Meguya Ryu

Nanoscale measurements of thermophysical properties, based on detecting temperature responses to periodic heat stimulation, can be achieved using a localized heating point instead of a localized sensing point. However, the concept of determining localized thermophysical properties via nano-heating as an alternative to nano-sensing has not yet been validated. In this study, we demonstrate the measurement of thermal diffusivity within a nanoscale-confined volume using a thermal scanning probe lithography (t-SPL) system. The sharp tip of the t-SPL probe is employed to locally and periodically heat the sample, which is placed on a pre-fabricated micro-thermocouple. Using the temperature wave analysis method, the thermal diffusivity of the sample is inferred from the frequency-dependent phase shift in the temperature response of a thermocouple. This technique was applied to the microscale structure of a chemically amplified negative-tone photoresist (mr-DWL). We show that confining the heat source to a nanoscale point contact can achieve spatial resolution at the nanoscale (10–100 nm), offering an alternative approach to miniaturizing the detector sensor.

Liquid crystals (LCs) are unique heat transfer media that exhibit large anisotropy in thermal properties depending on the direction of the director ( n ) of the LC state. This phenomenon is the basis of thermal conduction in ordered soft materials, and has been extensively studied to understand thermal conduction in soft materials. In this study, we used inelastic x-ray scattering (IXS) to investigate the anisotropic thermal diffusivity and collective dynamics in the terahertz region of a pyrimidine-type LC (PYP8O8). The dispersion relations at several frequencies corresponding to the LC state were analyzed in the directions parallel and perpendicular to n . The results showed that there was a significant difference between the anisotropy of the sound velocity and that of the attenuation coefficient ( Γ ) estimated from the shape parameter of the IXS spectrum. The results for the linewidth of inelastic excitation show Q 2 dependence that is far beyond the viscoelastic relaxation of the system, and the anisotropy in the collective dynamics predicted by Forster . [] in the hydrodynamic region can be extensively applied to the more localized collective motion of LC systems.

It is highly desirable to enhance the heat conduction of polymeric heat-dissipating materials for applications in power electronics, automotive components, light-emitting diodes, and telecommunication equipment. However, the thermal conductivity of polymeric materials is one to three orders of magnitude lower than that of metals and ceramics due to phonon scattering in amorphous regions. Several attempts have been made to overcome this limitation by increasing heat flow along the orientation axis of the self-assembly of liquid crystalline polymers, but the design of liquid crystalline polymers remains largely empirical. In this study, we developed a machine learning model that can predict with over 96% accuracy whether a polymer will form a liquid crystalline state based on its compositional or structural characteristics. By exploring the inverse mapping of this model, we identified a comprehensive set of chemical structures for liquid crystalline polyimides. De novo monomer synthesis and polymerization reactions of six selected polymers were performed, and all synthesized polymers were experimentally confirmed to form liquid crystalline structures with thermal conductivities ranging from 0.722 to 1.26 W m−1 K−1. These are the first liquid crystalline polymers predicted and discovered via machine learning.

Polarimetry is used to determine the Stokes parameters of a laser beam. Once all four S0,1,2,3 parameters are determined, the state of polarisation is established. Upon reflection of a laser beam with the defined S polarisation state, the directly measured S parameters can be used to determine the optical properties of the surface, which modified the S-state upon reflection. Here, we demonstrate polarimetry for the determination of surface anisotropies related to birefringence and dichroism from different materials, which have a common feature of linear patterns of different alignments and scales. It is shown that polarimetry in the back-reflected light is complementary to ellipsometry and four-polarisation camera imaging.

A thermal diffusivity measurement approach is proposed in which the sample is thermally excited by a periodic train of pulsed, spatially random laser light. The temperature field on the surface is observed by IR camera and the diffusion is recorded by a sequence of IR images. The analysis of the diffusion in time and space is followed by suitable models. Fitting of the spatiotemporal evolution of the surface temperature allows to determine the thermal diffusivity of clay brick with an accuracy of 5%.

A device consisting of a line- or spiral-shaped temperature sensor array on a two-dimensional (2D) silicon nitride (SiNx) membrane of thickness 50 or 150 nm is developed for use in the lock-in photothermal method to determine the in-plane thermal diffusivity of SiNx membranes in air and in vacuum. The results of 2D heat diffusion are analyzed by the quadrupole method, and the system is approximated to the one-dimensional (1D) fin standing in a surrounding media (the fin approximation). The results show that 2D thermal diffusion on the membrane is affected not only by heat exchange with the surrounding environment but also by parallel thermal diffusion caused by heat conduction in the air along the membrane surface. The measurement using photothermal heating and contact detection of the temperature response enables the phenomenon to be detected consistently at a wide frequency range of temperature waves (50–1000 Hz). The measured thermal diffusivity values of the SiNx membrane are much smaller than those of bulk material, which can be reasonably considered an effect of the confined state of the phonon in the nanoscale geometry of the membrane.

Four-polarisation camera was used to map absorbance of olivine micro-grains before and after high temperature annealing (HTA). It is shown that HTA of olivine xenolith at above 1200∘C in O2 flow makes it magnetised. Different mode of operation of polariscope with polarisation control before and after the sample in transmission and reflection modes was used. The reflection type was assembled for non-transparent samples of olivine after HTA. Sample for optical observation in transmission was placed on an achromatic plastic quarter-wavelength waveplate as a sample holder. Inspection for sample’s birefringence (retardance) as well as absorbance can be made. A best fit of transmitted intensity or transmittance T (hence absorbance A=−log10T) becomes accessible by simple best-fit using only three orientations (from measured four orientations by the camera). When intensity of transmitted light at one of the orientations was very low due to cross-polarised condition (polariser-analyser arrangement), the three-points fit can be used. Three-point fit in transmission and reflection modes was validated for T(θ)=Amp×cos(2θ−2θshift)+offset, where amplitude Amp, offset offset and orientation azimuth θshift are extracted for each pixel via the best fit.

Herein, we give an overview of several less explored structural and optical characterization techniques useful for biomaterials. New insights into the structure of natural fibers such as spider silk can be gained with minimal sample preparation. Electromagnetic radiation (EMR) over a broad range of wavelengths (from X-ray to THz) provides information of the structure of the material at correspondingly different length scales (nm-to-mm). When the sample features, such as the alignment of certain fibers, cannot be characterized optically, polarization analysis of the optical images can provide further information on feature alignment. The 3D complexity of biological samples necessitates that there be feature measurements and characterization over a large range of length scales. We discuss the issue of characterizing complex shapes by analysis of the link between the color and structure of spider scales and silk. For example, it is shown that the green-blue color of a spider scale is dominated by the chitin slab’s Fabry–Pérot-type reflectivity rather than the surface nanostructure. The use of a chromaticity plot simplifies complex spectra and enables quantification of the apparent colors. All the experimental data presented herein are used to support the discussion on the structure–color link in the characterization of materials.