Microwave enhanced ion-cut silicon layer transfer

Microwave heating has been used to decrease the time required for exfoliation of thin single-crystalline silicon layers onto insulator substrates using ion-cut processing. Samples exfoliated in a 2.45 GHz, 1300 W cavity applicator microwave system saw a decrease in incubation times as compared to conventional anneal processes. Rutherford backscattering spectrometry, cross sectional scanning electron microscopy, cross sectional transmission electron microscopy, and selective aperture electron diffraction were used to determine the transferred layer thickness and crystalline quality. The surface quality was determined by atomic force microscopy. Hall measurements were used to determine electrical properties as a function of radiation repair anneal times. Results of physical and electrical characterizations demonstrate that the end products of microwave enhanced ion-cut processing do not appreciably differ from those using more traditional means of exfoliation. © 2007 American Institute of Physics

Effect of substrate growth temperatures on H diffusion in hydrogenated Si/Si homoepitaxial structures grown by molecular beam epitaxy

We have investigated hydrogen diffusion in hydrogenated 〈100〉 Si/Si homoepitaxial structures, which were grown by molecular beam epitaxy at various temperatures. The substrate growth temperature can significantly affect the H diffusion behavior, with higher growth temperatures resulting in deeper H diffusion. For the Si/Si structure grown at the highest temperature of 800°C, H trapping occurs at the epitaxial Si/Si substrate interface, which results in the formation of (100) oriented microcracks at the interface. The mechanism of H trapping and the potential application of these findings for the development of a method of transferring ultrathin Si layers are discussed. © 2006 American Institute of Physics

Plasma hydrogenation of strained Si/SiGe/Si heterostructure for layer transfer without ion implantation

We have developed an innovative approach without the use of ion implantation to transfer a high-quality thin Si layer for the fabrication of silicon-on-insulator wafers. The technique uses a buried strained SiGe layer, a few nanometers in thickness, to provide H trapping centers. In conjunction with H plasma hydrogenation, lift-off of the top Si layer can be realized with cleavage occurring at the depth of the strained SiGe layer. This technique avoids irradiation damage within the top Si layer that typically results from ion implantation used to create H trapping regions in the conventional ion-cut method. We explain the strain-facilitated layer transfer as being due to preferential vacancy aggregation within the strained layer and subsequent trapping of hydrogen, which lead to cracking in a well controlled manner. © 2005 American Institute of Physics

H-induced platelet and crack formation in hydrogenated epitaxial Si/Si <inf>0.98</inf>B <inf>0.02</inf>/Si structures

An approach to transfer a high-quality Si layer for the fabrication of silicon-on-insulator wafers has been proposed based on the investigation of platelet and crack formation in hydrogenated epitaxial Si Si0.98 B0.02 Si structures grown by molecular-beam epitaxy. H-related defect formation during hydrogenation was found to be very sensitive to the thickness of the buried Si0.98 B0.02 layer. For hydrogenated Si containing a 130 nm thick Si0.98 B0.02 layer, no platelets or cracking were observed in the B-doped region. Upon reducing the thickness of the buried Si0.98 B0.02 layer to 3 nm, localized continuous cracking was observed along the interface between the Si and the B-doped layers. In the latter case, the strains at the interface are believed to facilitate the (100)-oriented platelet formation and (100)-oriented crack propagation. © 2006 American Institute of Physics

Combining ecosystem modeling with serious gaming in support of transboundary maritime spatial planning

The Maritime Spatial Planning (MSP) Challenge simulation platform helps planners and stakeholders understand and manage the complexity of MSP. In the interactive simulation, different data layers covering an entire sea region can be viewed to make an assessment of the current status. Users can create scenarios for future uses of the marine space over a period of several decades. Changes in energy infrastructure, shipping, and the marine environment are then simulated, and the effects are visualized using indicators and heat maps. The platform is built with advanced game technology and uses aspects of role-play to create interactive sessions; it can thus be referred to as serious gaming. To calculate and visualize the effects of planning decisions on the marine ecology, we integrated the Ecopath with Ecosim (EwE) food web modeling approach into the platform. We demonstrate how EwE was connected to MSP, considering the range of constraints imposed by running scientific software in interactive serious gaming sessions while still providing cascading ecological feedback in response to planning actions. We explored the connection by adapting two published ecological models for use in MSP sessions. We conclude with lessons learned and identify future developments of the simulation platform

Loss of convexity of simple closed curves moved by surface diffusion

We rigorously prove that there exists a simple, strictly convex, smooth closed curve which loses convexity but stays simple without developing singularities when it moves by its surface diffusion for a short time

Transit Timing and Duration Variations for the Discovery and Characterization of Exoplanets

Transiting exoplanets in multi-planet systems have non-Keplerian orbits which can cause the times and durations of transits to vary. The theory and observations of transit timing variations (TTV) and transit duration variations (TDV) are reviewed. Since the last review, the Kepler spacecraft has detected several hundred perturbed planets. In a few cases, these data have been used to discover additional planets, similar to the historical discovery of Neptune in our own Solar System. However, the more impactful aspect of TTV and TDV studies has been characterization of planetary systems in which multiple planets transit. After addressing the equations of motion and parameter scalings, the main dynamical mechanisms for TTV and TDV are described, with citations to the observational literature for real examples. We describe parameter constraints, particularly the origin of the mass/eccentricity degeneracy and how it is overcome by the high-frequency component of the signal. On the observational side, derivation of timing precision and introduction to the timing diagram are given. Science results are reviewed, with an emphasis on mass measurements of transiting sub-Neptunes and super-Earths, from which bulk compositions may be inferred.Comment: Revised version. Invited review submitted to 'Handbook of Exoplanets,' Exoplanet Discovery Methods section, Springer Reference Works, Juan Antonio Belmonte and Hans Deeg, Eds. TeX and figures may be found at https://github.com/ericagol/TTV_revie

Effects of insurance status on children's access to specialty care: a systematic review of the literature

<p>Abstract</p> <p>Background</p> <p>The current climate of rising health care costs has led many health insurance programs to limit benefits, which may be problematic for children needing specialty care. Findings from pediatric primary care may not transfer to pediatric specialty care because pediatric specialists are often located in academic medical centers where institutional rules determine accepted insurance. Furthermore, coverage for pediatric specialty care may vary more widely due to systematic differences in inclusion on preferred provider lists, lack of availability in staff model HMOs, and requirements for referral. Our objective was to review the literature on the effects of insurance status on children's access to specialty care.</p> <p>Methods</p> <p>We conducted a systematic review of original research published between January 1, 1992 and July 31, 2006. Searches were performed using Pubmed.</p> <p>Results</p> <p>Of 30 articles identified, the majority use number of specialty visits or referrals to measure access. Uninsured children have poorer access to specialty care than insured children. Children with public coverage have better access to specialty care than uninsured children, but poorer access compared to privately insured children. Findings on the effects of managed care are mixed.</p> <p>Conclusion</p> <p>Insurance coverage is clearly an important factor in children's access to specialty care. However, we cannot determine the structure of insurance that leads to the best use of appropriate, quality care by children. Research about specific characteristics of health plans and effects on health outcomes is needed to determine a structure of insurance coverage that provides optimal access to specialty care for children.</p

Isolation and fine mapping of Rps6: An intermediate host resistance gene in barley to wheat stripe rust

A plant may be considered a nonhost of a pathogen if all known genotypes of a plant species are resistant to all known isolates of a pathogen species. However, if a small number of genotypes are susceptible to some known isolates of a pathogen species this plant maybe considered an intermediate host. Barley (Hordeum vulgare) is an intermediate host for Puccinia striiformis f. sp. tritici (Pst), the causal agent of wheat stripe rust. We wanted to understand the genetic architecture underlying resistance to Pst and to determine whether any overlap exists with resistance to the host pathogen, Puccinia striiformis f. sp. hordei (Psh). We mapped Pst resistance to chromosome 7H and show that host and intermediate host resistance is genetically uncoupled. Therefore, we designate this resistance locus Rps6. We used phenotypic and genotypic selection on F2:3 families to isolate Rps6 and fine mapped the locus to a 0.1 cM region. Anchoring of the Rps6 locus to the barley physical map placed the region on two adjacent fingerprinted contigs. Efforts are now underway to sequence the minimal tiling path and to delimit the physical region harbouring Rps6. This will facilitate additional marker development and permit identification of candidate genes in the region