Resonance Raman Scattering Research Articles

Nanoscale Surface Roughness Effects on Photoluminescence and Resonant Raman Scattering of Cadmium Telluride

Nanoscale Surface Roughness Effects on Photoluminescence and Resonant Raman Scattering of Cadmium Telluride

Resonant Raman Scattering of Surface Phonon Polaritons Mediated by Excitons in WSe2 Films

Resonant Raman Scattering of Surface Phonon Polaritons Mediated by Excitons in WSe₂ Films

Ultraviolet Resonant Raman Scattering of Electrolyte Solutions.

Saltwater stands as the most prevalent liquid on Earth. Consequently, substantial interest has been directed toward its characterization, both as an independent system and as a solvent for complex structures such as biomacromolecules. In the last few decades, special emphasis was placed on the investigation of the hydration properties of ions for the fundamental role they play in numerous chemical processes. In this study, we employed multi-wavelength Raman spectroscopy to examine the hydration shell surrounding bromide ions in solutions of simple electrolytes, specifically lithium bromide, potassium bromide, and cesium bromide, at two different concentrations. Cation-induced differences among electrolytes were observed in connection to their tendency to form ion pairs. An increased sensitivity to reveal the structure of the first hydration shell was evidenced when employing ultraviolet excitation in the 228-266 nm range, under resonance conditions with the charge transfer transition to the solvent peaked at about 200 nm. Other than a significant increase in the Raman cross-section for the OH stretching band when shifting from pure water to the solution, a larger enhancement for the Raman signal of the H-O-H bending mode over the stretching vibration was observed. Thus, the bending band plays a crucial role in monitoring the H-bond structure of water around the anions related to the charge distribution within the first hydration shell of anions, being an effective probe of hydration phenomena.

Resonant Raman Scattering Study of Strain and Defects in Chemical Vapor Deposition Grown MoS2 Monolayers.

The development of bottom-up synthesis routes for semiconducting transition metal dichalcogenides (TMDs) and the assessment of their defects are of paramount importance to achieve their applications. TMD monolayers grown by chemical vapor deposition (CVD) can be subjected to significant strain and, here, Raman and photoluminescence spectroscopies are combined to characterize strain in over one hundred MoS2 monolayer samples grown by CVD. The frequency changes of phonons as a function of strain are analyzed, and used to extract the Grüneisen parameter of both zone-center and edge phonons. Additionally, the intensity of the defect-induced longitudinal acoustic (LA) and transverse acoustic(TA) Raman bands are discussed in relation to strain and electronic doping. The experimental mode-Grüneisen parameters obtained are compared with those calculated by density functional theory (DFT), to better characterize the type of strain and its resulting effects on Grüneisen parameters. The findings indicate that the use of Raman spectra to determine defect densities in 2D MoS2 must be always conducted considering strain effects. To the best of the authors' knowledge, this work constitutes the first report on double resonance Raman processes studied as a function of strain in 2D-MoS2. The new approach to obtain the Grüneisen parameter from zone-edge phonons in MoS2 can also be extended to other 2D semiconducting TMDs.

Pen direct writing of SERRS-based lateral flow assays for detection of penicillin G in milk.

Direct pen writing offers versatile opportunities for development of low-cost tests for point-of-care applications. In this work a lateral flow immunoassay (LFIA) test was fabricated by hand "writing" immunoprobes onto hand-cut nitrocellulose strips with a commercial fountain pen. The qualitative capabilities of the test were extended by addition of a Raman reporter and consequent design and fabrication of a Surface Enhanced Resonant Raman Scattering (SERRS)-LFIA test. As proof-of-concept, dual detection of penicillin G was achieved in milk with a visual LOD of 20 ppm and a dynamic range of 0.03-97.5 ppm. Evaluation against equivalent tests performed with conventionally prepared LFIA strips showed comparable results, thus demonstrating the validity of the test. These results demonstrate the potential for further decrease in cost and consequent broader use of LFIA tests in remote regions and resource-limited environments.

Unveiling Coherent Control of Halomethane Dissociation Induced by a Single Strong Ultraviolet Pulse.

We present a theoretical investigation into the coherent control of photodissociation reactions in halomethanes, specifically focusing on CH2BrCl by manipulating the spectral phase of a single femtosecond laser pulse. We examine the photodissociation of CH2BrCl under an ultrashort pulse with a quadratic spectral phase and reveal the sensitivity of both the total dissociation probability and the resulting radical products (Br+CH2Cl and Cl+CH2Br) to chirp rates. To gain insights into the underlying mechanism, we calculate the population distributions of excited vibrational states in the ground electronic state, demonstrating the occurrence of resonance Raman scattering (RRS) in the strong-field limit regime. By utilizing chirped pulses, we show that this RRS phenomenon can be suppressed and even eliminated through quantum destructive interference. This highlights the high sensitivity of photodissociation into Cl+CH2Br to the spectral phase, showcasing a phenomenon that goes beyond the traditional one-photon photodissociation of isolated molecules in the weak-field limit regime. These findings emphasize the importance of coherent control in the exploration and utilization of photodissociation in polyatomic molecules, paving the way for new advancements in chemical physics and femtochemistry.

Combination of resonance and non-resonance chiral Raman scattering in a cobalt(III) complex.

Resonance Raman optical activity (RROA) spectra with high sensitivity reveal details on molecular structure, chirality, and excited electronic properties. Despite the difficulty of the measurements, the recorded data for the Co(III) complex with S,S-N,N-ethylenediaminedisuccinic acid are of exceptional quality and, coupled with the theory, spectacularly document the molecular behavior in resonance. This includes a huge enhancement of the chiral scattering, contribution of the antisymmetric polarizabilities to the signal, and the Herzberg-Teller effect significantly shaping the spectra. The chiral component is by about one order of magnitude bigger than for an analogous aluminum complex. The band assignment and intensity profile were confirmed by simulations based on density functional and vibronic theories. The resonance was attributed to the S0®S3 transition, with the strongest signal enhancement of Raman and ROA spectral bands below about 800 cm-1. For higher wavenumbers, other excited electronic states contribute to the scattering in a less resonant way. RROA spectroscopy thus appears as a unique tool to study the structure and electronic states of absorbing molecules in analytical chemistry, biology, and material science.

(Invited) Efficient Inner-to-Outer Wall Energy Transfer in Highly Pure Double-Wall Carbon Nanotubes Revealed by Detailed Spectroscopy

The coaxial stacking of two single-wall carbon nanotubes (SWCNTs) into a double-wall carbon nanotube (DWCNT), forming a so-called one-dimensional van der Waals structure, leads to synergetic effects that dramatically affect the optical and electronic properties of both layers [1]. In this work, we explore these effects in purified DWCNT samples by combining absorption, wavelength-dependent infrared fluorescence−excitation (PLE), and wavelength-dependent resonant Raman scattering (RRS) spectroscopy. Purified DWCNTs are obtained by careful solubilization that strictly avoids ultrasonication [2] or by electronic-type sorting [3], both followed by a density gradient ultracentrifugation to remove unwanted SWCNTs that could obscure the DWCNT characterization [2]. Chirality-dependent shifts of the radial breathing mode vibrational frequencies and transition energies of the inner and outer DWCNT walls with respect to their SWCNT analogues are determined by advanced two-dimensional fitting of RRS and PLE data of DWCNT and their reference SWCNT samples. This exhaustive data set verifies that fluorescence from the inner DWCNT walls of well-purified samples is severely quenched, as previously evidenced in single-tube experiments [4]. Moreover, we find that this quenching occurs through efficient energy transfer from the inner to the outer DWCNT walls [5]. Combined analysis of the PLE and RRS results further reveals that this transfer is dependent on the inner and outer wall chirality, and we identify the specific combinations dominant in our DWCNT samples. These obtained results demonstrate the necessity and value of a combined structural characterization approach including PLE and RRS spectroscopy for bulk DWCNT samples.[1] S. Cambré et al, Small 2021, 17, 2102585[2] M. Erkens et al, Carbon 2021, 185, 113[3] H. Li et al, Nature Nanotechnol. 2017, 12, 1176[4] D. Levshov et al, Phys. Rev. B 2017, 96, 195410[5] M. Erkens et al, ACS Nano 2022, 16, 16038

Molecularly Imprinted Plasmonic Sensors for the Determination of Environmental Water Contaminants: A Review

The scarcity of clean water leads to the exploration of the possibility of using treated wastewater. However, monitoring campaigns have proven the presence of emerging contaminants, such as pharmaceuticals, pesticides and personal care products, not only in trace amounts. Various analytical methodologies have been developed over the last years for the quantification of these compounds in environmental waters. Facing the need to achieve a higher sensitivity, fast response and practical use via miniaturization, the potential of plasmonic sensors has been explored. Through the introduction of molecularly imprinted polymers (MIPs) as recognition elements, MIP-based plasmonic sensors seem to be a good alternative for monitoring a wide range of analytes in water samples. This work attempts to provide a general overview of this form of sensor, which has been reported as being able to sense different contaminants in waters using surface plasmon resonance (SPR) and surface-enhanced Raman-scattering (SERS) techniques. Particular emphasis is given to the fabrication/recognition procedure, including the preparation of MIPs and the use of metals and nanomaterials to increase the performance characteristics of the sensors.

Correlated Polarization Dependences between Surface-Enhanced Resonant Raman Scattering and Plasmon Resonance Elastic Scattering Showing Spectral Uncorrelation to Each Other

We investigated the origin of the identical polarization angle dependence between surface-enhanced resonant Raman scattering (SERRS) and plasmon resonance elastic scattering (PRES) for two types of single silver nanoparticle aggregates. The first type (Type I), in which the SERRS spectral envelopes are similar to the PRES spectra, shows the identical polarization dependence between the SERRS and PRES. The second type (Type II), in which the SERRS envelopes largely deviate from the PRES spectra, also exhibits identical polarization dependence. Scanning electron microscopy observations indicated that the aggregates were dimers. This unintuitive result was examined by calculating the electromagnetic enhancement by changing the morphology of the dimers. The calculations revealed that the Type I dimer generates SERRS directly by superradiant plasmons. The Type II dimer generates SERRS indirectly via subradiant plasmons, which receive light energy from superradiant plasmons. This indirect SERRS process clarifies that the interaction between the superradiant and subradiant plasmons results in an identical polarization dependence between SERRS and PRES for Type II dimers.

Probing Defects and Spin‐Phonon Coupling in CrSBr via Resonant Raman Scattering

AbstractUnderstanding the stability limitations and defect formation mechanisms in 2D magnets is essential for their utilization in spintronic and memory technologies. Here, defects in mono‐ to multilayer CrSBr are correlated with structural, vibrational, and magnetic properties. Resonant Raman scattering is used to reveal distinct vibrational defect signatures. In pristine CrSBr, it is shown that bromine atoms mediate vibrational interlayer coupling, allowing for distinguishing between surface and bulk defect modes. Environmental exposure is shown to cause drastic degradation in monolayers, with the formation of intralayer defects. This is in contrast to multilayers that predominantly show bromine surface defects. Through deliberate ion irradiation, the formation of defect modes is tuned: these are strongly polarized and resonantly enhanced, reflecting the quasi‐‐1D electronic character of CrSBr. Strikingly, pronounced signatures of spin‐phonon coupling of the intrinsic phonon modes and the ion beam‐induced defect modes are observed throughout the magnetic transition temperature. Overall, defect engineering of magnetic properties is possible, with resonant Raman spectroscopy serving as a direct fingerprint of magnetic phases and defects in CrSBr.

Efficient Inner-to-Outer Wall Energy Transfer in Highly Pure Double-Wall Carbon Nanotubes Revealed by Detailed Spectroscopy.

The coaxial stacking of two single-wall carbon nanotubes (SWCNTs) into a double-wall carbon nanotube (DWCNT), forming a so-called one-dimensional van der Waals structure, leads to synergetic effects that dramatically affect the optical and electronic properties of both layers. In this work, we explore these effects in purified DWCNT samples by combining absorption, wavelength-dependent infrared fluorescence-excitation (PLE), and wavelength-dependent resonant Raman scattering (RRS) spectroscopy. Purified DWCNTs are obtained by careful solubilization that strictly avoids ultrasonication or by electronic-type sorting, both followed by a density gradient ultracentrifugation to remove unwanted SWCNTs that could obscure the DWCNT characterization. Chirality-dependent shifts of the radial breathing mode vibrational frequencies and transition energies of the inner and outer DWCNT walls with respect to their SWCNT analogues are determined by advanced two-dimensional fitting of RRS and PLE data of DWCNT and their reference SWCNT samples. This exhaustive data set verifies that fluorescence from the inner DWCNT walls of well-purified samples is severely quenched through efficient energy transfer from the inner to the outer DWCNT walls. Combined analysis of the PLE and RRS results further reveals that this transfer is dependent on the inner and outer wall chirality, and we identify the specific combinations dominant in our DWCNT samples. These obtained results demonstrate the necessity and value of a combined structural characterization approach including PLE and RRS spectroscopy for bulk DWCNT samples.

SERS enhancement induced by the Se vacancy defects in ultra-thin hybrid phase SnSex nanosheets.

Improving the photo-induced charge transfer (PICT) efficiency by adjusting the energy levels difference between adsorbed probe molecules and substrate materials is a key factor for boosting the surface enhanced Raman scattering (SERS) based on the chemical mechanism (CM). Herein, a new route to improve the SERS activity of two-dimensional (2D) selenium and tin compounds (SnSex, 1 ≤ x ≤ 2) by the hybrid phase materials is researched. The physical properties and the energy band structure of SnSex were analyzed. The enhanced SERS activity of 2D SnSex can be attribute to the coupling of the PICT resonance caused by the defect energy levels induced by Se vacancy and the molecular resonance Raman scattering (RRS). This established a relationship between the physical properties and SERS activity of 2D layered materials. The resonance probe molecule, rhodamine (R6G), which is used to detect the SERS performance of SnSex nanosheets. The enhancement factor (EF) of R6G on the optimized SnSe1.35 nanosheets can be as high as 2.6 × 106, with a detection limit of 10-10 M. The SERS result of the environmental pollution, thiram, shows that the SnSex nanosheets have a practical application in trace SERS detection, without the participation of metal particles. These results demonstrate that, through hybrid phase materials, the SERS sensitivity of 2D layered nanomaterials can be improved. It provides a kind of foreground non-metal SERS substrate in monitoring or detecting and provide a deep insight into the chemical SERS mechanism based on 2D layered materials.

Pressure Tuning Resonance Raman Scattering in Monolayer, Trilayer, and Many-Layer Molybdenum Disulfide

Pressure Tuning Resonance Raman Scattering in Monolayer, Trilayer, and Many-Layer Molybdenum Disulfide

Exploring Resonance Raman Scattering with 4-Nitrophenol

Raman scattering is a powerful tool for revealing the vibrations of molecules, but as a nonlinear optical phenomenon, its signals can change via mechanisms like resonance enhancement that have no direct analogue in infrared spectroscopy. In this work, complementary measurements conducted on 4-nitrophenol and its conjugate base allow students to directly control the variables responsible for enhancement. Changing sample UV–vis absorbance with pH and excitation color with the addition of a diode laser allows students to explore the criteria for resonance Raman scattering: only the conjugate base and 405 nm laser in combination produce enhancement. Adjustments to the experiment make it suitable for either an upper-level undergraduate course lab or an independent inquiry project.

Dual Role of Au nanoparticles in the Catalytic Formation of an Amorphous Polynuclear Peroxo Complex and Surface Enhanced Resonance Raman Scattering

AbstractWe report the catalytic formation of bridged polynuclear peroxo complex of Co(II) and 2‐picolylamine (2‐PA) in aqueous alkaline medium on the surface of Au nanoparticle. The reaction followed sigmoidal kinetics both in absence and presence of the Au nanoparticle with an order of magnitude higher rate constant in the presence of nanoparticle. Importantly, using UV‐Vis spectroscopy, mass spectrometry and surface enhance resonance Raman scattering (SERRS), we conclude the formation of peroxo complex with 2‐PA acting as a monodentate ligand. The absorbance of the polynuclear complex at 595 nm and the extinction maximum of (agglomerated) the Au nanoparticles at 750 nm provided the right opportunity to pursue SERRS using 632.8 nm laser excitation. Density functional theoretical calculation indicated that the lowering of HOMO‐LUMO energy gap of 2‐PA bonded to the nanoparticle surface helped catalyze the reaction.

Angular Dependence of Multi-atom Resonant X-ray Raman Scattering

Angular Dependence of Multi-atom Resonant X-ray Raman Scattering

Conformational Selectivity of Merocyanine on Nanostructured Silver Films: Surface Enhanced Resonance Raman Scattering (SERRS) and Density Functional Theoretical (DFT) Study.

In this study, detailed structural and vibrational analysis of merocyanine has been investigated using Raman, surface enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS). The Raman, SERS and SERRS studies aided by density functional theoretical (DFT) calculations clearly established the prevalence of the trans- and cis-conformers of the protonated form of merocyanine (MCH+) in solid and acetonitrile solution. The binding characteristics of merocyanine adsorbed on nanostructured silver-coated films (SCFs) were investigated using excitation-dependent SERS, concentration-dependent SERRS and DFT studies. The conformers of merocyanine involved in the surface adsorption processes were recognized. The prominent marker bands observed at 1538 (ethylenic C=C stretch) and 1133 cm−1 (pyridinium C-N stretch) in the Raman spectrum of merocyanine in acetonitrile shifted to 1540 and 1126 cm−1, respectively on the nanostructured SCFs. The shift in the marker bands is associated with either the preferential binding of selective conformer or change in resonance equilibrium between the benzenoid and quinoid forms. The excitation wavelength dependent SERS spectrum infers that in addition to the major contribution from the electromagnetic enhancement, chemical (resonance) effect leads to the amplification of the 1540 cm−1 band. The concentration-dependent SERRS study showed maximum enhancement for the nanostructured SCFs functionalized with 1 μM concentration of merocyanine, indicative of monolayer coverage. For lower concentrations of merocyanine, the SERRS signal intensity reduced without any alteration in the peak positions. The SERRS study thus, revealed sub-nanomolar (0.1 nM) sensing of merocyanine using nanostructured SCFs with the analytical enhancement factor (AEF) of ∼ 1010 for the 1126 cm−1 and 1540 cm−1 Raman bands for MC concentration of 0.1 nM. In this study, combination of SERRS and DFT have clearly established the predominance of trans-MCH+ on the nanostructured silver surface with minor contribution from cis-MCH+, which remain exclusively bound to the surface via the phenoxyl ring O atom. This conformational surface selectivity of geometrical isomers of merocyanine using nanostructured surfaces can be further explored for energy efficient and economical separation of geometrical isomers.

Optically active cross-band transition in double-walled carbon nanotube and its impact on Raman resonances

Double-walled carbon nanotubes (DWNTs), often regarded as the simplest one-dimensional (1D) van der Waals moiré superlattices, are the ideal structures to explore the interlayer coupling, including mechanical and electronical coupling, at the nanoscale in 1D systems. By combining spatial modulation spectroscopy (SMS) and resonant Raman scattering (RRS) experiments on well-identified individual free-standing DWNTs with the calculations of their optical absorption by using the recursion method with non-orthogonal tight-binding (NTB) basis functions, we are able to unambiguously assign the nature, namely mirror transition or cross transition, of each optical transitions in DWNTs. Our study identifies and allows to determine the conditions of the mixing of the electronic states leading to the appearance of cross transitions in the optical absorption of DWNTs, beyond of the so-called Koshino's criteria previously derived. On the other hand, the striking behavior of the resonant excitation profile (REP) of the Raman active modes around the cross transition reveals the strong sensitivity of the modes intensity on the electronic interlayer coupling in DWNTs, emphasizing the relevance of Raman spectroscopy for studying the electronic and mechanical coupling at the nanoscale.

Surface Resonant Raman Scattering from Cu(110).

We report the first evidence of Raman scattering from surface phonons of a pristine metal surface. Our study reveals a Raman-active surface vibrational resonance on Cu(110) with a surprisingly large scattering efficiency. With the incident photon energy close to the energy of the Cu(110) surface state electronic transition, the Raman scattering from the surface optical resonance can be significantly enhanced, while any contribution from bulk phonons is absent.