The transient supersaturation in a system undergoing Ostwald ripening is related to the cluster formation energy E fc as a function of cluster size n. We use this relation to study the energetics of self-interstitial clusters in Si. Measurements of transient enhanced diffusion of B in Si-implanted Si are used to determine S͑t͒, and inverse modeling is used to derive E fc ͑n͒. For clusters with n . 15, E fc ഠ 0.8 eV, close to the fault energy of ͕113͖ defects. For clusters with n , 10, E fc is typically 0.5 eV higher, but stabler clusters exist at n ഠ 4 (E fc ഠ 1.0 eV) and n ഠ 8 (E fc ഠ 0.6 eV). [S0031-9007(99)09311-4]

Flow control consists of manipulating flows in an effective and robust manner to improve the global performances of transport systems or industrial processes. Plasma technologies, and particularly surface dielectric barrier discharge (DBD), can be a good candidate for such purpose. The present experimental study focuses on optical and electrical characterization of plasma sheet formed by applying a pulse of voltage with rising and falling periods of 50 ns for a typical surface DBD geometry. Positive and negative polarities are compared in terms of current behavior, deposited energy, fast-imaging of the plasma propagation, and resulting modifications of the surrounding medium by using shadowgraphy acquisitions. Positive and negative pulses of voltage produce streamers and corona type plasma, respectively. Both of them result in the production of a localized pressure wave propagating in the air with a speed maintained at 343 m/s (measurements at room temperature of 20 °C). This suggests that the produced pressure wave can be considered as a propagating sound wave. The intensity of the pressure wave is directly connected to the dissipated energy at the dielectric wall with a linear increase with the applied voltage amplitude and a strong dependence toward the rising time. At constant voltage amplitude, the pressure wave is reinforced by using a positive pulse. The present investigation also reveals that rising and decaying periods of a single pulse of voltage result in two distinct pressure waves. As a result, superposition or successive pressure wave can be produced by adjusting the width of the pulse.

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Growth regimes during homoepitaxial growth of GaN by ammonia molecular beam epitaxy J. Appl. Phys. 112, 054903 (2012) Defect microstructural evolution in ion irradiated metallic nanofoils: Kinetic Monte Carlo simulation versus cluster dynamics modeling and in situ transmission electron microscopy experiments Appl. Phys. Lett. 101, 101905 (2012) Anisotropic lattice relaxation in non-c-plane InGaN/GaN multiple quantum wells J. Appl. Phys. 112, 033513 (2012) Analysis of doping induced wafer bow during GaN:Si growth on sapphire End-of-range ͑EOR͒ defects are interstitial type dislocation loops which nucleate just beneath the crystalline/amorphous ͑c/a͒ interface formed by ion implantation in Si, after the preamorphization of the substrate, and during the ramping-up of the anneal. They originate from the presence of a high supersaturation of ''excess'' Si self-interstitial atoms located just beneath the c/a interface. Upon annealing, the mean radius of the defects increases while their density decreases through the exchange of Si self-interstitial atoms between the loops. The number of interstitials stored in the loops stays constant. For sufficiently high thermal budgets, when the nucleation is finished, and when the local equilibrium between extended and point defects is established, the coarsening of the EOR defects can be modeled through the Ostwald ripening theory applied to the dislocation loops geometry. Indeed, and as expected from the theory, the square of the mean radius of the loop population increases with time while the loop density decreases proportional to 1/t. Furthermore, the theoretical function describing the size distributions perfectly matches the time evolution of the experimental stack histograms, for different annealing temperatures. During the asymptotic steady-state coarsening regime, the activation energy for the loop coarsening is 4.4 eV, which is in the range of values given in the literature for self-diffusion in Si. Nevertheless, an activation energy of about 1-2 eV is found during the transient period preceding the local equilibrium, i.e., in the range of the migration energy of self-interstitials. The limiting phenomenon for the loop growth appears to be diffusion, since it is the hypothesis that leads to the best fit between theory and experiment. An estimate of D i C i * has been derived from the growth laws of the EOR defects. A value of about 1.8ϫ10 7 cm Ϫ1 s Ϫ1 at 1000°C is obtained and compares well with the values given in the literature.

Ge nanocrystals embedded in thermal SiO2 on top of a Si substrate are investigated using Raman spectroscopy and transmission electron microscopy. We observe that the Raman peak frequency of the Ge nanocrystals is strongly affected by compressive stress. In the case of large particles for which the phonon confinement-induced Raman shift can be neglected, the stress is measured taking into account isotopic composition effects induced by the ion implantation process used to produce the nanocrystals. The stress is proposed to originate from a liquid–solid phase transition in Ge.

Influence of average size and interface passivation on the spectral emission of Si nanocrystals embedded in SiO 2

A study of the relative thermal stability of perfect and faulted dislocation loops formed during annealing of preamorphized silicon wafers has been carried out. A series of transmission electron microscopy experiments has been designed to study the influence of the ion dose, the annealing ambient and the proximity of a free surface on the evolution of both types of loops. Samples were implanted with either 150 keV Ge+ or 50 keV Si+ ions to a dose of 2×1015 cm−2 and annealed at 900 °C in N2, N2O, and O2. The calculations of formation energy of both types of dislocation loops show that, for defects of the same size, faulted dislocation loops (FDLs) are more energetically stable than perfect dislocation loops (PDLs) if their diameter is smaller than 80 nm and vice versa. The experimental results have been analyzed within the framework of the Ostwald ripening of two existing populations of interstitial defects. It is found that the defect ripening is nonconservative if the surface is close to the end of range defect layer or if the sample is oxidized during annealing. In both cases, the knowledge of the formation energy of both types of dislocation loops allows a realistic estimate of the interstitial flux towards and from the surface, respectively, during annealing, in agreement with the experimental results. During a conservative ripening process, a direct correspondence exists between the formation energy of the two defect families and the number of atoms bound to them. In this case, the relative stability of FDLs and PDLs depends on the initial supersaturation of Si interstitial atoms created during implantation.

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