Interfacial properties of thermally oxidized Ta2Si on Si

Many refractory metal silicides have received great attention due to their potential for innovative developments in the silicon‐based microelectronic industry. However, tantalum silicide, Ta₂Si, has remained practically unnoticed since its successful application in silicon carbide technology as a simple route for a high‐k dielectric formation. The thermal oxidation of Ta₂Si produces high‐k dielectric layers, (O? Ta₂Si)‐based on a combination of Ta₂O₅ and SiO₂. In this work, we investigate the interfacial properties of thermally oxidized (850–1050 °C) Ta₂Si on commercial silicon substrates. The implications of diffusion processes in the dielectric properties of an oxidized layer are analyzed. In particular, we observe migration of tantalum pentoxide nanocrystals into the substrate with increasing oxidation temperature. An estimation of the insulator charge and interfacial O? Ta₂Si/Si trap density is also presented. Copyright © 2008 John Wiley & Sons, Ltd.     

States of Adsorbed Hydrogen and Their Effect on the Reaction of CO Oxidation on Pd and Ta

Various states of hydrogen are identified on the foil and film surfaces of palladium and tantalum by photoelectric, conductivity, and thermal desorption methods. They are formed in the course of ₂ diffusion through a membrane and in the course of adsorption from the gas phase. The effect of an ethylene pyrolysis product, pyrocarbon, on the activity in CO oxidation on the palladium surface with and without _ads is determined. The presence of hydrogen is found to weaken the effect of pyrocarbon. A study of hydrogen adsorption on the tantalum foil showed that hydrogen adsorption drastically declines in the presence of chemisorbed CO, but the H–Ta binding strength doubles. The fact that the sorption ability of tantalum is completely restored upon CO adsorption and partially restored upon ₂ chemisorption is achieved by thermochemical treatment in hydrogen.     

Synthesis of high-purity tantalum pentoxide from wastes formed in manufacture of lithium tantalate single crystals

Method for recovery of tantalum from wastes formed in manufacture of lithium tantalate single crystals to obtain high-purity tantalum pentaoxide for synthesis of LiTaO₃ stock is suggested. The extraction of tantalum with a mixture of extractive agents, dimethylamides of carboxylic acids of the C₁₀?CC₁₃ fraction and octanol-1 in Eskeide diluent, was studied.     

Preparation and characterisation of chromium and sodium tantalate layers by anodic spark deposition

A plasma-electrochemical synthesis was used to prepare chromium and sodium tantalate layers. These layers were deposited on a tantalum anode surface as ceramic compounds from aqueous electrolytes. The typical pore structure morphology of the tantalate layer was characterised by SEM as well as fractures which provide evidence of an intimate contact between layers and substrate. An XRD-study showed that the layers are composed of a mixture of Ta₂O₅ and either NaTaO₃ or CrTaO₄ depending on the electrolyte composition. Quantitative characterisation by EPM indicated higher chromium and tantalum concentrations on the electrolyte/layer interface than at the layer/tantalum interface. The chemical state of tantalum was investigated by means of XPS.     

Potassium fluorotantalate in solid, dissolved and molten conditions

Potassium fluorotantalate—K₂TaF₇ (K-salt) is used as an initial material for tantalum metal production. Current technology of tantalum metal powder is based on K-salt preparation from fluoric solutions in the form of small crystals and its reduction by sodium from the melt. The paper collects available data on K-salt preparation, structure and main properties of crystalline, dissolved and molten K-salt. The information could be useful for tantalum producers and researchers dealing with tantalum chemistry.     

Separation of niobium and tantalum with phenylarsonic acid

Phenylarsonic acid permits satisfactory separation of niobium and tantalum and estimation of tantalum from an oxalate solution containing sulphuric acid up to pH 5.8. For complete precipitation of niobium the pH should exceed 4.8. In mixtures, tantalum is precipitated below pH 3.0 and niobium is then precipitated above pH 5.0. When the oxalate concentration is high, recovery of niobium with cupferron is recommended. When the ratio of Nb₂O₅, to Ta₂O₅ exceeds 2:1, reprecipitation of tantalum is necessary. The effect of interfering ions is studied.     

Absorption of ammonia on tantalum hydroxide synthesized by a hydrofluoric acid method

Ammonia is strongly absorbed on tantalum hydroxide prepared by ammonia neutralization of TaF₇ ²⁻ or TaF₆ ⁻ complexes. FTIR analysis of tantalum hydroxide shows a characteristic peak around 1,400 cm⁻¹, attributed to NH₄ ⁺. TG and FTIR analyses show that the NH₄ ⁺ decomposes at about 500 °C. The correct chemical formula of tantalum hydroxide prepared by ammonia neutralization of TaF₇ ²⁻ or TaF₆ ⁻ is thus TaO _x (OH)_5-x (NH₄) _x . This conclusion is also confirmed by TG and FTIR analysis of tantalum hydroxide treated with various concentrations of inorganic acid at room temperature. The NH₄ ⁺ in tantalum hydroxide can be exchanged completely in aqueous HNO₃ solution, and the weight loss of the resulting sample is ended at about 415 °C by TG analysis. The NH₄ ⁺ can also be exchanged completely with aqueous H₂SO₄ solution; however, SO₄ ²⁻ is weakly absorbed on the tantalum hydroxide. Finally, the NH₄ ⁺ can be exchanged partially with aqueous H₃PO₄ solution; however, PO₄ ³⁻ is strongly absorbed on the tantalum hydroxide.     

Niobium,tantalum, and titanium fluoride solutions

Parameters for the preparation of concentrated tantalum, niobium, and titanium fluoride solutions by dissolution of their oxides or hydroxides in hydrofluoric acid were studied. Anatase titania, niobium oxide, and tantalum oxide calcined to 900°C were found to have high dissolution rates. Solid phases separated upon the dissolution of niobium, tantalum, and titanium oxides in hydrofluoric acid were identified as NbO₂F, TaO₂F, Ta₃O₇F, and TiOF₂. Niobium hydroxide dissolution in an autoclave at the atmospheric pressure gave various complex salts: NH₄NbOF₄ and (NH₄)₃Nb₂OF₁₁.     

Determination of trace impurities in tantalum powder and its compounds by inductively coupled plasma optical emission spectrometry using solvent extraction

A procedure was developed for the analysis of 18 trace impurity elements in capacitor-grade tantalum powder (Ta), potassium tantalum fluoride (K₂TaF₇), and tantalum pentoxide (Ta₂O₅) using inductively coupled plasma optical emission spectrometry (ICP-OES). The detection limits achieved were in the ppb levels. The samples were dissolved in hydrofluoric acid (HF) in a microwave digestion system and the Ta matrix was extracted using cyclo hexanone. The impurity traces remained almost completely in the aqueous phase. The text was submitted by the authors in English.     

Effect of tantalum on phase formation in the Fe-S system

Phase formation in the Fe_{1 ? x} -Ta _x -S system with 0 < x < 0.5 has been studied at temperatures up to 1273 K using X-ray diffraction. When the constituent elements are heated to 823 K, troilite (Tr), pyrrhotites (PoI, PoII, and Po_m), and pyrite (FeS₂) are formed. Tantalum at these temperatures only insignificantly dissolves in iron sulfides. In the range 823–1273 K, tantalum reacts with pyrrhotites PoII and Po_m and pyrite to yield PoI, FeTa₃S₆, and α-Fe. The solubility limit of tantalum in PoI is near Fe_0.98Ta_0.02S. The initiation temperature of the reaction between troilite and tantalum producing FeTa₃S₆ and α-Fe is 873 K. The unit cell parameters of tantalum change at 500 K, presumably due to the dissolution of iron and possibly sulfur (iron sulfide).     

Preparation and characterisation of chromium and sodium tantalate layers by anodic spark deposition

A plasma-electrochemical synthesis was used to prepare chromium and sodium tantalate layers. These layers were deposited on a tantalum anode surface as ceramic compounds from aqueous electrolytes. The typical pore structure morphology of the tantalate layer was characterised by SEM as well as fractures which provide evidence of an intimate contact between layers and substrate. An XRD-study showed that the layers are composed of a mixture of Ta₂O₅ and either NaTaO₃ or CrTaO₄ depending on the electrolyte composition. Quantitative characterisation by EPM indicated higher chromium and tantalum concentrations on the electrolyte/layer interface than at the layer/tantalum interface. The chemical state of tantalum was investigated by means of XPS. Received: 15 July 1997 / Revised: 5 March 1998 / Accepted: 9 March 1998     

Identification of phosphate anions in niobium and tantalum phosphates by means of infra-red spectra

Some niobium and tantalum phosphates have been prepared and their infra-red spectra have been recorded and compared with those of reference substances. It has been possible to identify P0₄^-3, P₂O₇^-4 and possibly P₃O10^-5 groups in different samples of niobium and tantalum phosphates.     

Ta(CNDipp)6: An Isocyanide Analogue of Hexacarbonyltantalum(0)

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 Ta⁰ 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.     

Separation of trace concentrations of tantalum from niobium and some other heavy metal ions by extraction with N-oxide of trioctylamine

The distribution of tantalum(V) between 0.1M trioctylamine oxide dissolved in xylene and sulphuric acid solutions has been studied. On the basis of results on the distribution, it is concluded that at sulphuric acid concentration 0.5M, tantalum is probably extracted by a solvate mechanism as the complex Ta(OH) (SO₄)₂·3TOAO. It has also been shown that tantalum can be quantitatively separated from niobium, uranium, thorium and rare earth elements by extraction with N-oxide of trioctylamine from 0.5M sulphuric acid solution.     

New octahedral Ta(V) hydrazido-substituted compounds for atomic layer deposition: Syntheses,X-ray diffraction structures of TaCl(NMe2)3[N(TMS)NMe2] and Ta(NMe2)4[N(TMS)NMe2], and fluxional behavior of the amido and hydrazido ligands in solution

The synthesis and structural characterization of new tantalum(V) compounds containing a single hydrazido(I) ligand are reported. Hydrazinolysis of TaCl(NMe₂)₄ using trimethylsilyl(dimethyl)hydrazine affords the compound TaCl(NMe₂)₃[N(TMS)NMe₂] in essentially quantitative yield. Metathetical replacement of the chloride ligand in TaCl(NMe₂)₃[N(TMS)NMe₂] by LiNMe₂ gives the all-nitrogen coordinated compound Ta(NMe₂)₄[N(TMS)NMe₂]. 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(NMe₂)₃[N(TMS)NMe₂] and Ta(NMe₂)₄[N(TMS)NMe₂] and the presence of an η²-hydrazido(I) ligand. Preliminary data using Ta(NMe₂)₄[N(TMS)NMe₂] as an ALD precursor for the preparation of tantalum nitride and tantalum oxide thin films are presented.     

Tin(II) Difluoride and Antimony(III) Trifluoride as Fluorine Donors in Reactions with Tantalum Halides in Various Solvents

Reactions of SnF₂and SbF₃with TaF₅and TaCl₅in acetonitrile and dimethyl sulfoxide were studied by ¹⁹F and ¹¹⁹Sn NMR. It was found that SnF₂and SbF₃behave as fluorine donors for tantalum(V). The anionic and cationic tantalum fluorochloride complexes form in acetonitrile, while [TaF₆]^–predominates in dimethyl sulfoxide. Tin(II) occurs in solution in the form of fluorine-containing polymeric cations.     

Enhanced lithium-ion intercalation and conduction of transparent tantalum oxide films by lithium addition with an atmospheric pressure plasma jet

An investigation is conducted on enhancing lithium-ion intercalation and conduction performance of transparent organo tantalum oxide (TaO _y C _z ) films, by addition of lithium via a fast co-synthesis onto 40 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates at the short exposed durations of 33–34 s, using an atmospheric pressure plasma jet (APPJ) at various mixed concentrations of tantalum ethoxide [Ta(OC₂H₅)₅] and lithium tert-butoxide [(CH₃)₃COLi] precursors. Transparent organo-lithiated tantalum oxide (Li _x TaO _y C _z ) films expose noteworthy Li⁺ ion intercalation and conduction performance for 200 cycles of reversible Li⁺ ion intercalation and deintercalation in a 1 M LiClO₄-propylene carbonate electrolyte, by switching measurements with a potential sweep from ?1.25 to 1.25 V at a scan rate of 50 mV/s and a potential step at ?1.25 and 1.25 V, even after being bent 360° around a 2.5-cm diameter rod for 1000 cycles. The Li⁺ ionic diffusion coefficient and conductivity of 6.2?×?10^?10 cm²/s and 6.0?×?10^?11 S/cm for TaO _y C _z films are greatly progressed of up to 9.6?×?10^?10 cm²/s and 7.8?×?10^?9 S/cm for Li _x TaO _y C _z films by co-synthesis with an APPJ.     

Unusual reactivity of tantalum pentakis(dimethylpyrazolate) with CS2: scission of the C=S bond and formation of dmpz3CS– ligand

The reaction beetwen tantalum pentakis(3,5-dimethyl-pyrazolate) and CS₂ afforded novel complex [Ta(=S)(dmpz)₂{(dmpz)₃CS}]. In this reaction the molecule of CS₂ undergoes scission with the migration of one sulfide to the tantalum atom while three pyrazolate residues migrate to carbon with the formation of unusual (dmpz)₃CS^– ligand. The structure of the product was established by X-ray diffraction.     

The formation and photolysis of tantalum sulfide cluster ions

Tantalum sulfide cluster ions were produced by direct laser ablation, and were studied with a tandem time-of-flight mass spectrometer. The main dissociation channel of the UV-photolysis (248 nm) of tantalum sulfide cluster ions is sequent S₂ loss. Structures with Ta₃S₄ and Ta₄S₆ as frameworks were suggested for the large tantalum sulfide cluster ions.The work was supported by the National Natural Science Fouldation of China.     

Catalytic diversity of diene complexes of niobium and tantalum on polymerizations of ethylene,norbornene, and methyl methacrylate

Half‐metallocene diene complexes of niobium and tantalum catalyzed three‐types of polymerization: (1) the living polymerization of ethylene by niobium and tantalum complexes, MCl₂(η⁴‐1,3‐diene)(η⁵‐C₅R₅) ( 1‐4 ; M = Nb, Ta; R = H, Me) combined with an excess of methylaluminoxane; (2) the stereoselective ring opening metathesis polymerization of norbornene by bis(benzyl) tantalum complexes, Ta(CH₂Ph)₂(η⁴‐1,3‐butadiene)(η⁵‐C₅R₅) ( 11 : R = Me; 12 : R = H) and Ta(CH₂Ph)₂(η⁴‐o‐xylylene)(η⁵‐C₅Me₅) ( 16 ); and (3) the polymerization of methyl methacrylate by butadiene‐diazabutadiene complexes of tantalum, Ta(η²‐RN=CHCH=NR)(η⁴‐1,3‐butadiene)(η⁵‐C₅Me₅) ( 25 : R = p‐methoxyphenyl; 26 : R = cyclohexyl) in the presence of an aluminum compound ( 24 ) as an activator of the monomer.