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We report a systematic study on the structural and electronic properties of Bi2Te3-xSex topological insulator alloy grown by molecular beam epitaxy(MBE). A mixing ratio of Bi2Se3 to Bi2Te3 was controlled by varying the Bi:Te:Se flux ratio. X-ray diffraction and Raman spectroscopy measurements indicate the high crystalline quality for the as-grown Bi2Te3-xSex films. Substitution of Te by Se is also revealed from both analyses. The surfaces of the films exhibit terrace-like quintuple layers and their size of the characteristic triangular terraces decreases monotonically with increasing Se content. However, the triangular terrace structure gradually recovers as the Se content further increases. Most importantly, the angle-resolved photoemission spectroscopy results provide evidence of single-Dirac-cone like surface states in which Bi2Te3-xSex with Se/Te-substitution leads to tunable surface states. Our results demonstrate that by fine-tuned MBEgrowth conditions, Bi2Te3-xSex thin film alloys with tunable topological surface states can be obtained, providing an excellent platform for exploring the novel device applications based on this compound. [ABSTRACT FROM AUTHOR]

In atomic-layer deposition (ALD), organoaluminum as trimethyl-aluminum (TMA) on a freshly molecular beam epitaxy grown In0.20Ga0.80As(001)-4 × 2 surface has three forms: Al bonding with 1, 2, and 3 methyl groups. The ALD method of using one pulse (0.1 s) of TMA plus one pulse (0.1 s) of water was ineffective in passivating the surface, as demonstrated by the increased intensity of the reacted surface components with high numbers of pulses. The intact TMA was physisorbed on the trough In atoms, while the methyl-deficient precursors are either bridged with two As atoms or on the row-edge As atoms. After the water pulse on the TMA-covered surface, a bond in the bridged As atoms was scissored off to produce the As-Al-CH3 and As-OH, and the physisorbed TMA was unaffected. TMA removed some row In atoms, which allowed the In and Ga atoms in the second layer to form OH bonds after the water exposure. The appearance of the As-OH bonds may cause interfacial defect density (Dit) a peak at the midgap. [ABSTRACT FROM AUTHOR]

The interfacial electronic structure of Ga2O3(Gd2O3) (GGO) on n-Ge(001) is determined using high-resolution synchrotron radiation photoemission. The excitation photon energy was specifically chosen to observe the interaction at the GGO/Ge interface (hv = 463 eV) as well as the possible diffusion of Ge up to the GGO surface (hν = 120 eV). The Ge 3d core-level spectra were fit to extract the contributing components. Photoemission measurements were done for four samples, as deposited, N2 annealed, CF4 plasma treated, and the combined CF4 plasma treated and N2 annealed. No surface passivation was employed prior to the dielectric deposition. SRPES data clearly showed that the elemental Ge in the as-deposited sample was effectively kept in the wafer. Prevention of Ge diffusion was attributed to formation of a thin germanatelike oxide layer. Other than contributions from bulk Ge, an analytical fit to the Ge 3d cores gives two components that are associated with bonding to Gd2O3 (GdGe*) and to Ga2O3 (GaGe*), which had chemical shifts of 3.46 and 1.80 eV, respectively. We hereby label them as MGe*, where M stands for either Gd2O3 or Ga2O3. Area occupations of the GdGe* and GaGe* oxides are ∼87% and ∼10%, respectively. A CF4 plasma treatment disturbs the film itself as well as the interfacial oxide so that the GGO surface begins to show both elemental Ge and Ga. Nevertheless, the follow-up N2 annealing produces the GdGe*+GaGe* layer with characteristics similar to those at the GGO/Ge interface. Both GdGe* and GaGe* states in the CN-treated sample show simultaneously a smaller chemical shift by 0.31 ± 0.02 eV than those in the as-deposited sample. The treatments also induce upward band bending on both the high κ and the Ge sides, which causes the valence band offset at the GGO/Ge interface to be 2.95 eV. [ABSTRACT FROM AUTHOR]

We use a novel three-layer model function to assess the effect of the electron donors Mg and Ca on the Si(001) surface. The model shows that the previously unassigned C and D contributions of the Si 2p spectrum are due to the third surface layer. The layer-wise response of the Si(001) surface to the deposition of Mg atoms shows that the essential character of the dimer reconstruction initially remains in place, but is modified in discernible ways by charge donated to the dimer atoms. At larger coverage a new, well-organized silicide structure emerges which is identified as Mg2Si. A study of the reaction with Ca reveals a Ca2Si overlayer at room temperature, but CaSi2 overlayer at high temperature. [ABSTRACT FROM AUTHOR]

Formation of silicon carbide upon deposition of C60 onto Si(001) at an elevated temperature of 800 °C was studied via synchrotron-radiation photoemission and low electron energy diffraction. The molecules are completely decomposed upon hitting on the hot surface, giving rise to a well-order 2×1 pattern. The C 1s and Si 2p core-level spectra, and valence-band spectra indicate characteristics of a Si-terminated β-SiC(001) 2×1 film. Two surface components corresponding to the terminated and ad-dimer Si atoms are well resolved in the Si 2p cores. By the spectral area ratio of both components, the adlayer atoms cover half of the surface, which agrees with the missing-row structure model [W. Lu et al., Phys. Rev. Lett. 81, 2292 (1998)]. [ABSTRACT FROM AUTHOR]

The amorphous Ir–Si layer of several nanometers thick on Si(100)2×1 deposited at room temperature has been characterized by using both low energy electron diffraction (LEED) and synchrotron photoemission techniques. The double domain Si(100)2×1 LEED pattern disappeared when the deposited Ir onto Si(100) was higher than 1 ML. The ultrathin amorphous Ir–Si layer consisted of three different Ir[sub x]Si[sub y] alloys, rather than a single homogeneous Ir[sub x]Si[sub y] alloy as predicted by the conventionally used Gibbs free energy calculation in the solid state amorphization. The growth of the amorphous Ir–Si layer on Si(100) strongly depended on the interaction between Ir and Si(100) at the initial stage of Ir deposition. Three types of Ir–Si bonding formed on Si(100) at 1 ML Ir coverage and gradually evolved to be three different amorphous Ir[sub x]Si[sub y] alloys. The growth mode of the amorphous Ir–Si layer was proposed to be the modified Stranski–Krastanov growth. The transition from layer-by-layer-like to island growth occurred at Ir coverage of ∼3 ML. The major amorphous Ir[sub x]Si[sub y] alloy switched from Si to Ir rich when Ir coverage is over ∼3 ML. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The material class of rare earth nickelates with high Ni3+ oxidation state is generating continued interest due to the occurrence of a metal-insulator transition with charge order and the appearance of non-collinear magnetic phases within this insulating regime. The recent theoretical prediction for superconductivity in LaNiO3thin films has also triggered intensive research efforts. LaNiO3 seems to be the only rare earth nickelate that stays metallic and paramagnetic down to lowest temperatures. So far, centimeter-sized impurity-free single crystal growth has not been reported for the rare earth nickelates material class since elevated oxygen pressures are required for their synthesis. Here, we report on the successful growth of centimeter-sized LaNiO3 single crystals by the floating zone technique at oxygen pressures of up to 150 bar. Our crystals are essentially free from Ni2+ impurities and exhibit metallic properties together with an unexpected but clear antiferromagnetic transition. [ABSTRACT FROM AUTHOR]

We performed interfacial electric and electronic studies of both in-situ and ex-situ atomic-layer deposited (ALD) Al2O3 films on InGaAs. Self-aligned inversion-channel metal-oxide-semiconductor field-effect-transistors (MOSFETs) with a 1 μm gate length (Lg) from the in-situ sample have extrinsic drain currents (Id) of 1.8mA/μm, transconductances (Gm) of 0.98mS/μm, and an effective mobility (μeff) of 1250 cm2/V s. MOSFETs that employ ex-situ ALD-Al2O3 have an Id of 0.56mA/μm, Gm of 0.28 mS/μm, and μeff of 410 cm2/V s. Synchrotron radiation photoemission reveals no AsOx residue at the Al2O3/InGaAs interface using the in-situ approach, whereas some AsOx residue is detected using the ex-situ method. [ABSTRACT FROM AUTHOR]

This study investigates the origin of long-puzzled high frequency dispersion on the accumulation region of capacitance-voltage characteristics in an n-type GaAs-based metal-oxide-semiconductor. Probed adatoms with a high Pauling electronegativity, Ag and Au, unexpectedly donate charge to the contacted As/Ga atoms of as-grown α2 GaAs(001)-2x4 surfaces. The GaAs surface atoms behave as charge acceptors, and if not properly passivated, they would trap those electrons accumulated at the oxide and semiconductor interface under a positive bias. The exemplified core-level spectra of the Al2O3/n-GaAs(001)-2x4 and the Al2O3/n-GaAs(001)-4x6 interfaces exhibit remnant of pristine surface As emission, thereby causing high frequency dispersion in the accumulation region. For the p-type GaAs, electrons under a negatively biased condition are expelled from the interface, thereby avoiding becoming trapped. [ABSTRACT FROM AUTHOR]