| 1. |
- Ghignone, Stefano, et al.
(författare)
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The Raman spectrum of florencite-(REE) [REEAl3(PO4)2(OH)6] : An integrated experimental and computational approach
- 2024
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Ingår i: Journal of Raman Spectroscopy. - 0377-0486 .- 1097-4555. ; 55:3, s. 394-405
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Tidskriftsartikel (refereegranskat)abstract
- Florencite is a hydrous light rare-earth elements (LREE) aluminium phosphate [REEAl3(PO4)2(OH)6], that amongst the REE-rich minerals is quite common. The main end-members are Ce-, La- and Nd-rich terms that were found in several genetic environments. Despite the large occurrence worldwide, to the authors' knowledge, florencite has attracted very few studies, particularly concerning the characterization of its Raman spectrum. We present a detailed study of the Raman spectrum of florencite, combining experimental measurements and theoretical calculations. Experimental Raman spectra (in the 100–1300 cm−1 spectral range) are measured on four florencite samples characterized by different chemical composition, that is, different REE abundance. The results highlight a remarkable coincidence between different Raman spectra measured on each sample, despite the significantly different chemical compositions in terms of their REE content. The same similarities were also observed in the computed spectra at the ab initio level; moreover, the calculations allowed the attributions of the different Raman signals to specific vibrational modes.
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| 2. |
- Hot, Dina, et al.
(författare)
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Investigation of laser-induced grating spectroscopy of O2 for accurate temperature measurements towards applications in harsh environments
- 2021
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 52:9, s. 1569-1581
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Tidskriftsartikel (refereegranskat)abstract
- We present an in-depth investigation of laser-induced grating spectroscopy (LIGS) for temperature measurements in practical applications using a narrow-band dye laser with 760 nm wavelength and a pulse duration of 8 ns as the source for the pump beams creating the laser-induced grating. The pump laser wavelength was set to be either resonant with the (Formula presented.) transition from the (Formula presented.) band of O2 for generation of thermal LIGS or nonresonant for generation of purely electrostrictive LIGS. Signals were generated in ambient air as well as in high-pressure or high-temperature dry air mixtures. Pump laser irradiances up to 11 GW/cm2 were used, which resulted in strong electrostrictive contribution to the overall LIGS signals at atmospheric pressure, with a low thermal contribution due to the weak absorption by the singlet O2 (Formula presented.). The advantage and disadvantage of thermal or electrostrictive LIGS for temperature measurements are discussed, as well as potential applications in high-pressure environments. Furthermore, the precision of the temperature measurement is discussed by comparing different analysis methods.
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| 3. |
- Le, Kim Cuong, et al.
(författare)
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Polarization effects in Raman spectroscopy of light-absorbing carbon
- 2021
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 1097-4555 .- 0377-0486. ; 52:6, s. 1115-1122
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Tidskriftsartikel (refereegranskat)abstract
- Raman spectroscopy is widely used for characterization of carbon-based mate- rials including light-absorbing carbonaceous (LAC) matter. However, informa- tion on polarization properties of these materials are generally lacking, and often the polarization characteristics of experiments are not presented in the literature thereby giving uncertainty to presented data. In this work, the polari- zation properties of various LACs are studied using Raman spectroscopy. The Raman spectra have been compared while varying the relative polarization, particularly the relative direction of the electric field between the incident light and the detected scattered light. Specifically, the intensity ratio between the D1 and G peaks (ID1/IG) was analyzed in parallel and perpendicular polarization configurations for samples taken from a sooting flame, in the exhaust of a soot generator and carbon blacks. In this work, the parallel and perpendicular polarization configurations mean that the polarization of the detected scattered light is parallel and orthogonal, respectively, to the linearly polarized incident light. It was found that the (ID1/IG) ratio decreased in the more ordered carbo- naceous structures when changing the polarization configuration from parallel to perpendicular. Additionally, based on the depolarization ratios (Dp < 0.75), the prominent Raman peaks of LAC were found to originate from totally sym- metric vibrations. For the G peak, the depolarization ratio was measured to be in the range 0.46–0.56 for all LAC materials.
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| 4. |
- Malyshev, Dmitry, et al.
(författare)
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Reference Raman Spectrum and Mapping of Cryptosporidium parvum Oocysts
- 2022
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Ingår i: Journal of Raman Spectroscopy. - : John Wiley & Sons. - 0377-0486 .- 1097-4555. ; 53:7, s. 1293-1301
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Tidskriftsartikel (refereegranskat)abstract
- Cryptosporidium parvum is a protozoan parasite and among the most infectious diarrhea-causing pathogens, leading to severe health problems for malnourished children and immunocompromised individuals. Outbreaks are common even in developed countries, originating from water or food contamination and resulting in suffering and large costs for society. Therefore, robust, fast and highly specific detection strategies of Cryptosporidium are needed. Label-free detection techniques such as Raman spectroscopy have been suggested, however high-resolution reported spectra in the literature are limited. In this work, we report reference Raman spectra at 3 cm-1 resolution for viable and inactivated Cryptosporidium oocysts of the species C. parvum, gathered at a single oocyst level using a laser tweezers Raman spectroscopy system. We furthermore provide tentative Raman peak assignments for the Cryptosporidium oocysts, along with Raman mapping of the oocysts’ heterogeneous internal structure. Finally, we compare the C. parvum Raman spectrum with other common enterotoxigenic pathogens: Escherichia coli, Vibrio cholerae, Bacillus cereus and Clostridium difficile. Our results show a significant difference between C. parvum Raman spectra and the other pathogens.
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| 5. |
- Milenov, Teodor, et al.
(författare)
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Raman fingerprint of the graphene buffer layer grown on the Si-terminated face of 4H-SiC(0001): Experiment and theory
- 2023
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Ingår i: Journal of Raman Spectroscopy. - : WILEY. - 0377-0486 .- 1097-4555.
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present the results of measurements of the Raman spectrum of the root 3x root 3R30 degrees reconstruction of graphene grown on 4H-SiC(0001), the so-called buffer layer. The extracted Raman spectrum of the buffer layer shows bands, different from those of graphene, which can be attributed to the interaction of the buffer layer with the SiC substrate. In particular, in the high-wavenumber region, at least three bands are observed in the wavenumber regions 1,350-1,420, 1,470-1,490 and 1,520-1,570 cm-1. The assignment of the buffer layer bands is supported here by tight-binding simulations of the one-phonon density of states for structures with a sufficiently large number of Si-C bilayers for reaching convergence. The converged phonon density of states is found to be in semi-quantitative agreement with the latter two bands, and therefore, the tight-binding predictions of the lattice dynamics of the structure can be used for their assignment to buffer layer vibrations. Namely, the Raman band at about 1,550 cm-1 can be assigned to modified in-plane optical phonon branches of graphene, while the Raman band at about 1,490 cm-1 can be assigned to modified folded parts of these branches inside the Brillouin zone of the buffer layer and can be considered as a Raman fingerprint of the buffer layer. We present the results of measurements of the Raman spectrum of the root 3x root 3R30 degrees reconstruction of graphene grown on 4H-SiC(0001), the so-called buffer layer (BL) in the wavenumber region 1,200-1,650 cm-1. The assignment of the BL bands is supported by tight-binding simulations of the one-phonon density of states (DOS) for structures with a sufficiently large number of Si-C bilayers for reaching convergence. The converged phonon DOS is found to be in semi-quantitative agreement with the experimental Raman spectra.image
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| 6. |
- Mozhzhukhina, Nataliia, et al.
(författare)
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Short-range ordering in the Li-rich disordered rock salt cathode material Li2VO2F revealed by Raman spectroscopy
- 2020
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 51:10, s. 2095-2101
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Tidskriftsartikel (refereegranskat)abstract
- Li‐rich disordered rock salt (DRS) materials are new promising high‐capacity cathode candidates for Li‐ion batteries. DRS structures were initially assumed to have a completely random cation and anion distribution, but recent reports suggest that some of these structures can exhibit local atomic arrangements, or short‐range ordering (SRO). Here, we prove the existence of SRO in the Li‐rich DRS material Li2VO2F by employing Raman spectroscopy supported by density functional theory (DFT) calculations. Our results suggest that this combination of Raman spectroscopy with computational tools is useful for SRO estimation in this new class of Li‐rich DRS cathode materials.
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| 7. |
- Thyr, Jakob, 1979-, et al.
(författare)
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Polarized and non-polarized Raman spectroscopy of ZnO crystals : Method for determination of crystal growth and crystal plane orientation for nanomaterials
- 2021
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Ingår i: Journal of Raman Spectroscopy. - : John Wiley & Sons. - 0377-0486 .- 1097-4555. ; 52:8, s. 1395-1405
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Tidskriftsartikel (refereegranskat)abstract
- Analysis and determination of crystal orientation and exposed surface facets remain a challenge in nanomaterial science. In this work we show that polarized and non-polarized Raman spectroscopy can be useful tools to determine crystal plane orientation and conveniently be applied to spatial dimensions limited only by the diffraction limit of the excitation laser. The methodology is exemplified for wurtzite structured ZnO. Three different crystal facets, (0001), (1-100), and (11-20) of ZnO are investigated with angle resolved polarized Raman spectroscopy. The polarization direction dependences of the main Raman peaks are characterized and related to the experimental vibrational modes in the crystal lattice and corroborated by density functional theory (DFT) calculations using two different hybrid functionals. By exploiting the symmetry of the modes and differences in Raman intensity of the optically activated phonons, a simple model is derived for determining the relation between the polar and non-polar crystal orientation. The results are generalized to allow peak intensity ratio analysis using Raman spectroscopy with a non-polarized light source, making it compatible with Raman mapping, as well as to include a critical discussion on the ability to determine the crystal plane orientation and exposed crystal facets using this model for nano dimensional ZnO and equivalent models for other nanomaterials. As the approach allows for use of non-polarized light sources, near-field excitations and local plasmons can in an extension be utilized for determination of crystal orientation and exposed planes in dimensions much smaller than the diffraction limit.
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| 8. |
- Öberg, Rasmus, et al.
(författare)
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Characterization of carfentanil and thiofentanil using surface-enhanced raman spectroscopy and density functional theory
- 2024
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Ingår i: Journal of Raman Spectroscopy. - : John Wiley & Sons. - 0377-0486 .- 1097-4555. ; 55:4, s. 481-492
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Tidskriftsartikel (refereegranskat)abstract
- Fentanyls are synthetic opioids up to 10,000 times more potent than morphine. Although initially developed for medical applications, fentanyl and its analogues have recently grown synonymous with the ongoing opioid epidemic. To combat the continued spread of these substances, there is a need for rapid and sensitive techniques for chemical detection. Surface-enhanced Raman spectroscopy (SERS) has the potential for trace detection of harmful chemical substances. However, vibrational spectra obtained by SERS often differ between SERS substrates, as well as compared with spectra from normal Raman (NR) spectroscopy. Herein, SERS and NR responses from two fentanyl analogues, carfentanil (CF) and thiofentanil (TF), were measured and analysed with support from density functional theory (DFT) modelling. Using commercially available silver nanopillar SERS substrates, the SERS signatures of samples diluted in acetonitrile between 0.01 and 1000 µg/mL were studied. Relative SERS peak intensities measured in the range of 220–1800 cm−1 vary with concentration, while SERS and NR spectra largely agree for CF at higher concentrations ((Formula presented.) 100 µg/mL). For TF, three distinct NR peaks at 262, 366 and 667 cm−1 are absent or strongly suppressed in the SERS spectrum, attributed to the lone-pair electrons of the thiophene's sulphur atom binding to the Ag surface. The concentration dependence of the Raman peak at (Formula presented.) 1000 cm−1, assigned to trigonal bending of the phenyl ring, approximately follows a Langmuir adsorption isotherm. This work elucidates similarities and differences between SERS and NR in fentanyl detection and discusses the chemical rationale behind these differences.
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