Articles you may be interested inStabilizing resistive switching performances of TiN/MgZnO/ZnO/Pt heterostructure memory devices by programming the proper compliance current Appl. Phys. Lett.We report the bi-epitaxial growth of ZnO and resistance switching characteristics of Pt/ZnO/TiNbased heterojunction devices fabricated on Si(001) substrates by pulsed laser deposition. The structural properties of the heterostructures characterized by XRD (h-2h, u scans) and TEM confirm that the ZnO films having hexagonal wurtzite structure (six-fold symmetry) grow biepitaxially on the TiN buffer layer (four-fold symmetry). The Pt(111) grows epitaxially on ZnO(0001). The epitaxial relationship between the various films is given as (111) Pt k (0001) ZnO k (001) TiN k (001) Si and [100] TiN k [100] Si , ½2 1 10 ZnO k [110] TiN or ½10 10 ZnO k ½110 TiN , and ½10 1 Pt k ½2 1 10 ZnO . The effect of ZnO growth temperature on the electrical properties of Pt/ZnO/TiN devices is studied and correlated with the microstructure of the ZnO/TiN interface. The Pt/ZnO/TiN devices exhibited good bi-polar resistance switching characteristics at voltages as low as 61 V. V C 2014 AIP Publishing LLC. [http://dx.
The multiferroic properties of mixed valence perovskites such as lanthanum strontium manganese oxide (LaSrMnO) (LSMO) demonstrate a unique dependence on oxygen concentration, thickness, strain, and orientation. To better understand the role of each variable, a systematic study has been performed. In this study, epitaxial growth of LSMO (110) thin films with thicknesses ∼15 nm are reported on epitaxial magnesium oxide (111) buffered AlO (0001) substrates. Four LSMO films with changing oxygen concentration have been investigated. The oxygen content in the films was controlled by varying the oxygen partial pressure from 1 × 10 to 1 × 10 Torr during deposition and subsequent cooldown. X-ray diffraction established the out-of-plane and in-plane plane matching to be (111) ∥ (0001) and ⟨11̅0⟩ ∥ ⟨101̅0⟩ for the buffer layer with the substrate, and an out-of-plane lattice matching of (110) ∥ (111) for the LSMO layer. For the case of the LSMO growth on MgO, a novel growth mode has been demonstrated, showing that three in-plane matching variants are present: (i) ⟨11̅0⟩ ∥ ⟨11̅0⟩, (ii) ⟨11̅0⟩ ∥ ⟨101̅⟩, and (iii) ⟨11̅0⟩ ∥ ⟨01̅1⟩. The atomic resolution scanning transmission electron microscopy (STEM) images were taken of the interfaces that showed a thin, ∼2 monolayer intermixed phase while high-angle annular dark field (HAADF) cross-section images revealed 4/5 plane matching between the film and the buffer and similar domain sizes between different samples. Magnetic properties were measured for all films and the gradual decrease in saturation magnetization is reported with decreasing oxygen partial pressure during growth. A systematic increase in the interplanar spacing was observed by X-ray diffraction of the films with lower oxygen concentration, indicating the decrease in the lattice constant in the plane due to the point defects. Samples demonstrated an insulating behavior for samples grown under low oxygen partial pressure and semiconducting behavior for the highest oxygen partial pressures. Magnetotransport measurements showed ∼36.2% decrease in electrical resistivity with an applied magnetic field of 10 T at 50 K and ∼1.3% at room temperature for the highly oxygenated sample.
We report a detailed investigation on the structure-property correlations in Ga and Al codoped ZnO films on c-sapphire substrates where the thin film microstructure varies from nanocrystalline to single crystal. We have achieved highly epitaxial films with very high optical transmittance (close to 90%) and low resistivity (∼110 μΩ-cm) values. The films grown in an ambient oxygen partial pressure (PO2) of 5 × 10−2 Torr and at growth temperatures from room temperature to 600 °C show semiconducting behavior, whereas samples grown at a PO2 of 1 × 10−3 Torr show metallic nature. The most striking feature is the occurrence of resistivity minima at relatively high temperatures around 110 K in films deposited at high temperatures. The measured optical and transport properties were found to be a strong function of growth conditions implying that the drastic changes are brought about essentially by native point defects. The structure-property correlations reveal that point defects play an important role in modifying the structural, optical, electrical, and magnetic properties and such changes in physical properties are controlled predominantly by the defect content.
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