Asymmetric leakage in (Ba, Sr)TiO3 nanoparticle/parylene-C composite capacitors

Magnetic and dielectric property control in the multivalent nanoscale perovskite Eu0.5Ba0.5TiO3

We report nanoscale Eu_0.5Ba_0.5TiO₃, a multiferroic in the bulk and candidate in the search to quantify the electric dipole moment of the electron. Eu_0.5Ba_0.5TiO₃, in the form of nanoparticles and other nanostructures is interesting for nanocomposite integration, biomedical imaging and fundamental research, based upon the prospect of polarizability, f-orbital magnetism and tunable optical/radio luminescence. We developed a [non-hydrolytic]sol-[H₂O-activated]gel route, derived from in-house metallic Ba_(s)/Eu_(s) alkoxide precursors and Ti{(OCH(CH₃)₂}₄. Two distinct nanoscale compounds of Ba:Ti:Eu with the parent perovskite crystal structure were produced, with variable dielectric, magnetic and optical properties, based on altering the oxidizing/reducing conditions. Eu_0.5Ba_0.5TiO₃ prepared under air/O₂ atmospheres produced a spherical core-shell nanostructure (30-35 nm), with perovskite Eu_0.5Ba_0.5TiO₃ nanocrystal core-insulating oxide shell layer (∼3 nm), presumed a pre-pyrochlore layer abundant with Eu³⁺. Fluorescence spectroscopy shows a high intensity ⁵D₀→⁷F₂ transition at 622 nm and strong red fluorescence. The core/shell structure demonstrated excellent capacitive properties: assembly into dielectric thin films gave low conductivity (2133 GΩ mm^-1) and an extremely stable, low loss permittivity of ε_eff∼25 over a wide frequency range (tan δ < 0.01, 100 kHz-2 MHz). Eu_0.5Ba_0.5TiO₃ prepared under H₂/argon produced more irregular shaped nanocrystals (20-25) nm, with a thin film permittivity around 4 times greater (ε_eff 101, tan δ < 0.05, 10 kHz-2 MHz, σ∼59.54 kΩ mm^-1). Field-cooled magnetization values of 0.025 emu g^-1 for EBTO-Air and 0.84 emu g^-1 for EBTO-Argon were observed. X-ray photoelectron spectroscopy analysis reveals a complex interplay of Eu^II/III/Ti^III/IV configurations which contribute to the observed ferroic and fluorescence behavior.

Structure and performance of dielectric films based on self-assembled nanocrystals with a high dielectric constant

Self-assembled films built from nanoparticles with a high dielectric constant are attractive as a foundation for new dielectric media with increased efficiency and range of operation, due to the ability to exploit nanofabrication techniques and emergent electrical properties originating from the nanoscale. However, because the building block is a discrete one-dimensional unit, it becomes a challenge to capture potential enhancements in dielectric performance in two or three dimensions, frequently due to surface effects or the presence of discontinuities. This is a recurring theme in nanoparticle film technology when applied to the realm of thin film semiconductor and device electronics. We present the use of chemically synthesized (Ba,Sr)TiO3 nanocrystals, and a novel deposition-polymerization technique, as a means to fabricate the dielectric layer. The effective dielectric constant of the film is tunable according to nanoparticle size, and effective film dielectric constants of up to 34 are enabled. Wide area and multilayer dielectrics of up to 8 cm(2) and 190 nF are reported, for which the building block is an 8 nm nanocrystal. We describe models for assessing dielectric performance, and distinct methods for improving the dielectric constant of a nanocrystal thin film. The approach relies on evaporatively driven assembly of perovskite nanocrystals with uniform size distributions in a tunable 7-30 nm size range, coupled with the use of low molecular weight monomer/polymer precursor chemistry that can infiltrate the porous nanocrystal thin film network post assembly. The intercrystal void space (low k dielectric volume fraction) is minimized, while simultaneously promoting intercrystal connectivity and maximizing volume fraction of the high k dielectric component. Furfuryl alcohol, which has good affinity to the surface of (Ba,Sr)TiO3 nanocrystals and miscibility with a range of solvents, is demonstrated to be ideal for the production of nanocomposites. The nanocrystal/furfuryl alcohol dispersions are suitable for the fabrication of thin films by chemical deposition techniques, including spin-coating, printing or a spraying process. To demonstrate the application of this technique to device fabrication, a multilayer capacitor with capacitance of 0.83 nF mm(-2) at 1 MHz is presented.