Enhanced electrical properties of amorphous In-Sn-Zn oxides through heterostructuring with Bi2Se3 topological insulators.

Amorphous indium tin zinc oxide (a-ITZO)/Bi2Se3 nanoplatelets (NPs) were fabricated using a two-step procedure. First, Bi2Se3 NPs were synthesized through thermal chemical vapor deposition at 600 °C on a glass substrate, and then a-ITZO was deposited on the surface of the Bi2Se3 NPs via magnetron sputtering at room-temperature. The crystal structures of the a-ITZO/Bi2Se3 NPs were determined via X-ray diffraction spectroscopy and high-resolution transmission electron microscopy. The elemental vibration modes and binding energies were measured using Raman spectroscopy and X-ray photoelectron spectroscopy. The morphologies were examined using field-emission scanning electron microscopy. The electrical properties of the a-ITZO/Bi2Se3 NPs were evaluated using Hall effect measurements. The bulk carrier concentration of a-ITZO was not affected by the heterostructure with Bi2Se3. In the case of the Bi2Se3 heterostructure, the carrier mobility and conductivity of a-ITZO were increased by 263.6% and 281.4%, respectively, whereas the resistivity of a-ITZO was reduced by 73.57%. This indicates that Bi2Se3 significantly improves the electrical properties of a-ITZO through its heterostructure, expanding its potential applications in electronic and thermoelectric devices.

Magnetic Properties and Microstructure of FePt(BN, X, C) (X = Ag, Re) Films.

A sputtered FePt(BN, Re, C) film, here boron nitride (BN), was compared to a reference sample FePt(BN, Ag, C). Intrinsically, these films illustrate a high anisotropy field (Hk) and perpendicular magnetocrystalline anisotropy (Ku),although the reference sample shows a higher value (Hk = 69.5 kOe, Ku = 1.74 × 107 erg/cm3) than the FePt(BN, Re, C) film (Hk = 66.9 kOe, Ku = 1.46 × 107 erg/cm3). However, the small difference in the anisotropy constant (K2/K1) ratio presents a close tendency in the angular dependence of the switching field. Extrinsically, the out-of-plane coercivity for the reference sample is 32 kOe, which is also higher than the FePt(BN, Re, C) film (Hc = 27 kOe), and both films present lower remanence (Mr(parallel)/Mr(perpendicular) = 0.08~0.12), that is, the index for perpendicular magnetic anisotropy. The higher perpendicular magnetization for both films was due to highly (001) textured FePt films, which was also evidenced by the tight rocking width of 4.1°/3.0° for (001)/(002) X-ray diffraction peaks, respectively, and high-enough ordering degree. The reference sample was measured to have a higher ordering degree (S = 0.84) than FePt(BN, Re, C) (S = 0.63). As a result, the Ag segregant shows stronger ability to promote the ordering of the FePt film; however, the FePt(BN, Re, C) film still has comparable magnetic properties without Ag doping. From the surface and elemental composition analysis, the metallic Re atoms found in the FePt lattice result in a strong spin-orbital coupling between transition metal Fe (3d electron) and heavy metals (Re, Pt) (5d electron) and we conducted high magnetocrystalline anisotropy (Ku). Above is the explanation that the lower-ordered FePt(BN, Re, C) film still has high-enough Ku and out-of-plane Hc. Regarding the microstructure, both the reference sample and FePt(BN, Re, C) show granular structure and columnar grains, and the respective average grain size and distributions are 6.60 nm (12.5%) and 11.2 nm (15.9%). The average widths of the grain boundaries and the aspect ratio of the columnar grain height are 2.05 nm, 1.00 nm, 2.35 nm, and 1.70 nm, respectively.

Zinc oxide nanostructures enhanced photoluminescence by carbon-black nanoparticles in Moiré heterostructures.

ZnO/carbon-black heterostructures were synthesized using a sol-gel method and crystallized by annealing at 500 °C under 2 × 10-2 Torr for 10 min. The crystal structures and binding vibration modes were determined by XRD, HRTEM, and Raman spectrometry. Their surface morphologies were observed by FESEM. The Moiré pattern that is observed in the HRTEM images confirms that the carbon-black nanoparticles were covered by the ZnO crystals. Measurements of optical absorptance revealed that the optical band gap of the ZnO/carbon-black heterostructures increased from 2.33 to 2.98 eV as the carbon-black nanoparticle content increases from 0 to 8.33 × 10-3 mol owing to the Burstein-Moss effect. The photoluminescence intensities at the near-band edge and of the violet, and blue light were increased by factors about 68.3, 62.8, and 56.8, respectively, when the carbon-black contents is of the 2.03 × 10-3 mol. This work reveals that the proper carbon-black nanoparticle content involved increases the PL intensities of the ZnO crystals in the short wavelength regime, supporting their potential application in the light-emitting devices.

Switching Field Distribution in BN/FePtCAg/MgTiON and FePtCAg/MgTiOBN Films.

BN is the currently required segregant for perpendicular FePt media. We found that BN can be diffused from the MgTiOBN intermediate layer during a high temperature process. The FePtCAg film sputtered on MgTiOBN layers illustrates higher perpendicular magnetocrystalline anisotropy (Ku) (1.43 × 107 erg/cm3) and coercivity (normal to film surface) (17 kOe) at 350 K compared to BN/FePtCAg/MgTiON film. From the microstructure, the FePtCAg film shows the granular structure on the MgTiOBN intermediate layer, but parts of the irregular FePt grains are agglomerated and partially separated in the matrix, with grains size being, on average, 26.7 nm. Cross-sectional imaging showed that the FePt grains have a truncated pyramid shape with a lower wetting angle, which is influenced by the surface energy of MgTiOBN. BN segregation at FePt grains or boundaries is still not clear. Using the electron energy loss spectrum (EELS), we found that part of the BN atoms were clearly observed in the FePt lattice and iron-boride oxide was indexed in the x-ray photoelectron spectroscopy (XPS) spectra. To determine the effects of BN segregant (from capping layer or intermediate layer) on the magnetic switching behavior of FePtCAg film, the intrinsic-(ΔHint = 6.17 kOe, 6.54 kOe) and extrinsic- (ΔHext = 0.80 kOe, 0.39 kOe) switching field distribution (SFD) were measured by plotting saturated major- and unsaturated minor- hysteresis loops to evaluate the crystal orientation and microstructure (grains volume and distribution) for BN/FePtCAg/MgTiON and FePtCAg/MgTiOBN films, respectively. The main contribution of intrinsic SFD is the c-axis misalignment for the BN/FePt/MgTiON sample; however, the dispersed magnetic anisotropy has a higher input to intrinsic SFD for FePtCAg/MgTiOBN/CrRu film.