Manifold preprocessing for laser‐induced breakdown spectroscopy under Mars conditions

Laser‐induced breakdown spectroscopy (LIBS) is currently being used onboard the Mars Science Laboratory rover Curiosity to predict elemental abundances in dust, rocks, and soils using a partial least squares regression model developed by the ChemCam team. Accuracy of that model is constrained by the number of samples needed in the calibration, which grows exponentially with the dimensionality of the data, a phenomenon known as the curse of dimensionality. LIBS data are very high dimensional, and the number of ground‐truth samples (i.e., standards) recorded with the ChemCam before departing for Mars was small compared with the dimensionality, so strategies to optimize prediction accuracy are needed. In this study, we first use an existing machine learning algorithm, locally linear embedding (LLE), to combat the curse of dimensionality by embedding the data into a low‐dimensional manifold subspace before regressing. LLE constructs its embedding by maintaining local neighborhood distances and discarding large global geodesic distances between samples, in an attempt to preserve the underlying geometric structure of the data. We also introduce a novel supervised version, LLE for regression (LLER), which takes into account the known chemical composition of the training data when embedding. LLER is shown to outperform traditional LLE when predicting most major elements. We show the effectiveness of both algorithms using three different LIBS datasets recorded under Mars‐like conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and Structural Characterization of β‐Ketoiminate‐Stabilized Gallium Hydrides for Chemical Vapor Deposition Applications

Bis‐β‐ketoimine ligands of the form [(CH₂)_n{N(H)C(Me)?CHC(Me)?O}₂] (LⁿH₂, n=2, 3 and 4) were employed in the formation of a range of gallium complexes [Ga(Lⁿ)X] (X=Cl, Me, H), which were characterised by NMR spectroscopy, mass spectrometry and single‐crystal X‐ray diffraction analysis. The β‐ketoimine ligands have also been used for the stabilisation of rare gallium hydride species [Ga(Lⁿ)H] (n=2 ( 7 ); n=3 ( 8 )), which have been structurally characterised for the first time, confirming the formation of five‐coordinate, monomeric species. The stability of these hydrides has been probed through thermal analysis, revealing stability at temperatures in excess of 200 °C. The efficacy of all the gallium β‐ketoiminate complexes as molecular precursors for the deposition of gallium oxide thin films by chemical vapour deposition (CVD) has been investigated through thermogravimetric analysis and deposition studies, with the best results being found for a bimetallic gallium methyl complex [L³{GaMe₂}₂] ( 5 ) and the hydride [Ga(L³)H] ( 8 ). The resulting films ( F5 and F8 , respectively) were amorphous as‐deposited and thus were characterised primarily by XPS, EDXA and SEM techniques, which showed the formation of stoichiometric ( F5 ) and oxygen‐deficient ( F8 ) Ga₂O₃ thin films.     

Molecular precursors to gallium oxide thin films

The donor-functionalised alkoxides [Et(2)Ga(OR)](2)(R = CH(2)CH(2)NMe(2)(1), CH(CH(2)NMe(2))(2)(2), CH(2)CH(2)OMe (3), CH(CH(3))CH(2)NMe(2)(4), C(CH(3))(2)CH(2)OMe (5)) were synthesised by the 1:1 reaction of Et(3)Ga with ROH in hexane or dichloromethane at room temperature. Reaction of Et(3)Ga with excess ROH in refluxing toluene resulted in the isolation of a 1:1 mixture of [Et(2)Ga(OR)](2) and the ethylgallium bisalkoxide [EtGa(OR)(2)](R = CH(2)CH(2)NMe(2)(6) or CH(CH(3))CH(2)NMe(2)(7)). X-ray crystallography showed that compound 6 is monomeric and this complex represents the first structurally characterised monomeric gallium bisalkoxide. Homoleptic gallium trisalkoxides [Ga(OR)(3)](2) were prepared by the 1:6 reaction of [Ga(NMe(2))(3)](2) with ROH (R = CH(2)CH(2)NMe(2)(8), CH(CH(3))CH(2)NMe(2)(9), C(CH(3))(2)CH(2)OMe (10)). The decomposition of compounds 1, 4, 5 and 8 were studied by thermal gravimetric analysis. Low pressure CVD of 1 and 5 resulted in the formation of thin films of crystalline Ga(2)O(3).     

Single-source precursors to gallium and indium oxide thin films

Gallium and indium oxide thin films have received much attention in recent years for their wide range of applications. This review summarises the literature concerning single-source precursors and the methods employed to deposit gallium and indium oxide thin films using these compounds. An update of the literature outlining compounds which are potential single-source precursors to these materials is also included.     

Scalable Production of Ambient Stable Hybrid Bismuth-Based Materials: AACVD of Phenethylammonium Bismuth Iodide Films**

Large homogeneous and adherent coatings of phenethylammonium bismuth iodide were produced using the cost-effective and scalable aerosol-assisted chemical vapor deposition (AACVD) methodology. The film morphology was found to depend on the deposition conditions and substrates, resulting in different optical properties to those reported from their spin-coated counterparts. Optoelectronic characterization revealed band bending effects occurring between the hybrid material and semiconducting substrates (TiO₂ and FTO) due to heterojunction formation, and the optical bandgap of the hybrid material was calculated from UV-visible and PL spectrometry to be 2.05 eV. Maximum values for hydrophobicity and crystallographic preferential orientation were observed for films deposited on FTO/glass substrates, closely followed by values from films deposited on TiO₂/glass substrates.     

Do columnar defects produce bulk pinning?

From magneto-optical imaging performed on heavy-ion-irradiated YBa(2)Cu(3)O(7-delta) single crystals, it is found that at fields and temperatures where strong single vortex pinning by individual irradiation-induced amorphous columnar defects is to be expected, vortex motion is limited by the nucleation of vortex kinks at the specimen surface. In the material bulk, vortex motion occurs through (easy) kink sliding. Depinning in the bulk determines the screening current only at fields comparable to or larger than the matching field, at which the majority of vortices is not trapped by an ion track.     

Titanium arsenide films from the atmospheric pressure chemical vapour deposition of tetrakisdimethylamidotitanium and tert-butylarsine

Thin films of titanium arsenide have been deposited from the atmospheric pressure chemical vapour deposition (APCVD) of [Ti(NMe(2))(4)] and (t)BuAsH(2) at substrate temperatures between 350-550 °C. Highly reflective, silver coloured films were obtained which showed borderline metallic-semiconductor resistivities. The titanium arsenide films were analyzed by scanning electron microscopy (SEM), Raman spectroscopy, wavelength dispersive analysis of X-rays (WDX), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The films showed variable titanium to arsenic ratios but at substrate temperatures of 500 and 550 °C films with a 1 : 1 ratio of Ti : As, consistent with the composition TiAs, were deposited. Powder XRD showed that all of the films were crystalline and consistent with the formation of TiAs. Both nitrogen and carbon contamination of the films were negligible.