Facing-target Reactive Sputtering Research Articles

In-situ fabricated amorphous silicon quantum dots embedded in silicon nitride matrix: Photoluminescence control and electroluminescence device fabrication

Herein, we report that high-quality SiN:H films embedded with Si QDs were in-situ fabricated and prepared by the reactive facing target sputtering, which relies on tuning N2 and Ar mixture gas flow ratio. The size of Si QDs in SiN:H films can be tuned from 3.87 nm to 1.40 nm, which exhibit color-tunable photoluminescence from red to blue in the visible region. The microstructure evolution and optical properties of SiN:H films embedded with Si QDs were analyzed by FTIR, Raman, PL, and TRPL measurements, respectively. Considering their unique emission properties, SiN:H films embedded with Si QDs were especially utilized as the emitting layer for fabricating high-performance EL SiN-based LEDs. The broad EL emission properties of the devices were explored by both experimental observations and a theoretical model. This work offers a novel idea to prepare high-quality SiN:H films embedded with Si QDs and a deep understanding of their optoelectronic properties.

Anomalous Hall effect of facing-target sputtered Fe3SnN epitaxial film

In this work, polycrystalline iron tin nitride films on different substrates with various nitrogen flow rates were deposited using the facing-target reactive sputtering method. Fe3SnN(111) epitaxial films were fabricated on both Al2O3(0001) and MgO(111) with two standard cubic centimeter per minute N2. The structures, electronic transport and magnetic properties were investigated systematically. The signs of the Hall resistivity slope in a high-field region are reversed when the temperature increases above 50 K, which suggests a temperature-induced transition of charge carriers from electron to hole. The longitudinal resistivity of films indicates metallic conductance mechanism. Different scaling laws were used to distinguish the physical mechanism underlying the observed anomalous Hall effect (AHE) in 60 nm thick Fe3SnN(111) epitaxial film. The skew scattering mechanism is demonstrated to play a dominant role in the AHE. This work not only offers a clear understanding of polycrystalline iron tin nitride films, but also contributes to the fabrication and applications of Fe3SnN(111) epitaxial films in spintronics.

Microstructure, magnetic and electronic transport properties of reactively facing-target sputtered epitaxial Mn4N films

The structure, magnetic and electronic transport properties of epitaxial Mn4N films fabricated by the facing-target reactive sputtering method have been investigated systematically. The high-quality growth of Mn4N films was confirmed by x-ray θ–2θ, pole figures and high-resolution transmission electron microscopy. The Mn4N films exhibit ferrimagnetic with strong perpendicular magnetic anisotropy. The saturation magnetization of Mn4N films decreases with increasing temperature, following the Bloch’s spin wave theory. The resistivity of Mn4N films exhibits metallic conductance mechanism. Debye temperature of Mn4N is estimated to be 85 K. The calculated residual resistivity ρ xx0 of the 78.8 nm-thick Mn4N film is 30.56 μΩ cm. The magnetoresistances of Mn4N films display a negative signal and butterfly shape. The sign of anisotropic magnetoresistance (AMR) is positive, which infers that the AMR is dominated by the spin-up conduction electrons. Moreover, the transformation of fourfold to twofold symmetry for AMR and twofold to onefold symmetry for planar Hall resistivity is attributed to tetragonal crystal field effect.

Anomalous Hall effect of facing-target sputtered ferrimagnetic Mn4N epitaxial films with perpendicular magnetic anisotropy

Epitaxial Mn4N films with different thicknesses were fabricated by facing-target reactive sputtering and their anomalous Hall effect (AHE) is investigated systematically. The Hall resistivity shows a reversed magnetic hysteresis loop with the magnetic field. The magnitude of the anomalous Hall resistivity sharply decreases with decreasing temperature from 300 K to 150 K. The AHE scaling law in Mn4N films is influenced by the temperature-dependent magnetization, carrier concentration and interfacial scattering. Different scaling laws are used to distinguish the various contributions of AHE mechanisms. The scaling exponent γ > 2 for the conventional scaling in Mn4N films could be attributed to the residual resistivity ρ xx0. The longitudinal conductivity σxx falls into the dirty regime. The scaling of is used to separate out the temperature-independent ρ xx0 from extrinsic contribution. Moreover, the relationship between ρ AH and ρxx is fitted by the proper scaling to clarify the contributions from extrinsic and intrinsic mechanisms of AHE, which demonstrates that the dominant mechanism of AHE in the Mn4N films can be ascribed to the competition between skew scattering, side jump and the intrinsic mechanisms.

Bending strain tailored exchange bias in epitaxial NiMn/ γ ′-Fe4N bilayers

The strain tunable exchange bias has attracted much attention due to its practical applications in flexible and wearable spintronic devices. Here, the flexible epitaxial NiMn/γ′-Fe4N bilayers are deposited by facing-target reactive sputtering. The maximum strain-induced change ratios of exchange bias field HEB and coercivity HC (|ΔHEB/HEB| and |ΔHC/HC|) are 51% and 22%, respectively. A large strain-induced |ΔHEB/HEB| appears in a thicker ferromagnetic layer, but a large |ΔHC/HC|) appears in a thinner ferromagnetic layer. At a compressive strain, the antiferromagnetic anisotropy of the tetragonal NiMn layer increases, resulting in an increased HC of NiMn/γ′-Fe4N bilayers. The bending-strain induced changes of anisotropy magnetoresistance and planar Hall resistance are also observed at low magnetic fields. The bending-strain tailored magnetic properties can be ascribed to the distributions of ferromagnetic and antiferromagnetic anisotropies.

Bending Strain-Tailored Magnetic and Electronic Transport Properties of Reactively Sputtered γ'-Fe4N/Muscovite Epitaxial Heterostructures toward Flexible Spintronics.

The strain modulation on the magnetic and electronic transport properties of the ferromagnetic films is one of the hot topics due to the practical applications in flexible and wearable spintronic devices. However, the large strain-induced saturation magnetization and resistance change is not easy to achieve because most of the ferromagnetic films deposited on flexible substrates are polycrystalline or amorphous. Here, the flexible epitaxial γ'-Fe4N/mica films are fabricated by facing-target reactive sputtering. At a tensile strain with a radius of curvature (ROC) of 3 mm, the saturation magnetization (Ms) of the γ'-Fe4N/mica film is tailored significantly with a maximal variation of 210%. Meanwhile, the magnetic anisotropy was broadly tunable at different strains, where the out-of-plane Mr/Ms at a tensile strain of ROC = 2 mm is six times larger than that at the unbent state. Besides, the strain-tailored longitudinal resistance Rxx and anomalous Hall resistivity ρxy appear where the drop of Rxx (ρxy) reaches 5% (22%) at a tensile strain of ROC = 3 mm. The shift of the nitrogen position in the γ'-Fe4N unit cell at different bending strains plays a key role in the strain-tailored magnetic and electronic transport properties. The flexible epitaxial γ'-Fe4N films have the potential applications in magneto- and electromechanical wearable spintronic devices.

Magnetoelectric coupling in γ′-Fe4N/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 multiferroic heterostructures

Epitaxial γ′-Fe4N films with different thicknesses were fabricated on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) substrates by facing-target reactive sputtering. The magnetoelectric coupling (MEC) in the samples was systematically investigated. Firstly, the magnetization along different in-plane directions is tunable by the electric field. It was found that MEC in the films on PMN-PT(011) is stronger than that on PMN-PT(001) due to the different in-plane magnetic anisotropy. Moreover, the magnetoelectric coupling is strongly related to the γ′-Fe4N film thickness, which can be ascribed to the competition between the strain and spin-dependent screening effect induced MEC. Additionally, the electric-field tailored remanent magnetization of the samples gradually increases with temperature due to the thermal agitation. Besides, the electric-field effect on the out-of-plane magnetic hysteresis loops is consistent with the in-plane cases. The results are of benefit to the development of the electric-field controlled spintronic devices.

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.

Properties of p-type N-doped Cu2O thin films prepared by reactive sputtering

We have investigated the electrical, optical, and structural properties of p-type nitrogen (N)-doped Cu2O thin films prepared at various nitrogen gas flow rates for application in heterojunction solar cells. The N-doped Cu2O thin films were fabricated by facing-target reactive sputtering. The hole concentration of the N-doped Cu2O thin films was affected by N2 gas flow rate. With increasing N2 gas flow rate from 0 to 0.5 sccm, the hole concentration and mobility of N-doped Cu2O films increased sharply. The resistivity, hole concentration, and mobility of the N-doped Cu2O films prepared at a N2 gas flow rate of 4 sccm were 1.9 Ω·cm, 2.0 × 1018 cm−3, and 3.4 cm2·V−1·s−1, respectively. The N-doped Cu2O films showed Cu2O(111) and Cu2O(200) diffraction peaks. Cu2O(200) diffraction peak intensity increased slightly with N2 gas flow rate. The Cu2O(200) peaks were stronger at a N2 gas flow rate of 4 sccm than at other gas flow rates.

Working Pressure Dependence of WO3-x Thin Films Prepared by Reactive Facing Targets Sputtering

Tungsten oxide (WO3-x) thin films for an electrochromic (EC) device were deposited at an oxygen flow ratio [O2/(Ar + O2)] of 0.7 using reactive facing-target sputtering with a variable working pressure. The correlation between the WO3-x thin films and EC properties was investigated. The films structural properties were measured by X-ray diffraction; the indium tin oxide diffraction peak was observed in all the films. The electrochemical and optical properties were measured by cyclic voltammetry and UV/Vis spectrometry. The WO3-x thin film obtained at 0.13 Pa displayed a maximum coloration efficiency of 31.42 cm2/C, which indicated superior EC properties.

Thickness Dependence of WO3-x Thin Films for Electrochromic Device Application

The phenomenon of color change in a particular material caused by an electrochemical reaction is called “electrochromism.” Since the discovery of the electrochromic phenomenon in tungsten oxide, amorphous WO3 is the most widely studied electrochromic material. Until now, WO3 remains the most promising candidate for electrochromic devices. Electrochromic devices can switch between two optical states (colored/bleached) by injection/extraction of ions and electrons, based on the modification of transmittance and reflectance that are induced by an applied external voltage. In this study, tungsten oxide (WO3-x) thin films were deposited onto an ITO-coated glass substrate by reactive facing-target sputtering, and their electrochromic properties studied as a function of film thickness. The X-ray diffraction patterns reveal the amorphous properties of all the WO3-x thin films prepared in this study. Of all the different samples prepared in this study, WO3-x thin film of thickness 500 nm exhibited the maximum coloration efficiency of 37.3 cm2/C.

Grain boundary magnetism and conductivity in polycrystalline Ti1−xMnxN films by reactive sputtering

Polycrystalline Ti1−xMnxN films with different Mn atomic fractions (x) were grown by reactive facing-target sputtering. The preferred lattice orientation changes from (200) to (111) with the increase of x, which makes the surface morphology evolve from spherical to triangular-pyramid-like islands. Weak grain-boundary ferromagnetism with a Curie temperature of higher than 305K has been observed. The saturation magnetization (Ms) and coercivity do not show a monotonous change with x. Asymmetric M–H curves can be observed at low temperatures, and the shift of M–H curves decreases with the increase of temperature because of the relaxation of the low-temperature pinned moments. All of the films show semiconducting-like behavior with a mechanism of thermal fluctuation-induced tunneling. Magnetoresistance (MR) is negative, but is very small. The small Ms and MR can be ascribed to the weakly ferromagnetic interaction of moments at grain boundaries and low spin polarization.

Electrochromic Properties of Tungsten Oxide Films Prepared by Reactive Sputtering

WO3-x thin films were deposited on induim tin oxide (ITO) glass substrates with various oxygen flow ratios from 0.55 to 0.7 by the reactive facing-target sputtering method, at a power density of 4 W/cm2 and room temperature. The structural properties of the WO3-x thin films were measured by X-ray diffractometry and Raman spectral analysis. As-deposited WO3-x thin films had an amorphous structure. In the Raman spectra, WO3-x thin films exhibited two strong peaks at 770 and 950 cm-1 attributed to the vibrations of W6+–O and W6+=O bonds, respectively. The electrochemical and optical properties of WO3-x thin films were measured by cyclic voltammetry and UV/vis spectrometry. The results showed the highest charge density at an oxygen flow ratio of 0.7 and the highest transmittance in the visible range. The maximum coloration efficiency was 30.82 cm2/C at an oxygen flow ratio of 0.7.

Microstructure and Magnetic Properties of the CoTiO2 Thin Films

Co (t nm)/TiO2(200 nm) films were prepared by DC facing-target magnetron reactive sputtering system onto glass substrates at room temperature. The influence of the Co distribution on microstructure and magnetic properties of films was investigated in detail. The results indicate that CoTiO2thin films with t= 2 nm island-type deposited showed a homogeneous structure, and pure ferromagnetic properties of thin films are only attributed to the CoTiO2phases. On the other hand, in case of thin films above t= 2nm, the overall ferromagnetic properties depended on both CoTiO2and CoTi phases.

Surface morphology, structure, magnetic and electrical transport properties of reactive sputtered polycrystalline Ti1−xFexN films

Polycrystalline Ti1−xFexN films with different Fe atomic fractions (x) were fabricated by reactive facing-target sputtering. The lattice orientation changes from (200) to (111) with the increase of x, which makes the surface morphology evolve from spherical, triangular-pyramid-like islands to random-leafs-like ones. The films are ferromagnetic with a Curie temperature of higher than 305K, and the saturation magnetization (Ms) is very small. Obvious asymmetric M–H curves are observed at low temperatures, and the shift of M–H curves decreases with the increasing temperature because of the relaxation of the pinned moments at low temperatures. All of the samples show semiconducting-like behavior with a mechanism of variable-range hopping at low-temperature range. Magnetoresistance (MR) is very small. The small Ms and MR can be explained by the facts that the interaction between Fe3+–N3−–Fe3+ is antiferromagnetic superexchange coupling, and no double exchange exists in Fe3+–N3−–Ti3+, which is different from that in the Cr-doped TiN films.

Polycrystalline iron nitride films fabricated by reactive facing-target sputtering: Structure, magnetic and electrical transport properties

Structure, magnetic and electrical transport properties of the reactive sputtered iron nitride films fabricated at different substrate temperatures (Ts) and nitrogen flow rates (FN2) were investigated systematically. The single-phase polycrystalline γ′-Fe4N film was obtained at FN2 = 20 sccm and Ts = 450 °C. The films are soft ferromagnetic at room temperature. The electrical resistivity (ρ) of the films fabricated at different FN2 and Ts decreases with the decreasing temperature, showing a metallic behavior. Meanwhile, a variety of magnetoresistance (MR) behaviors were observed depending on the applied magnetic field and measuring temperature. It can be deduced that the complex MR behaviors are dominated by Lorentz force, spin-orbit interaction, and weak localization effect.

Investigation of structure and magnetic properties of the as-deposited and post-annealed iron nitride films by reactive facing-target sputtering

Structure and magnetic properties of the as-deposited and post-annealed iron nitride films have been investigated systematically. A series of phases containing α-Fe, ɛ-Fe 3N, ξ-Fe 2N and γ″-FeN were obtained as nitrogen flow rate ( F N 2 ) increases from 0.5 to 30 sccm. An increase of the nitrogen concentration in the as-deposited films could be concluded from the phase transition with the increasing F N 2 . After being annealed, some of the iron nitride phases are decomposed and γ′-Fe 4N appears in the films. The magnetic characteristics are dependent on F N 2 , which can be ascribed to the facts that the nitrogen in the films turns the valence states of Fe into Fe + or Fe dipole with high magnetic momentum or ever H-like bond Fe +/dipole with low magnetic momentum based on the bond-band-barrier correlation mechanism.

Grain boundaries controlled magnetic and magnetotransport properties of reactively sputtered polycrystalline and epitaxial Fe3O4 films

Polycrystalline and epitaxial Fe3O4 films were fabricated by facing-target reactive sputtering on glass and 400 °C heated MgO (1 0 0) substrates. The formation of disordered and amorphous grain boundaries in the polycrystalline Fe3O4 films on glass was suppressed by substrate heating, and antiphase boundaries were found to form in the epitaxial Fe3O4 films grown on lattice matched MgO (1 0 0) substrates, which were directly verified by high-resolution transmission electron microscopy. The magnetic and magnetotransport properties of the Fe3O4 films are controlled by the type of boundaries and the antiferromagnetic coupling strength at the boundaries which are associated with the bond angle subtended by iron–oxygen–iron. The stronger the antiferromagnetic interaction across the boundaries, the slower is the saturation behaviour of magnetization. The magnetoresistance depends mainly on the gradually saturating magnetization at high fields and the antiferromagnetic coupling strength across the boundaries.

Influence of substrate temperature on growth of a-Si:H films by reactive facing target sputtering deposition

Hydrogenated amorphous silicon (a-Si:H) films were deposited by reactive facing target sputtering (FTS) technique with a mixture of Ar and H2 reaction gas. Fourier transform infrared (FTIR) absorption, Raman scattering and ultraviolet-visible optical absorption are used to investigate the microstructure and optical properties of the deposited films. The decrease of the concentration of bonded hydrogen, especially that of (Si-H2) n with increasing substrate temperature (Ts), was observed in FTIR spectra, suggesting the atomic density increases and the concentration of microvoids decrease in a-Si:H films. The increase of both the short range order and the intermediate range order of amorphous network for a-Si:H films were verified by Raman scattering spectra, in which increasing Ts decreasing the band width of TO and the scattering intensity ratio I TA/I TO were obtained. All above results clarify the effect of increasing Ts on the microstructure amelioration for a-Si:H films. The reduction of disordered domains is correlated with the film growing process, where the increased surface diffusion mobility and etching of weak bonds is induced by increasing Ts. Furthermore, analysis of optical absorption indicates that the films with a lower optical band gap and a narrower band edge can be obtained by this FTS technique.

Structure, optical, and magnetic properties of facing-target reactive sputtered Ti1−xFexO2−δ films

Structure, optical, and magnetic properties of the anatase Ti1−xFexO2−δ films fabricated by facing-target reactive sputtering were investigated. Structural analyses indicate that there are no impurity phases in the films and the grain size reaches maximum when Fe content x is 0.017. The optical band gap of the Ti1−xFexO2−δ films decreases with the increasing x. Photoluminescence (PL) spectra show that direct and indirect band-to-band transitions coexist, and the indirect radiative recombination can be regarded as a one photon and two phonon coupling courses. The PL intensity due to oxygen vacancies enhances and the refractive index of the fims increases with the increasing x. The Ti1−xFexO2−δ films exhibit room-temperature ferromagnetism due to the oxygen vacancies.