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Advances in Raman spectroscopy and imaging techniques for quality and safety inspection of horticultural products
摘要： This paper gives an overview of Raman technology for inspecting quality and safety of horticultural products. Emphasis is put on introduction and demonstration of Raman spectroscopy and imaging techniques for practical uses to assess the horticultural products. Raman scattering principles are presented first, followed by introduction and comparison to Raman measurement techniques, such as backscattering Raman spectroscopy, transmission Raman spectroscopy, spatially offset Raman spectroscopy, Raman chemical imaging, surface-enhanced Raman spectroscopy, etc. Raman measurement instruments, including excitation sources, wavelength separation devices, detectors, commercial integrated and custom-developed systems, and system calibration methods, are discussed and compared. Raman data analysis methods, such as data preprocessing, spectral mixture analysis, and quantitative analysis, are presented with examples for analyzing Raman spectral and image data of selected horticultural products including tomato and carrot. Raman spectroscopy and imaging applications for quality and safety evaluation of the horticultural products are also reviewed.
关键词： Horticultural products,Raman spectroscopy,Quality,Lasers,Safety,Chemical imaging
更新于2025-09-09 09:28:46
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Impact of Molecular Order on Polaron Formation in Conjugated Polymers
摘要： The nature of polaron formation has profound implications on the transport of charge carriers in conjugated polymers, but still remains poorly understood. Here we develop in situ electrochemical resonant Raman spectroscopy, a powerful structural probe that allows direct observation of polaron formation. We report that polaron formation in ordered poly(3-hexyl)thiophene (P3HT) polymer domains (crystalline phase) results in less pronounced changes in molecular conformation, indicating smaller lattice relaxation, compared to polarons generated in disordered polymer domains (amorphous phase) for which we observe large molecular conformational changes. These conformational changes are directly related to the effective conjugation length of the polymer. Furthermore, we elucidate how blending the P3HT polymer with phenyl C-61 butyric acid methyl ester (PCBM) affects polaron formation in the polymer. We find that blending disturbs polymer crystallinity, reducing the density of polarons that can form upon charge injection at the same potential, whilst the lost capacity is partly restored during post-deposition thermal annealing. Our study provides direct spectroscopic evidence for a lower degree of lattice reorganisation in crystalline (and therefore more planarised) polymers than in conformationally disordered polymers. This observation is consistent with higher charge carrier mobility and better device performance commonly found in crystalline polymer materials.
关键词： electrochemical resonant Raman spectroscopy,conjugated polymers,polaron formation,molecular order,PCBM,charge transport,P3HT
更新于2025-09-09 09:28:46
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Toward high-contrast AFM-TERS imaging: nano-antenna-mediated remote-excitation on sharp-tip silver nanowire probes
摘要： The tip-enhanced Raman spectroscopy (TERS) imaging technique is designed to provide correlated morphological and chemical information with a nanoscale spatial resolution by utilizing the plasmonic resonance supported by metallic nanostructures at the tip apex of a scanning probe. However, limited by the scattering cross-sections of these nanostructures, only a small fraction of the incident light can be coupled to the plasmonic resonance to generate Raman signals. The uncoupled light then directly excites background spectra with a diffraction-limited resolution, which becomes the background noise that often blurs the TERS image. Here, we demonstrate how this problem can be solved by physically separating the light excitation region from the Raman signal generation region on the scanning probe. The remote-excitation TERS (RE-TERS) probe, which can be fabricated with a facile, robust and reproducible method, utilizes silver nanoparticles as nano-antennas to mediate the coupling of free-space excitation light to propagating surface plasmon polaritons (SPPs) in a sharp-tip silver nanowire to excite Raman signals remotely. With this RE-TERS probe, a 10 nm spatial resolution was demonstrated on a single-walled carbon nanotube (SW-CNT) sample, and the strain distribution in a monolayer molybdenum disulfide (MoS2) was mapped.
关键词： plasmonic antenna,self-assembly,high spatial resolution,Tip-enhanced Raman spectroscopy imaging,stress-mapping,remote-excitation
更新于2025-09-09 09:28:46
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Raman fingerprint of two terahertz spin wave branches in a two-dimensional honeycomb Ising ferromagnet
摘要： Two-dimensional (2D) magnetism has been long sought-after and only very recently realized in atomic crystals of magnetic van der Waals materials. So far, a comprehensive understanding of the magnetic excitations in such 2D magnets remains missing. Here we report polarized micro-Raman spectroscopy studies on a 2D honeycomb ferromagnet CrI3. We show the definitive evidence of two sets of zero-momentum spin waves at frequencies of 2.28 terahertz (THz) and 3.75 THz, respectively, that are three orders of magnitude higher than those of conventional ferromagnets. By tracking the thickness dependence of both spin waves, we reveal that both are surface spin waves with lifetimes an order of magnitude longer than their temporal periods. Our results of two branches of high-frequency, long-lived surface spin waves in 2D CrI3 demonstrate intriguing spin dynamics and intricate interplay with fluctuations in the 2D limit, thus opening up opportunities for ultrafast spintronics incorporating 2D magnets.
关键词： micro-Raman spectroscopy,CrI3,spintronics,2D magnetism,spin waves
更新于2025-09-09 09:28:46
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Interfacial mechanical properties of double-layer graphene with consideration of the effect of stacking mode
摘要： The mechanical performance and the effect of the stacking mode of the double-layer graphene interface are studied. Three kinds of double-layer graphene-PET composite structure specimens with different stacking methods are designed. By combining micro-Raman spectroscopy with a micro-tensile loading device, in-situ and real-time measurements are carried out for the specimens during the uniaxial loading process. Based on mechanical analysis, a method for peak splitting of the Raman spectra of double-layer polycrystalline graphene is developed to extract the strain information for each layer of graphene. The strain distribution and shear stress distribution of graphene in each layer during the loading process are determined experimentally. The strain transfer between the two interfaces is analyzed, and the mechanical parameters of interfaces are given quantitatively; the interlayer shear stress of graphene is 0.084 MPa. Finally, double-layer graphene with different stacking modes is studied. The results show that the different lengths of the upper and lower layers of graphene lead to a stress concentration of 0.7–1 GPa at the boundary of the short layer of graphene when stacked. The stress concentration problem of double-layer graphene should be considered for the practical application in micro-electrical components.
关键词： interfacial mechanical property,Raman spectroscopy,edge effect,double-layer graphene interfaces
更新于2025-09-09 09:28:46
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High–pressure electrical conductivity and Raman spectroscopy of chalcanthite
摘要： The phase transitions and dehydration of chalcanthite were investigated by electrical conductivity and Raman spectroscopy at 1.0–24.0 GPa and 293–673 K in a diamond anvil cell. At ambient temperature, two secondary phase transitions were observed according to discontinuous changes in the slope of Raman shifts, full width at half maximum and electrical conductivities at (cid:1)7.3 and (cid:1)10.3 GPa. The dehydration temperatures were determined by the splitting of Raman peaks and changes in electrical conductivity as (cid:1)350 and (cid:1)500 K at respective (cid:1)3.0 and (cid:1)6.0 GPa. A positive relationship for chalcanthite between dehydration temperature and pressure is established.
关键词： dehydration,chalcanthite,phase transition,Raman spectroscopy,electrical conductivity
更新于2025-09-09 09:28:46
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Calculation of the Raman Q branch of hydrogen in water and comparison with experiments
摘要： Calculations of the Raman Q-branch line shifts and line widths of H2 in water at three different pressures and at 280 K are presented and compared with available experimental results. The calculations are based on a perturbative method in which the perturbation consists of those components of the H2–H2O interaction that depend on vibrational and/or rotational coordinates. In the unperturbed system the rotovibrational motion of the hydrogen molecule is separated from the dynamics of the rest of the system. The unperturbed rotovibrational motion of H2 is treated quantum mechanically whereas the dynamics of the rest of the system is calculated by classical molecular dynamics (MD). The MD calculations are repeated with two different models for the water–hydrogen potential energy. Both are Lennard-Jones models but in one the parameters are derived from the Lorentz–Bertholet combination rules and in the other they are taken from gas phase scattering data. The numerical results for the Raman Q-branch spectra are compared with the measurements in order to determine which model is more dependable.
关键词： molecular hydrogen in water,molecular dynamics,Raman spectroscopy
更新于2025-09-09 09:28:46
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Microstructure fabrication process induced modulations in CVD graphene
摘要： The systematic Raman spectroscopic study of a “mimicked” graphene device fabrication is presented. Upon photoresist baking, compressive stress is induced in the graphene which disappears after it is removed. The indirect irradiation from the electron beam (through the photoresist) does not significantly alter graphene characteristic Raman peaks indicating that graphene quality is preserved upon the exposure. The 2D peak shifts and the intensity ratio of 2D and G band, I(2D)/I(G), decreases upon direct metal deposition (Co and Py) suggesting that the electronic modulation occurs due to sp2 C-C bond weakening. In contrast, a thin metal oxide film deposited graphene does not show either the significant 2D and G peaks shift or I(2D)/I(G) decrease upon the metal deposition suggesting the oxide protect the graphene quality in the fabrication process.
关键词： compressive stress,fabrication process,Raman spectroscopy,graphene,metal deposition
更新于2025-09-09 09:28:46
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Orientation dependence of electric field induced phase transitions in lead-free (Na <sub/>0.5</sub> Bi <sub/>0.5</sub> )TiO <sub/>3</sub> -based single crystals
摘要： The orientation dependence of the electric field induced strain and phase transitions in 0.92(Na0.5Bi0.5)TiO3-0.06BaTiO3-0.02(K0.5Na0.5)NbO3 (NBT-6BT-2KNN) single crystals has been investigated. The evolution of Raman spectra with electric field reveals that a tetragonal ferroelectric phase is initially induced at E=14kV/cm and completed above E=25kV/cm for [001] oriented single crystals. When the electric field is applied along [111] direction, a partial phase transition from pseudocubic to rhombohedral structure is triggered at E=19kV/cm, which is higher than that for inducing tetragonal ferroelectric phase along [001] direction. Both field-induced phase structures and stability of NBT-6BT-2KNN single crystal are strongly associated with the crystallographic orientations. These results provide a better understanding to the field-induced macroscopic strain in lead-free NBT-based ferroelectrics.
关键词： X-ray diffraction,lead-free ferroelectrics,electric field induced phase transitions,Raman spectroscopy,NBT-based single crystals
更新于2025-09-09 09:28:46
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Raman Spectroscopy and Applications || Raman Mapping: Emerging Applications
摘要： Raman mapping is a noninvasive, label‐free technique with high chemical specificity and high potential to become a leading method in biological and biomedical applications. As opposed to Raman spectroscopy, which provides discrete chemical information at distinct positions within the sample, Raman mapping provides chemical information coupled with spatial information. The laser spot scans the investigated sample area with a preset step size and acquires Raman spectra pixel by pixel. The Raman spectra are then discriminated from each other by chemometric analysis, and the end result is a false color map, an image of the sample that contains highly precise structural and chemical information. Raman imaging has been successfully used for label‐free investigations at cellular and subcellular level. Cell compartments, cell responses to drugs and different stages of the cell cycle from the stem cell to the completely differentiated cell were successfully distinguished. This technique is also able to differentiate between healthy and cancer cells, indicating great potential for replacing conventional cancer detection tools with Raman detection in the future.
关键词： plants,algae,cells,medical diagnosis,tissues,Raman imaging,Raman mapping,Raman spectroscopy
更新于2025-09-04 15:30:14