Hidden magnetic configuration in epitaxial La(1-x) Sr(x) MnO3 films

We present an unreported magnetic configuration in epitaxial La(1-x) Sr(x) MnO3 (x ～ 0.3) (LSMO) films grown on strontium titanate (STO). X-ray magnetic circular dichroism indicates that the remanent magnetic state of thick LSMO films is opposite to the direction of the applied magnetic field. Spectroscopic and scattering measurements reveal that the average Mn valence varies from mixed Mn(3+)/Mn(4+) to an enriched Mn3+ region near the STO interface, resulting in a compressive lattice along the a, b axis and a possible electronic reconstruction in the Mn e(g) orbital (d(3)z(2)-r(2). This reconstruction may provide a mechanism for coupling the Mn3+ moments antiferromagnetically along the surface normal direction, and in turn may lead to the observed reversed magnetic configuration.     

Surface protonation and oxygen evolution activity of epitaxial La_(1-x)Sr_xCoO_3 thin films

As an alternative electrode material, transition metal oxides are promising candidates due to multivalent nature and oxygen vacancies present in the structure with facilitate redox reactions. The aim of this study is to explore the intrinsic mechanism of oxygen evolution reaction(OER) using two-dimensional thin film La_(1-x)Sr_xCoO_3 electrode as a model. Herein, we report a planar two-dimensional model La_(1-x)Sr_xCoO_3 electrode grown on a Nb-SrTiO_3 single-crystal substrate via pulsed laser deposition. The two-dimensional La_(1-x)Sr_xCoO_3 films offer different oxygen evolution activities at different pH electrolyte solutions. The mechanisms behind the variations of the oxygen evolution activity were discussed after comparing the oxygen evolution activity before and after treatments of the electrodes and measurements by various test methods. The results of this study offer a promising, low-cost electrode material for the efficient OER and a sustainable production of hydrogen fuel.     

Oxygen vacancies effects on phase diagram of epitaxial La_(1-x)Sr_xMnO_3 thin films

We investigated the effects of oxygen vacancies on the structural,magnetic,and transport properties of La_(1-x)Sr_xMnO_3(x=0.1,0.2,0.33,0.4,and 0.5)grown around a critical point(without/with oxygen vacancies)under low oxygen pressure(10 Pa)and high oxygen pressure(40 Pa).We found that all films exhibit ferromagnetic behavior below the magnetic critical temperature,and that the films grown under low oxygen pressures have degraded magnetic properties with lower Curie temperatures and smaller magnetic moments.These results show that in epitaxial La_(1-x)Sr_xMnO_3 thin films,the magnetic and transport properties are very sensitive to doping concentration and oxygen vacancies.Phase diagrams of the films based on the doping concentration and oxygen vacancies were plotted and discussed.     

MnxSi1-x磁性薄膜的结构研究

利用X射线衍射(XRD)和X射线吸收近边结构(XANES)方法研究了在Si(100)衬底上及600℃温度条件下用分子束外延(MBE)共蒸发方法生长的MnxSi1-x磁性薄膜的结构.由XRD结果表明,只有在高Mn含量(8%和17%)样品中存在着Mn4Si7化合物物相.而XANES结果则显示,对于Mn浓度在0.7%到17%之间的MnxSi1-x样品,其Mn原子的XANES谱表现出了一致的谱线特征.基于多重散射的XANES理论计算进一步表明,只有根据Mn4Si7模型计算出的理论XANES谱才能够很好的重构出MnxSi1-x样品的实验XANES谱.这些研究结果说明在MnxSi1-x样品中,Mn原子主要是以镶嵌式的Mn4Si7化合物纳米晶颗粒存在于Si薄膜介质中,几乎不存在间隙位和替代位的Mn原子.     

稀掺杂GaNxAs1－x(x≤0.03)薄膜的调制光谱研究

利用室温下压电调制反射光(PzR)谱技术系统测量了N掺杂浓度为0.0%—3%的分子束外延生长GaN_xAs_1-x薄膜，并对图谱中所观察的光学跃迁进行了指认.在GaN_0.005As_0.995和GaN_0.01As_0.99薄膜的PzR谱中观察到此前只在椭圆偏振谱中才看到的N掺杂相关能态E₁+Δ₁+Δ_N.当N掺杂浓度达到 关键词： 压电调制反射光谱(PzR) xAs_1-x薄膜')" href="#">GaN_xAs_1-x薄膜 分子束外延(MBE)     

The Hall effect in quench-condensed Ti1-x V x thin films

Measurements of the Hall coefficient of as quenched (amorphous) and annealed (polycrystalline) Ti–V alloy films are reported. The Hall coefficient is positive for both amorphous and polycrystalline films. The electrical resistivity for the as quenched samples is large (190 cm) and relatively independent of alloy concentration.     

Structural and electronic properties of InNxP1-x alloy in full range (0 ≤ x ≤1)

We have performed first-principles method to investigate structural and electronic properties of InN_xP_1?x ternary semiconductor alloy in full range (0 ≤ x ≤ 1) using density functional theory. We have used modified Becke–Johnson potential to obtain accurate band gap results. From the electronic band structure calculation we have found that InN_xP_1?x become metal between 47 and 80% of nitrogen concentration. Additional to our band gap calculations, we have also used the band anticrossing model. The band anticrossing model supplies a simple, analytical expression to calculate the physical properties, such as the electronic and optical properties, of III-N_xV_1?x alloys. The knowledge of the electron density of states is required to understand and clarify some properties of materials such as the band structures, bonding character and dielectric function. In order to have a deeper understanding of these properties of the studied materials, the total and partial density of states has been calculated. Finally, we have calculated the total bowing parameter b of studied alloys, together with three contributions b_VD, b_CE, and b_SR due to volume deformation, different atomic electron negativities and structural relaxation, respectively.     

Picosecond laser ablation of high-quality micro-grooves on CIGS (CuIn(1-x)Ga2Se x ) thin films

ABSTRACT

This paper presents a study of the effects of ablation direction, beam profile and outer environment on the width and morphology of micro-grooves ablated by a 10-ps, 532-nm laser with a changing range of fluences and scan speeds on 600?nm-thick CIGS (CuIn_(1-x)Ga₂Se _x ) thin films. Experiments show that rear-side ablation by picosecond laser with a flat top beam in water environment yields a larger groove width than normal front-side ablation with a Gaussian beam in air, which is attributed to different material removal mechanisms, uniform energy distribution and the refraction of laser in water. The heat-affected zone and irregular edges induced by the tearing effect are the main defects of groove morphology associated with front- and rear-side ablation processes, respectively. Our studies indicate that flat top beam ablation, in general, inhibits the over-ablation in the central region, thereby improving the uniformity of grooves, though it does not eliminate the heat-affected zone and irregularity of two edges. The straightness of groove edges is further improved with the flat top beam ablation carried out in a water environment, resulting from the action of the shock wave in water. Hence, the nearly perfect micro-grooves can be fabricated with rear-side flat top beam ablation under water, which are characterized by steep sidewalls, straight edges and intact glass substrate without cracks.     

First-principles calculation of alloy scattering in Ge(x)Si(1-x)

First-principles electronic structure methods are used to find the rates of intravalley and intervalley n-type carrier scattering due to alloy disorder in Si(1-x)Ge(x) alloys. The required alloy scattering matrix elements are calculated from the energy splitting of nearly degenerate Bloch states which arises when one average host atom is replaced by a Ge or Si atom in supercells containing up to 128 atoms. Scattering parameters for all relevant Delta and L intravalley and intervalley alloy scattering are calculated. Atomic relaxation is found to have a substantial effect on the scattering parameters. f-type intervalley scattering between Delta valleys is found to be comparable to other scattering channels. The n-type carrier mobility, calculated from the scattering rate using the Boltzmann transport equation in the relaxation time approximation, is in excellent agreement with experiments on bulk, unstrained alloys.     

Negligible magnetism in excellent structural quality Cr(x)Ti(1-x)O(2) anatase: contrast with high-T(C) ferromagnetism in structurally defective Cr(x)Ti(1-x)O(2)

We reexamine the mechanism of ferromagnetism in doped TiO(2) anatase, using epitaxial Cr:TiO(2) with excellent structural quality as a model system. In contrast to highly oriented but defective Cr:TiO(2) (approximately 0.5 micro(b)/Cr), these structurally superior single crystal films exhibit negligible ferromagnetism. Similar results were obtained for Co:TiO(2). We show for the first time that charge-compensating oxygen vacancies alone, as predicted by F-center mediated exchange, are not sufficient to activate ferromagnetism. Instead, the onset of ferromagnetism correlates with the presence of structural defects.     

The unique magnetic damping enhancement in epitaxial Co_2Fe_(1-x)Mn_xAl films

Uniform precession dynamics and its magnetic damping are investigated in epitaxial Co_2Fe_(1-x)Mn_xAl films by using the time-resolved magneto–optical Kerr effect under out-of-plane configuration.The decay time of uniform precession mode decreases, and thus the magnetic damping increases with the increase of external field.Moreover, the decay time decreases as x decreases, so that the enhancement of magnetic damping occurs in Fe-rich sample.Furthermore, the decay time decreases as the excitation fluence increases, which drops rapidly at low magnetic field comparing with the slow reduction at high magnetic field.This unique magnetic damping enhancement is attributed to the enhancement of homogeneous magnetization.     

Room-temperature ferromagnetism in a II-VI diluted magnetic semiconductor Zn(1-x)Cr(x)Te

The magnetic and magneto-optical properties of a Cr-doped II-VI semiconductor ZnTe were investigated. Magnetic circular dichroism measurements showed a strong interaction between the sp carriers and localized d spins, indicating that Zn(1-x)Cr(x)Te is a diluted magnetic semiconductor. The Curie temperature of the film with x=0.20 was estimated to be 300+/-10 K, which is the highest value ever reported for a diluted magnetic semiconductor in which sp-d interactions were confirmed. In spite of its high Curie temperature, Zn(1-x)Cr(x)Te film shows semiconducting electrical transport properties.     

Structural and electrical characterization of strontium bismuth tantalate (SBT) thin films

Ferroelectric strontium bismuth tantalate (SBT) thin films were deposited by thermal metalorganic chemical vapour deposition (MOCVD) onto a complex layered Pt/IrO₂/Ir/Ti(Al)N substrate. A study of ultra-violet (UV)-assisted rapid thermal processing (RTP) annealing strategies of the SBT thin films was performed. The influence of UV irradiation temperature and annealing atmosphere on the crystallinity of the deposited films was evaluated using both microstructural and electrical analysis techniques. A UV-RTP strategy in an oxygen atmosphere above 400 °C, followed by a furnace treatment at 700 °C, provided an optimum remnant polarization figure of merit.