Electronic structure of La (0001) thin films on W (110) studied by photoemission spectroscopy and first principle calculations

Surface states that have a dz2 symmetry around the center of the surface Brillouin zone(BZ)have been regarded common in closely-packed surfaces of rare-earth metals.In this work,we report the electronic structure of dhcp La(0001)thin films by ultrahigh energy resolution angle-resolved photoemission spectroscopy(ARPES)and first principle calculations.Our first principle analysis is based on the many-body approach,therefore,density function theory(DFT)combined with dynamic mean-field theory(DMFT).The experimentally observed Fermi surface topology and band structure close to the Fermi energy qualitatively agree with first principle calculations when using a renormalization factor of between 2 and 3 for the DFT bands.Photon energy dependent ARPES measurements revealed clear kZ dependence for the hole-like band around the BZ center,previously regarded as a surface state.The obtained ARPES results and theoretical calculations suggest that the major bands of dhcp La(0001)near the Fermi level originate from the bulk La 5d orbits as opposed to originating from the surface states.     

Direct observation of the f–c hybridization in the ordered uranium films on W(110)

A key issue in metallic uranium and its related actinide compounds is the character of the f electrons, whether it is localized or itinerant.Here we grew well ordered uranium films on a W(110) substrate.The surface topography was investigated by scanning tunneling microscopy.The Fermi surface and band structure of the grown films were studied by angle-resolved photoemission spectroscopy.Large spectral weight can be observed around the Fermi level, which mainly comes from the f states.Additionally, we provided direct evidence that the f bands hybridize with the conduction bands in the uranium ordered films, which is different from previously reported mechanism of the direct f–f interaction.We propose that the above two mechanisms both exist in this system by manifesting themselves in different momentum spaces.Our results give a comprehensive study of the ordered uranium films and may throw new light on the study of the 5 f-electron character and physical properties of metallic uranium and other related actinide materials.     

The effect of cesium metal clusters on the optical properties of cesium iodide thin films

Cesium metal clusters strongly affect the optical properties of cesium iodide thin films. The metal clusters are formed during film formation by thermal evaporation. The cesium cluster of 30–40 nm in the matrix of cesium iodide insulating thin films results in Surface Plasmon Resonance (SPR). The peak position of these SPR peaks showed a red shift. This was shown to be due to changes in the dielectric constant of CsI resulting from the strains in the films caused by the metal clusters themselves.     

Growth and photoluminescence properties of inclined ZnO and ZnCoO thin films on SrTiO_3（110） substrates

ZnO thin film growth prefers different orientations on the etched and unetched SrTiO 3（STO）（110） substrates.Inclined ZnO and cobalt-doped ZnO（ZnCoO） thin films are grown on unetched STO（110） substrates using oxygen plasma assisted molecular beam epitaxy,with the c-axis 42 inclined from the normal STO（110） surface.The growth geometries are ZnCoO[100]//STO[110] and ZnCoO[111]//STO[001].The low temperature photoluminescence spectra of the inclined ZnO and ZnCoO films are dominated by D 0 X emissions associated with A 0 X emissions,and the characteristic emissions for the 2 E（2G）→ 4A2（4F） transition of Co 2＋ dopants and the relevant phonon-participated emissions are observed in the ZnCoO film,indicating the incorporation of Co 2＋ ions at the lattice positions of the Zn 2＋ ions.The c-axis inclined ZnCoO film shows ferromagnetic properties at room temperature.     

Deposition of ZnO thin films on (100) γ-LiAlO_2 substrate

The resurgence in the study of ZnO continues. The now ready availability of good-quality single crystals and films[1,2] and discovery of lasing action in the materials[3] have generated new life in an old material. A direct semi- conductor with a gap energy of 3.3 eV[4], ZnO is in the position of being able to offer a challenge to GaN in the blue laser market[5]. The advantages of ZnO are the high quality of the material and the large exciton bind- ing energy (60 meV). The large exciton bi…     

Influence of growth morphology on the Néel temperature of CrRu thin films and heterostructures

Dimensionality effects on epitaxial and polycrystalline Cr_1?xRu_x alloy thin films and in Cr/Cr–Ru heterostructures are reported. X-ray analysis on Cr_0.9965Ru_0.0035 epitaxial films indicates an increase in the coherence length in growth directions (1 0 0) and (1 1 0) with increasing thickness (d), in the range 20≤d≤300 nm. Atomic force microscopy studies on these films shows pronounced vertical growth for d>50 nm, resulting in the formation of columnar structures. The Néel temperatures (T_N) of the Cr_0.9965Ru_0.0035 films show anomalous behaviour as a function of d at thickness d≈50 nm. It is interesting to note that this thickness corresponds to that for which a change in film morphology occurs. Experiments on epitaxial Cr_1?xRu_x thin films, with 0≤x≤0.013 and d=50 nm, give T_N–x curves that correspond well with that of bulk Cr_1?xRu_x alloys. Studies on Cr/Cr_0.9965Ru_0.0035 superlattices prepared on MgO(1 0 0), with the Cr layer thickness varied between 10 and 50 nm, keeping the Cr_0.9965Ru_0.0035 thickness constant at 10 nm, indicate a sharp decrease in T_N as the Cr separation layers reaches a thickness of 30 nm; ascribed to spin density wave pinning in the Cr layers for d<30 nm by the adjacent CrRu layers.     

Study on the delamination of tungsten thin films on Sb2Te3

To investigate the reliability of electrode materials for chalcogenide random access memory （C-RAM） applications, the geometry and time evolution of the worm-like delamination patterns on a tungsten/Sb2Te3 bilayer system surface are observed by field emission scanning electronic microscope （FESEM） and optical microscopy. The tungsten film stress and interface toughness are estimated using a straight-side model. After confirming the instability of this system being due to large compressive stress stored in the tungsten film and relative poor interface adhesion, a preliminary solution as the inset of a TiN adhesion layer is presented to improve the system performances.     

The growth of Ag films on a TiO2(110)-(1×1) surface

We report here the growth of Ag film and its thermal stability on the TiO₂(1 1 0)-(1×1) surface using combination techniques of low-energy ion scattering (LEIS), X-ray photoelectron spectroscopy (XPS), and low-energy electron diffraction (LEED). At a surface temperature as low as 125 K, a 2D growth of Ag films seems to occur for submonolayer coverages up to ∼0.8 ML. Annealing of low temperature grown Ag films to 500 K for coverage of 1–2.4 ML would result in the formation of metastable Ag layers with rest of Ag forming 3D needle-like islands on top of this Ag film.     

Origin of the noncubic anisotropy in Mn∶ (Y,Gd)3Fe5O12 thin films

Thin Mn YIG films exhibit a large noncubic anisotropy. We show that this anisotropy may be understood on the basis of a strong Jahn-Teller effect of octahedrally coordinated Mn³⁺ ions. The corresponding mechanism is simple — the strain caused by the film/substrate misfit orders the local Jahn-Teller distortions and, as a consequence, noncubic anisotropy appears. In particular, due to the nonparallel local coordinate systems of octahedral sites, an uniaxial anisotropy is predicted also for the (111) growth plane. It is pointed out that the interaction between the Jahn-Teller centres and/or their interaction with the lattice defects lower the magnitude of the anisotropy.The temperature dependence of the uniaxial anisotropy was measured on the (001) and (111) oriented films using the FMR method. The results are in qualitative agreement with the prediction of theory. Quantitative comparison of theory with the experiment is difficult, as little is known about the distribution of the strains due to the lattice defects and about the interaction between the Jahn-Teller centres.The authors are indebted to Dr. S. Krupika for many helpful discussions, to Dr. J. Kub for measuring the misfits and to Dr. J. imová for the analysis of the films used in our experiments.     

The microstructure and magnetic properties of electrodeposited Co–Pt thin films on Ru buffer layer

For high-density magnetic recording media, this study examined the crystal structure and the texture of electrodeposited cobalt–platinum (Co–Pt) films on Ru buffer layer. A 15-nm-thick Co–Pt film exhibited very high out-of-plane coercivity and squareness, which were 6248 Oe and 0.89, respectively. The coercivity, H_c, of Co–Pt films grown on Ru buffer layer decreased significantly with increasing thickness, possibly due to the lattice misfit of 5.4% between Co–Pt and Ru, leading to the decrease of perpendicular magnetic anisotropy (PMA) of Co–Pt films as indicated by the observed hexagonal-closed-packed (HCP) (1 1¯ 0 1) plane of Co–Pt films. According to nano beam diffraction pattern (NBDP), however, Co–Pt film grown on Ru layer of HCP exhibited mixed HCP and FCC phases. Also, cross-sectional TEM image suggests that the high PMA may result from the columnar structure of physically isolated Co–Pt grains with the c-axis perpendicular to the film plane.     

Effect of 90° domain walls on the low-field permittivity of PbZr(0.2)Ti(0.8)O3 thin films

We report on the contribution of 90° ferroelastic domain walls in strain-engineered PbZr(0.2)Ti(0.8)O(3) thin films to the room-temperature permittivity. Using a combination of phenomenological Ginzburg-Landau-Devonshire polydomain thin-film models and epitaxial thin-film growth and characterization, the extrinsic or domain wall contribution to the low-field, reversible dielectric response is evaluated as a function of increasing domain wall density. Using epitaxial thin-film strain we have engineered a set of samples that possess a known quantity of 90° domain walls that act as a model system with which to probe the contribution from these ferroelastic domain walls. We observe a strong enhancement of the permittivity with increasing domain wall density that matches the predictions of the phenomenological models. Additionally, we report experimentally measured bounds to domain wall stiffness in such PbZr(0.2)Ti(0.8)O(3) thin films as a function of domain wall density and frequency.     

Growth of thin films of TiN on MgO(100) monitored by high-pressure RHEED

Reflection high-energy electron diffraction (RHEED) operated at high pressure has been used to monitor the initial growth of titanium nitride (TiN) thin films on single-crystal (100) MgO substrates by pulsed laser deposition (PLD). This is the first RHEED study where the growth of TiN films is produced by PLD directly from a TiN target. At the initial stage of the growth (average thickness ∼2.4 nm) the formation of islands is observed. During the continuous growth the islands merge into a smooth surface as indicated by the RHEED, atomic force microscopy and field emission scanning electron microscopy. These observations are in good agreement with the three-dimensional Volmer–Weber growth type, by which three-dimensional crystallites are formed and later cause a continuous surface roughening. This leads to an exponential decrease in the intensity of the specular spot in the RHEED pattern as well.     

Second and third order nonlinear optical properties of nanostructured ZnO thin films deposited on α-BBO and LiNbO3

The nanocrystalline ZnO films were deposited on α-BaB₂O₄ (0 0 1 2) and LiNbO₃ (0 0 0 1) single crystals by RF-magnetron sputtering technique. Their structure was studied using X-ray diffractometry, scanning electron microscopy and atomic force microscopy. Besides, the optical absorption spectra were investigated. The second and third harmonic generation measurements were performed by means of the rotational Maker fringe technique using Nd:YAG laser at 1064 nm in picoseconds regime. Finally, the second and third order nonlinear susceptibilities were determined and their values have been found and compared.     

Effects of γ rays irradiation on structure and property of TiO2 thin films

TiO₂ thin films were deposited on a glass substrate by the radio frequency magnetron sputtering method, and annealed for 2 h at temperatures of 550°C. Then, ⁶⁰Co γ rays with different doses were used to irradiate the resulting TiO₂ thin films. The surface features of films before and after irradiation were observed by scanning electron microscope (SEM). Simultaneously, the crystal structure and optical properties of films before and after irradiation were studied by X-ray diffraction (XRD), UV–VIS transmission spectrum and Photoluminescence (PL) spectrum, respectively. The SEM analysis shows that the film is smooth with tiny particles on the film surface, and non-crystallization trend was clear after irradiated with γ rays. The XRD results indicated that the structure of the film at the room temperature mainly exists in the form of amorphous and mixed crystal at a sputtering power of 200 W, and non-crystallinity was more obvious after irradiation. Obvious difference can be found for the transmissibility of the irradiated and pre irradiation TiO₂ films by the UV-VIS spectra. The color becomes light yellow, and the new absorption edge also appeared at about 430 nm. PL spectra and photocatalysis experiments indicate that the photocatalysis degradation rate of the TiO₂ films on methylthionine chloride solution irradiated with the maximum dose can be increased to 90%.     

Effect of the stresses caused by substrate on the electrical conductivity of ferromagnetic manganite lanthanum–barium films

This is a complex study of the electrophysical and magnetic characteristics of epitaxial manganite La_0.7Ba_0.3MnO₃ (LBMO) films under conditions of crystal structure stresses caused by misfit in the lattice parameters of the LBMO crystal and a substrate. The substrate used had the lattice parameter smaller than that in the LBMO crystal. It is shown that the temperature dependence of the electrical resistance of the films at low temperatures is not dependent on the existence of stresses in the film and agrees well with the calculation with allowance made for the interaction of carriers with magnetic excitations in the presence of strongly correlated electronic states. The study of the ferromagnetic resonance line indicates an inhomogeneity of the ferromagnetic phase in the LBMO films and the increase in the ferromagnetic resonance line width with decreasing temperature.