Two-Dimensional Perovskite Crystals Formed by Atomic Layer Deposition of CaTiO3 on γ-Al2O3

A Study of Support Effects for the Water-Gas-Shift Reaction over Cu

The water–gas-shift (WGS) reaction was studied on a series of supported Cu catalysts in which the MgAl2O4 (MAO) support was modified by depositing ZnO, CeO2, Mn2O3 and CoO using Atomic Layer Deposition (ALD). Addition of Cu by one ALD cycle gave rise to catalysts with nominally 1-wt% Cu. A 1.1-wt% Cu/MAO catalyst prepared by ALD exhibited twice the dispersion but ten times the WGS activity of a 1-wt% Cu/MAO catalyst prepared by impregnation, implying that the reaction is structure sensitive. However, Cu catalysts prepared with the ZnO, CeO2, and Mn2O3 films showed negligible differences from that of the Cu/MAO catalyst, implying that these oxides did not promote the reaction. Cu catalysts prepared on the CoO film showed a slightly lower activity, possibly due to alloy formation. The implications of these results for the development of better WGS catalysts is discussed.

Modulating Interactions between Molten Polystyrene and Porous Solids Using Atomic Layer Deposition

Understanding and modulating the interactions between molten polymers and porous solids is important for numerous processes and phenomena including catalytic conversion of polymers and fabrication of nanocomposites and nanostructured materials. Although changing the surface composition of pores would enable modulation of interactions between polymers and nanoporous solids, it is challenging to achieve such a control without inducing significant changes to the size and structure of nanopores. In this work, we demonstrate that the interactions between molten polystyrene (PS) and disordered packings of SiO₂ nanoparticles (NPs) can be modulated by changing the surface composition of the NPs using atomic layer deposition (ALD). A disordered packing of silica NPs is modified with varying surface coverages of TiO₂, WO₃, and CaCO₃, with coverages estimated by the mass gain and the refractive index change of NP packings. Based on the time required to fully infiltrate these ALD-modified NP packings via capillarity, the contact angles for PS on different surfaces prepared via ALD are determined. The contact angle gradually changes from that of pure SiO₂ to that of the fully covered surfaces. The contact angles for PS on SiO₂, TiO₂, WO₃, and CaCO₃ are found to be 20, 62, 70, and 10°, respectively. Interestingly, the contact angles and interfacial energies between PS and the ALD-modified surfaces do not correlate strongly with the water contact angle of these surfaces; thus, caution must be exercised in predicting how a polymer would wet or interact with porous solids solely based on their hydrophilicity. The method presented in this work can be extended to study the interactions between a wide range of polymers and surfaces in porous media, which will have important implications for designing new catalytic materials for polymer upcycling reactions and novel NP-polymer composite films and membranes with enhanced mechanical and transport properties.

Excellent Bipolar Resistive Switching Characteristics of Bi4Ti3O12 Thin Films Prepared via Sol-Gel Process

Herein, Bi₄Ti₃O₁₂ (BIT) ferroelectric thin films were fabricated into Au/BIT/LaNiO₃/Si structures to demonstrate their memristor properties. Repeatable and stable bipolar resistive switching (RS) characteristics of the device are first reported in this work. The switching ratio of the device annealed in air reached approximately 10² at 0.1 and −0.1 V. The RS performance was not significantly degraded after 100 consecutive cycles of testing. We also explored the factors affecting the RS behavior of the device. By investigating the RS characteristics of the devices annealed in O_2, and in combination with XPS analysis, we found that the RS properties were closely related to the presence of oxygen vacancies. The devices annealed in air exhibited a markedly improved RS effect over those annealed in O₂. According to the slope fitting, the conduction mechanism of the device was the ohmic conduction and space charge limited current (SCLC). This study is the first to successfully apply BIT ferroelectric films to the RS layers of memristors. Additionally, a theory of conductive filaments is proposed to adequately explain the relationship between RS behavior and oxygen vacancies, providing meaningful inspiration for designing high-quality resistive random access memory devices.