Alexandre R. Paschoal

Raman evidence for pressure-induced formation of diamondene

Despite the advanced stage of diamond thin-film technology, with applications ranging from superconductivity to biosensing, the realization of a stable and atomically thick two-dimensional diamond material, named here as diamondene, is still forthcoming. Adding to the outstanding properties of its bulk and thin-film counterparts, diamondene is predicted to be a ferromagnetic semiconductor with spin polarized bands. Here, we provide spectroscopic evidence for the formation of diamondene by performing Raman spectroscopy of double-layer graphene under high pressure. The results are explained in terms of a breakdown in the Kohn anomaly associated with the finite size of the remaining graphene sites surrounded by the diamondene matrix. Ab initio calculations and molecular dynamics simulations are employed to clarify the mechanism of diamondene formation, which requires two or more layers of graphene subjected to high pressures in the presence of specific chemical groups such as hydroxyl groups or hydrogens.The synthesis of two-dimensional diamond is the ultimate goal of diamond thin-film technology. Here, the authors perform Raman spectroscopy of bilayer graphene under pressure, and obtain spectroscopic evidence of formation of diamondene, an atomically thin form of diamond.

A Comparative Study of the Photosensitizer Penetration into Artificial Caries Lesions in Dentin Measured by the Confocal Raman Microscopy.

This study utilized the confocal Raman microspectroscopy (CRM) technique for the first time to investigate the degree of the penetration of toluidine blue‐orto (TBO) in artificial caries lesions produced by two distinct caries‐inducing models. The dentin specimens (n = 10) were divided into three groups: control, in vitro and in situ. Thereafter, the lesion depth and the demineralization level were evaluated by cross‐sectional microhardness (CSMH). CRM mapping across the dentin surface was assessed after the dye application. The CSMH and CRM data were analyzed by t‐test and ANOVA, respectively (P < 0.05). The values of the lesion depth and the demineralization areas were higher for in situ samples (P < 0.05). The TBO penetration values (μm) for the control, in vitro and in situ groups were 44.8 ± 5.6, 46.1 ± 4.5 and 51.2 ± 8.5, respectively. There were no statistically significant differences among the groups (P > 0.05). The rate of TBO penetration was detected up to about <50 μm and the demineralization level did not influence the results. These results have showed promising parameters to develop new protocols for deep caries lesions management using photodynamic antimicrobial chemotherapy.

An Eco-Friendly Method of BaTiO3 Nanoparticle Synthesis Using Coconut Water

BaTiO3 nanoparticles were successfully synthesized by a new coconut water-based sol–gel method using Ba(CH3COO)2 and TiCl3 as the starting salts. The influence of the amount of coconut water and calcination conditions on the barium titanate crystallization was investigated. The resulting nanoparticles were characterized by thermogravimetric and differential thermal analysis, X-ray diffraction, scanning electron microscopy, and Raman and Fourier transform infrared (FTIR) spectroscopies. The ferroelectric tetragonal single phase of BaTiO3 was obtained in samples prepared with a ratio of coconut water volume (mL)/BaTiO3 mass (g) of 25 : 2 and 30 : 2, calcined at 1100°C, which was confirmed by XRD measurements. Crystallites with an average size of about 31 nm for both samples were obtained, and microscopy images revealed the presence of particles in the range of 40 to 60 nm. Raman and FTIR spectra confirmed the dominant tetragonal phase of BaTiO3, meanwhile traces of BaCO3 were identified in FTIR spectra.