Si衬底上生长的铁硅化合物结构和取向分析

采用分子束外延法分别在650-920℃的Si(110)和920℃的Si(111)衬底表面生长出铁的硅化物纳米结构,并主要分析了920℃高温下纳米结构的形貌、组成相及其与Si衬底的取向关系.扫描隧道显微镜(STM)研究表明,920℃高温下,Si(110)衬底上生长的铁硅化合物完全以纳米线的形式存在,且其尺寸远大于650℃低温下外延生长的纳米线尺寸;Si(111)衬底上生长出三维岛和薄膜两种形貌的铁硅化合物,其中三维岛具有金属特性且直径约300 nm、高约155 nm,薄膜厚度约2 nm.电子背散射衍射研究表明920℃高温下Si(110)衬底上生长的纳米线仅以β-FeSi2的形式存在,且β-FeSi2相与衬底之间存在唯一的取向关系:β-FeSi2(101)//Si(11 1);β-FeSi2[010]//Si[110];Si(111)衬底上生长的三维岛由六方晶系的Fe2Si相组成,Fe2Si属于164空间群,晶胞常数为a=0.405 nm,c=0.509 nm;与衬底之间的取向关系为Fe2Si(001)∥Si(111)和Fe2Si[1 20]//Si[112].     

一例可分离的双核铁氢自由基阳离子

成功分离得到了一例双核铁氢自由基阳离子盐cis-[Fe₂Cp₂（μ-H）（μ-PPh₂）（CO）₂]^·+[Al（OC（CF₃）₃）₄]^-（cis-1^·+[Al（OC（CF₃）₃）₄]^-）晶体，并使用单晶X射线衍射、电子顺磁共振、红外光谱、紫外-可见光谱以及密度泛函理论对它进行了表征和理论计算。电子顺磁共振和密度泛函理论计算分析表明，自由基的自旋密度主要均等分布于2个铁原子上。     

酸性离子液调控下咪唑硫酸四铁簇合物和铁-DMSO配合物的合成

FeCl₂与酸性离子液在乙醇中反应制备得到咪唑硫酸铁簇合物[HMIM]₂[Fe₂O（SO₄）₃（DMSO）₂]·0.5DMSO（1）和[HPIM]₄[Fe₄O₂（SO₄）₆（DMSO）₄]·2MeCN（2）,该类簇合物为四核铁簇Fe₄（O）₂（SO₄）₆（DMSO）₄结构,4个Fe原子通过中心μ₃-O桥、硫酸根上的μ₂-O和μ₃-O桥连接,形成共平面结构,中间的四核铁簇为-4价,4个质子化的咪唑正离子起电荷平衡作用。该簇合物的晶体结构属于三斜晶系中的P1空间群。变温磁化率测试表明该簇合物具有强的反铁磁性。但在类似的反应条件下,FeCl₃在酸性离子液反应没有得到类似的簇合物,而是得到DMSO配合物[FeCl₂（DMSO）₄][EtSO₄]·DMSO（3）。     

一维Bi2Fe4O9纳米棒阵列的无模板水热合成

以物质的量的比为1：1的Bi（NO₃）₃·5H₂O和Fe（NO₃）₃·9H₂O为反应原料,以NaOH为矿化剂,利用水热法在Ti基板上成功制备出一维Bi₂Fe₄O₉纳米棒阵列。对该纳米棒阵列分别进行XRD、FE-SEM、HR-TEM和UV-Vis测试,得到Bi₂Fe₄O₉纳米棒的直径为100nm,长度为3~4μm,并表现出良好的光吸收性能,禁带宽度约为1.9eV,对甲基紫溶液的光降解率达到86%,其活性明显高于市售P25（TiO₂）。该纳米棒阵列的生长方式完全遵循奥斯瓦尔德熟化（Ostwald ripening）单晶生长机理。     

Fe3+掺杂三维分级纳米Bi2WO6的合成及其光催化活性增强机理

利用水热法合成了Fe³⁺掺杂的三维分级纳米Bi₂WO₆,借助X射线衍射（XRD）、场发射扫描电镜（FE-SEM）、透射电镜（HRTEM）、能谱（EDS）、紫外可见漫反射（UV-Vis-DRS）等测试手段对所得样品的相组成、形貌和谱学特征进行了表征。选择罗丹明B为模型污染物研究所得样品在可见光下的催化活性。结果表明,Fe³⁺掺杂Bi₂WO₆为新颖的分级纳米结构,且Fe³⁺掺杂能有效提高Bi₂WO₆的光催化活性,Fe³⁺掺杂量对Bi₂WO₆活性的影响显著;实验结果还表明,所得Fe³⁺掺杂Bi₂WO₆催化剂的稳定性较好,易于回收。此外,还对Fe³⁺掺杂Bi₂WO₆的光催化活性增强机理进行了研究,缺电子的Fe³⁺作为电子捕获中心有利于促进光生电子-空穴对的分离,从而提高Bi₂WO₆的光催化活性。     

氰基桥联的Fe2Ni2单分子磁体的合成与磁性

利用三氰基构筑单元Bu₄N[Fe^Ⅲ（PzTp）（CN）₃]（PzTp=tetrakis（pyrazolyl）borate）和4,4''-二甲氧基-2,2''-联吡啶（4,4''-dmobpy）配体,合成了2例氰基桥联的Fe^Ⅲ₂Ni^Ⅱ₂四核配合物。单晶X射线衍射表明化合物[Fe^Ⅲ（PzTp）（CN）₃]₂[Ni^Ⅱ₂（4,4''-dmobpy）₄][Fe^Ⅲ（PzTp）（CN）₃]₂·2CH₃OH（1）和[Fe^Ⅲ（PzTp）（CN）₃]₂[Ni^Ⅱ₂（4,4''-dmobpy）₄]（PF₆）₂（2）具有四核四方形分子结构。直流磁化率测试表明配合物1和2均表现为分子内的铁磁耦合作用。交流磁化率测试表明配合物1和2在零场下具有慢磁弛豫行为,有效能垒分别为12.8和13.0 K。     

直流电弧自催化合成β-SiC纳米线

采用C,Si和SiO₂为反应原料,利用直流电弧法制备出长直的β-SiC纳米线。纳米线的直径为100～200 nm,长度为10～20 μm,并且沿着<111>方向生长。通过X射线衍射(XRD)、扫描电子显微术(SEM)、透射电子显微术(TEM)、拉曼光谱等手段,对β-SiC纳米线进行表征。探讨了β-SiC纳米线自催化气-液-固(VLS)生长机制。     

双核铁肟硼酸基多孔金属有机聚合物的合成、结构及其电催化析氧性能

采用氯化亚铁、2,6-二甲酰基-4-甲基苯酚二肟（H₃DFMP）和四（4-硼酸基苯基）甲烷（TBPM）,通过一步配位作用和硼酸酯化脱水聚合反应,合成了一例含金属的三维多孔有机聚合物（Fe₂-POP）。Fe₂-POP是以双核亚铁配位H₃DFMP的直线单元与TBPM的四面体单元连接而成的具有三维金刚石结构的多孔有机聚合物。对模型化合物的X射线单晶衍射分析验证了双核亚铁配合物单元的结构特征。红外光谱和固体核磁表征证明了Fe₂-POP中C=N和B-O键的形成。Fe₂-POP具有较高的比表面积（510 m²·g^-1）和均一的孔径（0.6~0.8 nm）。X射线光电子能谱表明了Fe₂-POP中二价铁的存在。扫描电子显微镜和透射电子显微镜显示该聚合物是由50~100 nm的球形颗粒组成。电化学测试表明,Fe₂-POP展现出了优异的电催化析氧性能,在10 mA·cm^-2电流密度下所需析氧反应过电位仅为258 mV,Tafel斜率为71.0 mV·dec^-1。     

双功能化磁性纳米修复剂对多重金属的快速、高效钝化行为

采用“一锅法”制备了四氧化三铁/半胱氨酸（Fe₃O₄/Cys）磁性纳米微球,随后对Fe₃O₄/Cys进行亚氨基二乙酸（IDA）修饰得到Fe₃O₄/Cys/IDA磁性双功能化纳米微球。研究发现Fe₃O₄/Cys中的L-Cys是通过—SH基团接枝到Fe₃O₄表面的,随后IDA分子中的羧基与Fe₃O₄/Cys中的—NH₂形成酰胺键,最终形成多支链多羧基的Fe₃O₄/Cys/IDA磁性纳米修复剂。基于修复剂表面短支链-长支链交替的多羧基结构,实现了羧基基团的高密度接枝。同时,Fe₃O₄/Cys/IDA磁性纳米微球对Pb²⁺、Cd²⁺、Cu²⁺、Co²⁺、Ni²⁺、Zn²⁺为专性吸附,而对Hg²⁺属于非专性吸附,且吸附重金属后得到的钝化产物均表现了良好的稳定性。另外,Fe₃O₄/Cys/IDA对重金属离子的吸附符合Langmuir模型,属于单层均相吸附,其吸附过程符合准二级动力学模型,最大吸附量为49.05 mg·g^-1。     

酸性离子液调控下咪唑硫酸四铁簇合物和铁-DMSO配合物的合成

FeCl₂与酸性离子液在乙醇中反应制备得到咪唑硫酸铁簇合物[HMIM]₂[Fe₂O（SO₄）₃（DMSO）₂]·0.5DMSO（1）和[HPIM]₄[Fe₄O₂（SO₄）₆（DMSO）₄]·2MeCN（2）,该类簇合物为四核铁簇Fe₄（O）₂（SO₄）₆（DMSO）₄结构,4个Fe原子通过中心μ₃-O桥、硫酸根上的μ₂-O和μ₃-O桥连接,形成共平面结构,中间的四核铁簇为-4价,4个质子化的咪唑正离子起电荷平衡作用。该簇合物的晶体结构属于三斜晶系中的P1空间群。变温磁化率测试表明该簇合物具有强的反铁磁性。但在类似的反应条件下,FeCl₃在酸性离子液反应没有得到类似的簇合物,而是得到DMSO配合物[FeCl₂（DMSO）₄][EtSO₄]·DMSO（3）。     

Structural and Optical Properties of ZnO Films with Different Thicknesses Grown on Sapphire by MOCVD

IntroductionZnOis one of the most promising materials for pro-ducing ultraviolet laser at room temperature because ofits wide direct band gap(Eg=3.37eV)and large ex-citonic binding energy of60meV.Recently,much at-tention has been paid to short-wavelength …     

Phase-controlled growth of metastable Fe5Si3 nanowires by a vapor transport method

We report the synthesis of single-crystalline nanowires (NWs) of metastable Fe5Si3 phase via an iodide vapor transport method. Free-standing Fe5Si3 NWs are grown on a sapphire substrate placed on a Si wafer without the use of any catalyst. The typical size of the Fe5Si3 nanowires is 5-15 microm in length and 100-300 nm in diameter. Synthesis of the metastable phase is induced by composition-dependent nucleation from the gas-phase reaction. Depending on the concentration ratio of FeI2(g) to SiI4(g), different phases of iron silicides are formed. The growth of nanowires is facilitated by the initial nucleation of silicide particles on the substrate and further self-seeded growth of the NWs. The present work not only provides a method for the synthesis of metastable Fe5Si3 nanowires but also suggests that the phase controlled synthesis can be further optimized to produce other metal-rich silicide nanostructures for future spintronic devices.     

锰的硅化物薄膜在Si(111)-7×7表面的固相反应生长

利用超高真空扫描隧道显微镜(STM)对沉积在Si(111)-7×7重构表面上的锰薄膜在300-650℃之间的固相反应进行了研究.锰原子最初在Si(111)衬底上形成锰的纳米团簇的有序阵列,经过300℃退火后,锰纳米团簇的尺寸增大并且纳米团簇阵列由有序变为无序;当退火温度达到400℃左右时,锰纳米团簇与硅衬底发生反应生成富锰的三维岛状物和由MnSi构成的平板状岛;500℃退火后生成物全部转变为MnSi平板状岛;650℃退火后生成物则由MnSi平板状岛全部转变为富硅的不规则的大三维岛,同时被破坏的衬底表面重新结晶形成7×7结构.     

Crystallization of textured PbTiO3 films deposited from gels

Sol-gel processed PbTiO₃ thin films have been deposited by spin coating onto different subtrates; Si[111], Si/Al, Si/SiO₂/Cr/Pt, MgO[100], SrTiO₃[100] and sapphire. Interactions between the substrate and PbTiO₃ films after heat treatment have been studied by X-ray diffraction and Rutherford Back Scattering. When deposited onto sapphire and Si[111], PbTiO₃ films exhibit a preferred orientation with (101) perpendicular to the substrate. These films become oriented along (100) onto MgO and (001) onto SrTiO₃[100] substrates. A strong channelling effect is observed by the RBS technique when the film is oriented along the c axis on SrTiO₃[100] suggesting that these films are epitaxially grown. The diffusion of metal atoms during the thermal treatment gives rise to the formation of lead silicate on Si[111] substrates. As a result a pyrochlore phase is formed. Lead titanate films on Si/SiO₂/Cr/Pt and Si/Al substrates are polycrystalline and do not exhibit any texture.     

Magnetische Messungen in den Mischphasen (T I,T II)3 {Si,Ge}; (T I,T II=Fe,Co, Ni)

Solid solutions of silicides and germanides having BiF₃ and Cu₃Au type structure have been measured in the ferromagnetic and paramagnetic region in the range between 80 K and 1270 K. The results are discussed by means of a model given byLecocq et al. for Fe₃Si, in the case of the silicides and with a modified model in the case of the germanides.     

Anisotropic catalytic activity of the orientation controlled Nd2NiO4 + δ/YSZ hetero-epitaxial system for SOFC cathode

Electrode–electrolyte hetero-epitaxial systems for solid oxide fuel cells (SOFCs) with two different configuration of Nd₂NiO_4 + δ(110)//YSZ(100) and Nd₂NiO_4 + δ(100)//YSZ(110) were successfully fabricated by pulsed laser deposition. Thin films of Nd₂NiO_4 + δ approximately 20 nm thick were grown on a commercial single crystal of YSZ. The preferred two-dimensional diffusion paths of the oxide ions were perpendicular to the substrate for both configurations and showed oxygen reduction capability different from each other. This opens up new research direction focusing on the details of anisotropic catalytic activity of SOFC cathode depending on the crystalline surface.     

Self-aligned Submonolayer Cobalt Silicide Formation Studied by Variable Temperature Scanning Tunneling Microscopy in UHV System

Epitaxial growth of defect free metal silicides with high thermal stability is important to ultra large scale integration devices (ULSI)^[1]. Cobalt silicide has been used as an interconnect in CMOS devices due to its low resistivity and good thermal stability^[2] and excellent lattice match between cobalt silicide and silicon^[3,4]. In the present work, we have investigated epitaxial growth of ultra-thin cobalt layer (ca. 10 Å) by electron beam evaporation of cobalt on Si(111) (7×7) surface followed by thermal annealing up to 700℃ in UHV system. The morphologies and the surface structures of epitaxial silicide formation were investigated by using scanning tunneling microscopy (STM). Adlayer structures of Co silicide after annealing were observed to coexist as the closely and loosely packed clusters at 230℃ separated by a boundary. A new structure with ring-like clusters has (l×l) configuration with 3.5 A spacing between hollows of vicinal clusters at 400℃. Si-rich CoSi₂ surfaces terminated by Si bilayers showed (2×2) structures after annealing at 480℃, in which Si-rich CoSi₂ clusters were observed to be very mobile at room temperature. As the surface was annealed to above 500℃, The domain island became regular triangles, where atomic resolution of the l×l surface of CoSi₂(111) were readily discernable. CoSi₂(111) surface is suggested to be terminated by a Si-bilayer.     

Hematite/Si nanowire dual-absorber system for photoelectrochemical water splitting at low applied potentials

Hematite (α-Fe(2)O(3)) was grown on vertically aligned Si nanowires (NWs) using atomic layer deposition to form a dual-absorber system. Si NWs absorb photons that are transparent to hematite (600 nm < λ < 1100 nm) and convert the energy into additional photovoltage to assist photoelectrochemical (PEC) water splitting by hematite. Compared with hematite-only photoelectrodes, those with Si NWs exhibited a photocurrent turn-on potential as low as 0.6 V vs RHE. This result represents one of the lowest turn-on potentials observed for hematite-based PEC water splitting systems. It addresses a critical challenge of using hematite for PEC water splitting, namely, the fact that the band-edge positions are too positive for high-efficiency water splitting.     

Enhanced growth of crystalline-amorphous core-shell silicon nanowires by catalytic thermal CVD using in situ generated tin catalyst

In this work,we prepared silicon nanowires(Si NWs) on both fluorine-doped SnO 2(FTO) coated glass substrate and common glass substrate by catalytic thermal chemical vapor deposition(CVD) using indium film as the catalyst.It is confirmed that indium can catalyze the growth of Si NWs.More importantly,we found that tin generated in situ from the reduction of SnO 2 by indium can act as catalyst,which greatly enhances the growth of Si NWs on FTO substrate.The obtained Si NWs have a uniform crystalline-amorphous core-shell structure that is formed via vapor-liquid-solid and vapor-solid growth of silicon sequentially.This work provides a strategy to prepare Si NWs in high yield by catalytic thermal CVD using the low melting point metal catalysts.