Metal Alkoxide Precursors Research Articles

Bi1-x-yTixSiyOz (BTSO) Thin Films for Dynamic Random Access Memory Capacitor Applications

Bi1–x–yTixSiyOz (BTSO) thin films were grown on eight inch diameter Ru/SiO2/Si or bare Si wafers by atomic layer deposition (ALD) method using Bi(mmp)3, Ti(mmp)4, and Si(OEt)4 [mmp = 1-methoxy-2-methyl-2-propoxide (OCMe2CH2OMe, Me = methyl); Et = ethyl] as metal alkoxide precursors and ozone (O3) as the oxidant gas. Transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS) analysis showed that the as-deposited films are amorphous and the cation compositional ratio of Bi:Ti:Si is 0.38:0.37:0.25 of films deposited at 325 °C on Ru/SiO2/Si Ru substrates. X-ray photoelectron spectroscopy (XPS) shows that the BTSO films are homogeneously dispersed without any phase-separation of the components. The BTSO films show excellent step coverage on a high aspect ratio (4) contact hole structure with a diameter of 300 nm. The leakage current density of BTSO films is on the order of 10–8 A cm–2 at 1 V, meeting present dielectric requirements for a dynamic random access memory storage capacitor with an equivalent oxide thickness of 2.1 nm. From the capacitance–voltage characteristics at 10 kHz of the Pt/BTSO/Ru capacitor, the estimated dielectric constant of amorphous BTSO films is ∼ 24.

Structural aspects of some modified metal-alkoxides and related molecular precursors to ceramic materials by the sol-gel processing

There is an increasing interest in designing better modified metal-alkoxide precursors for the deposition of metal-oxides and organic-inorganic hybrid materials by sol-gel/MOCVD techniques. In the alkoxide based sol-gel processes, gelation occurs through the development of a polymeric network formed as a consequence of the initial hydrolysis of the metal-alkoxides in the presence of water and its subsequent polymerization by condensation mechanism. Modifiers such as β-diketones, carboxylic acids, Schiff's bases, glycols etc. can modify the relative reaction rates (by chelation effect) providing a better route to the formation of the gelatinous precipitate required for ceramic material applications. Such organically modified metal-alkoxides and related precursors also allow the introduction of organic moieties for organic-inorganic hybrid material applications. Considerable amount of research work has been reported from our laboratories on various synthetic and structural aspects of derivatives containing M-O-C, M-S-C and M-N-C functionalities during the last three decades, yet much of the later developments coincided with the synthesis and characterization of the modified precursors for material applications. The present article deals with the synthesis and structural aspects of some modified metal-alkoxides and related precursors of some main group p-block and early d-block elements having potential applications in material science.

Preparation and characterization of mesoporous TiO 2–CeO 2 nanopowders respond to visible wavelength

Mesoporous TiO 2–CeO 2 nanopowders responding to visible wavelength were synthesized by using a surfactant assisted sol–gel technique. They were obtained using metal alkoxide precursors modified with acetylacetone (ACA) and laurylamine hydrochloride (LAHC) as surfactant. The samples were characterized by XRD, nitrogen adsorption isotherm, SEM, TEM, and selected area electron diffraction (SAED), respectively. The 95 mol% TiO 2–5 mol% CeO 2 system yielded single anatase phase, however, further addition of the CeO 2 formed cubic CeO 2 structure while anatase TiO 2 decreased. Additions of 5 and 10 mol% CeO 2 increased the surface area, but those of 25, 50, and 75 mol% CeO 2 did not affect it very much. By using this mixed metal oxides system, TiO 2 can be modified to respond to the visible wavelength. The mixed metal oxides had catalytic activity (evaluating the formation rate of I 3 −) about 2–3 times higher than pure CeO 2, while nanosize anatase type TiO 2 materials had no catalytic activity under visible light. The catalytic activity was almost proportional to the specific surface area. The formation rate of I 3 − was much improved by changing the calcination temperature and calcination period. Highest catalytic activity in this study was obtained for the 50 mol% TiO 2–50 mol% CeO 2 nanopowders calcined at 250 °C for 24 h.

Synthesis and assembly of high-quality cobalt ferrite nanocrystals prepared by a modified sol–gel technique

Colloidal cobalt ferrite nanocrystals were produced using a new sol–gel-like synthesis based on the procedure developed by O’Brien et al. (J. Am. Chem. Soc. 123 (2001) 12085) for the synthesis of BaTiO3 nanocrystals. This synthesis involves the single-stage high-temperature hydrolysis of the metal alkoxide precursors to obtain crystalline, uniform, organically coated nanoparticles which are well-dispersed in an organic solvent. The particles could be further manipulated to form Langmuir–Blodgett films consisting of close-packed nanocrystal monolayers. The structural and magnetic properties of these nanocrystals indicate similarity to bulk CoFe 2O 4 with a very high coercivity at low temperatures.

Growth of Hafnium Aluminate Thin Films by Liquid Injection MOCVD Using Alkoxide Precursors

AbstractThin films of Hf aluminate, (HfO2)x(Al2O3)1–x (Al = 8.4–38.5 at.‐%) have been deposited by liquid injection MOCVD using the metal alkoxide precursors [Hf(mmp)4] (mmp = OCMe2CH2OMe) and [Al(OiPr)3]. (HfO2)x(Al2O3)1–x thin films deposited at 500 °C had a thickness range of 7–13 nm and were high purity, with no carbon detected by Auger electron spectroscopy (AES) at the estimated detection limit of 0.5 at.‐%. Thick films of (HfO2)x(Al2O3)1–x containing more than ∼7 at.‐% Al were found by X‐ray diffraction (XRD) to be amorphous. High frequency capacitance–voltage (C–V) measurements indicate strong electron trapping and a high density of interface states.

Characterization of hafnium aluminate gate dielectrics deposited by liquid injection metalorganic chemical vapor deposition

Thin films of hafnium aluminate, with varying aluminum content, have been deposited by liquid injection metalorganic chemical vapor deposition using the metal alkoxide precursors hafnium methyl-methoxy-propanolate and aluminum iso-propoxide. X-ray diffraction analysis showed that the films were amorphous at aluminum concentrations above 7 at. %. Postdeposition annealing indicated that the oxide-transition temperature from amorphous to crystalline increased with aluminum content. Medium-energy ion scattering showed that up to 900 °C, internal oxidation of the silicon substrate had been inhibited. The capacitance–voltage characteristics of the films significantly improved following annealing in dry air.

Preparation and optical waveguide property of metal alkoxide solution-derived Pb(Zr0.5Ti0.5)O3 thick films

Pb(Zr 0.5 Ti 0.5 ) O 3 films with thickness of about 1.5 and 3.7 μm have been deposited on single-crystal SrTiO3 substrate by a sol-gel process from nonhydrolyzed metal alkoxide precursor. X-ray diffraction shows that the films exhibit a single perovskite phase with (001)-preferred orientation. Atomic force microscopy study indicates that the PZT film possesses a crack-free and smooth surface. The optical waveguide property has been examined by the prism-film coupling experiment. Four and 12 TE modes are observed for 1.5 and 3.7 μm PZT films, respectively.

Electrochemically induced sol-gel deposition of zirconia thin films.

A novel electrochemical method for deposition of ZrO(2) thin films is described. The films, 50-600 nm thick, were obtained by applying moderate positive or negative potentials (+2.5 V to -1.5 V versus SHE) on conducting surfaces immersed in a 2-propanol solution of zirconium tetra-n-propoxide [Zr(OPr)(4)] in the presence of minute quantities of water (water/monomer molar ratios in the range of 10(-5) to 10(-1)), which was the limiting reagent. Oxidative electrochemical formation of solvated H(+) and reductive formation of OH(-) catalyze the hydrolysis and condensation of the metal alkoxide precursor. The magnitude of the applied potential and its duration provide a convenient way of controlling the film thickness. The films consist of an amorphous phase, as revealed by XRD measurements. The effects of different parameters, such as the applied potential and its duration, the amount of added water and the current-time characteristics, were studied. A mechanism for the electrodeposition of the zirconia films which is in accordance with our findings is proposed.

Preparation and characterization of multi-coating PZT thick films by sol–gel process

The Pb(Zr 0.5Ti 0.5)O 3 films of a few micron in thickness have been successfully deposited by sol–gel technique from nonhydrolyzed metal alkoxide precursor solutions. X-ray diffraction shows that the films exhibit a single perovskite phase with (1 0 0)-preferred orientation. SEM study indicates that PZT films possess a dense microstructure with no crack and void. A Pt/PZT/LaNiO 3 capacitor has been fabricated and showed excellent ferroelectricity, with a remnant polarization up to 53 μC/cm 2. The optical waveguide property has been examined by the prism-film coupling experiment. Multimodes are excited, indicating that the PZT thick films are potentially useful for optical waveguide devices.

Thermal hysteresis of spin reorientation at Morin transition in alkoxide derived hematite nanoparticles

We present results on the structural and magnetic properties of highly crystalline α-Fe2O3 nanoparticles of average size ∼200 nm, synthesized from a novel sol-gel method using metal alkoxide precursor. These particles are multi-domain, showing the weak ferromagnetic–antiferromagnetic (WF-AF) transition (i.e., the Morin transition) at TM=256(2) K. Mössbauer measurements revealed a jump in hyperfine parameters (HP’s) at T∼TM, which also displays thermal hysteresis upon cooling or heating the sample. The analysis of HP’s as a function of temperature allowed us to discard temperature gradients as well as the coexistence of WF/AF phases as possible origins of this hysteretic behaviour. Instead, the hysteresis can be qualitatively explained by the small size and high-crystallinity of the particles, which hinder the nucleation of the WF or AF phases yielding metastable states beyond TM.

Morphological Control of Zn2SiO4:Mn Phosphor Particles by Adding Citric Acid in Spray Pyrolysis Process

Zn2SiO4:Mn phosphors for plasma display panels (PDP) application were synthesized by large-scale ultrasonic spray pyrolysis process using metal alkoxide precursor. To avoid the formation of irregular-shaped particles owing to the hollowness and phase-segregation characteristics of the silicon component, organic additive, citric acid (CA) was introduced in the spray pyrolysis. The influence of CA addition on the morphological and luminescent characteristics of the Zn2SiO4:Mn phosphor particles was investigated. The amount of CA addition is an important factor in controlling the morphological and luminous characteristics of Zn2SiO4:Mn phosphor particles. The particles prepared from the solution containing an appropriate amount of CA had a completely spherical shape, dense morphology, nonaggregation characteristics, and higher photoluminescence intensity than the commercial product, while those prepared from the solution containing excessive CA had an irregular shape, high porosity, rough surfaces, and lower brightness than the commercial product.

Preparation of supported yttrium alkoxides as catalysts for the polymerization of lactones and oxirane

AbstractTwo methods have been reported that allow yttrium alkoxides to be supported on porous silica and to be used afterward as heterogeneous catalysts in the ring‐opening polymerization of oxirane and ϵ‐caprolactone. In the two methods, [tris(hexamethyldisilyl)‐amide]yttrium {Y[N(SiMe3)2]3} is the metal alkoxide precursor. It is directly reacted with the silanol groups of the support, in the first method, and this is followed by alcoholysis of the unreacted amide groups. The flexibility of this method seems to be limited because the grafting density and the structure of the grafted Y alkoxide (less than one alkoxide by metal) are independent of the experimental conditions. In the second method, Y[N(SiMe3)2]3 is first reacted with 1 or 2 equiv of alcohol with the formation of the mixed Y alkoxide/amide. The amide functions are used to attach Y to the support. This method is free from side reactions, quite reproducible, and well suited to support one type of active species (monoalkoxide or dialkoxide). Preliminary experiments with ϵ‐caprolactone polymerization have confirmed the activity of the supported Y alkoxide, whatever preparation method is used. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 569–578, 2003

Aerogel thin film synthesis by a supercritical fluid-assisted sol–gel route in a single processing unit

Our low-T, supercritical fluid-assisted, sol–gel deposition method allows “one-pot” (single reactor vessel) processing; a metal alkoxide precursor is dissolved in a supercritical solvent, sol–gel hydrolysis and polymerisation reactions proceed on a wet substrate yielding a gel film deposit, which is then dried under supercritical conditions.

Textural stability of yttria-doped titania membranes

The textural stability of yttria-doped titania membranes prepared by the sol-gel method was studied using thermal analysis, X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and N2 physisorption techniques. In the membrane fabrication process, the hydrolysis time and geometry of the substituent group in the metal alkoxide precursor directly affected the particle size of the sol. An improvement in thermal stability was achieved in the 3 mol% yttria-doped titania membranes resulting in the retardation of the anatase-to-rutile phase transformation in the doped samples. This technology has potential application in preventing membrane cracking at high temperatures. XRD results revealed that pure and yttria-doped titanias transformed to more than 90% of rutile at temperatures higher than 600 and 800°C, respectively.

Growth of highly oriented LiNbO 3 thin films through structure controlled metal alkoxide precursor solution

Highly oriented LiNbO 3 thin films have been successfully synthesized by chemical solution deposition through a structure controlled metal-organic precursor. The homogeneous LiNbO 3 precursor solution was prepared by controlling the reaction of metal alkoxides and selecting the ligand for modification. LiNbO 3 thin films with c-axis preferred orientation were directly crystallized on sapphire C substrates from chemical solutions synthesized in this study. The epitaxial relation of LiNbO 3 film to sapphire substrate was found to depend strongly upon the precursor structure modified with β-diketone. 1-Phenyl-1,3-butanedione (PBD) was found to be superior to acetylacetone (acacH) and dibenzoylmethane (DBM) for the crystallization of epitaxial LiNbO 3 films. The results suggested that the existence of a benzene ring in the ligand strongly influenced the degree of orientation of synthesized films.

Investigation of interactions between a NLO-dye and metal alkoxide precursors of hybrid materials

AbstractInteractions between the dye Red 17 (4-(amino-N, N-diethanol)-2-methyl-4'-nitroazobenzene) having nonlinear optical (NLO) properties and metallo-organic sol-gel precursors M(OR)n (M = Ti, Zr, Si and Sn; R = CnH2n+1) have been investigated by means of UV-VIS spectrophotometry and liquid state NMR (1H, 29Si and 119Sn) techniques. The presence of titanium, zirconium or tin alkoxides make strong modifications in the UV-VIS absorption spectrum of the Red 17 in solution. On the contrary, when the Red 17 is grafted to alkoxysilyl groups, only minor changes were observed. The resulting bathochromic shift of about 30 nm observed with transition metal or tin alkoxides was found to be due to Lewis acid-base type interactions between the Red 17 and the metallic centre.

Aerosol synthesis of Ti–O powders via in-droplet hydrolysis of titanium alkoxide

A method to produce Ti–O powders by an in-droplet hydrolysis of metal alkoxide precursor is presented. Titanium n-tetrabutoxide, hydrolysis water, and acetic acid were included in the ethanolic precursor solution that was nebulized. The resulting aerosol was transported to a tubular flow reactor where the ethanol evaporation initiated a polycondensation reaction and solid particles were formed starting from droplet surface. Titanium hydrous oxide particles were obtained at 200°C in atmospheric pressure of nitrogen and air. The collected powders were characterized by XRD, TG–SDTA, BET, SEM, TEM, and IR- spectroscopy, as well as with aerosol impactor. The as-produced powder particles were amorphous, smooth on the surface, and either spherical or deflated in shape. Aerodynamic mass mean diameter was 2.7 μm. Nanocrystalline TiO 2 was obtained after thermal post-annealing for one hour. An expected tendency to convert to anatase crystalline phase up to 500°C and subsequently to rutile phase up to 900°C in the annealing was observed. The results show that the in-droplet hydrolysis is a viable method in preparing fine Ti–O powder particles with controlled properties.

Photocatalytic degradation of o-cresol sensitized by iron–titania binary photocatalysts

The degradation of ortho-cresol ( o-cresol) assisted by Fe/TiO 2 photocatalysts was investigated in oxygenated aqueous suspension in a spiral glass flow reactor. Iron–titania (1–10 wt.% Fe) mixed catalysts have been prepared by sol–gel impregnation method using metal alkoxide precursors. The surface structure of Fe/TiO 2 catalyst was studied by surface analysis with XPS and TEM techniques. Characterization of these catalysts, fired at different temperatures (in the range 500–900°C) using X-ray diffraction (XRD) showed that the sintering temperature and incorporation of iron ions mediate the phase transformation and growth of pseudobrookite (Fe 2TiO 5) phase at higher temperatures. The rate of degradation of o-cresol decreases with the increasing sintering temperature and iron content of the catalysts and the initial pH of the aqueous solution of o-cresol changes with the illumination time due to the formation of various acidic intermediate photoproducts.

Chemical solution technique to prepare perovskite PZT and PLZT thin films and powders

PbZr0.65Ti0.35O3 and Pb0.91La0.09Zr0.65Ti0.35O3 thin films with thickness of around 100 nm were prepared by the chemical solution deposition technique on Si (100) substrate. Complex metal alkoxide precursors were synthesized by alcoholisis and alcohol exchange reactions starting from metallorganics compounds. NMR spectroscopic techniques, 1H and 13C, and FTIR analysis were used to study the arrangement of the metals and oxygen in the precursor molecules. The films were deposited on Si (100) by spin coating technique and thermal treated by Rapid Thermal Processing for film crystallization. The thermal evolution and structural characterization were performed by DTA-TG/FTIR and by glazing incidence XRD and XRD powder. A PLZT powder with a well-crystallized perovskite structure was obtained at 700°C free of pyrochlore phase whereas the PLZT film exhibits a distorted perovskite structure and residual pyrochlore. The PZT films were less crystallized. The silicon substrate affects the crystal structure of the film. The residual acetylacetonate groups in the precursor of PLZT, would reduce the clustering of Zirconium species.

Chemical Vapor Deposition of Sr1−xBaxNb2O6 Thin Films Using Metal Alkoxide Precursors

A novel two-step metalorganic chemical vapor deposition process was used in this study to prepare Sr1−xBaxNb2O6 (SBN) thin films. Two thin layers of single-phase SrNb2O6 and BaNb2O6 were deposited alternately on a silicon substrate, and the solid solution of SBN was obtained by high-temperature annealing. The stoichiometry control of the SrNb2O6 and the BaNb2O6 thin films was achieved through deposition process control, according to the evaporation characteristics of double metal alkoxide. The evaporation behavior of double metal alkoxide precursors SrNb2(1-OC4H9)12 and BaNb2(1-OC4H9)12 was studied, and the results were compared with the evaporation of single alkoxide Nb(1-OC4H9)5.