Bi2Sr2CaCu2-xSnxO8+δ系列超导体的XRD和XPS研究

实验研究了Bi2 Sr2 CaCu2 -xSnxO8 δ的X射线衍射 (XRD)和光电子能谱 (XPS) .实验发现随着掺杂 (Sn)量的增加 ,晶格参数a和c都有所变化 ,O1s和Cu2 p芯能级谱也发生了变化 .实验结果表明 :在低掺杂量时 ,Sn主要呈二价态 ;而在高掺杂浓度时呈四价态 ;掺Sn对超导电性的影响与其他元素的掺杂不同 .这些实验结果支持化学环境在高温超导样品的电子结构中起着重要作用的结论 .     

ZnSb掺杂的Ge2Sb2Te5薄膜的相变性能研究

本文采用双靶(ZnSb靶和Ge₂Sb₂Te₅靶)共溅射制备了系列ZnSb掺杂的Ge₂Sb₂Te₅(GST)薄膜. 利用X射线衍射、透射电子显微镜、原位等温/变温电阻测量、X射线光电子能谱等测试研究了薄膜样品的非晶形态、电学及原子成键特性. 利用等温原位电阻测试表明ZnSb掺杂的Ge₂Sb₂Te₅薄膜具有更高的结晶温度. 采用Arrhenius 公式计算发现ZnSb掺杂的Ge₂Sb₂Te₅薄膜的十年数据保持温度均高于传统的Ge₂Sb₂Te₅薄膜的88.9℃. 薄膜在200, 250, 300和350℃ 下退火后的X射线衍射图谱表明ZnSb的掺杂抑制了Ge₂Sb₂Te₅薄膜从fcc态到hex态的转变. 通过对薄膜的光电子能谱和透射电镜分析可知Zn, Sb, Te原子之间键进行重组, 形成Zn–Sb 和Zn–Te 键, 且构成非晶物质存在于晶体周围. 采用相变静态检测仪测试样品的相变行为发现ZnSb掺杂的Ge₂Sb₂Te₅薄膜具有更快的结晶速度. 特别是(ZnSb)_24.3(Ge₂Sb₂Te₅)_75.7薄膜, 其结晶温度达到250℃, 十年数据保持温度达到130.1℃, 并且在70 mW激光脉冲功率下晶化时间仅～64 ns, 远快于传统Ge₂Sb₂Te₅薄膜的晶化时间～280 ns. 以上结果表明(ZnSb)_24.3(Ge₂Sb₂Te₅)_75.7薄膜是一种热稳定性好且结晶速度快的相变存储材料.     

Sm富勒烯的芯态光电子能谱

用X射线光电子能谱研究了Sm掺杂的固态C₆₀相衍变和芯电子态.在Sm_xC₆₀中Sm的含量x小于0.5时，样品是固溶相；在x=0.5和x=2.75之间的掺杂阶段，样品是这两个相的混合.在x=2.75和x=6之间的高掺杂阶段未观察到相分离的X射线光电子能谱证据.Sm 4f, 4d的实验数据表明Sm的价态是+2.二价Sm 3d_5/2芯态谱线存在两个子峰. 关键词： 60的Sm填隙化合物')" href="#">C₆₀的Sm填隙化合物 相结构 电子态 X射线光电子能谱     

Sn离子注入PbTe的热电性能和结构

对碲化铅(PbTe)在室温下进行了Sn离子注入(200keV,6×10¹⁶和1×10¹⁷ion/cm²).应用电学和热学测量、X射线衍射技术(XRD)和X射线光电子能谱(XPS)研究了Sn离子注入PbTe的热电性能和注入层结构. 关键词：     

Sb掺杂SrTio3透明导电薄膜的光电子能谱研究

用X射线光电子能谱和同步辐射光电子能谱研究了Sb掺杂的钙钛矿型氧化物SrTi1-xSbxO3(x=0.05,0.10,0.15,0.20)薄膜的电子结构.薄膜由紫外脉冲激光淀积在SrTiO3(001)单晶衬底上.该薄膜系列在可见光波段透明,透过率均超过90%.其导电性与掺杂浓度有关,当Sb掺杂浓度x=0.05时,薄膜显示金属型导电性.X射线光电子能谱和同步辐射光电子能谱研究结果表明,Sb掺杂在母化合物SrTiO3的禁带内引入了浅杂质能级和深杂质能级.浅杂质能级上的退局域化电子离化到导带中会产生一定的传导电 关键词： 光电子能谱 光学透过率 脉冲激光沉积薄膜     

磁控溅射制备W掺杂VO2/FTO复合薄膜及其性能分析

为了获得相变温度低且热致变色性能优越的光学材料, 室温下在F:SnO₂ (FTO)导电玻璃基板表面沉积钨钒金属膜, 再经空气气氛下的热氧化处理, 制备了W掺杂VO₂/FTO复合薄膜, 利用X射线光电子能谱、X射线衍射和扫描电镜对薄膜的结构和表面形貌进行了分析. 结果表明: 高温热氧化处理过程中没有生成W, F, V混合氧化物, W以替换V原子的方式掺杂. 与采用相同工艺和条件制备的纯VO₂/FTO复合薄膜相比, W掺杂VO₂薄膜没有改变晶面取向, 仍具有(110)晶面择优取向, 相变温度下降到35 ℃左右, 热滞回线收窄到4 ℃, 高低温下的近红外光透过率变化量提高到28%. 薄膜的结晶程度明显提高, 表面变得平滑致密, 具有很好的一致性, 对光电薄膜器件的设计开发和工业化生产具有重要意义. 关键词： W掺杂 2')" href="#">VO₂ FTO导电玻璃 磁控溅射     

非晶态(Fe1-xCox)78Si9.5B12.5合金的X射线光电子能谱研究

本文报道非晶态(Fe_1-xCo_x)₇₈Si_9.5B_12.5合金的X射线光电子能谱的实验结果,分别给出了Fe,Co,Si,B元素的内层电子能级的结合能以及费密面态密度随Co含量的变化关系。 关键词：     

Tm2O3相对于Si的能带偏移研究

利用分子束外延系统在Si (001) 衬底上制备了单晶Tm₂O₃薄膜, 利用X射线光电子能谱研究了Tm₂O₃相对于Si的能带偏移. 得出Tm₂O₃相对于Si的价带和导带偏移分别为3.1 eV± 0.2 eV和1.9 eV± 0.3 eV, 并得出了Tm₂O₃的禁带宽度为6.1 eV± 0.2 eV. 研究结果表明Tm₂O₃是一种很有前途的高k栅介质候选材料. 关键词： 2O₃')" href="#">Tm₂O₃ X射线光电子能谱 能带偏移     

钒掺杂W18O49纳米线的室温p型电导与NO2敏感性能

钨氧化物纳米线在高灵敏度低功耗气体传感器中极具应用潜力, 且通过掺杂改性可进一步显著改善其敏感性能. 本文以WCl₆为钨源, NH₄VO₃为掺杂剂, 采用溶剂热法合成了钒掺杂的W₁₈O₄₉纳米线. 利用扫描电镜、透射电镜、X射线衍射、X射线光电子能谱仪表征了纳米线的微结构, 并利用静态气敏性能测试系统评价了掺杂纳米线的NO₂敏感性能. 研究结果表明: 五价钒离子受主掺杂进入氧化钨晶格结构, 抑制了纳米线沿轴向的生长并导致了纳米线束的二次集聚; 室温下, 钒掺杂W₁₈O₄₉纳米线接触NO₂气体后表现出反常的p型响应特性; 随工作温度逐渐升高至约110 ℃时, 发生从p型到n型的电导特性转变; 该掺杂纳米线气敏元件对浓度低至80 ppb (1 ppb=10^-9) 的NO₂气体具有明显的室温敏感响应和良好的响应稳定性. 分析并探讨了钒掺杂W₁₈O₄₉纳米线的高室温敏感特性及其p-n电导转型机理, 认为钒掺杂W₁₈O₄₉纳米线在室温下的良好敏感响应及反常p型导电性与掺杂纳米线表面高密度非稳表面态诱导的低温气体强吸附有关. 关键词： 氧化钨 纳米线 气体传感器 室温灵敏度     

MoO3在多孔γ-Al2 O3中固熔分散的研究

用MoO₃与多孔γ-Al₂O₃载体以机械混合法制备了一系列MoO₃/γ-Al₂O₃样品.用扫描电子显微镜、X射线衍射、X射线光电子能谱分析、综合热分析(TG/DTA)和正电子湮没谱学研究了MoO₃加载于γ-Al₂O₃后固熔分散过程.分别测量了不同含量的MoO₃/γ-Al_{2关键词： 正电子湮没谱学 三氧化钼 分散 逐次加载}     

Effect of Sn doping on the martensitic and premartensitic transitions in Ni2MnGa

The effect of Sn doping at the Ga site of Ni₂MnGa is investigated through magnetic and magneto-transport measurements. Clear signatures of martensitic and premartensitic transitions are observed in the pure as well as in 5% Sn doped alloy. For 10% Sn doping, the martensitic transition vanishes, while the premartensitic transition remains visible at low temperature. All the samples are found to have a ferromagnetic ground state with saturation moment decreasing with increasing Sn concentration. The magnetocaloric effect near the martensitic transition in the pure and 5% Sn doped samples is found to be positive. However, the entropy change is found to decrease with increasing magnetic field, which is particularly prominent in the undoped sample. The samples also show negative magnetoresistance with anomalies at the martensitic and premartensitic transition points.     

Influence of Sb doping on crystal structure and electrical property of SnO2 nanoparticles prepared by chemical coprecipitation

Sb doped SnO₂ (ATO) nanoparticles with Sb doping concentrations ranging from 0% to 20% (Sb/Sb+Sn) have been prepared by chemical coprecipitation using metallic Sn and SbCl₃ as raw materials. The influence of Sb doping concentration on crystal structure and electrical property was studied in detail. Results indicated that all ATO nanoparticles possessed the same tetragonal rutile structure as that of bulk SnO₂. The average crystal size of the ATO nanoparticles decreased from 16 to 7 nm by increasing the Sb doping concentration. The unit-cell volume of ATO nanoparticles was either expanded or contracted, strongly depending on the Sb doping concentration. The electrical resistivity decreased sharply from 111 to minimum of 1.05 Ω cm when the Sb doping concentration was increased from 0% to 15% and then increased slightly to 1.42 Ω cm when the Sb doping concentration was increased from 15% to 20%. Finally, high resolution X-ray photoelectron spectroscopy (XPS) measurement was employed to investigate the valence state of Sb in samples with various Sb doping levels.     

P-n codoping induced enhancement of ferromagnetism in Mn-doped In2O3: A first-principles study

We have performed first-principles density functional theory calculation in order to investigate the feasibility of “p-n codoping method” in improving magnetic property of In₂O₃ based diluted magnetic semiconductors. We find that the ferromagnetic state is favored in Mn-doped In₂O₃, and Sn doping can increase magnetic moment in Mn-doped In₂O₃. These findings are in line with our earlier experimental observation. Along with previous works, we now have enough evidences to support that p-n codoping is a valid method to improve magnetism of oxides based diluted magnetic semiconductors.     

Synthesis,structural and electrical properties of Ti modified Bi2Sn2O7 pyrochlore

Polycrystalline ceramic samples of Bi₂Sn_2−xTi_xO₇ (x=0.00, 0.2, 0.4, 0.6 and 0.8) have been synthesized by standard high temperature solid state reaction method. The effect of homovalent cation (titanium) substitution on the Sn-site on the structural and electrical properties of the pure Bi₂Sn₂O₇ ceramic have been studied by X-ray diffraction followed by SEM, dielectric and dc conductivity studies. The structural analysis indicates that the increase of titanium contents do not lead to any secondary phase. The frequency and temperature dependent dielectric studies have been carried out. It is found that the Ti doping reduces the material particle size. The size of the particles are strongly influenced by the addition of titanium to the system. The substitution of Ti for Sn ions affected the degree of disorder and modified the dielectric properties leading to more resistive ceramic compounds. The activation energies of all the compounds were calculated using the relation σ=σ₀exp(−Ea/kT).     

Structure and superconductivity of Mg1−xPbxB2

A series of polycrystalline samples of Mg_1−xPb_xB₂ (0≤x≤0.10) were prepared by a solid state reaction method and their structure, superconducting transition temperature and transport properties were investigated by means of X-ray diffraction (XRD) and resistivity measurements. Mg_1−xPb_xB₂ compounds were shown to adopt an isostructural AlB2-type hexagonal structure in a relatively small range of lead concentration, x≤0.01. The crystalline lattice constants were evaluated and were found to exhibit slight length compression as x increases. The superconducting transition temperature (T_c) steadily decreases with Pb doping. It is suggested that the mechanism of superconductivity reduction by lead doping can be attributed to the chemical pressure effect.     

Evolution of electronic structure in Eu1−xLaxFe2As2

We report an angle-resolved photoemission spectroscopy study of electronic structures of Eu_1−xLa_xFe₂As₂ single crystals, in which the spin density wave transition is suppressed with La doping. In the paramagnetic state, the Fermi surface maps are similar for all dopings, with chemical potential shifts corresponding to the extra electrons introduced by the La doping. In the spin density wave state, we identify electronic structure signatures that relate to the spin density wave transition. Bands around M show that the energy of the system is saved by the band shifts towards high energies, and the shifts decrease with increasing doping, in agreement with the weakened magnetic order.     

Synthesis and characterizations of Ho2O3 modified SrBi2Nb2O9 ceramics

SrBi_2-xHo_xNb₂O₉ (0?≤?x?≤?0.5) ceramics were prepared through the conventional solid state route. The materials have been characterized by XRD, FTIR and SEM. All compounds were pure and well crystallized. In FTIR spectroscopy, the spectral patterns of the crystal structures of these polyphases are unique and smoothly different from each other. The grains were prone to become spherical with increasing x. Dielectric and electrical properties of these materials as a function of temperature at different frequencies have been carried out. The dielectric constant and dielectric loss were found to decrease with an increase of the holmium concentration at room temperature. Reaching up to x?=?0.4 and x?=?0.5, the diffusivity increases, leading to the occurrence of relaxor behavior. 20–30 at.% Ho doping on the Bi-site can fill up the oxygen vacancies and decrease the AC conductivity. However, at higher doping levels greater than 40% holmium oxide, the AC conductivity is found to increase.     

SnO2/TiO2 mixed oxide particles synthesized in doped premixed H2/O2/Ar flames

SnO₂/TiO₂ mixed oxides with primary particle size ranging between 5 nm d_p 12 nm were synthesized by doping a H₂/O₂/Ar flame with Sn(CH₃)₄ and Ti(OC₃H₇)₄ co-currently. The effects of “flow coordinate,” concentration and flame configurations were investigated with respect to particle size and morphology of the generated mixed oxides. In situ characterization of the mixed oxides was performed using the particle mass spectrometer (PMS), while XRD, TEM, BET and UV–Vis were performed ex situ. Results obtained showed that primary particle size of mixed oxides can be controlled by varying experimental parameters. The mixed oxides have interesting properties compared to those of the pure oxides of TiO₂ and SnO₂, which were also synthesized in flames earlier. Band gap tuning opportunities are possible using mixed oxides.     

First-principles study of the electronic and magnetic properties of a Nickel-Zinc ferrite: ZnxNi1−xFe2O4

Using first-principles density functional theory within the generalized gradient approximation method, the effect of Zn doping on electronic and magnetic properties of NiFe₂O₄ ferrite spinel has been studied. The crystal structure of the compounds is assigned to a pseudocubic structure and the lattice constant increases as the Zn concentration increases. Our spin-polarized calculations give a half-metallic state for NiFe₂O₄ and a normal metal state for Zn_xNi_1−xFe₂O₄ (0<x≤0.5). Based on the magnetic properties calculations, it is found that the saturation magnetic moment enhances linearly with increase in the Zn content in NiFe₂O₄. The Zn doping in NiFe₂O₄ also induces strong ferrimagnetism since it decreases the magnetic moment of A-sites.     

ARPES studies of c-axis intracell coupling in Bi2Sr2CaCu2O8+δ

Using angle-resolved photoemission spectroscopy we have performed a detailed study of bilayer splitting in Bi₂Sr₂CaCu₂O_8+δ as a function of doping level and temperature. In heavily overdoped samples where the splitting is the clearest, we extract an intracell coupling t_⊥∼55 meV. As a function of photon energy the intensity ratio of the bonding and antibonding bands varies, allowing us to detect the bilayer splitting effect in the optimal and underdoped regimes. Surprisingly, with reduced doping the intracell coupling is not measurably reduced. Upon cooling to the superconducting state, a gap Δ opens in both bands yet the magnitude of the splitting remains unchanged.