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The unique electrical properties of silicon nitride have increased the applications in microelectronics, especially in the manufacture of integrated circuits. Silicon nitride is mainly used as a passivation barrier against water and sodium ion diffusion and as an electrical insulator between polysilicon layers in capacitors. The interface with different materials, like semiconductors and metals, through soldering may induce residual strains in the final assembly. Therefore, the dentification and quantification of strain becomes strategically important in optimizing processes to enhance the performance, duration, and reliability of devices. This work analyzes the thermomechanical local strain of semiconductor materials used to realize optoelectronic components. The strain induced in the β-Si 3 N 4 chips by the soldering process performed with AuSn pre-formed on copper substrates is investigated by Raman spectroscopy in a temperature range of -50 to 180 °C. The variation in the position of the E 1g Raman peak allows the calculation of the local stress present in the active layer, from which the strain induced during the assembly process can be determined. The main reason for the strain is attributed to the differences in thermal expansion coefficients among the various materials involved, particularly between the chip, the interconnection material, and the substrate. Micro-Raman spectroscopy allows for the assessment of how different materials and assembly processes impact the strain, enabling more informed decisions to optimize the overall device structure.

Graphyne- and graphdiyne-like model systems have attracted much attention from many structural, theoretical, and synthetic scientists because of their promising electronic, optical, and mechanical properties, which are crucially affected by the presence, abundance and distribution of triple bonds within the nanostructures. In this work, we performed the two-step bottom-up on-surface synthesis of graphyne- and graphdiyne-based molecular wires on the Au(111). We characterized their structural and chemical properties both in situ (UHV conditions) through STM and XPS and ex situ (in air) through Raman spectroscopy. By comparing the results with the well-known growth of poly( p -phenylene) wires (namely the narrowest armchair graphene nanoribbon), we were able to show how to discriminate different numbers of triple bonds within a molecule or a nanowire also containing phenyl rings. Even if the number of triple bonds can be effectively determined from the main features of STM images and confirmed by fitting the C1s peak in XPS spectra, we obtained the most relevant results from ex situ Raman spectroscopy, despite the sub-monolayer amount of molecular wires. The detailed analysis of Raman spectra, combined with density functional theory (DFT) simulations, allowed us to identify the main features related to the presence of isolated (graphyne-like systems) or at least two conjugated triple bonds (graphdiyne-like systems). Moreover, other spectral features can be exploited to understand if the chemical structure of graphyne- and graphdiyne-based nanostructures suffered unwanted reactions. As in the case of sub-monolayer graphene nanoribbons obtained by on-surface synthesis, we demonstrate that Raman spectroscopy can be used for a fast, highly sensitive and non-destructive determination of the properties, the quality and the stability of the graphyine- and graphdiyne-based nanostructures obtained by this highly promising approach.

The main challenge for solar cell devices is harvesting photons beyond the visible by reaching the red-edge (650-780 nm). Dye-sensitized solar cell (DSSC) devices combine the optical absorption and the charge separation processes by the association of a sensitizer as a light-absorbing material (dye molecules, whose absorption can be tuned and designed) with a wide band gap nanostructured semiconductor. Conformational and environmental effects (i.e., solvent, pH) can drastically influence the photophysical properties of molecular dyes. This study proposes a combined experimental and computational approach for the comprehensive investigation of the electronic and vibrational properties of a unique class of organic dye compounds belonging to the family of red-absorbing dyes, known as squaraines. Our focus lies on elucidating the intricate interplay between the molecular structure, vibrational dynamics, and optical properties of squaraines using state-of-the-art density functional theory calculations and spectroscopic techniques. Through systematic vibrational and optical analyses, we show that (i) the main absorption peak in the visible range is influenced by the conformational and protonation equilibria, (ii) the solvent polarity tunes the position of the UV-vis absorption, and (iii) the vibrational spectroscopy techniques (infrared and Raman) can be used as informative tools to distinguish between different conformations and protonation states. This comprehensive understanding offers valuable insights into the design and optimization of squaraine-based DSSCs for enhanced solar energy conversion efficiency., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)