitations. Here we present microscopic calculations for core-level spectroscopy emphasizing the consequences of strong intra-atomic correlations of the 5f shell.

Polymers and polymer nanocomposites have been studied under conditions of extremely high heating rates. Traditionally, these materials have been examined by the flammability research community using methods which have heating rates on the order of 10 degrees C/min. In this study, we have examined how polypropylene-nanoclay (montmorillonite) and polypropylene-carbon nanotube nanocomposites behave subjected to heating rates on the order of one million degrees C/min when irradiated with a 1064 nm Nd-YAG variable pulse millisecond laser. Time-resolved temperature data and mass loss data was collected for each sample as well as post-mortem surface characterization using spectroscopy and electron microscopy. The analysis shows that the nanospecies are effective in providing a protective barrier that decreases the amount of degradation and mass loss to the underlying polymer material. The effect is clearly seen after irradiating with a single pulse and multiple pulses. A comparison between the performance of the nanoclay and carbon nanotube composites is given.

Synthesis of FeC2O42H2O nano particles was carried out by thermal double decomposition of solutions of oxalic acid dihydrate (C2H2O4 2H2O) and FeSO4 7H2O employing CATA -2R microwave reactor. Structural elucidation was carried out by employing X-ray diffraction, particle size and shape were studied by transmission electron microscopy and nature of bonding was investigated by Optical absorption and near-infrared spectral studies. The powder resulting from this method is possesses distorted rhombic octahedral structure. The particle grain size is about 50 nm. Details of optical transitions are mentioned in terms of energy states.

The intercluster interactions of iron/iron oxide core shell nanoclusters have been investigated, and their dependence on cluster size (d) has been discussed. A cluster deposition system is used to prepare core-shell nanoclusters with different d, varying from 9 to 14 nm.Transmission Electron Microscopy has been used for physical characterization, and Vibrating Sample Magnetometer for magnetic study. The cluster – cluster interactions have been investigated by field dependent isothermal remanent magnetization (IRM) and dc demagnetization (DCD) measurements at room temperature. Henkel plot shows more negative deviation from non- interacting case for bigger size nanoclusters than smaller size clusters.

Bulk structures of un-stabilized ZrO2-x with x in the 0 ≤ x ≤ 0.44 range under ambient pressure exist in three different structures (monoclinic, tetragonal and cubic). At ambient temperature and elevated pressures above 3.5 GPa, zirconia, at these compositions, a fourth phase is found, the orthorhombic structure. A dilute sol-gel method was used to produce nanoscale zirconia particles containing the unstabilized orthorhombic cotunnite structure for use in this project. Extensive characterization of this material indicates that the critical factor in determining the synthesized structures appears to be the number and placement of oxygen vacancies. These results also indicate that surface energy alone is not the controlling factor in determining the crystal structure synthesized.

There is a growing body of evidence that a number of mixed-valent and heavy-fermion materials show renormalized hybridization gaps either at the Fermi-energy or close to the Fermi-energy. In the former case, a heavy-fermion semiconducting state occurs and in the later case, the system remains metallic at low temperatures. The magnitudes of the hy-bridization gaps are observed to decrease with increasing temperature. The existence of a low-energy electronic energy scale creates a possibility that the Born-Oppenheimer ap-proximation may fail and that there may be a resonant coupling between the phonons and the electronic excitations. Here we argue that such a mechanism may be the cause of the phonon anomalies observed in neutron scattering experiments on the high-temperature phase of alpha-uranium.

Innovative printing technology enables fine feature deposition (below 10μm) of electronic materials onto low-temperature, non-planar substrates without masks. This could be a promising technology to meet the requirements of present and future microelectronic systems. Silver nanoparticles (NP) ink is widely used for printed electronics; however, its electrical conductivity is low compared to bulk materials. In order to improve the electrical conductivity of printed tracks for the aerosol printing technique, we developed a novel carbon nanotubes (CNTs)/silver NP ink by mechanical stirring and sonication. The produced sample inks with different concentration of CNTs that were printed with Aerosol Jet® printing system. We found that the CNTs bridged the defects in some printed silver lines, thereby lowering the electrical resistivity by 38%. However, no further improvements were observed with a higher CNT concentration in the silver NP ink samples. We hypothesize that CNT bridges connects the defects thus decreasing the resistivity of printed silver lines when CNT concentration is under the percolation level. However, when it is above a concentration threshold, the resistivity of printed silver lines stops decreasing and even increases because of Schottky barrier effect.