In-plane Epitaxial Growth Research Articles

Three-dimensionally oriented organization of hexagonal MIL-96 microplates toward superior film microstructure

Preferential orientation control of MOF films is advantageous for maximizing pore uniformity and minimizing grain boundary defects. Nonetheless, the preparation of MOF films with both in-plane and out-of-plane orientations remains a grand challenge. In this study, we reported the preparation of three-dimensionally oriented MIL-96 layers through combining morphology control of MIL-96 seeds with addition of PVP surfactants and arachidonic acids. Three-dimensionally oriented MIL-96 film was readily obtained through in-plane epitaxial growth. It is anticipated that the above protocol can be effective for obtaining diverse MOF films with three-dimensionally oriented organization.

A novel S-scheme 3D ZnIn2S4/WO3 heterostructure for improved hydrogen production under visible light irradiation

In-plane epitaxial growth of ZnIn2S4 nanosheets on the surface of hexagonal phase WO3 nanorods was achieved by a facile solvothermal method. The unique 3D heterostructure not only enlarged the specific surface area, but also red-shifted the absorption edge from 381 to 476 nm to improve the light harvesting ability, which largely enhanced the photocatalytic hydrogen evolution. The H2 production rate of the best performing ZnIn2S4/WO3 photocatalyst (ZIS-2.5/W, the material with a molar rate of ZnIn2S4 (ZIS) to WO3 (W) of 2.5) was 300 μmol·g−1·h−1, around 417 times and 2 times higher than the rates of pristine WO3 and ZnIn2S4, respectively. The apparent quantum efficiency for ZIS-2.5/W composite was up to 2.81% at 400 nm. Based on the difference in Fermi levels between WO3 and ZnIn2S4, and the distribution of the redox active sites on WO3/ZnIn2S4 heterostructure, a S-scheme electron transfer mechanism was proposed to illustrate the improved photocatalytic activity of WO3/ZnIn2S4 heterojunction, which not only stimulated the spatial separation of the photogenerated charge carriers, but also maintained the strong reduction/oxidation ability of the photocatalyst.

Anisotropic Gas Separation in Oriented ZIF‐95 Membranes Prepared by Vapor‐Assisted In‐Plane Epitaxial Growth

Control of the microstructure grain orientation, grain boundaries and thickness are crucial for MOF membranes. We report a novel synthesis strategy to prepare highly c-oriented ZIF-95 membranes through vapor-assisted in-plane epitaxial growth. In a mixed DMF/water vapor atmosphere, in-plane epitaxial growth of a ZIF-95 seeds layer was achieved to obtain an oriented and well-intergrown ZIF-95 membrane with a thickness of only 600 nm. Demonstrated by both experimental and simulation studies, the c-oriented ZIF-95 membrane displayed superior separation performance because a perfectly oriented structure resulted in a notable reduction of intercrystalline defects and transport pathways. For the separation of equimolar binary mixtures at 100 °C and 1 bar, the mixture separation factors of H2 /CO2 and H2 /CH4 were 32.2 and 53.7, respectively, with an H2 permeance of over 7.9×10-7 mol m-2 s-1 Pa-1 , which was 4.6 times higher than that of a randomly oriented ZIF-95 membrane.

Single-Mode Microwave Heating-Induced Concurrent Out-of-Plane Twin Growth Suppression and In-Plane Epitaxial Growth Promotion of b-Oriented MFI Film under Mild Reaction Conditions.

In this study, single-mode microwave heating was applied in epitaxial growth of b-oriented MFI seed monolayer prepared by facile manual assembly, resulting in the formation of well-intergrown and highly b-oriented MFI film with few twins. It exhibited a precise molecular sieving property at a reaction temperature no higher than 100 °C within 2 hours, therefore making it possible for easy operation in an open environment. The capability for concurrent suppression of undesired out-of-plane twin growth and promotion of in-plane epitaxial growth rate under mild reaction conditions was attributed to the obvious superiority of single-mode microwave heating in comparison with conventional multi-mode microwave heating in aspects of microwave field uniformity and intensity. Our research indicated that the single-mode microwave heating technique could potentially be a useful tool for improving the microstructure and therefore the performance of diverse zeolite films.

In-Plane Epitaxial Growth of Highly c-Oriented NH2 -MIL-125(Ti) Membranes with Superior H2 /CO2 Selectivity.

Preferred-orientation control has significant impact on the separation performance of MOF membranes. Under most conditions the preferred orientation of MOF membranes is dominated by the Van der Drift mechanism of evolutionary growth selection so that the obtained orientation may not be optimized for practical application. In this study, highly c-oriented NH2 -MIL-125 membranes were prepared on porous α-alumina substrates by combining oriented seeding and controlled in-plane epitaxial growth. Dynamic air-liquid interface-assisted self-assembly of c-oriented NH2 -MIL-125(Ti) seed monolayers, the use of layered TiS2 as the metal precursor, and single-mode microwave heating were crucial in ensuring the preferred c-orientation while simultaneously suppressing undesired twin growth. Owing to reduced grain boundary defects, the prepared c-oriented membranes showed an ideal H2 /CO2 selectivity of 24.8, which was 6.1 times higher than that of their randomly oriented counterparts under similar operating conditions.

Investigation on orientation, epitaxial growth and microstructure of a-axis-, c-axis-, (103)/(110)- and (113)-oriented YBa2Cu3O7−δ films prepared on (001), (110) and (111) SrTiO3 single crystal substrates by spray atomizing and coprecipitating laser chemical vapor deposition

a-axis-, c-axis-, (103)/(110)- and (113)-oriented YBa2Cu3O7−δ (YBCO) films were pareared by spray atomizing and coprecipitating laser chemical vapor deposition. The surface of the a-axis-oriented YBCO film consisted of rectangular needle-like grains whose in-plane epitaxial growth relationship was YBCO [100] // STO [001] (YBCO [001] // STO [100]), and that of the c-axis-oriented YBCO film consisted of dense flat surface with epitaxial growth relationship of YBCO [001] // STO [001] (YBCO [100] //STO [100]). For the (103)/(110)-oriented and (113)-oriented YBCO film, they showed wedge-shaped and triangle-shaped grains, with corresponding in-plane epitaxial growth relationship of YBCO [110] // STO [110] (YBCO [010] // STO [010]) and YBCO [100] // STO [100] (YBCO [113] // STO [111], respectively.

In-Plane Epitaxial Growth of Self-Assembled Ge Nanowires on Si Substrates Patterned by a Focused Ion Beam

We report a novel method for obtaining ordered arrays of self-assembled Ge nanowires (NWs) using Au seed catalysts, with the latter deposited using a focused ion beam (FIB). For this purpose we apply a three-step process involving first FIB nanopatterning, a second step of AuSi seed formation during UHV annealing, and third the nucleation and growth of Ge NWs by combining molecular-beam epitaxy (MBE) and the vapor–liquid–solid (VLS) process. We show that FIB allows for the local implantation of Au in the areas impacted by the ion beam; the implanted Au evolves during annealing into AuSi clusters, serving as nucleation seeds for the nucleation and growth of Ge NWs. We thus prove that FIB with gold ions is a successful method to obtain gold-catalyzed self-assembled nanowires. We obtain Ge NWs of homogeneous dimensions and oriented in-plane along [110] directions, as a consequence of a strain-driven process. Wire kinking is governed by surface morphological features. Based on our experimental results, we ela...

Fast epitaxial growth of a-axis- and c-axis-oriented YBa2Cu3O7−δ films on (1 0 0) LaAlO3 substrate by laser chemical vapor deposition

a-axis- and c-axis-oriented YBa2Cu3O7−δ (YBCO) films were epitaxially grown on (100) LaAlO3 substrates by laser chemical vapor deposition. The preferred orientation in the YBCO film changed from the a-axis to the c-axis with increasing laser powers from 77 to 158W (the deposition temperatures from 951 to 1087K). The a-axis-oriented YBCO film showed in-plane epitaxial growth of YBCO [001]//LAO [001], and the c-axis-oriented YBCO film showed that of YBCO [010]//LAO [001]. A c-axis-oriented YBCO film with a high critical temperature of 90K was prepared at a deposition rate of 90μmh−1, about 2–1000 times higher than that of metalorganic chemical vapor deposition.

THICKNESS EFFECTS ON THE EPITAXIAL NATURE OF THE SINGLE-PHASE MULTIFERROIC THIN FILMS

Multiferroic Bi 0.95 La 0.05 Fe 0.7 Sc 0.3 O 3 (BLFS) thin films with different thicknesses have been prepared on (1 0 0) LaAlO 3 (LAO) substrates using a sol–gel process and annealed in N 2 ambient at 650°C for 5 min. From the X-ray diffraction (XRD) analysis, it was observed that BLFS thin films had (h 0 0)-preferred orientation for the film thickness 63, 125, 186, and 240 nm and became isotropic thereafter. The films developed in-plane epitaxial growth with respect to the substrate. The surface morphology became denser and the surface roughness increased as thickness increased up to 241 nm. The highest dielectric constant observed for the 241 nm thick BLFS film too. No prominent of the leakage current density observed for the film thickness up to 241 nm. However, two fold increase in the leakage current density observed for the film thickness 382 nm. For the BLFS films with thickness 241 nm, we observed the highest dielectric constant (ε) value of 1675 and remnant polarization (Pr) polarization value of 52 μC/cm2 using a sol–gel spin coating process.

Epitaxial growth and luminescence properties of ZnO-based heterojunction light-emitting diode on Si(1 1 1) substrate by pulsed-laser deposition

An epitaxial ZnO heterojunction light-emitting diode with an n-ZnO/MgO/TiN/n+-Si structure is produced by pulsed-laser deposition. By introducing a thin MgO/TiN buffer and a low temperature (LT) ZnO buffer, layer-by-layer growth of high quality ZnO epi-layer on Si(1 1 1) has been realized, which was confirmed by in situ reflection high-energy electron diffraction (RHEED), transmission electron microscopy, high-resolution x-ray diffraction, resonant Raman spectra and photoluminescence spectroscopy. Combining in situ RHEED with Phi-scan XRD analysis, the in-plane epitaxial growth of ZnO[1 1 0]||MgO[1 0 ]||Si[1 0 ] has been demonstrated. The strong room temperature electroluminescence (EL) with a broad emission band ranging from 1.46 to 3.5 eV and centred at 2.31 eV could be observed from the diode under relative low injection current. Furthermore, the EL output light intensity is enhanced obviously by improving the ZnO crystal quality via inserting a ZnO LT buffer layer.