The double perovskite Sr2CrReO6 is an interesting material for spintronics, showing ferrimagnetism up to 635 K with a predicted high spin polarization of about 86%. We fabricated Sr2CrReO6 epitaxial films by pulsed laser deposition on (001)-oriented SrTiO3 substrates. Phase-pure films with optimum crystallographic and magnetic properties were obtained by growing at a substrate temperature of 700 degree C in pure O2 of 6.6x10-4 mbar. The films are c-axis oriented, coherently strained, and show less than 20% anti-site defects. The magnetization curves reveal high saturation magnetization of 0.8 muB per formula unit and high coercivity of 1.1 T, as well as a strong magnetic anisotropy.
We report herein fabrication and characterization of a thin-film transistor (TFT) using single-crystalline, epitaxial SrTiO3 film, which was grown by a pulsed laser deposition technique followed by the thermal annealing treatment in an oxygen atmosphere. Although TFTs on the polycrystalline epitaxial SrTiO3 films (as-deposited) exhibited poor transistor characteristics, the annealed single-crystalline SrTiO3 TFT exhibits transistor characteristics comparable with those of bulk single-crystal SrTiO3 FET: an on/off current ratio >10^5, sub-threshold swing ~2.1 V/decade, and field-effect mobility…
The interrelation between the epitaxial strain and oxygen deficiency in La0.7Ca0.3MnO3-δ thin films was studied in terms of structural and functional properties. The films with a thickness of 1000Å were prepared using a PLD system equipped with a RHEED facility and a pyrometric film temperature control. The epitaxial strain and the oxygen deficiency in the samples were systematically modified using three different substrates: SrTiO3, (LaAlO3)0.3-(Sr2AlTaO6)0.7 and LaSrAlO4, and four different oxygen pressures during film growth ranging from 0.27mbar to 0.1mbar. It could be demonstrated that th…
Ferromagnetic insulators play a crucial role in the development of low-dissipation quantum magnetic devices for spintronics. Epitaxial LaCoO3 thin film is a prominent ferromagnetic insulator, in which the robust ferromagnetic ordering emerges owing to epitaxial strain. Whereas it is evident that strong spin-lattice coupling induces ferromagnetism, the reported ferromagnetic properties of epitaxially strained LaCoO3 thin films were highly consistent. For example, even under largely modulated degree of strain, the reported Curie temperatures of epitaxially strained LaCoO3 thin films lie within 8…
We report x-ray synchrotron experiments on epitaxial films of uranium, deposited on niobium and tungsten seed layers. Despite similar lattice parameters for these refractory metals, the uranium epitaxial arrangements are different and the strains propagated along the a-axis of the uranium layers are of opposite sign. At low temperatures these changes in epitaxy result in dramatic modifications to the behavior of the charge-density wave in uranium. The differences are explained with the current theory for the electron-phonon coupling in the uranium lattice. Our results emphasize the intriguing …
We show that a ferromagnetic (FM) order in the orthorhombic CaRuO3, which is a non-magnetic and iso-structural analog of FM system SrRuO3, can be established and stabilized by the means of tensile epitaxial strain. Investigations on the structural and magnetic property correlations in the CaRuO3 films with different degrees of strain reveal that the FM moment increases with increasing the tensile strain. This is an experimental verification to the theoretical predictions of scaling of the tensile epitaxial strain and the magnetic order in this system. Our studies further establish that the ten…
Thin films of perovskite Ruthenates of the general formula ARuO3 (A = Ca and Sr) are versatile electrical conductors for viable oxide electronics. They are also scientifically intriguing, as they exhibit non-trivial electromagnetic ground states depending on the A-site element. Among them, realization of the cubic perovskite (3C) BaRuO3 thin film has been a challenge so far, because the 3C phase is metastable with the largest formation energy among the various polymorph phases of BaRuO3. In this study, we successfully prepared 3C BaRuO3 thin films employing epitaxial stabilization. The 3C BaRu…
Using pulsed laser deposition and a unique fast quenching method, we have prepared SrCoOx epitaxial films on SiTiO3 substrates. As electrochemical oxidation increases the oxygen content from x = 2.75 to 3.0, the films tend to favor the discrete magnetic phases seen in bulk samples for the homologous series SrCoO(3-n/8) (n = 0, 1, 2). Unlike bulk samples, 200nm thick films remain single phase throughout the oxidation cycle. 300 nm films can show two simultaneous phases during deoxidation. These results are attributed to finite thickness effects and imply the formation of ordered regions larger …
The structure, morphology, and electrical properties of epitaxial a-axis oriented thin films of Nd(0.2)Sr(0.8)MnO(3) are reported for thicknesses 10 nm <= t <= 150 nm. Films were grown with both tensile and compressive strain on various substrates. It is found that the elongated crystallographic c-axes of the films remain fully strained to the substrates for all thicknesses in both strain states. Relaxation of the a and b axes is observed for t>= 65 nm with films grown under tensile strain developing uniaxial crack arrays (running along the c axis) due to a highly anisotropic thermal expansion…
We have synthesized epitaxial NdNiO$_{3}$ ultra-thin films in a layer-by-layer growth mode under tensile and compressive strain on SrTiO$_{3}$ (001) and LaAlO$_3$ (001), respectively. A combination of X-ray diffraction, temperature dependent resistivity, and soft X-ray absorption spectroscopy has been applied to elucidate electronic and structural properties of the samples. In contrast to the bulk NdNiO$_{3}$, the metal-insulator transition under compressive strain is found to be completely quenched, while the transition remains under the tensile strain albeit modified from the bulk behavior.
Magneto-transport properties have been investigated for epitaxial thin films of B20-type MnSi grown on Si(111) substrates. Both Lorentz transmission electron microscopy (TEM) images and topological Hall effect (THE) clearly point to the robust formation of skyrmions over a wide temperature-magnetic field region. New features distinct from those of bulk MnSi are observed for epitaxial MnSi films: a shorter (nearly half) period of the spin helix and skyrmions, and an opposite sign of THE. These observations suggest versatile features of skyrmion-induced THE beyond the current understanding.
About ten years after ferroelectricity was first reported in doped HfO2 polycrystalline films, there is tremendous interest in this material and ferroelectric oxides are once again in the spotlight of the memories industry. Great efforts are being made to understand and control ferroelectric properties. Epitaxial films, which have fewer defects and a more controlled microstructure than polycrystalline films, can be very useful for this purpose. Epitaxial films of ferroelectric HfO2 have been much less investigated, but after the first report in 2015 significant progress has been achieved. This…
Doping ferroelectric Hf0.5Zr0.5O2 with La is a promising route to improve endurance. However, the beneficial effect of La on the endurance of polycrystalline films may be accompanied by degradation of the retention. We have investigated the endurance - retention dilemma in La-doped epitaxial films. Compared to undoped epitaxial films, large values of polarization are obtained in a wider thickness range, whereas the coercive fields are similar, and the leakage current is substantially reduced. Compared to polycrystalline La-doped films, epitaxial La-doped films show more fatigue but there is no…
The first epitaxial ferroelectric wurtzite film with clear polarization-electric field hysteresis behavior is presented. The coercive field of this epitaxial Al0.7Sc0.3N film on W/c-sapphire substrate is 0.4 +- 0.3 MV cm-1 (8 %) smaller than that of a conventional fiber textured film on a Pt/TiOx/SiO2/Si substrate, attributed to the 0.01 +- 0.007 Å smaller c-axis lattice parameter in the epitaxial film. The strain and decrease of the coercive field most likely originate from epitaxial strain rather than the mismatch in thermal coefficient of expansion. These results provide an insight for furt…
The discovery of high temperature superconductivity in FeSe films on SrTiO3 substrate has inspired great experimental and theoretical interests. First-principles density functional theory calculations, which have played an important role in the study of bulk iron-based superconductors, also participate in the investigation of interfacial superconductivity. In this article, we review the calculation results on the electronic and magnetic structures of FeSe epitaxial films, emphasizing on the interplay between different degrees of freedom, such as charge, spin, and lattice vibrations. Furthermor…
We have synthesized thermodynamically metastable Ca2IrO4 thin-films on YAlO3 (110) substrates by pulsed laser deposition. The epitaxial Ca2IrO4 thin-films are of K2NiF4-type tetragonal structure. Transport and optical spectroscopy measurements indicate that the electronic structure of the Ca2IrO4 thin-films is similar to that of Jeff = 1/2 spin-orbit-coupled Mott insulator Sr2IrO4 and Ba2IrO4, with the exception of an increased gap energy. The gap increase is to be expected in Ca2IrO4 due to its increased octahedral rotation and tilting, which results in enhanced electron-correlation, U/W. Our…
In order to obtain Ni-Mn-Ga epitaxial films crystallized in martensite structures showing Magnetic-Induced Rearrangement (MIR) of martensite variants, a fine control of the composition is required. Here we present how the co-sputtering process might be helpful in the development of Ni-Mn-Ga epitaxial films. A batch of epitaxial Ni-Mn-Ga films deposited by co-sputtering of a Ni-Mn-Ga ternary target and a pure manganese target has been studied. The co-sputtering process allows a precise control of the film compositions and enables keeping the epitaxial growth of Ni-Mn-Ga austenite during deposit…
The authors demonstrated that a full-Heusler Co2FeGe (CFG) alloy thin film was epitaxially grown by rapid-thermal-annealing-induced germanidation of an Fe/Co/pseudo-Ge(001)-on-insulator (GOI) multilayer formed on a Si-on-insulator (SOI) substrate. X-ray diffraction (XRD) measurements with the out-of-plane and in-plane configurations revealed that the CFG film was epitaxially grown along the [001] direction with the in-plane epitaxial relation of CFG[100]||GOI[100], although the film slightly contained a texture component. The strong (111) and (200) superlattice diffraction intensities indicate…
We have investigated the transport and optical properties along the c-axis of a-axis-oriented Sr2IrO4 epitaxial thin-films grown on LaSrGaO4 (100) substrates. The c-axis resistivity is approximately one order of magnitude larger than that of the ab-plane. Optical absorption spectra with E//b polarization show both Ir 5d intersite transitions and charge-transfer transitions (O 2p to Ir 5d), while E//c spectra show only the latter. The structural anisotropy created by biaxial strain in a-axis-oriented thin-films also changes the electronic structure and gap energy. These a-axis-oriented, epitaxi…
Epitaxial copper thin films were deposited by magnetron sputtering. The adatoms during deposition are influenced by deposition parameters which cause variations in thin film properties. XRD and FESEM studies were done to get an insight into the growth mechanisms of the films. A modeling has been done on the epitaxial thin film growth with sputtering process. The parameters during sputtering like, sputtering yield, pressure, temperature, current density, deposition time were related and an attempt has been made to analyze the sputtering process.
We present results on growth of large area epitaxial ReS2 thin film both on c plane sapphire substrate and MoS2 template by pulsed laser deposition (PLD). Films tend to grow with (0001) ReS2 perpendicular to (0001) Al2O3 and (0001) ReS2 perpendicular to (0001) MoS2 parallel to (0001) Al2O3 at deposition temperature below 300 deg C. Films are polycrystalline grown at temperature above 300 deg C. The smoothness and quality of the films are significantly improved when grown on MoS2 template compared to sapphire substrate. The results show that PLD is suitable to grow ReS2 epitaxial thin film over…
Transition metal oxide thin films show versatile electrical, magnetic, and thermal properties which can be tailored by deliberately introducing macroscopic grain boundaries via polycrystalline solids. In this study, we focus on the modification of the magnetic and thermal transport properties by fabricating single- and polycrystalline epitaxial SrRuO3 thin films using pulsed laser epitaxy. Using epitaxial stabilization technique with atomically flat polycrystalline SrTiO3 substrate, epitaxial polycrystalline SrRuO3 thin film with crystalline quality of each grain comparable to that of single-c…
We report on the effect of epitaxial strain on magnetic and optical properties of perovskite LaCrO3 (LCO) single crystal thin films. Epitaxial LCO thin films are grown by pulsed laser deposition on proper choice of substrates to impose different strain states. A combined experimental and theoretical approach is used to demonstrate the direct correlation between lattice-strain and functional properties. The magnetization results show that the lattice anisotropy plays a critical role in controlling the magnetic behavior of LCO films. The strain induced tetragonality in the film lattice strongly …
Few-layer PtSe2 films are promising candidates for applications in high-speed electronics, spintronics and photodetectors. Reproducible fabrication of large-area highly crystalline films is, however, still a challenge. Here, we report the fabrication of epitaxially aligned PtSe2 films using one-zone selenization of pre-sputtered platinum layers. We have studied the influence of the growth conditions on the structural and electrical properties of the films prepared from Pt layers with different initial thickness. The best results were obtained for PtSe2 layers grown at elevated temperatures (60…
We demonstrate high-quality epitaxial germanium (Ge) films on a metallic silicide, Fe3Si, grown directly on a Ge(111) substrate. Using molecular beam epitaxy techniques, we can obtain an artificially controlled arrangement of silicon (Si) or iron (Fe) atoms at the surface on Fe3Si(111). The Si-terminated Fe3Si(111) surface enables us to grow two-dimensional epitaxial Ge films, whereas the Fe-terminated one causes the three-dimensional epitaxial growth of Ge films. The high-quality Ge grown on the Si-terminated surface has almost no strain, meaning that the Ge films are not grown on the low-tem…
Epitaxial films have the potential to be used as model systems for fundamental investigations on the martensitic transformation in binary NiTi. In this paper, we discuss growth of binary NiTi thin films on single crystalline MgO substrates. Sputter deposition is used to grow NiTi films. Films prepared by complementary preparation routes (with different deposition temperatures and subsequent heat treatments) are investigated by X-ray diffraction, electron microscopy, atomic force microscopy, and electrical resistivity measurements, with the aim of optimizing film properties, particularly to obt…
We analyze X-ray diffraction data used to extract cell parameters of ultrathin films on closely matching substrates. We focus on epitaxial La2/3Sr1/3MnO3 films grown on (001) SrTiO3 single crystalline substrates. It will be shown that, due to extremely high structural similarity of film and substrate, data analysis must explicitly consider the distinct phase of the diffracted waves by substrate and films to extract reliable unit cell parameters. The implications of this finding for the understanding of strain effects in ultrathin films and interfaces will be underlined
Chalcogenide perovskites have emerged as a new class of electronic materials, but fundamental properties and applications of chalcogenide perovskites remain limited by the lack of high quality epitaxial thin films. We report epitaxial thin film growth of BaZrS3, a prototypical chalcogenide, by pulsed laser deposition. X-ray diffraction studies show that the films are strongly textured out of plane and have a clear in-plane epitaxial relationship with the substrate. Electron microscopy studies confirm the presence of epitaxy for the first few layers of the film at the interface, even though awa…
Epitaxial films of bismuth telluride topological insulators have received increasing attention due to potential applications in spintronic and quantum computation. One of the most important properties of epitaxial films is the presence of interface defects due to lateral lattice mismatch since electrically active defects can drastically compromise device performance. By describing hybrid reflections in hexagonal bismuth telluride films on cubic substrates, in-plane lattice mismatches were characterized with accuracy at least 20 times better than using other X-ray diffraction methods, providing…
Thin epitaxial films of metals on insulating substrates are essential for many applications, as conducting layers, in magnetic devices or as templates for further growth. In this work, we report on the growth of epitaxial Ru films on single-crystalline Al$_2$O$_3$(0001) substrates by magnetron sputtering and their subsequent systematic characterization using Rutherford backscattering spectrometry of He ions both in random and in channeling conditions. We include results of a Ru(0001) single crystal for comparison. Analysis of channeling shows that films thicker than 35 nm grow with (0001) orie…
We have investigated structural, transport, and optical properties of tensile strained (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$ (x = 0, 0.025, 0.05) epitaxial thin-films. While High-T$_c$ superconductivity is predicted theoretically in the system, we have observed that all of the samples remain insulating with finite optical gap energies and Mott variable-range hopping characteristics in transport. Cross-sectional scanning transmission electron microscopy indicates that structural defects such as stacking faults appear in this system. The insulating behavior of the La-doped Sr$_3$Ir$_2$O$_7$ thin-fil…
We have synthesized epitaxial Ba2IrO4 (BIO) thin-films on SrTiO3 (001) substrates by pulsed laser deposition and studied their electronic structure by dc-transport and optical spectroscopic experiments. We have observed that BIO thin-films are insulating but close to the metalinsulator transition boundary with significantly smaller transport and optical gap energies than its sister compound, Sr2IrO4. Moreover, BIO thin-films have both an enhanced electronic bandwidth and electronic-correlation energy. Our results suggest that BIO thin-films have great potential for realizing the interesting ph…
X-ray diffraction (XRD) data and analysis for epitaxial iron selenide thin films grown by pulsed laser deposition (PLD) are presented. The films contain $β$-FeSe and Fe$_7$Se$_8$ phases in a double epitaxy configuration with the $β$-FeSe phase (001) oriented on the (001) MgO growth substrate. Fe$_7$Se$_8$ simultaneously takes on two different epitaxial orientations in certain growth conditions, exhibiting both (101)- and (001)- orientations. Each of these orientations are verified with the presented XRD data. Additionally, XRD data used to determine the PLD target composition as well as mosaic…
