Tantalum Precursor Research Articles

Silyl‐Substituted ortho‐Terphenoxide Group 3–5 Complexes: Synthesis, Structure and Applications in Catalysis

AbstractThe complexation behavior of 3,3’‐silyl‐substituted ortho‐terphenoxide ligands o‐C6H4(C6H2‐2‐OH‐3‐SiR3‐5‐Me)2 (SiR3= SiPh3, SiMePh2, SiMe3, Sit‐BuMe2) with a range of yttrium, titanium, niobium and tantalum precursors was examined. The complexation of the ligands with [Y(N(SiHMe2)2)3(THF)2] yielded monomeric complexes, as confirmed by NMR spectroscopy and X‐ray crystallography for the methyldiphenylsilyl‐ and tert‐butyldimethylsilyl‐substituted complex. The triphenylsilyl‐substituted yttrium bis(dimethylsilyl)amido complex showed good activity in the intramolecular hydroamination reaction of aminoalkenes. Complexation with Ti(NMe2)4 yielded a mixture of products, depending on the silyl substituents and the solvent used for complexation. A mono‐ligated bimetallic titanium complex and a bisligated titanium complex were analyzed by X‐ray crystallography. Complexation with M(NMe2)5 (M=Nb, Ta) produced the corresponding monomeric ortho‐terphenoxide complexes as confirmed by NMR spectroscopy and X‐ray structure analysis of a niobium complex and 3 tantalum complexes.

Not So Similar: Different Ways of Nb(V) and Ta(V) Catecholate Complexation.

The reactions between catechol (H2cat) and niobium(V) or tantalum(V) precursors in basic aqueous solutions lead to the formation of catecholate complexes of different natures. The following complexes were isolated and characterized by single-crystal X-ray diffraction (SCXRD): (1) (NH4)3[NbO(cat)3]∙4H2O; (2) K2[Nb(cat)3(Hcat)]·2H2cat·2H2O; (3) Cs3[NbO(cat)3]·H2O; (4) (NH4)4[Ta2O(cat)6]·3H2O; (5) Cs2[Ta(cat)3(Hcat)]·H2cat; (6) Cs4[Ta2O(cat)6]·7H2O. The isolated crystalline products were characterized by elemental analysis, X-ray powder diffraction (XRPD), FTIR, and TGA. The structural features of these complexes, such as {Ta2O} unit geometry, Cs-π interactions, and crystal packing effects, are discussed.

Self-supported amorphous TaNx(Oy)/nickel foam thin film as an advanced electrocatalyst for hydrogen evolution reaction.

Chemical vapor deposited (CVD) amorphous tantalum-oxy nitride film on porous three-dimensional (3D) nickel foam (TaNx(Oy)/NF) utilizing tantalum precursor, tris(diethylamino)(ethylimino)tantalum(V), ([Ta(NEt)(NEt2)3]) with preformed Ta-N bonds is reported as a potential self-supported electrocatalyst for hydrogen evolution reaction (HER). The morphological analyses revealed the formation of thin film of core-shell structured TaNx(Oy) coating (ca. 236 nm) on NF. In 0.5 M H2SO4, TaNx(Oy)/NF exhibited enhanced HER activity with a low onset potential as compared to the bare NF (-50 mV vs. -166 mV). The TaNx(Oy)/NF samples also displayed higher current density (-11.08 mA cm-2vs. -3.36 mA cm-2 at 400 mV), lower Tafel slope (151 mV dec-1vs. 179 mV dec-1) and lower charge transfer resistance exemplifying the advantage of TaNx(Oy) coating towards enhanced HER performance. The enhanced HER catalytic activity is attributed to the synergistic effect between the amorphous TaNx(Oy) film and the nickel foam.

The effective Work-Function of atomic layer deposited TaN thin film using TBTDET precursor and NH3 reactant gas

We investigated the effect of capping metals and post annealing on the effective work function (EWF) of atomic layer deposited (ALD) tantalum nitride (TaN) using a metal oxide semiconductor (MOS) device with HfO2 gate dielectric. The tris(diethylam-ido)(tert-butylimido) tantalum (TBTDET) precursor and ammonia (NH3) were used as the tantalum precursor and the reactant gas, respectively. Increasing ALD TaN thickness leads to higher EWF regardless of the capping metals. When aluminum (Al) is used as the capping metal, the EWF range is 4.06 eV to 4.45 eV, which is suitable for the gate electrode of the n-type device, and for the tungsten (W) capping metal, the EWF range is 4.43 eV to 4.80 eV, acceptable for the gate electrode of the p-type device. These results are attributed that Al causes oxygen-scavenging, resulting in more oxygen vacancies within HfO2, whereas W reacts little with oxygen. The EWF versus ALD TaN thickness dependence of the Al and W capping cases is 55.7 meV/nm and 52.8 meV/nm, respectively. Additional heat treatment further increases EWF further for both cases, which is attributed to the reduction of carbon contents within TaN.

In vacuo investigations on the nucleation of TaCN by plasma enhanced atomic layer deposition

The nucleation of TaCN films during plasma enhanced atomic layer deposition (PEALD) using pentakis-(dimethylamino)tantalum (PDMAT) in combination with H2/Ar plasma was investigated on several substrate surfaces by X-ray photoelectron spectroscopy (XPS) without vacuum break. A cluster tool combining a process reactor with a surface analysis unit under high vacuum conditions ensures a direct qualification and quantification of the chemical surface composition by XPS starting from the very first precursor pulse. Due to the high sensitivity of in vacuo XPS measurements, tantalum can be detected at the substrate surface already after the very first precursor pulse of the PEALD process. The amount of adsorbed tantalum precursor molecules on the silicon oxide surface is much higher compared to the H-terminated Si and low-k surfaces. The early cycles are characterized by the onset of TaO bonds. A TaO interface layer grows on the substrate surface until all the reactive OH-groups are consumed. This is followed by the emergence of TaC and TaN bonds when the homogenous growth mode begins. The PEALD nucleation of TaCN was also investigated on low-k substrates (SiCOH). The homogeneous film body on all substrates consist of Ta- carbide -nitride, and -oxide compounds. In summary, we obtained precise information about the initital tantalum precursor adsorption on several substrate materials and explored the capability to enhance the initial growth on low-k substrates. These examples demonstrate as well that in-vacuo XPS measurements are ideally suited for studying film growth nucleation.

Hybrid Suspension/Solution Precursor Plasma Spraying of a Complex Ba(Mg1/3Ta2/3)O3 Perovskite: Effects of Processing Parameters and Precursor Chemistry on Phase Formation and Decomposition

Ba(Mg1/3Ta2/3)O3 (BMT) has a high melting point and is envisioned as a thermal barrier coating material. In this study, a hybrid suspension/solution precursor plasma spray process with a radio frequency thermal plasma torch is designed to deposit BMT nanostructured coatings. Six combinations of chemical reagents are investigated as coating precursors: one BMT powder suspension and five Ta2O5 suspensions in nitrate- or acetate-based solutions. X-ray photoelectron spectroscopy is used to evaluate the element evaporation during plasma spraying, while a thermogravimetric/differential thermal analysis is applied to investigate the BMT formation. Parameters such as precursor chemistry, plasma power, spraying distance and substrate preheating are studied with regard to the coating phase structure. Twice the Mg stoichiometric amount with a power of 50 kW shows the best results when using nanocrystallized Ta2O5 as a tantalum precursor. When choosing nitrates as Ba and Mg precursors, crystallized BMT is obtained at lower plasma power (45 kW) when compared to acetates (50 kW). BaTa2O6, Ba3Ta5O15, Ba4Ta2O9, Mg4Ta2O9 are the main secondary phases observed during the BMT coatings deposition. Because of the complicated acetate decomposition process, the coating deposition rate from nitrate precursors is 1.56 times higher than that from acetate precursors.

Atomic layer deposition of amorphous Ni-Ta-N films for Cu diffusion barrier

Novel Ni-doped TaN (Ni-Ta-N) films are deposited by remote plasma-enhanced atomic layer deposition (ALD) with pentakis(dimethylamino)tantalum, nickelocene, and NH3 precursors for Cu diffusion barriers. Various Ni-Ta-N films with different compositions are achieved by changing the deposition cycles (n) of Ni sublayer while fixing the deposition cycles of TaN sublayer at 2. As n increases from 1 to 6, the root-mean-square roughness of the deposited film increases from 0.150 to 0.527 nm, and the resistivity decreases from 0.18 to 1.1 × 10−2 Ω cm. After annealing at 400 °C for 30 min in the forming gas (N2/H2), these films still maintain an amorphous texture and demonstrate a negligible reduction of resistivity and a weak increase of density. Subsequently, the barrier effects of the Ni-Ta-N films with different compositions are compared against Cu diffusion after annealing. The results reveal that the Ni-Ta-N films with n ≤ 4 exhibit barrier effects comparable with the ALD TaN film even after annealing at 550 °C. Further, a 3 nm ultrathin Ni-Ta-N film with n = 4, corresponding to an addition of ∼22 at. % Ni to TaN, cannot only reduce the film resistivity by 78% but also effectively block Cu diffusion after annealing at 450 °C for 30 min.

Early/Late Heterobimetallic Tantalum/Rhodium Species Assembled Through a Novel Bifunctional NHC-OH Ligand.

The straightforward synthesis of a new unsymmetrical hydroxy-tethered N-heterocyclic carbene (NHC) ligand, HL, is presented. The free ligand exhibits an unusual OH-carbene hydrogen-bonding interaction. This OH-carbene motif was used to yield 1) the first tantalum complex displaying both a Fischer- and Schrock-type carbene ligand and 2) a unique NHC-based early/late heterobimetallic complex. More specifically, the protonolysis chemistry between the ligand's hydroxy group and imido-alkyl or alkylidene-alkyl tantalum precursor complexes yielded the rare monometallic tantalum-NHC complexes [Ta(XtBu)(L)(CH2 tBu)2 ] (X=N, CH), in which the alkoxy-carbene ligand acts as a chelate. In contrast, HL only binds to rhodium through the NHC unit in [Rh(HL)(cod)Cl] (cod=cycloocta-1,5-diene), the hydroxy pendant arm remaining unbound. This bifunctional ligand scaffold successfully promoted the assembly of rhodium/tantalum heterobimetallic complexes upon either 1) the insertion of [Rh(cod)Cl]2 into the Ta-NHC bond in [Ta(NtBu)(L)(CH2 tBu)2 ] or 2) protonolysis between the free hydroxy group in [Rh(HL)(cod)Cl] and one alkyl group in [Ta(NtBu)(CH2 tBu)3 ].

Amorphous and Crystalline Sodium Tantalate Composites for Photocatalytic Water Splitting.

A facile hydrothermal synthesis protocol for the fabrication of sodium tantalates for photocatalytic water splitting is presented. Mixtures of tantalum and sodium ethoxide precursors were dispersed in ethanol, and ammonium hydroxide solution was used as mineralizer. By adjusting the amount of mineralizer, a variety of sodium tantalates with various morphologies, textural parameters, band gaps, crystal phases, and degrees of crystallinity were fabricated. The reaction was carefully monitored with a pressure sensor inside the autoclave reactor, and the obtained samples were characterized using X-ray diffraction, transmission electron microscopy, N2-physisorption, and ultraviolet-visible light spectroscopy. Among the series, the amorphous sample and the composite sample that consists of amorphous and crystalline phases showed superior activity toward photocatalytic hydrogen production than highly crystalline samples. Particularly, an amorphous sodium tantalate with a small fraction of crystalline nanoparticles with perovskite structure was found to be the most active sample, reaching a hydrogen rate of 3.6 mmol h(-1) from water/methanol without the use of any cocatalyst. Despite its amorphous nature, this photocatalyst gave an apparent photocatalyst activity of 1200 μmol g(-1) L(-1) h(-1) W(1-), which is 4.5-fold higher than highly crystalline NaTaO3. In addition, the most active sample gave promising activity for overall water splitting with a hydrogen production rate of 94 μmol h(-1), which is superior to highly crystalline NaTaO3 prepared by conventional solid-solid state route.

A microwave molecular solution based approach towards high-κ-tantalum(V)oxide nanoparticles: synthesis, dielectric properties and electron paramagnetic resonance spectroscopic studies of their defect chemistry.

Stable dispersions of tantalum oxide nanoparticles are accessible from solutions of tantalum(V) complexes with a mixed malonato and alkanolato ligand sphere in ethoxyethanol by microwave processing. The malonato ligand is cleaved during decomposition and acetic acid or acetic acid esters are formed as derived from in situ spectroscopic studies. The solubility of the tantalum precursor and the obtained particle size therefrom depend strongly on the type of alkanolato ligand moiety. Dispersions of the molecular complexes possess good film forming properties. Films with low surface roughness can be obtained by spincoating. These exhibited a dielectric constant of about 15 and disruptive strengths above 1.5 MV cm(-1). The electrical measurements indicate that the presence of moisture is detrimental with respect to the dielectric performance of the films. After removal of the solvent from the suspensions of the nanoparticles, the residue can be redispersed in aprotic solvents. The particles can be isolated therefrom by precipitation with pentane. XRD and HRTEM indicate that the material remains amorphous up to temperatures of 750 °C. XPS proved that only Ta2O5 is formed as lower oxidation states of Ta cannot be detected. A detailed EPR study allows us to gain insight into the surface defect chemistry. Multiple types of oxygen vacancies exist at the surface of the Ta2O5 particles which are influenced by additional calcination and annealing in a vacuum.

Synthesis of tantalum carbide and nitride nanoparticles using a reactive mesoporous template for electrochemical hydrogen evolution

Tantalum carbide and nitride nanocrystals were prepared through the reaction of a tantalum precursor with mesoporous graphitic (mpg)-C3N4. The effects of the reaction temperature, the ratio of the Ta precursor to the reactive template (mpg-C3N4), and the selection of the carrier gas (Ar, N2 and NH3) on the resultant crystal phases and structures were investigated. The produced samples were characterized using powder X-ray diffraction (XRD), CHN elemental analyses, thermogravimetric analyses (TGA), nitrogen sorption, a temperature-programmed reaction with mass spectroscopy (MS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The results indicate that the different tantalum phases with cubic structure, TaN, Ta2CN, and TaC, can be formed under a flow of nitrogen when formed at different temperatures. The Ta3N5 phase with a Ta5+ oxidation state was solely obtained at 1023 K under a flow of ammonia, which gasified the C3N4 template and was confirmed by detecting the decomposed gaseous products via MS. Significantly, the formation of TaC, Ta2CN, and TaN can be controlled by altering the weight ratio of the C3N4 template relative to the Ta precursor at 1573 K under a flow of nitrogen. The high C3N4/Ta precursor ratio generally resulted in high carbide content rather than a nitride one, consistent with the role of mpg-C3N4 as a carbon source. Electrochemical measurements revealed that the synthesized nanomaterials were consistently able to produce hydrogen under acidic conditions (pH 1). The obtained Tafel slope indicates that the rate-determining step is the Volmer discharge step, which is consistent with adsorbed hydrogen being weakly bound to the surface during electrocatalysis.

Conformal Atomic Layer Deposition of TA-Based Diffusion Barrier Film Using a Novel Mono-Guanidinate Precursor

In this work, we present elaboration of Ta-based thin films by ALD from a novel tantalum precursor, the eta2-N,N'-isopropylethylguanidinato-tetra-diethylamino tantalum ([eta2-(i)PrNC(NEt2)NEt]Ta(NEt2)4, IEGTDEAT). Ammonia was used as reducing agents. The experimental conditions were optimized by quartz microgravimetry, studying the influence of duration of precursors and purge pulses and the substrate temperature. An optimal deposition temperature of 260 degrees C was showed. Ta-based thin films deposited on planar and patterned substrates showed a perfect conformality and continuity, even at low number of cycles.

Synthesis of Ordered Porous Graphitic‐C3N4 and Regularly Arranged Ta3N5 Nanoparticles by Using Self‐Assembled Silica Nanospheres as a Primary Template

Uniform-sized silica nanospheres (SNSs) assembled into close-packed structures were used as a primary template for ordered porous graphitic carbon nitride (g-C(3)N(4)), which was subsequently used as a hard template to generate regularly arranged Ta(3)N(5) nanoparticles of well-controlled size. Inverse opal g-C(3)N(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(3)N(4) pores with tantalum precursors, followed by nitridation in an NH(3) flow gave regularly arranged, crystalline Ta(3)N(5) nanoparticles that are connected with each other. The surface areas of the Ta(3)N(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(3)N(4). Polycrystalline hollow nanoparticles of Ta(3)N(5) were also obtained by infiltration of a reduced amount of the tantalum source into the g-C(3)N(4) template. An improved photocatalytic activity for H(2) evolution on the assembly of the Ta(3)N(5) nanoparticles under visible-light irradiation was attained as compared with that on a conventional Ta(3)N(5) bulk material with low surface area.

Ferroelectric and Photocatalytical Properties of Ta-Based and Nb-Based Oxide Ceramics and Powders from Environmentally Friendly Water-Soluble Tantalum and Niobium Precursors

Due to the great potentials of tantalite and niobate materials in ferroelectric and photocatalytic applications, development of proper tantalum or niobium precursors is urgently need. In this work, a simple novel route to synthesize environmentally friendly aqueous tantalum and niobium precursors has been developed using cheap and stable Nb2O5 or Ta2O5 as starting source. Using home-made Ta and Nb precursors, several photocatalytic nanopowders such as BiNbO4 and BiTaO4, and ferroelectric ceramics such as 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (PMN-PT), have been prepared by a modified PC method. These powders and ceramics from polymeric precursors have low crystalline temperature and transformation temperature with uniform grain distribution, compared to conventional solid phase reaction (SSR). Pure triclinic phase of BiNbO4 powders can be obtained at 700°C instead of 1020°C of SSR, with excellent photodegradation activity of methyl violet. PC-derived PMN-PT ceramics also exhibit better ferroelectric and piezoelectric properties. All these indicate that this is an attractive and flexible approach using environmentally friendly water-soluble tantalum and niobium precursors for fabrication of tantalate and nibonate functional materials.

Growth and Characterization of Ti‐Ta‐O Thin Films on Si Substrates by Liquid Injection MOCVD for High‐k Applications from Modified Titanium and Tantalum Precursors

AbstractTitanium oxide (TiO2) and titanium‐tantalum oxide (Ti‐Ta‐O) thin films are deposited by liquid injection (LI) metal‐organic (MO) CVD using metal amide‐malonate complexes, [Ti(NR2)2(dbml)2], and tantalum, [Ta(NMe2)4(dbml)] (R = Me, Et; dbml = di‐tert‐butylmalonato). TiO2 and Ti‐Ta‐O films are deposited on Si(100) in the temperature ranges 350–650 °C and 500–700 °C, respectively. The structure, morphology, and chemical composition of the films are evaluated by X‐ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Rutherford backscattering spectroscopy (RBS), and X‐ray photoelectron spectroscopy (XPS). The electrical properties of the films, namely the dielectric properties, are assessed by carrying out capacitance‐voltage (C‐V) measurements on metal‐oxide‐semiconductor (MOS) capacitor structures.

Effects of Doping Elements on Residual Oxygen/Nitrogen Contents in Red Pigment of Tantalum Nitrides (Ta<sub>3</sub>N<sub>5</sub>)

Tantalum nitride (Ta3N5) is a nontoxic red pigment that is being developed as a substitute for Cd-related pigments Ta3N5 is produced by the nitridation and heat treatment of amorphous Tantalum precursors. Doping elements were added in the precursor manufacturing stage to improve the red color tone of tantalum nitride. Grain growth was observed in nitrides that formed second phases, such growth led to an increase in the average grain size comprared to undoped nitrides, and the colors declined as the oxygen content increased. Nitrides that did not form second phases in response to doping elements remained a single-phase Ta3N5 and exhibited an excellent red color with a high nitrogen content. We determined that a change in the oxygen/nitrogen contents affected the color manifestation, which depended on the amount by which doping was increased.

탄탈륨 질화물(Ta3N5)의 적색도 향상에 미치는 NH4Cl의 영향

The Tantalum nitride has attracted wide at attention as issues related to the toxicity of Cd-related materials. But in the titration process of TaCl? solution with NH₄OH, NH₄Cl, as a by product, was remained in the prepared Tantalum precursor. The tantalum precursor with NH₄Cl was nitrided by ammonolysis. The red color tone of Ta₃N? was reduced by the residual NH₄Cl reduce. Therefore, amorphous Tantalum precursor was prepared by filtering process with as hydrous ethanol to remove the NH₄Cl. In the case of using Tantalum precursor without NH₄Cl, we successfully synthesized the Tantalum nitride with good red color. The value of red color tone was improved from a * =36.8 to a * =53.0. The synthesized powder was characterized by XRD, SEM, the Nitrogen / Oxygen Determinator, TG-DTA, and the CIE L * a * b * colorimeter.

On gaseous phase of ALD precursors by means of thermodynamics

The thermal stability of the pentakis(dimethylamino) tantalum (PDMAT) precursor used in the Atomic Layer Deposition (ALD) TaN process has been studied from 343 to 723 K using a specific reactor coupled with a Knudsen cell mass spectrometer. This reactor is built as tandem cells: an evaporation cell and a cracking cell. This reactor tries to simulate the conditions found in the bubbler of the ALD system by the evaporation cell and in the hot reaction zone of ALD by the cracking cell. Experiments showed that the saturated gaseous phase (originated from PDMAT evaporation) is composed of Ta(N(CH3)2)4(g), and in smaller amounts of Ta(N(CH3)2)5(g) and OTaN4C8H24(g). Cracking experiments, performed at different temperatures, showed that PDMAT is a minor component of the gaseous phase, meanwhile Ta(N(CH3)2)4(g), and HN(CH3)2(g), are the major gaseous species that decompose at higher temperatures. Oxygen containing molecules are also observed in all temperature range.

Synthesis, Characterization, and Applications of Water-Soluble Tantalum Carboxylate Precursors via a Flux Method

A novel, simple, and feasible route for synthesizing air-stable, water-soluble tantalum precursors has been developed using moisture-insensitive Ta 2 O 5 as a starting source of the Ta element, based on the conventional basic flux method. Various analytical techniques have been used to characterize the formation mechanism, purity, and thermal decomposition features of these Ta precursors including tantalum oxalate, tantalum peroxo-tartarate, and tantalum peroxo-citrate. These Ta precursor solutions have a higher Ta ion purity over 99.0 wt% and a lone shelf life. Using home-made Ta precursors, photocatalyst powders of 1 mol% Ta-doped ZnO and ferroelectric films of SrBi 2 Ta 2 O 9 on Pt/TiO 2/ SiO 2 /Si substrates have been prepared by a modified polymerizable complex (PC) route. Ta-doped ZnO powders from polymeric precursors show hexagonal wurtzite structures with uniform smaller grain sizes of 25 nm and a larger specific surface area of 32 m 2 /g. Moreover, they exhibit excellent photocatalytical activity under visible light irradiation compared with pure ZnO powders. PC-derived SrBi 2 Ta 2 O 9 films also show comparable ferroelectric and dielectric properties with those from the metalorganic decomposition method. All these qualities indicate that water-soluble Ta precursors are potential and competitive candidates for photocatalyst and ferroelectric applications.

Preparation, characterization of the Ta-doped ZnO nanoparticles and their photocatalytic activity under visible-light illumination

This paper describes a novel catalyst of the Ta-doped ZnO nanocrystals prepared by a modified polymerizable complex method using the water-soluble tantalum precursor as the sources of Ta. The catalysts were characterized by means of various analytical techniques as a function of Ta content ( x=0–4 mol%) systematically. A remarkable advantage of the results was confirmed that dopant Ta enhanced the visible-light absorption of ZnO and the low-solubility tantalum doping could restrain the growth of crystal and minish the particle size. The relationship between the physicochemical property and the photocatalytic performance was discussed, and it was found that the photocatalytic activity in the photochemical degradation of methylene blue under visible-light irradiation ( λ⩾420 nm) was dependent on the contents of the dopant, which could affect the particle size, concentration of surface hydroxyl groups and active hydrogen-related defect sites, and the visible-light absorption. The highest photocatalytic activity was obtained for the 1.0 mol% Ta-doped ZnO sample.