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We report the growth of high quality topological insulator Bi2Se3 thin films on a single layer, transitional metal dichalcogenide MoS2 film via van der Waals epitaxy in a planar geometry. In stark contrast to the reported growth of using 3-D crystalline substrates such as Al2O3(0001), Bi2Se3 thin films grown on a 2-D template made of single layer MoS2 showed excellent crystallinity starting immediately from the growth of the first quintuple layer. Excellent crystallinity of Bi2Se3 thin films is attained, with the increased size of the triangular shaped Bi2Se3 domains and 2–3 times enhancement in mobility, along with the observation of Shubnikov–de Haas oscillations in the magnetoresistance. Our approach of adopting a van der Waals type template may be extended to the thin film growth of other low dimensional layered materials. [ABSTRACT FROM AUTHOR]

Single crystal ferromagnetic Fe3Si(111) films were grown epitaxially on GaAs(111)A by molecular beam epitaxy. These hetero-structures possess extremely low surface roughness of 1.3 Å and interfacial roughness of 1.9 Å, measured by in-situ scanning tunneling microscope and X-ray reflectivity analyses, respectively, showing superior film quality, comparing to those attained on GaAs(001) in previous publications. The atomically smooth interface was revealed by the atomic-resolution Z (atomic number)-contrast scanning transmission electron microscopy (STEM) images using the correction of spherical aberration (Cs)-corrected electron probe. Excellent crystallinity and perfect lattice match were both confirmed by high resolution x-ray diffraction. Measurements of magnetic property for the Fe3Si/GaAs(111) yielded a saturation moment of 990 emu/cm³ with a small coercive field ≤1 Oe at room temperature. [ABSTRACT FROM AUTHOR]

A high-quality high-σ/Ge interface has been achieved by combining molecule beam epitaxy grown Ge epitaxial layer and in-situ deposited high j dielectric. The employment of Ge epitaxial layer has sucessfully buried and/or removed the residue of unfavorable carbon and native oxides on the chemically cleaned and ultra-high vacuum annealed Ge(100) wafer surface, as studied using angleresolved x-ray photoelectron spectroscopy. Moreover, the scanning tunneling microscopy analyses showed the significant improvements in Ge surface roughness from 3.5Å to 1Å with the epi-layer growth. Thus, chemically cleaner, atomically more ordered, and morphologically smoother Ge surfaces were obtained for the subsquent deposition of high j dielectrics, comparing with those substrates without Ge epi-layer. The capacitance-voltage (C-V) characteristics and low extracted interfacial trap density (Dit) reveal the improved high-σ/Ge interface using the Ge epi-layer approach. [ABSTRACT FROM AUTHOR]

High κ gate dielectrics of HfO2 and Al2O3 were deposited on molecular beam epitaxy-grown In0.2Ga0.8As pristine surface using in-situ atomic-layer-deposition (ALD) without any surface treatment or passivation layer. The ALD-HfO2/p-In0.2Ga0.8As interface showed notable reduction in the interfacial density of states (Dit), deduced from quasi-static capacitance-voltage and conductance-voltage (G-V) at room temperature and 100?°C. More significantly, the midgap peak commonly observed in the Dit(E) of ALD-oxides/In0.2Ga0.8As is now greatly diminished. The midgap Dit value decreases from ≥15?×?1012?eV-1?cm-2 for ALD-Al2O3 to ∼2-4?×?1012?eV-1?cm-2 for ALD-HfO2. Further, thermal stability at 850?°C was achieved in the HfO2/In0.2Ga0.8As, whereas C-V characteristics of Al2O3/p-In0.2Ga0.8As degraded after the high temperature annealing. From in-situ x-ray photoelectron spectra, the AsOx, which is not the oxidized state from the native oxide, but is an induced state from adsorption of trimethylaluminum and H2O, was found at the ALD-Al2O3/In0.2Ga0.8As interface, while that was not detected at the ALD-HfO2/In0.2Ga0.8As interface. [ABSTRACT FROM AUTHOR]

Molecular beam epitaxy deposited Ga2O3(Gd2O3) on Ge, without a commonly employed interfacial layer of GeON, has demonstrated excellent electrical properties, such as a high κ value of 14.5, a low electrical leakage current density, and well behaved C-V characteristics even being subjected to 500 °C annealing in N2 ambient for 5 min. In situ angle-resolved x-ray photoelectron spectroscopy (XPS) studies have revealed an abrupt Ga2O3(Gd2O3)/Ge interface without forming any interfacial layer. Further XPS studies explained the outstanding thermodynamic stability of the Ga2O3(Gd2O3)/Ge heterostructure. [ABSTRACT FROM AUTHOR]

Reports the epitaxial growth of single-crystal gadolinium oxide dielectric thin films on gallium arsenide. Structure of the thin films; Dielectric constant; Typical breakdown field; Observation of accumulation and inversion layers; Use of capacitance-voltage measurements; Potential impact of research on the compound semiconductor industry.

Extensive structural and magnetic analyses of Hf1-xCoxO2 thin films grown by molecular beam epitaxy are reported. Nearly cobalt cluster-free film with x=0.04–0.1 was obtained via 100 °C growth, and Co ions are inferred to be located at interstitial site. Ferromagnetic behavior was observed up to 300 K in both magnetization curves and temperature dependence of the moment. Via post-oxygen-annealing studies, a qualitative correlation between saturation magnetization and oxygen vacancy concentration is established, consistent with the impurity-band exchange model, and that the occurrence of ferromagnetic insulator behavior in the Co doped HfO2 is more probable than Co doped ZnO, TiO2, and SnO2 systems for doping concentrations under cation percolation threshold. [ABSTRACT FROM AUTHOR]

Nanometer thick cubic HfO2 doped with 19 at. % Y2O3 (YDH) epitaxial films were grown on GaAs (001) using molecular beam epitaxy. Structural studies determined the epitaxial orientation relationships between the cubic YDH films and GaAs to be (001)GaAs//(001)YDH and [100]GaAs//[100]YDH. The YDH structure is strain relaxed with a lattice constant of 0.5122 nm with a small mosaic spread of 0.023° and a twist angle of 2.9°. The YDH/GaAs interface is atomically abrupt without evidence of reacted interfacial layers. From C-V and I-V measurements a 7.7 nm thick YDH film has an enhanced dielectric constant κ∼32, an equivalent oxide thickness of ∼0.94 nm, an interfacial state density Dit∼7×1012 cm-2 eV-1, and a low leakage current density of 6×10-5 A/cm2 at 1 V gate bias. [ABSTRACT FROM AUTHOR]

High-quality HfO2 films of technologically important thickness ranging from 1.8 to 17 nm have been grown epitaxially on GaAs (001) by molecular beam epitaxy. Thorough structural and morphological investigations were carried out by x-ray scattering and high-resolution transmission electron microscopy. The films exhibit an atomically sharp interface with the substrate and are of a monoclinic phase with predominant (001)-plane epitaxy between the HfO2 films and GaAs, in spite of a large lattice mismatch of >8.5%. [ABSTRACT FROM AUTHOR]

The crystal structure of scandium oxide films epitaxially grown on α-Al2O3 (0001) under an ultrahigh-vacuum is studied by single-crystal x-ray diffraction. The Sc2O3 film grows in bixbyite phase on the basal (0001) surface of the sapphire substrate with its <111> axis aligned parallel to the substrate normal. In-plane orientation of the film, however, exhibits two distinct growth directions that are defined by the two possible surface orientations of the stepped α-Al2O3 substrate. The atomic structure of the high-quality epitaxial film is fully relaxed and the film has unusual thickness uniformity. [ABSTRACT FROM AUTHOR]

Investigates the in situ growth of single-crystalline-like La[sub 2-x]Sr[sub x]CuO[sub 4] epitaxial thin films by off-axis sputtering. Properties of the films; Use of the high-resolution scanning electron microscope; Analysis of superconductivity and transport as a function of doping.

Examines the growth and characterization of heteroepitaxial BST/SRO on silicon films for potential charge storage applications. Display of a high degree of crystallinity with minimal interdiffusion; Crystallographic relations between the layers; Factor attributed for the observation of a strong frequency dependence on both dielectric constant and loss tangent.

We compare the superlattice modulation, microstructure, and epitaxy of Tl2Ba2Ca2Cu3O10 thin films grown on MgO [100] and SrTiO3 [100] substrates by dc diode sputtering. Films grown on MgO were found to be quite clean with the c axis perpendicular to the substrate. However, no in-plane orientational relationship to the substrate was found. Films grown on SrTiO3, on the other hand, showed very good epitaxy to the substrate despite the presence of second phases. Films grown on MgO also exhibited a longer coherence length of the superlattice modulation than those grown on SrTiO3 under identical conditions. [ABSTRACT FROM AUTHOR]

The strain/relaxation behavior of nanometer thick Y2O3 (111) epitaxially grown on Si (111) has been investigated with x-ray diffraction using synchrotron radiation. The authors systematically measured a series of Bragg reflections to determine the lattice parameters of Y2O3 films with thickness ranging from 1.6 to 9.5 nm. The strain state of the oxide lattice along surface normal and lateral directions is analyzed as a function of the oxide thickness. The spectra of Si 2p and Y 3d, obtained with in situ angle-resolved x-ray photoelectron spectroscopy on Y2O3 5 nm thick, showed no Y silicide but a very small incorporation of Si into the Y2O3 films at the interface. [ABSTRACT FROM AUTHOR]

In-situ molecular beam epitaxy (MBE) Y 2 O 3 films 1–2 nm thick were epitaxially grown on GaAs(001)−4×6 reconstructed surfaces. Despite a large lattice mismatch, the hetero-structure exhibits outstanding thermal stability to 900 °C with excellent capacitance-voltage ( C-V ) characteristics. Low interfacial trap densities ( D it 's ) of (3–5)×10 11 eV −1 cm −2 were obtained using the conductance method ( G-V ) without discernible peaks at the mid-gap. The frequency dispersion of the measured C-V s of the Y 2 O 3 /GaAs(001) is ~4.6% for p -GaAs and ~12.4% for n -GaAs. In contrast, the atomic layer deposited Al 2 O 3 on GaAs(001) shows large D it with a peak at the mid-gap, large C-V frequency dispersion, and low thermal stability at temperatures higher than 600 °C. Synchrotron radiation photoemission results show intactness of the interfacial structure in the MBE-Y 2 O 3 /GaAs, while removal of the surface As atoms is found in the ALD-Al 2 O 3 /GaAs system. [ABSTRACT FROM AUTHOR]

We report the growth of high quality topological insulator Bi2Se3 thin films on a single layer, transitional metal dichalcogenide MoS2 film via van der Waals epitaxy in a planar geometry. In stark contrast to the reported growth of using 3-D crystalline substrates such as Al2O3(0001), Bi2Se3 thin films grown on a 2-D template made of single layer MoS2 showed excellent crystallinity starting immediately from the growth of the first quintuple layer. Excellent crystallinity of Bi2Se3 thin films is attained, with the increased size of the triangular shaped Bi2Se3 domains and 2–3 times enhancement in mobility, along with the observation of Shubnikov–de Haas oscillations in the magnetoresistance. Our approach of adopting a van der Waals type template may be extended to the thin film growth of other low dimensional layered materials. [ABSTRACT FROM AUTHOR]

Abstract: The epitaxial growth of Gd2O3 on GaAs (001) has given a low interfacial density of states, resulting in the demonstration of the first inversion-channel GaAs metal-oxide-semiconductor field-effect transistor. Motivated by the significance of this discovery, in this work, cross-sectional scanning tunneling microscopy is employed herein to obtain precise structural and electronic information on these epitaxial films and interfaces. At the interface, the interfacial stacking of Gd2O3 films is directly correlated with the stacking sequence of the substrate GaAs. Additionally, from the local electronic states across the gate oxides, the spatial extent of the GaAs wavefunctions into the oxide dielectric may suggest a minimum Gd2O3 thickness to be of bulk properties. [Copyright &y& Elsevier]