Lawson criterion for ignition exceeded in an inertial fusion experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion

Strain relaxation of pseudomorphic Si1-xGex/Si(100) heterostructures after Si+ ion implantation

The strain relaxation of pseudomorphic Si1-xGex layers (x=0.21,...,0.33) was investigated after low-dose Si+ ion implantation and annealing. The layers were grown by molecular-beam epitaxy or chemical vapor deposition on Si(100) or silicon-on-insulator. Strain relaxation of up to 75% of the initial strain was observed at temperatures as low as 850 degreesC after implantation of Si ions with doses below 2x10(14) cm(-2). We suggest that the Si implantation generates primarily dislocation loops in the SiGe layer and in the underlying Si which convert to strain relaxing misfit segments. The obtained results are comparable to strain relaxation achieved after He+ implantation with doses of 1-2x10(16) cm(-2). (C) 2004 American Institute of Physics

Strain relaxation induced by He-implantation at the Si1-xGex/Si(100) interface investigated by positron annihilation

Relaxation of 110 nm thick Si0.72Ge0.28 epitaxial layers grown on Si (100) substrate by molecular beam epitaxy have been studied by a variable energy slow positron beam. He-implantation at 18 keV energy and 2-3 x 10(16) ions cm(-2) fluence and subsequent annealing has been used to create a defect zone with large cavities in the substrate, at approximately 180-240 nm from the surface, in order to enhance strain relaxation in the SiGe layer. Positrons detected a significant difference in the cavity profile between single implantations with 2 x 10(16) and 3 x 10(16) ions cm(-2) fluence. e(+) trapping in the SiGe layer and at the interface was found to be below the limit of the resolution of the slow positron technique. (C) 2002 Elsevier Science B.V. All rights reserved

Strain relaxation of pseudomorphic Si1-xGex/Si(100) heterostructures by Si+ ion implantation

Strain relaxation of pseudomorphic Si1-xGex layers (x = 0.21-0.33) grown by chemical vapor deposition or molecular-beam epitaxy on Si(1 0 0) or silicon-on-insulator was investigated after low-fluence Si+ ion implantation and annealing. Strain relaxation of up to 75% of the initial pseudomorphic strain was observed at temperatures as low as 850 degrees C after implantation of Si+ ions with fluences below 2 x 10(14) cm(-2). We suggest that the Si implantation generates a high density of dislocation loops in the SiGe layer and in the underlying Si, which convert to strain relaxing misfit segments. The obtained results are comparable to strain relaxation achieved after He+ implantation with fluences of 0.7-2 x 10(16) cm(-2). (c) 2005 Elsevier B.V. All rights reserved