expansion increases the bandwidth and reduces the density of states (DOS) of the Fermi level, however, the strong orbital hybridization between Ru 4d and O 2p of SRO will enhance the DOS, resulting in ferromagnetic interaction and metallicity, and the Curie temperature (T c ) of bulk SRO as high as 160 K. [16,17] SRO also has good electrical conductivity, thermal property, and chemical inertia, and has a high lattice matching degree on a variety of commonly used substrates. [18,19] Recent research on SRO heterostructures and superlattices with ultra-thin SRO layer further show remarkable phenomena. Typical examples include the ferroelectric tunable topological Hall effect (THE), [20][21][22][23][24] skyrmion in BaTiO 3 /SrRuO 3 , [9] and spin chirality fluctuation in 2D SRO ferromagnets with perpendicular magnetic anisotropy. [25] Besides, SRO is also used extensively in the study of anomalous Hall effect (AHE). [8,9,26,27] In SRO, both the AHE and THE of the SRO/STO heterostructure show a strong SRO thickness (t SRO ) dependence. If the thickness is not accurate or uniform, areas with different thicknesses will be superimposed, resulting in an artificial THE signal. [28] Therefore, a layer-by-layer growth mode is desired to precisely regulate the thickness at the unit cell (u.c.) level.However, quite different from many perovskite oxides such as La 2/3 Sr 1/3 MnO 3 , LaCoO 3 , and SrTiO 3 , where a layerby-layer growth mode can persist for even 100 unit cells, the SRO usually quickly transits from layer-by-layer mode into step-flow mode. According to previous studies, when SRO thin film is grown on a TiO 2 -terminated (001) STO substrate, the terminated atomic layer changes from the B-site to the A-site in the first period, [29,30] resulting in the transition from 2D layerby-layer mode to step-flow mode. In step-flow growth mode, the RHEED intensity does not oscillate and remains stable, making the thickness of the films impossible to be intuitively monitored by RHEED. Therefore, it is difficult to accurately control the thickness of superlattices and multilayer films.In this paper, we report the exploration of layer-by-layer growth of SRO. The epitaxial SRO thin films and (SRO n /STO 5 ) 10 superlattices were grown on TiO 2 -terminated (001) STO substrates. The single TiO 2 -terminated (001) STO substrates were obtained through standard buffered oxide etch (BOE) One of the keys to the construction of metal oxide heterostructures is the short characteristic length scale, which requires controlled growth and interface engineering on an atomic level. At present, the growth mode of SrRuO 3 (SRO) thin films grown on TiO 2 -terminated (001) SrTiO 3 (STO) substrates usually transitions from 2D layer-by-layer to step-flow at the first few growth periods, which is not conducive to the construction of superlattices or multilayer films. In this paper, persistent layer-by-layer growth of SRO thin films is demonstrated by regulating the growth conditions. As a result, the thickness can be precisely controlled down to a sing...
Designing a broad-spectrum gas sensor capable of identifying gas components in complex environments, such as mixed atmospheres or extreme temperatures, is a significant concern for various technologies, including energy, geological science, and planetary exploration. The main challenge lies in finding materials that exhibit high chemical stability and wide working temperature range. Materials that amplify signals through non-chemical methods could open up new sensing avenues. Here, we present the discovery of a broad-spectrum gas sensor utilizing correlated two-dimensional gas (C-2DEG) at a delta-doped LaAlO3/SrTiO3 interface with LaFeO3. Our study revealed that a back-gating on this 2DEG can induce a non-volatile metal to insulator transition, which consequently can activate the 2DEG to sensitively and quantitatively probe very broad gas species, no matter whether these are polar, non-polar, or inert gases. Such C-2DEG sensor remains stable in almost any atmosphere within a wide temperature range, and its readout is a simple measurement of electric resistance change, thus providing a very low-cost and high-efficient sensing technique.
How to promote the resistance switching ratio, enlarge the operating temperature range and accelerate the switching speed is at the forefront of ionic gating electronics. Usually, most attention has been paid to materials with metal‐to‐insulator transition (MIT), e.g., VO2 and SmNiO3. Here, Sr‐doped nickelate (Nd0.8Sr0.2NiO3) films which do not exhibit MIT are used for electric field control of H‐doping and to detect the variation of resistance, lattice, and electronic structures. The experimental results directly show a giant resistive switching by more than 105 at the full temperature range (2 K–300 K) and lattice modulation by 3.4%. More importantly, much faster switching speeds can be achieved in Nd0.8Sr0.2NiO3 devices than in nondoped NdNiO3 ones. Such high switching performance is demonstrated to arise from strongly suppressed Ni–O hybridization after H doping. The results of this study provide a new material paradigm for developing energy‐efficient neuromorphic computing. Further, the doping effect on device performance also suggests a novel approach to develop correlated perovskite oxide transistors in order to fulfill practical applications.
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