Donor ionization in size controlled silicon nanocrystals: The transition from defect passivation to free electron generation

We studied the photoluminescence spectra of silicon and phosphorus co-implanted silica thin films on (100) silicon substrates as a function of isothermal annealing time. The rapid phase segregation, formation, and growth dynamics of intrinsic silicon nanocrystals are observed, in the first 600 s of rapid thermal processing, using dark field mode X-TEM. For short annealing times, when the nanocrystal size distribution exhibits a relatively small mean diameter, formation in the presence of phosphorus yields an increase in the luminescence intensity and a blue shift in the emission peak compared with intrinsic nanocrystals. As the mean size increases with annealing time, this enhancement rapidly diminishes and the peak energy shifts further to the red than the intrinsic nanocrystals. These results indicate the existence of competing pathways for the donor electron, which depends strongly on the nanocrystal size. In samples containing a large density of relatively small nanocrystals, the tendency of phosphorus to accumulate at the nanocrystal-oxide interface means that ionization results in a passivation of dangling bond (Pb -centre) type defects, through a charge compensation mechanism. As the size distribution evolves with isothermal annealing, the density of large nanocrystals increases at the expense of smaller nanocrystals, through an Ostwald ripening mechanism, and the majority of phosphorus atoms occupy substitutional lattice sites within the nanocrystals. As a consequence of the smaller band-gap, ionization of phosphorus donors at these sites increases the free carrier concentration and opens up an efficient, non-radiative de-excitation route for photo-generated electrons via Auger recombination. This effect is exacerbated by an enhanced diffusion in phosphorus doped glasses, which accelerates silicon nanocrystal growth

Fournier's gangrene: Still highly lethal

Five patients with necrotizing soft tissue infections of the perineum and scrotum are presented. There were one female and four male patients, aged from 35 to 70 years. Portals of entry were perirectal abscesses in four cases and a scrotal abscess in one case. All patients required extensive surgical debridement and intravenous broad-spectrum antibiotics. Operative debridement involved the scrotum, the perineal and inguinal area, the upper thighs and the anterior abdominal wall. One patient required transverse loop colostomy and one loop sigmoidostomy. One patient was reoperated on after inadequate drainage of a perirectal abscess. Three patients were referred to our unit after some delay, while one patient did not seek medical care until after being febrile for 2 weeks. Despite aggressive debridement, this last patient died of fulminant sepsis. Fournier’s gangrene, which is not so rare as in generally considered, is still associated with a high mortality, which can be reduced only by improving medical awareness and early treatment both of the primary cause and of necrotizing fasciitis

Benign multicystic peritoneal mesothelioma: a case report

<p>Abstract</p> <p>Introduction</p> <p>We report the case of a patient with a benign multicystic peritoneal mesothelioma and describe its appearance on computed tomography scans and ultrasonography, in correlation with gross clinical and pathological findings.</p> <p>Case presentation</p> <p>A 72-year-old Caucasian woman presented to our emergency department with acute abdomen signs and symptoms. A clinical examination revealed a painful palpable mass in her left abdomen. Abdominal ultrasonography and computed tomography demonstrated the presence of a large cystic mass in her left upper abdomen, adjacent to her left hemidiaphragm. The lower border of the mass extended to the upper margin of her pelvis. A complete resection of the lesion was performed. Pathological analysis showed a benign multicystic peritoneal mesothelioma.</p> <p>Conclusions</p> <p>Benign multicystic peritoneal mesothelioma is a rare lesion with a non-specific appearance on imaging. Its diagnosis always requires pathological analysis.</p