J.M. Hampikian

Nanoindentation measurements of combustion CVD Al2O3 and YSZ films

Abstract Combustion chemical vapor deposition (combustion CVD) was used to deposit thin films of yttria stabilized zirconia (YSZ) and alumina (Al 2 O 3 ). Nanoindentation analysis for hardness, modulus and fracture toughness of the films as well as several bulk materials, including single crystal Al 2 O 3 , MgO, SiO 2 , YSZ and polycrystalline Al 2 O 3 was conducted. YSZ films that were produced with a total cation molarity of 0.005 M possessed significant surface roughness that was not conducive to nanoindentation measurements. The lower concentration investigated, 0.002 M provided a repeatable deposition condition that produced thin films with consistent hardness and modulus values. Load-displacement measurements at very low loads (up to total displacements of 200 nm) showed that the Al 2 O 3 films tended to plastically deform, whereas the YSZ films showed less of a tendency to do so. For Al 2 O 3 films that were 0.38±0.09 μm thick, the modulus, hardness and fracture toughness values were 28.6±1.6 GPa, 479±15 GPa and 2.22±0.31 MPa m 0.5 , respectively; for YSZ films that were 0.65±0.05 μm thick, the values were 16.1±4.6 GPa, 388±89 GPa and 1.67±0.46 MPa m 0.5 , respectively. These values were found to be consistent with the values measured via nanoindentation in this work for bulk samples of Al 2 O 3 and YSZ, as well as to those reported in the literature.

Combustion chemical vapor deposition of CeO2 film

Abstract Thin ceria (CeO 2 ) films were deposited onto a-plane sapphire substrates via combustion chemical vapor deposition using toluene as a solvent and Ce(III) 2-ethylhexanoate (Ce-2EH) and tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)(IV) cerium (Ce-(TMHD) 4 ) as chemical precursors. Depositions were made at a substrate temperature of 1000°C using several precursor concentrations and aerosol size distributions. Ceria assumes the fluorite (cubic) structure in the polycrystalline films. Films produced with low concentrations (∼0.001 M) of Ce-2EH display a preferred orientation in which the (200) axis is perpendicular to sapphire substrates. Similar low concentration of Ce-(TMHD) 4 yield films with (111) preferred orientation. High precursor concentrations ((0.002 M) and/or large aerosol size distributions yielded films containing ceria clusters that appear to have nucleated in the gas phase and adhered to the substrates in addition to material that nucleated on the substrates.

Formation and thermal stability of aluminium nanoparticles synthesized via yttrium ion implantation into sapphire

Yttrium ion implantation of 1 1 2 3 alumina resulted in the formation of metallic aluminium–yttrium, face centred cubic (a0=0.41 nm) spherical nanocrystals (∼ 12 nm in diameter) embedded in an amorphous matrix. A fluence of 5×1016Y+/cm2 implanted at ambient temperature and accelerating energies of 150 or 170 keV yielded this result. Crystalline nanoparticles were not present in the amorphous matrix for implantations done with identical conditions but lower energy (100 keV). Substrates implanted at 150 keV were annealed in laboratory air for times ranging from 20 to 90 min and temperatures ranging from 1000 to 1400°C. A clear progression of morphologies resulted from these annealing treatments. A 1000°C, 90 min anneal produced ∼13% recrystallization of the amorphous region and induced the formation of crystallites of a metastable Y–Al alloy. An 1100°C, 90 min anneal demonstrated ∼40% recrystallization of the amorphous region, accompanied by the formation of partially aligned internal grains of Y2O3. Electron diffraction shows that the Y–Al alloy crystallites which formed in the 1000°C anneal are also present at 1100°C. A highest temperature anneal of 1400°C, 60 min induced essentially complete recrystallization of the amorphous phase, the dissolution of the metastable Y–Al alloy, the retention of the internal yttria grains, and the formation of partially oriented external grains of yttria resulting from the segregation of yttrium to the substrate surface.

Implantation parameters affecting aluminum nano-particle formation in alumina

The formation of nano-dimensional metallic Al precipitates in alumina due to the reduction of the host matrix as a result of ambient temperature ion implantation of Y ions is examined. The formation and growth of Al precipitates are dependent on both the Y ion dose and the energy available to the matrix, as reported here. Reducing the ion dose from 5 × 1016 to 2.5 × 1016 ions/cm2 results in smaller precipitates; 10.7 ± 1.8 nm to 9.0 nm ± 1.2 nm, respectively, for incident ion energies of 150 keV, based upon particle size measurements obtained using energy filtered transmission electron microscopy. Below a fluence of 2.5 × 1016, particle formation is not detected. The energy available to the matrix was varied; first, by controlling the incident ion energy (varied between 60 and 150 keV) while holding the substrate at ambient temperature, and second, by controlling the substrate temperature (varied between 44 and 873 K) while holding the incident ion energy constant at 150 keV. Experiments conducted with incident ion energies of 110 keV or higher produce crystalline Al precipitates; whereas implantations at 100 keV produce amorphous Al particles and implantations at 60 keV produce no detectable precipitates. The implantations carried out as a function of temperature produce successively smaller precipitates with decreasing temperature to 77 K (6.7 ± 1.0 nm), below which no precipitates are detected. An Arrhenius activation energy for the formation of the aluminum precipitates of 1.7 kJ/mole has been calculated using the volume of precipitates formed as a function of inverse temperature. This low activation energy suggests that radiation enhanced diffusion (RED) is responsible for particle growth during these implantations.

Shock compaction and strengthening of nanocrystalline NiAl

The microstructural characteristics and strengthening mechanisms of shock-consolidated nanocrystalline B2-phase NiAl intermetallic are discussed in this paper. Nanophase NiAl powders prepared by mechanical alloying were shock consolidated at a peak pressure of 4–6 GPa, to ≈83% theoretical maximum density (T.M.D.). Characterization by transmission electron microscopy (TEM) revealed that the structure of the shock-consolidated sample was retained at the nanoscale. The compacts showed evidence of grain boundary dislocations, subgrains, distorted regions, and shear bands. Investigation of the relationship between microhardness and grain size for nanocrystalline stoichiometric intermetallic NiAl powder compacts, showed that the micro-hardness increased with decreasing grain size. The strengthening mechanism was observed to be consistent with the Hall-Petch behavior dominated by dislocation generation at grain boundary ledges.

Synthesis and Characterization of α-Alumina Films Via Combustion Chemical Vapor Deposition

α-Alumina films are useful for high-temperature, wear, and semiconductor device applications because of their good oxidation resistance, high hardness values, and electrical properties. α-Alumina films have been previously synthesized using techniques such as chemical vapor deposition, sol-gel, physical vapor deposition, and plasma spraying. This paper presents an alternative approach for producing high quality dense α-alumina coatings using a flame-assisted process called combustion chemical vapor deposition (CCVD). This process is an open atmosphere technique that does not require the use of a reaction chamber. In this work alumina films were grown on YSZ at temperatures ranging from 900 to 1500°C. At lower temperatures only amorphous alumina was grown, but as the deposition temperature increased different alumina phases were formed. At 1100°C, a thin highly crystalline θ-Al 2 O 3 coating was formed. At temperatures higher than 1100°C thick θ-Al 2 O 3 coatings were deposited on the YSZ. Coatings were characterized by scanning electron microscopy (SEM) and x-ray diffraction (XRD).

The examination of calcium ion implanted alumina with energy filtered transmission electron microscopy

Ion implantation can be used to alter in the optical response of insulators through the formation of embedded nano-sized particles. Single crystal alumina has been implanted at ambient temperature with 50 keV Ca{sup +} to a fluence of 5 {times} 10{sup 16} ions/cm{sup 2}. Ion channeling, Knoop microhardness measurements, and transmission electron microscopy (TEM) indicate that the alumina surface layer was amorphized by the implant. TEM also revealed nano-sized crystals {approx}7--8 nm in diameter. These nanocrystals are randomly oriented, and exhibit a face-centered cubic structure (FCC) with a lattice parameter of 0.409 nm {+-} 0.002 nm. The similarity between this crystallography and that of pure aluminum suggests that they are metallic aluminum nanocrystals with a slightly dilated lattice parameter, possibly due to the incorporation of a small amount of calcium. Energy-filtered transmission electron microscopy (EFTEM) provides an avenue by which to confirm the metallic nature of the aluminum involved in the nanocrystals. EFTEM has confirmed that the aluminum present in the particles is metallic in nature, that the particles are oxygen deficient in comparison with the matrix material and that the particles are deficient in calcium, and therefore not likely to be calcia. The particles thus appear to be FCC Al (possibly alloyed with a few percent Ca) with a lattice parameter of 0.409nm. A similar result was obtained for yttrium ion implantation into alumina.

Nanocrystal Formation Via Yttrium Ion Implantation into Sapphire

Ion implantation has been used to form nanocrystals in the near surface of single crystal {alpha}-Al{sub 2}O{sub 3}. The ion fluence was 5 x 10{sup 16} Y{sup +}/cm{sup 2}, and the implant energies investigated were 100, 150, and 170 keV. The morphology of the implanted region was investigated using transmission electron microscopy, x-ray energy dispersive spectroscopy, Rutherford backscattering spectroscopy and ion channeling. The implantation causes the formation of an amorphous surface layer which contains spherical nanosized crystals with a diameter of {approximately}13 nm. The nanocrystals are randomly oriented and exhibit a face-centered cubic structure with a lattice parameter of {approximately}4.1 A {+-} .02 A. Preliminary chemical analysis shows that these nanocrystals are rich in aluminum and yttrium and poor in oxygen relative to the amorphous matrix.