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During the solidification of solder joints composed of near-eutectic Sn–Ag–Cu alloys, the Sn phase grows rapidly with a dendritic growth morphology, characterized by copious branching. Notwithstanding the complicated Sn growth topology, the Sn phase demonstrates single crystallographic orientations over large regions. Typical solder ball grid array joints, 900 μm in diameter, are composed of 1 to perhaps 12 different Sn crystallographic domains (Sn grains). When such solder joints are submitted to cyclic thermomechanical strains, the solder joint fatigue process is characterized by the recrystallization of the Sn phase in the higher deformation regions with the production of a much smaller grain size. Grain boundary sliding and diffusion in these recrystallized regions then leads to extensive grain boundary damage and results in fatigue crack initiation and growth along the recrystallized Sn grain boundaries.

Depth profile of trapped charges in oxide layer of 6HSiC metal-oxide-semiconductor structures Gold surfaces have been found to be hydrophilic only after exhaustive preparation and with the ultimate care in sample preparation and treatment. The use of a combination of ultraviolet ͑UV͒ light and ozone has been described as a viable method of producing a clean, hydrophilic, gold surface. We have found that gold surfaces, which have been either stored in the laboratory after vacuum deposition or purchased as high purity standards, are oxidized by a combination of UV light and ozone generated from a mercury lamp. The samples were characterized with x-ray photoelectron spectroscopy ͑XPS͒ and ion scattering spectroscopy ͑ISS͒ prior to and after exposure to UV/ozone in a stainless steel box in laboratory air. After the cleaning process gold surfaces were found by XPS to contain less carbon and to be enriched in oxygen. The O 1s on the cleaned surface, which was not present on the untreated surface, consisted of two peaks that are attributed to gold oxide and hydroxyl. The oxide layer was found to be 17Ϯ4 Å thick by variable angle XPS depth profiling with an initial stoichiometry of Au 2 O 3 . The oxide was found to be stable to extended exposure to UHV and water and ethanol rinses. ISS compositional depth profiles confirmed the oxide layer thickness and that the hydrated surface layer is removed in the initial sputtering of the oxidized gold. Implications of these results related to the mechanism of self-assembly of thiols on gold are discussed.

The authors report the postoperative magnetic resonance (MR) imaging findings in 36 patients with advanced Parkinson's disease who underwent unilateral microelectrode-guided posteroventral pallidotomy. The lesions were placed within 1 mm of the ventral border of the globus pallidus internus (GPi) to include pallidothalamic outflow pathways. Sequential MR studies were obtained within 1 to 3 days postoperatively and at 6-month follow-up examination. Thirty-four (94%) of the 36 patients enjoyed sustained moderate or marked improvement of their parkinsonian symptoms 6 months postoperatively. Transient side effects occurred in five patients (14%), but there were no persistent complications. The pallidal radiofrequency lesions were prolate spheroid-shaped and were composed of three concentric zones in the early postoperative studies. The mean volume of the middle zone, corresponding to the area of hemorrhagic coagulation necrosis, was 44.4 +/- 17.6 mm3; the mean lesion volume as defined by the outer zone, corresponding to perilesional edema, was 262.2 +/− 111.6 mm3. Additional edema spreading to the internal capsule was noted in 32 of 34 cases and to the optic tract in 11 of 34 cases. In two patients small ischemic infarctions involving the corona radiata were found, and in one a venous infarction was detected. Ischemic infarction resulted in mild transient Broca's aphasia in one patient, but there was no detectable neurological deficit in the other two. The mean volume of late-phase (6 months) lesions was 22 +/− 28.8 mm3. In three patients no lesion was identified despite sustained clinical improvement. The lesion was located in the posteroventral GPi in all cases except in one patient in whom it was confined to the GP externus (GPe). This 49-year-old woman did not experience sustained benefit. The authors found no consistent correlations between lesion size and location and clinical outcome as measured by a global outcome score, the Unified Parkinson's Disease Rating Scale motor, activities of daily living, and bradykinesia “off” scores or rating of dyskinesias. Lesioning of pallidal and subpallidal pathways may contribute to the sustained clinical benefit in this series. Magnetic resonance imaging analysis showed that intraoperative microelectrode recording facilitated accurate placement of the lesion in this critical area.

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