Versatile control of metal-assisted chemical etching for vertical silicon microwire arrays and their photovoltaic applications.

A systematic study was conducted into the use of metal-assisted chemical etching (MacEtch) to fabricate vertical Si microwire arrays, with several models being studied for the efficient redox reaction of reactants with silicon through a metal catalyst by varying such parameters as the thickness and morphology of the metal film. By optimizing the MacEtch conditions, high-quality vertical Si microwires were successfully fabricated with lengths of up to 23.2 µm, which, when applied in a solar cell, achieved a conversion efficiency of up to 13.0%. These solar cells also exhibited an open-circuit voltage of 547.7 mV, a short-circuit current density of 33.2 mA/cm(2), and a fill factor of 71.3% by virtue of the enhanced light absorption and effective carrier collection provided by the Si microwires. The use of MacEtch to fabricate high-quality Si microwires therefore presents a unique opportunity to develop cost-effective and highly efficient solar cells.

Filter-free image sensor pixels comprising silicon nanowires with selective color absorption.

The organic dye filters of conventional color image sensors achieve the red/green/blue response needed for color imaging, but have disadvantages related to durability, low absorption coefficient, and fabrication complexity. Here, we report a new paradigm for color imaging based on all-silicon nanowire devices and no filters. We fabricate pixels consisting of vertical silicon nanowires with integrated photodetectors, demonstrate that their spectral sensitivities are governed by nanowire radius, and perform color imaging. Our approach is conceptually different from filter-based methods, as absorbed light is converted to photocurrent, ultimately presenting the opportunity for very high photon efficiency.

Si microwire solar cells: improved efficiency with a conformal SiO2 layer.

Silicon microwire arrays have attracted considerable attention recently due to the opportunity they present as highly efficient and cost-effective solar cells. In this study, we report on efficient Si microwire array solar cells with areas of 1 cm(2) and Air Mass 1.5 Global conversion efficiencies of up to 10.6%. These solar cells show an open-circuit voltage of 0.56 V, a short-circuit current density of 25.2 mA/cm(2), and a fill factor of 75.2%, with a silicon absorption region that is only 25 µm thick. In particular, the maximum overall efficiency of the champion device is improved from 8.71% to 10.6% by conformally coating the wires with a 200 nm thick SiO2 layer. Optical measurements reveal that the layer reduces reflection significantly over the entire visible range.

Prospective multiple outcomes study of outpatient lumbar microdiscectomy: should 75 to 80% success rates be the norm?

OBJECT: The authors assessed the efficacy and outcomes of lumbar microdiscectomy performed on an outpatient basis by administering six questionnaires before and at five time points after surgery. The results were compared with those reported in literature in which the success rates vary between 70% and 80% and in excess of 90%. The authors use the methodology and data derived from their study to evaluate critically the relevance of these two categories of success rates. METHODS: This is a prospective study of 212 consecutive, eligible patients who underwent outpatient microscopic discectomy for the treatment of lumbar disc herniation: no previous lumbar lesion had been treated. Data were collected from questionnaires given to the patients before and at five time points after surgery, including at a variable final follow-up examination (mean 2 years postoperatively). Data were collated and analyzed independently by individuals other than the operating surgeons. In both bi- and multivariate analyses, only two preoperative parameters were prognostically significant. The first factor was Workers' Compensation status, which had a negative effect on outcome. The second factor was patient age, which also had a negative effect and was linear with increasing age between 25 years and 56 years--that is, the ages most commonly encountered in cases of herniated disc. Successful outcome rates were as follows: leg pain relief according to a visual analog scale (VAS), 80%; back pain relief (VAS), 77%; Oswestry Low Back Disability Index, 78%; satisfaction with the results of surgery, 76%; return to normal daily activities, 65%; and return to work, 61%. CONCLUSIONS: The findings of this study support the evidence that lumbar microdiscectomy performed on an outpatient basis is a very safe and effective means of treating sciatic pain due to disc herniation. The authors believe that their outcome success rates of 75 to 80% are more realistic than those of 90% or more found in some reports.