RESUMEN
The investigation of materials' behavior under high-temperature and high-pressure conditions, such as the correlation with structural characteristics and thermal properties, holds significant importance. However, the challenges associated with the experimental implementation have, to a certain extent, constrained such research endeavors. We utilized the ultrafast laser based non-contact thermal measurement method combined with an externally heated moissanite-anvil-cell to characterize the thermal conductivity of [10-10] oriented SiO2 crystals under high temperature (300-830 K) and high pressure (0-15 GPa) conditions. We investigated the impact of extreme conditions on the microstructure from both Raman spectroscopy and thermal perspectives. The presence of kinetic hindrances associated with the transformation of α-quartz to coesite and stishovite was identified and confirmed. It expands the comprehension and application of the SiO2 pressure-temperature phase diagram in this range and provides insights into the intricate relationship between extreme environments and material structure formation through the analysis of thermal characteristics.
RESUMEN
The thickness of the metal-transducer nano-film is an essential parameter for high-pressure time-domain-thermoreflectance (TDTR) measurements. In this article, an accurate method was proposed to determine the transducer thickness in high-pressure conditions using the pressure-volume equation of state combined with an image processing method. Both the elastic and plastic deformation of the sample squeezed in diamond anvil cells were considered in this method. High-pressure TDTR measurements on thermal conductivity of MgO and mica were further taken for comparing the influence from different thickness-characterization methods up to â¼18 GPa, and the proposed method accurately captured the effect of plastic deformation on thermal conductivity for the first time. This work can not only help achieve more accurate TDTR measurements under high-pressure but also provide valuable guidance for the diamond anvil cell application in nanoscale research.
RESUMEN
Ultrathin, transparent, and free-standing films assembled from low-dimensional nanomaterials (LDMs) are promising for various applications, including transparent heaters and membranes. However, the intact separation of the assembled films, especially those with controlled ultrathin thickness from deposited substrates, is a tremendous challenge, particularly for fast peeling off via self-detaching. Herein, we propose a versatile method to rapidly peel off ultrathin assembled LDM films, including three types of carbon nanotubes, vermiculite, Ag nanowires, and carbon nanotube@graphene, by dissolving the MXene interlayer from the layer-by-layer filtered MXene/LDM Janus films using diluted H2 O2 . The MXene sacrificial interlayers play dual roles, including physical isolation of LDM films from filter membranes and the production of bubbles that buoy ultrathin LDM films, making them free-standing. The integrality and self-detaching rate of the LDM films are determined by the loading and reactivity of the MXene interlayers. The intact LDM films can self-detach in 80 s by dissolving the optimized MXene interlayer and producing bubbles. The as-made free-standing ultrathin LDM films can be transferred to arbitrary substrates and exhibit outstanding performance as transparent heaters. This scalable method provides an efficient and versatile method to produce ultrathin, transparent, and free-standing LDM films and finds new applications for the growing MXene family.
RESUMEN
Utilizing high-pressure to modulate optical properties, such as thermoreflectance (dR/dT), over a wide range has received much attention. Nevertheless, how the pressure exerts on the complex dielectric constant and finally on dR/dT remains elusive. Here, we perform a thoroughly experimental and theoretical investigation on dR/dT of Al nano-film from 0 to 25 GPa. The dR/dT values exhibit a sine-like pressure-dependence, with the zero-crossing appearing at around 6 GPa. These special phenomena are well explained from electron transition viewpoints. The first-principles calculations show that the energy difference of parallel bands is enlarged from 1.45 to 2 eV, thereby increasing the threshold for electron transitions. The lifted threshold changes the optical absorption rates of Al and the density of states of the electrons involving interband transitions; finally, the resulting dR/dT exhibits such a pressure-dependent behavior. Our findings provide a deep insight on pressure-induced electronic transitions and photon-electron interactions in metals.
