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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.

In this perspective, we give an overview of several less explored structural and optical characterisation techniques useful for biomaterials. New insights into the structure of natural fibres 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 cor- respondingly different length scales (nm-to-mm). When the sample features, such as the alignment of certain fibres, cannot be characterised optically, polarisation analysis of the optical images can provide further information on feature alignment. The 3D complexity of biological samples necessitates that there be feature measure- ments and characterisation over a large range of length scales. We discuss the issue of characterising complex shapes by analysis of the link between the color and struc- ture 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-P ́erot 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 characterisation of materials.

It has been found that a fluorophore-linked adamantylideneadamantane 1,2-dioxetane derivative showed an isomeric difference in the reactivities of crystalline-state chemiluminescence (CL) under isothermal heating conditions, while there are still unsolved problems on the conditions for intracrystalline reactions. To confirm the suitable heating conditions for initiating crystalline-state CL reactions of the isomers, the CL reactions in their crystal samples heated at elevated temperature were investigated with monitoring of CL light emission and thermogravimetry-differential thermal analysis (TG-DTA) measurements together with a simultaneous measurement method of thermal diffusivity and light emission, to provide the information on suitable temperature range for the crystalline-state CL reactions and on the reactivities depending on open and closed conditions of the crystal samples. The newly developed simultaneous measurement method provides a methodology for a single crystal to analyze the relationship between a change of the thermophysical property of inside of the crystal and the progress of a crystalline-state CL reaction.

Microlens arrays (MLAs) which are increasingly popular micro-optical elements in compact integrated optical systems were fabricated by femtosecond direct laser write (fs-DLW) technique in the low-shrinkage SZ2080TM photoresist. High fidelity definition of 3D surfaces on IR transparent CaF2 substrates allowed to achieve ∼ 50% transmittance at chemical fingerprinting spectral region 2-5 μm wavelengths since MLAs were only ∼ 10 μm high corresponding to the numerical aperture of 0.3 (the lens height is comparable with the IR wavelength). To combine diffractive and refractive capabilities in miniaturised optical setup, a graphene oxide (GO) grating acting as a linear polariser was also fabricated by fs-DLW by ablation of a 1 μm-thick GO thin film. Such an ultra-thin GO polariser can be integrated with the fabricated MLA to add dispersion control at the focal plane. Pairs of MLAs and GO polarisers were characterised throughout visible-IR spectral window and numerical modeling was used to simulate their performance. Good match between experimental results of MLA focusing and simulations was achieved.

We demonstrate extraordinarily spectrally selective narrowband mid-infrared radiation via coupling of plasmon resonance and molecular vibration. Absorbance and thermal emittance with resonant peak FWHM ≤ 124 nm at λ = 5.73 μm, corresponding to a Q-factor of ∼92.3 were obtained.

Mechanically responsive crystals have been increasingly explored, mainly based on photoisomerization. However, photoisomerization has some disadvantages for crystal actuation, such as a slow actuation speed, no actuation of thick crystals, and a narrow wavelength range. Here we report photothermally driven fast-bending actuation and simulation of a salicylideneaniline derivative crystal with an o-amino substituent in enol form. Under ultraviolet (UV) light irradiation, these thin ( 40 μm) crystals did not due to photoisomerization; in contrast, thick crystals bent very quickly (in several milliseconds) due to the photothermal effect, even by visible light. Finally, 500 Hz high-frequency bending was achieved by pulsed UV laser irradiation. The generated photothermal energy was estimated based on the photodynamics using femtosecond transient absorption. Photothermal bending is caused by a nonsteady temperature gradient in the thickness direction due to the heat conduction of photothermal energy generated near the crystal surface. The temperature gradient was calculated based on the one-dimensional nonsteady heat conduction equation to simulate photothermally driven crystal bending successfully. Most crystals that absorb light have their own photothermal effects. It is expected that the creation and design of actuation of almost all crystals will be possible via the photothermal effect, which cannot be realized by photoisomerization, and the potential and versatility of crystals as actuation materials will expand in the near future.

THz band-pass filters were fabricated by laser ablation of micro-foils of stainless steel and Kapton. Their spectral performance was tested in transmission and re- flection at the THz beamline at the Australian Synchrotron (AuSy). A 25 μm Kapton film performed as a Fabry-Pérot etalon with a free spectral range of FSR = 119 cm−1, high finesse Fc ≈ 17, and was tuneable over ~10 μm (at ~5 THz band) with β = 30° tilt. The structure of the THz beam focal region as extracted by the first mirror (slit) shows a complex polarisation-wavelength- position dependence across the beam. This is important for polarisation sensitive measurements (in transmission and reflection) and requires normalisation at each orientation of linear polarisation.

Polarisation analysis in the mid-infrared fingerprint region was carried out on thin (∼1 μm) Si and SiO2 films evaporated via glancing angle deposition (GLAD) method at 70∘ to the normal. Synchrotron-based infrared microspectroscopic measurements were carried out on the Infrared Microspectroscopy (IRM) beamline at Australian Synchrotron. Specific absorption bands, particularly Si-O-Si stretching vibration, was found to follow the angular dependence of ∼cos2θ, consistent with the absorption anisotropy. This unexpected anisotropy stems from the enhanced absorption in nano-crevices, which have orientation following the cos2θ angular dependence as revealed by Fourier transforming the image of the surface of 3D columnar films and numerical modeling of light field enhancement by sub-wavelength nano-crevices.

Capabilities of the Attenuated Total Reflection (ATR) at THz wavelengths for increased sub-surface depth characterisation of (bio-)materials is presented. The penetration depth of a THz evanescent wave in biological samples is dependent on the wavelength and temperature and can reach 0.1-0.5 mm depth due to strong refractive index change ∼0.4 of the ice-water transition; this is quite significant and important when studying biological samples. Technical challenges are discussed when using ATR for uneven, heterogeneous, high refractive index samples with possibility of frustrated total internal reflection (a breakdown of the ATR reflection-mode into transmission-mode). Local field enhancements at the interface are discussed with numerical/analytical examples. Maxwell’s scaling was used to model behaviour of absorber-scatterer inside materials at the interface with ATR prism for realistic complex refractive indices of bio-materials. Modality of ATR with polarisation analysis is proposed and its principle illustrated, opening an invitation for its experimental validation. The sensitivity of the polarised ATR mode to the refractive index between the sample and ATR prism is revealed. Design principles of polarisation active optical elements and spectral filters are outlined. The results and concepts are based on experiments carried out at the THz beamline of the Australian Synchrotron.

Controlling thermoelastic anisotropy of liquid crystals (LCs) is important for achieving reliable structural stability and efficient heat dissipation, especially for high-performance LC devices. A solid understanding of the thermoelastic anisotropy and its relation with the LC molecular structure is, however, still missing. Here, we studied the direction-dependent mechanical and thermal properties of 5-n-octyl-2-(4-n-octyloxy-phenyl)-pyrimidine (PYP8O8) in a wide temperature range, covering five phases (i.e., crystalline, smectic C, smectic A, nematic, and liquid), by Brillouin light spectroscopy and temperature wave analysis, respectively. We found that the mechanical anisotropy is much smaller than the thermal anisotropy at LC phases; both anisotropies show strong phase dependence, with the biggest change occurring at the crystalline to LC phase transition; and the anisotropy of the phonon mean-free path correlates with the structural anisotropy of the rigid core of the LC molecule. The analysis of the temperature-dependent thermoelastic anisotropy of LCs yields insights into structure-based phonon engineering.

Domain structure of paracetamol -- popular antipyretic analgesic -- was investigated by infrared (IR) spectroscopy using synchrotron radiation. Absorbance and retardance maps reveal molecular orientation inside the micro-domains of the paracetamol form II which has a better water solubility and compressibility compared to the commercially used forms I. The developed method of analysis representing orientation of optical slow(fast)-axis is compared with azimuthal orientation of the absorbance at several specific IR bands using vector maps. High brightness of synchrotron radiation and hyper-spectral mapping of structural domains in paracetamol clearly reveals the domain boundaries and can potentially be used to observe \emph{in situ} intra-phase transformations of paracetamol forms-I, II, III and melting, which are important for making medical tablets and powders by an industrial process., eight figures in the main text and one in supplement

Anisotropy of absorbance (dichroism) and birefringence limits spatial resolution, sensitivity during quantitative detection of trace analytes, as well as spectral imaging in the near-IR and mid-IR spectral ranges. Here we show hyperspectral imaging capable of determining retardance and absorbance due to small changes in the real and imaginary parts of the refractive index ∼Δn and ∼Δκ at each single point of a measurement at diffraction limited resolution. This single-beam technique allows the retrieval of the phase and amplitude information by virtue of a twice different angular dependence of Δn and Δκ on the sample orientation angle. It has potential applications in analytical science, multi-dimensional optical memory devices, and forensic/defense/sensor fields.

Here we report on the laser manufacturing of glass true 3D micro-optics. We demonstrate the feasibility of producing individual free-form geometry elements such as lenses, prisms, gratings proving the potential of integration into monolith stacked components. This is achieved by combining ultrafast laser 3D nanolithography and subsequent thermal post-treatment (calcination) - a novel approach introduced for additive manufacturing of inorganic materials [Nanoscale Horiz. 4, 647 (2019)]). The laser made pristine micro-optical components maintain their predefined shape while material is converted from hybrid polymer to glass corresponding to its inherent refractive index and transparency. This approach enables both realization of complex geometries and variation of material properties simultaneously.

We recently introduced a polariscopy method which can determine feature orientation below the diffraction limit. Measuring transmission at four linear polarisations (0,45,90,135°), information about the orientation of absorbers or patterns and features inside an object could be determined. This is applicable to transmitted/absorbed and scattered/reflected light as well, across the EM-spectrum. We investigate the feasibility of applying this technique to remote sensing satellites. Altimeters are able to determine many oceanographic parameters based on the surface height mapping (e.g., current directions, tidal waves etc). The nature of this measurement means the range and azimuth lateral resolution differs greatly, 100 km to 1 km scale. Synthetic aperture radar (SAR) data contains polarisation information and provides imaging of planetary surfaces. We aim to demonstrate the four polarisation technique in aerial imaging for recognition of feature alignment patterns which are beyond spatial resolution. Information from conventional intensity images (scalar) are augmented by the revealed orientation (vectorial) demonstrated for transmission/scattering in the visible spectrum. Visible as well as SAR imaging timetry can benefit from this augmented resolution.

The four polarisation method is adopted for measurement of molecular orientation in dielectric nanolayers of metal-insulator-metal (MIM) metamaterials composed of gold nanodisks on polyimide and gold films. Hyperspectral mapping at the chemical finger printing spectral range of 4–20 μμm was carried out for MIM patterns of 1–2.5 μμm period (sub-wavelength). Overlay images taken at 0,π4,π2,3π4 orientation angles and subsequent baseline compensation are shown to be critically important for the interpretation of chemical mapping results and reduction of spurious artefacts. Light field enhancement in the 60-nm-thick polyimide (I in MIM) was responsible for strong absorption at the characteristic polyimide bands. Strong absorbance A at narrow IR bands can be used as a thermal emitter (emittance E=1−R), where R is the reflectance and A=1−R−T, where for optically thick samples the transmittance is T=0.

Based on the principle of the periodic heating method by using cantilever thermocouple nanoprobes, we developed a method and an apparatus to measure the thermal diffusivity of soft materials on a microscale. The contact position of the probe tip with the sample surface was defined by using the phenomenon that the DC component of the thermal electromotive force (EMF) of the probe changes significantly upon contact (i.e., the vertical temperature gradient near the sample surface changes significantly). This contact position was set as the surface reference position where the variation of the thermal contact conductance between the sample surface and the sensor probe is minimized. The phase shift from the micro-heater was measured by the AC component of the probe’s thermal EMF and used to accurately determine the thermal diffusivity of micro-sized soft materials. The thermal diffusivity of the microstructured photoresist was determined with a deviation of ±3%.

This study has demonstrated that 3D columnar micro-films/coatings can be deposited over pre-patterned surfaces with sub-micrometer periodic patterns. Four-angle polarisation analysis of thin (0.4 − 1~μm) Si and SiO2 films, evaporated via glancing angle deposition (GLAD) at 70° to the normal, was carried out in reflection mode using synchrotron infrared microspectroscopy at the Australian Synchrotron. The angular dependence of absorbance followed A(θ) ∝ cos 2θ, confirmed for Si substrates patterned by electron beam lithography and plasma etching, which were used to make checkerboard patterns of Λ = 0.4~μm period on Si. Retardance control by birefringence of a patterned SiO2 substrate coated by columnar SiO2 is promising for UV-visible applications due to the use of the same material to endow polarisation control.

The thermal properties of novel nanomaterials play a significant role in determining the performance of the material in technological applications. Herein, direct measurement of the temperature diffusivity of cellulose nanocomposite films was carried out by the micro-contact method. Polymer films containing up to 2%wt. of nanocellulose were synthesised by a simple chemical process. Films of a high optical transmittance T ≈ 80 % (for a 200- μ m-thick film), which were up to 44% crystalline, were characterised. Two different modalities of temperature diffusivity based on: 1) a resistance change and 2) micro-thermocouple detected modulation of a heat wave, were used for the polymer films with cross-sections of ∼ 100 μ m thickness. Twice different in-plane α ‖ and out-of-plane α ⊥ temperature diffusivities were directly determined with high fidelity: α ‖ = 2 . 12 × 10 − 7 m 2 /s and α ⊥ = 1 . 13 × 10 − 7 m 2 /s. An amorphous polyethylene terephthalate (PET) fiber was measured for comparison α ‖ = 1 . 15 × 10 − 7 m 2 /s. This work provides an example of a direct contact measurement of thermal properties of nanocellulose composite films. The thermal diffusivity, which is usually high in strongly interconnected networks and crystals, was investigated for the first time in this composite.

The thermal properties of novel nanomaterials play a significant role in determining the performance of the material in technological applications. Herein, direct measurement of the temperature diffusivity of nanocellulose-doped starch&ndash, polyurethane nanocomposite films was carried out by the micro-contact method. Polymer films containing up to 2 wt%. of nanocellulose were synthesised by a simple chemical process and are biodegradable. Films of a high optical transmittance T&asymp, 80% (for a 200 &mu, m thick film), which were up to 44% crystalline, were characterised. Two different modalities of temperature diffusivity based on (1) a resistance change and (2) micro-thermocouple detected voltage modulation caused by the heat wave, were used for the polymer films with cross sections of &sim, 100 &mu, m thickness. Twice different in-plane &alpha, ‖ and out-of-plane &alpha, &perp, temperature diffusivities were directly determined with high fidelity: &alpha, ‖=2.12&times, 10&minus, 7 m2/s and &alpha, =1.13&times, 7 m2/s. This work provides an example of a direct contact measurement of thermal properties of nanocellulose composite biodegradable polymer films. The thermal diffusivity, which is usually high in strongly interconnected networks and crystals, was investigated for the first time in this polymer nanocomposite.

The viscosity of uncured epoxy resins is usually increased by their incorporation of dispersed fillers such as carbon nanotubes (CNTs). The present authors found that for the aliphatic epoxy resin, i.e. diethylene glycol diglycidyl ether, the viscosity increase is greatly suppressed when graphene oxide nanoribbons (GONRs) are dispersed instead of CNTs. The present study aims to compare the effects of CNT and GONR dispersions in this resin on the adhesive, tensile and thermal properties of the cured resin. GONR dispersions were found to be more effective than CNT dispersions at increasing the fracture toughness, lap shear strength and peel strength of the cured resin. A simple analysis based on a two-element Maxwell model was presented, which reproduced the differences in the temperature and velocity dependences of the lap shear strength and peel strength. This model suggested that the increase in the adhesive strength was due to the increase in the intrinsic adhesive failure energy for the GONR dispersions, while it was due to the increase in the viscoelastic energy dissipation within the resin for the CNT dispersions.

A thermocouple of Au-Ni with only 2.5-micrometers-wide electrodes on a 30-nm-thick Si3N4 membrane was fabricated by a simple low-resolution electron beam lithography and lift off procedure. The thermocouple is shown to be sensitive to heat generated by laser as well as an electron beam. Nano-thin membrane was used to reach a high spatial resolution of energy deposition and to realise a heat source of sub-1 micrometer diameter. This was achieved due to a limited generation of secondary electrons, which increase a lateral energy deposition. A low thermal capacitance of the fabricated devices is useful for the real time monitoring of small and fast temperature changes, e.g., due to convection, and can be detected through an optical and mechanical barrier of the nano-thin membrane. Temperature changes up to ~2x10^5 K/s can be measured at 10 kHz rate. A simultaneous down-sizing of both, the heat detector and heat source strongly required for creation of thermal microscopy is demonstrated. Peculiarities of Seebeck constant (thermopower) dependence on electron injection into thermocouple are discussed. Modeling of thermal flows on a nano-membrane with presence of a micro-thermocouple was carried out to compare with experimentally measured temporal response., 5 figures

Capabilities of the attenuated total reflection (ATR) at THz wavelengths for increased sub-surface depth characterisation of (bio-)materials are presented. The penetration depth of a THz evanescent wave in biological samples is dependent on the wavelength and temperature and can reach 0.1–0.5 mm depth, due to the strong refractive index change ∼0.4 of the ice-water transition; this is quite significant and important when studying biological samples. Technical challenges are discussed when using ATR for uneven, heterogeneous, high refractive index samples with the possibility of frustrated total internal reflection (a breakdown of the ATR reflection mode into transmission mode). Local field enhancements at the interface are discussed with numerical/analytical examples. Maxwell’s scaling is used to model the behaviour of absorber–scatterer inside the materials at the interface with the ATR prism for realistic complex refractive indices of bio-materials. The modality of ATR with a polarisation analysis is proposed, and its principle is illustrated, opening an invitation for its experimental validation. The sensitivity of the polarised ATR mode to the refractive index between the sample and ATR prism is numerically modelled and experimentally verified for background (air) spectra. The design principles of polarisation active optical elements and spectral filters are outlined. The results and proposed concepts are based on experimental conditions at the THz beamline of the Australian Synchrotron.

To control thermal properties in nano- and micro scale is one of the important topics with regards to the phonon engineering. Recently, the mechanical molecular crystals have been developed, which have the potential applications of actuators and soft robots. Most of the crystal motions are induced by photoisomerization or mechanical stress. Thermal phase transition and the photothermal effect are considered as the underlying mechanism for the motions, such as bending, twisting, jumping, and rotating, etc., of the mechanical molecular crystals, called soft crystals. However, due to the lack of the measured data of heat transport properties such as thermal diffusivity or thermal conductivity of single crystals in micro volume size, the quantitative analysis of thermal phenomena in the molecular crystals has not yet been quantitatively analyzed. For example, the photo-thermally induced temperature rise produces the localized temperature distribution near the surface, and thermal diffusivity should be utilized to calculate the temperature distribution in the specimen. To overcome such situation, we propose a micro scale temperature wave analysis (micro-TWA) method to measure the thermal diffusivity of soft crystals in micro scale. (Figure 1) This method enables to measure the axial orientation in single crystals. Furthermore, coupled with the photo-thermal stimulation, the kinetic measurement of thermal diffusivity under the stress induced and photo induced field has been realized. Demonstration of the super elastic phase transition of soft crystal, 3,5- difluorobenzoic acid (3,5−F2bza) and terephthalamide(TPA) will be presented. This is a proposal of the new measurement method, because the experimental determination of the thermal diffusivity in micro scale of organic single crystals, under operating the deformation control, is still a challenge. The experimental validity is discussed with the theoretical analysis using the reference sample. Figure 1

Chemiluminescence (CL) produces photon by a chemical reaction of a CL substrate to give a product in the excited state. Because emitted photons are readily detectable, CL is a powerful tool to monitor a chemical event in an analyte. In the materials science, CL will be useful to analyze an event at the molecular level in a solid material for developing functional devises. For instance, CL has been used to measure mechanical forces applied to polymers.1 In this study, we have investigated CL reactions in molecular crystals, to create the chemistry of “soft crystals”2 as reaction fields. For this purpose, we investigated CL properties of adamantylideneadamantane 1,2-dioxetanes (Adox) conjugated with a fluorophore in the crystalline state. We report here characteristic CL properties of the Adox derivatives and talk about the molecular mechanism of the crystalline-state CL.3 Adox is one of stable 1,2-dioxetanes, and its thermal decomposition partially gives the excited singlet (S1) or triplet (T1) state of 2-adamantanone (AdCO).4 The S1 state of AdCO can fluoresce weakly with the maximum at 420 nm. A designed Adox derivative 1 has a non-π-conjugatively linked phthahlimide as a crystal structure modulator and the emitting moiety by accepting energy from the excited AdCO. We first prepared syn- and anti-isomers of the Adox derivative 1 and investigated their CL properties in crystals. The isomers showed contrastive CL properties by heating their crystal samples at 160 °C. Each crystal structure of the isomers has its own distinctive packing pattern of the Adox and phthalimide moieties, and the clear differences in CL intensities, emission maxima and reaction kinetics of the isomers are well correlated to the packing patterns. Thus, CL emission properties and reaction kinetics in the crystalline-state were precisely manipulated by the crystal structures. To understand the crystalline-state CL reactions in detail, we further investigated CL of modified Adox derivatives along with thermoanalytical studies. The results provide information on the origins of the characteristic CL behaviors and the reaction mechanism in soft crystals. 1) Chen, Y.; Spiering, A. J. H.; Karthikeyan, S.; Peters, G. W. M.; Meijer, E. W.; Sijbesma, R. P., Nat. Chem., 2012, 4, 559. 2) Kato, M.; Ito, H.; Hasegawa, M.; Ishii, K., Chem. Eur. J., 2019, 25, 5105. 3) Matsuhashi, C.; Ueno, T.; Uekusa, H.; Sato-Tomita, A.; Ichiyanagi, K.; Maki, S.; Hirano, T., Chem. Commun., 2020, 56, 3369. 4) Hummelen, J. C.; Luider, T. M.; Wynberg, H., Pure Appl. Chem., 1987, 59, 639. Figure 1