Origin of perpendicular magnetic anisotropy in amorphous thin films

The emergence of perpendicular magnetic anisotropy (PMA) in amorphous thin films, which eventually transforms the magnetic spins form an in-plane to the out-of-plane configuration, also known as a spin-reorientation transition (SRT), is a fundamental roadblock to attain the high flux concentration advantage of these functional materials for broadband applications. The present work is focused on unfolding the origin of PMA in amorphous thin films deposited by magnetron sputtering. The amorphous films were deposited under a broad range of sputtering pressure (1.6–6.2 mTorr), and its effect on the thin film growth mechanisms was correlated to the static global magnetic behaviours, magnetic domain structure, and dynamic magnetic performance. The films deposited under low-pressure revealed a dominant in-plane uniaxial anisotropy along with an emerging, however feeble, perpendicular component, which eventually evolved as a dominant PMA when deposited under high-pressure sputtering. This change in the nature of anisotropy redefined the orientation of spins from in-plane to out-of-plane. The SRT in amorphous films was attributed to the dramatic change in the growth mechanism of disorder atomic structure from a homogeneously dispersed to a porous columnar microstructure. We suggest the origin of PMA is associated with the columnar growth of the amorphous films, which can be eluded by a careful selection of a deposition pressure regime to avoid its detrimental effect on the soft magnetic performance. To the author’s best knowledge, no such report links the sputtering pressure as a governing mechanism of perpendicular magnetisation in technologically important amorphous thin films.

Comparative Study of Pd/B4C X-ray Multilayer Mirrors Fabricated by Magnetron Sputtering with Kr and Ar Gas

Ultrathin Pd/B4C multilayers are suitable X-ray mirrors working at the photon energy region of 7–20 keV. To further improve the layer structure, Pd/B4C multilayers with a d-spacing of 2.5 nm were fabricated by magnetron sputtering using the heavy noble gas Kr and compared with the conventional ones fabricated by Ar. Although the Kr-sputtering process can work at a lower pressure, the interface width—especially the interface roughness—is a little larger than that made by Ar. A stronger polycrystallization and a lower content of sputter gas atoms were found in the Kr-made sample, which can be explained by the joint effect from less recoiled particles and lower sputtering pressure. A good reflectance of 68% of the Kr made multilayer was measured at 10 keV, which is only slightly lower than that of the Ar made sample (71%).

Controlled Sputtering Pressure on High-Quality Sb2Se3 Thin Film for Substrate Configurated Solar Cells

Magnetron sputtering has become an effective method in Sb2Se3 thin film photovoltaic. Research found that post-selenization treatments are essential to produce stoichiometric thin films with desired crystallinity and orientation for the sputtered Sb2Se3. However, the influence of the sputtering process on Sb2Se3 device performance has rarely been explored. In this work, the working pressure effect was thoroughly studied for the sputtered Sb2Se3 thin film solar cells. High-quality Sb2Se3 thin film was obtained when a bilayer structure was applied by sputtering the film at a high (1.5 Pa) and a low working pressure (1.0 Pa) subsequently. Such bilayer structure was found to be beneficial for both crystallization and preferred orientation of the Sb2Se3 thin film. Lastly, an interesting power conversion efficiency (PCE) of 5.5% was obtained for the champion device.

Sputtering pressure influenced structural, electrical and optical properties of RF magnetron sputtered MoO3 films

MoO3 films were deposited by RF magnetron sputtering technique on glass and silicon substrates held at 473 K by sputtering of metallic molybdenum target at an oxygen partial pressure of 4 × 10−2 Pa and at different sputtering pressures in the range of 2 Pa to 6 Pa. The influence of sputtering pressure on the structure and surface morphology, electrical and optical properties of the MoO3 thin films was studied. X-ray diffraction studies suggest that the films deposited at a sputtering pressure of 2 Pa were polycrystalline in nature with mixed phase of α- and β-phase MoO3, while those formed at sputtering pressure of 4 Pa and above were of α-phase MoO3. Scanning electron micrographs showed a decrement in the size of the particles and their shapes changed from needle like structure to dense films with the increase of sputtering pressure. Fourier transform infrared spectroscopic studies confirmed the presence of characteristic vibration modes of Mo=O, Mo–O and Mo–O–Mo related to MoO3. Electrical resistivity of the MoO3 films decreased from 6.0 × 104 Ω cm to 2 × 104 Ω cm with an increase of sputtering pressure from 2 Pa to 6 Pa, respectively. Optical band gap of the films decreased from 3.12 eV to 2.86 eV with the increase of sputtering pressure from 2 Pa to 6 Pa, respectively.