We report on the lattice location of Er in Si using the emission channeling technique. The angular distribution of conversion electrons emitted by the decay chain 167 Tm ͑t 1͞2 9.25 d͒ ! 167m Er ͑2.27 s͒ was monitored with a position-sensitive detector following room temperature implantation and annealing up to 950 ± C. Our experiments give direct evidence that Er is stable on tetrahedral interstitial sites in float-zone Si. We also confirm that rare earth atoms strongly interact with oxygen, which finally leads to their incorporation on low-symmetry lattice sites in Czochralski Si. [S0031-9007(97) Rare earth doping of Si is known to result in the formation of luminescent centers and is considered as a possible way to manufacture Si-based optoelectronic devices [1]. Among the various rare earth elements, Er is of special interest since its atomic transition at 1.54 mm matches the absorption minimum of SiO 2 , a highly desirable feature both for signal transmission through glass fiber cables and optical on-chip communication. Luminescence at this wavelength from Er-implanted Si was already established several years ago [2]. Meanwhile Er-based light-emitting diodes operating at room temperature have been reported [3]. The basic understanding of Er luminescence in Si, however, is far from complete. This concerns both the lattice sites of Er and the role of codopants such as O, N, or F, which were found to have a beneficial influence on luminescence yield. Photoluminescence (PL) spectroscopy studies have identified a number of Er-related centers with different crystal surroundings in Si [4]. The most intense PL yield was due to two centers having cubic and axial symmetry, respectively. While the cubic center occurred in both float-zone (FZ) and Czochralski (CZ) Si and was attributed to tetrahedral ͑T ͒ interstitial Er, the center with axial symmetry was observed only in CZ Si and ascribed to Er-O complexes. The existence of tetrahedral interstitial Er would be also in agreement with theoretical studies, which predict that T sites are the most stable sites for all oxidation states of isolated Er atoms in Si [5]. Direct lattice location using the Rutherford backscattering (RBS) channeling technique only suggested substitutional [6] or hexagonal ͑H͒ interstitial Er [7,8]. The reasons for these discrepancies, however, are unclear.To study the lattice sites and damage recovery after rare earth implantation, we have applied conversion electron emission channeling [9] combined with position sensitive detection. Emission channeling makes use of the fact that charged particles emitted from radioactive isotopes in single crystals experience channeling or blocking effects along low-index crystal directions. This leads to an anisotropic particle emission yield from the crystal surface which depends in a characteristic way on the lattice sites occupied by the emitter atoms. While this technique as such is not new and, in case of rare earths, was already used once for the lattice location of 175 Yb in Si [10], we have for the fi...

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Straining of annealed isotactic polypropylene beyond yield results in the formation of 0.4-4 vol % of microvoids with sizes of about 5-30 nm. The creep behavior as well as the complex shear and tensile modulus of polypropylene are strongly influenced by the presence of the very small concentration of microvoids, acting as structural defects. The storage modulus in the glassy state may be decreased by 30 % (shear modulus) or 15 % (tensile modulus) relative to the defect-flee state. Possible interpretations are discussed.

Fe-sulicides were formed by annealing MBE-deposited thin 57 Fe layers with thicknesses between 20 A and 60 A on (7x7) reconstructed Si(1 11) substrates. During the growth the substrate was held at room temperature. The silicide formation upon annealing in the temperature range of 200'C to 900'C was studied in-situ with RH-EED. Samples were studied with in-situ CEMS (Conversion Electron Mossbauer Spectroscopy) as well as with ex-situ CEMS after covering with Ag to prevent oxidation. RBS/Channeling was used to study the epitaxial quality and the structure of these layers.Using the 57 Fe nuclear probe, it is shown that silicide formation occurs at the interface already at room temperature. Metastable silicides with cubic structure are observed in the low temperature annealing range, and characterized by their Mossbauer parameters. At higher temperatures stable e-FeSi and r3-FeSi 2 are formed.

Heteroepitaxial ErSi1.7 layers with excellent crystallinity (χmin of Er is 1.5%) have been prepared by high-dose 90 keV Er implantation into a Si(111) substrate using channeled implantation. Such an ErSi1.7/Si system offers a rare opportunity to study comprehensively the structure, orientation, and strain using Rutherford backscattering spectrometry and channeling analysis. We found that the minimum yield and width of the [0001] dip of the Er atoms are quite different from that of the Si atoms in the silicide layer. It is confirmed that the azimuthal orientation of the hexagonal ErSi1.7 layer to the cubic Si substrate is ErSi1.7 [0001] ∥ Si[111] and ErSi1.7 {112̄0} ∥ Si {110}, and that the epilayer is compressively strained. Besides, by using the angular scan and image scan, we reveal that the dips of the {101̄0} family are missing for the Si atoms in the epilayer but do exist for the Er atoms in the same epilayer. The reason for this drastic difference is explained by the separate {101̄0} planes and the different steering potential of the Si and Er atoms in ErSi1.7.