Abstract
Synchrotron sources with high photon flux, small source size, and broad energy range have revolutionized ultrafine characterization of condensed matter. With the addition of the pressure dimension realized by the use of diamond anvil cells, enormous progress has been achieved throughout high-pressure science. This is particularly so for synchrotron-based infrared microspectroscopy (SIRMS) with its very high signal-to-noise ratio, high spatial resolution, and extended measurement conditions. SIRMS has high sensitivity, providing a platform for the investigations of the very small amounts of material that need to be used in high-pressure research. This review summarizes developments in SIRMS, focusing on instrumentation and high-pressure measurements. Applications to measurements of infrared reflectance and absorption are presented, illustrating how SIRMS results play a crucial role in advancing understanding of the crystalline phase transitions, electronic transitions, metallization, lattice dynamics, superconductivity, and novel functional behavior. New insights into spectroscopic properties, together with some cutting edge issues and open problems, are also briefly discussed.
Highlights
Arising from the nature of light–matter interaction, infrared spectroscopy (IRS) can detect the motions of molecular bonds, such as vibration and rotation, upon absorption of IR light
High-pressure, high-temperature (HPHT) treatment of diamonds can lead to a color enhancement effect that makes it possible to turn a brown diamond into a colorless one, which is of interest for visible/near-IR diamond anvil cell (DAC) experiments
When integrated with DAC-based technique, IRMIS is a powerful and suitable tool for investigating hydrous minerals under high-pressure conditions for the following reasons: (i) changes in the strength of hydrogen bonds are usually estimated based on frequency shifts in OH-stretching modes, which can be directly derived from IR results; (ii) a quantitative characterization of the water content of minerals can be obtained from IRS owing to its high sensitivity; (iii) at high pressures, hydrous minerals are highly disordered
Summary
Arising from the nature of light–matter interaction, infrared spectroscopy (IRS) can detect the motions of molecular bonds, such as vibration and rotation, upon absorption of IR light. The small divergence angle of synchrotron radiation provides an opportunity to achieve diffraction-limited spatial resolution, making it promising for microspectroscopic studies on individual sample spots at the microscale.[28] In addition, their ultrahigh brilliance enables synchrotron light sources to be continuum sources with spectral coverage from the far-IR to x-rays, which is crucial for research on picosecond-level pump–probe dynamics, where varying photon wavelengths are required.[27]. Pressure is believed to be an effective post-synthesis method for improving material performance, and in situ spectroscopic studies are a critical requirement for exploring the underlying mechanism with further development in materials engineering in mind.[32] Compared with its in-laboratory IR counterpart, synchrotron-based infrared microspectroscopy (SIRMS) is suitable for high-pressure studies (even more so for ultrahigh-pressure cases), because the beam spot of the IR synchrotron radiation can be focused tightly on a sample and its size is a good match with the diameter of the gasket hole in a DAC. Considering the latest research progress, we illustrate how SIRMS has been employed in high-pressure science and why it plays such an important role in advancing our understanding of high-pressure phenomena
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