Evolution of vacancy-related defects upon annealing of ion-implanted germanium

Positron annihilation spectroscopy was used to study defects created during the ion implantation and annealing of Ge. Ge and Si ions with energies from 600 keV to 2 MeV were implanted at fluences between 1×10 exp 12 cm exp−2 and 4×10 exp 14 cm exp−2. Ion channeling measurements on as-implanted samples show considerable lattice damage at a fluence of 1×10 exp 13 cm exp −2 and a fluence of 1×10 exp 14 cm exp -2 was enough to amorphize the samples. Positron experiments reveal that the average free volume in as-irradiated samples is of divacancy size. Larger vacancy clusters are formed during regrowth of the damaged layers when the samples are annealed in the temperature range 200–400 °C. Evolution of the vacancy-related defects upon annealing depends noticeably on fluence of ion implantation and for the highest fluences also on ion species.Peer reviewe

Recombination via transition metals in solar silicon : the significance of hydrogen-metal reactions and lattice sites of metal atoms

The move towards lower cost sources of solar silicon has intensified efforts to investigate the possibilities of passivating or reducing the recombination activity caused by deep states associated with transition metals. This is particularly important for the case of the slow diffusing metals early in the periodic sequence which are not removed by conventional gettering. In this paper we examine reactions between hydrogen and transition metals and discuss the possibility of such reactions during cell processing. We analyse the case of hydrogenation of iron in p-type Si and show that FeH can form under non-equilibrium conditions. We consider the electrical activity of the slow diffusing metals Ti, V and Mo, how this is affected in the presence of hydrogen, and the stability of TM-H complexes formed. Finally we discuss recent experiments which indicate that resiting of some transition metals from the interstitial to substitutional site is possible in the presence of excess vacancies, leading to a reduction in recombination activity

Gettering of interstitial iron in silicon by plasma enhanced chemical vapour deposited silicon nitride films

It is known that the interstitial iron concentration in silicon is reduced after annealing silicon wafers coated with plasma-enhanced chemical vapour deposited (PECVD) silicon nitride films. The underlying mechanism for the significant iron reduction has remained unclear and is investigated in this work. Secondary ion mass spectrometry (SIMS) depth profiling of iron is performed on annealed iron- contaminated single-crystalline silicon wafers passivated with PECVD silicon nitride films. SIMS measurements reveal a high concentration of iron uniformly distributed in the annealed silicon nitride films. This accumulation of iron in the silicon nitride film matches the interstitial iron loss in the silicon bulk. This finding conclusively shows that the interstitial iron is gettered by the silicon nitride films during annealing over a wide temperature range from 250o C to 900o C, via a segregation gettering effect. Further experimental evidence is presented to support this finding. Deep-level transient spectroscopy (DLTS) analysis shows that no new electrically active defects are formed in the silicon bulk after annealing iron-containing silicon with silicon nitride films, confirming that the interstitial iron loss is not due to a change of the chemical structure of iron related defects in the silicon bulk. In addition, once the annealed silicon nitride films are removed, subsequent high temperature processes do not result in any reappearance of iron. Finally, the experimentally measured iron decay kinetics are shown to agree with a model of iron diffusion to the surface gettering sites, indicating a diffusion-limited iron gettering process for temperatures below 700o C. The gettering process is found to become reaction-limited at higher temperatures

Prevention and Treatment of Childhood Obesity: Care Received by a State Medicaid Population

Based on chart review for a representative cluster sample of North Carolina Medicaid enrollees aged 3 to 5 years (n = 1951) and 13 to 16 years (n = 1922) years, this study describes prevalence, practice patterns, and comorbidities related to overweight/obese immediately prior to 2007 Expert Recommendations. In total, 16% of children in both age groups were overweight, and 20% (ages 3–5 years) and 25% (ages 13–16 years) were obese. For 3- to 5-year-olds, body mass index percentile was infrequently recorded (22%) or plotted on growth charts (24%), and weight status category was rarely documented (10%). Results were similar for adolescents (21%, 20%, and 12%, respectively). In both groups, documentation of counseling in nutrition or physical activity was rare (16% for ages 3–5 years; 7% for ages 13–16 years). In adolescents, approximately 20% received recommended laboratory screening and overweight/obesity was significantly associated with chart-documented asthma, back pain, prediabetes, gastroesophageal reflux disease, hypertension, and sleep apnea. Whether improvements in documentation of care followed these new guidelines deserves further research

Oxidative stress and life histories: unresolved issues and current needs

Life-history theory concerns the trade-offs that mold the patterns of investment by animals between reproduction, growth, and survival. It is widely recognized that physiology plays a role in the mediation of life-history trade-offs, but the details remain obscure. As life-history theory concerns aspects of investment in the soma that influence survival, understanding the physiological basis of life histories is related, but not identical, to understanding the process of aging. One idea from the field of aging that has gained considerable traction in the area of life histories is that life-history trade-offs may be mediated by free radical production and oxidative stress. We outline here developments in this field and summarize a number of important unresolved issues that may guide future research efforts. The issues are as follows. First, different tissues and macromolecular targets of oxidative stress respond differently during reproduction. The functional significance of these changes, however, remains uncertain. Consequently there is a need for studies that link oxidative stress measurements to functional outcomes, such as survival. Second, measurements of oxidative stress are often highly invasive or terminal. Terminal studies of oxidative stress in wild animals, where detailed life-history information is available, cannot generally be performed without compromising the aims of the studies that generated the life-history data. There is a need therefore for novel non-invasive measurements of multi-tissue oxidative stress. Third, laboratory studies provide unrivaled opportunities for experimental manipulation but may fail to expose the physiology underpinning life-history effects, because of the benign laboratory environment. Fourth, the idea that oxidative stress might underlie life-history trade-offs does not make specific enough predictions that are amenable to testing. Moreover, there is a paucity of good alternative theoretical models on which contrasting predictions might be based. Fifth, there is an enormous diversity of life-history variation to test the idea that oxidative stress may be a key mediator. So far we have only scratched the surface. Broadening the scope may reveal new strategies linked to the processes of oxidative damage and repair. Finally, understanding the trade-offs in life histories and understanding the process of aging are related but not identical questions. Scientists inhabiting these two spheres of activity seldom collide, yet they have much to learn from each other

Milk yield estimation during suckling using the double oxytocin injection-milking and the double weighing-suckling methods in dairy goats

The aim was to verify the validity of the double oxytocin-milking (DOT) method as milk yield estimator during the suckling period of lactating dairy goats. To this end, it was necessary to determine whether the weighing suckling weighing (WSW) and DOT methods of milk yield estimation satisfied the criteria to be considered valuable, the accuracy between both methods and the suitability of DOT to evaluate actual milk. At parturition, sixty lactating Murciano Granadina breed goats were separated into 2 groups, in mixed (MS; n = 24) and artificial rearing (ARS; n = 36) management systems. Until the sixth week of lactation (weaning), MS goats suckled one kid while kids from ARS goats were artificially reared; moreover, goats in both systems were submitted to once-a-day milking. Once per week, actual milk yield for ARS goats and potential milk yield were recorded using DOT method for all goats, except for 12 goats in ARS which remained as a control. Twelve goats from each management system were used to evaluate diurnal variation in milk production (DVM) by DOT method for 6 consecutive days in week 4 of lactation. No difference in DVM was found by DOT method in 4-h milk production of goats in MS (P = 0.099) or ARS (P = 0.220), which allowed sixfold multiplication of milked milk volume to obtain potential milk per day. ARS goats subjected to a weekly DOT and control group goats showed a similar (P = 0.379) lactation curve for the first 6 weeks of lactation. The DOT method slightly overestimated (3.4%, P = 0.005) the milk yield evaluated by WSW method for goats under an MS, but fitted the actual milk obtained by common milk records for the group of goats in an ARS submitted to the DVM test (P = 0.357) and the group in ARS alone (P = 0.163). The DOT method applied for 8 consecutive days led to a drop of 6 12% in milk yield during the following week for both production systems. In conclusion, DOT was an accurate method to estimate milk yield during the first weeks of lactation both in MS and ARS under the conditions of this experiment. © 2013 Elsevier B.V. All rights reserved.Fernández Martínez, N.; Balasch Parisi, S.; Pérez Baena, I.; Rodríguez Garcia, M.; Peris Ribera, CJ. (2013). Milk yield estimation during suckling using the double oxytocin injection-milking and the double weighing-suckling methods in dairy goats. Small Ruminant Research. 112(1-3):181-185. doi:10.1016/j.smallrumres.2012.12.023S1811851121-