Position-sensitive detector systems, initially developed for the detection of X-rays, have been adapted for their use in electron emission channeling experiments. Each detection system consists of a 30.8×30.8 mm 2 22×22-pad Si detector, either of 0.3 mm, 0.5 mm or 1 mm thickness, four 128-channel preamplifier chips, a backplane trigger circuit, a sampling analog to digital converter, a digital signal processor, and a personal computer for data display and storage. The operational principle of these detection systems is described, and characteristic features such as energy and position resolution and maximum count rate, which have been determined from tests with conversion electrons and β − particles in the energy range 40-600 keV, are presented.

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...

We report results of a 14.1   kg d measurement with 15 superheated droplet detectors of total active mass 0.208 kg, comprising the first stage of a 30 kg d Phase II experiment. In combination with the results of the neutron-spin sensitive XENON10 experiment, these results yield a limit of |a(p)|<0.32 for M(W)=50 GeV/c² on the spin-dependent sector of weakly interacting massive particle-nucleus interactions with a 50% reduction in the previously allowed region of the phase space, formerly defined by XENON, KIMS, and PICASSO. In the spin-independent sector, a limit of 2.3×10⁻⁵ pb at M(W)=45 GeV/c² is obtained.

International audienceWe report an improved SIMPLE experiment comprising four superheated droplet detectors with a total exposure of 0.42 kgd. The result yields similar to factor 10 improvement in the previously-reported results, and-despite the low exposure-is seen to provide restrictions on the allowed phase space of spin-dependent coupling strengths almost equivalent to those from the significantly larger exposure NAIAD-CDMS/ZEPLIN searches. (c) 2005 Elsevier B.V. All rights reserved