The annealing of Bi, Cr, and Mn, implanted in ZnO, has been studied by Rutherford backscattering, ion channeling, and secondary ion mass spectroscopy. Implantation of ∼1016 ions/cm2 of any of these elements produces large concentrations of Zn interstitials, but no completely amorphous region. The temperature at which these interstitials anneal is a function of the implant species. Other defects produced by the implantation, which give rise to dechanneling and a consequent increased scattering probability in the tails of backscattering spectra, anneal at significantly higher temperature. This annealing is also a function of the implant species. Motion of the implant ions themselves does not occur when the interstitials anneal; it takes place above 700 °C for Bi and Mn, and above 1000 °C for Cr.
We have measured the microwave-induced melting and damage to the near-surface region of arsenic-implanted silicon for 1–2 μs pulses at a frequency of 2.856 GHz and an incident pulse power of up to 9 MW. Rectangular samples were irradiated by single-pass TE10 traveling wave pulses inside a WR-284 waveguide, and time-resolved in situ and post-irradiation studies were performed to characterize the material modifications induced by the microwave pulses. The test chamber where the specimens were irradiated was either evacuated to a pressure of 10−7–10−6 Torr or filled with a 30-psig pressure of Freon-12. Incident, transmitted, and reflected powers were monitored with directional couplers and fast diodes. The results of the time-resolved optical measurements for samples irradiated in vacuum show that melting of the near-surface region occurs for pulse powers exceeding 3 MW, and that the surface melting is accompanied by a large increase in the reflected microwave power. The onset of the enhanced reflectivity is measured at an earlier time as the microwave power is increased, and once the abrupt increase in the reflectivity is observed, it persists throughout the remainder of the pulse. Simultaneous with the onset of surface damage, we observe a large enhancement in the emission of light from the sample. Results are presented for the temporal behavior and spectral components of the fluorescence as a function of the incident microwave power. The gas pressure in the test cell was also monitored, and a large increase in the gas pressure was detected at the same pulse power as the threshold for the sudden increase in the microwave reflectivity. The large increments in the reflected microwave power, light emission, and gas pressure are attributed to the formation of a plasma due to gas breakdown at (or near) the sample surface. Examination of the irradiated specimens shows that the melting and damage are not homogeneous over the surface, and the degree of energy deposition from the microwave pulses depends on the ambient gas in the test cell. Using secondary ion mass spectrometry, we find that microwave pulses at a power of 8 MW cause melting and vaporization of the near-surface region up to depths that exceed 1 μm.
The necessity, design, and characterization of an ultra-high purity (>99.999999%, >&nines) discharge gas delivery system for quadrupole-based glow discharge mass spectrometer are described. This system greatly reduces common contaminants arising from residual gases (e.g., CO', Arc', ArN', A d ' , etc.). The utility of the system is shown in the analysis of NIST SRM 685-W high-purity gold. Sub-ppm detection levels are readily achieved and maintained for all metals. Low background levels for some non-metals, including C, N, and 0, are also reported. The ability to quantify such species is shown in the generation of a calibration curve for carbon using NIST steel standards.One of the demands placed on our laboratory is the measurement of concentrations of nearly all elements in metal matrices down to single ppm levels. Many of these metals are difficult to dissolve and for some it is impossible to keep all elements simultaneously in solution; this renders use of solution-based elemental analytical techniques, such as inductively coupled plasma mass spectrometry, invalid. An example of such a material is the iridium-tungstenthorium alloy used to encapsulate the PUO, heat sources for deep-space probes.Several considerations make glow-discharge mass spectrometry an attractive method for us. There are, however, obstacles to overcome. One of the most persistent challenges encountered in plasma-based trace analysis by mass spectrometry is the interferences caused by molecular ions. These ions, generated by interaction of the discharge gas with itself, the components of air, and constituents of the sample, often lie at the same nominal mass positions as isotopes of interest in the sample. For the commonly used argon-based discharges, examples are at mass 56, where ArO+ obscures '6Fe, mass 54, where ArN+ interferes with %Fe, and mass 52, where both Arc+ and the major Cr isotope lie. Inductively coupled plasma mass spectrometry (ICP-MS) has only limited means of addressing this issue: the plasma operates in air at atmospheric pressure, making nitrogen and oxygen adduct ions endemic to the process. Glow discharges, on the other hand, operate in closed systems and offer the possibility of addressing the problem.There thus seems to be no inherent reason why they cannot be used for the type of analyses we are required toIn most glow-discharge mass spectrometers, the discharge cell containing the sample is housed in a high vacuum chamber. There is thus no source of gas, aside from that involved in delivering the support gas and any adsorbed gases introduced with the sample. For analysis of metals, which would not be expected to have high concentrations of adsorbed gases, it should be possible to construct a system that generates spectra virtually free of adduct ions ascribable to the components of air. To accomplish this, one must have a vacuum system with good base pressure perfOlTIl.Author for correspondence. (cu.Tom) so that outgassing of internal surfaces does not generate significant quantities of gases that migrate into the...
Thin films of Ho,Ba2Cu3O7 _ x and Y!Ba2Cu3O7 __ x were deposited on SrTiO3 and A12O3 substrates by pulsed laser deposition of high-Tc bulk superconductor pellets in vacuum. Following annealing in O2 at 800-900 °C the films were superconducting with typical Tc (50%) = 89 K and transition widths of 10 K.Rutherford backscattering spectrometry (RBS) and secondary ion mass spectrometry (SIMS) were utilized to study the stoichiometry of the asdeposited films for laser energy densities between 0.11 and 4.5 J cm"2. The films were deficient in holmium and yttrium for energy densities below 0.6 and 0.4 J cm"2, respectively. The films were stoichiometric for fluences above 0.6 J cm"2. In addition, preliminary time dependence and spectroscopic observations of the laser-produced plasma are presented. The results indicate an ablation mechanism that at high energy densities preserves stoichiometry. TEM and x-ray characterization of annealed, superconducting HO|Ba2Cu3O7 _ x films on (100) SrTiO3 showed mixed regions of epitaxially oriented 1:2:3 material with either the c axis or a axis oriented along the surface normal. The a-axis-oriented material grew preferentially in the films with b, c, twinning.
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