Three-dimensional materials analysis by confocal Raman microspectroscopy

MEMS-based portable confocal Raman spectroscopy rapid imaging system

Aiming at the miniaturization and rapid imaging requirements of a portable confocal Raman system, a MEMS-based portable confocal Raman spectroscopy rapid imaging method is proposed in this study. This method combines the dual 2D MEMS mirror scanning method and the grid-by-grid scanning method. The dual 2D MEMS mirror scanning method is used for the miniaturization design of the system, and the grid-by-grid scanning method is used for rapid imaging of Raman spectroscopy. Finally, the rapid imaging and miniaturization design of a portable confocal Raman spectroscopy system are realized. Based on this method, a portable confocal Raman spectroscopy rapid imaging system with an optical probe size of just 98m m×70m m×40m m is constructed. The experimental results show that the imaging speed of the system is 45 times higher than that of the traditional point-scan confocal Raman system, and the imaging speed can be further improved according to the requirements. In addition, the system is used to swiftly identify agate ore, and the material composition distribution image over a 126µm 2×126µm 2 region is obtained in just 16 min. This method provides a new solution for the rapid imaging and miniaturization design of the confocal Raman system, as well as a new technical means for rapid detection in deep space exploration, geological exploration, and field detection.

Studying the concentration of polymers in blended microplastics using 2D and 3D Raman mapping

The combination of different polymers in the form of blended plastics has been used in the plastic industry for a long time. Nevertheless, analyses of microplastics (MPs) have been mainly limited to the study of particles made of single-type polymers. Accordingly, two members of the Polyolefins (POs) family, i.e., Polypropylene (PP) and Low-density Polyethylene (LDPE) are blended and extensively studied in this work due to their applications in industry as well as abundance in the environment. It is shown that 2-D Raman mapping only provides information about the surface of blended MPs (B-MPs). While complimentary 3-D volume analysis is needed to fully understand the presence of various polymers in such complex samples. Therefore, 3-D Raman mapping is applied to visualize the morphology of the distribution of polymers within the B-MPs together with the quantitative estimation of their concentrations. A parameter defined as the concentration estimate error (CEE) evaluates the precision of the quantitative analysis. Furthermore, the impact of four excitation wavelengths 405, 532, 633, and 785 nm is investigated on the obtained results. Finally, the application of a line-shaped laser beam profile (line-focus) is introduced for reducing the measurement time from 56 to 2 h.

Characterization of the adsorption of Ru-bpy dyes on mesoporous TiO2 films with UV-Vis, Raman, and FTIR spectroscopies

In the present work the adsorption of a new dye, [Ru(dcbpyH(2))(2)(bpy-TPA(2))](PF(6))(2), and the well-known (Bu(4)N)(2)[Ru(dcbpyH)(2)(NCS)(2)] complex on mesoporous anatase films were investigated to clarify the role of the carboxylate groups in the anchoring process of the dyes on the semiconductor surface. For this purpose UV-vis, Raman, resonance Raman, and ATR-FTIR spectroscopies have been used. The results of the Raman experiments at different excitation wavelengths demonstrate that photoinduced charge-transfer processes take place efficiently between the adsorbate and the substrate. Moreover, this is the first time that the Raman spectrum of a Ru-bpy dye (in this case, the dye N719) adsorbed on TiO(2) has been obtained without the resonance condition, only by means of SERS enhancement. The coordination of both complexes on the TiO(2) paste films is proposed to occur via bidentate or bridging linkage.

Influence of the solvent on the surface-enhanced raman spectra of ruthenium(II) bipyridyl complexes

In the present work a new dye, [Ru(dcbpyH2)2(bpy-TPA2)](PF6)2, and the well-known (Bu4N)2[Ru(dcbpyH)2(NCS)2] complex were investigated. The electronic transitions of both dyes showed solvatochromic shifts due to specific interactions of the ligands with the solvent molecules. The surface-enhanced Raman (SER) spectra of the dyes dissolved in water, ethanol, and acetonitrile were measured in silver and gold colloidal solutions. The results demonstrate that the dyes were adsorbed on the metallic nanoparticles in different ways for different solvents. It was also found that in the gold colloid, the aqueous solutions of both dyes did not produce any SERS signal, whereas in ethanolic solution the SERS effect was very weak. Deprotonation, H-bonding, and donor-acceptor interactions seem to determine these different behaviors. Our results indicate the important role of the charge-transfer mechanism in SERS.

Measuring Diffusion of Molecules into Individual Polymer Particles by Confocal Raman Microscopy

Raman microscopy is a powerful method for providing spatially resolved, chemically selective information about the composition of materials. With confocal collection optics, the method is well suited to the analysis of small particles in contact with liquid solutions. In this work, the transport of an organic solvent component into small polystyrene particles is investigated. An inverted confocal Raman microscope is used to acquire spectra from individual 75-microm polystyrene particles in contact with acetonitrile/water mixtures. Monitoring the Raman scattering from the C[triple bond]N stretching mode of acetonitrile provides a measure of solvent uptake into the polymer material. The small collection volume defined by the confocal optics provides the micrometer spatial resolution needed to track solvent concentration at different locations within the particle with 30-s time resolution. The volume fraction of acetonitrile in water in the surrounding solution was varied in order to determine the concentration dependence of the diffusion kinetics. Modeling the transport of molecules into a particle was addressed by using finite element methods for the evaluation of the coupled space- and time-dependent differential equations that govern the molecular transport. The results indicate that the diffusion coefficient changes with the local solvent concentration in the polymer. At longer times, with the highest acetonitrile concentrations, an evolution of the solvent transport mechanism was observed, from a diffusive rate that depends on local concentration to a linear increase in concentration with time accompanied by measurable swelling of the particle volume.

Spatially resolved analysis of small particles by confocal Raman microscopy: depth profiling and optical trapping

Raman microscopy is a powerful method to provide spatially resolved information about the chemical composition of materials. With confocal collection optics, the method is well suited to the analysis of small particles, either resting on a surface or optically trapped at a laser focus, where the confocal collection volume optimizes the signal from the particle. In this work, the sensitivity and spatial selectivity of detecting Raman scattering from single particles was determined as a function of particle size. An inverted confocal Raman microscope was used to acquire spectra of individual surface-bound and optically trapped polystyrene particles with sizes ranging between 200 nm and 10 microm. The particles are in contact with aqueous solution containing perchlorate ion that served as a solution-phase Raman-active probe to detect interferences from the surrounding medium. The collection volume is scanned through single particles that are attached to the surface of the coverslip, and the sensitivity and selectivity of detection are measured versus particle size. The results compare favorably with a theoretical analysis of the excitation profile and confocal collection efficiency integrated over the volumes of the spherical particles and the surrounding solution. This analysis was also applied to the detection of particles that are optically trapped and levitated above the surface of the coverslip. The results are consistent with the optical trapping of particles at or near the excitation beam focus, which optimizes excitation and selective collection of Raman scattering from the particle.