Hydrogen Generation from Hydrolysis and Methanolysis of Guanidinium Borohydride

Metal-catalyzed hydrolysis and methanolysis of guanidinium borohydride (C­(NH₂)₃BH₄ or GBH) for hydrogen generation are reported. GBH is comparatively stable in water with only 0.3 equiv of H₂ liberated in 24 h at 25 °C while it reacts vigorously with methanol, releasing more than 3.2 equiv of H₂ within only 17 min. Even at 0 °C, there was still nearly 2.0 equiv of H₂ released after 2 h, but no H₂ liberation was observed for hydrolysis under the same conditions. Various metal chlorides were adopted to enhance the reaction kinetics of the hydrolysis and methanolysis, of which CoCl₂ exhibits the highest activity in both cases. With the addition of 2.0 mol % CoCl₂ at 25 °C, the methanolysis of GBH could generate 4 equiv of H₂ within 10 min with a maximum hydrogen generation rate of 9961.5 mL·min^<b>–</b>1·g^<b>–</b>1 while only 1.8 equiv of H₂ was obtained under the same conditions at a maximum hydrogen generation rate of 692.3 mL·min^<b>–</b>1·g^<b>–</b>1 for hydrolysis. Compared with hydrolysis, methanolysis of GBH possesses much faster reaction kinetics, rendering it an advantage for hydrogen generation, especially at subzero areas. It was proposed that the faster reaction kinetics of methanolysis of BH₄^– containing compounds is ascribed to the more electron donating methoxy group than that of hydroxyl group. Moreover, a comparison between hydrolysis and methanolysis of GBH indicates that the loss of the first H from BH₄^– controls the hydrolysis kinetics instead of the cleavage of the O–H bond

Vertically Aligned Nanocomposite BaTiO₃:YMnO₃ Thin Films with Room Temperature Multiferroic Properties toward Nanoscale Memory Devices

Self-assembled epitaxial BaTiO₃:YMnO₃ (BTO:YMO) vertically aligned nanocomposite thin films have been fabricated on SrTiO₃ (001) substrates using pulsed-laser deposition. A room temperature multiferroic response has been demonstrated in the thin films. Enormous strain has been generated in both phases (e.g., 1.4% compressive strain in BTO and 6.8% tensile strain in YMO out-of-plane) because of the large lattice mismatch. By tuning the deposition frequency, the microstructure and strain of the nanocomposite films are tailored, which leads to the property tuning in the nanocomposite films. It is found that strain plays an important role on the magnetic ordering of YMO and thus results in the room temperature ferromagnetic response. Combined with the ferroelectric response in the BTO:YMO nanocomposite thin films, a new room temperature multiferroic two-phase nanocomposite has been demonstrated. The room temperature magnetoelectric coupling has been demonstrated for this new system. Overall, the BTO:YMO thin film presents promising applications in sensors, data storage, and memory devices

Vertically Aligned Nanocomposite BaTiO₃:YMnO₃ Thin Films with Room Temperature Multiferroic Properties toward Nanoscale Memory Devices

Self-assembled epitaxial BaTiO₃:YMnO₃ (BTO:YMO) vertically aligned nanocomposite thin films have been fabricated on SrTiO₃ (001) substrates using pulsed-laser deposition. A room temperature multiferroic response has been demonstrated in the thin films. Enormous strain has been generated in both phases (e.g., 1.4% compressive strain in BTO and 6.8% tensile strain in YMO out-of-plane) because of the large lattice mismatch. By tuning the deposition frequency, the microstructure and strain of the nanocomposite films are tailored, which leads to the property tuning in the nanocomposite films. It is found that strain plays an important role on the magnetic ordering of YMO and thus results in the room temperature ferromagnetic response. Combined with the ferroelectric response in the BTO:YMO nanocomposite thin films, a new room temperature multiferroic two-phase nanocomposite has been demonstrated. The room temperature magnetoelectric coupling has been demonstrated for this new system. Overall, the BTO:YMO thin film presents promising applications in sensors, data storage, and memory devices

Continuous Tuning of Phase Transition Temperature in VO₂ Thin Films on <i>c</i>‑Cut Sapphire Substrates via Strain Variation

Vanadium dioxide (VO₂) thin films with controlled thicknesses are deposited on <i>c</i>-cut sapphire substrates with Al-doped ZnO (AZO) buffer layers by pulsed laser deposition. The surface roughness of AZO buffer layers is varied by controlling oxygen pressure during growth. The strain in the VO₂ lattice is found to be dependent on the VO₂ thickness and the VO₂/AZO interface roughness. The semiconductor-to-metal transition (SMT) properties of VO₂ thin films are characterized and the transition temperature (<i>T</i>_c) is successfully tuned by the VO₂ thickness as well as the VO₂/AZO interface roughness. It shows that the <i>T</i>_c of VO₂ decreases with the decrease of film thickness or VO₂/AZO interface roughness. Other SMT properties of the VO₂ films are maintained during the <i>T</i>_c tuning. The results suggest that the strain tuning induced by AZO buffer provides an effective approach for tuning <i>T</i>_c of VO₂ continuously

Strain and Interface Effects in a Novel Bismuth-Based Self-Assembled Supercell Structure

Bi₂FeMnO₆ (BFMO) thin films with both conventional pseudocubic structure and novel supercell structure have been grown on SrTiO₃ (001) substrates with different thicknesses of CeO₂ buffer layers (ranging from 6.7 to 50.0 nm) using pulsed laser deposition. The correlation between the thickness of the CeO₂ buffer layer and the structure of the BFMO films shows that the CeO₂ buffer layer, as thin as 6.7 nm, is sufficient in triggering the novel BFMO supercell structure. This may be ascribed to the interfacial strain between the BFMO supercell structure and the CeO₂ buffer layer which also serves as a seed layer. The buffer layer thickness is found to be critical to control the microstructure and magnetism of the formed BFMO supercell structures. Thin seed layers can produce a smoother interface between the BFMO film and the CeO₂ buffer layer, and therefore better ferrimagnetic properties. Our results have demonstrated that strain and interface could be utilized to generate novel thin film structures and to tune the functionalities of thin films

Self-Assembled Magnetic Metallic Nanopillars in Ceramic Matrix with Anisotropic Magnetic and Electrical Transport Properties

Ordered arrays of metallic nanopillars embedded in a ceramic matrix have recently attracted considerable interest for their multifunctionality in advanced devices. A number of hurdles need to be overcome for achieving practical devices, including selections of metal–ceramic combination, creation of tunable and ordered structure, and control of strain state. In this article, we demonstrate major advances to create such a fine nanoscale structure, i.e., epitaxial self-assembled vertically aligned metal–ceramic composite, in one-step growth using pulsed laser deposition. Tunable diameter and spacing of the nanopillars can be achieved by controlling the growth parameters such as deposition temperature. The magnetic metal–ceramic composite thin films demonstrate uniaxial anisotropic magnetic properties and enhanced coercivity compared to that of bulk metal. The system also presents unique anisotropic electrical transport properties under in-plane and out-of-plane directions. This work paves a new avenue to fabricate epitaxial metal–ceramic nanocomposites, which can simulate broader future explorations in nanocomposites with novel magnetic, optical, electrical, and catalytical properties

Novel Layered Supercell Structure from Bi₂AlMnO₆ for Multifunctionalities

Layered materials, e.g., graphene and transition metal (di)­chalcogenides, holding great promises in nanoscale device applications have been extensively studied in fundamental chemistry, solid state physics and materials research areas. In parallel, layered oxides (e.g., Aurivillius and Ruddlesden–Popper phases) present an attractive class of materials both because of their rich physics behind and potential device applications. In this work, we report a novel layered oxide material with self-assembled layered supercell structure consisting of two mismatch-layered sublattices of [Bi₃O_3+δ] and [MO₂]_1.84 (M = Al/Mn, simply named BAMO), i.e., alternative layered stacking of two mutually incommensurate sublattices made of a three-layer-thick Bi–O slab and a one-layer-thick Al/Mn–O octahedra slab in the out-of-plane direction. Strong room-temperature ferromagnetic and piezoelectric responses as well as anisotropic optical property have been demonstrated with great potentials in various device applications. The realization of the novel BAMO layered supercell structure in this work has paved an avenue toward exploring and designing new materials with multifunctionalities