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  • 11
    Electronic Resource
    Electronic Resource
    Interfacial structure of molecular beam epitaxial grown cubic-GaN films on GaAs(001) probed by x-ray gazing-angle specular reflection (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2981-2983 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on a study of interfacial structure of GaN films grown on GaAs(001) substrates by plasma-assisted molecular beam epitaxy using x-ray grazing-angle specular reflection. We show that interfacial layers with electron densities differing from those of GaN and GaAs were formed upon deposition of GaN. It is also found that the interfacial structure of our systems depends strongly on the course of the initial layer deposition. The phase purity of the GaN films was examined by x-ray reciprocal space mapping. A simple kinetic growth model suggested by our results has been presented. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123986
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  • 12
    Electronic Resource
    Electronic Resource
    Strain relaxation in high electron mobility Si1−xGex/Si structures (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 2881-2886 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the strain relaxation in Si1−xGex/Si (001) structures with high electron mobility grown by molecular beam epitaxy. The structures contain a Si1−xGex layer with linearly graded composition, followed subsequently by a uniform composition buffer Si1−yGey, a thin Si layer serving as two-dimensional electron gas channel, and a modulationn-doped Si1−xGex layer. We found that a major part of the graded layer is basically completely strain relaxed, whereas a very thin layer close to the graded-uniform layer interface, as well as the uniform alloy buffer, are just partly relaxed. We performed also model calculations of the strain status of a graded-uniform two-layer system using an equilibrium approach. It is found that for ourSi0.7Ge0.3 systems, the residual strains of the samples with different composition, grading rate, and a uniform buffer thickness of 0.6 μm is almost the same at equilibrium. However, experiments show a clear dependence of the residual strain on the grading rate of the graded buffer. The higher the grading rate, the higher is the residual strain in the constant composition alloy buffer. This indicates that with a lower grading rate, the structure is closer to equilibrium, and is thus, thermally more stable. Furthermore, lower grading rates produce also smoother surfaces. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366281
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  • 13
    Electronic Resource
    Electronic Resource
    Strain relaxation of Ge1−xSix buffer systems grown on Ge (001) (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 789-791 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the strain relaxation behavior of biaxial tensile strained Ge1−xSix buffer systems grown on Ge (001) by a high-resolution x-ray reciprocal space mapping technique. The molecular beam epitaxy grown structures contain a linearly graded buffer, followed by a uniform buffer and a modulation-doped heterostructure with a high mobility two-dimensional hole gas in a Ge channel. Our quantitative measurements of the in-plane strain show that the lower part of the graded buffer is completely strain relaxed, while the top part of this region and the uniform alloy buffer are partly strain relaxed showing a linear increase of strain towards to surface. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115468
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  • 14
    Electronic Resource
    Electronic Resource
    Evolution of strain relaxation in compositionally graded Si1−xGex films on Si(001) (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 223-225 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-resolution x-ray reciprocal space mapping was employed to determine the in-depth strain distribution of Si1−xGex films with linear composition gradings between 4.2% and 15% Ge per μm, and thicknesses between 0.4 and 1.7 μm. The variation of grading and thickness parameters of the samples provides a complete picture of the overall relaxation behavior of linearly graded epilayers. The x-ray data show a top layer of grading-dependent residual strain whereas the lower parts of the films are completely and/or partly relaxed with respect to the Si substrate. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114674
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  • 15
    Electronic Resource
    Electronic Resource
    Surface scattering of x rays from InP (001) wafers (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 3317-3319 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the surface scattering of x rays from mechanical-chemical polished InP (001) wafers with sulfur and/or iron doping. The scattering intensities in the scans transverse to the specular reflection rod were found to contain two components. A simple surface model was proposed to explain the experimental data. The results were also compared with those obtained from crystal truncation rod measurements. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112446
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  • 16
    Electronic Resource
    Electronic Resource
    Relaxed Ge0.9Si0.1 alloy layers with low threading dislocation densities grown on low-temperature Si buffers (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 3160-3162 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Relaxed GexSi1−x epilayers with high Ge fractions but low threading dislocation densities have been successfully grown on Si (001) substrate by employing a stepped-up strategy and a set of low-temperature GeySi1−y buffers. We show that even if the Ge fraction rises up to 90%, the threading dislocation density can be kept lower than 5×106 cm−2 in the top layers, while the total thickness of the structure is no more than 1.7 μm. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121579
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  • 17
    Electronic Resource
    Electronic Resource
    Relaxed Si0.7Ge0.3 layers grown on low-temperature Si buffers with low threading dislocation density (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3132-3134 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Si0.7Ge0.3 epilayers with low threading dislocation density have been grown on Si (001) substrates by introducing a low temperature Si buffer. Such a structure can be used as the buffer for the growth of device structures. In comparison with the conventional compositionally graded buffer system, it has the advantages of having lower threading dislocation density, smaller thickness for required degree of relaxation, and smoother surface. Experimental evidence suggests that an anomalous relaxation mechanism has been involved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120268
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  • 18
    Electronic Resource
    Electronic Resource
    X-ray analysis of spontaneous lateral modulation in (InAs)n/(AlAs)m short-period superlattices (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 219-221 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The lateral composition modulation in (InAs)n/(AlAs)m short-period superlattices was studied by means of synchrotron x-ray diffraction. By choosing specific diffraction vectors having a large component closely parallel to the modulation direction, we are able to observe a number of lateral satellite peaks around the zero-order short-period superlattice peak. A model, incorporating both composition and strain, is used to simulate the intensities of these satellites. Our results provide a quantitative fit and permit the evaluation of the composition amplitude. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1338499
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  • 19
    Electronic Resource
    Electronic Resource
    Direct and indirect effects of elevated CO2 on transpiration from Quercus myrtifolia in a scrub-oak ecosystem (2003)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 9 (2003), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Elevated atmospheric carbon dioxide (Ca) usually reduces stomatal conductance, but the effects on plant transpiration in the field are not well understood. Using constant-power sap flow gauges, we measured transpiration from Quercus myrtifolia Willd., the dominant species of the Florida scrub-oak ecosystem, which had been exposed in situ to elevated Ca (350 µmol mol−1 above ambient) in open-top chambers since May 1996. Elevated Ca reduced average transpiration per unit leaf area by 37%, 48% and 49% in March, May and October 2000, respectively. Temporarily reversing the Ca treatments showed that at least part of the reduction in transpiration was an immediate, reversible response to elevated Ca. However, there was also an apparent indirect effect of Ca on transpiration: when transpiration in all plants was measured under common Ca, transpiration in elevated Ca-grown plants was lower than that in plants grown in normal ambient Ca. Results from measurements of stomatal conductance (gs), leaf area index (LAI), canopy light interception and correlation between light and gs indicated that the direct, reversible Ca effect on transpiration was due to changes in gs caused by Ca, and the indirect effect was caused mainly by greater self-shading resulting from enhanced LAI, not from stomatal acclimation. By reducing light penetration through the canopy, the enhanced self-shading at elevated Ca decreased stomatal conductance and transpiration of leaves at the middle and bottom of canopy. This self-shading mechanism is likely to be important in ecosystems where LAI increases in response to elevated Ca.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2003.00557.x
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  • 20
    Electronic Resource
    Electronic Resource
    Leaf senescence of Quercus myrtifolia as affected by long-term CO2 enrichment in its native environment (2000)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 6 (2000), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The long-term effects of elevated (ambient plus 350 μmol mol−1) atmospheric CO2 concentration (Ca) on the leaf senescence of Quercus myrtifolia Willd was studied in a scrub-oak community during the transition from autumn (December 1997) to spring (April 1998). Plants were grown in large open-top chambers at the Smithsonian CO2 Research Site, Merritt Island Wildlife Refuge, Cape Canaveral, Florida. Chlorophyll (a + b) concentration, Rubisco activity and N concentration decreased by 75%, 82%, and 52%, respectively, from December (1997) to April (1998) in the leaves grown at ambient Ca. In contrast, the leaves of plants grown at elevated Ca showed no significant decrease in chlorophyll (a + b) concentration or Rubisco activity, and only a 25% reduction in nitrogen. These results indicate that leaf senescence was delayed during this period at elevated Ca. Delayed leaf senescence in elevated Ca had important consequences for leaf photosynthesis. In elevated Ca the net photosynthetic rate of leaves that flushed in Spring 1997 (last year's leaves) and were 13 months old was not different from fully-expanded leaves that flushed in 1998, and were approximately 1 month old (current year's leaves). In ambient Ca the net photosynthetic rate of last year's leaves was 54% lower than for current year's leaves. When leaves were fully senesced, nitrogen concentration decreased to about 40% of the concentration in non-senesced leaves, in both CO2 treatments. In April, net photosynthesis was 97% greater in leaves grown in elevated Ca than in those grown at ambient. During the period when elevated Ca delayed leaf senescence, more leaves operating at higher photosynthetic rate would allow the ecosystem dominated by Q. myrtifolia to gain more carbon at elevated Ca than at ambient Ca.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2000.00347.x
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