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1.
Controlled coammonolysis of elementalkylamides in aprotic organic solvents at low temperatures have been shown to result in the formation of polyazanes. The synthetic procedure developed may be addressed as “sol‐gel‐route in the ammono system”. Pyrolysis of these novel polymer precursors gave access to multinary nitrides. For the model systems Si(NHMe) 4/B(NMe 2) 3, Si(NHMe) 4/Ti(NMe 2) 4, and Si(NHMe) 4/Ta(NMe 2) 5 polymeric boro‐, titano and tantalosilazanes were obtained. Pyrolysis in ammonia at 1000 °C yielded amorphous silicon boron nitride, silicon titanium nitride and silicon tantalum nitride powders; further heating of the nitride powders at 1500 °C in nitrogen atmosphere led to the formation of partly crystalline composites of α‐Si 3N 4 and amorphous silicon boron nitride for the Si/B/N system, a composite of finely dispersed TiN and amorphous silicon titanium nitride for the Si/Ti/N system, and crystalline TaN and amorphous silicon nitride for the Si/Ta/N system. Furthermore, the structure and pyrolysis chemistry of the polymeric intermediates, as well as the morphology of the pyrolysis products, were studied by NMR, MAS‐NMR, FT‐IR, DTA‐TG‐MS, XRD, SEM, EDX and elemental analyses. 相似文献
2.
The effect of substrate temperature and N2/Ar flow ratio on the stoichiometry, structure and hardness of TaN x coatings prepared on (111) Si substrates by DC reactive sputtering was investigated. For the structural, chemical and morphological analysis, X‐ray diffraction (XRD), Auger electron scanning and atomic force microscopy were respectively used. Hardness values of thin films were determined using the work of indentation model from nanoindentation measurements. TaN stoichiometric coatings were obtained for samples deposited at room temperature. The stoichiometric TaN phase was not obtained by increasing the temperature up to 773 K, even when increasing the N 2/Ar flow ratio. Even when a saturation in nitrogen content was achieved, nitrogen vacancies are still present in those samples. For coatings prepared at 773 K and low N 2/Ar flow ratio, a phase mixture between TaN x and cubic α‐Ta was observed, while a cubic structure δ‐TaN was formed by increasing the N 2/Ar flow ratio. A maximum in hardness and (38 GPa) was obtained for the sample deposited at 773 K and a N 2/Ar flow ratio of 0.2, which presented a δ‐TaN cubic crystalline structure and a roughness value of 1.6 nm. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
A mixture of Ta and 25 mass% Cu elemental powders was subjected to mechanical alloying in a high-energy ball mill up to 60 h. The results are composite particles formed by nanocrystalline Cu and amorphous Ta phases. Thermal stability of amorphous was investigated by DSC. The XRD, FTIR and EDX analyses of Ta–25 mass% Cu powder milled for 60 h performed after DSC at 800 and 900 °C have revealed large amounts of Ta nitride and Ta oxides even though the milling process was done in Ar atmosphere. This is due to high reactivity of Ta fine particles with oxygen and nitrogen from air. During manipulations of the powder (taking samples from vials and its investigation), the adsorption phenomena on its surface occur, and both surface-adsorbed N2 and O2 are processed with powder and embedded in it. While heating of Ta–25% Cu milled powder in DSC, nitrogen and oxygen diffusion into tantalum is activated, and Ta2N and TaO2/Ta2O5 compound forms. 相似文献
4.
The nitrogen content in tantalum nitride (TaN x) thin films, where x indicates that TaN x is not generally stoechiometric, can be measured directly by XPS. This is the purpose of the present study. However, the XPS spectra of TaN x present electron energy loss spectroscopy (EELS) peaks that lead to a complex peak fitting, particularly for self‐passivated thin films. A complete peak fitting procedure based upon Tougaard's background, the Doniach‐Sunjic Function and EELS peaks, is presented. It is applied to two self‐passivated TaN x thin films elaborated by reactive sputtering and presenting a different nitrogen content. The physical properties of these surfaces are interpreted in terms of Ta 4f 7/2 chemical states directly dependent on the nitrogen content. The main results are discussed and improvements are proposed to the method. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
5.
Na 0.74Ta 3O 6, a Low‐Valent Oxotantalate with Multiple Ta–Ta Bonds The title compound was prepared in a sealed tantalum tube through the reaction of Ta 2O 5, tantalum and Na 2CO 3 in a NaCl flux at 1570 K within 5 d. The crystal structure of Na 0.74Ta 3O 6 (a = 713.5(1), b = 1027.4(2), c = 639.9(1) pm, Immm, Z = 4) was determined by single crystal X‐ray means. The structure is isomorphous with NaNb 3O 5F [1]. The characteristic structural units are triply bonded Ta1 2 dumb‐bells with eight square‐prismatically co‐ordinated O ligands. Four Ta2, each octahedrally surrounded by O atoms, are side‐on bonded weakly to the binuclear Ta 2O 8 complex, thus forming a Ta 6 propellane‐like cluster. The lattice parameters of three additional M xTa 3O 6 phases, M = Li, Mn, and Yb, are reported. 相似文献
6.
The direct fluorination of intimately mixed niobium and tantalum powders gives a range of mixed‐metal pentafluorides [Nb xTa 4‐xF 20] (x = 1 2 , 2 3 , 3 4 ) as discreet species isostructural with tantalum pentafluoride (x = 0 1 ). The crystal structures of 1–4 are indistinguishable by X‐ray crystallography. Complex 1 crystallizes in the monoclinic space group C2/m with a = 9.5462(13), b = 14.3578(19), c = 5.0174(7) Å, β = 97.086(2)°, Z = 2. The geometry about the tantalum atom is distorted octahedral with 2 short and 2 slightly longer Ta‐F terminal, and 2 Ta‐F bridging distances. The angles at the bridging fluorine atoms are 172.9(5)°. 相似文献
7.
Adsorption and activation of dinitrogen (N 2) is an indispensable process in nitrogen fixation. Metal nitride species continue to attract attention as a promising catalyst for ammonia synthesis. However, the detailed mechanisms at a molecular level between reactive nitride species and N 2 remain unclear at elevated temperature, which is important to understand the temperature effect and narrow the gap between the gas phase system and condensed phase system. Herein, the 14N/ 15N isotopic exchange in the reaction between tantalum nitride cluster anions Ta 314N 3- and 15N 2 leading to the regeneration of 14N 2/ 14N 15N was observed at elevated temperature (393-593 K) using mass spectrometry. With the aid of theoretical calculations, the exchange mechanism and the effect of temperature to promote the dissociation of N 2 on Ta3N3? were elucidated. A comparison experiment for Ta 314N 4-/ 15N 2 couple indicated that only desorption of 15N 2 from Ta 314N 415N 2- took place at elevated temperature. The different exchange behavior can be well understood by the fact that nitrogen vacancy is a requisite for the dinitrogen activation over metal nitride species. This study may shed light on understanding the role of nitrogen vacancy in nitride species for ammonia synthesis and provide clues in designing effective catalysts for nitrogen fixation. 相似文献
8.
TaON and Ta 3N 5 thin films of different thicknesses were prepared by pulsed laser deposition of tantalum oxide followed by ex situ thermal nitridation under ammonia. The nitridation was carried out in flowing gas in the 600–800 °C temperature range. The dependence of tantalum oxynitride and nitride crystalline phases formation on nitridation reaction parameters was investigated. Structural and microstructural characteristics were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). 相似文献
9.
Synthesis, Structure, and Properties of the Tantalum‐rich Silicide Chalcogenides Ta 15Si 2Q xTe 10–x (Q = S, Se) The quaternary tantalum silicide chalcogenides Ta 15Si 2Q xTe 10–x (Q = S, Se) are accessible from proper, compacted mixtures of the respective dichalcogenides, silicon and elemental tantalum at 1770 K in sealed molybdenum tubes. The structures were determined from the strongest X‐ray intensities of fibrous crystals with cross sections of about 3 μm and confirmed by fitting the profile of single phase X‐ray diffractograms. The phases Ta 15Si 2S 3.5Te 6.5 and Ta 15Si 2Se 3.5Te 6.5 crystallize in the monoclinic space group C2/m with two formula units per unit cell, a = 2393.7(1) pm, b = 350.08(2) pm, c = 1601.2(1) pm, β = 124.700(4)°, and a = 2461.3(2) pm, b = 351.70(2) pm, c = 1601.7(1) pm, β = 124.363(5)°, respectively. Tri‐capped trigonal prismatic Ta 9Si clusters stabilized by encapsulated Si atoms can be seen as the characteristic unit of the structure. The clusters are fused into twin columns which are connected by additional Ta atoms, thus forming corrugated layers. The remaining valences at the surfaces of the layered Ta–Si substructure are saturated by those of chalcogen atoms which are coordinated only from one side by three, four or five Ta atoms. Few bridging covalent Ta–S–Ta and Ta–Se–Ta bonds and, otherwise, dispersive interactions between the Q atoms hold these nearly one nanometer wide slabs together. The phases are moderate metallic conductors. There is no evidence for any electronic instability within 10–310 K in spite of the high anisotropy of the structures. 相似文献
10.
Treatment of tetraethylammonium hexacarbonyltantalate, [Et 4N][Ta(CO) 6], with 1.1 equivalents of molecular iodine (I 2) in tetrahydrofuran (THF) at 200 K, followed by the addition of 6.0 equivalents of 2,6‐diisopropylphenyl isocyanide (CNDipp) and slow warming to 293 K over a 24 h period gave the tantalum(I) iodide derivative hexakis(2,6‐diisopropylphenyl isocyanide‐κ C)iodidotantalum(I), [TaI(C 13H 17N) 6] or TaI(CNDipp) 6, 1 . Recrystallization of this substance from pentane provided deep‐red nearly black parallelepipeds of the product, which was characterized by single‐crystal X‐ray diffraction. Addition of 1 in THF at 200 K to a suspension of an excess (5.8 equivalents) of caesium graphite (CsC 8), followed by warming, filtration, and solvent removal, afforded a dark‐green oily solid of unknown composition, from which several red–brown rhombohedral plates of the ditantalum salt heptakis(2,6‐diisopropylphenyl isocyanide‐κ C)tantalum hexakis(2,6‐diisopropylphenyl isocyanide‐κ C)tantalate, [Ta(C 13H 17N) 7][Ta(C 13H 17N) 6] or [Ta(CNDipp) 7][Ta(CNDipp) 6], 2 , were harvested. Salt 2 is a unique substance, as it is the only known example of a salt containing a homoleptic cation, [ MLx] +, and a homoleptic anion, [ MLy] ?, with the same transition metal and π‐acceptor ligand L. In solution, 2 undergoes full comproportionation to afford the recently reported 17‐electron paramagnetic zerovalent tantalum complex Ta(CNDipp) 6, the only known isolable Ta L6 complex of Ta 0. 相似文献
11.
Summary We prepared thin films of tantalum oxide on SiO 2/Si substrates by thermal oxidation of tantalum. The different oxide layers and their interfaces were characterized by SIMS, AES, and XPS. Characteristic structures were obtained after different oxidation procedures. The comparative discussion of AES and SIMS depth profiles makes possible an unequivocal characterization of the reactive interfaces between the oxides of Ta and Si. The Ta 2O 5/SiO 2 interface in particular shows non-stoichiometries which depend on the oxidation procedures and which determine the performance characteristics of pH-sensitive Ta 2O 5 field-effect transistors.
Tiefenprofile von Ta2O3/SiO2/Si-Strukturen: Eine kombinierte Untersuchung mit Röntgen-Photoemissions-, Auger-Elektronen- und Sekundär-Ionen-Massen-Spektrometrie 相似文献
12.
N-doped NaTaO 3 catalysts were synthesized via a sol–gel method followed by a subsequent calcination process under NH 3 atmosphere. The as prepared samples were characterized by XPS, XRD, UV–Vis DRS, and BET analyses. All XRD peaks of the sample calcined at 900 °C matched with pure perovskite NaTaO 3 while peaks of TaON and Na 2Ta 4O 11 were found for that calcined at 1,000 °C. The DRS of samples shown cutoff edge has red shifted, from 315 nm of pure to 391 nm of N-doped NaTaO 3. N-doping helps to narrow the band gap, and the prepared sample was visible light sensitive. The XPS spectrum of Ta4 p3&N1 s shown two new peaks at 398.3 and 401.4 eV appear in the N-doped sample corresponding to Ta–N bonds and adsorption nitride, respectively. Photocatalytic activity of the catalysts was evaluated using Rhodamine B dye. The result demonstrated that the sample calcined under NH 3 had a higher photocatalytic activity than that of P25 under visible light. The NaTaO 3/TaON heterojunction played an important role on promoting photoactivity. 相似文献
13.
We demonstrate the utilization of parallel angle-resolved X-ray photoelectron spectroscopy (pAR-XPS) as a useful tool to analyze ultrathin sputtered tantalum nitride (TaN) thin films in complementary metal-oxide-semiconductor (CMOS) trenches. The chemical composition of TaN was estimated by pAR-XPS using a Theta 300i from Thermo Fischer. An improved lateral resolution was achieved by analyzing periodic structures. The XPS data was correlated with transmission electron microscopy (TEM) in combination with energy-dispersive X-ray spectroscopy (EDX) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) data. The results show that the nitrogen content in the TaN thin films was about 6% higher at the sidewall compared with the top and bottom of the trench. 相似文献
14.
Hexakis(2,6‐diisopropylphenylisocyanide)tantalum is the first isocyanide analogue of the highly unstable Ta(CO) 6 and represents the only well‐defined zerovalent tantalum complex to be prepared by conventional laboratory methods. Two prior examples of homoleptic Ta 0 complexes are known, Ta(benzene) 2 and Ta(dmpe) 3, dmpe=1,2‐bis(dimethylphosphano)ethane, but these have only been accessed via ligand co‐condensation with tantalum vapor in a sophisticated metal‐atom reactor. Consistent with its 17‐electron nature, Ta(CNDipp) 6 undergoes facile one‐electron oxidation, reduction, or disproportionation reactions. In this sense, it qualitatively resembles V(CO) 6, the only paramagnetic homoleptic metal carbonyl isolable under ambient conditions. 相似文献
15.
Nanocrystalline zirconium carbonitride (Zr‐C‐N) and zirconium oxide (ZrO 2) films were deposited by chemical vapor deposition (CVD) of zirconium‐ tetrakis‐diethylamide (Zr(NEt 2) 4) and ‐ tert‐butyloxide (Zr(OBu t) 4), respectively. The films were deposited on iron substrates and characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS). The Zr‐C‐N films show blue, golden brown or bronze colours, with colour stability depending upon the precursor composition (pure metal amide or mixed with Et 2NH). The deposition temperature showed no pronounced effect on the granular morphology of the Zr‐C‐N films. The XRD data of the films correspond to the formation of carbonitride phase whereas the XPS analyses revealed a strong surface oxidation and incorporation of oxygen in the film. The films deposited using a mixture of Zr(NEt 2) 4 and Et 2NH showed higher N content, better adhesion and scratch resistance when compared to films obtained from the CVD of pure Zr(NEt 2) 4. Subject to the precursor composition and deposition temperature (550‐750 °C), the microhardness values of Zr‐C‐N films were found to be in the range 2.11‐5.65 GPa. For ZrO 2 films, morphology and phase composition strongly depend on the deposition temperature. The CVD deposits obtained at 350 °C show tetragonal ZrO 2 to be the only crystalline phase. Upon increasing the deposition temperature to 450 °C, a mixture of tetragonal and monoclinic modifications was formed with morphology made up of interwoven elongated grains. At higher temperatures (550 and 650 °C), pure monoclinic phase was obtained with facetted grains and developed texture. 相似文献
16.
The synthesis and structural characterization of new tantalum(V) compounds containing a single hydrazido(I) ligand are reported. Hydrazinolysis of TaCl(NMe 2) 4 using trimethylsilyl(dimethyl)hydrazine affords the compound TaCl(NMe 2) 3[N(TMS)NMe 2] in essentially quantitative yield. Metathetical replacement of the chloride ligand in TaCl(NMe 2) 3[N(TMS)NMe 2] by LiNMe 2 gives the all-nitrogen coordinated compound Ta(NMe 2) 4[N(TMS)NMe 2]. VT 1H NMR studies support the existence of low-energy pathways involving rotation about the Ta–N bonds of the ancillary amido and hydrazido ligands in both hydrazido-substituted compounds. X-ray crystallographic analyses confirm the octahedral disposition about the tantalum metal in TaCl(NMe 2) 3[N(TMS)NMe 2] and Ta(NMe 2) 4[N(TMS)NMe 2] and the presence of an η2-hydrazido(I) ligand. Preliminary data using Ta(NMe 2) 4[N(TMS)NMe 2] as an ALD precursor for the preparation of tantalum nitride and tantalum oxide thin films are presented. 相似文献
17.
The Metal‐rich Layer Structure of Ta 6STe 3 Ta 6S 1+xTe 3–x was prepared from an appropriate mixture of 2 H–Ta 1.3S 2, TaTe 2, and Ta in a fused tantalum tube at 1273 K within 3 d. The results of a X‐ray single crystal structure analysis for a phase near the Te‐rich limit of the homogeneity range are reported. Ta 6S 1.00Te 3.00(1) crystallizes in the triclinic space group P1, a = 993.14(8) pm, b = 1032.18(8) pm, c = 1378.78(11) pm, α = 79.32(1)°, β = 81.36(1)°, γ = 85.74(1)°, Z = 6, Pearson symbol aP60, 6048 I o > 2σ (I o), 286 variables, wR 2 = 0.067. The metal‐rich layer structure of Ta 6STe 3 comprises distorted icosahedral Ta 13 clusters and related deltahedral cluster fragments complemented by chalcogen atoms. The centred clusters consist of 11, 12, 13, 14, or 16 atoms. They interpenetrate into lamellae in which the tantalum and chalcogen atoms are spatially segregated according to [Q–Ta 3–Q]. The signature of the structure is a lenticular heptagonal antiprismatic Ta 30 cluster which seems to be excised from the pentagonal antiprismatic columnar structure of Ta 6S. The Ta 30 clusters and distorted icosahedral Ta 13 clusters are connected and fused into puckered layers. The rest of the tantalum valences are used for heteronuclear bonding. The chalcogen atoms having three to six next tantalum atoms coat the corrugated, tetrahedrally close‐packed layers. Ta 6STe 3 is a moderate metallic conductor (ρ 293 K = 3 × 10 –4 Ωcm) exhibiting typical temperature independent paramagnetic properties. 相似文献
18.
The title compound, (C 4H 12N) 4[Ta 6Cl 18]Cl, crystallizes in the cubic space group . The crystal structure contains two different types of coordination polyhedra, i.e. four tetrahedral [(CH 3) 4N] + cations and one octahedral [(Ta 6Cl 12)Cl 6] 3− cluster anion, and one Cl − ion. The presence of three different kinds of Cl atoms [bridging (μ 2), terminal and counter‐anion] in one molecule makes this substance unique in the chemistry of hexanuclear halide clusters of niobium and tantalum. The Ta 6 octahedron has an ideal Oh symmetry, with a Ta—Ta interatomic distance of 2.9215 (7) Å. 相似文献
19.
Uniform‐sized silica nanospheres (SNSs) assembled into close‐packed structures were used as a primary template for ordered porous graphitic carbon nitride (g‐C 3N 4), which was subsequently used as a hard template to generate regularly arranged Ta 3N 5 nanoparticles of well‐controlled size. Inverse opal g‐C 3N 4 structures with the uniform pore size of 20–80 nm were synthesized by polymerization of cyanamide and subsequent dissolution of the SNSs with an aqueous HF solution. Back‐filling of the C 3N 4 pores with tantalum precursors, followed by nitridation in an NH 3 flow gave regularly arranged, crystalline Ta 3N 5 nanoparticles that are connected with each other. The surface areas of the Ta 3N 5 samples were as high as 60 m 2 g −1, and their particle size was tunable from 20 to 80 nm, which reflects the pore size of g‐C 3N 4. Polycrystalline hollow nanoparticles of Ta 3N 5 were also obtained by infiltration of a reduced amount of the tantalum source into the g‐C 3N 4 template. An improved photocatalytic activity for H 2 evolution on the assembly of the Ta 3N 5 nanoparticles under visible‐light irradiation was attained as compared with that on a conventional Ta 3N 5 bulk material with low surface area. 相似文献
20.
Electropolymerization of pyrrole on tantalum (Ta) electrodes was carried out in buffer solutions (0.04 M phosphoric acid, 0.04 M acetic acid, 0.04 M boric acid and 0.2 M sodium hydroxide) containing 0.1 M sodium ptoluenesulfonate (TsONa) under galvanostatic conditions and it was found that a polypyrrole (PPy) and a tantalum oxide (Ta 2O 5) layer are formed on a Ta electrode by an electrochemical oxidation process. The conditions of this simultaneous formation were studied in respect to current density (i d), pyrrole concentration ([Py]), pH and the amount of electricity. Under certain conditions ([Py] = 0.25 M, pH = 1.8, i d = 10–20 mA cm ?2, the amount of electricity = 1 C), 6–8 μm thick PPy films were efficiently formed on homogeneous 30–50 nm thick Ta 2O 5 layers. The PPy film showed a high electrical conductivity (110 s cm ?1), adhered well and covered the Ta 2O 5 layer. The resulting PPy/Ta 2O 5/Ta system is therefore proved to have excellent properties as a capacitor. 相似文献
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