Mechanisms of arsenic clustering in silicon

A model of arsenic clustering in silicon is proposed and analyzed. The main feature of the proposed model is the assumption that negatively charged arsenic complexes play a dominant role in the clustering process. To confirm this assumption, electron density and concentration of impurity atoms incorporated into the clusters are calculated as functions of the total arsenic concentration. A number of the negatively charged clusters incorporating a point defect and one or more arsenic atoms are investigated. It is shown that for the doubly negatively charged clusters or for clusters incorporating more than one arsenic atom the electron density reaches a maximum value and then monotonically and slowly decreases as total arsenic concentration increases. In the case of doubly negatively charged cluster incorporating two arsenic atoms, the calculated electron density agrees well with the experimental data. Agreement with the experiment confirms the conclusion that two arsenic atoms participate in the cluster formation. Among all present models, the proposed model of clustering by formation of doubly negatively charged cluster incorporating two arsenic atoms gives the best fit to the experimental data and can be used in simulation of high concentration arsenic diffusion.Comment: 13 pages, 4 figures. Revised and shortened version of the paper has been published in Phys. Rev. B, Vol.74 (3), art. no. 035205 (2006

Experimental probing of exchange interactions between localized spins in the dilute magnetic insulator (Ga,Mn)N

The sign, magnitude, and range of the exchange couplings between pairs of Mn ions is determined for (Ga,Mn)N and (Ga,Mn)N:Si with x < 3%. The samples have been grown by metalorganic vapor phase epitaxy and characterized by secondary-ion mass spectroscopy; high-resolution transmission electron microscopy with capabilities allowing for chemical analysis, including the annular dark-field mode and electron energy loss spectroscopy; high-resolution and synchrotron x-ray diffraction; synchrotron extended x-ray absorption fine-structure; synchrotron x-ray absorption near-edge structure; infra-red optics and electron spin resonance. The results of high resolution magnetic measurements and their quantitative interpretation have allowed to verify a series of ab initio predictions on the possibility of ferromagnetism in dilute magnetic insulators and to demonstrate that the interaction changes from ferromagnetic to antiferromagnetic when the charge state of the Mn ions is reduced from 3+ to 2+.Comment: 12 pages, 14 figures; This version contains the detailed characterization of the crystal structure as well as of the Mn distribution and charge stat

Pediatric trauma and emergency surgery: an international cross-sectional survey among WSES members

Background: In contrast to adults, the situation for pediatric trauma care from an international point of view and the global management of severely injured children remain rather unclear. The current study investigates structural management of pediatric trauma in centers of different trauma levels as well as experiences with pediatric trauma management around the world. Methods: A web-survey had been distributed to the global mailing list of the World Society of Emergency Surgery from 10/2021-03/2022, investigating characteristics of respondents and affiliated hospitals, case-load of pediatric trauma patients, capacities and infrastructure for critical care in children, trauma team composition, clinical work-up and individual experiences with pediatric trauma management in response to patients´ age. The collaboration group was subdivided regarding sizes of affiliated hospitals to allow comparisons concerning hospital volumes. Comparable results were conducted to statistical analysis. Results: A total of 133 participants from 34 countries, i.e. 5 continents responded to the survey. They were most commonly affiliated with larger hospitals (&gt; 500 beds in 72.9%) and with level I or II trauma centers (82.0%), respectively. 74.4% of hospitals offer unrestricted pediatric medical care, but only 63.2% and 42.9% of the participants had sufficient experiences with trauma care in children ≤ 10 and ≤ 5 years of age (p = 0.0014). This situation is aggravated in participants from smaller hospitals (p &lt; 0.01). With regard to hospital size (≤ 500 versus &gt; 500 in-hospital beds), larger hospitals were more likely affiliated with advanced trauma centers, more elaborated pediatric intensive care infrastructure (p &lt; 0.0001), treated children at all ages more frequently (p = 0.0938) and have higher case-loads of severely injured children &lt; 12 years of age (p = 0.0009). Therefore, the majority of larger hospitals reserve either pediatric surgery departments or board-certified pediatric surgeons (p &lt; 0.0001) and in-hospital trauma management is conducted more multi-disciplinarily. However, the majority of respondents does not feel prepared for treatment of severe pediatric trauma and call for special educational and practical training courses (overall: 80.2% and 64.3%, respectively). Conclusions: Multi-professional management of pediatric trauma and individual experiences with severely injured children depend on volumes, level of trauma centers and infrastructure of the hospital. However, respondents from hospitals at all levels of trauma care complain about an alarming lack of knowledge on pediatric trauma management

Correction to: Two years later: Is the SARS-CoV-2 pandemic still having an impact on emergency surgery? An international cross-sectional survey among WSES members

Background: The SARS-CoV-2 pandemic is still ongoing and a major challenge for health care services worldwide. In the first WSES COVID-19 emergency surgery survey, a strong negative impact on emergency surgery (ES) had been described already early in the pandemic situation. However, the knowledge is limited about current effects of the pandemic on patient flow through emergency rooms, daily routine and decision making in ES as well as their changes over time during the last two pandemic years. This second WSES COVID-19 emergency surgery survey investigates the impact of the SARS-CoV-2 pandemic on ES during the course of the pandemic. Methods: A web survey had been distributed to medical specialists in ES during a four-week period from January 2022, investigating the impact of the pandemic on patients and septic diseases both requiring ES, structural problems due to the pandemic and time-to-intervention in ES routine. Results: 367 collaborators from 59 countries responded to the survey. The majority indicated that the pandemic still significantly impacts on treatment and outcome of surgical emergency patients (83.1% and 78.5%, respectively). As reasons, the collaborators reported decreased case load in ES (44.7%), but patients presenting with more prolonged and severe diseases, especially concerning perforated appendicitis (62.1%) and diverticulitis (57.5%). Otherwise, approximately 50% of the participants still observe a delay in time-to-intervention in ES compared with the situation before the pandemic. Relevant causes leading to enlarged time-to-intervention in ES during the pandemic are persistent problems with in-hospital logistics, lacks in medical staff as well as operating room and intensive care capacities during the pandemic. This leads not only to the need for triage or transferring of ES patients to other hospitals, reported by 64.0% and 48.8% of the collaborators, respectively, but also to paradigm shifts in treatment modalities to non-operative approaches reported by 67.3% of the participants, especially in uncomplicated appendicitis, cholecystitis and multiple-recurrent diverticulitis. Conclusions: The SARS-CoV-2 pandemic still significantly impacts on care and outcome of patients in ES. Well-known problems with in-hospital logistics are not sufficiently resolved by now; however, medical staff shortages and reduced capacities have been dramatically aggravated over last two pandemic years

Tailoring the exchange coupling in IrMn/NiFe films and nanodots by interface confinement

The scientific interest towards antiferromagnetic (AFM) materials has been increasing continuously mainly because of their crucial role in the operating principle of modern, miniaturized spintronic devices. In spin valves and tunnel junctions, a fine control of the magnetization reversal process in the ferromagnetic (FM) electrodes is usually achieved through the interface exchange coupling with an AFM layer [1]: the torque action exerted by the interfacial AFM spins on the FM ones brings about the insurgence of an unidirectional exchange anisotropy for the FM magnetization, and then of the exchange bias (EB) effect. Moreover, since the strategic importance of the EB effect in the technology of magnetoresistive spin valves and tunnel junctions and the increasing demand of miniaturization of modern devices (magnetic sensors, high-density data storage media), it is admittedly crucial to expand the description of the EB mechanism so as to include the effects of spatial confinement. The exchange interaction between AFM and FM interfacial spins depends, in polycrystalline systems, on the magnetic anisotropy of the bulk AFM phase and on the size distribution of the crystalline AFM grains [2]. Recent investigations have proposed the presence of disordered AFM spins at the AFM/FM interface, with spin-glass-like magnetic properties [3]. With this respect, we have recently observed that, at low temperature, these disordered AFM spins are frozen in a magnetic disordered state and are collectively involved in the exchange coupling with the FM moments, showing a magnetic correlation length, lambda [4]. With increasing temperature, lambda progressively shortens (we have established that at T ~ 100 K the frozen collective regime breaks up) even if the AFM spins do not enter the full paramagnetic regime due to the polarizing action of adjacent FM and AFM spins. Due to that, when interface confinement is observed, namely passing from a continuous film to a nanodot or when the morphology of the AFM/FM interface is modulated at the nanoscale, lambda is expected to play a role in the EB effect. In this contribution, we present our study on the mechanism of the magnetic exchange coupling in the Ir25Mn75/Ni20Fe80 system. The interface confinement has been accomplished in different ways: by producing that system in form of arrays of dots with different size D = 1000, 500, 300, 140 nm and by inserting, in the continuous films, a Cu spacer with a nominal thickness, tCu, of the order of 1Å. Due to the small tCu value, Cu islands, whose presence was confirmed by X-Ray Absorption Fine Structure investigations, are obtained at the AFM/FM interface. The EB properties of the samples, i.e. exchange field HEX and coercivity HC, and their thermal dependance, were investigated by SQUID and MOKE magnetometers in the 5-300 K temperature range. The role of  in the dots arrays was reflected by the strong dependence of HEX on D. In more detail, at 5 K HEX ~ 750 Oe when D = 1000 nm, whilst HEX ~ 1100 Oe when D = 1000 nm; when D = 140 nm, HEX decreases down to ~ 100 Oe [5]. In the continuous films with the Cu insertion at the interface, we observed that, at high temperature, the change in the HEX value may be explained just in terms of a dilution effect, namely in terms of the reduction of the extension of the AFM/FM interface. Differently, at low temperature, i.e. when lambda approaches the interdistance between Cu islands, the HEX values strongly depend on tCu, namely on Cu islands size/interdistance. These findings will be presented and discussed, taking also into account the results of micromagnetic calculations. [Research sponsored by MIUR Italy, project RBFR10E61T-NANOREST.]1. C. Chappert, A. Fert, F.N.V. Dau, Nature Mater. 6, 813 (2007) 2. G. Lhoutellier et al. J. Appl. Phys. 120, 193902 (2016) 3. V. Baltz et al. Phys. Rev. B 81, 052404 (2010). 4. F. Spizzo et al., Phys. Rev. B. 91, 064410 (2015) 5. F. Spizzo et al., J. Magn. Magn. Mater. 400, 242 (2016