Yu-Hsiang A. Wang

Synthesis of Shape-Controlled Monodisperse Wurtzite CuInxGa1–xS2 Semiconductor Nanocrystals with Tunable Band Gap

Monodisperse wurtzite CuIn(x)Ga(1-x)S(2) nanocrystals have been synthesized over the entire composition range using a facile solution-based method. Depending on the chemical composition and synthesis conditions, the morphology of the nanocrystals can be controlled in the form of bullet-like, rod-like, and tadpole-like shapes. The band gap of the nanocrystals increases linearly with increasing Ga concentration, with band gap values for the end members being close to those observed in the bulk. Colloidal suspensions of the nanocrystals are attractive for use as inks for low-cost fabrication of thin film solar cells by spin or spray coating.

Controlled Growth of Monodisperse Self-Supported Superparamagnetic Nanostructures of Spherical and Rod-Like CoFe2O4 Nanocrystals

Novel shape- and structural-controlled superparamagnetic nanostructures composed of self-supported spherical and rod-like CoFe(2)O(4) colloidal nanocrystals have been prepared by thermolysis of a stoichiometric Co(2+)Fe(2)(3+)-oleate complex in organic solution with periodic injection of hexane for controlling the nucleation, assembly, and growth of the nuclei.

Magnetization relaxation and structure of CoFeGe alloys

The magnetic relaxation of 10 and 50 nm thin films of (CoFe)100−xGex (0 at. %≤x≤35 at. %) alloys was investigated by broadband ferromagnetic resonance (FMR) experiments. 10 nm thin films exhibit a significant two magnon contribution to the FMR linewidth. The 50 nm films exhibit very low damping constants of α≈0.0025 and relaxation rates as low as 33 MHz in the composition range of 20 at. %≤x≤30 at. % Ge after annealing. Structural characterization revealed B2 order for these compositions. First principles calculations confirm a pseudogap in the minority channel for B2 ordered (CoFe)75Ge25 which may cause the low damping parameters and high ΔRA in CoFeGe based current perpendicular to the plane giant magnetoresistance spin valves.

Half-metallic electronic structures of quaternary ferromagnetic chalcospinels: CdxCu1−xCr2S4 and CdxCu1−xCr2Se4

First-principles calculations indicate that the chalcogenide spinels CdxCu1−xCr2S4 and CdxCu1−xCr2Se4 can be ferromagnetic metals, half-metals, or semiconductors depending on the Cd concentration x. In particular, CdxCu1−xCr2S4 can be tuned to be effectively half-metallic for x values between 0.25 and 0.875 and CdxCu1−xCr2Se4 can be half-metallic for x between 0.625 and 0.875. For x 0.875 both systems are predicted to be ferromagnetic semiconductors.

Colloidal Synthesis of Magnetic CuCr2S4 Nanocrystals and Nanoclusters

Nanocrystals and nanoclusters of the room-temperature magnetic spinel CuCr(2)S(4) have been synthesized using a facile solution-based method. The synthesis involves hot injection of an excess of 1-dodecanethiol (1-DDT) into a boiling coordinating solvent containing CuCl(2) and CrCl(3)·6H(2)O. Using octadecylamine (ODA) as a solvent yields cube-shaped nanocrystals with an average size of 20 ± 2 nm, while with oleylamine (OLA), nanoclusters with an average size of 31 ± 2.5 nm are obtained. In both cases, powder X-ray diffraction patterns confirmed the formation of the pure spinel phase without any impurities. While the synthesized powders are superparamagnetic near room temperature, they exhibit ferromagnetic behavior at lower temperatures, with magnetization (M(S)) values of 30 emu/g (1.63 μ(B)/f.u.) and 33 emu/g (1.79 μ(B)/f.u.) for the ODA- and OLA-capped nanocrystals and nanoclusters, respectively, at 5 K.

Induced half-metallicity in Cr-based ferromagnetic chalcospinels with anion substitutions: CuCr2S(Se)4−xEx (E=F, Cl, Br), Cu(Cd)Cr2S(Se)4−x, and CdCr2S(Se)4−xDx (D=N, P, As)

First-principles calculations of the electronic structures of chalcogenide spinels with anion vacancy and substitutions are presented. Our calculations predict that Cu(Cd)Cr2S(Se)4−x, CuCr2S(Se)4−xEx (E=F, Cl, Br), and CdCr2S(Se)4−xDx (D=N, P, As) can be half-metallic over a range of concentrations. The magnetic moment is found to scale approximately linearly on adding or withdrawing electrons and varies between 5.0 and 6.0 μB/f.u.