Nucleation and growth process of atomic layer deposition platinum nanoparticles on strontium titanate nanocuboids

Bismuth oxide nanoparticles induce oxidative stress and apoptosis in human breast cancer cells

Metal nanomaterials such as bismuth oxide nanoparticles (Bi₂O₃NPs) have been extensively used in cosmetics, dental materials, pulp capping, and biomedical imaging. There is little knowledge about the health risk of Bi₂O₃NPs in humans, which warrants a thorough toxicity investigation of Bi₂O₃NPs at the cellular level. In this experiment, we investigated the cytotoxic effect of Bi₂O₃NPs on human breast cancer (MCF-7) cells over 24 and 48 h. MCF-7 cells were exposed to Bi₂O₃NPs at varying doses (0.1, 0.5, 1.0, 5, 10, 20, 40 μg/mL) for 24 and 48 h. We assessed the toxicity of Bi₂O₃NPs by measuring its effect on the viability and oxidative stress biomarkers, e.g., GSH, SOD, and catalase in MCF-7 cells. The pro-apoptotic effects of Bi₂O₃NPs on MCF-7 cells were determined via evaluating dysfunction of mitochondrial membrane potential (MMP), caspase-3 activity, externalization of phosphatidylserine, and chromosome condensation. Furthermore, apoptotic cells were evaluated using 7-AAD fluorescence stain and Annexin V-FITC. Bi₂O₃NPs induced oxidative stress in MCF-7 cells in a time- and dose-dependent manner. Bi₂O₃NPs increased the rate of both necrotic cells and apoptotic cells. In addition, the blue fluorescence of MCF-7 cells with condensed chromatin was increased in a time- and dose-dependent manner. In conclusion, the present study highlights the potential toxic effects of Bi₂O₃NPs at the cellular level and suggests further investigation of Bi₂O₃NPs before any medical purposes.

Surface mobility and impact of precursor dosing during atomic layer deposition of platinum:in situmonitoring of nucleation and island growth

The nucleation rate and diffusion-driven growth of Pt nanoparticles are revealed within situX-ray fluorescence and scattering measurements during ALD: the particle morphology at a certain Pt loading is similar for high and low precursor exposures.

Electrical Properties of Ultrathin Platinum Films by Plasma-Enhanced Atomic Layer Deposition

The ability to deposit thin and conformal films has become of great importance because of downscaling of devices. However, because of nucleation difficulty, depositing an electrically stable and thin conformal platinum film on an oxide nucleation layer has proven challenging. By using plasma-enhanced atomic layer deposition (PEALD) and TiO₂ as a nucleation layer, we achieved electrically continuous PEALD platinum films down to a thickness of 3.7 nm. Results show that for films as thin as 5.7 nm, the Mayadas-Shatzkes (MS) model for electrical conductivity and the Tellier-Tosser model for temperature coefficient of resistance hold. Although the experimental values start to deviate from the MS model below 5.7 nm because of incomplete Pt coverage, the films still show root mean square electrical stability better than 50 ppm over time, indicating that these films are not only electrically continuous but also sufficiently reliable for use in many practical applications.

From Single Atoms to Nanoparticles: Autocatalysis and Metal Aggregation in Atomic Layer Deposition of Pt on TiO2 Nanopowder

A fundamental understanding of the interplay between ligand-removal kinetics and metal aggregation during the formation of platinum nanoparticles (NPs) in atomic layer deposition of Pt on TiO₂ nanopowder using trimethyl(methylcyclo-pentadienyl)platinum(IV) as the precursor and O₂ as the coreactant is presented. The growth follows a pathway from single atoms to NPs as a function of the oxygen exposure (P_O2 × time). The growth kinetics is modeled by accounting for the autocatalytic combustion of the precursor ligands via a variant of the Finke-Watzky two-step model. Even at relatively high oxygen exposures (<120 mbar s) little to no Pt is deposited after the first cycle and most of the Pt is atomically dispersed. Increasing the oxygen exposure above 120 mbar s results in a rapid increase in the Pt loading, which saturates at exposures >> 120 mbar s. The deposition of more Pt leads to the formation of NPs that can be as large as 6 nm. Crucially, high P_O2 (≥5 mbar) hinders metal aggregation, thus leading to narrow particle size distributions. The results show that ALD of Pt NPs is reproducible across small and large surface areas if the precursor ligands are removed at high P_O2 .