Possible cage motion of interstitial Fe in α-Al 2 O 3

In addition to spectral components due to Fe^2?+? and Fe^3?+?, a single line is observed in emission Mössbauer spectra following low fluence (<10¹⁵ cm^???2) implantation of ⁵⁷Fe*, ⁵⁷Mn and ⁵⁷Co in α-Al₂O₃. For the ⁵⁷Co and ⁵⁷Mn implantations, the intensity of the single line is found to depend on the emission angle relative to the crystal symmetry axis. This angular dependence can be explained by a non-isotropic f-factor and/or motion of the Fe ion between sites in an interstitial cage. It is argued that interstitial cage motion is a more likely explanation, as this can account for the lack of quadrupole splitting of the line.     

Isothermal defect annealing in semiconductors investigated by time-delayed Mössbauer spectroscopy: application to ZnO

The theory for so-called Time-Delayed-Measurements is outlined. This method allows for isothermal annealing studies in emission Mössbauer spectroscopy utilizing radioactive beams. The usefulness of this method is illustrated by the example of the annealing of a magnetic defect in ZnO.     

Mössbauer study of Fe in GaAs following 57Mn + implantation

The metastable 2S state in muonic hydrogen is particularily interesting because a measurement of the Lamb shift could reduce the uncertainty in the proton charge radius by an order of magnitude. The most important prerequisite for such a measurement is a sufficiently large population and lifetime of the 2S state. We have determined the long-lived and short-lived 2S population, the deexcitation mechanisms and lifetimes, and the cascade time in μp.     

Magnetism at single isolated iron atoms implanted in graphite

M?ssbauer spectra obtained after implantation of 57Fe into highly oriented pyrolytic graphite (HOPG) show a combined magnetic and quadrupole interaction with a magnetic hyperfine field Bhf = 32.6 T at 14 K. Though magnetic effects in nominally diamagnetic HOPG have been reported recently, no experiment has previously shown the existence of magnetism at the atomic scale. The results suggest that magnetic ordering occurs by coupling of the Fe magnetic moment to structural and/or electronic magnetic defects induced by the probe atoms' implantation damage.     

Application of external magnetic field to characterize magnetic oxides in the carbonaceous chondrite Orgueil

Magnetite is the most common magnetic phase in carbonaceous chondrites. Comprehensive and detailed investigations of this magnetite with X-ray diffraction and electron microprobe have revealed minute amounts of substitutional impurities (e.g. Ni) in the magnetite, but no other magnetic oxides have been found in these meteorites. Using an external magnetic field and Mössbauer spectroscopy, we have found a component in the Mössbauer spectrum that we attribute to maghemite. The relative area of this component implies that maghemite accounts for approximately 12% of the magnetic oxides in Orgueil.     

A highly selective and sensitive fluorescent PET (photoinduced electron transfer) chemosensor for Zn(II)

The naphthalimide derivative 1 was designed as a fluorescence PET sensor for Zn(II); 1 showed excellent selectivity for Zn(II) at pH 7.4, even in the presence of other competitive cations, the emission, being pH independent above pH 3.5, was switched on upon Zn(II) recognition.     

Cd(II) sensing in water using novel aromatic iminodiacetate based fluorescent chemosensors

[structure: see text]. Compounds 1 and 2 were designed as fluorescent chemosensors for Cd(II). For both, a selective determination of Cd(II) over Zn(II) was achieved. The fluorescence emission of both was pH-independent and switched off between pH 3-11 in 100% water. Whereas the recognition of Cd(II) at pH 7.4 gave rise to the formation of charge-transfer complexes (exciplexes) for both (lambdamax ca. 500 and 506 nm, respectively), the recognition of Zn(II) only switched on the (monomeric) anthracene emission of 2, while for 1 it was red-shifted (lambdamax = 468 nm).     

pH driven self-assembly of a ternary lanthanide luminescence complex: the sensing of anions using a beta-diketonate-Eu(III) displacement assay

The synthesis and the photophysical evaluation of a novel pH dependent lanthanide luminescent self-assembly in water between a cyclen based europium complex and a beta-diketonate is described and its use as a luminescent sensor in displacement assays for anions such as acetate, bicarbonate and lactate, where the Eu(III) emission was quenched upon anion recognition.     

Caught in the Loop: Binding of the [Ru(phen)2(dppz)]2+ Light-Switch Compound to Quadruplex DNA in Solution Informed by Time-Resolved Infrared Spectroscopy

Ultrafast time-resolved infrared (TRIR) is used to report on the binding site of the [Ru(phen)₂(dppz)]²⁺ “light-switch” complex with both bimolecular (Oxytricha nova telomere) and intramolecular (human telomere) guanine-quadruplex structures in both K⁺ and Na⁺ containing solutions. TRIR permits the simultaneous monitoring both of the “dark” and “bright” states of the complex and of the quadruplex nucleobase bases, the latter via a Stark effect induced by the excited state of the complex. These data are used to establish the contribution of guanine base stacking and loop interactions to the binding site of this biologically relevant DNA structure in solution. A particularly striking observation is the strong thymine signal observed for the Na⁺ form of the human telomere sequence, which is expected to be in the anti-parallel conformation.