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A method has been derived and is currently being used to plot normalized pole figures by computer techniques. As the pole distribution traces, i.e., intensity of the diffracted X-ray beam, versus angular position of the specimen are not an acceptable input for the computer, the data required from such traces are entered onto IBM punch cards. Corrections for defocusing effects may be readily made as the data are transferred from the Brown recorder traces to IBM punch cards. It is possible to program other correction factors into the computer operations providing that these correction factors or curves can be established accurately. The computer translates angular position of the specimen into reactiiinear coordinates which are an identical representation of stereographic coordinates. This computer method has been used in conjunction with the Schulz reflection technique, but modification of the computer program permits its use with other quantitative X-ray techniques for determining preferred orientation.
The feasibility of using computer techniques to plot inverse pole figures has been considered.
Crop phenotype is usually expressed in terms of characteristics like plant height, leaf architecture and leaf area index (LAI). In the case of maize, stalk diameter is seldom quantified because its measurement does not readily lend itself to automation. Justification for automating the measurement of stalk diameter and plant spacing is based on the finding that stalk diameter was able to account for about 65% of the variability in maize yield per plant in three irrigated field studies. A high-speed reflectance sensor and simulation apparatus was developed to explore the potential for automating maize stalk diameter assessment. The prototyped system accurately measured both stalk diameter and plant spacing in the laboratory at simulated velocities up to 12 km/h.
New evolutionary correlations have been discovered to apply to the population of Planetary Nebulae (FN) in the Magellanic Clouds. Firstly, the age of the nebular shell is found to follow a relationship τ = 890[(Mneb/M⊙) (Vexp/km s−1)]0,6 yr, which is shown to be consistent with a model in which the total energy of the ionised and swept up gas drives the expansion down the density gradient in the precursor AGE wind. Secondly, a tight correlation is found between the expansion velocity and a combination of the Excitation Class and the Hβ flux. This appears to be determined by the mass of the planetary nebula nuclear star. These correlations provide strong observational support for the idea that the PN shells are ejected at low velocity during the Asymptotic Giant Branch phase of evolution, and that they are continually accelerated during their nebular lifetimes.
Management of newborns with cyanotic CHD and bilateral adrenal haemorrhages has not previously been described in the literature. These abnormalities present unique challenges due to the potential for haemodynamic instability, need for open heart surgery and associated systemic anticoagulation in the newborn period, and the risk of catastrophic bleeding.
We report on a comprehensive study of the defect structure in GaN grown on c-oriented sapphire by gas source molecular beam epitaxy and metal organic vapour phase epitaxy. Transmission electron microscopy is used to investigate the defect structures which are dominated by threading dislocations perpendicular to the sapphire surface and stacking faults. Additionally, dislocation densities are determined. For determination of dislocation densities by x-ray diffraction we employ a model that uses the linewidth of x-ray rocking curves for this purpose. Finally, Rutherford backscattering spectrometry is performed to complement the structural investigation.
We have synthesized single-crystal epitaxial MgZnO films by pulsed-laser deposition. High-resolution transmission electron microscopy, X-ray diffraction and Rutherford backscattering spectroscopy/ion channeling were used to characterize the microstructure, defect content, composition and epitaxial single-crystal quality of the films. In these films with up to ∼ 34 atomic percent Mg incorporation, an intense ultraviolet band edge photoluminescence at room temperature and 77 K was observed. The highly efficient photoluminescence is indicative of the excitonic nature of the material. Transmission spectroscopy revealed that the excitonic structure of the alloys was clearly visible at room temperature. Post-deposition annealing in oxygen reduced the number of defects and improved the optical properties of the films. The potential applications of MgZnO alloys in a variety of optoelectronic devices are discussed.
Strain relaxed Si1−xGex buffer layers are of great importance as virtual substrates for Si1−xGex/Si quantum well structures and devices. We apply He+ ion implantation and subsequent annealing on pseudomorphic, MBE-grown Si1−xGex/Si(100) heterostructures with an implantation depth of about 100 nm below the Si1−xGex/Si interface. A narrow defect band is generated inducing the formation of strain relieving misfit dislocations during subsequent thermal annealing. Efficient strain relaxation was demonstrated for Si1−xGex layers with Ge fractions up to 30 at. %. The variation of the implantation dose and the annealing conditions changes the dislocation configuration and the He bubble structure. At a dose of 2×1016 cm−2 a high degree of relaxation is accompanied by a low density of threading dislocations of about 107 cm−2 for a Ge content of 30%. An additional increase of the Ge content can be achieved by annealing in oxygen. The oxidation of Si1−xGex leads to the formation of SiO2 while the Ge atoms are rejected from the oxide leading to a pile-up of Ge below the oxidation front. The heterostructures were analyzed using X-ray diffraction, Rutherford backscattering/channeling spectrometry and transmission electron microscopy.
Silicon wafers have been implanted with H+ (90 keV) to doses of 5.0E15/ cm2 and 2.OE16/cm2. The wafers were annealed in nitrogen at temperatures between 450 and 700°C for times between 10 and 60 min. The electrically active carrier profiles were measured by capacitance voltage and spreading resistance techniques. The residual damage was measured by TEM and RBS. The electrical measurements were essentially the same in both FZ and CZ silicon implying that oxygen is not playing a role in the donor formation which was observed. The donor concentration peaks near the projected range of the hydrogen after annealing at temperatures between 450–500°C. As reported previously 1000 H+ ions generate 1 donor in the implant peak. In addition, the donor concentration between the surface and Rp has increased more than a factor of 10 above the background concentration after a 450°C 10 min anneal. Anneals of 550°C for 30 min or more annihilates essentially all of the donors. The RBS results show small amounts of damage for the 5.0E15/cm2 implant dose but considerable crystal damage with a dose of 2.0E16/cm2, even after a 500°C, 30 min anneal. Cross-sectional TEM analysis of 500°C annealed samples showed a large number of small loops at depths corresonding to the depth of the peak electrical carrier concentration. The donors are directly correlated to the implant damage and resultant defects. SIMS data shows little diffusion for anneals of 500°C or less but after 550°C, 30 min the peak H concentration decreases by approximately a factor of 10.
We have employed high resolution ion channeling and TEM methods to investigate the damage production and dynamic annealing processes which take place in (100) silicon bombarded at elevated temperatures. Two important observations have arisen from our results i) We have observed an amorphisation process for Sb-implanted silicon at 250°C which is more akin to amorphisation processes in metals, whereby the impurity (Sb) appears to influence the stability of amorphous zones associated with individual ion tracks. ii) We have demonstrated that previously amorphised layers in silicon can be recrystallised through a solid phase epitaxial process by subsequent bombardment with He+, Ar+ and Sb+ ions at substrate temperatures of 300–400°C, which are significantly below normal thermal regrowth temperatures of >500°C.
A supralinear dose dependence for the amorphous transformation was observed in NiTi during bombardment with 2.5 MeV Ni+ ions. These results are consistent with a mechanism that requires cascade overlap to obtain a critical defect density for the amorphous transformation. Direct amorphization in the cascades was not resolvable. The temperature dependence of the minimum dose required for complete amorphous transformation had the same form as that observed for amorphization of silicon. Amorphization caused by electron bombardment required a higher dose than by ion bombardment. Different degrees of homogeneity of the damage state between ions and electrons can explain the dose dependence on particle type.
Arsenic and argon implantation damage is characterized by Rutherford backscattering in GaAs undoped VPE buffer layers grown on Cr-O doped semi-insulating substrates and capless annealed in a H2 −As4 atmosphere provided by AsH3. The damage detected in the RBS channeled spectra varies as a function of the ion mass, the implant depth and the annealing temperature of the stress-free controlled atmosphere technique. This damage is discussed in terms of the stoichiometric disturbances introduced by the implantation process. The as-implanted and annealed damage characteristics of the Ar and As implants are correlated to the electrical activation characteristics of Si and Se implants in GaAs, respectively.
We have studied the formation of heavily doped n-type layers in LPE GaInAs using ion implantation. 400 keV selenium ions have been implanted in dose ranges of 5 × 1013 to 1 × 1015 cm−2 at room temperature. For the high dose implants we have reproducibly achieved activities of 20–40% and sheet Hall mobilities of 700–1000 cm−2 V−1 s−1 and peak carrier concentrations of about 1019 cm−3. TEM and RBS results indicate that for long time anneals residual damage persists in the implanted layers, however, anneals at 800°C for 30 seconds perfectly recrystallize the implanted layers.
Samples of n+-GaAs implanted with 300 keV protons have been examined using high resolution electron microscopy, capacitance-voltage profilometry, and infrared reflectance. In contrast to previously reported results, electron microscopic examination of the as-implanted samples revealed the presence of dislocation loops and/or precipitates both near the wafer surface and at the bottom of the implanted layer. These results are corroborated by electrical and optical measurements.
Study† of Near Surface Structure and Composition for High Dose Implantation of Cr+ into Si
The dependence of the implanted layer composition on total dose, dose rate and target chamber environment for Cr+ implanted Si have been studied by means of Rutherford Back Scattering (RBS) and Auger Electron Spectroscopy (AES). Implantation of Cr+ for doses up to 2 × 1018 ions/cm2 and a fixed dose rate and energy were carried out in an ultra high vacuum (UHV) system as well as in a diffusion pumped vacuum (DPV) system. For the former, the maximum Cr concentration was about 42%. On the other hand, implantation of Cr in a DPV system resulted in a much higher peak concentration (86%) and retention.
Both the RBS and AES results positively demonstrate the existence of extensive surface carbon for a Si-rich surface and a chromium oxide layer for the Cr-rich surface. This result suggests that the interaction of oxygen or carbon occurs preferentially and depends on the surface composition.
No surface compositional variation could be observed by the RBS experiments for Cr implanted in a UHV system for different dose rates. In contrast, for implantation in a DPV system, higher concentrations can be achieved for lower dose rates.
We report the preliminary results of a study to determine the dependence of the near surface composition and structure on total dose, dose rate, vacuum condition and substrate orientation for Al implantation into Si (111) and Si (100) with doses up to 2 × 10l8 ions/cm2. Our studies include the results of Rutherford Back Scattering (RBS), Auger Electron Spectroscopy (AES) and x-ray diffraction measurements on samples implanted with a 100 keV energy in a diffusion pumped vacuum (DPV) system (10−6 Torr) with and without a LN2 trap and in an ultra high vacuum (UHV) system (2–4) x 10−8 Torr.
Results of high dose rate (50 μA/cm2 ) implantation into Si (111) in an untrapped DPV system indicate that Al segregates with a preferred (111) orientation. For a dose of 1 × 1018 ions/cm2 the surface is Al-rich to a depth of 2500Å while for lower doses the surface is silicon-rich. A carbon build-yp occurred for samples prepared by low dose rate (5 μA/cm2 ) implantation. However, no Al segregation could be observed for doses of less than 1018 ions/cm2 . A similar behavior has been observed for Si (100) except that Al segregation occurs with a polycrystalline structure. Moreover, the segregated Al is present at depths greater than the projected range.
When implantation was carried out in a DPV system with a LN2 trap, no carbon peaks could be observed by RBS regardless of the dose rate. For these conditions, as well as for the implantation of Al in an UHV system, we find Al segregation with a polycrystalline structure independent of the dose rates and target orientations we used. Al is observed at a depth greater by a factor of two than the expected value from the Rpcalculations. The Al depth penetration increases with the dose of implantation.
In this paper, the first comprehensive and computationally-efficient two-dimensional model is reported for boron implants into (100) single-crystal silicon with explicit dependence on energy, dose, implant angles, mask height, mask orientation, and rotation of the wafer during the implant. The model and its implementation into SUPREM 4 are described, and where possible, the explicit dependencies are illustrated.