The relationship between microstructure and mechanical properties has been investigated in Argiope trifasciata dragline silk fibers (major ampullate silk, MAS) by X-ray diffraction, Raman spectroscopy and tensile testing. We have analyzed three fractions of the material, i.e. amorphous, highly oriented nanocrystals and weakly oriented material, for different values of the macroscopic alignment parameter α, calculated as the relative difference between the length of the fiber and its length when supercontracted. Two distinct regimes have been identified: for low values of the alignment parameter α, microstructural changes are dominated by the reorientation of the nanocrystals; however, at high values (α > 0.5) of the alignment parameter, an increase in the fraction of the crystalline phase is revealed. The two regimes are also reflected in the mechanical behaviour, which can be explained by microstructural changes. This finding of the two distinct regimes in the microstructural evolution, which separates the reorientation and the increase in the crystalline phase, will be valuable to develop and validate molecular models of natural and artificial silk fibers, as well as to deepen our present knowledge of the origin of the outstanding properties of MAS fibers. In addition, we have analyzed the characteristics of the crystal lattice, and discussed the relationship between the percentage of short side-chain residues and the unit cell dimensions in different silks.

In this study, we have employed infrared (IR) absorption spectroscopy, visible Raman spectroscopy, and x-ray absorption near edge structure (XANES) to quantify the hydrogen (H) content in hydrogenated amorphous carbon ($a$ -C:H) films. $a$ -C:H films with a hydrogen content varying from 29 to $47\text{at}\text{.}\%$ have been synthesized by electron cyclotron resonance chemical vapor deposition at low substrate temperatures $\left(<120°\text{C}\right)$ applying a wide range of bias voltage, $V_b$ , $\left(-300\text{V}<V_b<+100\text{V}\right)$ . With the application of high negative $V_b$ , the $a$ -C:H films undergo a dehydrogenation process accompanied by a sharp structural modification from polymer- to fullerenelike films. The trend in the H content derived from elastic recoil detection analysis (ERDA) is quantitatively reproduced from the intensity of the C–H bands and states in the IR and XANES spectra, respectively, as well as from the photoluminescence (PL) background drop in the Raman spectra. Using the H contents obtained by ERDA as reference data, semiquantitative expressions are inferred for the amount of bonded hydrogen as a function of the experimental spectroscopic parameters, i.e., the integrated area of the IR C–H stretching band at about $2900{\text{cm}}^{-1}$ , the PL background in visible Raman spectra, and the XANES intensity of the ${\sigma }^{\ast }\text{-CH}$ peak.

A careful and wide comparison between Al and Ga as substitutional dopants in the ZnO wurtzite structure is presented. Both cations behave as n-type dopants and their inclusion improves the optical and electrical properties of the ZnO matrix, making it more transparent in the visible range and rising up its electrical conductivity. However, the same dopant/Zn ratio leads to a very different doping efficiency when comparing Al and Ga, being the Ga cation a more effective dopant of the ZnO film. The measured differences between Al- and Ga-doped films are explained with the hypothesis that different quantities of these dopant cations are able to enter substitutionally in the ZnO matrix. Ga cations seem to behave as perfect substitutional dopants, while Al cation might occupy either substitutional or interstitial sites. Moreover, the subsequent charge balance after doping appear to be related with the formation of different intrinsic defects that depends on the dopant cation. The knowledge of the doped-ZnO films microstructure is a crucial step to optimize the deposition of transparent conducting electrodes for solar cells, displays, and other photoelectronic devices.