Applications of metamaterials in the realization of efficient devices in the terahertz band have recently been considered to achieve wave deflection, focusing, amplitude manipulation and dynamical ...modulation. Terahertz metamaterials offer practical advantages since their structures have typical sizes of hundreds microns and are within the reach of current three-dimensional (3D) printing technologies. Here, we propose terahertz photonic structures composed of dielectric rods layers made of acrylonitrile styrene acrylate realized by low-cost, rapid, and versatile fused deposition modeling 3D-printing. Terahertz time-domain spectroscopy is employed for the experimental study of their spectral and dynamic response. Measured spectra are interpreted by using simulations performed by an analytical exact solution of the Maxwell equations for a general incidence geometry, by a field expansion as a sum over reciprocal lattice vectors. Results show that the structures possess specific spectral forbidden bands of the incident THz radiation depending on their optical and geometrical parameters. We also find evidence of disorder in the 3D printed structure resulting in the closure of the forbidden bands at frequencies above 0.3 THz. The size disorder of the structures is quantified by studying the dynamics diffusion of THz pulses as a function of the numbers of layers of dielectric rods. Comparison with simulations of light diffusion in photonic crystals with increasing disorder allows estimating the size distributions of elements. By using a Mean Squared Displacement model, from the broadening of the pulses' widths it is also possible to estimate the diffusion coefficient of the terahertz radiation in the photonic structures.
In the present paper, we investigate the effects of alkali and operational temperature on NiO capacitive and optical properties. The NiO samples were prepared by a straightforward, surfactant-free ...hydrothermal synthesis, employing Ni(NO
)
and either urea or moderately sterically hindered triethylamine (TEA). The syntheses were followed by calcinations at either 400 or 600 °C. NiO samples were characterized by XRD, scanning electron microscopy, and nitrogen adsorption isotherms. The optical properties were investigated by reflectance spectroscopy, and the pseudocapacitance was studied by cyclic voltammetry and galvanostatic charge charge-discharge measurements. We found that the synthesis with TEA yielded nanoflowers whereas the morphology of the synthesis with urea varied with the calcination temperature and resulted in nanoparticles or nanoslices at calcination temperatures of 400 and 600 °C, respectively. The NiO samples prepared at a lower temperature displayed a favorable combination of surface area and porosity that allowed for high performance with capacitances of 502 and 520 F g
at a current density of 1 A g
for nanoflowers and nanoparticles, respectively. The band gaps of all the samples were compatible with the estimated nanoparticle sizes. Finally, we used the synthesized NiO samples for the preparation of screen-printed electrodes (SPEs) modified by drop-casting and probed them against a Fe(CN)
probe.
The link between morphology and properties is well-established in the nanoparticle literature. In this report, we show that different approaches in the synthesis of copper oxide can lead to ...nanoparticles (NPs) of different size and morphology. The structure and properties of the synthesized NPs are investigated with powder X-ray diffraction, scanning electron microscopy (SEM), and diffuse reflectance spectroscopy (DRS). Through detailed SEM analyses, we were able to correlate the synthetic pathways with the particles' shape and aggregation, pointing out that bare hydrothermal pathways yield mainly spheroidal dandelion-like aggregates, whereas, if surfactants are added, the growth of the nanostructures along a preferential direction is promoted. The effect of the morphology on the electronic properties was evaluated through DRS, which allowed us to obtain the electron bandgap in every system synthesized, and to find that the rearrangement of threaded particles into more compact structures leads to a reduction in the energy difference. The latter result was compared with Density Functional Theory (DFT) computational models of small centrosymmetric CuO clusters, cut from the tenorite crystal structure. The computed UV-Vis absorption spectra obtained from the clusters are in good agreement with experimental findings.
The vibrational properties of molecular crystals in the terahertz range are controlled by the interplay of intermolecular and intramolecular interactions. The resulting delocalized normal modes span ...a substantial number of atoms within the unit cell of the molecular crystals and cannot be easily attributed to a specific stretching or bending mode. Several compounds were studied to understand the nature of normal modes. However, a systematic analysis of saccharides is still missing. This study investigates the terahertz vibrational properties of various saccharides, including glucose, galactose, lactose, cellobiose, and cellulose. The terahertz spectra were measured using terahertz time-domain spectroscopy. The samples were carefully characterized, and the residual Fabry–Perot oscillations were removed to obtain the absorption coefficient and refractive index of the saccharides. Density functional theory simulations were used to obtain theoretical terahertz spectra, considering hydrogen bonding interactions with an enhanced version of the van der Waals non-local density functional. The results revealed differences in low-energy vibrational modes frequencies, influenced by molecular structure properties, hydrogen bonding networks, and water content. Librations and internal vibrations were identified as dominant dynamics in the saccharides, with significant mixing between intermolecular and intramolecular vibrations. This comprehensive analysis sheds light on the vibrational behavior of saccharides in the terahertz range.
ZnO has many technological applications which largely depend on its properties, which can be tuned by controlled synthesis. Ideally, the most convenient ZnO synthesis is carried out at room ...temperature in an aqueous solvent. However, the correct temperature values are often loosely defined. In the current paper, we performed the synthesis of ZnO in an aqueous solvent by varying the reaction and drying temperatures by 10 °C steps, and we monitored the synthesis products primarily by XRD). We found out that a simple direct synthesis of ZnO, without additional surfactant, pumping, or freezing, required both a reaction (TP) and a drying (TD) temperature of 40 °C. Higher temperatures also afforded ZnO, but lowering any of the TP or TD below the threshold value resulted either in the achievement of Zn(OH)2 or a mixture of Zn(OH)2/ZnO. A more detailed Rietveld analysis of the ZnO samples revealed a density variation of about 4% (5.44 to 5.68 gcm−3) with the synthesis temperature, and an increase of the nanoparticles’ average size, which was also verified by SEM images. The average size of the ZnO synthesized at TP = TD = 40 °C was 42 nm, as estimated by XRD, and 53 ± 10 nm, as estimated by SEM. For higher synthesis temperatures, they vary between 76 nm and 71 nm (XRD estimate) or 65 ± 12 nm and 69 ± 11 nm (SEM estimate) for TP = 50 °C, TD = 40 °C, or TP = TD = 60 °C, respectively. At TP = TD = 30 °C, micrometric structures aggregated in foils are obtained, which segregate nanoparticles of ZnO if TD is raised to 40 °C. The optical properties of ZnO obtained by UV-Vis reflectance spectroscopy indicate a red shift of the band gap by ~0.1 eV.
In this study, the employment of the X-ray irradiation as bioremediation method to treat parchment has been deeply investigated. In particular, the effect of the irradiation doses on the structural ...stability of collagen, the main constituent of parchment, has been evaluated on a series of modern parchment samples by means of different opto-thermal and spectroscopic techniques in order to obtain the dose-dependent effect of irradiation on collagen. Moreover, the long-term behavior of the irradiated parchment has been considered by analyzing the same series of samples after being hygrothermally artificially aged. Characterizations by light transmission analysis, Fourier transform infrared spectroscopy and the ultraviolet–visible–near infrared (UV–Vis–NIR) reflectance one have been performed for the identification of the radio-induced effect on the parchment structure even in a dose range much wider than the need for sterilization. The obtained results have proved the safeness of the method in the short and long term confirming the applicability of this emerging procedure.
The degradation process of cellulose-made materials was investigated by means of nuclear magnetic resonance (NMR) spectroscopy, with particular emphasis on the role of water and on the hydration ...mechanism of cellulose fibrils. To accomplish this, the structure and dynamics of water within ancient and modern samples with different aging histories were investigated. The results mainly indicated that hydrolytic and oxidative reactions provoked the formation of acidic by-products. Furthermore, degradation processes were enhanced by higher amounts of water giving a progressive consumption of the amorphous regions of the cellulose. We propose NMR experiments as a benchmark for characterization of the degradation state of paper, as well as for investigating the effectiveness of restoration treatments.
We measured the optical absorption spectra of thermally treated, gamma irradiated LiF crystals, as a function of temperature in the range 16–300K. The temperature dependence of intensity, peak ...position and bandwidth of F and M absorption bands were obtained.
High‐resolution NMR images on three different present‐day wood samples and an archaeological wood specimen were presented and discussed. Although the spatial resolution is still low to perform ...dendrology for the exact identification of the wooden species, the T2‐spin‐density weighted images exhibit contrasts that are in excellent agreement with optical histological images. On the other hand, T2* and T1‐weighted images provide physiological information that is not obtainable by the usual light microscopic investigations. Moreover, the diffusion‐weighted images show the anisotropic behaviour of the water diffusion coefficient quantified along and perpendicularly to vascular bundles (vessels and tracheids), which can be related to the morphology and size of wooden microstructure. This work suggests that high‐resolution multiparametric MRI may be a useful tool to increase the information obtainable from the waterlogged archaeological wood remains in a completely non‐invasive and non‐destructive approach. Therefore, it would be desirable to further develop the hardware and functional characteristics of MRI scanners to improve their potential application in the field of wooden cultural heritage.
MRI on three different present‐day wood samples and an archaeological wood specimen were presented and discussed. Although the spatial resolution is still low to perform dendrology for exact identification of the wooden species, NMR images exhibit contrasts that are in excellent agreement with optical histological images. Moreover, multiparametric MRI provides multiple structural and functional information that allows obtaining more information than just the structural information provided by optical imaging.
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