Bibliothek

Notizen: Solid-phase-epitaxial (SPE) regrowth from selectively As+-implanted amorphous Si is analyzed by cross-sectional transmission electron microscopy. SPE regrowth in the (100) wafers proceeds into both vertical and lateral directions simultaneously. For (111) samples, SPE regrowth in the diagonal direction, i.e., 〈100〉 direction near the mask edge, is dominant. In addition to the end of range defects and projected range defects, in the SPE process, defects of a third type are generated just beneath the implantation mask edge. Differences in mask material which control the applied stress at the mask edge have little influence on edge defect generation. Substrate orientation and mask pattern direction play important roles in the edge defect formation mechanism.

Notizen: B+-implanted Si layers preamorphized with 100-keV Ge+ implantation have been evaluated using Rutherford backscattering spectrometry and the van der Pauw technique. We suggest that the lower structural recovery, 98% of Si occupies substitutional sites, arises from the difference in tetrahedral covalent radii among Si, Ge, and B atoms. Electrical properties of dual Ge+/B+-implanted layers are discussed by a two-carrier model consisting of both electron and hole. The conversion temperature from the p- to the n-type varies from ∼15 to ∼ 125 °C with increasing electrical activation of the boron acceptor. The activation saturates at annealing temperatures above 800 °C. This restriction is due to the presence of the level and/or the defect induced in the preamorphization process.

Notizen: Using undulator radiation from 2 to 8 keV, quantum efficiencies [QE(E)] of gold photocathodes, microchannel plates (MCP), and silicon surface barrier (SSB) detectors have been investigated. For the gold photocathodes, the detailed structure of QE(E) near the M absorption edges has been presented. Also, the secondary electron conversion efficiency of gold has been calculated using the mass absorption coefficient given by a relativistic Hartree–Slater model and by the semiempirical values of Henke et al., respectively. Extended x-ray absorption fine structure (EXAFS) has been observed in the secondary electron current of the gold photocathode as well as in the detection current responses of an MCP and of an SSB detector. Furthermore, the new findings adding to our recent paper1 have been summarized as follows: (i) EXAFS above the Si-K edge in the MCP response depends on photon incident angles, and (ii) a little upshift of the starting point energy of EXAFS in the MCP response is observed. These detailed characteristics and their interpretation are described in the following: (i) The current responses of the MCP are obtained as a function of the incident x-ray energy for θ=13° (the bias angle of the MCP), and 40° by using a gold-monitor current. Here, θ denotes the incident angle of the photons to the channel. The data for θ=40° show a smaller jump near the Si-K edge as compared with the data for θ=13°.This is explained as follows: The incident photons for θ=13° are irradiated to and absorbed in the MCP ingredient of SiO2, while photons for θ=40° are incident to the electrode region. (The depth of the electrode coating is more than 10 μm from the MCP surface, while the photons are absorbed at less than 8 μm from the surface for θ=40°.) Thus, the data for θ=40° strongly reflect the characteristics of the electrode, but not of SiO2. The data for several values of θ consistently indicate that the height of this jump becomes smaller with increasing θ. (ii) The observed upshift of the starting point energy of EXAFS in the MCP response presents a contrast to EXAFS in the SSB detector response, in which upshift is not observed. This upshift is ascribed to the molecular structure of SiO2 (the chemical shift); that is, some valence electrons are removed from the Si atoms due to the oxidation (i.e., SiO2). Thus, the screening effects of the valence electrons on the core electron-nucleus attraction are reduced. This results in the shift of binding energy towards the higher-energy side. On the other hand, EXAFS in the SSB detector response reflects the characteristics of Si.

Notizen: The characteristics of microchannel plates (MCPs) for detection of x rays have been investigated using synchrotron radiation in the energy range from 1.8 to 8 keV. The current response curve of MCPs is measured with approximately continuous x-ray energy variation, which is added to the previous data [T. Kondoh et al., Rev. Sci. Instrum. 59, 252 (1988)]. It is confirmed that there is a minimum in the current response at the x-ray energy of about 4 keV. The precise current response curve has been completed for the wide x-ray energy range from 0.6 to 20 keV. A transition in the incident angle dependence of current response is found from the feature based on single cylindrical photocathode model for soft x rays to that based on multiple channel activation due to the penetration of x rays through channel walls for hard x rays. In the current response of MCPs the structure similar to that in EXAFS is observed near the Si K edge.

Notizen: Current response characteristics of microchannel plates (MCPs) x-ray detectors have been measured in a wide energy range from 0.6 to 82 keV using synchrotron radiation. In the current response curve with continuous photon energy, some discontinuities have been observed to correspond to absorption edges of elements which are the constituents of MCP glass and electrode materials (Si, Pb, Ba, and Fe). The dependence of the MCP response on the incident angle of x rays to the channel axis, θ, is also investigated. The characteristics change from the cot θ dependence for soft x rays (hν〈4 keV) to the sec θ one for hard x rays (hν〉60 keV). These results could provide guidelines on the design of x-ray diagnostic instruments using MCPs.