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Raman spectroscopy is applied for non-destructive characterization of strain in crystalline thin films. The analysis makes use of the numerical value of the mode Grüneisen parameter γ, which relates the fractional change in the frequency of a Raman-active vibrational mode and the strain-induced fractional change in the unit cell volume. When in-plane, compressive biaxial strain in aliovalent doped CeO2-films is relieved by partial substrate removal, the films exhibit values of γ for the F2g vibrational mode which are ∼30% of the literature values for bulk ceramics under isostatic stress. This discrepancy has been attributed to a negative contribution from the anelastic (time-dependent) mechanical properties of aliovalent-doped ceria. Here we propose a way to "separate" anelastic and elastic contributions to the F2g mode Grüneisen parameter. Mechanically elastic yttria (Y2O3) films on Ti/SiO2/Si substrate serve as "control". The values of γ calculated from the change in frequency of the ∼375 cm−1 F2g Raman-active mode are close to the literature values for bulk yttria under isostatic stress. This work should serve to provide a protocol for characterization of selective sensitivity to different strain components of doped ceria thin films. [ABSTRACT FROM AUTHOR]

The magnetic properties of undoped, bulk CeO2 are not fully understood. In contrast to nanocrystalline ceria that exhibits paramagnetism attributed to Ce3+ at grain surfaces, bulk ceria is weakly paramagnetic, despite the absence of magnetic ions. In the present work, the magnetic susceptibility of bulk ceria ceramics doped with Lu3+, which has neither spin nor orbital angular momentum, was measured in order to assess the relative contributions of the crystal lattice, residual Ce3+ and oxygen vacancies to the overall bulk magnetization. We observed a magnetic response consisting of two parts: temperature independent (5–300 K) magnetic susceptibility, and Curie–Weiss paramagnetism. The temperature independent susceptibility decreases linearly with Lu content, and becomes diamagnetic at 30 mol% Lu. The Curie–Weiss magnetism visible at low temperatures was identified as resulting from a few ppm of Fe contaminant. However, Fe contamination does not contribute to the temperature independent paramagnetism. No contribution from Ce3+ could be detected. The fact that the magnetization decreases with Lu content, even though the concentration of oxygen vacancies, and the lattice defects associated with them, increases, indicates that neither is coupled to the magnetic field. Weak, temperature-independent paramagnetism in non-metals is usually attributed to a second order, Van Vleck-type magnetization. However, Van Vleck paramagnetism requires that the population of the first excited state be constant within the range of temperatures investigated. We discuss possible modifications of the large band gap electronic structure of undoped ceria which could account for our observations. [ABSTRACT FROM AUTHOR]

We describe two alternative and complementary purification methods for halorhodopsin and bacteriorhodopsin. The first relies on a unique form of detergent micelles which we have called engineered-micelles. These are specifically conjugated in the presence of [hydrophobic chelator:Fe2+] complexes and form detergent aggregates into which membrane proteins partition, but hydrophilic water-soluble proteins do not. The approach was tested on the membrane protein, bacteriorhodopsin (bR), with five non-ionic detergents (OG, OTG, NG, DM, and DDM), commonly used in purification and crystallization of membrane proteins, in combination with the commercially available bathophenanthroline or with one of the three synthesized phenanthroline derivatives (Phen-C10, Phen-C8 and Phen-C6). Our results show that bR is extracted efficiently (60-86%) and directly from its native membrane into diverse detergent aggregates with preservation of its native conformation, while 90-95% of an artificial contaminating background is excluded. For implementation of the second method, based on engineered-membranes, the use of detergents, which in some cases may produce protein denaturation, is not required at all. Protein-containing membranes are conjugated via the same hydrophobic [chelator:metal ion] complexes but maintain the membrane protein in its native bilayer environment throughout the process. This method is demonstrated on the membrane protein halorhodopsin from Natronomonas pharaonis (phR) and leads to good recovery yields (74-89%) and removal of >85% of artificial background impurities while preserving the native state of phR. The detailed structure of the hydrophobic chelator used has been found to have a marked effect on the purity and yield of both methods. [ABSTRACT FROM AUTHOR]

The crown form of nona-octanoyloxy tribenzocyclononatriene (C8) with C3symmetry was prepared and separated into its enantiomers (C8Aand C8B) by HPLC. Like the racemate, the neat enantiomers are also mesogenic, exhibiting two mesophases, M and Colh. Differential scanning calorimetry, X-ray diffraction, carbon-13 NMR and UV circular dichroism are used to study the structural and dynamic properties of these chiral mesophases. The high-temperature mesophase (Colh) was identified by X-ray diffraction as columnar hexagonal; this phase is thermally unstable, undergoing racemization on heating before its clearing point is reached. The low-temperature mesophase (M) is most likely also columnar, but its symmetry could not be determined. In comparison with the racemate, the chiral mesophases are less well ordered, more tightly packed and they have a lower tendency to crystallize. On the other hand they are considerably more mobile, as reflected in their NMR spectra. No helical structure has been identified in the X-ray diffraction of the mesophases. [ABSTRACT FROM AUTHOR]

Raman spectroscopy is applied for non-destructive characterization of strain in crystalline thin films. The analysis makes use of the numerical value of the mode Grüneisen parameter γ , which relates the fractional change in the frequency of a Raman-active vibrational mode and the strain-induced fractional change in the unit cell volume. When in-plane, compressive biaxial strain in aliovalent doped CeO 2 -films is relieved by partial substrate removal, the films exhibit values of γ for the F 2g vibrational mode which are ∼30% of the literature values for bulk ceramics under isostatic stress. This discrepancy has been attributed to a negative contribution from the anelastic (time-dependent) mechanical properties of aliovalent-doped ceria. Here we propose a way to "separate" anelastic and elastic contributions to the F 2g mode Grüneisen parameter. Mechanically elastic yttria (Y 2 O 3 ) films on Ti/SiO 2 /Si substrate serve as "control". The values of γ calculated from the change in frequency of the ∼375 cm -1 F 2g Raman-active mode are close to the literature values for bulk yttria under isostatic stress. This work should serve to provide a protocol for characterization of selective sensitivity to different strain components of doped ceria thin films.