RESUMEN
The ignition delay time of the hypergolic ionic liquids, 1-ethyl-3-methylimidazolium dicyanamide [EMIM][C2N3] and 1,3-dimethyl imidazolium dicyandiamide [DMIM][C2N3], can be controlled to approximately 20 ms by adding 1-amino-4-methylpiperazine while keeping the vapor pressure below 1 torr at 298 K.
RESUMEN
Cracking has been recognized as a major obstacle degrading material properties, including structural stability, electrical conductivity, and thermal conductivity. Recently, there have been several reports on the nanosized cracks (nanocracks), particularly in the insulating oxides. In this work, we comprehensively investigate how nanocracks affect the physical properties of metallic SrRuO3 (SRO) thin films. We grow SRO/SrTiO3 (STO) bilayers on KTaO3 (KTO) (001) substrates, which provide +1.7% tensile strain if the SRO layer is grown epitaxially. However, the SRO/STO bilayers suffer from the generation and propagation of nanocracks, and then, the strain becomes inhomogeneously relaxed. As the thickness increases, the nanocracks in the SRO layer become percolated, and its dc conductivity approaches zero. Notably, we observe an enhancement of the local optical conductivity near the nanocrack region using scanning-type near-field optical microscopy. This enhancement is attributed to the strain relaxation near the nanocracks. Our work indicates that nanocracks can be utilized as promising platforms for investigating local emergent phenomena related to strain effects.
RESUMEN
We investigate an evolution of the surface electronic state of the Bi1.5Sb0.5Te1.7Se1.3 single crystal, which is one of the most bulk insulating topological insulators, by examining terahertz light emitted from the sample surface upon the illumination of the near-infrared femtosecond laser pulses. We find that the surface state with a flat band bending can appear in the course of the natural maturation process of the surface state in an ambient air. Furthermore, we demonstrate that the evolution of the surface electronic state can be accelerated, decelerated, or even stopped by controlling environmental conditions to contain different amount of H2O, in particular.
RESUMEN
We investigate the surface states of topological insulator (TI) Bi2Se3 thin films grown on Si nanocrystals and Al2O3 substrates by using terahertz (THz) emission spectroscopy. Compared to bulk crystalline Bi2Te2Se, film TIs exhibit distinct behaviors in the phase and amplitude of emitted THz radiation. In particular, Bi2Se3 grown on Al2O3 shows an anisotropic response with a strong modulation of the THz signal in its phase. From x-ray diffraction, we find that the crystal plane of the Bi2Se3 films is inclined with respect to the plane of the Al2O3 substrate by about 0.27°. This structural anisotropy affects the dynamics of photocarriers and hence leads to the observed anisotropic response in the THz emission. Such relevance demonstrates that THz emission spectroscopy can be a sensitive tool to investigate the fine details of the surface crystallography and electrostatics of thin film TIs.
