Synthesis and characterisation of zirconium-amido guanidinato complex: a potential precursor for ZrO2 thin films

A new zirconium complex, bis-(ethylmethylamido)-bis-(N,N'-diisopropyl-2-ethylmethylamidoguanidinato)-zirconium(iv) {[(N(i)Pr)(2)C(NEtMe)](2)Zr(NEtMe)(2)}, was synthesised by partial replacement of amide ligands with bidentate guanidinate ligands. The monomeric Zr complex was characterised by (1)H-NMR, (13)C-NMR, EI-MS, elemental analysis, and single crystal X-ray diffraction studies. The thermal properties of the compound was studied by thermogravimetric and differential thermal analysis (TG/DTA). The new Zr compound is thermally stable and can be sublimed quantitatively which renders it promising for thin film growth using vapor deposition techniques like chemical vapor deposition (CVD) and atomic layer deposition (ALD). The use of this complex for CVD of ZrO(2) on Si(100) substrates was attempted in combination with oxygen as the oxidant. Stoichiometric ZrO(2) films with preferred orientation at lower growth temperatures was obtained and the films were almost carbon free. The preliminary electrical characterisation of ZrO(2) films showed encouraging results for possible applications in dielectric oxide structures.     

Hydrogen bonding patterns in the cocrystals of 5-nitrouracil with several donor and acceptor molecules

: Cocrystals of 5-nitrouracil with solvent molecules, dioxane, pyridine, DMSO, formamide and ethanol as well as with piperazine, N, N'-dimethylpiperazine, 3-aminopyridine and diazabicyclo [2.2.2]octane obtained by deliberate inclusion, have been examined by X-ray crystallography. The tape structure found in the parent centric form of nitrouracil is retained with some modifications in the cocrystals with dioxane, piperazine, diazabicyclo [2.2.2]octane, N,N'-dimethylpiperazine, pyridine and DMSO, with the guest molecules forming alternate tapes. In cocrystals involving formamide, ethanol and 3-aminopyridine, the molecular tapes exhibit mixed compositions. The observed bonding patterns have been classified into six schemes. Interestingly, quadruple type hydrogen bonding patterns are seen in cocrystals containing 3-aminopyridine or ethanol and water, while a network of acyclic tetrahedral pentamers of water is found in the cocrystal containing diazabicyclo [2.2.2]octane and water.     

The Hydrogenation of the Zintl Phase NdGa Studied by in situ Neutron Diffraction

The hydrogenation of the Zintl phase NdGa was studied by in situ neutron powder diffraction. We find a compositional range of 0.1 < x < 0.8 in NdGaH_1+x. Hydrogen atoms are located in two different positions, in HNd₄ tetrahedra, and close to the polyanionic chains. For the latter, the Ga–H distance in NdGaH_1.66 is quite long (ca. 200 pm) with a trigonal bipyramidal Nd₃Ga₂ surrounding of hydrogen atoms. Hydrogen poor NdGaH_<1 phases as known for similar systems were not observed. The changing hydrogen content shows no measureable effect on the unit cell volume, but on lattice parameter ratios. Superstructures occur for 0.53 < x < 0.66 and 0.73 < x < 0.8, leading to a doubling or tripling of the lattice parameter a. They are probably caused by partial hydrogen ordering. The threefold superstructure contains a ¹_∞[(Ga–H–Ga–H–Ga)^6–] moiety with hydrogen bridging two gallium chains.     

Fluorescence and Nonlinear Optical Response of Graphene Quantum Dots Produced by Pulsed Laser Irradiation in Toluene

Graphene quantum dots (GQDs), the zero dimensional (0D) single nanostructures, have many exciting technological applications in diversified fields such as sensors, light emitting devices, bio imaging probes, solar cells, etc. They are emerging as a functional tool to modulate light by means of molecular engineering due to its merits, including relatively low extend of loss, large outstretch of spatial confinement and control via doping, size and shape. In this article, we present a one pot, facile and ecofriendly synthesis approach for fabricating GQDs via pulsed laser irradiation of an organic solvent (toluene) without any catalyst. It is a promising synthesis choice to prepare GQDs due to its fast production, lack of byproducts and further purification, as well as the control over the product by accurate tuning of laser parameters. In this work, the second (532 nm) and third harmonic (355 nm) wavelengths of a pulsed nanosecond Nd:YAG laser have been employed for the synthesis. It has been found that the obtained GQDs display fluorescence and is expected to have potential applications in optoelectronics and light-harvesting devices. In addition, nonlinear optical absorption of the prepared GQDs was measured using the open aperture z-scan technique (in the nanosecond regime). These GQDs exhibit excellent optical limiting properties, especially those synthesized at 532 nm wavelength.