高介电栅介质材料HfO_2掺杂后的物理电学特性(英文)

采用激光分子束外延法(LMBE)在P型Si(100)衬底上沉积了(HfO2)x(Al2O3)Y(NiO)1-x-y,栅介质薄膜,研究了其热稳定性以及阻挡氧扩散的能力.X射线衍射表明在HfO2中掺入Ni和Al元素明显提高了其结晶温度.原子力显微镜测试显示:在N2中退火后薄膜表面是原子级平滑连续的,没有发现针孔.900℃N2中退火后的薄膜在高分辨透射电镜下没有发现硅酸盐界面层.实验结果表明在氧化物薄膜与硅衬底之间引入Ni-Al-O置入层能够防止硅酸盐低介电界面层的生成,这有利于MOS晶体管的进一步尺度缩小.     

Si(111)衬底上多层石墨烯薄膜的外延生长

利用固源分子束外延(SSMBE)技术, 在Si(111)衬底上沉积碳原子外延生长石墨烯薄膜, 通过反射式高能电子衍射(RHEED)、红外吸收谱(FTIR)、拉曼光谱(RAMAN)和X射线吸收精细结构谱(NEXAFS)等手段对不同衬底温度(400、600、700、800℃)生长的薄膜进行结构表征. RAMAN和NEXAFS结果表明: 在800℃下制备的薄膜具有石墨烯的特征, 而 400、600和700℃生长的样品为非晶或多晶碳薄膜. RHEED和FTIR结果表明, 沉积温度在600℃以下时C原子和衬底Si原子没有成键, 而衬底温度提升到700℃以上, 沉积的C原子会先和衬底Si原子反应形成SiC缓冲层, 且在800℃沉积时缓冲层质量较好. 因此在Si衬底上制备石墨烯薄膜需要较高的衬底温度和高质量的SiC缓冲层.     

激光脉冲外延生长Pb(Zr0.52Ti0.48)O3薄膜及其特性研究

利用激光脉冲法在LaAlO3衬底上沉积制备LaNiO3薄膜作为底电极并外延生长(100) Pb(Zr0.52Ti0.48)O3铁电薄膜,系统研究了生长温度对PZT外延结构和电学特性的影响.研究发现当生长温度高于550℃时即可得到外延(100)PZT薄膜.在对所制备的PZT薄膜的结构和性能测试表明,650℃下生长的PZT薄膜外延性最佳,并且表现出优异的介电和铁电性能,介电常数ε、剩余极化Pr和矫顽场Ec分别为900、26.5 μC/cm2和52.1kV/cm.试验还证实这种外延PZT薄膜具有优良的抗疲劳特性,可用于铁电存储器的制备中去.     

衬底温度对磁控溅射制备外延ZnO薄膜结构特性的影响

在不同的衬底温度下,采用磁控溅射方法在蓝宝石(0001)衬底上制备了外延生长的ZnO薄膜.采用原子力显微镜(AFM)、X射线衍射仪(XRD)、可见-紫外分光光度计系统研究了衬底温度对ZnO薄膜微观结构和光学特性的影响.AFM结果表明在不同村底温度制备的ZnO薄膜具有较为均匀的ZnO晶粒,且晶粒的尺寸随衬底温度的增加逐渐增大.XRD结果显示不同温度生长的ZnO薄膜均为外延生长,400℃生长的薄膜具有最好的结晶质量;光学透射谱显示在370nm附近均出现一个较陡的吸收边,表明制备的ZnO薄膜具有较高的质量,其光学能带隙随着衬底温度的增加而减小.     

柔性ITO衬底上铜酞菁薄膜有序生长的X射线衍射研究

采用石英晶体微天平实时监测薄膜生长速率,通过控制衬底温度与薄膜生长速率,在柔性ITO导电衬底上真空蒸发沉积了铜酞菁薄膜.X射线衍射分析表明,适当提高衬底温度与薄膜生长速率,可促进薄膜的有序生长.当衬底温度为90℃,生长速率为10nm/min时,薄膜的有序度最高,薄膜晶型呈(相和(200)晶面.     

射频磁控溅射纳米SiC薄膜及其拉曼和红外分析

用射频磁控溅射法在玻璃衬底上制备出一系列衬底温度不同的纳米碳化硅薄膜,衬底温度分别为室温,200、400、600、700℃,并对样品进行了Raman和傅立叶红外测试分析.结果表明,随衬底温度的升高,薄膜结晶度提高,其晶粒尺寸为纳米数量级.通过FTIR不仅观察到SiC的TO声子在红外被激活,而且LO声子在粒径很小或薄膜很薄时也能在红外被激活,体现了纳米SiC较强的红外吸收特性.     

钙钛矿型氧化物SrTiO3/BaTiO3多层膜的激光分子束外延生长研究

用激光分子束外延技术在SrTiO3(001)衬底上外延生长SrTiO3/BaTiO3多层膜,通过反射式高能电子衍射(RHEED)原位实时监测并结合原子力显微镜(AFM),研究了不同基片温度下所生长薄膜的表面平整度,利用X射线衍射(XRD)对外延薄膜进行了结构分析,结果表明薄膜具有二维生长模式,在基片温度为380～470℃之间生长的薄膜具有原子级光滑,并且具有完全C轴取向.同时运用X射线光电子能谱(XPS)研究了薄膜界面的互扩散,结果表明降低制备薄膜时的基片温度有利于减少互扩散.     

MOCVD法在MgO(100)衬底上生长m面ZnMgO薄膜

本文采用金属有机化学气相沉积(MOCVD)法在MgO(100)衬底上成功生长了非极性的m面(1010)ZnMgO薄膜。研究了衬底温度对ZnMgO薄膜生长取向的影响。X射线衍射(XRD)分析结果表明当衬底温度为400℃时可以获得单一取向的m面ZnMgO薄膜。采用扫描电子显微镜(SEM)观察到ZnMgO薄膜表面平整,由条纹状结构组成。透射电子显微镜(TEM)分析进一步证明ZnMgO为具有m面取向的单晶薄膜。X射线光电子能谱(XPS)定量分析表明ZnMgO薄膜中Mg含量为3at.%。     

衬底温度对ZnO薄膜生长过程及微观结构的影响研究

以醋酸锌水溶液为前驱体,采用改进的超声喷雾热解法在Si(100)衬底上沉积ZnO薄膜,以X射线衍射(XRD)、扫描电镜(SEM)等手段分析所得ZnO薄膜的晶体结构和微观形貌,着重考察了衬底温度对ZnO薄膜生长过程及微观结构的影响.结果表明,在衬底温度为500℃下所得ZnO薄膜表面均匀光滑,属六方纤锌矿结构,且沿c轴择优生长,晶粒尺寸的为40～50nm;衬底温度对ZnO薄膜生长过程影响显著,随衬底温度的升高,薄膜生长速率存在一极限值,且ZnO薄膜的c轴取向趋势增强,晶粒尺寸得到细化.     

GaN薄膜的制备及其振动光谱的密度泛函理论研究

以氧化镓为镓源, 用溶胶-凝胶和高温氨化二步法, 在Si(111)衬底上制备出GaN薄膜. X射线衍射(XRD)分析表明制备的GaN薄膜是六角纤锌矿结构; 扫描电子显微镜(SEM)图片显示GaN晶粒的尺寸<100nm; 薄膜的红外光谱(FTIR)中有GaN的E1 (TO)声子模式. 用密度泛函理论(DFT)计算了氮化镓小团簇的振动频率. 结果表明: 富镓氮化镓团簇的振动频率在六方晶系纤锌矿结构GaN的光学声子峰值附近; 富氮氮化镓团簇中的N--N键的振动频率为2200cm^-1. 用氮化镓团簇的频谱对所制薄膜的红外光谱作了进一步分析.     

Effect of the composition on the bandgap width of high-κ MexTiyOz (Me = Hf, Ta, Sr) layers

To explore the possibility of bandgap engineering in Ti-oxide based insulators, we investigated the effect of added cations of another kind (Hf, Ta, Sr) on the optical absorption and photoconductivity of thin titanate films. A bandgap of 3.1-3.4 eV, typical for pure polycrystalline TiO₂, was found in crystallized Sr_xTi_yO_z of different composition as well as in amorphous Ta₂Ti₃O_z. By contrast, the gap width of Hf titanates increases starting from 3.5 eV for 30% Hf/(Hf + Ti) to 4.2 eV for 84% Hf/(Hf + Ti). We suggest that this gap widening is associated with reduced interaction between electron states of neighboring Ti cations as influenced by a wide-gap (E_g = 5.6 eV) HfO₂ sub-network.     

Chemical control of superconducting properties of (Y, Ca)(Sr, Ba)2Cu2.7Ga0.3O7?δ

The partial substitution of Ga at the Cu(1) (chain) sites of the YBa₂Cu₃O₇ structure allows synthesis at ambient pressure of Ba-free analogs, e.g., YSr₂Cu_2.7Ga_0.3O_7– . Materials with this composition have been found to be nonsuperconducting, but superconductivity has been induced by one or more of the following methods: Ca substitutions at the Y site; Ba substitutions at the Sr site; annealing in high-pressure oxygen. The influence of these chemical manipulations onT _c has been monitored and all methods have been found to enhanceT _c . The electronic effects of Ba substitutions have been deduced indirectly using powder neutron diffraction, and such substitutions appear to result in a redistribution of hole density into the Cu(1) sites from the superconducting CuO₂ planes.     

Two-gap superconductivity in R2Fe3Si5 (R=Lu,Sc) and Sc5Ir4Si10

Abstract

R₂Fe₃Si₅ (R= Sc, Y, Lu) contains nonmagnetic iron and has a relatively high superconducting transition temperature T_c among iron-containing superconductors. An anomalous temperature dependence of specific heat C(T) has been reported for polycrystalline samples down to 1 K. We have grown R₂Fe₃Si₅ single crystals, confirmed the anomalous C(T) dependence, and found a second drop in specific heat below 1 K. In Lu₂Fe₃Si₅, we can reproduce C(T) below T_c, assuming two distinct energy gaps 2Δ ₁/k_BT_c = 4.4 and 2Δ ₂/k_BT_c = 1.1, with nearly equal weights, indicating that Lu₂Fe₃Si₅ is a two-gap superconductor similar to MgB₂. Hall coefficient measurements and band structure calculation also support the multiband contributions to the normal-state properties. The specific heat in the Sc₂Fe₃Si₅ single crystals also shows the two-gap feature. R₅Ir₄Si₁₀ (R = Sc, rare earth) is also a superconductor where competition between superconductivity and the charge-density wave is known for rare earths but not for Sc. We have performed detailed specific heat measurements on Sc₅Ir₄Si₁₀ single crystals and found that C(T) deviates slightly from the behavior expected for weak-coupling superconductors. C(T) for these superconductors can also be reproduced well by assuming two superconducting gaps.     

Some thermodynamic aspects of the high-temperature transition in doped V2O3

Measurements of the entropy change are reported for the high-temperature metal-insulator (MI) transitions in the (V_1–xCr_x)₂O₃ and (V_1–xAl_x)₂O₃ systems. It is emphasized that the entropy of the I phase exceeds that of the M phase. Evidence is presented to show that the M and I phases coexist over a narrow temperature range. The transformation is attended by enormous hysteresis effects; these indicate that the lattice plays an important role in the transition. The probable role of Cr³⁺ and Al³⁺ as a dopant in the V₂O₃ lattice is briefly discussed. A phase diagram for the dilute V₂O₃-Al₂O₃ alloy system is presented.     

First-principles study on electronic structure, phase stability, and optical properties of In2X2O7 (X═C, Si, Ge or Sn)

In₂Ge₂O₇ and In₂Si₂O₇ are commonly used as scintillation materials. More studies on In₂X₂O₇ (X═C, Si, Ge, or Sn) are important to explore the possibility of using these materials for optoelectronic devices. This work presents results dealing with structural properties, electronic structure, chemical bonding, carrier effective masses, and optical spectra of polymorphs of In₂X₂O₇ obtained from first-principles calculations. The monoclinic phase of In₂Ge₂O₇, cubic and monoclinic phases of In₂Si₂O₇, as well as cubic phase of In₂Sn₂O₇ are known in scientific literature. From the total energy calculations at high pressure/strain we have found that the monoclinic phase of In₂Si₂O₇, In₂Ge₂O₇, and In₂Sn₂O₇ can be transformed into the cubic phase. The cubic phase of In₂Ge₂O₇ and In₂Sn₂O₇ is found to be more stable than the monoclinic phase. However, the monoclinic phase of In₂C₂O₇ and In₂Si₂O₇ is more stable than the cubic phase. The phase stability study suggests that In₂C₂O₇ is not stable, and that it might dissociate into corresponding binary oxides. Effective masses of electrons and holes have been estimated. Analysis of optical properties shows that in Si solar cells In₂Si₂O₇ and In₂Sn₂O₇ can be used as antireflection coating layer.     

Two-gap superconductivity in R2Fe3Si5 (R=Lu,Sc) and Sc5Ir4Si10

R₂Fe₃Si₅ (R= Sc, Y, Lu) contains nonmagnetic iron and has a relatively high superconducting transition temperature T_c among iron-containing superconductors. An anomalous temperature dependence of specific heat C(T) has been reported for polycrystalline samples down to 1 K. We have grown R₂Fe₃Si₅ single crystals, confirmed the anomalous C(T) dependence, and found a second drop in specific heat below 1 K. In Lu₂Fe₃Si₅, we can reproduce C(T) below T_c, assuming two distinct energy gaps 2Δ ₁/k_BT_c = 4.4 and 2Δ ₂/k_BT_c = 1.1, with nearly equal weights, indicating that Lu₂Fe₃Si₅ is a two-gap superconductor similar to MgB₂. Hall coefficient measurements and band structure calculation also support the multiband contributions to the normal-state properties. The specific heat in the Sc₂Fe₃Si₅ single crystals also shows the two-gap feature. R₅Ir₄Si₁₀ (R = Sc, rare earth) is also a superconductor where competition between superconductivity and the charge-density wave is known for rare earths but not for Sc. We have performed detailed specific heat measurements on Sc₅Ir₄Si₁₀ single crystals and found that C(T) deviates slightly from the behavior expected for weak-coupling superconductors. C(T) for these superconductors can also be reproduced well by assuming two superconducting gaps.     

The Study of Hole Distribution in High-Tc Tl- and Hg-based 1212 Type Cuprates via High-Resolution X-Ray Absorption Near Edge Structure

High resolution O K-edge and Cu L₃-edge X-ray absorption near-edge-structure (XANES) spectra of the high-T_c cuprates of (Tl_0.5Pb_0.5)Sr₂(Ca_1–xY_x)Cu₂O₇ (Tl-1212) and (Hg_0.5Pb_0.5)Sr₂(Ca_1–xY_x)Cu₂O₇ (Hg-1212) in powder form were measured using a bulk sensitive total-fluorescence-yield technique. Near the O 1s edge, the pre-edge peak with maxima at 528.3 eV is ascribed to the transitions to O 2p holes located in the CuO₂ planes. The intensity of this pre-edge peak increases with increasing doping level of Ca²⁺ into the Y³⁺ sites in Tl-1212 and Hg-1212. In the Cu L-edge absorption spectra, high-energy shoulders at around 933 eV are attributed to the transitions to the Cu(2p_3/2)^–13d¹⁰L states in the CuO₂ layers, where L denotes the O 2p ligand hole. The behavior of these shoulders in Tl-1212 and Hg-1212 correlates with that of the pre-edge peak at 528.3 eV in the O K-edge absorption spectra. The results can lead us to understand the hole distribution in high-T_c cuprates which will give a direction to find new high-T_c materials.     

Structural and magnetic study of nitrided Co74Fe8B12Si6 and Co74Fe4Mn4B12Si6 ribbons

The nitriding thermochemical treatment (NTT) is commonly used for steels. In this paper, the experimental conditions required for NTT, and the influence of such treatments on the structure and hysteresis loops of Co₇₄Fe₈B₁₂Si₆ and Co₇₄Fe₄Mn₄B₁₂Si₆ ribbons are reported. The results have been compared with those obtained with ribbons treated according to conventional thermal treatment (CTT) as well.     

Superconductivity at 103 K in CdBa2(Ca0.7Y0.3)Cu2Oy

A cadmium analogue of the mercury system with nominal composition CdBa₂(Ca_1–xY_x)Cu₂O_y has been synthesized. Thex=0 samples contain about 12 vol.% of the 1212 phase but are not superconducting. Thex=0.3 samples are superconducting atT _on = 103 K. The EDX analysis of 18 microcrystals shows a broad cationic distribution of the different components. The observed broad superconducting transition is attributed to the variousT _c of the different microcrystals.     

Synthesis, composition, and structure of superconducting (Y, Ca)Sr, Ba)2Cu2GaO7?δ

The superconducting properties of Y_1–y Ca _y Sr₂Cu₂GaO_7– have been examined and related to the Ca content,y, and the use of annealing treatments at 350 bar oxygen. Superconductivity withT _c up to 41 K was found only for high-pressure-annealed samples, and the structural effects of Ca substitution and high-pressure treatment were examined using powder neutron diffraction. Small but significant changes in Cu-Cu and Cu-O distances were found and suggest that the Cu ions are more highly charged in superconducting samples. Partial substitution of Ba for Sr was found to be possible (up to 20%) to give samples which, after annealing in high-pressure oxygen, were superconducting at temperatures up to 68 K.