An official website of the United States government
Temperature dependent Raman intensity of 2D materials features very rich information about the material's electronic structure, optical properties, and nm-level interface spacing. To date, there still lacks rigorous consideration of the combined effects. This renders the Raman intensity information less valuable in material studies. In this work, the Raman intensity of four supported multilayered WS 2 samples are studied from 77 K to 757 K under 532 nm laser excitation. Resonance Raman scattering is observed, and we are able to evaluate the excitonic transition energy of B exciton and its broadening parameters. However, the resonance Raman effects cannot explain the Raman intensity variation in the high temperature range (room temperature to 757 K). The thermal expansion mismatch between WS 2 and Si substrate at high temperatures (room temperature to 757 K) make the optical interference effects very strong and enhances the Raman intensity significantly. This interference effect is studied in detail by rigorously calculating and considering the thermal expansion of samples, the interface spacing change, and the optical indices change with temperature. Considering all of the above factors, it is concluded that the temperature dependent Raman intensity of the WS 2 samples cannot be solely interpreted by its resonance behavior. The interface optical interference impacts the Raman intensity more significantly than the change of refractive indices with temperature.
more »
« less
Raman Spectroscopy on Free-Base Meso-tetra(4-pyridyl) Porphyrin under Conditions of Low Temperature and High Hydrostatic Pressure
We present a Raman spectroscopy study of the vibrational properties of free-base meso-tetra(4-pyridyl) porphyrin polycrystals under various temperature and hydrostatic pressure conditions. The combination of experimental results and Density Functional Theory (DFT) calculations allows us to assign most of the observed Raman bands. The modifications in the Raman spectra when excited with 488 nm and 532 nm laser lights indicate that a resonance effect in the Qy band is taking place. The pressure-dependent results show that the resonance conditions change with increasing pressure, probably due to the shift of the electronic transitions. The temperature-dependent results show that the relative intensities of the Raman modes change at low temperatures, while no frequency shifts are observed. The experimental and theoretical analysis presented here suggest that these molecules are well represented by the C2v point symmetry group.
more »
« less
- Award ID(s):
- 1848418
- PAR ID:
- 10533357
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Molecules
- Volume:
- 29
- Issue:
- 10
- ISSN:
- 1420-3049
- Page Range / eLocation ID:
- 2362
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Raman spectroscopy-based temperature sensing usually tracks the change of Raman wavenumber, linewidth and intensity, and has found very broad applications in characterizing the energy and charge transport in nanomaterials over the last decade. The temperature coefficients of these Raman properties are highly material-dependent, and are subjected to local optical scattering influence. As a result, Raman-based temperature sensing usually suffers quite large uncertainties and has low sensitivity. Here, a novel method based on dual resonance Raman phenomenon is developed to precisely measure the absolute temperature rise of nanomaterial (nm WS 2 film in this work) from 170 to 470 K. A 532 nm laser (2.33 eV photon energy) is used to conduct the Raman experiment. Its photon energy is very close to the excitonic transition energy of WS 2 at temperatures close to room temperature. A parameter, termed resonance Raman ratio (R3) Ω = I A 1g / I E 2g is introduced to combine the temperature effects on resonance Raman scattering for the A 1g and E 2g modes. Ω has a change of more than two orders of magnitude from 177 to 477 K, and such change is independent of film thickness and local optical scattering. It is shown that when Ω is varied by 1%, the temperature probing sensitivity is 0.42 K and 1.16 K at low and high temperatures, respectively. Based on Ω, the in-plane thermal conductivity ( k ) of a ∼25 nm-thick suspended WS 2 film is measured using our energy transport state-resolved Raman (ET-Raman). k is found decreasing from 50.0 to 20.0 Wm −1 K −1 when temperature increases from 170 to 470 K. This agrees with previous experimental and theoretical results and the measurement data using our FET-Raman. The R3 technique provides a very robust and high-sensitivity method for temperature probing of nanomaterials and will have broad applications in nanoscale thermal transport characterization, non-destructive evaluation, and manufacturing monitoring.more » « less
-
Abstract Vibrational Raman optical activity (ROA) spectra were calculated under off‐resonance, near‐resonance, and at‐resonance conditions for(A) and under off‐resonance conditions for(B) using a new driver software for calculating the ROA intensities from complex (damped) time‐dependent linear response Kohn‐Sham theory. The off‐resonance spectra ofAandBshow many similarities. At an incident laser wavelength of 532 nm, used in commercial ROA spectrometers, the spectrum ofAis enhanced by near‐resonance with the ligand‐field transitions of the complex. The near‐resonance spectrum exhibits many qualitative differences compared with the off‐resonance case, but it remains bi‐signate. Even under full resonance with the ligand‐field electronic transitions, the ROA spectrum ofAremains bi‐signate when the electronic transitions are broadened such as to yield absorption line widths that are comparable with those in the experimental UV‐vis absorption and electronic circular dichroism spectra.more » « less
-
Solid-state laser refrigeration of semiconductors remains an outstanding experimental challenge. In this work, we show that, following excitation with a laser wavelength of 532 nm, bulk diamond crystals doped with H3 centers both emit efficient up-conversion (anti-Stokes) photoluminescence and also show significantly reduced photothermal heating relative to crystals doped with nitrogen–vacancy (NV) centers. The H3 center in diamond is a highly photostable defect that avoids bleaching at high laser irradiances of 10–70 MW/cm[Formula: see text] and has been shown to exhibit laser action, tunable over the visible band of 500–600 nm. The observed reduction of photothermal heating arises due to a decrease in the concentration of absorbing point defects, including NV-centers. These results encourage future exploration of techniques for H3 enrichment in diamonds under high-pressure, high-temperature conditions for the simultaneous anti-Stokes fluorescence cooling and radiation balanced lasing in semiconductor materials. Reducing photothermal heating in diamond through the formation of H3 centers also opens up new possibilities in quantum sensing via optically detected magnetic resonance spectroscopy at ambient conditions.more » « less
-
Abstract. Inclusion–host elastic thermobarometers are widely used to determine the pressure and temperature (P–T) histories of metamorphic rocks. Complex metamorphic P–T paths can affect the pressures that develop in host–inclusion systems. There are limited experimental studies that investigate how changing P–T conditions may re-equilibrate or “reset” residual pressures of inclusions. To evaluate re-equilibration of the quartz-in-garnet (QuiG) elastic thermobarometer, we performed single-, two-, and three-stage isothermal experiments. In the first stage of the experiments, oxide starting materials hydrothermally crystallised to grow garnet crystals with quartz inclusions between 700 and 800 °C and 1.0 and 3.2 GPa with constant P–T conditions for 48 h. In the second and third stage of the experiments, we isothermally changed pressure by 1.0 to 1.2 GPa for durations up to 38 d. We used Raman spectroscopy to measure strain-induced changes to the 128, 207, and 465 cm−1 Raman bands of quartz inclusions to determine the inclusion pressures (Pinc) and entrapment pressures (Ptrap) at the experimental temperature. The multi-stage experiments show that elasticity primarily controlled changes to Pinc values that occur from Ptrap through quenching to room conditions and that Pinc values measured at room conditions along with elastic modelling can be used to accurately calculate Ptrap. Quartz Pinc values in two-stage experiments re-equilibrated to give Pinc values between P1 and P2. The three-stage isothermal experiments show that the observed changes to inclusion pressures are reversible along different P–T paths to restore the re-equilibrated Pinc values back to their original entrapment isomeke at Ptrap. For rocks that underwent protracted metamorphism along complicated P–T paths, the re-equilibration experiments and viscoelastic calculations show that QuiG may underestimate maximum Ptrap conditions.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/molecules29102362
