Sr Ti O 3 (STO) thin films were deposited at 370°C by atomic layer deposition using H2O as the oxidant, and Ti(O–iPr)2(thd)2 and Sr(thd)2 as Ti, and Sr precursors, respectively. Denser STO films were produced at this deposition temperature. The saturated growth rate was 0.15Å∕cycle. The adoption of a thin crystallized seed layer resulted in crystallized perovskite STO films at the as-deposited state without higher temperature post-annealing. A tox of 0.72nm (dielectric constant of 108) and a low leakage current density (∼10−7A∕cm2 at 0.8V) were obtained from a planar capacitor structure consisting of Pt∕20-nm-thick STO/Ru (bottom).

SrTiO 3 ͑STO͒ thin films were grown on Si wafer, Pt-and Ru-coated Si wafers, respectively, by an atomic layer deposition ͑ALD͒ technique using conventional metallorganic precursors, Sr͑C 11 H 19 O 2 ͒ 2 ͑Sr͑thd͒ 2 ͒ and Ti͑Oi-C 3 H 7 ͒ 4 ͑TTIP͒ as Sr-and Tiprecursors, respectively, with a remote-plasma activated H 2 O vapor as the oxidant at a wafer temperature of 250°C. Patterned Si wafers with contact holes having a diameter of 0.13 and 1 µm depth ͑aspect ratio of 8͒ was used in order to test the film-thickness and cation-composition conformalities over the contact hole surface. The ALD behavior of the STO film was critically dependent on the Sr͑thd͒ 2 source heating temperature. When the Sr source temperature was Ͻ ϳ200°C ͓Sr͑thd͒ 2 melting temperature͔ stoichiometric STO films were deposited with a good process reliability. Excellent film thickness and cation composition conformalities ͑nonuniformity Ͻ3%͒ over the severe contact hole structure were obtained by the optimized precursor supply and deposition conditions. It was also observed that most of the input TTIP precursor molecules did not chemically adsorb on the SrO surface, possibly due to oversaturation of the SrO surface by the Sr͑thd͒ 2 molecules or thermally modified Sr͑thd͒ 2 molecules as a result of the heating process of the Sr͑thd͒ 2 when the Sr-source temperature was Ͼ ϳ200°C. This difficulty resulted in a nonuniform cation composition ratio along the contact hole.High-dielectric constant thin films such as SrTiO 3 ͑STO͒ and ͑Ba,Sr͒TiO 3 ͑BSTO͒ 1-5 have attracted great interest as the capacitor dielectrics of dynamic random access memory ͑DRAM͒ devices. Recently, these materials have also been actively studied for the high-frequency tunable devices, 6,7 decoupling capacitors, 8 and gate dielectric 9,10 applications. Among these, the DRAM capacitor applications require conformal deposition over a 3-dimensional structure with a feature size Ͻ0.1 m in terms of film thickness and composition, which is not required in other applications.The low-temperature ͑Ͻ500°C͒ metallorganic chemical vapor deposition ͑MOCVD͒ process has been extensively studied for producing STO and BSTO thin films for DRAM applications due to its good film step coverage over a severe 3D surface topology, and nondamaging deposition on the underlying electrode stack. 11,12 However, conformal deposition over the entire surface area of such an extreme geometry in terms of the chemical composition as well as the thickness has not necessarily been confirmed even for lowtemperature MOCVD processes. The authors have reported extensive experimental results on the composition and thickness variations of the MOCVD STO and BSTO films deposited at wafer temperatures ranging from 420 to 440°C on a capacitor hole pattern with dimensions of 0.15 ϫ 0.40 ϫ 0.57 ͑depth͒ m 3 where two shower-head-type and one dome-type MOCVD chamber with two different precursor sets were used. 13,14 From the study, it was found that obtaining a conformal composition and film thickness over the 3D geometry using th...

Atomic layer deposited SrTinormalO3 (STO) thin films were grown using Sr(normalC11normalH19normalO2)2 and Ti(Oi-normalC3normalH7)4 with a remote plasma activated or thermal normalH2O vapor as oxidant at growth temperatures ranging from 190to270°C . The as-grown films were amorphous and showed a low effective dielectric constant of ∼20 with a low leakage current density ( <10−7A∕cm2 at 1V ). The chemical binding status of the Sr ions varied with the degree of crystallization of the STO film. A reasonable film growth rate and stoichiometric cation composition were obtained when the vaporization temperature of Sr-precursor was <200°C with the thermal normalH2O vapor. The low density of the as-grown film induced a large shrinkage in the film thickness which caused microcracking of the crystallized films during postannealing, even with the increased normalH2O supply. Adoption of thin (∼5nm) crystallized seed layer before the main layer STO growth improved the microstructure after the crystallization and the leakage current performance. As a result of the process optimization, the best electrical properties of an STO film grown on a Ru electrode were 0.45nm for the equivalent oxide thickness and 1×10−3A∕cm2 for the leakage current density at 1V .

Solvent molecules within zeolite pores provide interactions that influence the stability of reactive intermediates and impact rates and selectivities for catalytic reactions. We show the kinetic and thermodynamic consequences of these interactions and reveal their origins using alkene epoxidations in titaniumsubstituted *BEA (Ti-BEA) zeolites. Epoxidation turnover rates vary widely among primary n-alkenes (C 6 −C 18 ) in hydrophilic (Ti-BEA-OH) and hydrophobic (Ti-BEA-F) catalysts in aqueous acetonitrile (CH 3 CN). Apparent activation enthalpies (ΔH app ‡ ) and entropies (ΔS app ‡) increase with alkene carbon number in both catalysts; however, the span of ΔH app ‡ values in Ti-BEA-OH (68 kJ mol −1 ) greatly exceeds that in Ti-BEA-F (18 kJ mol −1 ). These trends, and commensurate gains in ΔS app ‡ , reflect the displacement and reorganization of solvent molecules that scale with the size of transition states and the numbers of solvent molecules stabilized by silanol defects near active sites. Experimental and computational assessments of intrapore solvent composition from 1 H NMR, infrared spectroscopy, and grand canonical molecular dynamics (GCMD) simulations show that Ti-BEA-OH uptakes larger quantities of both CH 3 CN and H 2 O than Ti-BEA-F. The Born−Haber decomposition of simulated enthalpies of adsorption (ΔH ads,epox ) for C 6 −C 18 epoxides attributes ΔH ads,epox that become more endothermic for larger adsorbates to the displacement of greater numbers of solvent molecules bound to silanol defects into the bulk solvent. A strong correlation between ΔH app ‡ and ΔH ads,epox (from GCMD and isothermal titration calorimetry) gives evidence that the disruption of solvent structures provides excess thermodynamic contributions (e.g., G ε ) that depend on the solvent composition in the pores, the excluded volume of reactive species, and the density of silanol groups near active sites. Altering G ε values offers opportunities to control selectivities and rates of reactions through the design of extended active site environments.

The type and density of structural defects within zeolites and zeotypes affect the stabilities of adsorbed species, which, in turn, impact the performance of these materials as catalysts and adsorbents. Despite the recognized importance of silanol groups (SiOH) on the properties of a zeolite catalyst or adsorbent, the densities of SiOH have not been quantitatively linked to the concentration of hydroxide (OH − ) and fluoride (F − ) ions within the synthesis gel. Here, we present a method for the synthesis of siliceous or heteroatom-substituted MFI zeolites (M-MFI; M = Si, Ti, Nb, or Ta) with tunable densities of SiOH, which depend simply on the ratio of hydrofluoric acid (HF) to structuredirecting agent (SDA; tetrapropylammonium hydroxide) used within the synthesis gel. The equilibrated ion exchange between OH − and F − ions forms tetrapropylammonium fluoride in situ, which does not lead to the formation of SiOH defects within M-MFI. Comparisons of infrared spectra from 15 distinct M-MFI materials show that the densities of SiOH groups within M-MFI decrease linearly with the ratio of HF/SDA, independent of the identity of the heteroatom within the framework. Materials synthesized within purely OH − media possess SiOH densities 3 and 100 times greater than analogous materials synthesized with HF/SDA ratios of 1 and 1.5, respectively. The use of HF forms metal fluoride complexes, detected by Raman spectroscopy, which are not readily incorporated into the zeolite framework during synthesis and lead to a decrease in the efficiency of transition-metal incorporation with increasing amounts of HF. The quantity of the heteroatom incorporated into the framework increases linearly with the concentration of metal precursor in the synthesis gel, which provides a method to mitigate the lower yields introduced by the use of HF. Comparisons between H 2 O vapor adsorption isotherms show that M-MFI materials synthesized with an HF/SDA ratio of 1.5 adsorb 4−10-fold less H 2 O than M-MFI synthesized with equal amounts of HF and SDA and 100 times less H 2 O than M-MFI synthesized in OH − media. Comparisons of water uptake within hydrophobic M-MFI materials show that framework Ti and Nb sites stabilize 5 and 7−8 H 2 O molecules, respectively, near saturation vapor pressures. These findings provide a flexible strategy to control the densities of silanol and hydroxyl groups (e.g., Nb-OH) within MFI and will likely extend to the synthesis of other zeolite frameworks.