More Like this

1. Energy and Charge Transport in 2D Atomic Layer Materials: Raman-Based Characterization

   https://doi.org/10.3390/nano10091807  

   Wang, Ridong; Wang, Tianyu; Zobeiri, Hamidreza; Li, Dachao; Wang, Xinwei (September 2020, Nanomaterials)

   As they hold extraordinary mechanical and physical properties, two-dimensional (2D) atomic layer materials, including graphene, transition metal dichalcogenides, and MXenes, have attracted a great deal of attention. The characterization of energy and charge transport in these materials is particularly crucial for their applications. As noncontact methods, Raman-based techniques are widely used in exploring the energy and charge transport in 2D materials. In this review, we explain the principle of Raman-based thermometry in detail. We critically review different Raman-based techniques, which include steady state Raman, time-domain differential Raman, frequency-resolved Raman, and energy transport state-resolved Raman techniques constructed in the frequency domain, space domain, and time domain. Detailed outlooks are provided about Raman-based energy and charge transport in 2D materials and issues that need special attention. 

   more » « less
2. Hyper-Raman optical activity of biologically relevant chiral molecules

   https://doi.org/10.1117/12.2545530  

   Marble, Christopher B.; Xu, Xingqi; Keppler, Mark A.; Gil, Eddie M.; Petrov, Georgi I.; Wang, Dawei; Yakovlev, Vladislav V.; Razeghi, Manijeh; Lewis, Jay S.; Khodaparast, Giti A.; et al (March 2020, Hyper-Raman optical activity of biologically relevant chiral molecules)

   The optical activity of Raman scattering provides insight into the absolute configuration and conformation of chiral molecules. Applications of Raman optical activity (ROA) are limited by long integration times due to a relatively low sensitivity of the scattered light to chirality (typically 10^-3 to 10^-5). We apply ROA techniques to hyper-Raman scattering using incident circularly polarized light and a right-angle scattering geometry. We explore the sensitivity of hyper- Raman scattering to chirality as compared to spontaneous Raman optical activity. Using the excitation wavelength at around 532 nm, the photobleaching is minimized, while the hyper-Raman scattering benefits from the electronic resonant enhancement. For S/R-2-butanol and L/D-tartaric acid, we were unable to detect the hyper-Raman optical activity at the sensitivity level of 1%. We also explored parasitic thermal effects which can be mitigating by varying the repetition rate of the laser source used for excitation of hyper-Raman scattering. 

   more » « less
3. Perspectives on interfacial thermal resistance of 2D materials: Raman characterization and underlying physics

   https://doi.org/10.1007/s44251-024-00037-6  

   Liu, Jing; Al Keyyam, Ibrahim; Xie, Yangsu; Wang, Xinwei (February 2024, Surface Science and Technology)

   Abstract Interfacial thermal resistance plays a crucial role in efficient heat dissipation in modern electronic devices. It is critical to understand the interfacial thermal transport from both experiments and underlying physics. This review is focused on the transient opto-thermal Raman-based techniques for measuring the interfacial thermal resistance between 2D materials and substrate. This transient idea eliminates the use of laser absorption and absolute temperature rise data, therefore provides some of the highest level measurement accuracy and physics understanding. Physical concepts and perspectives are given for the time-domain differential Raman (TD-Raman), frequency-resolved Raman (FR-Raman), energy transport state-resolved Raman (ET-Raman), frequency domain ET-Raman (FET-Raman), as well as laser flash Raman and dual-wavelength laser flash Raman techniques. The thermal nonequilibrium between optical and acoustic phonons, as well as hot carrier diffusion must be considered for extremely small domain characterization of interfacial thermal resistance. To have a better understanding of phonon transport across material interfaces, we introduce a new concept termed effective interface energy transmission velocity. It is very striking that many reported interfaces have an almost constant energy transmission velocity over a wide temperature range. This physics consideration is inspired by the thermal reffusivity theory, which is effective for analyzing structure-phonon scattering. We expect the effective interface energy transmission velocity to give an intrinsic picture of the transmission of energy carriers, unaltered by the influence of their capacity to carry heat. 

   more » « less
4. Raman Match: Application for automated identification of minerals from Raman spectroscopy data

   https://doi.org/10.2138/am-2023-9227  

   Berrada, Meryem; McFall, Alan; Chen, Bin (January 2025, American Mineralogist)

   Kung, Jennifer (Ed.)

   Abstract Raman spectroscopy is a rapid, nondestructive analysis technique used in various scientific disciplines, including mineralogy, chemistry, materials science, and biology. The analysis of Raman spectra and the identification of specific substances in unknown samples can be complex and time-consuming due to the large database of Raman spectra. The Raman Match application was developed to simplify and automate the sample identification process through a search and match method. The application integrates the well-established RRUFF Raman database with the Python programming language. It provides a user-friendly graphical interface to load Raman spectra, identify and fit peaks, match peaks to the reference libraries, visualize the results, and generate publication-ready figures. The application offers a swift and automated method for mineral identification using Raman spectroscopy in laboratory and field settings and during planetary exploration missions to extraterrestrial environments with constraints on time and resources. 

   more » « less
5. Understanding chemical enhancements of surface-enhanced Raman scattering using a Raman bond model for extended systems

   https://doi.org/10.1063/5.0124553  

   Chen, Ran; Jensen, Lasse (November 2022, The Journal of Chemical Physics)

   In this work, we extend a previously developed Raman bond model to periodic slab systems for interpreting chemical enhancements of surface-enhanced Raman scattering (SERS). The Raman bond model interprets chemical enhancements as interatomic charge flow modulations termed Raman bonds. Here, we show that the Raman bond model offers a unified interpretation of chemical enhancements for localized and periodic systems. As a demonstration of the Raman bond model, we study model systems consisting of CO and pyridine molecules on Ag clusters and slabs. We find that for both localized and periodic systems, the dominant Raman bonds are distributed near the molecule–metal interface and, therefore, the chemical enhancements are determined by a common Raman bond pattern. The effects of surface coverage, thickness, and roughness on the chemical enhancements have been studied, which shows that decreasing surface coverage or creating surface roughness increases chemical enhancements. In both of these cases, the inter-fragment charge flow connectivity is improved due to more dynamic polarization at the interface. The chemical enhancement is shown to scale with the inter-fragment charge flow to the fourth power. Since the inter-fragment charge flow is determined by the charge transfer excitation energy, the Raman bond model is connected to the transition-based analysis of chemical enhancements. We also show that the SERS spectra of localized and periodic systems normalized by inter-fragment charge flows can be unified. In summary, the Raman bond model offers a unique framework for understanding SERS spectra in terms of Raman bond distributions and offers a connection between localized and periodic model systems of SERS studies. 

   more » « less