Catalytic Applications of Non-Centrosymmetric Oxide Nanomaterials.

Noble-metal-free catalytic nanoparticles hold the promise being abundant, low-cost materials having a small environmental footprint and excellent performance, albeit inferior to that of noble metal counterparts. Several materials have a long-standing history of success in photocatalysis, in particular titanium dioxide, and in recent years more complex oxides and added functionality have emerged with enhanced performance. We will discuss different approaches related to the use of non-centrosymmetric and polar oxide nanoparticles and how the bulk photovoltaic effect, piezoelectricity, and pyroelectricity add to photocatalysis and tribocatalysis. We pay special attention to discriminate between the role of free versus that of bound charges within the catalyst, which is crucial to disentangle the different contributions to the catalytic reaction for the benefit of the overall enhanced catalytic performance in e.g. wastewater treatment and ultimately water-splitting.

A Complementary Metal Oxide Semiconductor Process-Compatible Ferroelectric Tunnel Junction.

In recent years, experimental demonstration of ferroelectric tunnel junctions (FTJ) based on perovskite tunnel barriers has been reported. However, integrating these perovskite materials into conventional silicon memory technology remains challenging due to their lack of compatibility with the complementary metal oxide semiconductor process (CMOS). This communication reports the fabrication of an FTJ based on a CMOS-compatible tunnel barrier Hf0.5Zr0.5O2 (6 unit cells thick) on an equally CMOS-compatible TiN electrode. Analysis of the FTJ by grazing angle incidence X-ray diffraction confirmed the formation of the noncentrosymmetric orthorhombic phase (Pbc21, ferroelectric phase). The FTJ characterization is followed by the reconstruction of the electrostatic potential profile in the as-grown TiN/Hf0.5Zr0.5O2/Pt heterostructure. A direct tunneling current model across a trapezoidal barrier was used to correlate the electronic and electrical properties of our FTJ devices. The good agreement between the experimental and theoretical model attests to the tunneling electroresistance effect (TER) in our FTJ device. A TER ratio of ∼15 was calculated for the present FTJ device at low read voltage (+0.2 V). This study suggests that Hf0.5Zr0.5O2 is a promising candidate for integration into conventional Si memory technology.