Influence of Interface Structure of Co/Cu （100） Superlattices on Electronic Structure and Giant Magnetoresistance

Electronic structures and magnetoresistance （MR） of Co3 Cu5 and Co3 Cur models as well as their interface atom exchange models Co2 CuCoCu4 and Co2 CuCoCu6 are investigated by the tlrst-principles pseudopotential planewave method based on density functional theory. Charge transfer, magnetic moment, density of states, spin asymmetry factor, and MR ratio are discussed. The results show that the values of charge transfer and spin asymmetry factor at the Fermi level of Co layers are closely related to the neighbouring background of the Co layer. The Co layer with two sides adjacent to the Cu layer would transfer more charge to the Cu layer than other neighbouring background and have the largest spin asymmetry factor at the Fermi level. The Co layer with two neighbouring Co layers （interior Co） would gain a little charge and have the smallest spin asymmetry factor at the Fermi level. Two-current model is used to evaluate the MR ratio of Co2CuCoCu4 （Co2CuCoCu6） to be larger than that of Co3 Cu5 （Co3 CUT）, which can be explained by the charge transfer and spin asymmetry factor.     

Controlled Growth of Zn-Polar ZnO Films on Al-Terminated α-Al2O3(0001) Surface by Using Wurtzite MgO Buffer

The controlled growth of Zn-polar ZnO fihns on Al-terminated α-Al203 （0001） substrates is investigated by the radio-frequency plasma-assisted molecular beam epitaxy method. Prior to the growth, α-Al2O3 （0001） surface is modified by an ultrathin MgO layer, which serves as a uniform template for epitaxy of Zn-polar ZnO films. The microstructures of ZnO/MgO/Al2O3 interface are investigated by in-situ reflection high-energy electron diffraction observations and ex-situ high-resolution transmission electron microscopy characterization. It is found that under Mg-rich condition, the achievement of the wurtzite MgO ultrathin layer plays a key role in the subsequent growth of Zn-polar ZnO. An interracial atomic model is proposed to explain the mechanism of polarity selection of both MgO and ZnO films.     

Ab initio investigation of the structural and unusual electronic properties of α-CuSe （klockmannite）

In this article, a computational analysis has been performed on the structural properties and predominantly on the electronic properties of the α-CuSe （klockmannite） using density functional theory. The studies in this work show that the best structural results, in comparison to the experimental values, belong to the PBEsol-GGA and WC-GGA functionals. However, the best results for the bulk modulus and density of states （DOSs） are related to the local density approximation （LDA） functional. Through utilized approaches, the LDA is chosen to investigate the electronic structure. The results of the electronic properties and geometric optimization of α-CuSe respectively show that this compound is conductive and non-magnetic. The curvatures of the energy bands crossing the Fermi level explicitly reveal that major charge carriers in CuSe are holes, whose density is estimated to be 0.86×1022 hole/cm3. In particular, the Fermi surfaces in the first Brillouin zone demonstrate interplane conductivity between （001） planes. Moreover, the charge carriers among them are electrons and holes simultaneously. The conductivity in CuSe is mainly due to the hybridization between the d orbitals of Cu atoms and the p orbitals of Se atoms. The former orbitals have the dual nature of localization and itinerancy.     

Temperature dependence of Cu20 orientations in the oxidation of Cu （111）/ZnO （0001） by oxygen plasma

The role of temperature on the oxidation dynamics of Cu20 on ZnO （0001） was investigated during the oxidation of Cu （111）/ZnO （0001） by using oxygen plasma as the oxidant. A transition from single crystalline Cu20 （111） orientation to micro-zone phase separation with multiple orientations was revealed when the oxidation temperature increased above 300 ~ C. The experimental results clearly show the effect of the oxidation temperature with the assistance of oxygen plasma on changing the morphology of Cu （111） film and enhancing the lateral nucleation and migration abilities of cuprous oxides. A vertical top-down oxidation mode and a lateral migration model were proposed to explain the different nucleation and growth dynamics of the temperature-dependent oxidation process in the oxidation of Cu （lll）/ZnO （0001）.     

Density functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clusters

The density functional theory B3PW91 with LANL2DZ basis sets has been used to study the possible geometries of Mg2Nin （n - 1-8） clusters. For the lowest energy structures of the clusters, stabilities, electronic properties, and natural bond orbital （NBO） are calculated and discussed. The results show that the doped Mg atoms reduce the stabilities of pure Ni clusters. The Mg2Ni2, Mg2Ni4, and Mg2Ni6 clusters are more stable than neighboring clusters. The system appears magic number characteristics. In addition, the hybridization phenomenon occurs, owing to the interaction of Mg and Ni. The result of charge transfer is that Ni atom is negative and the Mg atom is positive. We also conclude that the 3p and 4d orbitals of the Ni atom have an effect on the stabilities of the clusters.     

The Distinguished Charge-Trapping Capability of the Memory Device with Al2O3-Cu2O Composite as the Charge Storage Layer

A memory device Si/Al2O3/Al2O3-Cu2O/Al2O3/Pt is fabricated by using atomic layer deposition and r~magnetron sputtering techniques. The memory device including the composite of Al2O3 and Cu2O as the charge storage layer shows a distinguished charge trapping capability. At a working voltage of ±11 V a memory window of 9.22 V is obtained. The x-ray photoelectron spectroscopic study shows a shoulder from Cu2＋ ions around the peak of Cu1＋ ions. It is suggested that the charge-trapping mechanism should be attributed to the defect states formed by the inter-diffusion at the interface of two oxides.     

Interfacial potential approach for Ag/ZnO （0001） interfaces

Systematic approaches are presented to extract the interfacial potentials from the ab initio adhesive energy of the interface system by using the Chen–M ¨obius inversion method. We focus on the interface structure of the metal（111）/Zn O（0001）in this work. The interfacial potentials of Ag–Zn and Ag–O are obtained. These potentials can be used to solve some problems about Ag/Zn O interfacial structure. Three metastable interfacial structures are investigated in order to check these potentials. Using the interfacial potentials we study the procedure of interface fracture in the Ag/Zn O（0001） interface and discuss the change of the energy, stress, and atomic structures in tensile process. The result indicates that the exact misfit dislocation reduces the total energy and softens the fracture process. Meanwhile, the formation and mobility of the vacancy near the interface are observed.     

Energy loss on of low energy ion N^＋q grazing the A1（111） surface

The total energy loss of N^＋q ions （for v 〈 Bohr velocity） grazing on the Al（111） has been simulated without any ＇fit＇ parameter and compared with the experimental data. The energy loss due to the charge exchange, happening before the N^＋q hits the Al（111） surface, is studied. The present simulation shows that the energy loss strongly depends on the charge state of the projectile and the lattice orientation of Al（111） surface. The calculated total energy loss agrees with experimental data very well.     

Temperature dependence of Cu2O orientations in the oxidation of Cu（111）/ZnO（0001） by oxygen plasma

The role of temperature on the oxidation dynamics of Cu2O on ZnO (0001) was investigated during the oxidation of Cu (111)/ZnO (0001) by using oxygen plasma as the oxidant. A transition from single crystalline Cu2O (111) orientation to micro-zone phase separation with multiple orientations was revealed when the oxidation temperature increased above 300°C. The experimental results clearly show the effect of the oxidation temperature with the assistance of oxygen plasma on changing the morphology of Cu (111) film and enhancing the lateral nucleation and migration abilities of cuprous oxides. A vertical top-down oxidation mode and a lateral migration model were proposed to explain the different nucleation and growth dynamics of the temperature-dependent oxidation process in the oxidation of Cu (111)/ZnO (0001).     

Charge trapping behavior and its origin in Al_2O_3/SiC MIS system

Charge trapping behavior and its origin in Al2O3/SiC MOS structure are investigated by analyzing the capacitance–voltage(C–V) hysteresis and the chemical composition of the interface. The C–V hysteresis is measured as a function of oxide thickness series for an Al2O3/SiC MIS capacitor. The distribution of the trapped charges, extracted from the C–V curves, is found to mainly follow a sheet charge model rather than a bulk charge model. Therefore, the electron injection phenomenon is evaluated by using linear fitting. It is found that most of the trapped charges are not distributed exactly at the interface but are located in the bulk of the Al2O3 layers, especially close to the border. Furthermore, there is no detectable oxide interface layer in the x-ray photoelectron spectroscope(XPS) and transmission electron microscope(TEM)measurements. In addition, Rutherford back scattering(RBS) analysis shows that the width of the Al2O3/SiC interface is less than 1 nm. It could be concluded that the charge trapping sites in Al2O3/SiC structure might mainly originate from the border traps in Al2O3 film rather than the interface traps in the interfacial transition layer.     

Investigation of a 4H-SiC metal-insulationsemiconductor structure with an A1203/SiO2 stacked dielectric

Atomic layer deposited （ALD） Al2O3/dry-oxidized ultrathin SiO2 films as a high-k gate dielectric grown on 8° off-axis 4H-SiC （0001） epitaxial wafers are investigated in this paper. The metal-insulation-semiconductor （MIS） capacitors, respectively with different gate dielectric stacks （Al2O3/SiO2, Al2O3, and SiO2） are fabricated and compared with each other. The I-V measurements show that the Al2O3/SiO2 stack has a high breakdown field （≥12 MV/cm） comparable to SiO2, and a relatively low gate leakage current of 1 × 10-7 A/cm2 at an electric field of 4 MV/cm comparable to Al2O3. The 1-MHz high frequency C-V measurements exhibit that the Al2O3/SiO2 stack has a smaller positive flat-band voltage shift and hysteresis voltage, indicating a less effective charge and slow-trap density near the interface.     

High-mobility germanium p-MOSFETs by using HCI and （NH4）2S surface passivation

To achieve a high-quality high-κ/Ge interfaces for high hole mobility Ge p-MOSFET applications, a simple chemical cleaning and surface passivation scheme is introduced, and Ge p-MOSFETs with effective channel hole mobility up to 665 cm2/V.s are demonstrated on a Ge （111） substrate. Moreover, a physical model is proposed to explain the dipole layer formation at the metal-oxide-semiconductor （MOS） interface by analyzing the electrical characteristics of HCl- and （NH4）2S-passivated samples.     

Influence of annealing temperature on passivation performance of thermal atomic layer deposition Al_2O_3 films

Chemical and field-effect passivation of atomic layer deposition （ALD） Al2O3 films are investigated, mainly by corona charging measurement. The interface structure and material properties are characterized by transmission electron microscopy （TEM） and X-ray photoelectron spectroscopy （XPS）, respectively. Passivation performance is improved remarkably by annealing at temperatures of 450 ℃ and 500 ℃, while the improvement is quite weak at 600 ℃, which can be attributed to the poor quality of chemical passivation. An increase of fixed negative charge density in the films during annealing can be explained by the Al2O3/Si interface structural change. The Al–OH groups play an important role in chemical passivation, and the Al–OH concentration in an as-deposited film subsequently determines the passivation quality of that film when it is annealed, to a certain degree.     

Dissociations of O2 molecules on ultrathin Pb（111） films： first-principles plane wave calculations

Using first-principles calculations,we systematically study the dissociations of O₂ molecules on different ultrathin Pb（111） films.According to our previous work revealing the molecular adsorption precursor states for O₂,we further explore why there are two nearly degenerate adsorption states on Pb（111） ultrathin films,but no precursor adsorption states existing at all on Mg（0001） and Al（111） surfaces.The reason is concluded to be the different surface electronic structures.For the O₂ dissociation,we consider both the reaction channels from gas-like and molecularly adsorbed O₂ molecules.We find that the energy barrier for O₂ dissociation from the molecular adsorption precursor states is always smaller than that from O₂ gas.The most energetically favorable dissociation process is found to be the same on different Pb（111） films,and the energy barriers are found to be influenced by the quantum size effects of Pb（111） films.     

First-principles study of Ar adsorptions on the （111） surfaces of Pd, Pt, Cu, and Rh

In the present paper we give a detailed report on the results of our first-principles investigations of Ar adsorptions at the four high symmetry sites on M （111） （M =Pd, Pt, Cu, and Rh） surfaces. Our studies indicate that the most stable adsorption sites of Ar on Pd （111） and Pt （111） surfaces are found to be the fcc-hollow sites. However, for Ar adsorptions on Cu （111） and Rh （111） surfaces, the most favorable site is the on-top site. The density of states （DOS） is analyzed for Ar adsorption on M （111） surfaces, and it is concluded that the adsorption behavior is dominated by the interaction between 3s, 3p orbits of Ar atoms and the d orbit of the base metal atoms.     

Effect of Al^3＋ on Photoluminescence Properties of Eu^3＋-Doped BaZr（BO3）2 Phosphors

We discuss the influence of Al^3＋ on the charge transfer state （CTS） and the photoluminescence properties of BaZr（BO3）2：Eu. The results reveal that there is a red shift which is about 20nm for the charge transfer state when doping with Al^3＋ and indicate the formation of ‘free＇ electrons due to the change of microstructures. In addition, the influence or Al^3＋ doping on the PPR is analysed and a new explanation is raised based on the photo luminescent mechanism. It is the CTS intensity rather than the CTS energy that influences the peak-peak ratio.     

Ultrathin Pb film growth on Cu（111） studied by photoemission

The valence bands and the Pb 5d,Cu 3p core levels of Pb films evaporated on Cu(111) were measured by synchrotron radiation photoemission and characterized by low-energy electron diffraction(LEED) and Auger electron spectroscopy(AES).The variation of the surafce state at the center of the surface Brillouin zone (SBZ) of Cu(111) with Pb coverage shows that the submonolayer Pb grows on Cu(111) at room temperature(RT) as two-dimensional(2D) islands.With the Pb coverage increasing,the Pb 5d5/2 core level shifts to higher binding energy monotonically.While the Cu 3p3/2 core level is shifted toward higher binding energy by about 120 meV due to the deposition of 1.0ML Pb.At low Ph coverage,subsequent annealing at 200℃ gives rise to Pb-Cu surface alloy formation in the first layer of Cu(111).The Pb 5d core level is shifted toward Fermi level by 20-30 meV due to the surface alloying.An assumption about electron charge transfer from Cu to Pb was adopted to interpret the observed cored level shifts.2001 Published by Elsevier Science Ltd.     

Atomic Diffusion in Cu/Si （111） and Cu/SiO2/Si （111） Systems by Neutral Cluster Beam Deposition

The Cu films are deposited on two kinds of p-type Si （111） substrates by ionized duster beam （ICB） technique. The interface reaction and atomic diffusion of Cu/Si （111） and Cu/SiO2/Si （111） systems are studied at different annealing temperatures by x-ray diffraction （XRD） and Rutherford backscattering spectrometry （RBS）. Some significant results are obtained： For the Cu/Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs when annealed at 230℃. The diffusion coefficients of the samples annealed at 230℃ and 500℃ are 8.5 ×10^-15 cm^2.s^-1 and 3.0 ×10^-14 cm^2.s^-1, respectively. The formation of the copper-silicide phase is observed by XRD, and its intensity becomes stronger with the increase of annealing temperature. For the Cu/SiO2//Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs and copper silicides are formed when annealed at 450℃. The diffusion coefficients of Cu in Si are calculated to be 6.0 ×10^-16 cm^2.s^-1 at 450℃, due to the fact that the existence of the SiO2 layer suppresses the interdiffusion of Cu and Si.     

Characterization of Al2O3 Thin Films on GaAs Substrate Grown by Atomic Layer Deposition

Al2O3 thin films are grown by atomic layer deposition on GaAs substrates at 300℃. The structural properties of the Al2O3 thin film and the Al2O3/GaAs interface are characterized using x-ray diffraction （XRD）, high- resolution transmission electron microscopy （HRTEM）, and x-ray photoelectron spectroscopy （XPS）. The XRD results show that the as-deposited Al2O3 film is amorphous. For 30 atomic layer deposition growth cycles, the thicknesses of the Al2O3 thin film and the interface layer from the HRTEM are 3.3 nm and 0.Snm, respectively. XPS analyses reveal that the Al2O3/GaAs interface is almost free from As2O3.     

Electronic structure and magnetic properties of （Mn,N）-codoped ZnO

The electronic structures and magnetic properties of（Mn, N）-codoped Zn O are investigated by using the firstprinciples calculations. In the ferromagnetic state, as N substitutes for the intermediate O atom of the nearest neighboring Mn ions, about 0.5 electron per Mn^2＋ion transfers to the N^2-ion, which leads to the high-state Mn ions（close to ＋2.5）and trivalent N3-ions. In an antiferromagnetic state, one electron transfers to the N2-ion from the downspin Mn2＋ion,while no electron transfer occurs for the upspin Mn^2＋ion. The（Mn, N）-codoped Zn O system shows ferromagnetism,which is attributed to the hybridization between Mn 3d and N 2p orbitals.