CVD Grown Tungsten Oxide for Low Temperature Hydrogen Sensing: Tuning Surface Characteristics via Materials Processing for Sensing Applications.

The intrinsic properties of semiconducting oxides having nanostructured morphology are highly appealing for gas sensing. In this study, the fabrication of nanostructured WO3 thin films with promising surface characteristics for hydrogen (H2 ) gas sensing applications is accomplished. This is enabled by developing a chemical vapor deposition (CVD) process employing a new and volatile tungsten precursor bis(diisopropylamido)-bis(tert-butylimido)-tungsten(VI), [W(Nt Bu)2 (Ni Pr2 )2 ]. The as-grown nanostructured WO3 layers are thoroughly analyzed. Particular attention is paid to stoichiometry, surface characteristics, and morphology, all of which strongly influence the gas-sensing potential of WO3 . Synchrotron-based ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), X-ray photoelectron emission microscopy (XPEEM), low-energy electron microscopy (LEEM) and 4-point van der Pauw (vdP) technique made it possible to analyze the surface chemistry and structural uniformity with a spatially resolved insight into the chemical, electronic and electrical properties. The WO3 layer is employed as a hydrogen (H2 ) sensor within interdigitated mini-mobile sensor architecture capable of working using a standard computer's 5 V 1-wirebus connection. The sensor shows remarkable sensitivity toward H2 . The high, robust, and repeatable sensor response (S) is attributed to the homogenous distribution of the W5+ oxidation state and associated oxygen vacancies, as shown by synchrotron-based UPS, XPS, and XPEEM analysis.

Thermal atomic layer deposition of rhenium nitride and rhenium metal thin films using methyltrioxorhenium.

The growth of rhenium nitride and rhenium metal thin films is presented using atomic layer deposition (ALD) with the precursors methyltrioxorhenium and 1,1-dimethylhydrazine. Saturative, self-limiting growth was determined at 340 °C for pulse times of ≥4.0 s for methyltrioxorhenium and ≥0.1 s for 1,1-dimethylhydrazine. An ALD window was observed from 340 to 350 °C with a growth rate of about 0.60 Å per cycle. Films grown at 340 °C revealed a root mean square surface roughness of 2.7 nm for a 70 nm thick film and possessed a composition of ReN0.14 with low O and C content of 1.6 and 2.6 at%, respectively. Enhanced nucleation on in situ grown TiN, relative to thermal SiO2, enabled a conformality of 98% on high aspect ratio trenched structures. Subjecting the ReN0.14 thin films to thermal or chemical and thermal treatments reduced the nitrogen content to ≤1.6 at%, yielding a film purity of about 96 at% rhenium and resistivities as low as 51 µΩ cm. The Re metal film thicknesses on the trenched structures remained intact during the post-deposition annealing treatments and the films did not delaminate from the substrate surfaces.

Correction: Luminescent Nd2S3 thin films: a new chemical vapour deposition route towards rare-earth sulphides.

Correction for 'Luminescent Nd2S3 thin films: a new chemical vapour deposition route towards rare-earth sulphides' by Stefan Cwik et al., Dalton Trans., 2019, 48, 2926-2938.

Luminescent Nd2S3 thin films: a new chemical vapour deposition route towards rare-earth sulphides.

Neodymium sulphide (Nd2S3) belongs to the exciting class of rare earth sulphides (RES) and is projected to have a serious potential in a wide spectrum of application either in pure form or as dopant. We demonstrate a facile and first growth of Nd2S3 thin films via metal-organic chemical vapour deposition (MOCVD) at moderate process conditions using two new Nd precursors, namely tris(N,N'-diisopropyl-2-dimethylamido-guanidinato)Nd(iii) and tris(N,N'-diisopropyl-acetamidinato)Nd(iii). The promising thermal properties and suitable reactivity of both Nd precursors towards elemental sulphur enabled the formation of high purity γ-Nd2S3. While the process temperature for film growth ranged from 400 °C to 600 °C, the films were crystalline above 500 °C. We also demonstrate that the as-deposited γ-Nd2S3 are luminescent, with the optical bandgap ranging from 2.3 eV to 2.5 eV. The process circumvents post-deposition treatments such as sulfurisation to fabricate the desired Nd2S3, which paves the way for large scale synthesis and also opens up new avenues for exploring the potential of this class of materials with properties for functional applications.

Fabrication of zinc-dicarboxylate- and zinc-pyrazolate-carboxylate-framework thin films through vapour-solid deposition.

Fabrication of three-dimensional metal-organic framework (MOF) thin films has been investigated for the first time through the conversion of a ZnO layer via a pure vapour-solid deposition reaction at ambient pressure. The fabrication of MOF thin films with a dicarboxylate linker, (DMA)2[Zn3(bdc)4] (1) (bdc = 1,4-benzenedicarboxylate), and a carboxy-pyrazolate linker, [Zn4O(dmcapz)6] (2) (dmcapz = 3,5-dimethyl-4-carboxypyrazole), involves the deposition of the linker and/or the preparation of a composite film preliminarily and its subsequent conversion into a MOF film using closed cell thermal treatment. Furthermore, it was possible to isolate thin films with a MOF-5 isotype structure grown along the [110] direction, using a carboxy-pyrazolate linker. This was achieved just by the direct reaction of the ZnO film and the organic linker vapors, employing a simple route that demonstrates the feasibility of MOF thin film fabrication using inexpensive routes at ambient pressure.

Integrating AlN with GdN Thin Films in an in Situ CVD Process: Influence on the Oxidation and Crystallinity of GdN.

The application potential of rare earth nitride (REN) materials has been limited due to their high sensitivity to air and moisture leading to facile oxidation upon exposure to ambient conditions. For the growth of device quality films, physical vapor deposition methods, such as molecular beam epitaxy, have been established in the past. In this regard, aluminum nitride (AlN) has been employed as a capping layer to protect the functional gadolinium nitride (GdN) from interaction with the atmosphere. In addition, an AlN buffer was employed between a silicon substrate and GdN serving as a seeding layer for epitaxial growth. In pursuit to grow high-quality GdN thin films by chemical vapor deposition (CVD), this successful concept is transferred to an in situ CVD process. Thereby, AlN thin films are included step-wise in the stack starting with Si/GdN/AlN structures to realize long-term stability of the oxophilic GdN layer. As a second strategy, a Si/AlN/GdN/AlN stacked structure was grown, where the additional buffer layer serves as the seeding layer to promote crystalline GdN growth. In addition, chemical interaction between GdN and the Si substrate can be prevented by spatial segregation. The stacked structures grown for the first time with a continuous CVD process were subjected to a detailed investigation in terms of structure, morphology, and composition, revealing an improved GdN purity with respect to earlier grown CVD thin films. Employing thin AlN buffer layers, the crystallinity of the GdN films on Si(100) could additionally be significantly enhanced. Finally, the magnetic properties of the fabricated stacks were evaluated by performing superconducting quantum interference device measurements, both of the as-deposited films and after exposure to ambient conditions, suggesting superparamagnetism of ferromagnetic GdN grains. The consistency of the magnetic properties precludes oxidation of the REN material due to the amorphous AlN capping layer.

Simultaneous introduction of various palladium active sites into MOF via one-pot synthesis: Pd@[Cu3-xPdx(BTC)2]n.

Simultaneous incorporation of palladium within Pd-Pd and/or Pd-Cu paddlewheels as framework-nodes and Pd nanoparticle (NP) dispersion into MOF have been achieved for the first time via one-pot synthesis. In particular, the framework substitution of Cu(2+) by Pd(2+) as well as the pore loading with PdNPs have been confirmed and characterized by XPS. The obtained solids featuring such multiple Pd-sites show enhanced catalytic activity in the aqueous-phase hydrogenation of p-nitrophenol (PNP) with NaBH4 to p-aminophenol (PAP).

Sc2O3, Er2O3, and Y2O3 thin films by MOCVD from volatile guanidinate class of rare-earth precursors.

Alternative novel precursor chemistries for the vapor phase deposition of rare-earth (RE) oxide thin films were developed by synthesising the homoleptic guanidinate compounds tris(N,N'-diisopropyl-2-dimethylamidoguanidinato)-scandium(III) [Sc(DPDMG)(3)] (1), tris(N,N'-diisopropyl-2-dimethylamidoguanidinato)-erbium(III), [Er(DPDMG)(3)] (2) and tris(N,N'-diisopropyl-2-dimethylamidoguanidinato)-yttrium(III), [Y(DPDMG)(3)] (3). All three compounds are monomeric as revealed by single crystal X-ray diffraction (XRD) analysis, nuclear magnetic resonance (NMR) and electron impact mass spectrometry (EI-MS). The thermal analysis revealed that the compounds are volatile and very stable under evaporation conditions. Therefore the complexes were evaluated as precursors for the growth of Sc(2)O(3), Er(2)O(3) and Y(2)O(3) thin films, respectively, by metal-organic chemical vapor deposition (MOCVD). Uniform Sc(2)O(3), Er(2)O(3) and Y(2)O(3) films on Si(100) substrates with reproducible quality were grown by MOCVD by the combination of the respective guanidinate precursors and oxygen in the temperature range 350-700 °C. The structural, morphological, compositional and electrical properties of the films were investigated in detail. The most relevant film properties are highlighted in relation to the distinct advantages of the novel precursor chemistries in comparison to the commonly used literature known RE precursors. This study shows that compounds 1-3 are very good precursors for MOCVD yielding Sc(2)O(3), Er(2)O(3) and Y(2)O(3) thin films which are stoichiometric and display suitable electrical properties for their potential use as high dielectric constant (high-k) materials.