The hydrogen bond (H-bond) in organic-water molecules is essential in nature. Combining with the charge - transfer analyses, we investigated the penetrating molecular-orbitals in glycine-water clusters, which give evidences of the covalent-like characteristics of H-bonds in this system. Besides, the infrared spectral features provide a rare opportunity to discover the exceedingly-evident redshifts of symmetric stretching modes (Symst) in water on forming H-bond, in contrast to the slightly-redshifted asymmetric stretching modes (Asyst) in water. To explain these intriguing behaviors, we further analyzed the nuclear vibrating patterns, which clearly reveal that H-bond retains two unexpected effects on nuclear motions in water: (i) Intensifying donor Symst, and (ii) Inhibiting donor Asyst. Furthermore, we also quantified the impact of anharmonic quantum fluctuations on each hydrogen bond. For the stretching modes involved in H-bonds, red shifts up to more than one hundred wave numbers are observed under anharmonic vibration, explicitly indicating the increased ‘covalency’ of H-bonds. These finds shed light on the essential understanding of H-bonding comprehensively, and should provide incentives for future experimental studies.
Metamaterials with subwavelength structural features show unique electromagnetic responses that are unattainable with
natural materials. Recent research on these artificial materials has been pushed forward to the terahertz region because of
potential applications in biological fingerprinting, security imaging, remote sensing, and high frequency magnetic and
electric resonant devices. Active control of their properties could further facilitate and open up new applications in terms
of modulation and switching. Liquid crystals, which have been the subject of research for more than a century, have the
unique properties for the development of many other optical components such as light valves, tunable filters and tunable
lenses. In this paper, we investigated the transmitted spectral modulation in terahertz range by using liquid crystals (5CB
and TEB300) covering on the fabricated double-ring resonators to realize the shift of the resonance frequency. Our
obtained results indicate the low frequency resonance shows the obvious blue-shift, while the location of high frequency
resonance is nearly unchanged. We believe this phenomenon is related to not only the refractive index of the covering
liquid crystals but also the resonant mechanism of both resonances.
Characterization of doped ZnCdTe crystals as terahertz (THz) emitters is studied in detail. By measuring the absorption
of THz wave and analyzing the phase matching condition in these crystals, it is found that the dispersion property of
crystals and the self-absorption of THz waves in these crystals play important roles in THz radiation. It is also found that
the direct current (DC) resistivity of the crystal for THz emitter application should be greater than 106Ωcm. The THz
generation efficiency increases as their DC resistivity increases, but the efficiency saturates and even declines when the
resistivity goes beyond 106Ωcm.