All-nitrogen coordinated amidinato/imido complexes of molybdenum and tungsten: syntheses and characterization.

The first all-nitrogen coordinated bis(alkylamidinato)/bis(alkylimido) complexes of molybdenum and tungsten, [Mo(NtBu)(2){(iPrN)(2)CMe}(2)]and [W(NtBu)(2){(iPrN)(2)CMe}(2)], have been synthesized and fully characterized by (1)H and (13)C NMR spectroscopy, elemental analyses, high-resolution electron impact mass spectrometry, and Fourier transform infrared spectroscopy. Density functional theory calculations of the tungsten complex allow for geometry optimization and structural characterization by assignment of the NMR data, in particular a comparison of the experimental (13)C NMR signals with the calculated ones. Both compounds sublime without decomposition at 130 °C and 1 mTorr and show rapid decomposition above 250 °C, hence representing promising vapor-phase deposition routes for metal nitride based thin-film materials.

The residual stress in as-built Laser Powder Bed Fusion IN718 alloy as a consequence of the scanning strategy induced microstructure.

The effect of two types of scanning strategies on the grain structure and build-up of Residual Stress (RS) has been investigated in an as-built IN718 alloy produced by Laser Powder Bed Fusion (LPBF). The RS state has been investigated by X-ray diffraction techniques. The microstructural characterization was performed principally by Electron Backscatter Diffraction (EBSD), where the application of a post-measurement refinement technique enables small misorientations (< 2°) to be resolved. Kernel average misorientation (KAM) distributions indicate that preferably oriented columnar grains contain higher levels of misorientation, when compared to elongated grains with lower texture. The KAM distributions combined with X-ray diffraction stress maps infer that the increased misorientation is induced via plastic deformation driven by the thermal stresses, acting to self-relieve stress. The possibility of obtaining lower RS states in the build direction as a consequence of the influence of the microstructure should be considered when envisaging scanning strategies aimed at the mitigation of RS.

Homoleptic gadolinium guanidinate: a single source precursor for metal-organic chemical vapor deposition of gadolinium nitride thin films.

Deposition of a rare earth nitride thin film using a chemical gas phase deposition technique is reported for the first time. The gadolinium tris-guanidinate complex [Gd{((i)PrN)(2)CNMe(2)}(3)] is found to be an effective single source precursor for the MOCVD growth of gadolinium nitride (GdN) thin films.

Probing the pathways of free charge generation in organic bulk heterojunction solar cells.

The fact that organic solar cells perform efficiently despite the low dielectric constant of most photoactive blends initiated a long-standing debate regarding the dominant pathways of free charge formation. Here, we address this issue through the accurate measurement of the activation energy for free charge photogeneration over a wide range of photon energy, using the method of time-delayed collection field. For our prototypical low bandgap polymer:fullerene blends, we find that neither the temperature nor the field dependence of free charge generation depend on the excitation energy, ruling out an appreciable contribution to free charge generation though hot carrier pathways. On the other hand, activation energies are on the order of the room temperature thermal energy for all studied blends. We conclude that charge generation in such devices proceeds through thermalized charge transfer states, and that thermal energy is sufficient to separate most of these states into free charges.

Microgradient-heaters as tools for high-throughput experimentation.

A microgradient-heater (MGH) was developed, and its feasibility as a tool for high-throughput materials science experimentation was tested. The MGH is derived from microhot plate (MHP) systems and allows combinatorial thermal processing on the micronano scale. The temperature gradient is adjustable by the substrate material. For an Au-coated MGH membrane a temperature drop from 605 to 100 °C was measured over a distance of 965 µm, resulting in an average temperature change of 0.52 K/µm. As a proof of principle, we demonstrate the feasibility of MGHs on the example of a chemical vapor deposition (CVD) process. The achieved results show discontinuous changes in surface morphology within a continuous TiO2 film. Furthermore the MGH can be used to get insights into the energetic relations of film growth processes, giving it the potential for microcalorimetry measurements.

Mixed amido/imido/guanidinato complexes of niobium: potential precursors for MOCVD of niobium nitride thin films.

Novel mixed amido/imido/guanidinato complexes of niobium are reported. The complexes were synthesized by insertion of two equivalents of di-isopropylcarbodiimide (i-Pr-cdi) or bis-cyclohexylcarbodiimide (Cy-cdi) respectively, into the niobium-amido bonds of [Nb(NR(2))(3)(N-t-Bu)] (, R = Me; , R = Et) starting out from [NbCl(3)(N-t-Bu)(py)(2)] and the respective LiNR(2) reagent (py = pyridine). Four representative examples of these mixed ligand amido/imido/guanidinato compounds were synthesized and were characterized by (1)H-NMR, (13)C-NMR, (15)N-NMR, CHN-analysis, mass spectrometry and infra-red spectroscopy. The molecular structures of [Nb(NR(2)){eta(2)-(i-Pr-N)(2)C(NR(2))}(2)(N-t-Bu)] (, R = Me; , R = Et) in the solid state were determined by single-crystal X-ray diffraction studies and are discussed together with the molecular structure of the starting compound [Nb(NMe(2))(3)(N-t-Bu)] (). The thermal properties of the new compounds depend on the substitution at the guanidinato ligand. Complexes of i-Pr-cdi are significantly more volatile than complexes of Cy-cdi as revealed by thermogravimetric analysis. Preliminary experiments using as a single-molecule source for metal-organic chemical vapour deposition (MOCVD) in the absence of ammonia indicate the formation of the stoichiometric, and surprisingly carbon-free, cubic niobium nitride phase.