Ultrathin SiC buffer layers have been grown on Si (100) substrates by atmospheric pressure chemical vapor deposition. The evolution of buffer layer morphological properties as a function of carbonization parameters is investigated by atomic force microscopy. Based on the quantitative analysis of the dependences of void density, void depth, void width, and surface roughness on carbonization parameters, a buffer layer growth model is proposed, and the effects of carbonization parameters on buffer layer morphology are clarified. The void density is related to the carbonization temperature, temperature ramp-up rate, and C3H8 concentration by affecting the initial SiC nuclei density. The void size is evolved with processing time and mainly dependent on the carbonization temperature but slightly affected by C3H8 and H2. The buffer layer morphology is deteriorated with increasing H2 flow rate when the C3H8 concentration is fixed.

This study reviews the results of the surgical management of 154 cases of ruptured aneurysm of the sinus of Valsalva. Of the patients0 73% were male, with an average age of 28 years. An associated ventricular septal defect was found in 40% and 23% had aortic valvar regurgitation. The aneurysms originated from the right coronary sinus in 79% and from the non-coronary sinus in the remainders. The aneurysms ruptured into the right ventricle in 73%, into the right atrium in 27% and into the left ventricle in less than 1%. Operative mortality was 4.5%. Long-term follow-up was achieved in 80% of patients, with a mean duration of 5.7 years and a range from two months to 29 years. Preoperative aortic regurgitation and preoperative functional class (NYHA III or IV) were both predictive of a worse long-term outcome. The optimal surgical approach was closure of the distal end of the fistula by direct suture together with reinforcement of the aortic sinus with a Dacron patch.