Facing-target Magnetron Sputtering Research Articles

Anomalous and topological Hall effects of ferromagnetic Fe3Sn2 epitaxial films with kagome lattice

Fe3Sn2, a ferromagnetic alloy with a kagome lattice, has attracted much attention from research communities owing to its special crystal structure and symmetry, which gives rise to numerous intriguing magneto-electronic properties, including the topological Hall effect, skyrmionic bubbles, Dirac cones, and Weyl points. To study such physical properties, Fe3Sn2 epitaxial films without buffer layers are in urgent need. In this work, we fabricated the Fe3Sn2 epitaxial films without buffer layers using the facing-target magnetron sputtering method, and their magneto-electronic transport properties were investigated systematically. It is found that the sign of the Hall resistivity slope in a high-field region is reversed when the temperature decreases below 100 K, suggesting a temperature-induced transition of charge carriers from electrons to holes. Moreover, a non-negligible topological Hall resistivity subtracted from the anomalous Hall resistivity is depicted, and its value is comparable to that of the Fe3Sn2 single crystals. These results not only offer a clear understanding of ferromagnetic Fe3Sn2 films with the kagome lattice but also provide guidance for fabrication and application of epitaxial Fe3Sn2 films.

Primitive exchange coupling in CoPt/MnN layered structures: Exchange coupling established during deposition

Bilayer and trilayer films with ferromagnetic CoPt and antiferromagnetic MnN constituent layers have been prepared by facing-target magnetron sputtering with a 6 Oe magnetic field applied to an in-plane direction of the growing film. Primitive exchange coupling, which signifies the exchange coupling occurred without conventional field cooling, has been investigated systematically by varying the component layer thickness. It has been shown that the interfacial spin configuration that initiates exchange coupling can be established at the interface when the MnN layer grows on the surface of the CoPt layer under a small field. The primitive exchange coupling shows an increasing tendency with increasing the MnN layer thickness, and a decreasing tendency with increasing the coupled CoPt layer thickness. And the coercivity of the coupled CoPt layer remain almost unchanged within the whole thickness range of both MnN and CoPt, which suggests the coercivity of the coupled CoPt layer is not only affected by exchange coupling.

Photocatalytic properties of transparent oxide thin films prepared by facing target magnetron sputtering

ABSTRACTIn this study, we fabricated indium tin oxide (ITO) films, which are well-known transparent oxide materials with low resistance and high transmittance. Their photocatalytic effect was investigated by using Rhodamine B (C28H31CIN2O3) solution. Facing target magnetron sputtering (FTS) was employed to deposit films on the substrate. The characteristics of the prepared films were analyzed using a UV-Vis spectrophotometer, a drop shape analyzer, a field emission scanning electron microscope, and a X-ray diffractometer. All samples exhibited optical transmittances of over 85% and resistance values under 50 ohm/sq. Moreover, as-prepared films were confirmed to have photocatalytic properties as seen from a decrease of Rhodamine B absorbance in their presence.

Properties of ITO-stacked AgNWs films prepared on flexible substrates by low damage sputtering

ABSTRACTIn this study, we fabricated the ITO-stacked AgNWs films on the various substrates and investigated their electrical, structural, and mechanical properties. Firstly, we coated Ag nanowires (AgNWs) layer on the soda-lime glass substrate and polymer substrate such as polyestersulfone (PES) and polycarbonate (PC) by using modified spin-coating method. And then, Indium Tin Oxide (ITO) film was deposited on coated-AgNWs layer by using facing targets magnetron sputtering (FTS) method at the room temperature. All samples prepared on various substrates have transmittance of about 80% in the visible range (300–800 nm) and low resistance of under 10 ohm/sq. And we investigated the properties of ITO-stacked AgNWs prepared on flexible substrate (PES, PC) by Lab-made bending machine. After substrate bending of 1000 times, the sheet resistance of prepared ITO single film 33.9 increased over 20000 ohm/sq and the sheet resistance of ITO-stacked AgNWs films increased from 8.38 to 19.33 ohm/sq in PES substrate and 6.69 to 24.42 ohm/sq in PC substrate.

Ti Capping Layer Effects in Microstructure and Magnetic Properties of Sputter-Deposited FePt Thin Film

Ti/FePt/Fe nano-thin films were fabricated by a DC facing-target magnetron sputtering method onto glass substrates at room temperature and were subsequently annealed in situ in vacuum. The impacts of the Ti capping layer on microstructural and magnetic properties of the FePt films were investigated in detail. X-ray diffraction (XRD) patterns demonstrate that the film is deposited onto glass substrates and the addition of a Ti layer forms ternary TiFePt, and binary PtTi and FeTi alloys. The results reveal refined granularity, decreased roughness, and enhanced coercivity and degree of squareness after the introduction of a Ti capping layer.

Inverse Magnetoresistance in Polymer Spin Valves.

In this work, both negative and positive magnetoresistance (MR) in solution-processed regioregular poly(3-hexylthiophene) (RR-P3HT) is observed in organic spin valves (OSVs) with vertical La2/3Sr1/3MnO3 (LSMO)/P3HT/AlOx/Co configuration. The ferromagnetic (FM) LSMO electrode with near-atomic flatness is fabricated by a DC facing-target magnetron sputtering method. This research is focused on the origin of the MR inversion. Two types of devices are investigated in details: One with Co penetration shows a negative MR of 0.2%, while the other well-defined device with a nonlinear behavior has a positive MR of 15.6%. The MR measurements in LSMO/AlOx/Co and LSMO/Co junctions are carried to exclude the interference of insulating layer and two FM electrodes themselves. By examining the Co thicknesses and their corresponding magnetic hysteresis loops, a spin-dependent hybrid-interface-state model by Co penetration is induced to explain the MR sign inversion. These results proven by density functional theory (DFT) calculations may shed light on the controllable interfacial properties in designing novel OSV devices.

Role of surface-electrical properties on the cell-viability of carbon thin films grown in nanodomain morphology

Carbon thin films, having a combination of unique physical and chemical properties, exhibit an interesting biocompatibility and biological response to living entities. Here, the carbon films are developed in the morphology form of nano-domains with nanoscale inter-domain separations, tuned by plasma conditions in the facing target magnetron sputtering process. The wettability and surface energy are found to have a close relation to the inter-domain separations. The chemical structure of carbon films exhibited the relative enhancement of sp3 in comparison to sp2 with the increase of domain separations. The cell-viability of these films shows promising results for L929 mouse fibroblast and Saos-2 bone cells, when inter-domain separation is increased. Electrical conductivity and surface energy are identified to play the key role in different time-scales during the cell-proliferation process. The contribution from electrical conductivity is dominant in the beginning of the cultivation, whereas with the passage of time (~3–5 d) the surface energy takes control over conductivity to enhance the cell proliferation.

Hysteresis behavior during facing target magnetron sputtering

Abstract The target-to-target distance affects the hysteresis behavior during reactive facing target sputtering. A decreasing target-to-target distance results in a shift of the first critical point towards lower reactive gas flows while only a minor effect on the position of the second critical point is noticed. Based on a time-dependent and spatially-resolved simulation model for reactive sputtering for multiple metallic targets, it is possible to elucidate the main mechanisms for these shifts. The slight difference in position of the second critical point can be understood from the perspective of target deposition. The shift in the first critical point under decreasing target separation is dominated by the decrease in the effective gettering area.

Enhanced photoelectrochemical performance of {001}TiO2/{001}SrTiO3 epitaxial heterostructures

The anatase TiO2 films with controllable {001} highly reactive facets were fabricated on {001}SrTiO3 substrate with various total work pressure (TWP) by direct current facing-target magnetron sputtering (DCFTMS). X-ray diffraction (XRD), scanning electron microscopy (SEM), surface roughness tester (SRT), and X-ray photoelectron spectroscopy (XPS) were employed to confirmed the influence of different TWPs on the interface of TiO2/SrTiO3 heterostructured with epitaxial preferred growth of the anatase {001}TiO2 facet. The mechanisms of enhanced photoelectrochemical properties were explored by transient photocurrent (TP), current–potential (I–V), cyclic voltammetry (CV), polarization (Tafel), electrochemical impedance spectroscopy (EIS), and Mott–Schottky (M–S) curves, which can be ascribed to the formation of high-quality heterojunction between {001}TiO2 thin film and {001}SrTiO3 substrate, which suppress the recombination of photogenerated electron–hole pairs effectively.

Investigation of γ′-Fe4N thin films deposited on Si(1 0 0) and GaAs(1 0 0) substrates by facing target magnetron sputtering

γ′-Fe4N thin films with good soft magnetic properties were successfully prepared on single crystal Si(100) and GaAs(100) substrates with Fe buffer layer by facing target magnetron sputtering. The microstructure and magnetic properties of the samples at low temperature were investigated. Both structural and magnetic properties of the films were shown to be influenced by the substrate. Specifically, the film deposited on the GaAs exhibited a strong preferred orientation along the (100) plane, while the film deposited on Si exhibited higher saturation magnetization (Ms) and lower coercivity (Hc). The results suggest that the coercivity is probably related to the intrinsic stress and that Ms increases whereas Hc decreases with decreasing lattice mismatch. The Mr/Ms ratio decreased with decreasing temperature due to the effect of the thermal disturbance on the magnetization. Both films had a single easy magnetized direction parallel to the substrate plane.

Sign change of magnetoresistance in Gd-doped amorphous carbon granular films.

Gd/C granular films with 11% Gd were fabricated by facing-target magnetron sputtering at room temperature and then annealed at 300-650 °C for 1.5 h. A magnetoresistance of -82% was obtained in the Gd/C films annealed at 650 °C at 3 K under a magnetic field of 50 kOe. A sign change of the magnetoresistance from negative to positive and then back to negative was observed in all samples as the temperature decreases. Grain boundary scattering effects, wave-function-shrinkage, cotunneling and Gd-Gd interactions account for the mechanisms of the magnetoresistance effects in different temperature regions. The sign of the magnetoresistance also varies as the magnetic field increases. At the transition temperature of 25 K, the wave-function-shrinkage effect competes with cotunneling and Gd-Gd interactions at different magnetic fields. The competition between the wave-function-shrinkage effect and the grain boundary scattering effect is approximately at the transition temperature of 100 K. The temperature range of positive magnetoresistance expands and transition temperatures are changed as the annealing temperature increases. It is related to the expansion of the temperature region for the wave-function-shrinkage effect which occurs in the Mott variable range hopping conduction mechanism.

Electrical, Optical and Structural Properties of AZO Thin Film Deposited Using Facing Targets Magnetron Sputtering System with Inductively Coupled Plasma

Electrical, Optical and Structural Properties of AZO Thin Film Deposited Using Facing Targets Magnetron Sputtering System with Inductively Coupled Plasma

Temperature-Insensitive Hydrogen Sensor With Polarization-Maintaining Photonic Crystal Fiber-Based Sagnac Interferometer

We demonstrated a temperature-insensitive hydrogen ( $H_{2}$ ) sensor based on polarization-maintaining photonic crystal fiber (PM-PCF). The sensing element is a section of PM-PCF coated with Pd/Ag composite film and is incorporated into a single mode fiber Sagnac loop interferometer. The birefringence of PM-PCF is modulated by $H_{2}$ absorption that induces deformation of the Pd/Ag composite film, resulting in shift of the interference spectrum at the output of the Sagnac interferometer. A magnetron facing target sputtering technique with special Pd/Ag rectangular target structures is developed to deposit Pd/Ag composite film on the cylindrical surface of the PM-PCF and the atomic ratio of Pd/Ag composite film is controlled by setting appropriate volume ratio in rectangular target. An empirical linear relationship between atomic ratio and volume ratio was obtained and the $H_{2}$ sensing capacity with different atomic ratio of Pd/Ag composite films was investigated experimentally. The results showed that increasing the proportion of Pd in the composite film improves the $H_{2}$ detection sensitivity. The sensitivity can also be improved by using as longer length of Pd/Ag coated PM-PCF. With ∼100 mm long coated PM-PCF as the sensing element, we obtained ∼1.310 nm shift in the interference spectrum for $H_{2}$ concentration from 0 to 1%. The sensitivity coefficient is ∼131 pm% in the range of 1% to 4% $H_{2}$ concentration. The sensor has low temperature dependence and good repeatability.

Large negative magnetoresistance and ferromagnetism induced by interfacial spins in granular Cr/C films

Cr/C composite films with 7.9 and 8.5at% Cr contents were fabricated by facing-target magnetron sputtering. Cr nanoparticles are embedded in amorphous carbon matrix, and Cr atoms bond with C atoms at the interface. The Cr/C films were found to exhibit ferromagnetism in the temperature range of 2–300K, which is probably induced by uncompensated spins at the surface of Cr nanoparticles. Spin-dependent magnetoresistance (up to −19.5% at 90kOe and 2K) was observed in the Cr/C films. The negative MR originates from the alignment of the uncompensated spins at the interface between nanoparticles and matrix. The spin polarization which comes from the interfacial p–d hybridization was calculated to be 21% and 17% in the Cr/C films with 7.9% and 8.5% Cr, respectively.

Structural and Electrical Properties of ZnO Films Deposited with Low-Temperature Facing Targets Magnetron Sputtering (FTS) System with Changes in H<SUB>2</SUB> and O<SUB>2</SUB> Flow Rate

ZnO has been studied as a strong candidate for high-quality TCO in accordance with increasing demand to replace ITO. The origin of n-doping in ZnO is not clearly understood, but recently, the H2 effect has received attention due to the role it plays in O-rich and O-poor conditions. In spite of recent rapid developments, controlling the electrical conductivity of ZnO has remained a major challenge. To control the electrical conductivity of ZnO, this study was performed using an FTS system with H2 and O2 addition at low processing temperature. The structural and electrical properties of ZnO thin films deposited at various H2 and O2 flow rates were investigated using XRD and a sheet resistance meter. In response to changes in H2 and O2 flow rates, the crystallization and related grain size of the ZnO films were somewhat changed. The sheet resistance increased from approximately 10(-1) to approximately 10(4) M ohm/sq. when the O2 flow rate was increased, and the resistance decreased from approximately 10(-1) to approximately 10(-4) M ohm/sq. when the H2 flow rate was increased. The increase of sheet resistance with O2 flow rates could be explained by decrease of oxygen vacancies. The decrease of sheet resistance with H2 flow rates could be explained by increase of the electrons from interstitial hydrogen atoms. The plasma characteristics were analyzed using optical emission spectroscopy (OES). But, the overall spectrum did not change with the H2 and O2 gas flow rates. So, the dramatic changes in the electrical properties of ZnO thin films could be considered to be a result of changes in chemical composition of the thin films rather than the plasma status.

Effects of rapid thermal annealing on the room-temperature NO2-sensing properties of WO3 thin films under LED radiation

WO3 thin films were sputtered onto alumina substrates by DC facing-target magnetron sputtering. One sample was rapid-thermal-annealed (RTA) at 600 °C in a gas mixture of N2:O2 = 4:1, and as a comparison, another was conventionally thermal-annealed at 600 °C in air. The morphology of both was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the crystallization structure and phase identification were characterized by X-ray diffraction (XRD). The NO2-sensing measurements were taken under LED light at room temperature. The sensitivity of the RTA-treated sample was found to be high, up to nearly 100, whereas the sensitivity of the conventionally thermal-annealed sample was about five under the same conditions. From the much better selectivity and response-recovery characteristics, it can be concluded that compared to conventional thermal annealing, RTA has a greater effect on the NO2-sensing properties of WO3 thin films.

Evolution of magnetoresistance mechanisms in granular Co/C films with different conduction regimes

Co/C granular films with 3–21% Co content are fabricated by facing-target magnetron sputtering. As the Co content increases, the isolated Co particles in the a-C matrix gradually connect with each other, and consequently the electrical transport of the Co/C films changes from insulating to metallic conduction. The insulating samples show spin-dependent negative magnetoresistance (MR), which is related to the alignment of the spins at the interface between Co particles and the carbon matrix. Interfacial spin polarization P0 is related to the amount of interfacial hybridization, which is influenced by the size of sp2 carbon clusters in the a-C matrix. Metallic samples show the competition of negative MR and positive linear MR. Negative MR observed at low temperatures is caused by a weak localization effect and is suppressed when the magnetic field is above 15 kOe. Positive linear MR is observed at high fields and high temperatures, and could be explained by quantum electron–electron interaction theory. The magnetotransport properties in the Co/C films are significantly influenced by the configuration of Co particles and, consequently, the conduction regime rather than the size of sp2 carbon clusters in the a-C matrix.

Microstructural and Magnetic Properties of C/FePt/Ti Films by Facing Sputtering

C/FePt/Ti nano-thin films were prepared by DC facing-target magnetron sputtering system onto glass substrates at room temperature and subsequently in situ annealed for 500 °C 30 min in vacuum. The influence of C capping layer on microstructural and magnetic properties of the FePt films were investigated in detail. Atomic force microscopy (AFM) images indicate that C can effectively isolate the particles, refine particle, and distribute; however, the particle size distribution is uneven for too much C. The easy magnetic axial orientation is changed with the C layer thickness.

Study on electronic transport and magnetic properties for antiperovskite Mn3CuNx thin films fabricated with different N2 flow rates

The antiperovskite Mn3CuNx thin films are successfully deposited on single crystal Si (100) substrates using facing target magnetron sputtering. The effects of nitrogen content on the structures and physical properties of the Mn3CuNx thin films are investigated. The crystal structure, composition, surface morphology and the temperature dependence of resistivity and magnetization are characterized by X-ray diffraction, Auger electron spectroscopy, atomic force microscope, X-ray photoelectron spectroscopy, physical property measurement systems and superconducting quantum interference device. It is found that the thin film has an antiperovskite structure and a preferred orientation along (200) plane. The surface roughness and particle size increase with N content increasing. N content has little influence on the electronic transport behavior of the film. All the films display semiconductor-like behaviors, i.e. their resistivities monotonically decrease considerably, which is different from the bulk counterpart. The film undergoes a magnetic transition from ferrimagnetic to paramagnetic with the increase of temperature. Moreover, the Curie temperature (TC) increases as the N content decreases, owing to the effect of N deficiency on the interaction of Mn6N octahedron.

Preparation and characteristic of phase transition vanadium oxide thin films by rapid thermal process

Metal-insulator phase transition VOX thin film is fabricated on a Si 100 substrate after the metal V thin film, prepared by direct current facing targets magnetron sputtering has been rapidly thermally treated first in pure oxygen environment and then in pure nitrogen environment. The thermal treatment conditions are 430℃/40 s, 450℃/40 s, 470℃/40 s, 450℃/30 s, 450℃/50 s in pure oxygen environment and 500℃/15 s in pure nitrogen environment. XRD, XPS, AFM and SEM are imployed to analyze the crystalline structure, valentstate and the components, morphology of the thin film. The electrical and optical characteristic of the thin film are analyzed by the Four-point probe method and THz time domain spectrum technology. Results reveal that after 450℃/40 s rapid thermal treatment in pure oxygen environment the metal V thin film turns into VOX thin film which has low properties of phase transition. Before and after heating, the change of resistivity reaches 2 orders of magnitude and the range of the THz transmission intensity shows smooth change. In order to improve the properties of phase transition, the VOX thin film is treated by 500℃/15 s rapid thermal process in pure nitrogen environment. After that, we find that the thin film shows a good phase transition performance, accompanied by a sheet square resistance drop of above 3 orders of magnitude and a 56.33% reduction in THz transmission intensity.