Synthesis and Fluorescence of Europium-Doped Barium Fluoride Cubic Nanocolumns

Europium-doped barium fluoride cubic nanocolumns were synthesized from the quaternary water in oil reverse microemulsions. In this process, the aqueous cores of water/cetyl trimethyl ammonium bromide (CTAB)/n-butanol/n-octane reverse microemulsions were used as microreactors for the precipitation of europium doped barium fluoride. XRD analysis shows that under the dopant concentration of 0.06% (molar fraction), the products are single phase. The result products are cubic column-like with about 30～50 nm edge length of cross section, and about 200 nm of length obtained from the transmission electron microscopy (TEM), and atomic force microscopy (AFM). Under the 0.06% (molar fraction) of dopant concentration, the fluorescence of Eu 2+ and Eu 3+ under the 589 of excitation wavelength is observed.

Direct Structural Evidences of Epitaxial Growth Ge<SUB>1-X</SUB>Mn<SUB>X</SUB>Nanocolumn Bi-Layers on Ge(001)

Molecular Beam Epitaxy (MBE) system equipped with in-situ Reflection High-Energy Electron Diffraction (RHEED) has been used for (Ge, Mn) thin film growth and monitoring the surface morphology and crystal structure of thin films. Based on the observation of changes in RHEED patterns during nanocolumn growth, we used a real-time control approach to realize multilayer structures that consist of two nanocolumn layers separated by a Ge barrier layer. Transmission Electron Microscopy (TEM) has been used to investigate the structural properties of the GeMn nanocolumns and GeMn/Ge nanocolumns bi-layers samples.

Preliminary Study on the Magnetic Properties of GeMn Nanocolumn/Ge Multilayers

Ge0.94Mn0.06 nanocolumn thin film is a unique phase of GeMn diluted magnetic semiconductors (DMS) which exhibit Curie temperature (TC) > 400 K. The multilayers of Ge0.94Mn0.06 nanocolumns separated by nano-scaled spacers represent great interests for spintronic applications, such as spin valves or giant magneto-resistance (GMR) multilayers. In this article, we present the results obtained from the preliminary study on the exchange coupling in two types of GeMn nanocolumn/Ge multilayers. All the samples have been grown using molecular beam epitaxy (MBE). The superconducting quantum interference device (SQUID) magnetometer has been used to determine the magnetic properties of the samples. In the multilayer system Ge/[Ge0.94Mn0.06(40 nm)/Ge(d nm)]9/Ge0.94Mn0.06(40 nm)/Ge, no exchange coupling can be observed. Inversely, exchange coupling between the layers exists and depends on the thickness of the Ge spacers for the GeMn nanocolumns/Ge multilayer spin valve systems. The exchange coupling in the nanocolumns multilayer systems has been shown to be complex due to the leakage field induced by neighboring nanocolumns and the magnetic anisotropy of nanocolumns.

Nanostructured Columns from Self-assemblyof Complementary Molecular Components

Nanostructured columns with a length about several tens of micrometer and a diameter of about 80 nm were obtained by molecular recognition directed self-assembly of a pair of comple- mentary molecular components, 4-amino-2 , 6-didodecylamino-1 , 3, 5-triazine(M) and 5- (4-dode- cyloxybenzylidene )-(1H, 3H)-2, 4, 6-pyrimidinetrione (B) in chloroform. In this system, with positive cooperativity, π-aromatic stacking and van der Waals interactions as well as hydrogen bonds cause the formation of the nanocolumns.

Direct Comparison of Catalyst-Free and Catalyst-Induced GaN Nanowires

GaN nanowires have been grown by molecular beam epitaxy either catalyst-free or catalyst-induced by means of Ni seeds.Under identical growth conditions of temperature andⅤ/Ⅲratio,both types of GaN nanowires are of wurtzite structure elongated in the Ga-polar direction and are constricted by M-plane facets.However,the catalyst-induced nanowires contain many more basal-plane stacking faults and their photoluminescence is weaker.These differences can be explained as effects of the catalyst Ni seeds.

Self-assembled formation of long, thin, and uncoalesced GaN nanowires on crystalline TiN films

We investigate in detail the self-assembled nucleation and growth of vertically oriented GaN nanowires by molecular beam epitaxy on crystalline TiN films. We demonstrate that this type of substrate allows for the growth of long and thin GaN nanowires that do not suffer from coalescence, a problem common to the growth on Si and other substrates. Only beyond a certain nanowire length that depends on the nanowire density and exceeds here 1.5 bun, coalescence takes place by bundling, i.e. the same process as on Si. By analyzing the nearest neighbor distance distribution, we identify the diffusion-induced repulsion of neighboring nanowires as the main mechanism limiting nanowire density during nucleation on TiN. Since on Si the final density is determined by shadowing of the impinging molecular beams by existing nanowires, it is the difference in adatom surface diffusion that enables the formation of nanowire ensembles with reduced density on TiN. These nanowire ensembles combine properties that make them a promising basis for the growth of core-shell heterostructures.