Krisztian Niesz

Large-scale engineered synthesis of BaTiO3 nanoparticles using low-temperature bioinspired principles

We report here a robust, large-scale synthesis of BaTiO3 nanopowders using a bioinspired process that first was developed on a much smaller scale. The most advantageous points of this protocol are that it takes place at nearly room temperature (25 °C), overcomes many limitations encountered in other scale-up processes (such as the need for external drivers, e.g., heat, radiation or pressure), bypasses the use of surfactants and templates and does not necessitate pH adjustment. The use of a single-source, bimetallic alkoxide with the vapor diffusion of a hydrolytic catalyst (H2O) provides the necessary conditions for facile crystallization and growth of small, well-defined BaTiO3 nanoparticles at mild temperatures, yielding batches of up to 250 ± 5 g in a green process. Extension of this method to kilogram-scale production of BaTiO3 nanocrystals in semicontinuous and continuous processes is feasible.

Bio-inspired nanofabrication of barium titanate

Complex metal oxides such as BaTiO3 are widely sought materials in the ceramic and electronic industries due to their piezoelectric, ferroelectric, and dielectric properties. The synthesis of BaTiO3 typically requires harsh reaction conditions such as high temperature and pressure that provide poor control over composition, crystal structure, and nanoscale morphology. In contrast, living organisms are able to maintain impressive regulation over the crystallization of inorganic materials during naturally occurring mineralization processes. Here, we present a few general principles from biomineralizing systems that can be harnessed for synthetic materials as well as successful bio-inspired approaches that have been demonstrated for the fabrication of BaTiO3 nanostructures.

Bio-inspired synthesis and laser processing of nanostructured barium titanate thin films: implications for uncooled IR sensor development

The Army requires passive uncooled IR sensors for use in numerous vehicle and weapons platforms, including driver vision enhancement (DVE), rifle sights, seeker munitions, and unattended ground sensors (UGSs) and unattended aerial vehicles (UAVs). Recent advances in bio-inspired/biomimetic nanomaterials synthesis, laser material processing, and sensor design and performance testing, offer the opportunity to create uncooled IR detector focal-plane arrays with improved sensitivity, low thermal mass, and fast response times, along with amenability to low-cost, rapid prototype manufacture. We are exploring the use of genotype-inspired, digitally-scripted laser direct-write techniques, in conjunction with the kinetically controlled catalytic process for the growth of nanostructured multimetallic perovskites, to develop a novel approach to the fabrication of precision patterned 2-D focal-plane arrays of pyroelectric perovskite-based materials. The bio-inspired growth of nanostructured, multimetallic perovskite thin-films corresponds to the use of kinetically controlled vapor diffusion for the slow growth of pure, highly crystalline 6-nm barium titanate (BaTiO3) nanoparticles. This unique vapor-diffusion sol-gel route enables the formation of stoichiometric cubic-phase nanoparticles at room temperature and ambient pressure in the absence of a structure-directing template. Novel laser direct-write processing and synchronized electro-optic pulse modulation techniques have been utilized to induce site-selective, patterned phase transformation of microscale aggregates of the BaTiO3 nanoparticles from the non-pyroelectric cubic polymorph to the pyroelectric tetragonal polymorph. This paper reports on our initial collaborative investigations, including comprehensive structural characterization (XRD, TEM, and SEM) of the BaTiO3 nanoparticles and thin-films, along with preliminary laser-induced phase transformation results.

Pyroelectric films synthesized by low-temperatures and laser-processed for uncooled infrared detector applications

Infrared (IR) photon detectors based on III-V semiconductor quantum structures such as type-II superlattices [1] and quantum well infrared photodetectors (QWIPs) [2] require atomically flat interfaces, which are achieved through expensive, high-vacuum growth techniques such as molecular beam epitaxy (MBE). These structures are fabricated into detector arrays which are bump-bonded to Silicon (Si) Read-Out Integrated Circuits (ROICs). IR detector applications involving high resolution and fast refresh rates use highly sensitive photon detectors which require external cooling; making them bulky, expensive, and therefore impractical for equipping each soldier on the battlefield [3]. Uncooled thermal detectors tend to be lower cost, but the challenge is in developing materials that are thermally compatible with Si readout electronics. Thermal detectors convert incident radiation to heat. When a pyroelectric material is subjected to a temperature change, a dipole is induced, which sets up an electric potential. The resulting pyroelectric current can be read by the Si electronics. IR detectors based on perovskite oxides such as Barium Titanate (BaTiO3) are of interest in part because of their lack of need for cryogenic cooling, which makes them relatively more affordable and operationally simpler than cooled photon detector systems. Using a biologically-inspired low-temperature nanoparticle deposition technique, direct-write laser phase conversion, and micro-electro-mechanical systems (MEMS) fabrication techniques, we are working towards an uncooled IR focal plane array (FPA) process compatible with monolithic integration of the detector pixels directly onto ROICs.