High-resolution Raman Measurements Research Articles

Label-free drug interaction screening via Raman microscopy

Development of a simple, label-free screening technique capable of precisely and directly sensing interaction-in-solution over a size range from small molecules to large proteins such as antibodies could offer an important tool for researchers and pharmaceutical companies in the field of drug development. In this work, we present a thermostable Raman interaction profiling (TRIP) technique that facilitates low-concentration and low-dose screening of binding between protein and ligand in physiologically relevant conditions. TRIP was applied to eight protein-ligand systems, and produced reproducible high-resolution Raman measurements, which were analyzed by principal component analysis. TRIP was able to resolve time-depending binding between 2,4-dinitrophenol and transthyretin, and analyze biologically relevant SARS-CoV-2 spike-antibody interactions. Mixtures of the spike receptor-binding domain with neutralizing, nonbinding, or binding but nonneutralizing antibodies revealed distinct and reproducible Raman signals. TRIP holds promise for the future developments of high-throughput drug screening and real-time binding measurements between protein and drug.

Residual Stress Measurements in PVD Coatings of Carbide Cutting Tools Directly in the Cutting Edge

Residual stress measurements directly in the coated cutting edge are not possible with X-ray diffraction (XRD) due to the diameter of the X-ray beam. On the other hand, Raman microscopy enables measurements on the micrometer scale. Parameter variations in the PVD process were used to provide different residual stress states in (Al,Ti)N coatings on carbide cutting tools. They were examined by XRD in regions that can be reliably measured. The same area was then examined by Raman microscopy to determine the relationship of Raman peaks to the residual stress. Local high-resolution Raman measurements were then taken at the cutting edge and further influences on the Raman peak position besides residual stresses were excluded. In order to analyze the relationship between Raman peak shift and residual stress state, measurements were performed during a bending load. Finally, an outlook on further investigations is given.

Development of a spatial heterodyne Raman spectrometer with echelle-mirror structure.

Spatial heterodyne Raman spectroscopy is a spectroscopic detection technique that is particularly suitable for Raman measurements. The spectral range of traditional spatial heterodyne Raman spectrometer (SHRS) is limited by its spectral resolution and the number of detector elements. We propose an SHRS with an echelle-mirror structure that employs multiple diffraction orders to achieve a broad spectral coverage and high spectral resolution simultaneously. This SHRS is used to obtain the Raman spectra of organic liquids, inorganic solid targets, and mixed targets. Observations of aqueous solutions, and minerals are presented. In addition, anti-Stokes Raman shifts are also presented. The proposed SHRS technique shows good performance for broadband, high-resolution Raman measurements.

Correlation between surface morphology and defect structure of heteroepitaxial diamond grown on off‐axis substrates

The topographic surface features that develop during chemical vapour deposition of heteroepitaxial diamond on off‐axis Ir/YSZ/Si(001) and their implications on the incorporation and modification of 0D and 1D defects have been studied. After growth with nitrogen in the gas phase, the surface has split into alternating stripes of opposite inclination. The terrace regions are tilted towards the crystallographic [001] axis, while the risers are tilted in the opposite direction. AFM measurements on the macroscopic terraces reveal a microscopic substructure consisting of terraces and risers on a smaller length scale. Cross‐section SEM images display inclined dark and bright striations. In photoluminescence maps, the stripes ending at risers show a higher NV and SiV emission intensity thus indicating a stronger defect incorporation of colour centres. Relative growth rates on terrace and riser areas have been evaluated. In high resolution Raman measurements, the cross‐section maps display bands of high line width embedded in a background of lower line width. Conversion of these data into dislocation density maps reveals local variations by one order of magnitude. The tilt angle of the threading dislocation bundles is attributed to an interaction induced by the lateral step flow on the off‐axis growth surface.Scheme of the investigated diamond samples.

Phonon strain shift coefficients in Si1−xGex alloys

A comprehensive study of the biaxial strain-induced shift of the Si1−xGex Raman active phonon modes is presented. High-resolution Raman measurements of Si1−xGex/Si heterostructures have been compared to x-ray diffraction data. Our approach, unlike previous works, is effective to decouple and quantify separately the effect of strain and composition on the phonon frequencies, yielding an accurate determination of the phonon strain shift coefficients in the entire composition range. Our results show that the strain shift coefficients are independent of the composition, a result which is in good agreement with theoretical calculations, performed within the framework of valence force-field theory.

Ce 3+-doped lutetium yttrium orthosilicate crystals: Structural characterization

In this work we investigate the structural properties of Ce:Lu 2(1− x) Y 2 x SiO 5 (LYSO) crystals as a function of cerium incorporation by means of low-temperature high-resolution Raman measurements. Czochralski grown single-crystal LYSO samples were obtained with a ratio of yttrium to lutetium ions 10:90 (Ce:Lu 1.8Y 0.2SiO 5) and a variation in the cerium concentration in the 0–750 ppm range. A red shift of the Raman bands, related to a decrease of the unit cell, is observed as function of the cerium concentration in the crystal. By analyzing the low wave number vibrational modes and the polarized Raman measurements, the substitutional role of cerium ions in the rare-earth sites occupied by yttrium ions is infrared. In addition, since the rare earth can occupy two independent different crystallographic sites, the analysis of the Raman spectra allows to distinguish the preferred site by cerium ions in the doping process.

Highly perfect inner tubes in CVD grown double-wall carbon nanotubes

The synthesis of double-wall carbon nanotubes (DWCNTs) with highly unperturbed inner shells is reported using the catalytic vapor deposition method. Temperature dependent and high resolution Raman measurements show an enhanced phonon life-time of the inner tubes with respect to the outer ones and similar diameter SWCNTs. This proves that the inner tubes are unperturbed similar to the inner tubes in peapod-grown DWCNTs. The presence of the outer tube is argued to protect the inner tube from interaction with impurities and also to stabilize the growth of defect free inner tubes. The current material underlines the application potential of DWCNTs.

Raman line shape of the A1 longitudinal optical phonon in GaN

High-resolution Raman measurements of the A1 longitudinal optical (LO) phonon in GaN reveal a complex line shape that can be explained in terms of the angular dispersion of LO phonons in this material. A simple geometrical model of the line shape makes it possible to extract the true anharmonic full width at half maximum 2Γ of the A1(LO) mode. The value of this parameter, 2Γ=2.4 cm−1 at 20 K, is in much better agreement with time-domain measurements by Tsen and co-workers [Appl. Phys. Lett. 72, 2132 (1998)] than any previous frequency-domain measurement. The results indicate that angular dispersion effects must be carefully considered in any analysis of Raman spectra from noncubic crystals.

Investigation of the Anomalous Raman Line Shape of the TO Phonon in GaP

The Raman spectrum of the transverse optical (TO) phonon in GaP is known to exhibit an asymmetric line shape at room temperature, broadened to lower energies. High resolution Raman measurements on GaP crystals at low temperature reveal a characteristic fine structure in the line shape of the TO phonon that has been studied systematically by variation of the isotopic composition of the gallium atoms. Calculations of the Raman spectra based on third-order anharmonic phonon–phonon coupling account for the experimental findings. In this paper we give an extended view into the nature of the line shape. The understanding of the low temperature line shape is necessary for the interpretation of changes in the spectra with rising temperature. The temperature dependence of the TO Raman line of natural GaP is presented as well as a qualitative explanation for the broadening in terms of anharmonic effects.

Yibrational coupling in disordered systems: Solid Hz and Di

Abstract High-resolution Raman measurements were performed of the intramolecular vibrational transition in mixed crystals of (o-H2) x (p-H2)1-x and (o-D2) x (p-D2)1-x The spectra obtained clearly show the effect of coupling between the vibrational states of the two constituent molecules. Calculations of the line shapes by the coherent potential approximation and by diagonalization of the dynamical matrix of a 5324 molecule supercell are compared with the experimental results.

Vibrational relaxation of the F center in NaI and NaBr.

High-resolution Raman measurements have been performed to study the coupling of lattice modes to the F center in NaBr and NaI. In both cases, a prominent line near or in the region of the energy gap between the acoustic and optical phonon bands dominates the Raman spectrum. Its linewidth was measured and extrapolated to 0 K it turned out to be about 3 and 0.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, respectively, for NaBr and NaI. These values are related to the lifetime of the local vibrational excitations, showing a relatively fast vibrational relaxation. Calculating the nonradiative transition probability during the vibrational relaxation in the electronic excited state, the efficiency of reaching the relaxed excited state (RES) of the F center is analyzed. The calculations show that, if the experimental value of the vibrational lifetime is used, the model predicts a high probability of reaching the RES in the case of NaBr. In the case of NaI the prediction strongly depends on the choice of the electronic matrix element for the interstate nonradiative transition. By comparison with similar cases of vibronic transition matrix elements reported in the literature, the efficiency of reaching the RES in NaI is expected in the range 0.05 to 1.

Asymmetric line shapes and time-resolved measurements: Vibrons in alpha -Arx(N2)1-x mixed crystals.

High-resolution Raman measurements were performed on the $^{14}\mathrm{N}_{2}$ vibrons and the $^{15}\mathrm{N}_{2}$ internal vibration in mixed crystals of \ensuremath{\alpha}-${(}^{15}$${\mathrm{N}}_{2}$${)}_{0.013}$${(}^{14}$${\mathrm{N}}_{2}$${)}_{0.937}$${\mathrm{Ar}}_{0.05}$. In contrast to what was assumed for the analysis of previous time-resolved coherent anti-Stokes Raman-scattering measurements, asymmetric line shapes are found. We relate the asymmetry to inhomogeneous broadening resulting from perturbations of the perfect lattice structure by the Ar substitution. We discuss the consistency of these frequency-domain results with those of previous time-resolved measurements and finally show how the asymmetry is contained in the time domain.

Precise measurements of the gap energy of folded acoustic phonons in Si/Si1-xGex superlattices.

We report high-resolution Raman measurements of the gap widths of folded longitudinal-acoustic phonons in Si/${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ superlattices. The first four gap widths at the minizone boundary were studied systematically. It was found that to fit the measured gap widths by Rytov theory one has to use a reduced sound velocity and density from that of bulk Si for the Si layers and a higher sound velocity and density of the alloy layers than the value deduced by linear interpolation. In the high-resolution measurements fine structure of the phonon peaks was observed together with a linewidth narrowing when approaching the minizone boundary. The variation of the scattering intensities recorded at different wavelengths and for several orders of folding provides an opportunity for a precise test of light scattering theory near the minizone boundary.

High resolution Raman measurements of the temperature dependence of the phonon linewidth in lithium formate monohydrate crystals

Using a coupled interferomcter-spectrometer with a resolution < 0.01 cm −1 we have measured the Raman linewidth and integrated intensifies of some external modes (79 and 104 cm −1 A 1 modes, 76, 131 and 173 cm −1 A 2 modes and 82, 113 and 163 cm −1 B 1 modes) and of the internal A 1 mode at 1372 cm −1 of lithium formate monohydrate in the temperature range 10–300 K This material is an efficient nonlinear crystal with interesting electro-optic properties and technical applications. The spontaneous Raman data were analyzed and interpreted in terms of phonon relaxation by three-phonon down and up process, which are desribed by the cubic anharmonicity of the interaction potential. The data were also used for the explanation of the temperature dependence of the threshold intensity for stimulated Raman scattering.

High resolution Raman measurements of the temperature variation of the bandwidth of some lattice phonons and of one internal vibron of α-oxalic acid

Using a tandem interferometer—spectrometer system we measured the bandwidth as a function of temperature of three lattice phonons and one internal vibron of α-oxalic acid over a broad temperature range. The temperature evolution of the bandwidth of the lattice phonons is linear with T in the classical regime. This proves that only three-phonon decay processes are responsible for the relaxation. We have found that the experimental data are easily interpreted in terms of one down- and one up-conversion three-phonon process. The bandwidth of the internal vibron at 819 cm −1 however, shows a clear non-linear behavior as a function of temperature. The experimental data are correctly reproduced assuming that the overall relaxation has two contributions, one due to a three-phonon down-conversion processes and one caused by a four-phonon dephasing mechanism.

Temperature dependence of the bandwidths and frequencies of some anthracene phonons. High-resolution Raman measurements

Using a coupled interferometer—spectrometer with a resolution of 0.02 cm−1 we have measured the Raman band profiles of the four low-frequency anthracene phonons ω1(ag), ω2(ag), ω6(bg) and ω7(bg) in the temperature range 2–70 K. These phonons possess very narrow bandwidth at low temperature which are convinently measured under high resolution. In particular the two lowest-frequency phonons ω1(ag) and ω6(bg) have a bandwidth at 2 K of 0.045 cm−1. The other two phonons ω7(bg) and ω2(ag) have bandwidths at 2 K of 0.165 and 0.4 cm−1, respectively. A detailed analysis of the bandwidth variation with temperature was made in terms of three-phonon decay processes. The exrerimental variation of the bandwidth with temperature was correctly reproduced assuming a single down-and up-process. The following results were obtained: ω1(ag): 49.45 cm−1 = 2×24.72 cm−1, 49.45 cm−1 = 98.45 cm−1 −49.0 cm−1; ω6(bg): 57.50 cm−1 = 2×28.75 cm−1, 57.50 cm−1 = 108.50 cm−1 −51.0 cm−1; ω7(bg): 71.20 cm−1 = 2×35.6 cm−1, 71.20 cm−1 = 120.20 cm−1 −49.0 cm−1: ω2(ag): 82.40 cm−1 = 57.50 cm−1 +24.9 cm−1, 82.40 cm−1 = 138.4 cm−1 −56 cm−1. The efficiency of the down- and up-processes is discussed in terms of the two-phonon density of states. The bandwidths at 2 K follows very closely the variation of the two-phonon sum density of states, whereas the relative importance of the up-processes follows well the two-phonon difference density of states. The anharmonic frequency shifts are corrected for the thermal expansion of the crystal using the Grüneisen single-phonon parameters and the thermal expansion coefficients given in the literature. This permits an estimation of the variation of the anharmonic shifts in the temperature range studied.