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.     

Novel photoluminescence properties of InAlO3（ZnO）m superlattice nanowires

One-dimension InAlO 3 (ZnO) m superlattice nanowires were successfully synthesized via chemical vapor deposition.Transmission electron microscopy measurements reveal that the nanowires have a periodic layered structure along the 0001 direction.The photoluminescence properties of InAlO 3 (ZnO) m superlattice nanowires are studied for the first time.The near-band-edge emissions exhibit an obvious red shift due to the formation of the localized tail states.The two peaks centered at 3.348 eV and 3.299 eV indicate a lever phenomenon at the low-temperature region.A new luminescence mechanism is proposed,combined with the special energy band structure of InAlO 3 (ZnO) m.     

A density functional theory study on the adsorption of CO and O₂ on Cu-terminated Cu₂O（111） surface

The adsorptions of CO and O2 molecules individually on the stoichiometric Cu-terminated Cu2O(111) surface are investigated by first-principles calculations on the basis of the density functional theory.The calculated results indicate that the CO molecule preferably coordinates to the Cu2 site through its C atom with an adsorption energy of -1.69 eV,whereas the O2 molecule is most stably adsorbed in a tilt type with one O atom coordinating to the Cu2 site and the other O atom coordinating to the Cu1 site,and has an adsorption energy of -1.97 eV.From the analysis of density of states,it is observed that Cu 3d transfers electrons to 2π orbital of the CO molecule and the highest occupied 5σ orbital of the CO molecule transfers electrons to the substrate.The sharp band of Cu 4s is delocalized when compared to that before the CO molecule adsorption,and overlaps substantially with bands of the adsorbed CO molecule.There is a broadening of the 2π orbital of the O2 molecule because of its overlapping with the Cu 3d orbital,indicating that strong 3d-2π interactions are involved in the chemisorption of the O2 molecule on the surface.     

Structural and electrical properties of SrTiO3 thin films as insulator of metal-ferroelectric-insulator-semiconductor （MFIS） structures

SrTiO₃ (STO) thin films were deposited on p-Si(100) substrates at various substrate temperatures from 300℃ to 700℃ by radio frequency (RF) magnetron sputtering technique. Their structure and electrical properties were investigated. It was found that the transition from amorphous phase to polycrystalline phase occurred at the substrate temperatures 300--400℃. Their crystallinity became better when the substrate temperatures further increased. The dielectric and leakage current measurements were carried out by using the Si/STO/Pt metal--insulator--semiconductor (MIS) structures at room temperature. It was found that the fixed charge density decreased and both the interface trap density and the dielectric constant increased when the substrate temperatures were increased. The leakage current mechanisms for STO MIS structures with STO films prepared at 700℃ followed the space charge limited current (SCLC) under the low applied electric field and the Poole--Frenkel emission under the high one. In addition, the resistivity for films prepared at 700℃ was higher than 10¹¹\Omega \cdot cm under the voltage lower than 10V (corresponding to the electric field of 1.54\times 10³kV\cdotcm^-1). It suggested that the STO films prepared at 700℃ were suitable for acting as the insulator of metal--ferroelectric--insulator--semiconductor (MFIS) structures.     

Preparation and the physical properties of antiperovskite-type compounds Cd_1-xIn_x NNi₃（0 ≤x≤ 0.2） and Cd_1-yCu_yNNi₃（0≤y≤0.2）

Two series of Cd1-xInx NNi3(0 ≤x≤ 0.2) and Cd1-yCuyNNi3(0≤y≤0.2) samples were prepared from CdO, In2O3 , CuO, and nickel powders under NH3 atmosphere at 773K. The structural and physical properties were investigated by means of X-ray powder diffraction temperature-dependent resistivity and magnetic measurements. X-ray powder diffraction results showed that the Cd 1 x In x NNi 3 and Cd 1 y Cuy NNi 3 compounds have a typical antiperovskite structure, and the CdNNi3, Cd0.9 In 0.1 NNi3 , and Cd0.9Cu0.1NNi3 compounds show metallic temperature-dependent resistivity and exhibit a Fermi liquid behavior at low temperature. In contrast to the paramagnetism previously reported, the CdNNi 3 sample exhibits very soft and weak ferromagnetism, and no superconductivity was found in the Cd 1 x In x NNi 3 and Cd 1 y Cu y NNi 3 samples down to 2 K. Each sample exhibited very soft and weak ferromagnetism, and the temperature dependence of the magnetization of the Cd 1-xInx NNi 3 and Cd1-y Cu y NNi 3 samples can be well fitted to the combination of a Bloch term and a Curie–Weiss term.     

Structural and physical properties of BiFeO3 thin films epitaxially grown on SrTiO3（001） and polar（111） surfaces

The influence of surface polarity on the structural properties of BiFeO3 （BFO） thin films is investigated. BFO thin films are epitaxially grown on SrTiO3 （STO） （100） and polar （111） surfaces by oxygen plasma-assisted molecular beam epitaxy. It is shown that the crystal structure, surface morphology, and defect states of BFO films grown on STO substrates with nonpolar （001） or polar （111） surfaces perform very differently. BFO/STO （001）is a fully strained tetragonal phase with orientation relationship （001）[100]BFOII（001）[100]STO, while BFO/STO （111） is a rhombohedral phase. BFO/STO （111） has rougher surface morphology and less defect states, which results in reduced leakage current and lower dielectric loss. Moreover, BFO films on both STO （001） and STO （111） are direct band oxides with similar band gaps of 2.65 eV and 2.67 eV, respectively.     

The doping effects of BiFe_1-xCo_xO₃（x=0.0-0.8） in layered perovskite Bi₄Ti₃O₁₂ ceramics

Bi5Fe1-xCoxTi3O15(x = 0.0, 0.2, 0.4, 0.5, 0.6, and 0.8) multiferroic ceramics are synthesized in two steps using the solid state reaction technique. X-ray diffraction patterns show that the samples have four-layer Aurivillius phases. At room temperature (RT), the samples each present a remarkable coexistence of ferromagnetism (FM) and ferroelectricity (FE). The remnant polarization (2P r ) reaches its greatest value of 14 μC/cm 2 at x = 0.6. Remnant magnetization (2M r ) first increases and then decreases, and the greatest 2M r is 7.8 menu/g when x = 0.5. The magnetic properties for x = 0.4 are similar to those for x = 0.6, indicating that the magnetic properties originate mainly from the coupling between Fe 3+ and Co 3+ ions, rather than from their own magnetic moments.     

The crystal structures and physical properties of the solid solution compound Ba₅Y_8-xMn₄O_21-1.5x（x = 0,1）

New oxometallides with the formula Ba5Y8 xMn4O21 1.5x(x = 0,1) are prepared through an atmospherecontrolled solid-state reaction.Two single-phase samples with Ba/Y/Mn atomic ratios 5/8/4(Y8) and 5/7/4(Y7) are obtained.The crystal structures and the physical properties of the compounds are investigated by X-ray powder diffraction,magnetization,conductivity,and dielectricity measurements.The Ba5Y8 xMn4O21 1.5x compound is demonstrated to be a Y-deficient solid solution.The solid solution compound Ba5Y8 xMn4O21 1.5x crystallizes into tetragonal symmetry with the space group I4/m.Detailed structure analysis by Rietveld refinement of the X-ray powder diffraction data reveals that the Y vacancies occur preferentially at the Y(2) site.Thermal magnetization measurements indicate the presence of antiferromagnetic interaction between Mn ions in the compounds,and temperature-dependent resistivity measurements show that insulator-semiconductor transitions occur around 175 K and 170 K for the Y8 and Y7 samples,respectively.Strong frequency dependences of the dielectric constant are observed above ～175 K for the two compounds.     

Structural analysis and crystal-field calculations of Nd³⁺ in Gd_x Lu_1-x TaO₄（x = 0.85） polycrytalline

The crystal structural parameters of Nd 3+-doped rare earth orthotantalate Gd x Lu 1 x TaO 4(x = 0.85) are determined by applying the Rietveld refinement to its X-ray diffraction,and its emission and excitation spectra at 77 K are analysed.The relativistic model of ab initio self-consistent DV-Xα method,which is applied to the cluster NdO 8 in Gd x Lu 1 x TaO 4,and the effective Hamiltonian model are used to investigate its spin-orbit and crystal-field parameters.The free-ions and crystal-field parameters are fitted to the experimental energy levels at 77 K with a root-mean-square deviation of 14.92 cm 1.According to the crystal-field calculations,96 levels of Nd 3+ are assigned.Finally,the fitting results of free-ions and crystal-field parameters are compared with those already reported for Nd 3+:YAlO 3.The results indicate that the free-ion parameters are similar to those of the Nd3+ in Gdx Lu1-x TaO4 and YAlO 3 hosts,and the crystal-field interaction of Nd3+ in Gdx Lu1-x TaO4 is stronger than that in YAlO 3.     

Predictions of pressure-induced structural transition,mechanical and thermodynamic properties of α-and β-Si₃N₄ ceramics:ab initio and quasi-harmonic Debye modeling

The plane-wave pseudo-potential method within the framework of ab initio technique is used to investigate the structural and elastic properties of α-and β-Si3N4.The ground-state parameters accord quite well with the experimental data.Our calculation reveals that α-Si3N4 can retain its stability to at least 40 GPa when compressed at 300 K.The α→β phase transformation would not occur in a pressure range of 0-40 GPa and a temperature range of 0-300 K.Actually,the α→β transition occurs at 1600 K and 7.98 GPa.For α-and β-Si3N4,the c axes are slightly more incompressible than the a axes.We conclude that β-Si3N4 is a hard material and ductile in nature.On the other hand,β-Si3N4 is also found to be an ionic material and can retain its mechanical stability in a pressure range of 0-10 GPa.Besides,the thermodynamic properties such as entropy,heat capacity,and Debye temperature of α-and β-Si3N4 are determined at various temperatures and pressures.Significant features in these properties are observed at high temperature.The calculated results are in good agreement with available experimental data and previous theoretical values.Many fundamental solid-state properties are reported at high pressure and high temperature.Therefore,our results may provide useful information for theoretical and experimental investigations of the Si3N4 polymorphs.     

First-principles study of mechanical stability and thermal properties of MNNi₃ （M=Zn,Mg,Al） under pressure

The mechanical stability,elastic,and thermodynamic properties of the anti-perovskite superconductors MNNi 3(M=Zn,Mg,Al) are investigated by means of the first-principles calculations.The calculated structural parameters and elastic properties of MNNi 3 are in good agreement with the experimental and the other theoretical results.From the elastic constants under high pressure,we predict that ZnNNi 3,MgNNi 3,and AlNNi 3 are not stable at the pressures above 61.2 GPa,113.3 GPa,and 122.4 GPa,respectively.By employing the Debye model,the thermodynamic properties,such as the heat capacity and the thermal expansion coefficient,under pressures and at finite temperatures are also obtained successfully.     

Effect of annealing temperature on microstructures and optical properties of Ba<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>TiO<Subscript>3</Subscript> films

Evolution of microstructure and optical property with annealing temperature has been examined for Ba_0.9Sr_0.1TiO₃ films derived from one single precursor solution containing polyethylene glycol polymer. The films sintered below 750°C exhibit a uniform phase structure across the cross-sections and an ordinary optical thin film feature, while the Ba_0.9Sr_0.1TiO₃ films crystallized at 750°C or higher temperature render a lamellar texture consisting of dense and porous Ba_0.9Sr_0.1TiO₃ layers and a good performance as a one-dimensional photonic crystal. The discrepancy in cross-sectional morphology and reflectance property observed in these Ba_0.9Sr_0.1TiO₃ films has been preliminarily explained.     

Theoretical study of ZnO adsorption and bonding on Al_2O_3(0001) surface

Sapphire (α-Al2O3) and silicon (Si) are widely applied as the substrates of the highquality ZnO thin films prepared by pulse laser deposition (PLD) and molecule beamepitaxy (MBE) technology. The adhesion, diffusivity, and bonding of the particles on thesubstrates play a significant role in the forming and initial growing of nucleation for filmgrowth, and directly influence the quality of the entire thin films[1]. No sufficient studiesand experiments are available on the surface atomic str…     

Molecular-beam epitaxy of topological insulator Bi2Se3 （111） and （221） thin films

This paper presents an overview of the growth of Bi2Se3, a prototypical three-dimensional topological insulator, by molecular-beam epitaxy on various substrates. Comparison is made between the growth of Bi2 Se3 （111） on van der Waals （vdW） and non-vdW substrates, with attention paid to twin suppression and strain. Growth along the [221] direction of Bi2Se3 on InP （001） and GaAs （001） substrates is also discussed.     

Effect of process parameters and post-deposition annealing on the microwave dielectric and optical properties of pulsed laser deposited Bi<Subscript>1.5</Subscript>Zn<Subscript>1.0</Subscript>Nb<Subscript>1.5</Subscript>O<Subscript>7</Subscript> thin films

Bismuth Zinc niobate (Bi_1.5Zn_1.0Nb_1.5O₇) thin films were deposited by pulsed laser deposition (PLD) method on fused silica substrates at different oxygen pressures. The structural, microwave dielectric and optical properties of these thin films were systematically studied for both the as-deposited and the annealed films at 600°C. The as-deposited films were all amorphous in nature but crystallized on annealing at 600°C in air. The surface morphology as studied by atomic force microscopy (AFM) reveals ultra-fine grains in the case of as-deposited thin films and cluster grain morphology on annealing. The as-deposited films exhibit refractive index in the range of 2.36–2.53 (at a wavelength of 750 nm) with an optical absorption edge value of 3.30–3.52 eV and a maximum dielectric constant of 11 at 12.15 GHz. On annealing the films at 600°C they crystallize to the cubic pyrochlore structure accompanied by an increase in band gap, refractive index and microwave dielectric constant.     

Synchrotron-Radiation Photoemission Study of Growth and Stability of Au Clusters on Rutile TiO2(110)-1×1

利用同步辐射高分辨光电子能谱研究了金团簇在部分还原TiO₂-(1×1)表面的生长和稳定性．价带谱实验结果观察到非常少量金团簇的沉积导致了Ti3+的3d峰完全消失,表明金团簇成核在TiO₂-(1×1)表面的氧缺陷位．Au4f芯电子光电子能谱实验结果证明了TiO₂-(1×1)表面氧缺陷位向金团簇转移电荷．还对比研究了化学剂量比和部分还原的TiO₂-(1×1)表面上金团簇的热稳定性．当金团簇尺寸相近时部分还原的TiO₂-(1×1)表面上金团簇要比化学剂量比的TiO₂-(1×1)面上金团簇稳定;在相同的表面上尺寸大的金团簇要比尺寸小的金团簇稳定．     

Effects of deposition temperature and post-annealing on structure and electrical properties in (La<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>)CoO<Subscript>3</Subscript> films grown on silicon substrate

(La_0.5Sr_0.5)CoO₃ (LSCO) thin films have been fabricated on silicon substrate by the pulsed laser deposition method. The effects of substrate temperature and post-annealing condition on the structural and electrical properties are investigated. The samples grown above 650°C are fully crystalline with perovskite structure. The film deposited at 700°C has columnar growth with electrical resistivity of about 1.99×10⁻³ Ω cm. The amorphous films grown at 500°C were post-annealed at different conditions. The sample post-annealed at 700°C and 10⁻⁴ Pa has similar microstructure with the sample in situ grown at 700°C and 25 Pa. However, the electrical resistivity of the post-annealed sample is one magnitude higher than that of the in situ grown sample because of the effect of oxygen vacancy. The temperature dependence of resistivity exhibits semiconductor-like character. It was found that post-annealing by rapid thermal process will result in film cracks due to the thermal stress. The results are referential for the applications of LSCO in microelectronic devices.     

Characteristics of the crystalline and luminescence properties of a-plane GaN films grown on γ-LiAlO2 （302） substrates

A method of clarifying bioaerosol particles is proposed based on T-matrix. Size and shape characterizations are simultaneously acquired for individual bioaerosol particles by analyzing the spatial distribution of scattered light. The particle size can be determined according to the scattering intensity,while shape information can be obtained through asymmetry factor(AF) . The azimuthal distribution of the scattered light for spherical particles is symmetrical,whereas it is asymmetrical for non-spherical ones,and the asymmetry becomes intense with increasing asphericity. The calculated results denote that the 5 –10 scattering angle is an effective range to classify the bioaerosol particles that we are concerned of. The method is very useful in real-time environmental monitoring of particle sizes and shapes.     

Laser-induced voltage effects in CaaCoaO9 thin films on tilted LaAlO3（001） substrates grown by chemical solution deposition

Laser-induced voltage effects in c-axis oriented Ca3Co4O9 thin films have been studied with samples fabricated on 10°tilted LaAIO3 （001） substrates by a simple chemical solution deposition method. An open-circuit voltage with a rise time of about 10 ns and full width at half maximum of about 28 ns is detected when the film surface is irradiated by a 308-nm laser pulse with a duration of 25 ns. Besides, opemcircuit voltage signals are also observed when the film surface is irradiated separately by the laser pulses of 532 nm and 1064 nm. The results indicate that Ca3Co4O9 thin films have a great potential application in the wide range photodetctor from the ultraviolet to near infrared regions.     

Specific features of the formation of Ba<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> ferroelectric thin films on different substrates by radio-frequency sputtering

Epitaxial thin films of Ba _x Sr_{1 ? x} TiO₃ solid solutions on MgO(001) and NdGaO₃(011) single-crystal substratesare prepared by radio-frequency cathode sputtering of a ceramic target with stoichiometric composition on a magnetron-sputtering apparatus. The main qualitative differences in optical, structural, and electrical properties of the ferroelectric films prepared are determined, and their substantial dependence on the choice of the substrate is revealed.