[en] The surface structure of a lamellar polystyrene-block-polybutadiene-block-polymethylmethacrylate (SBM) triblock copolymer forms a complex reconstruction, which breaks the two-dimensional continuous translational symmetry of an ideal (homogeneous) SBM surface. Despite the very different types of matter and order, our findings reveal a remarkable analogy with the well-known phenomenon of surface reconstruction of single crystals, in particular, with the (2 x 1) ''buckling row'' reconstruction of the Si(100) surface. Similarities and differences between both classes of materials are discussed on the basis of symmetry considerations
Journal
Physical Review Letters; ISSN 0031-9007; 
; v. 87(3); p. 035505-035505.4
; v. 87(3); p. 035505-035505.4
[en] Using the radioactive acceptor 111In as PAC probe atom, Cd-Cu pairs in Si are observed after the decay of 111In to 111Cd. In the temperature range between 100 K up to the dissociation temperature of the pairs (235 K) an increasing dynamic relaxation of the PAC signal is observed. The relaxation rate is reversible within this temperature range. This observation is discussed in the framework of the model of a local diffusion of the Cu atom over the four tetrahedral interstitial sites next ot the substitutional Cd atom. (orig.)
Journal
Nuclear Instruments and Methods in Physics Research. Section B; ISSN 0168-583X; ; CODEN NIMBE; v. 63(1/2); p. 202-204
; CODEN NIMBE; v. 63(1/2); p. 202-204
[en] PAC measurements at 111In, yielding information on the amount of formed In-H pairs, and four point resistivity measurements were combined to study the correlation between pair formation and electrical deactivation of acceptors in p-Si samples during passivation with H and thermal reactivation. Passivation was performed by means of low energy (200 eV) H+ implantation which proved to be quite efficient at 400 K. A complete passivation of the In profile with a peak concentration of 1018 cm-3 could be achieved. The results show, that the deactivation and reactivation of the In acceptors quantitatively coincide with the formation and dissociation of In-H pairs. (orig.)
Journal
Nuclear Instruments and Methods in Physics Research. Section B; ISSN 0168-583X; ; CODEN NIMBE; v. 63(1/2); p. 205-208
; CODEN NIMBE; v. 63(1/2); p. 205-208
[en] The combination of photoluminescence spectroscopy with the radioactive isotopes 7Be, 71As, 111Ag, 111In, 191Pt, 193Au and 197Hg is shown to provide definitive proof of the chemical identity of impurities producing photoluminescence spectra in all classes of semiconductors. The isotope 71As is used to show that radioactive isotopes can provide a powerful means of producing and studying a fundamental crystal defect such as an anti-site. Factors governing the luminescence intensities which can lead to apparently anomalous results are also discussed
Journal
[en] The formation and properties of acceptor-hydrogen pairs in GaN have been studied using radioactive 111mCd acceptors and the perturbed γγ angular correlation spectroscopy (PAC). After H-loading by low energy implantation (100 eV) at temperatures between 295K and 473 K, the formation of two Cd-H complexes involving about 30% of the Cd-acceptors is observed. The complexes have been identified as single hydrogen atoms bound to the Cd acceptor in two different configurations. The dissociation enthalpies of these configurations have been determined as 1.1(1) eV and 1.8(1) eV, respectively
Source
Ponce, F.A. (ed.) (Xerox Palo Alto Research Center, CA (United States)); Moustakas, T.D. (ed.) (Boston Univ., MA (United States)); Akasaki, I. (ed.) (Meijo Univ., Nagoya (Japan)); Monemar, B.A. (ed.) (Linkoeping Univ. (Sweden)); Materials Research Society symposium proceedings, Volume 449; 1278 p; ISBN 1-55899-353-3; ; 1997; p. 961-966; Materials Research Society; Pittsburgh, PA (United States); 1996 Fall meeting of the Materials Research Society (MRS); Boston, MA (United States); 2-6 Dec 1996; Available from Materials Research Society, 9800 McKnight Road, Pittsburgh, PA 15237 (United States) $68.00
; 1997; p. 961-966; Materials Research Society; Pittsburgh, PA (United States); 1996 Fall meeting of the Materials Research Society (MRS); Boston, MA (United States); 2-6 Dec 1996; Available from Materials Research Society, 9800 McKnight Road, Pittsburgh, PA 15237 (United States) $68.00
[en] Ternary semiconductors of type □AIIB2IIIC4VI with an ordered array of vacancies were investigated by PAC. Thereby the six probes 111Cd, 117Cd(117In), 111In(111Cd), 111Ag(111Cd), 77Br(77Se) and 77Kr(77Br) were applied. The positions of the different probes are determined and the corresponding electric field gradients by the WIEN 95 code calculated. By 111Ag(111Cd)-probes the vacancies could be substituted. The electronic charge density distributions are discussed. At elevated temperatures the substances show order-disorder transitions. As compared to the X-ray diffraction patterns the beginning of disorder is observed by PAC at distinctly lower temperatures
Journal
[en] The interaction between substitutional and interstitial donors and single or double acceptors in Si, GaAs, InP, and InAs has been studied by perturbed angular correlation spectroscopy (PAC). For the case of Si, complex formation between substitutional donors (As, P) and different radioactive acceptors (111In, 111Cd, 117Cd) has been observed. The formation of Cd-hydrogen pairs using either 111Cd or 117Cd is discussed for GaAs, InP, and InAs
Journal
[en] In 50 patients with a ''white hole'' in their scintigram - among them 44 patients with a history of myocardial infarction - the relation between its relative volume and the ventriculographically determined ejection fraction was studied retrospectively. A relative volume of the ''white hole'' larger than 13.7% showed a specificity of 93% and a sensitivity of 45% for a decreased ejection fraction and had a significant correlation of r=-0.54 (alpha=0.01) with the ejection fraction. Thus the relative volume of the ''white hole'' derived automatically from 221TI-SPECT is an easy-to-determine additional parameter which allows an at least semiquantitative statement about the function of the left ventricle. (orig.)
[de]
Es wurde bei 50 Patienten - darunter 44 Infarktpatienten - , deren Szintighramm das ''white hole''-Phaenomen aufwies, retrospektiv dessen relative Groesse, bezogen auf das mittlere Ventrikelvolumen, mit der aus der Kontrastventrikulographie bestimmten Auswurffraktion korreliert. Eine relative ''white hole''-Groesse von 13,7% wurde als oberer Grenzwert festgelegt. Es errechnete sich eine Sensitivitaet von 45% und eine Spezifitaet von 93%, dass bei Patienten mit vergroessertem ''white hole'' eine verminderte Auswurffraktion vorlag. Die Sensitivitaet fuer das Vorliegen einer normalen Auswurffraktion bei normaler Groesse des ''white hole'' lag bei 72% bei einer Spezifitaet von 82%. Der positive Vorhersagewert (Vorliegen einer verminderten Auswurffraktion bei einer ''white hole''-Groesse von mehr als 13,7%) lage bei 82%. Damit erweist sich das relative Volumen des ''white hole'' als einfach zu bestimmender ergaenzender Parameter, der eine zumindest semiquantitative Funktionsaussage im Rahmen der 201-Tl-Myokardszintigraphie zulaesst. (orig.)Journal