First-principles study of He in Si

Effects of He+ and H+ Co-Implantation with High Energy on Blisters and Craters of Si and SiO2-On-Si Wafers

In this paper, effects of He+ and H+ co-implantation with high implantation energy on surface blisters and craters at different annealing conditions are systematically investigated. Surface morphology as well as defect microstructure are observed and analyzed by various approaches, such as scanning electron microscopy (SEM), optical microscopy (OM), atomic force microscopy (AFM), and Raman spectroscopy. It is found that after 500 °C annealing and above for 1 h, surface blisters and exfoliation are observed for Si and SiO2-on-Si wafers except for the samples implanted with only He+ ions. AFM images reveal that the heights of blisters in Si and SiO2-on-Si wafers are 432 nm and 397 nm respectively and the thickness of transfer layer is at the depth of about 1.4 μm, which is consistent with the projected range of He+ and H+ ions. Raman spectroscopy demonstrates that higher annealing temperature can lead to a stronger intensity of the VH2 peak. Under the same implantation parameters, surface morphology of Si and SiO2-on-Si wafers is different after annealing process. This phenomenon is discussed in detail.

Contributed Review: The feasibility of a fully miniaturized magneto-optical trap for portable ultracold quantum technology

Experiments using laser cooled atoms and ions show real promise for practical applications in quantum-enhanced metrology, timing, navigation, and sensing as well as exotic roles in quantum computing, networking, and simulation. The heart of many of these experiments has been translated to microfabricated platforms known as atom chips whose construction readily lend themselves to integration with larger systems and future mass production. To truly make the jump from laboratory demonstrations to practical, rugged devices, the complex surrounding infrastructure (including vacuum systems, optics, and lasers) also needs to be miniaturized and integrated. In this paper we explore the feasibility of applying this approach to the Magneto-Optical Trap; incorporating the vacuum system, atom source and optical geometry into a permanently sealed micro-litre system capable of maintaining 10(-10) mbar for more than 1000 days of operation with passive pumping alone. We demonstrate such an engineering challenge is achievable using recent advances in semiconductor microfabrication techniques and materials.

First-principles calculations of helium and neon desorption from cavities in silicon

Combining density functional theory, the nudged elastic band technique, and the ultradense fluid model, we investigated the desorption process of He and Ne in silicon. Our results show that the internal surfaces of gas-filled bubbles are not a limiting factor during desorption experiments, since the surface reconstruction opens diffusion paths easier than in the bulk. We show that the vibrational contribution to the energy of helium in the bulk has to be considered in order to determine realistic pressures in the bubbles, when comparing experiments and simulations. At the maximum of desorption, an average pressure of 1-2 GPa is computed.

Using evidence from nanocavities to assess the vibrational properties of external surfaces

Internal surfaces of nanocavities are an exceptionally useful laboratory wherein one can spotlight the factors ruling the intricate interplay between morphology and chemistry at silicon surfaces. At the same time, they offer unparalleled opportunities to validate the assignment of vibrational signals of silicon-terminating species under almost ideal experimental conditions. In the case of hydrogen, evidence will be provided of the detailed evolution of H-related species at surfaces depending on their orientation. Also, preliminary results concerning nitrogen at and around nanocavity surfaces will be reported.

Gettering of metals by voids in silicon

The gettering efficiency of copper and platinum by cavities formed in silicon after high dose helium implantation and thermal processing has been investigated. The formation of helium bubbles and their evolution into cavities has been investigated by transmission electron microscopy; the measured values of void density, diameter and the width of the void layer can be interpreted by assuming a simple coalescence model. Metal impurities intentionally introduced in silicon by ion implantation are efficiently gettered inside these cavities, probably due to the large amount of unsatured bonds at the void internal surface. Processing at temperatures higher than 1000oC causes a release of the trapped metal atoms which can be gettered again by repeating the process. The method is demonstrated on real devices such as large area diodes (a particle detector) and bipolar transistors. The capability to localize in depth and across the wafer surface on the gettering sites allows the development of a new gettering engineering.