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11.
Morenzoni E. Birke M. Hofer A. Kottmann F. Litterst J. Matthias B. Meyberg M. Niedermayer Ch. Prokscha Th. Schatz G. Wutzke Th. 《Hyperfine Interactions》1996,97(1):395-406
During the last few decades, a variety of methods has been developed which makes use of polarized positive muons as a microscopic probe of the magnetic properties of condensed matter (muon spin rotation, relaxation, resonance,SR). Until now, available beams for SR studies have delivered 100% polarized muons with energies in the MeV range, resulting in a deep penetration of the muons into the sample material under investigation. This presently limits the applications of theSR technique to the study of the bulk characteristics of matter. To be able to control the implantation depth, a very low energy beam of polarized muons is being developed at the Paul Scherrer Institute. Very slow polarized muons (kinetic energy 10 eV, polarization 90%) are obtained from the moderation of a high energy muon beam in a thin film of an appropriate condensed gas. These muons can be used as a source for a beam of tunable energy between a few tens of eV and some tens of keV. Implantation depths in the range of few to a few hundreds of nanometers can thus be achieved by varying the energy. 相似文献
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E. Morenzoni E. M. Forgan H. Glückler T. J. Jackson H. Luetkens Ch. Niedermayer T. Prokscha T.M. Riseman M. Birke A. Hofer J. Litterst M. Pleines G. Schatz 《Hyperfine Interactions》2001,133(1-4):179-195
The recent development at the Paul Scherrer Institute of a beam of low energy muons allows depth dependent muon spin rotation and relaxation investigations in thin samples, multilayers and near surface regions (low energy SR, LE-SR). After a brief overview of the LE-SR method, some representative experiments performed with this technique will be presented. The first direct determination of the field profile just below the surface of a high-temperature superconductor in the Meissner phase illustrates the power and sensitivity of low energy muons as near-surface probe and is an example of general application to depth profiling of magnetic fields. The evolution of the flux line lattice distribution across the surface of a YBa2Cu3O7 film in the vortex phase has been investigated by implanting muons on both sides of a normal-superconducting boundary. A determination of the relaxation time and energy barrier to thermal activation in iron nanoclusters, embedded in a silver thin film matrix (500nm), demonstrates the use of slow muons to measure the properties of samples that cannot be made thick enough for the use of conventional SR. Other experiments investigated the magnetic properties of thin Cr(001) layers at thicknesses above and below the collapse of the spin density wave. 相似文献
15.
Mössbauer spectra of very dilute solutions of 57Fe2+ ions in propane-(1,2)diol show distinct anomalies in the quadrupole splitting, the linewidth and the recoilfree fraction near the glass transition temperature. The observed time and temperature dependence of these anomalies can be correlated with structural relaxation processes which occur in a glass upon stabilization into the supercooled liquid phase. 相似文献
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W. T. Herrera C. Rojas-Ayala I. S. Din��la E. C. Passamani M. Kraken J. Engelke E. Baggio-Saitovitch F. J. Litterst 《Hyperfine Interactions》2011,203(1-3):143-147
Films of ytterbium doped with iron (0.3?C1.6 at.% Fe) have been prepared by co-deposition of atomic beams of the elements onto Kapton substrates under high vacuum. Iron is immiscible in ytterbium and various iron species are expected to occur. XRD reveals a mixture of fcc and hcp ytterbium. The Mössbauer spectra are interpreted with contributions from monomeric iron on interstitial sites, two types of neighboring substitutional iron aggregates and two types of clusters formed upon diffusion. The present data supplement earlier data obtained for 0.5 and 5 at.% Fe. There is no systematic correlation of cluster formation with increasing iron concentration. There are indications that clusters are formed more easily for thin films. We conclude that cluster formation occurs mainly on the film surface and is limited by the slow diffusion from inside films. 相似文献
18.
M. Westhoff P. Litterst S. Maddula B. Bödeker J. I. Baumbach 《International Journal for Ion Mobility Spectrometry》2011,14(4):139-149
Human breath analysis is a powerful and especially a non-invasive technique for the monitoring and hopefully also for the
diagnosis of respiratory diseases, including chronic obstructive pulmonary disease (COPD). The exhaled breath of 95 patients
suffering COPD and of 35 healthy controls was investigated using an Ion Mobility Spectrometer (IMS) coupled to a Multi-Capillary
Column (MCC) without any pre-separation or pre-enrichment. Starting with the results from a Mann–Whitney-Wilcoxon rank sum
test to find analytes with the highest potential with respect to differentiation, box and whisker plots, metabolic maps and
probability charts were introduced and compared. In addition, the sensitivity, specificity, positive and negative predictive
values and the accuracy of the relation were also summarized. The findings were compared to the results of a principal component
analysis. Finally, decision trees were introduced to visualize the interdependencies between the analytes and the classifications.
The application of these biostatistical methods with simultaneous inclusion of several VOCs for disease classification by
ion mobility spectrometry of human breath will provide much more information than using single peaks and single concentration
dependencies for disease classification and discrimination of various groups. Towards the future application of potential
biomarkers for clinical diagnostic procedures, complex analytical methods, such as ion mobility spectrometry, need statistical
and bioinformatical tools which are simple in application, visualize the results and support decisions on the basis of the
data obtained from measurements of analytes in exhaled human breath. 相似文献
19.
G. M. Kalvius L. Asch D. R. Noakes R. Keitel J. H. Brewer E. J. Ansaldo F. J. Litterst B. Boucher J. Chappert A. Yaouanc T. Yamazaki K. Nagamine K. Nishiyama O. Hartmann R. Wäppling 《Hyperfine Interactions》1986,31(1-4):303-308
Crystalline (cr-) Dyag [CsC] structure] orders antiferro-magnetically with TN≅60K; amorphous (am-) DyAg ferro-magnetically with TC≈-18K. We measured the longitudinal field (LF) μ+SR relaxation functions GZZ(t) for 5K<T<300K using surface muons. In the paramagnetic state. cr-DyAg gives an exponential GZZ (t) in the relaxation rate rising first slowly then more rapidlynear TN; no decoupling is observed in LF up to 0.4T. In the ordered state we see a Lorentzian Kubo-Toyabe GZZ(t), becoming nearly static at the lowest temperatures. Its static width is very narrow (Δ≈-7 MHz), and full dceoupling is
achieved here in 0.1 T. On approaching TN, the fluctuation rate and the static width increase mootonically bt the field distribution remains Loratzian. A LF of 0.4T
is then insufficient to quench the fast exponential relaxation. In paramagnetic am-DyAg, the μ+ depolarization is always much faster then in cr-DyAg. At lower temperatures it is better described by a root-exponential
than an exponential GZZ(t). Below TC an exponentially relaxing signal with 1/3 amplitude is seen. The decoupling effect of LF up to 0.4T was negligible at all
temperatures. 相似文献
20.
L. Asch S. Barth F. N. Gygax G. M. Kalvius A. Kratzer F. J. Litterst K. Mattenberger W. Potzel A. Schenck O. Vogt 《Hyperfine Interactions》1986,31(1-4):443-446
UAs has the NaCl structure and undergoes a first order transition into a type I (single k) antiferromagnetic state at 123
K, followed by a second first order transition at 62 K into a type IA (double k) antiferromagnetic structure. μSR spectra
of a powder sample were taken in zero and transverse fields up to 0.3 T. They cover the paramagnetic and the two antiferromagnetic
states. The most significant features of our data are: i) a first increase of relaxation rate below T=180 K; ii) a sudden
jump in both, relaxation rate and frequency shift at T=123 K, together with a small decrease in initial asymmetry (≈15%);
iii) no μ+ spin rotation in zero field in the type I state; iv) an overlay, of 3 spectra in the type IA state. Two of these spectra
show spin rotation in zero field. Their frequencies are clearly temperature dependent. In a transverse field of 5 and 10 mT
the external field adds nearly fully to the internal field.
Work supported in part by the Bundesministerium fur Forschung und Technologie, Federal Republic Germany. 相似文献