Garry Glaspell

Laser synthesis of bimetallic nanoalloys in the vapor and liquid phases and the magnetic properties of PdM and PtM nanoparticles (M = Fe, Co and Ni)

In this work, we present several examples of the synthesis and characterization of bimetallic nanoparticle alloys using the Laser Vaporization Controlled Condensation (LVCC) method. In the first example, the vapor phase synthesis of Au-Ag, Au-Pd, and Au-Pt nanoparticle alloys are presented. The formation of nanoalloys is concluded from the observation of one plasmon absorption band at a wavelength that varies linearly with the gold mole fraction in the nanoalloy. Both XRD data and HRTEM-EDX data confirm the formation of nanoparticle alloys and not simply mixtures of the two metal nanoparticles. Irradiation of a mixture of Au/Ag nanoparticles dispersed in water with the 532 nm unfocused laser results in efficient alloying while the 1064 nm laser radiation results only in evaporation and size reduction of the unalloyed nanoparticles. Selective absorption of the femtosecond 780 nm radiation by large Au aggregates results in the formation of smaller aggregates with fractal structures, and no evidence for the Au-Ag alloy formation. The synthesis of palladium and platinum nanoparticles alloyed with transition metals such as iron and nickel using the LVCC method is also presented. The alloyed nanoparticles (FePd, FePt, NiPd, NiPt, and FeNi) are found to be superparamagnetic.

Vapor-phase synthesis of metallic and intermetallic nanoparticles and nanowires: Magnetic and catalytic properties*

In this paper, we present several examples of the vapor-phase synthesis of intermetallic and alloy nanoparticles and nanowires, and investigate their magnetic and catalytic properties. In the first example, we report the vapor-phase synthesis of intermetallic aluminide nanoparticles. Specifically, FeAl and NiAl nanoparticles were synthesized via laser vaporization controlled condensation (LVCC) from their bulk powders. The NiAl nanoparticles were found to be paramagnetic at room temperature, with a blocking temperature of approximately 15 K. The FeAl nanoparticles displayed room-temperature ferromagnetism. In the second example, we report the vapor-phase synthesis of cobalt oxide nanoparticle catalysts for low-temperature CO oxidation. The incorporation of Au and Pd nanoparticles into the cobalt oxide support leads to significantly improved catalytic activity and stability of the binary catalyst systems. Finally, we report the synthesis of nanowires of Ge, Mg, Pd, and Pt using the vapor-liquid-solid (VLS) method where the vapor-phase growth of the wire is catalyzed using a proper metal catalyst present in the liquid phase.

Reversible paramagnetism to ferromagnetism in transition metal-doped TiO2 nanocrystals prepared by microwave irradiation

TiO2 nanoparticles doped with 1%, 5%, and 10% M (M=Co, Fe, and Ni) were prepared by microwave irradiation and characterized using x-ray diffraction, transmission electron microscopy, and magnetometry. The as-prepared samples are found to be paramagnetic at room temperature, with the magnetic susceptibility following the Curie-Weiss law in the investigated range of 2–300K. However, transformation from paramagnetism to room-temperature ferromagnetism (RTFM) was observed by hydrogenating the samples at 400°C. Reheating in air converted the samples back to paramagnetic while rehydrogenating the samples again induced ferromagnetism. It is argued that the reversible RTFM observed is due to interaction between the dopant metal ions and oxygen vacancies produced during hydrogenation. X-ray diffraction of the hydrogenated Co- and Fe-doped samples shows only a single TiO2 phase suggesting that the observed RTFM may be intrinsic, but for the Ni-doped samples the magnetism may arise from metallic Ni on the surfaces o...

Nanoparticles in Astrochemistry: Synthesis and Characterization of Meteorite Dust Nanoparticles

Interstellar dust particles (IDPs) constitute most of the solid matter in the universe. Large quantities of IDPs are also present in the Solar System and fall on Earth. IDPs are also of interest as they can catalyze astrochemical reactions and prebiotic synthesis, and their organic contents are believed to have contributed to the origins of life. Their chemical composition is similar to carbonaceous chondrite comets, asteroids and meteorites. The IDPs are microporous web‐like aggregates of 10–100 nm phyllosilicate particles with morphologies similar to particles produced by the Laser Vaporization Controlled Condensation (LVCC) method. IDPs are available only as microscopic samples, and simulated IDPs are needed to study their chemical and catalytic effects. To produce such simulated IDPs, we formed nanoparticles from carbonaceous chondrite meteorites by LVCC processing. The compositions, morphologies, particle size distribution, FTIR spectra, and catalytic properties of the meteorite‐based nanoparticles w...

Utilizing upconverting phosphors for the detection of TNT

Herein we purpose to utilize upconverting phosphors to detect explosives. To detect TNT, antibodies specific to TNT are conjugated to the surface. The role of the antibodies is two fold; to bind a quencher and to accept TNT. The quencher is a bifunctional molecule, with one end containing a TNT analog and the other end being a dark fluorescent quenching dye. The dye is chosen so that the luminescence from the phosphor will be absorbed preventing it from emitting, reducing luminescence from the phosphor. However, in the presence of TNT the quencher that is bound with DNT will be displaced. With the quencher displaced the phosphor will be able to emit light indicating TNT is present in the select area.

Formation of rare-earth upconverting nanoparticles using laser vaporization controlled condensation

Rare earth doped upconverting nanoparticles have been synthesized via laser vaporization controlled condensation (LVCC) and their photoluminescence properties were characterized using 980 nm laser diode excitation. This procedure is highly tunable, specifically by increasing the Yb3+ to Er3+ concentration the observed green emission decreases and the observed red emission increases. We have also shown that nearly equal peaks of blue, green and red emissions producing a virtually white upconverter could be synthesized by appropriately mixing Tm3+, Ho3+, and Er3+. We have also investigated the upconversion efficiency in a variety of lattices including Y2O3, Gd2O3 and La2O3. TEM confirmed that the as-formed particles were ~ 10 nm in size and XRD indicated that the overall crystal structure was predominately cubic.