Electron microscope studies of InxGav1−xAs/GaAs/Si grown by metalorganic chemical vapor deposition

The microstructure of In_xGa_1−xAs/GaAs (5 nm/5 nm, x < 0 to 1.0), as grown by a metalorganic chemical vapor deposition two-step growth technique on Si(100) at 450‡C, and subsequently annealed at 750‡C, is investigated using plan-view and cross-sectional transmission electron microscopy. The variations in resultant island morphology and strain as a function of the In content were examined through the comparison of the misfit dislocation arrays and moirés observed. The results are discussed in relation to the ways in which the island relaxation process changes for high In content.     

Research bronchoscopies do not adversely affect HIV-infected individuals' future health-care decisions

STUDY OBJECTIVES: Asymptomatic HIV-infected individuals are increasingly recruited for studies involving invasive procedures such as bronchoscopy. We sought to determine the response to and outcome of a request for a research bronchoscopy in HIV-positive individuals with no respiratory disease, and whether this would adversely affect future decisions to have a medically indicated bronchoscopy. DESIGN AND SETTING: Prospective, semistructured, questionnaire-based study in a London teaching hospital HIV outpatient clinic. PARTICIPANTS: One hundred and seven consecutive HIV-infected eligible individuals. Thirty-one healthy volunteers served as a control group for the subjective response to bronchoscopy. MAIN OUTCOME MEASURES: Subjects' attitudes and responses to requests for bronchoscopy and subsequent behavior when they required medically indicated bronchoscopy. RESULTS: Seventy-five patients (70%) agreed to the procedure in principle, predominantly for altruistic reasons. Thirty-nine subjects underwent bronchoscopy. Five percent found it worse than expected; and 79% agreed to another research bronchoscopy (performed in 11 subjects approximately 2 years later). All patients said they would undergo bronchoscopy again for diagnostic purposes (required in seven during the study). When compared to a healthy volunteer population within the same study, postbronchoscopy symptoms were similar in frequency although somewhat different in nature. Subjects felt that a clear explanation of what was involved enhanced their participation in this research. CONCLUSIONS: Invasive research procedures such as bronchoscopy can be performed and are repeatable in a healthy HIV-infected population. Performance of procedures for research purposes does not appear to adversely affect future health-care decisions.     

The application of high resolution electron microscopy to the study of oxidation

High resolution electron microscopy has been used to examine both the similarities and differences in the growth morphologies of Fe₂O₃, Cr₂O₃ as formed on iron alloys, and MgO as formed by burning Mg in moist air. A general discussion is also given of the relative advantages and disadvantages of a variety of TEM techniques as applicable to the study of oxidation phenomena.     

The relative importance of multiple inelastic scattering in the quantification of EELS

A comparison is given of energy loss results obtained for the L and K edges of aluminium as a function of specimen thickness, crystallographic orientation and collection angle. It is demonstrated that as the thickness is increased post-loss elastic scattering is generally important in reducing the fraction of electrons collected. The implications for the quantification of EELS data are discussed while a comparison of the Fe/C ratio in cementite demonstrates the improved consistency which can be obtained when comparing K and L losses at lower energy separation than are the losses for aluminium.     

The relative accuracy of axial and non-axial methods for the measurement of lattice spacings

The various different transmission electron microscopical techniques available for the measurement of lattice spacings are discussed, and the limited situations under which lattice fringe spacing measurement is the most appropriate approach are considered. The relative accuracy of measurements on images obtained under axial and non-axial conditions is further considered, and the generally greater accuracy of the latter technique demonstrated. Further results on the use of the method for the measurement of the carbon content of retained austenite in a dual phase steel are included.     

Patenting propagated data signals: what hath God wrought?

The US Patent Office is now issuing patents on propagated data signals that embody computer programs. Result: patent infringement can now occur in a mouse click. While patents have always been available for new and useful processes, machines, manufactures, and compositions of matter, the extension of patent law to computer data signals is new. After losing a series of battles in the courts, the Patent Office now considers a computer program embodied in a carrier wave to be a manufacture, and hence patentable subject matter. This rather surprising development provides a powerful weapon against software patent infringement over the Internet; and it represents a dangerous snare for the telecommunications industry. Is there anything beyond the reach of patent law? The Supreme Court remains steadfast in this: patents cannot be obtained for abstract ideas, laws of nature, and natural phenomena     

Chemical and Structural Changes in Manganese-Doped Yttria-Stabilized Zirconia Studied by Electron Energy Loss Spectroscopy Combined with Electron Diffraction

Solid solution of manganese in yttria-stabilized zirconia (YSZ) may occur in the electrolyte of solid oxide fuel cells. Possible changes in valence, coordination, and site occupancy of Mn in YSZ are of interest. Also, subsequent structural modification of the cubic YSZ, as well as the possible ordering of vacancies, has important consequences for the ionic conductivity. Electron energy loss spectroscopy was used to measure the O K and the Mn L edge of Mn in solid solution in a zirconia host lattice. The ratio Mn L ₃/ L ₂was determined for some manganese oxides and for Mn in solid solution. It is shown that the L ₃/ L ₂ratio does not simply reflect the oxidation state of the Mn ions in solid solution. Selected area diffraction experiments were also made in the TEM. This showed ordering of the cations and the anion vacancies at high doping levels. It is concluded that the number of O ions surrounding each Mn ion may be very important in interpreting the obtained L ₃/ L ₂ratio.     

The use of transmission electron microscopy for the assessment of interphase boundaries

The relative merits of the different ways in which the transmission electron microscope (TEM) has been commonly used to examine the form of interphase boundaries are assessed, and the potential application of the newly developed Fresnel Method is discussed. This paper is based on a presentation made in the symposium “The Role of Ledges in Phase Transformations” presented as part of the 1989 Fall Meeting of TMS-MSD, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Phase Transformations Committee of the Materials Science Division, ASM INTERNATIONAL.     

High resolution imaging of defects in sigma phase in a stainless steel

The high resolution axial lattice imaging technique has been applied to the study of the faults which commonly occur in the sigma phase which can be formed from ferrite in a duplex high chromium stainless steel on ageing at 973 K. It was noted that axial lattice fringe images at (001)_σ show no detailed correspondences with thickness and it was further demonstrated that lattice fringe displacements in axial images at strain free boundaries can be used to give an accurate measure of the magnitude of the associated lattice displacements. The displacement vectors associated with the common (100)_σ faults in the material were classified.