Influence of halide precursor type and its composition on the electronic properties of vacuum deposited perovskite films.

We fabricate mixed halide perovskite films through dual-source vacuum deposition of PbX2 (X = Cl, Br, and I) and methyl ammonium iodide (MAI) precursors with various deposition ratios. Vacuum deposition is an optimal way for film fabrication because it gives a uniform perovskite film which is free from contamination such as metallic phase lead, residual solvent, and moisture. The ionization potential and bandgap of MAPb(I1-yBry)3 film are controlled by changing the halide composition and lattice constant. In contrast, MAPb(I1-yCly)3 film shows negligible difference from MAPbI3 in terms of structural and electronic properties, which is due to poor Cl incorporation in the film from the MACl removal during crystal formation. An excess supply of MAI is necessary to form a perovskite crystal structure. Based on the elemental stoichiometry analysis, the additional methyl ammonium cation with respect to Pb in the film plays a critical role in changing the electron affinity and energy level alignment.

Lipid crystals mechanically stimulate adjacent extracellular matrix in advanced atherosclerotic plaques.

OBJECTIVE: Although lipid crystals (LCs) have received attention as a causative factor of plaque rupture, the mechanisms by which they increase plaque vulnerability are unknown. We examined whether solid-state LCs physically affect the adjacent extracellular matrix (ECM) using a combination of multimodal nonlinear optical (MNLO) imaging and finite element analysis (FEA). METHODS: The changes of ECMs affected by lipids in atherosclerotic arteries in apolipoprotein E-deficient mice (n = 32) fed a high-fat diet for 20-30 weeks were micro-anatomically visualized by a 3D MNLO imaging platform including CARS for lipids, TPEF for elastin, and SHG for collagen. RESULTS AND CONCLUSION: The TPEF signal of elastin was increased at the peripheral regions of LCs (<10 µm) compared with foam cell regions. In order to confirm the increase of elastin, biochemical assay (western blot) was performed. The protein level of elastin was increased approximately 2.25-fold (p = 0.024) in LC-rich arteries. Under the hypothesis that the increase of elastin resulted from the mechanical stimulus from solid-state LCs, MNLO images were subjected to FEA to simulate the displacement according to the expanding magnitude of the vessel during cardiac cycles. We found that microscale focal stress was increased specifically around the LCs. These FEA results corresponded with the increase of elastin observed by TPEF. These data suggest that LCs mechanically stimulate the adjacent ECM to alter the composition of ECM and cause vessel remodeling. The combination of MNLO imaging and FEA has great potential to verify the mechanical predictions in cardiovascular diseases.

Hardness variation with indenter sharpness in an Au thin-film.

The effects of the indenter shape on hardness were studied from thin-film nanoindentations. Two Berkovich indenters with different operating histories were prepared and their morphologies were measured with an atomic force microscope. The curvature radii of both indenters that were measured through an image analysis were 58.8 nm and 732.2 nm, respectively. The nanoindentations were carried out on a 1.2 microm-thick Au thin-film with a Nanoindenter XP system with both indenters. Various nanoindentation data with indenter exchanges were surveyed, and they showed that the peak indentation loads under the blunter indenter were higher than those of the sharper indenter at the same indentation depths. The indenter sharpness parameter was used to correct the raw nanoindentation curves. The corrected curves overlapped well and the resulting hardness values were consistent regardless of the indenter sharpness. The intrinsic hardness values of the Au thin-film from both indenters agreed with each other, with only a 0.6% difference. This means the indenter sharpness was properly corrected and that the sharpness must be considered when the contact properties are measured at shallow indentations.

Nanoscale characterization of acid and thermally treated collagen fibrils.

Type I collagen is a major extracellular matrix component and its hierarchical structure plays an essential role in the regulation of cellular behavior. Here, we have analyzed the changes in the morphological, chemical, and mechanical properties of collagen fibrils induced by acidic and thermal treatments and the influence on the cellular response of MC3T3-E1 cells. Morphological changes induced by the disintegration of the fibrillar structure of collagen were observed using atomic force microscopy. The changes in the surface chemistry due to the disassembly of native collagen fibrils were observed using time-of-flight secondary ion mass spectroscopy (ToF-SIMS). ToF-SIMS spectra were very sensitive to changes in the molecular configuration of the collagen fibrils induced by acidic and thermal treatments due to the extreme surface specificity. In addition, ToF-SIMS showed clear and reproducible changes in the surface amino acid composition corresponding to the acidic and thermal treatments of collagen fibrils. Based on the quantitative map of surface elastic modulus measured by contact-resonance force microscopy, acid and thermally treated collagen showed a lower elastic modulus than native collagen fibrils. Compared with native collagen fibrils, reduced cell spreading and decreased viability of MC3T3-E1 cells were observed on both the acid and thermally treated collagen.