Raman spectra from symmetric hydrogen bonds in water by high-intensity laser-induced breakdown

Enhanced Moisture Stability of Lithium-Rich Antiperovskites for Sustainable All-Solid-State Lithium Batteries

Lithium-rich antiperovskites (LiRAPs) solid electrolytes have attracted extensive interest due to their advantages of structural tunability, mechanical flexibility, and low cost. However, LiRAPs are instinctively hygroscopic and suffer from decomposition in air, which not only diversifies their electrochemical performances in present reports but also hinders their application in all-solid-state lithium batteries (ASSLBs). Herein, the origin of the hygroscopicity, and also the effect of the hygroscopicity on the electrochemical performances of Li_3-x (OH_x )Cl are systematically investigated. Li_3-x (OH_x )Cl is demonstrated to be unstable in the air and prone to decompose into LiOH and LiCl. Nevertheless, with fluorine doping on chlorine sites, the hygroscopicity of LiRAPs is suppressed by weakening the intermolecular hydrogen bond between LiRAPs and H₂ O, forming a moisture-resistive Li_3-x (OH_x )Cl_0.9 F_0.1 . Taking advantage of its low melting point (274 °C), two prototypes of ASSLBs are assembled in the ambient air by means of co-coating sintering and melt-infiltration. With LiRAPs as the solder, low-temperature sintering of the ASSLBs with low interfacial resistance is demonstrated as feasible. The understanding of the hygroscopic behavior of LiRAPs and the integration of the moisture-resistive LiRAPs with ASSLBs provide an effective way toward the fabrication of the ASSLBs.

Coherent Raman comb generation in H2O2aqueous solutions by crossing-pump stimulated Raman scattering

The cascaded stimulated Raman scattering (SRS) of 30% H₂O₂ aqueous solutions was investigated using a pulsed Nd: YAG laser with a wavelength of 532 nm. The transfer of excess electrons between H₂O₂ and H₂O molecules enhanced the SRS. Together, the decomposition of H₂O₂ and the intense SRS Stokes led to the generation of the crossing-pump effect of H₂O₂ aqueous solutions and the appearance of a new peak at 4229 cm^-1 that is excited by Stokes as the pump source. Crossing-pump not only reduced the threshold but also generated the broadband-coherent Raman comb, defined as a coherent radiation wavelength ranging from 434 to 831 nm (i.e., a Raman shift ranging from -4225 to 6756 cm^-1). The anti-Stokes SRS was attributed to the four-wave mixing (FWM) process.

Tunable-shift stimulated Raman scattering in water by chirped 50 fs to 4.5 ps UV-pulses

Forward stimulated Raman scattering (SRS) induced by focused 400 nm pulses chirped to different pulse durations is observed in water and heavy water. The first Stokes Raman peak shift is shown to be tunable in the range of ${{3500 {-} 4200}}\;{{\rm{cm}}^{- 1}}$ in water and ${{2450 {-} 3250}}\;{{\rm{cm}}^{- 1}}$ in heavy water. It is demonstrated that the Stokes peak shift increases for shorter pulse durations and higher intensities.

Estimating the effective pressure from nanosecond laser-induced breakdown in water

Nanosecond laser-induced breakdown (LIB) in liquids (e.g., water) can produce dynamic high pressure and high temperature. However, since high pressure needs to negate the effect of high temperature to some degree, it is only partially effective. As a result, it is difficult to directly measure the effective pressure due to the transient and complex LIB process. Here, we presented a simple method based on Raman spectroscopy to indirectly determine the effective pressure caused by LIB in liquid pure H₂O and low concentration H₂O-H₂O₂ mixtures. By comparing the Raman shifts of the ice-VII mode for pure H₂O and H₂O-H₂O₂ mixtures under laser pumping and static high pressure, the LIB effective pressure can be first estimated. The empirical equation was then derived base on the correlation of the LIB effective pressure to ice-VII-point stimulated Raman scattering thresholds for pure and mixture water solutions, which can be used to estimate the LIB effective pressures for other different mixture water solutions with the uncertainty of 0.14-0.25 Gpa. Hopefully, our study here would advance the measurements of effective pressure in the LIB process.

Enhanced stimulated Raman scattering of water by KOH

Stimulated Raman scattering (SRS) of water and a 1 M KOH-H₂O solution are investigated using a Nd:YAG laser in both forward and backward directions. An obvious enhanced SRS signal is realized by dissolving KOH in liquid water. Compared with pure water, the performance improvements include the appearance of low-wavenumber Raman peaks, higher Raman intensity, an increased Raman gain, and an enhanced hydrogen bonding network. In this paper, the SRS enhancement phenomenon is explained from both the hydrogen bonding structure and the mechanism of stimulated Raman scattering. We consider it to be a very important SRS enhancement technique, which is low cost, simple, but reliable. Meanwhile, it can easily be extended to other alkali hydroxides.

Exploring the hydrogen bond kinetics of methanol–water solutions using Raman scattering

Stimulated Raman scattering was used to clearly show the hydrogen bond kinetics of water–methanol mixed solutions.

Exotic Spectra and Lattice Vibrations of Ice X Using the DFT Method

A typical vibrational spectrum in the ice phase has four separate bands: Translation, libration, bending, and stretching. Ice X, the final ice phase under high pressure, shows an exotic vibrational spectrum. Based on harmonic approximation, an ideal crystal of ice X has one peak, at 998 cm^-1, for Raman scattering and two peaks, at 450 cm^-1 and 1507 cm^-1, for infrared absorption in this work. These three characteristic peaks are indicators of the phase transition between ice VII and VIII and ice X. Despite many experimental and theoretical works on ice X, only this study has clearly indicated these characteristic peaks in the region of the IR band. The phonon density of states shows quite different features than ice VIII, which could be verified by inelastic neutron scattering in the future. The dynamic processes of 15 vibrational normal modes are discussed and the typical hydrogen bonds are missing.

A Raman spectroscopy study on the effects of intermolecular hydrogen bonding on water molecules absorbed by borosilicate glass surface

The structural forms of water/deuterated water molecules located on the surface of borosilicate capillaries have been first investigated in this study on the basis of the Raman spectral data obtained at different temperatures and under atmospheric pressure for molecules in bulk and also for molecules absorbed by borosilicate glass surface. The strongest two fundamental bands locating at 3063cm^-1 (2438cm^-1) in the recorded Raman spectra are assigned here to the OH (OD) bond stretching vibrations and they are compared with the corresponding bands observed at 3124cm^-1 (2325cm^-1) in the Raman spectrum of ice Ih. Our spectroscopic observations have indicated that the structure of water and deuterated water molecules on borosilicate surface is similar to that of ice Ih (hexagonal phase of ice). These observations have also indicated that water molecules locate on the borosilicate surface so as to construct a bilayer structure and that strong and weak intermolecular hydrogen bonds are formed between water/deuterated molecules and silanol groups on borosilicate surface. In accordance with these findings, water and deuterated water molecules at the interface of capillary have a higher melting temperature.

Dynamic high pressure induced strong and weak hydrogen bonds enhanced by pre-resonance stimulated Raman scattering in liquid water

355 nm pulsed laser is employed to excite pre-resonance forward stimulated Raman scattering (FSRS) of liquid water at ambient temperature. Due to the shockwave induced dynamic high pressure, the obtained Raman spectra begin to exhibit double peaks distribution at 3318 and 3373 cm^-1 with the input energy of 17 mJ,which correspond with OH stretching vibration with strong and weak hydrogen (H) bonds. With laser energy rising from 17 to 27 mJ, the Stokes line at 3318 cm^-1 shifts to 3255 and 3230 cm^-1 because of the high pressure being enlarged. When the energy is up to 32 mJ, only 3373 cm^-1 peak exists. The strong and weak H bond exhibit quite different energy dependent behaviors.

High-performance glucose biosensor based on chitosan-glucose oxidase immobilized polypyrrole/Nafion/functionalized multi-walled carbon nanotubes bio-nanohybrid film

A highly electroactive bio-nanohybrid film of polypyrrole (PPy)-Nafion (Nf)-functionalized multi-walled carbon nanotubes (fMWCNTs) nanocomposite was prepared on the glassy carbon electrode (GCE) by a facile one-step electrochemical polymerization technique followed by chitosan-glucose oxidase (CH-GOx) immobilization on its surface to achieve a high-performance glucose biosensor. The as-fabricated nanohybrid composite provides high surface area for GOx immobilization and thus enhances the enzyme-loading efficiency. The structural characterization revealed that the PPy-Nf-fMWCNTs nanocomposite films were uniformly formed on GCE and after GOx immobilization, the surface porosities of the film were decreased due to enzyme encapsulation inside the bio-nanohybrid composite materials. The electrochemical behavior of the fabricated biosensor was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometry measurements. The results indicated an excellent catalytic property of bio-nanohybrid film for glucose detection with improved sensitivity of 2860.3μAmM(-1)cm(-2), the linear range up to 4.7mM (R(2)=0.9992), and a low detection limit of 5μM under a signal/noise (S/N) ratio of 3. Furthermore, the resulting biosensor presented reliable selectivity, better long-term stability, good repeatability, reproducibility, and acceptable measurement of glucose concentration in real serum samples. Thus, this fabricated biosensor provides an efficient and highly sensitive platform for glucose sensing and can open up new avenues for clinical applications.

Phase-interfacial stimulated Raman scattering generated in strongly pumped water

We have observed unusual blue-shifted radiations in water pumped by a strong 532-nm nanosecond laser. Properties including divergence, polarizations, and pulse shapes of the unusual radiations are measured and compared with those of the regular stimulated Raman scattering (SRS) in water. The unusual radiations are attributed to the parametric anti-Stokes SRS that occurs on the interface of water and ionization plasma (or gas) formed in the laser-induced breakdown of water.

Onset of ice VII phase of liquid water: role of filamentation in stimulated Raman scattering

Energy dependent evolution of Stokes and anti-Stokes lines of ice VII via forward stimulated Raman scattering (FSRS) during propagation of a 30 ps laser pulse through liquid water, confirming structural change over GPa pressure range, is studied. Self-focusing of the intense laser pulses is observed to ionize the medium generating free electrons that dominate the evolution of SRS signals. The confinement of plasma-generated free electrons by filamentation is observed to enhance the signature Raman modes of ice VII by reducing the SRS threshold.

Hydrated-electron resonance enhancement O-H stretching vibration of water hexamer at air-water interface

Raman scattering of the O-H stretching vibration mode inside water, as well as near and at the air-water interface, was investigated by laser-induced breakdown (LIB). An intense and characteristic higher wavenumber Raman shift of the O-H vibration was observed at the air-water interface, which was attributed to the hydrated-electron resonance enhancement of the O-H stretching vibration mode of water hexamer. The hydrated electron in the water hexamer structure was formed by excess electrons injected into the gas-like phase with low hydrogen bond order under LIB. The electron-phonon coupled mechanism was discussed.