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TiO2 (rutile) thin films were deposited via a hydrothermal process by adjusting the amount of ethanol, deposition time, and temperature. Especially, various amounts of ethanol generated different degrees of supersaturation in precursor solution. It allowed us to systematically change the width, lengths, and crystallinity of a vertically aligned 1-D nanorod structure of TiO2 films. The oriented attachment, confirmed by scanning electron microscopy and transmission electron microscopy, was shown to be responsible for their lateral growth of TiO2 nanorods bundled by numerous well-oriented nanowires and their vertical growth. TiO2 nanorod thin films were also characterized via X-ray diffraction and UV-Vis-NIR spectrophotometer to find a correlation between the process conditions and nanostructural evolution. Dye sensitized solar cells were assembled to relate the nanostructures of TiO2 films with the effectiveness of its role as a photoelectrode.

Nanostructured TiO2 thin films were prepared via a low-temperature solution processing. We have previously calculated the degree of supersaturation (s) for TiO2 precursor solution to systematically tailor the development of TiO2 nanostructures in the range of s = 70–200. In this article, we focused more on a lower supersaturation regime (s < 70), from which we were able to obtain various shapes and sizes of nanostructures of TiO2 thin films. A film consisting of “rutile” phase nanoblades was observed when the degree of supersaturation was s = 15–70. To further lower the supersaturation (s < 15), hydrothermal processing had to be used, for which a film consisting of “rutile” phase nanorods was obtained. The resulting thin films were evaluated for band gap energies and dielectric properties. The band gap energy for those rutile thin films decreased from 3.22 to 2.99 eV when the supersaturation was lowered from s = 70 to 15. The dielectric constant (k) of the rutile film processed from s = 50 showed the best performance with k~50 at 1 MHz.

We have developed a “two-step” solution-based processing to deposit high-k ceramic thin films. Electrochemically pre-coated amorphous titania layers were “hydrothermally” or “hydrothermal-electrochemically” converted to crystalline BaTiO3 films at ≤90°C. In hydrothermal process, an in situ electrochemical protection (ECP) mechanism enables utilization of common metallic substrates (e.g., Cu), which otherwise suffer corrosion from the precursor. Microstructural evolution of BaTiO3 films along with the effectiveness of ECP is discussed in this article. Derived BaTiO3 shows a dielectric constant of ~80 at 100 kHz, which makes it a promising candidate for high-density microelectronic capacitor applications.

Current microelectronics devices based on flexible as well as rigid substrates demand high dielectric constant (k) films to be grown on conductive substrate from a low-cost, low-temperature deposition technique. In this study, we produced high-k titania (TiO 2 ) fihns through an affordable electrodeposition protocol from the electrochemical bath maintained at about 0°C. The deposition occurs through a rapid hydrolysis mechanism of titanium containing ions in the precursor solution aided by electrochemically generated hydroxyl ions formed near the cathode surface (copper (Cu) substrate). Upon attaining a sufficient supersaturation level, such hydrolyzed species precipitate to form a titania thin film on the cathode surface. While depositing from a highly acidic precursor solution, Cu substrate was protected by a cathodic potential (-3 to ―5 V against the counter electrode). The resultant titania films show nanoparticulate structures evolved from nucleation and growth events of the in situ precipitated particles. Much higher deposition rate (about 1 μm/ min) was observed compared with that of typical chemical bath deposition. The resultant fihns with a thickness of 1500 nm grown on Cu exhibit very high dielectric properties (e.g., k ∼ 30, capacitance density > 110 nF/in. 2 at 100 kHz) and moderate breakdown voltage (V B ) (∼17.5 V). These properties indicate the potential of electrodeposited titania films to be used as a small-area thin-film capacitor for miniaturized electronic devices.

Both the electrical and mechanical properties of silica thin films deposited by liquid phase deposition (LPD) have been evaluated in this study. Silica thin films have been prepared on glass surface by immersing it in a supersaturated Hexafluorosilicic acid (H 2 SiF 6 )-based solution at a low temperature of 50°C. The as-deposited LPD silica fihns exhibit a low dielectric constant (k) that varies from 1.7 to 2.7 depending on the film morphology and fluorine content of the film. Young's modulus of these films was measured in the range of 18.9-24.5 GPa by a nanoindentation technique. The combination of extremely low k and fairly high modulus made this low-temperature-processed LPD silica films a very promising candidate for an interlayer dielectric film for the next-generation semiconductor devices.

Titanium oxide (TiO{sub 2}) thin films can be prepared by controlled hydrolysis of a titanium tetrachloride (TiCl{sub 4}) precursor in an aqueous solution at temperatures below 100 C. As part of an effort to understand the formation of such TiO{sub 2} films, the kinetics of the nucleation, growth, and aggregation of TiO{sub 2} nanoparticles in aqueous solutions of TiCl{sub 4} were studied using dynamic light scattering and a transmission electron microscope (TEM). A higher degree of supersaturation, produced by a higher solution temperature, a higher concentration of TiCl{sub 4}, or a higher pH, results in a shorter nucleation induction time, a faster initial growth/aggregation rate, and a larger aggregate size. The interfacial energy of TiO{sub 2} nanoparticles was found to be 0.072 J/m{sup 2} from the homogeneous nucleation theory. Further investigations by a high-resolution scanning electron microscope (SEM) and TEM for the as-deposited films showed the structure hierarchy organized from nanocrystalline particles precipitated in the supersaturated solution. As a result, the effect of solution conditions on the nucleation, growth, and aggregation of TiO{sub 2} nanoparticles can provide useful guidance for tailoring of microstructures of the TiO{sub 2} films.

The tensile creep behavior of two rare-earth dopant systems, lanthanum- and yttrium-doped alumina, are compared and contrasted in order to better understand the role of oversized, isovalent cation dopants in determining creep behavior. It was found that, despite some microstructural differences, these systems displayed qualitatively a similar improvement in creep resistance, supporting the hypothesis that creep is strongly influenced by segregation. Differences in primary creep behavior and activation energy for steady-state creep were, however, observed for these systems. Given these results, it is expected that creep behavior can be further optimized by adjusting the dopant level and by controlling the microstructure.

Oversized dopant ions such as yttrium and lanthanum segregate to grain boundaries and reduce the tensile creep rate of α-Al 2 O 3 by 2-3 orders of magnitude. One explanation for this behavior is that the oversized segregants give rise to a site-blocking effect for grain boundary diffusion. It has also been speculated that the dopant ions modify the grain boundary structure in alumina and reduce the creep rate by promoting the formation of special (e.g., coincidence site lattice (CSL)) grain boundaries. In order to test the latter hypothesis, we have used electron backscattered Kikuchi diffraction to characterize the misorientation and special grain boundary distribution for undoped and 1000-ppm-yttrium-doped alumina. The results show that the grain boundary structure in alumina (as characterized by the frequency of selected CSLs and misorientation distribution) was not significantly changed by the addition of yttrium, indicating that creep retardation results mainly from site-blocking.

High-spatial-resolution analytical electron microscopy using energy-dispersive X-ray (EDX) and electron energy-loss spectrometry (EELS) of yttrium- and lanthanum-doped Al2O3 has been conducted to ascertain the level of segregation of these impurities to grain boundaries. Line profile analyses indicate that the segregation is confined to a layer thickness of

It is believed that the segregation of oversized dopant ions to grain boundaries in Al 2 O 3 hinders grain-boundary diffusion, thereby reducing the tensile creep rate in this system by ∼2-3 orders of magnitude. In order to explain this improvement in creep behavior, it is helpful to characterize both the effective cation and interstitial volumes at grain boundaries, because the relative openness of some boundary structures suggests a great accommodation of oversized ions. In this study, the boundary volume is determined by a spatially local Voronoi construction, which highlights cation (Al 3+ ) substitutional sites as well as large interstitial voids. In particular, we examine the spatial distribution of free volume near grain boundaries and, in addition, the dependence of the driving force for segregation on misfit strain in doped Al 2 O 3 . We interpret our results in light of recent evidence that selective codoping can provide a more efficient means of filling available space near boundaries, thereby further enhancing creep resistance.

The microstructural features and tensile creep behavior of Al 2 O 3 doped with Nd 2 O 3 at levels ranging from 100 to 1000 ppm (Nd:Al atomic ratio) were systematically investigated. Compositional mapping, using both high-resolution scanning transmission electron microscopy and secondary ion mass spectroscopy revealed that, for all of the compositions studied, the Nd 3+ ions were strongly segregated to the Al 2 O 3 grain boundaries. Microstructural observations revealed that the solubility of Nd 2 O 3 was between 100 and 350 ppm. Tensile creep tests were conducted over a range of temperatures (1200°-1350°C) and stresses (20-75 MPa). Both the stress and grain-size exponents were analyzed. In selected experiments, controlled grain-growth anneals were used to enable creep testing of samples of the same average grain size but different neodymium concentrations. Independent of dopant level, the neodymium additions decreased the creep rate by 2-3 orders of magnitude, compared with that of undoped Al 2 O 3 . The value of the apparent creep activation energy increased with increased dopant concentration and then saturated at dopant levels exceeding the solubility limit. Overall, the results of the present study were consistent with a creep-inhibition mechanism whereby oversized segregant ions reduce grain-boundary diffusivity by a site-blocking mechanism.