液相电化学沉积法制备高氮含量CNx薄膜及性能的研究

采用液相电化学沉积法,以二氰二胺的丙酮溶液为沉积液,以镀有ITO(铟锡氧化膜)的导电玻璃为衬底制备了CNx薄膜.初步探讨了沉积温度和沉积电压对薄膜中氮含量的影响.通过XPS、FTIR光谱、SEM和US-Vis光谱对得到的CNx薄膜的化学结合状态、结构形貌和光学性质进行了表征,并用高电阻仪对薄膜的绝缘性进行了分析.XPS结果表明,CNx薄膜中碳氮主要以单键连接,sp3杂化的C—N键占85%.在IR光谱中,仅出现了C—N键和CN双键的吸收峰.SEM图谱显示CNx薄膜呈颗粒状,粒径平均为80nm左右.在水浴加热条件下沉积的CNx薄膜在200～300nm近紫外区为非线性吸收.薄膜的电阻率随氮含量的增加而增大,测量值在1012～1016Ω·cm之间.     

Ca9Y(PO4)7:Ce3+,Tb3+纳米荧光粉的制备及发光性能

采用水热法制备出Ca_9Y(PO4)7∶Ce~(3+),Tb~(3+)纳米荧光粉,通过XRD、SEM和荧光光谱等对样品进行了分析,研究在Ca_9Y(PO4)7基质中引入Ce~(3+),Tb~(3+)离子对发光性能的影响规律。研究发现因Tb~(3+)离子自身能量交叉驰豫的存在,使得单掺Tb~(3+)时,通过调节Tb~(3+)离子的浓度可以实现对发光颜色的控制。同时研究了Ce~(3+)-Tb~(3+)之间的能量传递为电多极相互作用的偶极-四极机制,Ce~(3+)-Tb~(3+)之间最大的能量传递效率为55.6%。Ca_9Y(PO4)7∶Ce~(3+),Tb~(3+)的发光颜色可以通过激活离子之间的能量传递和共发射得到可控调节。SEM分析表明荧光粉颗粒尺寸在100 nm左右,分散性好。     

α-Al2O3(0001)表面吸附ZnO的DFT研究

建立了α-Al2O3(0001)2×1表面薄片吸附模型,采用基于DFT动力学赝势方法,对ZnO分子的吸附生长进行了计算.详细地研究了ZnO分子在表面吸附的成键方式以及表面化学键特性.在较稳定的吸附位上,ZnO化学键[(0.185±0.01)nm]与最近邻的表面Al—O键有30°的偏转角度,Zn在表面较稳定的化学吸附位置偏离表面O六角对称约30°.通过吸附能量、原子布居数和态密度的分析,ZnO的O2-与表面上的Al3+形成的化学键表现出强离子键特征;而Zn2+同基片表面O2-形成的化学键有明显的共价键成分.     

SO42-改性后的TiO2(锐钛和/或金红石)表面上MoO3的分散性质研究

采用红外(IR)、拉曼(Raman)、X-射线衍射(XRD)、程序升温还原(TPR)等方法考察了经硫酸根改性后的金红石(SR)与锐钛矿(SA)的混合比例变化时的负载型催化剂，MoO₃ / TiO₂(SR+SA)，的一些物理化学性质(如活性组分MoO₃的分散行为、表面酸碱性、氧化还原性)的变化规律。结果表明：对于MoO₃ / TiO₂(SR+SA)样品，低含量MoO₃表面分散时倾向于优先与混合载体中的改性金红石(SR)发生作用；TiO₂载体表面SO₄^2-的存在，使得载体表面产生了新的酸性位，导致样品中表面分散的钼物种主要以聚合八面体状态存在。     

Eu0.5RE0.5Fe0.5Mn0.5O3的57Fe Msosbauer谱研究

利用固相反应合成了Eu0.5RE0.5Fe0.5Mn0.5O3(RE=La,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Y)等化合物。测量了其XRD谱及57FeMssbauer谱。实验发现,随着RE原子序数的增加,样品的晶胞体积减小,Fe在化合物中处于Fe3+的高自旋状态,57Fe的四极裂矩与样品的畸变参数D成线性关系。     

La1-xCaxMnO3外延薄膜的制备、结构及磁电阻效应

采用溶胶-凝胶旋涂法在单晶LaAlO3 (100)基片上生长了La1-xCaxMnO3(x=0, 0.05, 0.1, 0.2)外延薄膜. 利用X射线衍射仪(XRD)、 原子力显微镜(AFM)、 聚焦离子束系统(FIB)、 X射线光电子能谱分析仪(XPS)、 振动样品磁强计(VSM)和磁性测量系统(MPMS)对样品的结构、 形貌、 价态、 居里温度和磁电阻效应进行了研究. 结果表明, 薄膜为立方钙钛矿结构, 具有明显的(100)外延生长取向和平整的表面. 在居里温度附近, 样品发生铁磁-顺磁转变. 随着Ca2+掺杂量的增加, 样品的居里温度升高, La0.8Ca0.2MnO3的居里温度为264 K. 随温度的变化, 样品发生了金属-绝缘体转变. 样品还具有较大的磁电阻效应, 在H=2.0 T, T=210 K时, La0.95Ca0.05MnO3的磁电阻达到80.9%.     

不同制备方法和反应条件对Fe_2O_3形貌和晶型转变的影响

研究了吸附相反应技术、浸渍法以及沉淀法制备Fe2O3的过程中,反应环境的变化对粒子形貌和晶型转变过程的影响。当吸附层是主要反应场所时,生成的粒子与SiO2表面以较强的化学键键合,焙烧过程中Fe2O3的晶型变化和粒子团聚被有效地抑制,焙烧后Fe2O3粒子维持稳定的γ-Fe2O3晶型和高分散的小粒子。而在乙醇体相中反应生成的粒子,仅通过物理作用与SiO2表面结合,不能有效抑制其向α-Fe2O3晶型的转变和粒子的团聚。吸附相反应制备过程中,当水量持续增加或者体系温度升高,反应环境逐渐从吸附层向乙醇体相中转变,SiO2对Fe2O3晶型转变的抑制作用减弱,从而导致样品中逐渐出现α-Fe2O3晶型。     

自组装DNA与[Co(phen)3]2+/3+相互作用的表面增强拉曼光谱法研究

对金基体上自组装ssDNA及dsDNA与钴邻菲啉配合物离子([Co(phen)3]2+/3+)相互作用进行电化学现场表面增强拉曼光谱(SERS)研究,获得相互作用位点及相互作用模式的信息.dsDNA与[Co(phen)3]2+/3+存在一定的嵌插作用,即配合物通过配体邻菲啉(phen)环以嵌插模式结合在碱基A-T及G-C富集区,同时与磷酸二酯键PO2结合,并伴随dsDNA螺旋构象由B型向A型转变;而[Co(phen)3]2+/3+则是以静电模式与ssDNA的磷酸二酯键PO2及脱氧核糖组成的骨架相互作用.     

焙烧温度和掺杂浓度对Ca1-xSmxWO4发光性能的影响

采用水热法制备了不同Sm~(3+)掺杂量和不同焙烧温度的CaWO_4:Sm~(3+)系列荧光粉。用X射线衍射仪(XRD)、扫描电镜(SEM and EDS)、荧光分光光度计(FL)、傅里叶变换红外光谱仪(FIIR)和HORIBA Fluoromax-4仪等手段对样品的组成、结构、形貌、发光性质和量子效率进行分析和表征。分析结果表明:所得产物都为白钨矿结构。在405 nm近紫外光激发下,产物的发射光谱都有3个主发射峰组成,分别位于566、606和650 nm处,归属于Sm3+的4G5/2→6HJ/2(J=5,7,9)跃迁。随着Sm~(3+)的物质的量分数的增加,样品发光强度先增强后减弱,当Sm~(3+)的物质的量分数为1%时发光强度达到最高。对实验数据进行分析确定了钐离子间的能量传递类型为离子交换作用;并计算了能量传递的临界距离为2.46 nm。     

衬底温度对Fe3N薄膜生长和磁性的影响

采用直流磁控溅射方法, 以Si(100) 单晶片为衬底, 在衬底温度为150～450 ℃的范围内得到了ε-Fe3N薄膜样品. 利用 XRD, SEM和VSM等表征手段, 研究了衬底温度对ε-Fe3N薄膜的生长和磁性的影响. 实验结果表明, 随着衬底温度的升高, 薄膜的生长速率、晶粒尺寸和单位质量磁化强度均增大, 而矫顽力呈现先增加后减小的变化趋势, 当衬底温度为350 ℃时, 矫顽力达到最大值18.72 kA/m, 可以认为此时薄膜样品的晶粒尺寸接近于交换作用长度.     

衬底温度对强流脉冲离子束烧蚀沉积类金刚石薄膜化学结构的影响

采用强流脉冲离子束(High-intensitypulsedionbeam,HIPIB)烧蚀技术在Si(100)基体上沉积类金刚石(Diamond-likecarbon,DLC)薄膜,衬底温度的变化范围为298～673K.利用Raman光谱和X射线光电子谱(XPS)对DLC薄膜的化学结合状态与衬底温度之间关系进行研究.薄膜XPS的C1s谱的解谱分析得出薄膜中含有sp³C(结合能为285.5eV)和sp²C(结合能为284.7eV)成分,根据解谱结果评价薄膜中sp³C含量.根据XPS分析可知,衬底温度低于473K时,sp³C的含量大约为40%左右;随着沉积薄膜时衬底温度的提高,sp³C的含量降低,由298K时的42.5%降到673K时的8.1%,从573K开始发生sp³C向sp²C转变.Raman光谱表明,随着衬底温度的提高,Raman谱中G峰的峰位靠近石墨峰位,G峰的半峰宽降低,D峰与G峰的强度比I_D/I_G增大,说明薄膜中的sp³C的含量随衬底温度增加而减少.     

Influence of the composition of BCN films deposited by reactive magnetron sputtering on their properties

Compounds of the B--C--N system are very promising to produce superhard coatings with good tribological, chemical, and thermal properties. To investigate the influence of the composition of BCN films on their properties, films with five different compositions at nearly constant nitrogen content were deposited on silicon wafers by magnetron sputtering from hexagonal boron nitride and graphite targets operated in RF and DC mode, respectively. The compositions and binding states of the films were determined by XPS. The nitrogen content was found to be almost constant for all films at about a 40 at-%, whereas boron and carbon compositions ranged between 15-35 and 25-50 at-%, respectively. The electronic and bonding structure of the coatings were analyzed by REELS using three different electron beam energies to obtain information at different depths. An increase of the carbon content of the films resulted in a significant shift of the pi-pi* interband transition with respect to the energy loss corresponding to h-BN. The absence of the pi-pi* transition in the energy loss spectra acquired at a beam energy of 1900 eV indicates the existence of a very thin overlayer mostly sp(2) bonded and probably with a distorted hexagonal structure. The position of the bulk plasmon losses corresponded to the hexagonal phase for the overlayer and presented a shift of more than 1.5 eV to the higher energy loss direction for the spectra obtained at 1900 eV beam energy. This shift and the absence of the sp(2)-bond fingerprint induced the possibility of an underlying disordered structure with a majority of sp(3) bonds.     

Changing Rules of Bonding Electron Pair Correlation Energies of CH3X （X = F, OH, NH2） Systems

1 INTRODUCTION It has been known that the electron correlation energy of molecular systems was, and still is, one of the most serious bottleneck problems to the chemis- try accuracy of computational quantum chemistry. Since L鰓din[1] gave the definition …     

Hydrogenated polycrystalline diamond films: Elastic and inelastic electron reflectivity

The microstructure and properties of carbon-based thin films depend on the deposition process and conditions used, including pressure, gas phase composition, and substrate temperature, as well as the energy of the reactive species (atoms or ions). For instance concerning diamond films, each method results in different type of films which may differ in terms of diamond grain size (from nano to micro), grain boundary nature, hydrogen content, defect density, amorphous or graphitic components, morphological properties and different chemical and physical properties. Among them, the well-known negative electron affinity, very attractive for the detection and emission of electrons, and high conductivity of diamond surfaces are properties of fully hydrogenated diamond surfaces. Similarly, diamond grain size may influence the electronic and optical properties of the films. More generally the chemical and physical characterization of the uppermost surface atomic layer of diamond films presents a great challenge.In this review we present results on hydrogen bonding configuration in hydrogenated polycrystalline diamond films of varying size (few nanometers up to micrometers) obtained by high resolution electron energy loss spectroscopy (HREELS). More precisely we will present energy loss spectra extended up to 800 meV, as well as elastic and inelastic reflectivity curves (associated to different vibrational modes of hydrogenated diamond surfaces), measured over the 3–18 eV electron energy range. We will show in particular that due to the specific features of diamond bulk electronic band structure, which is maintained up to the surface in the case of fully hydrogenated diamond, it is possible to extract from these data valuable information about the surface properties and composition such as diamond or graphitic like nature of the films, surface versus lattice nature of the vibrational modes.     

Effect of Ion Energy on Structure and Composition of Cathodic Arc Deposited Alumina Thin Films

The effect of energy supplied to the growing alumina film on the composition and structure has been investigated by varying substrate temperature and substrate bias potential. The constitution and composition were studied by X-ray diffraction and elastic recoil detection analysis, respectively. Increasing the substrate bias potential from −50 to −100 V caused the amorphous or weakly crystalline films to evolve into stoichiometric, crystalline films with a mixture of the α- and γ-phase above 700 ^oC, and γ-phase dominated films at temperatures as low as 200 ^oC. All films had a grain size of <10 nm. The combined constitution and grain size data is consistent with previous work stating that γ-alumina is thermodynamically stable at grain sizes <12 nm [McHale et al., Science 277, 788 (1997)]. In order to correlate phase formation with synthesis conditions, the plasma chemistry and ion energy distributions were measured at synthesis conditions. These results indicate that for a substrate bias potential of −50 V, ion energies in excess of 100 eV are attained, both from a high energy tail and the accelerated ions with charge >1. These results are of importance for an increased understanding of the evolution of film composition and microstructure, also providing a pathway to γ-alumina growth at temperatures as low as 200 ^o C.     

Synthesis, characterization, and photochemical and computational investigations of Ru(II) heterocyclic complexes containing 2,6-dimethylphenylisocyanide (CNx) ligand

The isocyanide ligand forms complexes with ruthenium(II) bis-bipyridine of the type [Ru(bpy)(2)(CNx)Cl](CF(3)SO(3)) (1), [Ru(bpy)(2)(CNx)(py)](PF(6))(2) (2), and [Ru(bpy)(2)(CNx)(2)](PF(6))(2) (3) (bpy = 2,2'-bipyridine, py = pyridine, and CNx = 2,6-dimethylphenylisocyanide). The redox potentials shift positively as the number of CNx ligands increases. The metal-to-ligand charge-transfer (MLCT) bands of the complexes are located at higher energy than 450 nm and blue shift in proportion to the number of CNx ligands. The complexes are not emissive at room temperature but exhibit intense structured emission bands at 77 K with emission lifetimes as high as 25 micros. Geometry optimization of the complexes in the singlet ground and lowest-lying triplet states performed using density functional theory (DFT) provides information about the orbital heritage and correlates with X-ray and electrochemical results. The lowest-lying triplet-state energies correlate well with the 77 K emission energies for the three complexes. Singlet excited states calculated in ethanol using time-dependent density functional theory (TDDFT) and the conductor-like polarizable continuum model (CPCM) provide information that correlates favorably with the experimental absorption spectra in ethanol.     

A comparative first-principles study of orbital hybridization in two-dimensional C, Si, and Ge

Information on orbital hybridization is very important to understand the structural, physical, and chemical properties of a material. Results of a comparative first-principles study on the behaviours of orbital hybridization in the two-dimensional single-element phases by carbon, silicon, and germanium are presented. From the well-known three-dimensional hexagonal lonsdaleite structure, in which the atoms are in ideal sp(3)-bonding, the layer spacing along c-axis is gradually stretched to simulate the evolutions of structural and electronic properties from three-dimensional to two-dimensional lattice configurations in the three materials. A turning point of the total system energy due to the sp(3) to sp(2) transition is observed during this process in carbon. In contrast, no such phenomenon is found in silicon and germanium. The differences in electronic structure and bonding behaviour are further examined through comparative investigation of atomic angular-momentum projected density of states and electronic energy band spectrums of these materials. We demonstrate that the valence electronic orbital in the two-dimensional hexagonal crystals of Si and Ge shows sp(3)-like behaviour for the partial hybridization of s and p(z), which leads to their different lattice configurations to graphene. The role of π-bonds in stabilizing the flat configuration of graphene is also discussed.     

Theoretical studies on the structure and aromaticity of Ti2P6+

Cationic cluster Ti2P6+ has been studied within density functional theory. The structure of this cluster is predicted to be a slightly distorted tetragonal prism. The dissociation energy of this cationic cluster is higher than that of the known sandwich compound, [(P5)2Ti]2-, because of the different bonding in these two compounds. In Ti2P6+, the hybridization of P atoms of the ring is sp3. The bonding between the metal atoms and the P ring is mainly sigma-pi. While in [(P5)2Ti]2-, the P atoms take sp2 hybridization, the bonding between the metal atom and the rings is the typical pi-pi interaction. The electronic delocalization is another stabilizing factor for Ti2P6+. The nuclear independent chemical shift indicates that Ti2P6+ is a three-dimensional aromatic molecule. The predicted infrared and NMR help to identify the Ti2P6+ conformations in experiment.     

Chemical functionalization of carbon nanotubes by carboxyl groups on stone-wales defects: a density functional theory study

Chemical functionalization of carbon nanotubes with Stone-Wales (SW) defects by carboxyl (COOH) groups is investigated by density functional calculations. Due to the localized donor states induced by the SW defect, the binding of the COOH group with the defective carbon nanotube is stronger than that with the perfect one. A quasi-tetrahedral bonding configuration of carbon atoms, indicating sp3 hybrid bonding, is formed in the adsorption site. The charge distribution analysis shows that, in comparison with benzoic acid, the localized or delocalized pi states on the nanotube would affect the polarities of chemical bonds of the COOH group without losing the acidity. Furthermore, it is found that the double-adsorption system (two COOH groups are respectively adsorbed on two individual carbon atoms of the SW defect) is more energetically favorable than the monoadsorption one. The adsorption of COOH groups leads to a significant change of the electronic states around the Fermi level, which is advantageous for the electrical conductivity. The functionalization by introducing functional groups on the topological defects provides a pathway for applications of carbon nanotubes in chemical sensors and nanobioelectronics.