TiN_(12)团簇的制备研究

以高纯氮气为载气,通过532nm的激光轰击由Ti、BN粉末混合压制成的样品,生成了钛氮团簇,确定了最稳定钛氮团簇的组成为TiN12。以四氟化钛和三甲基叠氮硅烷为原料,在液氮冷却下开展了钛氮团簇的化学法合成,对所得产物进行了IR、NMR表征,确定其结构为Ti(N3)4。用密度泛函理论(DFT)对TiN12的结构进行了优化,发现存在一种Ti(N3)4形式的具有对称的正四面体结构的稳定构型,这与化学法合成的TiN12的IR和NMR谱相符。不过,仍需进一步确定激光轰击法和化学合成法产生的TiN12是否具有相似的结构。     

激光溅射法生成金属掺杂氮原子团簇CuNn 、ZnNn 和ScNn

以高纯氮气为载气,通过激光分别轰击Cu/BN、Zn/BN和Sc/BN压制成的样品,首次生成了相应团簇CuNn 、ZnNn 和ScNn ,得到了团簇质谱图,确定了CuNn 、ZnNn 和ScNn 团簇中最稳定的组成分别为CuN4 、ZnN6 和ScN12 。     

锰/磷、钛/磷二元团簇的激光溅射产生与光解

利用激光溅射法直接产生了锰/磷、钛/磷二元团簇正、负离子MxPy±(M=Mn、Ti),并用串级飞行时间质谱仪研究了团簇离子的组成与激光光解规律.实验表明钛与磷间成簇的能力强于锰与磷间成簇的能力,且MPy+(M=Ti、Mn)团簇离子系列表现出峰强度随所含磷原子数目的奇偶性变化,这可能与P4结构的特殊稳定性有关.激光光解实验表明,失去中性P2、P4的通道为主要光解通道.随着团簇离子的生长,锰/磷团簇正离子逐渐由富磷簇向富金属簇过渡,钛/磷则趋向于形成钛原子数目与磷原子数目接近相等的团簇正离子,而二者与磷形成的团簇负离子MxPy-(M=Mn、Ti)逐渐趋向于x≈y,随样品中磷含量增加,锰/磷易形成富磷簇,钛/磷的组成趋向不改变.     

激光溅射法生成金属掺杂氮团簇CuN_n~+、ZnN_n~+和ScN_n~+

以高纯氮气为载气,通过激光分别轰击Cu/BN、Zn/BN和Sc/BN压制成的样品,首次生成了相应团簇CuN_n~+、ZnN_n~+和ScN_n~+,得到了团簇的质谱图,确定了CuN_n~+、ZnN_n~+和ScN_n~+团簇中最稳定的组成分别为CuN_4~+、ZnN_6~+和ScN_(12)~+。     

C24和B12N12团簇的结构与稳定性

本文采用量子化学密度泛函理论的B3LYP/6-31G*方法,对C24和B12N12团簇的12种异构体进行了优化,并对它们的几何构型、振动频率、核独立化学位移(NICS)和结合能进行了理论探讨, 比较了C24和B12N12团簇结构的稳定性。研究表明:C24团簇的最稳定几何构型为类石墨结构d,B12N12团簇的最稳定结构为4/6笼状结构g。C24异构体的稳定性大小顺序为d > b > f > c > a > e。B12N12团簇异构体稳定性大小顺序为a > f> c> d > e >b。     

碱土金属叠氮化合物(MgN_6)_n(n=1～5)团簇结构与性质的密度泛函理论研究

利用密度泛函理论在B3LYP/6-311G*水平上对碱土金属叠氮化合物(MgN6)n(n=1～5)团簇各种可能构型进行了几何优化,预测了各团簇的最稳定结构。并对最稳定结构的成键特性、电荷分布、振动特性及稳定性进行理论研究。结果表明,叠氮化合物中叠氮基以直线型存在,MgN6团簇最稳定结构为直线型;(MgN6)2团簇最稳定结构为Mg2N2四元环平面结构;(MgN6)n(n=3～5)团簇最稳定结构是由2个叠氮基与2个Mg原子首先构成近似菱形,再由近似菱形延伸形成的链状结构。叠氮基中间的N原子显示正电性,两端的N原子显示负电性,且与Mg直接作用的N原子负电性更强,金属Mg原子和N原子之间形成很强的离子键。(MgN6)n(n=1～5)团簇最稳定结构的IR光谱分为4个部分,其最强振动峰均位于2209～2313cm-1,振动模式为叠氮基中N-N键的反对称伸缩振动。稳定性分析显示,(MgN6)3和(MgN6)5团簇相对于其他团簇较为稳定。     

1,5-苯并二氮杂的合成及其生物活性研究

采用两种方法: 以三氧化铝为载体邻苯二胺与查尔酮为原料的无溶剂合成法和以PPA(多聚磷酸)为催化剂邻苯二胺与苯乙酮的一锅合成法, 合成了1,5-苯并二氮杂, 产物收率为53.7%～74.5%. 通过¹H NMR, ¹³C NMR, MS, IR, 元素分析等手段对所合成的化合物进行了结构确定, 并测试了它们对菌和乙酰胆碱酶的抑制活性.     

(4S)-4-羧基杂氮硅三环的合成

利用L-N, N-双(β-羟乙基)丝氨酸及L-N, N-双(β-羟乙基)苏氨酸与三乙氧基硅烷或氯烷基三乙氧基硅烷反应合成了具有手性的(4S)-4-羧基杂氮硅三环(1-5), 并运用IR, 1H NMR, EI-MS等手段表征了结构。证据显示存在着贯穿笼状结构的N→Si配键。     

(HCaN3)n (n＝1～5)团簇结构与性质的密度泛函理论研究

利用密度泛函理论在B3LYP/6-311G*水平上对叠氮化合物(HCaN₃)_n (n＝1～5)团簇各种可能构型进行了几何优化, 预测了各团簇的最稳定结构. 并对最稳定结构的成键特性、电荷分布、振动特性及稳定性进行理论研究. 结果表明, HCaN₃团簇最稳定结构为折线型, (HCaN₃)_n (n＝2～4)团簇最稳定结构为叠氮基端位N原子与Ca原子相互链接形成平面环状结构, (HCaN₃)₅团簇最稳定结构为立体钟形结构. 团簇最稳定结构中金属Ca原子均显示正电性, H原子均显示负电性, 叠氮基中间的N原子显示正电性, 叠氮基两端的N原子显示负电性, 且和Ca原子直接作用的N原子的负电性更强. Ca-N键和Ca-H键为典型的离子键, 叠氮基内N原子之间是共价键. 最稳定结构的IR光谱主要分为3个部分, 其最强振动峰均位于2193～2302 cm^－1段, 振动模式为叠氮基中N-N键的反对称伸缩振动. 叠氮基在团簇和晶体中结构不变, 始终以直线型存在, 说明金属叠氮化合物团簇可以很好地模拟其晶体的局域成键和局域电荷转移等特性. 稳定性分析显示, (HCaN₃)₃团簇相对于其他团簇更稳定.     

(Mg3N2)n(n=1～4)团簇结构与性质的密度泛函研究

用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G*基组水平上对(Mg3N2)n(n=1～4)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.并对最稳定结构的振动特性、成键特性、电荷特性和稳定性等进行了理论分析.结果表明:(Mg3N2)n=1～4团簇易形成笼状结构,其最稳定构型中N原子配位数以3、4较多见;团簇主要由Mg-N键组成,Mg-N键长为0.194～0.218nm,Mg-Mg 键长为0.262～0.298 nm;N原子的平均自然电荷为-2.06 e,Mg原子的平均自然电荷为 1.37 e;(Mg3N2)2团簇有相对较高的动力学稳定性.     

Theoretical Study on the Electronic Structures of Small TinNm （n ＋ m = 5, 6） Clusters

45 isomers of TinNm （n ＋ m = 5, 6） clusters, including linear, some planar and some stero configurations, have been predicted by density functional theory method. For five-atom clusters Ti3N2 and Ti2N3, the most stable structures are trigonal bipyramid in D3h symmetry, and for TiaN cluster, the isomer with one nitrogen atom occupying the center of quasi-tetrahedron is the most stable. In the isomers of Ti4N2 and Ti3N3, the planar networks are more stable, but for Ti2N4, the six-membered ring configuration is the most favorable. Most linear structures can form weak-strong bonds alternately with higher energy. As regards to planar structures, the more Ti-N bonds are formed, the more stable they will be; for stero closed polyhedral isomers, their energies are lower.     

Reactivity of titanium dimer and molecular nitrogen in rare gas matrices. Vibrational and electronic spectra and structure of Ti2N2

The reactivity of diatomic titanium with molecular nitrogen has been investigated in rare gas matrices. The formation of Ti2N2 from the condensation of effusive beams of Ti and N2 in neon and argon matrices is observed after sample deposition. Our results also show that the in situ formation results from the spontaneous reaction at 9 K of ground state Ti2 with N2. Several low-lying excited states of Ti2N2 are also observed between 0.78 and 1.1 eV above the ground state, leading to a complex sequence of interacting vibronic transitions, merging into a broad continuum above 1.25 eV. Observations of Ti2(14)N2, Ti2(15)N2 and Ti2(14)N(15)N isotopic data enable the determination of all fundamental vibrations in the ground electronic state. Semi-empirical harmonic potential calculations lead to estimates of 3.22 N cm(-1) for the Ti-N bond force constant and 90 +/- 5 degrees for the bond angles. Comparisons with TiN diatomic data suggest a near square-planar structure with 175 +/- 3 pm TiN bond distance. Quantum chemical calculations at various levels indicate a 1A(g) ground state with a Ti-N distance close to 180 pm and 89 degrees for the NTiN bond angle, and give fundamental frequencies in excellent agreement with the experimentally observed values. Further MRCI calculations on all low-lying states enable an interpretation of the complex electronic spectrum in the NIR region.     

氮化钛纳米线的结构特征及其对Ⅴ(Ⅱ)/Ⅴ(Ⅲ)的电极过程

Titanium nitride nanowires (TiN NWs) were directly prepared on a Ti foil by a hydrothermal method followed by nitridation in ammonia atmosphere. The composition, microstructure, and electrochemical properties of the TiN NWs were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry(CV), and electrochemical impedance spectroscopy (EIS). The results show that the nanowires have diameters of 20-50 nm and are 5 μm long. The surfaces of the TiN NWs comprise Ti-N, Ti-O, and O-Ti-N chemical states. The electrochemical activity and reversibility for the electrode processes of Ⅴ(Ⅱ)/Ⅴ(Ⅲ) couple on the TiN NWs are significantly improved due to the introduced Ti-N, Ti-O, and O-Ti-N chemical states. The transfer resistance for the cathodic reduction of Ⅴ(Ⅲ) on the TiN NWs is about 20 times and 10 times smaller than on TiO₂ NWs and graphite electrodes, respectively. The rate constant of charge transfer on the TiN NWs electrode was determined to be 5.21×10^-4 cm·s_-1, which is about 5 times larger than the rate constant on graphite electrodes (9.63×10^-5 cm·s^-1).     

N4+的生成与检测

用从Nd:YAG激光器发出的波长532nm的激光(能量约为10mJ/pulse)溅射由BN、ZrN粉末分别压成的直径13mm、厚度约2～5mm的固体压片样品,生成了含氮团簇N4+。实验中,用高纯氮气为载气,辅助含氮团簇的生成并冷却激光溅射所产生的团簇。反射式飞行时间质谱仪监测反应过程证实N4+的存在,且其存在时间超过200μs。     

Small cluster models of the surface electronic structure and bonding properties of titanium carbide, vanadium carbide, and titanium nitride

Density functional theory (DFT) calculations on stoichiometric, high-symmetry clusters have been performed to model the (100) and (111) surface electronic structure and bonding properties of titanium carbide (TiC), vanadium carbide (VC), and titanium nitride (TiN). The interactions of ideal surface sites on these clusters with three adsorbates, carbon monoxide, ammonia, and the oxygen atom, have been pursued theoretically to compare with experimental studies. New experimental results using valence band photoemission of the interaction of O(2) with TiC and VC are presented, and comparisons to previously published experimental studies of CO and NH(3) chemistry are provided. In general, we find that the electronic structure of the bare clusters is entirely consistent with published valence band photoemission work and with straightforward molecular orbital theory. Specifically, V(9)C(9) and Ti(9)N(9) clusters used to model the nonpolar (100) surface possess nine electrons in virtually pure metal 3d orbitals, while Ti(9)C(9) has no occupation of similar orbitals. The covalent mixing of the valence bonding levels for both VC and TiC is very high, containing virtually 50% carbon and 50% metal character. As expected, the predicted mixing for the Ti(9)N(9) cluster is somewhat less. The Ti(8)C(8) and Ti(13)C(13) clusters used to model the TiC(111) surface accurately predict the presence of Ti 3d-based surface states in the region of the highest occupied levels. The bonding of the adsorbate species depends critically on the unique electronic structure features present in the three different materials. CO bonds more strongly with the V(9)C(9) and Ti(9)N(9) clusters than with Ti(9)C(9) as the added metal electron density enables an important pi-back-bonding interaction, as has been observed experimentally. NH(3) bonding with Ti(9)N(9) is predicted to be somewhat enhanced relative to VC and TiC due to greater Coulombic interactions on the nitride. Finally, the interaction with oxygen is predicted to be stronger with the carbon atom of Ti(9)C(9) and with the metal atom for both V(9)C(9) and Ti(9)N(9). In sum, these results are consistent with labeling TiC(100) as effectively having a d(0) electron configuration, while VC- and TiN(100) can be considered to be d(1) species to explain surface chemical properties.     

Oxidation Behaviour of PACVD-(Ti,Al)N Wear Resistance Layers

 Sputtered (Ti,Al)N hard coatings are successfully used for dry high speed cutting. These films show a lower oxidation rate than TiN or TiC coatings. In our work (Ti,Al)N films were deposited on WC-6%Co substrates at a temperature of 490°C by plasma-assisted chemical vapour deposition (PACVD) using a gas mixture of TiCl₄/AlCl₃/N₂/Ar/H₂. Investigation of microstructure, crystalline structure and chemical composition was carried out using SEM, WDXS, TEM, AES and XRD techniques. The chemical composition of the deposited films showed a Al to Ti ratio of 1.33. The film thickness was 5.5 μm. Films showed a fine crystalline size, the metastable fcc crystal structure and a columnar growth. The film surface was under low compressive stress up to several 100 MPa. For (Ti,Al)N/WC-Co compounds the oxidation behaviour up to 1100°C (high temperature range) was studied. Therefore, samples were annealed or rapidly heated in air and under high vacuum condition using the laser shock method. The results show decomposition of the (Ti,Al)N structure to the TiN and the AlN phases at temperature values above 900°C. Heating in air causes growing of a thin aluminum oxide layer at the film surface, which is a barrier for further oxygen diffusion to the alumina-film boundary. Additionally, at temperatures above 900°C oxidation of the WC-6%Co substrate surface was obtained in regions of opened cracks and film delamination.     

Optical spectra and structure of CdP4 nanoclusters fabricated by incorporation into zeolite and laser ablation

CdP(4) nanoclusters were fabricated by incorporation into the pores of zeolite Na-X and by deposition of the clusters onto a quartz substrate using the laser ablation-evaporation technique. Absorption and photoluminescence (PL) spectra of CdP(4) nanoclusters in zeolite were measured at temperatures 4.2, 77, and 293 K. Both absorption and PL spectra consist of two blue-shifted bands. We performed DFT calculations to determine the most stable clusters configuration in the size region up to the size of the zeolite Na-X supercage. The bands observed in absorption and PL spectra were attributed to the emission of (CdP(4))(3) and (CdP(4))(4) clusters with binding energies of 3.78 and 4.37 eV per atom, respectively. The Raman spectrum of CdP(4) clusters in zeolite proved the fact of creation of (CdP(4))(3) and (CdP(4))(4) clusters in zeolite pores. The PL spectrum of CdP(4) clusters produced by laser ablation consists of a single band that was attributed to the emission of the (CdP(4))(4) cluster.     

铅、硫团簇的形成、反应与光解

用激光直接溅射和串级溅射两种方法产生铅／硫二元团簇,并用串级飞行时间质谱仪研究了二元团簇的组份及光解规律,用激光直接溅射铜＋硫混合样品时,组成为PbnSn-1 和PbnSn-的团簇丰度最大,是二元团簇的结构骨架和稳定组份,而用激光串级溅射铅样品和硫样品,通过铅团簇与硫团簇的反应,则可得到PbnSm (n=1-3,m=0-9)和PbnSm-(n=1-7,m=0-9)。这两种二元团簇的产生方法对应两种不同的团簇形成机理。     

Photoelectron spectroscopic and theoretical study of aromatics-Pb(m) anionic complexes (aromatics = C6H5, C5H4N, C4H3O, and C4H4N; m = 1-4): a comparative study

The reactions between lead vapored by laser ablation and different aromatic molecules (C6H6, C5H5N, C4H4O, or C4H5N) seeded in argon carrier gas were studied by a reflectron time-of-flight mass spectrometer (RTOF-MS) with a photoelectron spectrometer. The adiabatic electron affinities (EAs) of the dominant anionic products PbmC6H5(-), Pb(m)C5H4N(-) (m = 1-4) and Pb(m)C4H3 (-), Pb(m)C4H4N(-) (m = 1-3) dehydrogenated complexes are obtained from the photoelectron spectra with 308 and 193 nm photon, respectively. It is found that the EAs of Pb(m)C4H4N are higher than those of Pb(m)C6H5, Pb(m)C5H4N, and Pb(m)C4H3O with the same metal number m. The possible structures for Pb(m)C4H4N(-) complexes were calculated with density functional theory (DFT) and the most stable structure was confirmed. The adiabatic detachment energies for the most stable structure were in agreement with the experimental PES results. The calculated density of state (DOS) agrees with the experimental PES spectrum well. It was confirmed by the theoretical calculations that the C4H4N group bonds on lead clusters through the Pb-N sigma bond.     

First‐principles study of the TiN(111)/ZrN(111) interface

The TiN(111)/ZrN(111) interface was studied by first‐principles method to provide the theoretical basis for developing the TiN/ZrN coatings. Twelve geometry structures of TiN(111)/ZrN(111) interfaces were established. The calculated interfacial work of adhesion reveals that the N‐terminated TiN/N‐terminated ZrN interface with TL site shows the strongest stability. For this TiN(111)/ZrN(111) interface, the results of the partial density of state indicate that the chemical bonding at the interface appeals both ionic and covalent characteristic, which is same as that in the bulk materials. The partial density of states for Zr, Ti, and N atoms at the interface are very similar with those in the bulk, which reveals that the electronic structure transition at the interface is smooth. The results of charge density and charge density difference demonstrate that the lost charge of Ti atom is larger than that of Zr atom, indicating that TiN is more ionic than ZrN. Calculations of the work of fracture indicate that the mechanical failure of the ZrN(111)/TiN(111) interface will take place at the interface. Besides that, the calculation result of the TiN(111)/ZrN(111) interface implies that the TiZrN₂ phase might be formed at the interface because the contacting of the N―N bond is the most stable.