RESUMO
We have developed improved analyzer multilayers for the detection of aluminium (Al) and boron (B) on silicon (Si) wafers with wavelength-dispersive x-ray fluorescence spectrometers. For the detection of Al on Si wafers we show that WSi(2)/Si and Ta/Si multilayers provide detection limits that are 42% and 60% better, respectively, than with currently used W/Si multilayers. For the detection of B on Si wafers we show that La/B(4)C multilayers improve the detection limit by approximately 28% compared with a conventionally used Mo/B(4)C multilayer.
RESUMO
La/B(4)C multilayers have been fabricated by magnetron sputtering for use as x-ray mirrors at energies below 190 eV, particularly for detection of boron K and alpha x rays at 183 eV, their performance has been compared with that of Mo/B(4)C multilayers, which are currently the best-performing multilayers for this energy range. Transmission electron microscopy and synchrotron soft-x-ray reflectometry were used to study the structural quality of the multilayers and their performance as x-ray mirrors. The results show a significant improvement of the peak reflectivity and the spectral purity, indicating that La/B(4)C has a high potential to replace Mo/B(4)C in many x-ray optical applications below 190 eV.
RESUMO
Lentigo maligna is a precancerosis or a melanoma in situ, whose level of malignancy has not yet been definitively clarified. Recurrences are not rare after excision, even when an ample safe margin is observed. One reason for this is the existence of a subclinical ramification in the marginal area of the lentigo maligna. Such subclinical ramifications were investigated by means of excision with histological monitoring of the margins by the paraffin section technique. There was a clear relationship between the frequency of these ramifications and the clinical safe margin left in 64 excisions. With the aid of parametric evaluation methods the distribution of the subclinical portion referred to the distance from the clinical margin could be determined with a special formula. If an invasion, in the form of a lentigo maligna melanoma had already taken place, then the subclinical portion within the marginal area was significantly more extensive. For the treatment of lentigo maligna, and especially of lentigo maligna melanoma, we therefore recommend excision with histological monitoring of the margins. There were no local recurrences within an average follow-up period of about 2 1/2 years.
