Oriented MgO Substrates Research Articles

Magnetic properties of Mn2N0.86 (111) thin film grown on MgO (001) substrate by molecular beam epitaxy

(111)-oriented Mn2N0.86 thin films were fabricated on (001)-oriented MgO substrates by plasma-assisted molecular beam epitaxy. In-situ reflection high-energy electron diffraction and ex-situ X-ray diffraction results demonstrated that the (111)-oriented Mn2N0.86 thin films were single phase. The rocking curve manifested a very good crystallinity of Mn2N0.86 (111) phase and the thickness of the film was studied by X-ray reflectivity. The magnetic properties of the (111)-oriented Mn2N0.86 thin films were investigated and room-temperature ferromagnetism that was absent in the bulk samples was observed. Strain imposed by the substrates was proposed to explain this phenomenon.

Control of Preferential Orientation of La<sub>1-x</sub>Sr<sub>x</sub>MnO<sub>3</sub> Thin Films by Pulsed Laser Deposition

La1-xSrxMnO3 (LSMO) thin films were grown on (100)- and (110)-oriented MgO substrates by pulsed laser deposition, so as to control the preferential orientation of the films. At the optimum deposition temperature (Td = 923K), LSMO thin films with a dense texture and a smooth surface were prepared. The XRD patterns and X-ray pole figures indicated that the LSMO thin films were epitaxially grown on MgO substrates, due to the small lattice mismatch between the films and substrates The possible orientation relationships were found to be LSMO (100) [100] // MgO (100) [100] and LSMO (110) [110] // MgO (110) [110], as for the (100) and (110) MgO substrates, respectively.

Highly conductive Nb doped BaSnO3 thin films on MgO substrates by pulsed laser deposition

Ba(NbxSn1-x)O3 (BNSO) films were epitaxially grown on (001) oriented MgO substrates with Nb doping content from 0.00 to 0.15 by pulsed laser deposition. The structural, electrical, and optical properties of the films were investigated in detail by x-ray diffraction, x-ray photoelectron spectroscopy, Hall effect and transmittance spectroscopy. The lowest room temperature resistivity value of 4.81 × 10−4 Ω cm with carrier concentration and mobility of 6.59 × 1020/cm3 and 19.65 cm2/V was observed in the film at x = 0.05, indicating an excellent electrical conductivity. All the BNSO films exhibit a high transmittance of more than 80% in the visible range. The variation of band gap Eg with Nb doping content was interpreted by the Burstein-Moss effect and the occurrence of octahedral tilt distorting. Excellent optical and electrical properties suggest that BNSO films have potential applications in the optoelectronic devices as transparent and conducting oxide material.

Hardness of Cr(N,O) thin films on (001)-, (011)-, and (111)-oriented MgO substrates

The epitaxial growth of Cr(N,O) thin films on (001)- and (011)-oriented MgO substrates as well as a (200)-oriented polycrystalline Cr(N,O) thin film on MgO(111) were performed using pulsed laser deposition. Data obtained from Rutherford backscattering spectroscopy and electron energy loss spectroscopy indicated that Cr(N,O) on (001)-, (011)-, and (111)-oriented MgO substrates contained chromium, nitrogen and oxygen. Nano-indentation showed negligible differences in the hardness values of Cr(N,O) films on (001)-, (011)-, and (111)-oriented MgO substrates, the two former having values of approximately 36 GPa. These results indicate that the hardness of Cr(N,O) is independent of both the growth morphology brought about by the substrate orientation and grain boundary effects. Finally, Cr(N,O) films on all substrates exhibited greater hardness than a comparison specimen consisting of epitaxial CrN on MgO(001).

Epitaxial ferroelectric 0.3Pb(In1/2Nb1/2)O3–0.38Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 thin films grown on (110)-oriented MgO substrates

Ferroelectric 0.3Pb(In1/2Nb1/2)O3–0.38Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 (PIN–PMN–PT) epitaxial thin films with a perovskite phase were grown on (110)-oriented MgO substrates by sputter deposition method. The structure of the PIN–PMN–PT films was found very sensitive to the growth condition. The single perovskite phase obtained under optimized processing condition was substantially relaxed from lattice-mismatch strain down to at least 11nm in thickness due to the formation of an ultrathin interfacial layer of twin domains. Compared to other technically important relaxor ferroelectrics such as PMN–PT, the PIN–PMN–PT thin films have a higher Curie temperature and a large coercive field, which are very promising for piezoelectric applications in micro/nano-electromechanical systems.

Polarized Raman scattering study of PSN single crystals and epitaxial thin films

This paper describes a detailed analysis of the dependence of Raman scattering intensity on the polarization of the incident and inelastically scattered light in PbSc 0.5 Nb 0.5 O 3 (PSN) single crystals and epitaxially compressed thin films grown on (100)-oriented MgO substrates. It is found that there are significant differences between the properties of the crystals and films, and that these differences can be attributed to the anticipated structural differences between these two forms of the same material. In particular, the scattering characteristics of the oxygen octahedra breathing mode near 810 cm-1 indicate a ferroelectric state for the crystals and a relaxor state for the films, which is consistent with the dielectric behaviors of these materials.

Copper diffusion into single-crystalline TiN studied by transmission electron microscopy and atom probe tomography

TiN/Cu bilayers were grown by unbalanced DC magnetron sputter deposition on (001)-oriented MgO substrates. Pole figures and electron back-scatter diffraction orientation maps indicate that both layers in the as-deposited state are single-crystalline with a cube-on-cube epitaxial relationship with the substrate. This is confirmed by selected area electron diffraction patterns. To study the efficiency of the TiN barrier layer against in-diffusion of Cu, we annealed samples at 900°C for 1h in vacuum and at 1000°C for 12h in Ar atmosphere. The single-crystalline structure of the TiN layer is stable up to annealing temperatures of 1000°C as shown by high resolution transmission electron microscopy. While no Cu diffusion was evident after annealing at 900°C, scanning transmission electron microscopy images and energy-dispersive X-ray spectrometry maps show a uniform diffusion layer of about 12nm after annealing at 1000°C for 12h. Concentration depth profiles obtained from 3D atom probe tomography reconstructions confirm these findings and reveal that the TiN film is slightly substoichiometric with a N/Ti ratio of 0.92. Considering this composition, we propose a lattice diffusion mechanism of Cu in TiN via the formation of Cu–N vacancy complexes. The excellent diffusion barrier properties of single-crystalline TiN are further attributed to the lack of fast diffusion paths such as grain boundaries.

Ferromagnetic Resonance Studies of Exchange Biased CoO/Fe Bilayer Grown on MgO Substrate

Dynamic and static magnetizations of an exchange biased bilayer system which is constructed as a proximity of a CoO layer on an Fe-layer grown on the (100) oriented MgO substrate by ion beam sputtering technique have been investigated by ferromagnetic resonance (FMR) and vibrating sample magnetometry (VSM) techniques. The room-temperature FMR measurements reveal that the Fe layer is epitaxially grown on MgO substrate with four-fold magnetocrystalline anisotropy and the hard magnetization axis of the sample is the [100] crystallographic directions of MgO substrate. We have determined the g-value, effective magnetization, magnetocrystalline anisotropy constants and contributions to FMR linewidth due to the intrinsic Gilbert damping and inhomogeneity of magnetization by using Landau–Lifshitz–Gilbert (LLG) equation. We observed an unusual FMR line shape attributed to impedance switching of resonance cavity and complex component of conductivity of sample system. The low-temperature FMR measurement shows asymmetric hysteretic behavior of resonance field related to magnetic coupling of ferromagnetic and antiferromagnetic layers. From both FMR and VSM measurements between 10–300 K, the magnetocrystalline anisotropy is observed to dominate above blocking temperature, while unidirectional anisotropy is observed to dominate below blocking temperature over internal magnetic anisotropy. FMR spectra have a comparatively small linewidth between 40–100 Oe, which indicates to a high crystallinity of the Fe film. Gilbert constant was calculated as 0.007 from the linewidth fitting of FMR spectra. This small value is a suitable for reducing the critical switching current used in magnetic tunneling junction. Detailed exchange bias studies were carried out for hard and easy axis of the sample in the temperature range of 10–300 K. From both low-temperature FMR and VSM measurements, the blocking temperature of the system was determined as ∼60 K.

Intricacies of strain and magnetic field induced charge order melting in Pr 0.5Ca 0.5MnO 3 thin films

Thin films of the half-doped manganite Pr 0.5Ca 0.5MnO 3 were grown on (1 0 0) oriented MgO substrates by pulsed laser deposition technique. In order to study the effect of strain on the magnetic field induced charge order melting, films of different thicknesses were prepared and their properties were studied by X-ray diffraction, electrical resistivity and magnetoresistance measurements. A field induced charge order melting is observed for films with very small thicknesses. The charge order transition temperature and the magnetic field induced charge order melting are observed to depend on the nature of strain that is experienced by the film.

Impedance spectroscopy analysis of Ba0.7Sr03TiO3/La0.7Sr0.3MnO3 heterostructure

Impedance spectroscopy technique has been used to study the effect of grains and grain boundaries in a heterostructure constituted with ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric Ba0.7Sr0.3TiO3 (BST) layers grown by pulsed laser deposition technique on (1 0 0) oriented MgO substrate. Frequency and temperature dependence of the complex impedance and complex electric modulus were measured in (BST20u.c,/LSMO10u.c)25 over a temperature range of 360–500 K. Non-Debye relaxation was observed in the investigated system. An equivalent circuit and the modified constant phase element circuit were used to describe the impedance spectroscopy, and excellent agreement between the calculated and measured curves was obtained from each model. The activation energy (∼0.25 eV–0.48 eV) has been obtained from Arrhenius fitting of different relaxation processes present in the material, and its characteristic values support a model of Maxwell–Wagner relaxation in the heterostructured film at elevated temperatures and in the low frequency range. The electrical ac and dc conductivity studies showed that the heterostructure possesses negative temperature coefficient of resistance properties. It was found that the resistance of grain boundaries was larger than the resistance of intra-grains.

Growth, structural and electrical properties of polar ZnO thin films on MgO (100) substrates

ZnO films have been grown on (100) oriented MgO substrates by pulsed-electron beam deposition in the room temperature to 500°C range. Highly (00·2) textured films are obtained for a growth temperature higher than 200°C, and epitaxial films are formed at 500°C with the following epitaxial relationships: (1-1·0)ZnO // (110)MgO and (11·0)ZnO // (110)MgO, despite the difference in symmetry between film and substrate. The low temperature resistivity curves evidenced a metal–semiconductor transition for the ZnO films grown in the 300 to 500°C range which has been interpreted in the frame of the model of conductivity in disordered oxides.

High proton conduction in grain-boundary-free yttrium-doped barium zirconate films grown by pulsed laser deposition

Reducing the operating temperature in the 500-750 °C range is needed for widespread use of solid oxide fuel cells (SOFCs). Proton-conducting oxides are gaining wide interest as electrolyte materials for this aim. We report the fabrication of BaZr(0.8)Y(0.2)O(3-δ) (BZY) proton-conducting electrolyte thin films by pulsed laser deposition on different single-crystalline substrates. Highly textured, epitaxially oriented BZY films were obtained on (100)-oriented MgO substrates, showing the largest proton conductivity ever reported for BZY samples, being 0.11 S cm(-1) at 500 °C. The excellent crystalline quality of BZY films allowed for the first time the experimental measurement of the large BZY bulk conductivity above 300 °C, expected in the absence of blocking grain boundaries. The measured proton conductivity is also significantly larger than the conductivity values of oxygen-ion conductors in the same temperature range, opening new potential for the development of miniaturized SOFCs for portable power supply.

Study of physical properties of integrated ferroelectric/ferromagnetic heterostructures

Superlattices (SLs) with different periodicity of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric Ba0.7Sr0.3TiO3 as constitutive layers were fabricated on conducting LaNiO3 coated (001) oriented MgO substrates using pulsed laser deposition. The crystallinity, ferroelectric, and magnetic properties of the SLs were studied over a wide range of temperatures and frequencies. The structure exhibited ferromagnetic behavior at 300 K and ferroelectric behavior over a range of temperatures between 100 and 300 K. A frequency-dependent change in dielectric constant and tangent loss were observed above the ferromagnetic-paramagnetic temperature. The frequency-dependent dielectric anomalies are attributed to the change in metallic and magnetic nature of LSMO and also the interfacial effect of two different phases that are connected alternatively in series. The effect of ferromagnetic LSMO layers on ferroelectric properties of the SLs indicated strong influence of the interfaces. The asymmetric behavior of ferroelectric loop and the capacitance-voltage relationship suggest development of a built field in the SLs due to high strain across the interfaces.

Structural and Magneto-Electric Properties of Pulsed Laser Deposited Ferroelectric/Ferromagnetic Heterostructure

AbstractAsymmetric superlattices (SLs) with ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric Ba0.7Sr0.3TiO3 (BST) as constitutive layers were fabricated on conducting LaNiO3 (LNO) coated (001) oriented MgO substrates using pulsed laser deposition (PLD). The crystallinity, ferroelectric and magnetic properties of the SLs were studied over a wide range of temperatures and frequencies. The structure exhibited ferromagnetic behavior at 300K, and ferroelectric behavior over a range of temperatures between 100K and 300K. The dielectric response as a function of frequency obeys normal behavior below 300 K, whereas it follows Maxwell–Wagner model at elevated temperatures. The effect of ferromagnetic LSMO layers on ferroelectric properties of the SL indicated strong influence of the interfaces. The asymmetric behavior of ferroelectric loop and the capacitance-voltage relationship suggest development of a built field in the SLs due to high strain across the interfaces.

Study of cross‐sections of magnetite thin films by means of electron backscatter diffraction (EBSD)

AbstractBy means of electron backscatter diffraction (EBSD), we studied the grain orientation of cross‐sections of magnetite (Fe3O4) thin films grown on (001) oriented MgO substrates. Earlier studies showed that the magnetic properties of the magnetite films are dominated by the presence of so‐called anti‐phase boundaries (APBs). The use of cross‐sections of thin‐films enables to study the growth mechanism in a more direct way. The EBSD maps reveal that the first magnetite layer on the MgO substrate is comprised of many small, misoriented magnetite grains. Subsequent layers show the desired (001) orientation with a ±5° misorientation. The misorientations found in the cross‐section of the film resemble those obtained in EBSD measurements at the sample surface. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Reactive ion etching of FePt using inductively coupled plasma

We propose a reactive ion etching (RIE) process of an L1 0-FePt film which is expected as one of the promising materials for the perpendicular magnetic recording media. The etching was carried out using an inductively coupled plasma (ICP) RIE system and an etching gas combination of CH 4/O 2/NH 3 was employed. The L1 0-FePt films were deposited on (1 0 0)-oriented MgO substrates using a magnetron sputtering system. The etching masks of Ti were patterned on the FePt films lithographically. The etch rates of ∼16 and ∼0 nm/min were obtained for the FePt film and the Ti mask, respectively. The atomic force microscopy (AFM) analyses provided the average roughness ( R a) value of 0.95 nm for the etched FePt surface, that is, a very flat etched surface was obtained. Those results show that the highly selective RIE process of L1 0-FePt was successfully realized in the present study.

Effect of Substrate Temperature on the Different Diffuseness of Subsequent Interfaces in Binary Multilayers

Epitaxial, coherent Mo/V multilayers were deposited by magnetron sputtering on (001) oriented MgO substrates at 873K (sample MoV-T), 923K (sample MoV-U) and 973K (sample MoV-V), respectively. In order to estimate the concentration profiles in our multilayers, a superlattice refinement modelling procedure has been used on high-angle XRD symmetric scans. The Mo/V interfaces were always sharper than V/Mo ones (in this notation the order of element reflects the sequence of deposition: e.g. the Mo/V interface was formed by the deposition of the V on the Mo surface). Furthermore the interface diffuseness was only slightly different at the lowest substrate temperature, but the difference increased with increasing temperature and an abrupt concentration jump could be observed at the Mo/V interface in the sample, sputtered at the 973 K. This indicates that during deposition the interfacial mixing by impact exchange events is important and thermally activated processes (surface diffusion and/or jumps driven by segregation) are less effective. With increasing substrate temperature the thickness of the V/Mo interfaces were unchanged while the Mo/V interface became shaper and sharper i.e. thermally activated jumps were more active during deposition of V atoms. Thus in forming Mo/V interfaces the segregation tendency of V to the Mo surface results in enhanced exchanges between V atoms (buried in the near surface layers of the Mo substrate) and surface Mo atoms, leading to more sharper interface with increasing temperature. On the other hand during the formation of the V/Mo interfaces the chemical thickness of the interface, provided again by impact exchanges, was practically unchanged.

Deposition of single-crystal Ti2AlN thin films by reactive magnetron sputtering from a 2Ti:Al compound target

Single-crystal Ti2AlN (0001) thin films were grown on (111) oriented MgO substrates kept at 830°C by ultrahigh vacuum dc reactive magnetron sputtering from a compound 2Ti:Al target in a mixed Ar∕N2 discharge. The effects of variations in the nitrogen partial pressure on the phase composition of the films were studied. Results from transmission electron microscopy, x-ray diffraction, and elastic recoil detection analysis show a narrow region for growth of Ti2AlN MAX phase with respect to the nitrogen content in the discharge. Perovskite Ti3AlN and intermetallic Ti3Al and TiAl phases dominate at nitrogen depletion. For overstoichiometric deposition conditions with respect to Ti2AlN, a phase mixture with NaCl-structured TiN is obtained. Epitaxial growth is observed with a layer-by-layer mode on the 0001 basal planes for all phases. A superstructure in the TiN phase is also observed along [111] with the repetition distance of 7.34Å, most likely related to Al segregation. Nanoindentation shows that the film hardness increases from 11to27GPa with increasing nitrogen content and corresponding phase transformations from Ti–Al intermetallics to Ti3AlN, Ti2AlN, and TiN.

Misorientations in [001] magnetite thin films studied by electron backscatter diffraction and magnetic force microscopy

Magnetite thin films grown on [001] oriented MgO substrates are analyzed by means of electron backscatter diffraction (EBSD) analysis and magnetic force microscopy in applied fields. The EBSD technique enables the crystallographic orientation of individual grains to be determined with a high spatial resolution up to 20nm on such ceramic samples. A high image quality of the recorded Kikuchi patterns was achieved enabling multiphase scans and high spatial resolution measurements. Upon annealing in air, the magnetic properties of the magnetite thin films were found to change considerably. Using the EBSD analysis, we find that misoriented grains remaining after the annealing step form small islands with a size of about 100nm. The size and distribution of these islands correspond well to the observations of antiferromagnetic pinning centers within the magnetic domain structures carried out by magnetic force microscopy on the same samples.

Epitaxial film growth and magnetic properties ofCo2FeSi

We have grown thin films of the Heusler compound Co_2FeSi by RF magnetron sputtering. On (100)-oriented MgO substrates we find fully epitaxial (100)-oriented and L2_1 ordered growth. On Al_2O_3 (11-20) substrates, the film growth is (110)-oriented, and several in-plane epitaxial domains are observed. The temperature dependence of the electrical resistivity shows a power law with an exponent of 7/2 at low temperatures. Investigation of the bulk magnetic properties reveals an extrapolated saturation magnetization of 5.0 mu_B/fu at 0 K. The films on Al_2O_3 show an in-plane uniaxial anisotropy, while the epitaxial films are magnetically isotropic in the plane. Measurements of the X-ray magnetic circular dichroism of the films allowed us to determine element specific magnetic moments. Finally we have measured the spin polarization at the surface region by spin-resolved near-threshold photoemission and found it strongly reduced in contrast to the expected bulk value of 100%. Possible reasons for the reduced magnetization are discussed.