Room Temperature Raman (RT-Raman)
Introduction to Raman Spectroscopy:
Raman spectroscopy is a technique used to analyze molecular vibrations, providing valuable insights into the composition and structure of materials. Named after Sir C.V. Raman, it involves the inelastic scattering of light, offering a unique fingerprint for each molecule.
How to Measure Raman:
Measurement involves illuminating a sample with monochromatic laser light, and analyzing the scattered light for inelastic scattering. The resulting spectrum is then examined to identify molecular vibrations, chemical bonds, and structural information.
Applications of Raman:
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Chemistry: Identifying molecular structures, and studying chemical reactions.
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Biology: Analyzing biomolecules, cellular components, and tissues.
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Materials Science: Characterizing materials, studying polymers, and analyzing crystal structures.
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Pharmaceuticals: Quality control, drug formulation, and studying pharmaceutical compounds.
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Environmental Science: Monitoring pollutants, and analyzing soil and water samples.
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Geology: Studying minerals, rocks, and geological formations.
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Forensics: Analyzing substances for criminal investigations.
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Semiconductor Industry: Characterizing materials in semiconductor devices.
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Art and Cultural Heritage Conservation: Identifying pigments, and studying historical artifacts.
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Food Industry: Analyzing food components, and detecting contaminants.
These applications highlight the versatility of Raman spectroscopy in providing valuable insights into the composition and structure of various materials across different scientific disciplines.
Crystal-phase Studies
In this work, they studied the crystal-phase controllability in 2D GaTe nanomaterials by using Raman scattering as a technique for characterizing crystal phases. Figure 1 displays Raman spectra of GaTe/GaAs(001) at different growth temperatures (350-525 °C). The Raman spectrum of the 375 °C sample primarily exhibits two broad features at 126 and 141 cm−1, indicating weak in-plane optical anisotropy. The broadening in the linewidth of these peaks in the 350 °C sample suggests lower crystal quality. This spectrum indicates the dominant presence of the h-GaTe phase in the film. As the growth temperature surpasses 400 °C, characteristic peaks of m-GaTe at ∼58, 64, 74, 109, 114, 161, 172, 196, 209, 270, and 285 cm−1 become more prominent. Notably, there is a significant increase in the intensity of the Ag ∼ 114 cm−1 and Bg ∼ 161 cm−1 modes with rising temperature, indicating the robust development of m-GaTe nanorods. Additionally, the 126 cm−1 mode (h-GaTe characteristic peak) intensifies rapidly compared to the 114 cm−1 mode (m-GaTe characteristic peak) in the 525 °C sample, with the intensity ratio approaching ∼1. This phenomenon may be attributed to the formation of h-GaTe triangles at high temperatures, as observed in SEM images.
Reference:
S. H. Huynh, N. Q. Diep, T. V. Le, S. K. Wu, C. W. Liu, D. L. Nguyen, H. C. Wen, W. C. Chou, V. Q. Le, and T. T. Vu. Molecular Beam Epitaxy of Two-Dimensional GaTe Nanostructures on GaAs(001) Substrates: Implication for Near-Infrared Photodetection. ACS Appl. Nano Mater. 2021, 4, 9, 8913–8921
Transition materials
Raman spectroscopy is employed for monitoring surface groups, with a systematic study investigating the impact of etching solution composition, specifically HF concentration, on MXene film Raman spectra (Figure 2). The resonant excitation wavelength used for all Ti3C2Tx tests was 785 nm. Spectra from delaminated restacked films were collected to avoid roughness effects, mapping a 10 x 10 μm region and averaging 100 spectra. Figure 2a compares multilayer samples produced by three etching methods, including an in-situ HF method where the multilayer sample, obtained by drying the clay material, shows intercalated Li ions without delamination. The addition of TMAOH intercalant after HF-etching results in a dramatic shift of the A1g(C) peak position of the delaminated film to 730 cm-1, indicating increased interlayer spacing. The A1g(C) peak downshifts with increasing HF concentration, as shown in Figure 2b, suggesting a correlation with defects. Comparing different etching methods (Figure 2c), the resonance peak shifts notably only in HF-HCl etching, indicating variations in electronic properties. The study also explores differences in electronic properties between samples produced by LiF/HCl and HF/HCl methods, emphasizing the need for further investigations into the correlation between Raman shift and defect concentration, particularly considering factors such as flake size.
Biology research
The study investigates bacterial biofilm specimens using Raman spectroscopy, focusing on the relative intensity and normalized Raman spectra in specific bands associated with lipids, proteins, and carbohydrates (Figure 3a). Differences in the lipid, Amide, and carbohydrate regions were observed in both FT-IR and Raman spectra. The Raman spectra of lipids, related to hydrocarbon chains, were detected in three spectroscopic regions. Variances in the intensity of the 1445–1461 cm−1 band (Figure 3b), attributed to saturated lipids, indicated alterations in lipid amounts and compositions during biofilm maturation. Amide VI bands were distinguishable, with significant variations in intensities, particularly in the Amide I and III bands (Fig. 3b,c), suggesting different protein compositions among bacterial strains. The shifting of the wavenumber position of the (1→6)-α-glycosidic bond band and specific Raman peaks indicated differences in glucan and glucose contents. Additional spectral regions were identified as signatures of polysaccharides, proteins, and lipids in the bacterial biofilm matrix, with partial overlap with nucleic acids, especially the DNA region. The study highlights the potential of Raman spectroscopy in characterizing biofilm components and their variations.
Reference:
Barbara Gieroba, Mikolaj Krysa, Kinga Wojtowicz, Adrian Wiater, Małgorzata Pleszczy´nska, Michał Tomczyk, and Anna Sroka-Bartnicka. The FT-IR and Raman Spectroscopies as Tools for Biofilm Characterization Created by Cariogenic Streptococci. Int. J. Mol. Sci. 2020, 21, 3811. https://www.mdpi.com/1422-0067/21/11/3811
Substrate Studies
Figure 4 displays micro-Raman scattering spectra of m-, a-, and c-plane GaN substrates, revealing eight phonon modes, including a defect-mediated mode. Group theory analysis identifies nonpolar EL2-EH2 phonons and polar A1 and E1 modes, each with split LO and TO components. The Raman tensor properties dictate scattering intensity, varying for A1, E1, and 2 modes. Both nonpolar low-frequency and high-frequency modes are present in all-plane GaN substrates, showcasing their non-polar nature. Deviations in wavenumber values, compared to literature, hint at residual stress from initial growth on sapphire substrates. Remarkably, the weakly observed BL1 mode in m- and a-plane GaN substrates, along with a frequency aligning with calculations, suggests the breakdown of translational crystal symmetry induced by defects. The anisotropic lattice nature of hexagonal wurtzite crystal is evident, with certain modes observable exclusively in specific planes. Silent modes, attributed to crystal symmetry breakdown, demonstrate the influence of defects and impurities in w-GaN samples. This study highlights the unique characteristics and anisotropy of hexagonal wurtzite crystal structures in GaN substrates.
Reference:
Mingzheng Wang, Ke Xu, and Shijie Xu. Photoluminescence and Raman Scattering Signatures of Anisotropic Optical Properties in Freestanding m-, a- and c-Plane GaN Substrates. J. Phys. Chem. C 2020, 124, 33, 18203–18208.
https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.0c04959