Single Crystalline Substrates Research Articles

Orientation-dependent photoluminescence properties of Pr3+ doped Ba0.85Ca0.15Ti0.90Zr0.10O3 thin films

Tuning the photoluminescence properties of rare earth doped ferroelectric thin films is extremely important for developing novel optical-electro devices. Here, the (001), (011) and (111)-oriented Pr3+ doped Ba0.85Ca0.15Ti0.90Zr0.10O3 (BCTZ:Pr3+) epitaxial thin films were prepared on Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystalline substrates by pulsed laser deposition. The effects of crystal orientation on the photoluminescence properties of BCTZ:Pr3+ thin films were systematically investigated. Under the excitation of a 492 nm light, all the films exhibit strong green emission peak around 544 nm, which is ascribed to the transition of 3P0→3H5 of Pr3+ ions. Particularly, the emission intensity strongly depends on the crystal orientation with stronger intensity of (001) (16.76%) and (111)-oriented (19.56%) BCTZ:Pr3+ thin films than that of (011)-oriented one. The dependence of photoluminescence on the orientation can be attributed to different electron-phonon interactions and surface roughnesses. This work provides a novel strategy for the improvement of photoluminescence properties in lanthanides doped ferroelectric films.

LSAT (001) termination: An investigation on the influence of annealing parameters on topography

La0.18Sr0.82Al0.59Ta0.41O3 (LSAT) is a commonly used single-crystalline substrate for the epitaxial growth of thin films. However, a systematic end-to-end study of influential parameters on the surface termination is lacking. In this regard, our extensive investigation provides an insight into various annealing parameters influencing atomic termination on understudied LSAT (001), suggesting a possible inevitable scenario of LSAT termination with concomitant mound formation. Annealing parameter optimizations are directly found to influence SrO mound size and density. Whereas annealing temperature, annealing duration, and rate of heating/cooling affect the step and terrace features. A terrace width as wide as ∼178 nm was achieved. Furthermore, lanthanum vapor aids to reduce SrO mound formation; however, complete removal of the same was not achieved. Altogether, this study presents an alternate insight into a largely unexplored section of LSAT (001) surface termination, which is necessary to have a complete solution for realizing a future mound-free atomic single-termination.

All-Chemical YBCO-Based Architecture Using a Simplified Multilayer Buffer Deposition

Chemical solution deposition (CSD) is a versatile and cheap technique widely used for both buffer layer and YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7−<i>δ</i></sub> (YBCO) epitaxial film growth. One of the main limits hindering the widespread use of the CSD technique in the field of coated conductors is the limited film thickness that can be reached without degradation. Among the different strategies adopted to obtain thicker film by CSD, increase of precursor solution concentration and viscosity can be mentioned. Another interesting approach is the use of multilayer deposition in order to overcome the limits of CSD technique. Multilayer deposition has been so far realized by performing a complete heat treatment - or at least a pyrolysis step - after each deposited layer, resulting in increased processing time and overall cost. In this contribution, we show that an epitaxial multilayer buffer can be easily obtained by means of multiple successive depositions, in which after each layer only a fast drying step of the precursor solution is carried out. In this way, only a single conversion heat treatment can be used. This approach not only allows a significant reduction on the processing time but also it is more suitable for the growth on metallic template. The viability of this approach is shown by using multilayer Zr-doped CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> buffer deposition on single crystalline YSZ substrate. It is shown that, up to 8 layers, no significant structural and morphological degradation of the buffer layer occurs. Further, YBCO film grown by CSD was used to test the suitability of multilayer buffer. YBCO film grown on multilayer buffer shows excellent superconducting properties, with zero-resistance critical temperature up to 92 K and a critical current density exceeding 1 MA/cm2 at 77 K in self field.

Mechanical tuning of room temperature magnetism in flexible manganite/mica heterostructures

Flexible materials have attracted increasing attention due to their potential application in wearable or implantable circuits and systems. Here, the La0.67Sr0.33MnO3 (LSMO) thin films have been grown on single crystalline mica substrates and the impact of mechanical strain on the magnetic properties is investigated through varying external mechanical bending. The in-plane saturated magnetic moment decreases firstly with increasing radius of curvature (ROC) and then increases after attaining a minimum value of MS = 187 emu/cm3 at ROC = 3.0 mm. The nonmonotonous dependence of magnetic moment on ROC can be attributed to the mechanical bending-triggered lateral tensile strain, which can not only enhance the Jahn-Teller splitting and reduce the double-exchange interaction, but also enable the neighboring ferromagnetic domain switching in the LSMO films. Moreover, the out-of-plane magnetic anisotropy can also be reinforced by exerting mechanical tensile strain. Meanwhile, the superior mechanical antifatigue character is found in the LSMO/mica structures. These flexible LSMO thin films with highly tunable magnetism and excellent mechanical durability exhibit promising prospect in designing stable flexible spintronic devices and wearable sensors.

Structural and optical properties of Ba0.5Sr0.5TiO3 thin films on single crystalline substrates

The present investigation reports on structural and microstructural information of the Ba0.5Sr0.5TiO3 (BST-0.5) film deposited over single crystalline Si (100), MgO (100), and LaAlO3 (100) substrate using pulsed laser deposition (PLD) method. In this study, initial experiments were carried out by depositing BST-0.5 films at 1023 K and with oxygen partial pressures of 0.13 Pa and 13.33 Pa on Si (100) substrates. X-ray diffraction (XRD) analysis indicated the formation of a highly crystalline perovskite cubic phase for film deposited at substrate temperature 1023 K. Another set of depositions were carried out at the substrate temperature of 873 K and 1023 K and with oxygen partial pressure of 13.33 Pa. The XRD analysis indicated that deposition at 13.33 Pa has produced BST-0.5 films of increased crystallinity at the substrate temperature of 1023 K. Raman spectra obtained for BST thin film deposited on these three substrates confirmed the formation of the cubic phase. BST thin films were also prepared on LaAlO3 (100) and MgO (100) to investigate the optical properties of film prepared under the best deposition conditions such as 1023 K and 13.33 Pa. The bandgap energies were found to be in the range of 3.93–3.97 eV for these substrates. The measurements of optical properties of the BST-0.5 film coated on LaAlO3 substrate showed about ∼75% transmittance compared to MgO substrate. Higher extinction coefficient for the BST-0.5 thin film was observed for the film coated on MgO substrate in the UV and visible region compared to that of the film coated on LaAlO3 substrate. The refractive index as a function of wavelength was found to be 1.945 and 2.023 for BST-0.5 thin film coated on MgO and LaAlO3, respectively. The enhanced optical properties of the BST film coated on LaAlO3 substrate are discussed in relation to higher crystallinity and epitaxial growth of thin films obtained because of lower lattice mismatch.

Noncollinear magnetic order in epitaxial thin films of the centrosymmetric MnPtGa hard magnet

Magnetic systems exhibiting spin-canted states have garnered much attention recently for their promising rich exotic properties driven by the real-space spin textures and competing magnetic orders. In this study, we present the structural and magnetic properties of hexagonal 60 nm MnPtGa epitaxial thin films grown by magnetron sputtering on Al2O3(0001) single-crystalline substrates. The MnPtGa film crystallizes in the centrosymmetric P63/mmc (No. 194) space group, showing perpendicular magnetic anisotropy along the c-axis, with a Curie temperature TC = 263 K. In addition, the MnPtGa film undergoes a spin reorientation transition at Tsr = 160 K. We investigated the MnPtGa magnetic ground states using single-crystal neutron diffraction. A structurally forbidden (001) magnetic Bragg reflection emerges below Tsr, indicating the existence of a spin-canted state, where the magnetic moments align ferromagnetically perpendicular to the basal plane, and a non-zero in-plane component exhibits an antiferromagnetic ordering along the c-axis. At 2 K, the refined magnetic moments of Mn are μz = 4.2(4) μB and μx = 1.5(3) μB, projected onto the c-axis and basal plane, respectively. Hence, we determined a 20° Mn spin canting angle off from the c-axis.

High-Mobility Metastable Rock-Salt Type (Sn,Ca)Se Thin Film Stabilized by Direct Epitaxial Growth on a YSZ (111) Single-Crystal Substrate.

Metastable cubic (Sn1-xPbx)Se with x ≥ 0.5 is expected to be a high mobility semiconductor due to its Dirac-like electronic state, but it has an excessively high carrier concentration of ∼1019 cm-3 and is not suitable for semiconductor device applications such as thin film transistors and solar cells. Further, thin films of (Sn1-xPbx)Se require a complicated synthesis process because of the high vapor pressure of Pb. We herein report the direct growth of metastable cubic (Sn1-xCax)Se films alloyed with CaSe, which has a wider bandgap and lower vapor pressure than PbSe. The cubic (Sn1-xCax)Se epitaxial films with x = 0.4-0.8 are stabilized on YSZ (111) single crystalline substrates by pulsed laser deposition. (Sn1-xCax)Se has a direct-transition-type bandgap, and the bandgap energy can be varied from 1.4 eV (x = 0.4) to 2.0 eV (x = 0.8) by changing x. These films with x = 0.4-0.6 show p-type conduction with low hole carrier concentrations of ∼1017 cm-3. Hall mobility analysis suggests that the hole transport would be dominated by 180° rotational domain structures, which is specific to (111) oriented epitaxial films. However, it, in turn, clarifies that the in-grain carrier mobility in the (Sn0.6Ca0.4)Se film is as high as 322 cm2/(Vs), which is much higher than those in thermodynamically stable layered SnSe and other Sn-based layered semiconductor films at room temperature. Therefore, the present results prove the potential of high mobility (Sn1-xCax)Se films for semiconductor device applications via a simple thin-film deposition process.

Correlation between two- and three-dimensional crystallographic lattices for epitaxial analysis. II. Experimental results.

While the crystal structure of the polymorph phase can be studied in three dimensions conveniently by X-ray methods like grazing-incidence X-ray diffraction (GIXD), the first monolayer is only accessible by surface-sensitive methods that allow the determination of a two-dimensional lattice. Here, GIXD measurements with sample rotation are compared with distortion-corrected low-energy electron diffraction (LEED) experiments on conjugated molecules: 3,4;9,10-perylenetetracarboxylic dianhydride (PTCDA), 6,13-pentacenequinone (P2O), 1,2;8,9-dibenzopentacene (trans-DBPen) and dicyanovinyl-quaterthiophene (DCV4T-Et2) grown by physical vapor deposition on Ag(111) and Cu(111) single crystals. For these molecular crystals, which exhibit different crystallographic lattices and crystal orientations as well as epitaxial properties, the geometric parameters of the three-dimensional lattice are compared with the corresponding geometry of the first monolayer. A comparison of the monolayer lattice from LEED investigations with the multilayer lattices determined by rotated GIXD experiments reveals a correlation between the first monolayer and the epitaxial growth of three-dimensional crystals together with lattice distortions and re-alignment of molecules. The selected examples show three possible scenarios of crystal growth on top of an ordered monolayer: (i) growth of a single polymorph, (ii) growth of three different polymorphs; in both cases the first monolayer serves as template. In the third case (iii) strong lattice distortion and distinct molecular re-alignments from the monolayer to epitaxially grown crystals are observed. This is the second part of our work concerning the correlation between two- and three-dimensional crystallographic lattices for epitaxial analysis. In the first part, the theoretical basis has been derived which provides a mathematical relationship between the six lattice parameters of the three-dimensional case and the three parameters obtained for the two-dimensional surface unit cell, together with their orientation to the single-crystalline substrate. In this work, a combined experimental approach of GIXD and LEED is introduced which can be used to investigate the effect of the epitaxial monolayer on the structural properties of molecular crystals grown on top.

Electric Field Effects on Charge Conduction for LaMnO3 Controlled La0.7Ca0.3MnO3 Manganite

Control over the different electronic states in mixed valent manganites advances the development of oxide based electronic devices. In this context, carrier density is one of the key aspects that controls the electronic ground states of manganites in a sparkling way since it does not create any impurity within the manganite lattice, unlike chemical doping process. LaMnO3–δ / La0.7Ca0.3MnO3 / LaAlO3 (LMO / LCMO / LAO) manganite based heterostructure was fabricated by low cost chemical solution deposition (CSD) method where thickness of LMO ∼ 50 nm and LCMO ∼ 100 nm were grown on (100) single crystalline substrate. Structural quality and epitaxial nature of heterostructure was verified by performing X–ray diffraction (XRD) ϕ–scan measurement on grown La0.7Ca0.3MnO3 / LaAlO3 (LCMO / LAO) 100 nm thin film and LMO / LCMO / LAO heterostructure. Understanding of few other structural, morphological and chemical aspects of presently studied LMO / LCMO interface and LMO / LCMO / LAO heterostructure has been presented through grazing incidence X–ray diffraction (GIXRD), Rocking curve XRD, cross sectional scanning electron microscopy (SEM), atomic force microscopy (AFM) and X–ray photoelectron spectroscopy (XPS) measurements. Electric field modulated charge conduction for LCMO manganite channel has been understood in the context of field effect configuration (FEC) based transport measurements where temperature dependent LCMO channel resistance was recorded under different control electric fields applied across LMO / LCMO interface in LMO / LCMO / LAO heterostructure. Thermal hysteretic resistance measurements for LCMO manganite channel under zero control electric field exhibit metal to insulator phase transition at TP with finite width of the hysteretic resistance behaviours between two thermal cycles, i.e. cooling and heating. This has been understood on the basis of phase separation scenario, freezing effect and non–reversible electronic phase transformation. Applied control electric field induced improvement in resistance of LCMO manganite channel and reduction in value of TP have been understood on the basis of charge injection process, strain induced disorder dependent charge conduction, phase separation based movements of metal–insulator interface and negligibly small Joule heating effect. Realization of insulating phase fraction, arrested during thermal cycles, has been discussed for the explanation of reduced width of the hysteretic resistance behaviours of LCMO channel upon increase in control electric field applied across LMO / LCMO interface. Possible charge conduction mechanisms have been understood on the basis of Zener double exchange (ZDE) polynomial law for obtained metallic state of LCMO channel. Variation in electroresistance (ER) of LCMO manganite channel with temperature under different control electric fields (applied across LMO / LCMO interface) has been discussed on the basis of charge injection process with an effective role of phase separation scenario of LCMO channel in LMO / LCMO / LAO heterostructure.

Atomic layer-by-layer etching of graphene directly grown on SrTiO3 substrates for high-yield remote epitaxy and lift-off

Epitaxial lift-off techniques, which aim to separate ultrathin single-crystalline epitaxial layers off of the substrate, are becoming increasingly important due to the need of lightweight and flexible devices for heterogeneously integrated ultracompact semiconductor platforms and bioelectronics. Remote epitaxy is a relatively newly discovered epitaxial lift-off technique that allows substrate-seeded epitaxial growth of ultrathin films through few layers of graphene. This universal epitaxial lift-off technique allows freestanding single-crystal membrane fabrication very quickly at low cost. However, the conventional method of remote epitaxy requires transfer of graphene grown on another substrate to the target single-crystalline substrate, which results in organic and metallic residues as well as macroscopic defects such as cracks and wrinkles, significantly reducing the yield of remote epitaxy. Here, we show that direct growth of thick graphene on the target single-crystalline substrate (SrTiO3 for this study) followed by atomic layer etching (ALE) of the graphene layers create a defect- and residue-free graphene surface for high yield remote epitaxy. We find that the ALE efficiently removes one atomic layer of graphene per cycle, while also clearing multi-dots (clumps of carbon atoms) that form during nucleation of the graphene layers. Our results show that direct-grown graphene on the desired substrate accompanied by ALE might potentially be an ideal pathway toward commercialization of remote epitaxy.

The layered growth and thermoelectric properties of the Mg2Sn films

The Mg2Sn films with layered structure of a modulation period of 0.5∼0.7 μm thickness, containing a small amount metal Mg phase, were prepared on single crystalline Si substrate using the Mg-Sn alloy target and metal Mg target by alternative magnetron sputtering. The phase composition, surface and cross-section morphology, X-ray photoelectron spectroscopy, Hall data and thermoelectric properties of the deposited Mg2Sn films were studied. The results showed that the content of metal Mg phase in deposited Mg2Sn films can be modulated by controlling single sputtering time on metal Mg target. The resistivity and Seebeck coefficient first increase and then decrease with increasing the content of metal Mg phase in deposited Mg2Sn films. The higher Seebeck coefficient and power factor can be obtained when Mg2Sn films contains a small amount of metal Mg phase. It is beneficial to an increase in both Seebeck coefficient and power factor that the deposited films have layered structure.

Experimental and theoretical study of hole scattering in RF sputtered p-type Cu2O thin films

One of the key materials of interest for p-type oxide semiconductor thin film electronics is cuprous oxide (Cu2O), due to its relatively high hole mobility. In this work, we use experiments, analytical models, and density functional theory calculations to study the scattering mechanisms that determine Hall mobility in two Cu2O samples. First, we examine a polycrystalline Cu2O thin film deposited by RF magnetron sputtering, and second, a single-crystalline Cu2O bulk substrate. Temperature-dependent Hall measurements indicate that neutral impurity and grain boundary scattering are dominant for the polycrystalline Cu2O thin film, while phonon scattering is dominant for single-crystalline Cu2O. Our first-principles calculations show that the room-temperature intrinsic hole mobility of Cu2O is 106 cm2 V−1 s−1, indicating the great promise of the material for p-type electronic devices. This intrinsic mobility is limited by phonon scattering, with the most dominant scattering modes having phonon energies of 88.4 and 17.1 meV. These results indicate that the key pathways to increase the hole mobility in Cu2O thin films are by reducing the impurity concentration and by increasing grain size. Our work thus sets the stage for the future development of high performance Cu2O-based p-type thin film transistors.

Epitaxial Growth of SiC Films on 4H-SiC Substrate by High-Frequency Induction-Heated Halide Chemical Vapor Deposition

SiC epitaxial wafers offer enormous potential for a wide range of telecom technologies due to their excellent properties. The experimental process was simulated by software, and the contour of gas flow velocity and raw material mass fraction inside the chamber were obtained. SiC films were epitaxially grown on 4H-SiC single crystalline substrates at different temperatures for one batch, using SiCl4, CH4, and H2 as precursors. With increasing temperature, the crystal phase changed from 4H-SiC at 1773 K to a mixture of 4H- and 3C-SiC, and then a mixture of 3C-SiC and graphite at higher than 1923 K. The film was mainly (004)-oriented 4H-SiC and (111)-oriented 3C-SiC.

Epitaxial all-bcc-Co50Fe50/Cu/Co50Fe50 current-in-plane giant magnetoresistive spin-valves on Si(0 0 1) substrate

Following the high magnetoresistance (MR) ratio reported for fully epitaxial CoFe/bcc-Cu/CoFe current-in-plane giant magnetoresistance (CIP-GMR) grown on MgO(001) single crystalline substrate, we attempted to grow epitaxial CoFe/bcc-Cu/CoFe CIP-GMR devices on industrially viable Si(001) substrate through an epitaxial NiAl buffer layer. We found that the deposition of MgO insulation layer on the NiAl buffer layer is crucial to prevent current shunting in the NiAl layer which reduces MR ratio. The epitaxial CIP-GMR device grown on Si(001) exhibited sufficiently high MR ratio up to 15.9(±0.1)% at room temperature; however, it is somehow lower than that grown on the MgO(001) substrate, 20.6(±0.1)%. Detailed microstructural analysis revealed that fcc phase of Cu presented in the bcc-Cu spacer, which is considered to be the reason for the lower MR ratio of the device grown on Si(001) substrate.

A novel anisotropic saturation magnetization phenomenon in flexible Mn-doped BiFeO3 thin films for wearable device

Pure inorganic flexible thin film with anisotropic magnetism is crucial for high temperature flexible/wearable spintronic devices and magnetic sensors. Here, a pure inorganic flexible Mn-doped BiMn0.05Fe0.95O3 (BMFO) thin film with a novel anisotropic saturation magnetization phenomenon is demonstrated on (001)-oriented fluorophlogopite (F-Mica) single-crystalline substrates by sol–gel method. The results of XRD indicate that the intensity ratios of the (101) and (110) direction increases with the increase in thicknesses. And an obvious anisotropy behavior in magnetization was observed in the thicker flexible BMFO thin films, and the anisotropic magnetization is slowly weakened as the thickness decreases. Meanwhile, the saturation magnetization (Ms) of both in-plane and out-of-plane increases with the increase in the thickness. These results indicate that the thickness can modulate the anisotropic magnetism for the flexible BMFO thin films. The maximum value of (Ms-in-plane-Ms-out-of-plane) is obtained in the flexible BMFO sample with the thickness of 550 nm. Moreover, the real nonvolatile ferroelectric polarization with Pr = 58.22 μC/cm2 was obtained in the flexible BMFO sample with the thickness of 336 nm. These flexible BMFO thin films with anisotropic saturation magnetism, mechanical anti-fatigue characters and well ferroelectric properties are promising for the applications in high temperature flexible spintronics and magnetic sensors.

Nanoscale-Thick Ni-Based Half-Heusler Alloys with Structural Ordering-Dependent Ultralow Magnetic Damping: Implications for Spintronic Applications

Atomic ordering and its consequence on the crystal structure are fundamental issues in the application of half-metallic Heusler alloys considered as a high spin-polarized electron source. NiMnSb is a promising half-metallic half-Heusler alloy for spintronic devices due to its low magnetic damping, non-centrosymmetric crystal structure, and rich anisotropies. Here, we report a high-quality half-metallic epitaxial nano-scale thick NiMnSb alloy film grown on a Cr/Ag-buffered MgO (001) single crystalline substrate. High temperature deposition is a crucial parameter for crystal growth and magneto-dynamic properties such as damping, anisotropy, magnetization, etc. After investigating the ferromagnetic resonance (FMR) spectroscopy using a time-resolved magneto-optical Kerr (TRMOKE) microscope and calculating the crystal structure using VESTA and the density of states from first-principles calculations, we discuss how the deposition temperature influences the crystal ordering, damping, and magnetization. Ultralow Gilbert damping with high anisotropic field and saturation magnetization were found for the highly ordered C1b structured nano-scale thick NiMnSb film deposited at 573 K. We also found quite nice agreement between theoretical and experimental data of crystal ordering and damping that explains how the ordering affects the magnetic parameter as well as sample quality. Furthermore, the negative anisotropic magnetoresistance ratio implies the robust bulk half-metallicity. Such unique combination of highly ordered half-metallic NiMnSb alloy in the nano-scale regime with ultralow damping can be regarded as an advantage for applications in spintronic devices.

Epitaxial growth of aligned MgO nanowire arrays on a single crystalline substrate.

MgO nanostructures with different morphologies were fabricated by regulating the composition of raw materials, using the chemical vapor deposition method with gold as a catalyst. Polycrystalline MgO nanopillars were prepared using only Mg3N2 as the raw material. Single crystalline nanowire arrays can be obtained by adding carbon powder into the raw material. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used for the detailed characterization of (100) nanowire arrays. Besides the vertical growth direction [100], the nanowires change into two kinds of orientations after growing to a certain length: 〈111〉 and 〈001〉. The epitaxial growth was attributed to the lattice match and regulation of the concentration of the Mg source. The variation of growth orientations was probably caused by the difference in surface energy and reaction temperature.

Microstructure of a coated single crystalline René N5 part repaired by epitaxial laser deposition

Laser Metal Deposition has been applied to the repair and manufacture of single crystalline Ni-based superalloys components. The extensive research carried out so far showed that single crystalline depositions of the same alloy of the substrate, or similar, can be produced in appropriate conditions. However, repair is often performed on previously refurbished parts, combining materials with different compositions and structures. In this work we investigated the deposition of René N4 Ni superalloy on a René N5 single crystalline part previously coated by TIG welding with René 195. Deposition was performed on the (100) surface of the single crystalline substrate. The results show that the multilayer deposits inherit the single crystalline structure and orientation of the original crystal when the material is laid down on the single crystalline regions of the substrate. Above the polycrystalline René 195 a heavily textured columnar dendritic solidification structure develops, similar to the structure of directionally solidified cast alloys. Above the dilution zone of the first deposited layer, both the chemical composition and the microstructure of the deposited René N4 alloy remain constant across all the deposited layers showing that repairing is feasible even on heterogeneous substrates. Several heat treatments aimed at developing a suitable γ/γ’ microstructure within the deposited material were tested and an optimized heat treatment method consisting of a solution step, followed by two ageing steps at specific temperatures was devised. • Over the single crystal, the deposit maintains the orientation of the substrate. • Above the coating, solidification structure is similar to a directionally cast alloy. • The coating does not interfere with the deposit orientation over the single crystal. • A three-stage heat treatment is required to obtain the γ/γ’ microstructure.

Thickness dependence of spin–orbit torques in Pt/Co structures on epitaxial substrates

We investigate the Pt thickness dependence of spin–orbit torques (SOTs) in Co/Pt layers grown on single crystalline SrTiO3 and LaAlO3 and amorphous SiO2 substrates. We measure the SOT-induced effective damping-like fields and spin Hall magnetoresistances of the Co/Pt (tPt) samples, where tPt varies from 0.5 to 5.5 nm. We find that the Co/Pt layers grown on the single crystalline substrates show weaker thickness dependence of the SOT than the samples on the SiO2 substrate, which cannot be explained by the conventional bulk spin Hall effect in the Pt layer. This indicates that there is a non-negligible interfacial SOT originating from the Pt/substrate interface, which is more pronounced for thinner Pt. These results provide a way to design SOT material structures with enhanced SOT efficiency by incorporating interfacial SOT.

Transparent and High‐Absolute‐Effectiveness Electromagnetic Interference Shielding Film Based on Single‐Crystal Graphene

AbstractWith the rapid development of wireless electronic facilities, the demand for high‐performance electromagnetic shielding films has swiftly increased. Graphene is a desirable electromagnetic interference (EMI) shielding material due to its excellent electrical conductivity and light transmittance. Previous studies mostly focus on polycrystalline graphene sheets and the performances are far below the theoretical value due to poor crystal quality. In this paper, the authors demonstrate a flexible ultrathin transparent EMI film based on large‐area single crystal graphene (SCG), which is grown on single crystalline Cu substrates by chemical vapor deposition. Their flexible transparent EMI films show ultrahigh electromagnetic shielding effectiveness (SE). This can be attributed to the high crystalline quality and outstanding electronic conductivity of the as‐used graphene film. The electromagnetic shielding effectiveness of the SCG/MgF/SCG sandwiched structure can reach over 8.10 dB, and the normalized electromagnetic SE is up to 5.5 × 107 dB cm2 g−1, much higher than the recorded materials. Moreover, their large area single‐crystal graphene EMI films exhibit a high and broad wavelength transmittance from visible to infrared range (e.g., infrared transmittance of 94% at 5000 nm). A flexible EMI lid of SCG has been investigated for effectively blocking WIFI signals and phone radiation.