Modeling of abnormal grain growth in (111) oriented and nanotwinned copper

Uni-modal, not bi-modal, of abnormal grain growth has been observed in (111) oriented and nano-twinned Cu films. Because of the highly anisotropic microstructure, our kinetic analysis and calculation showed that it is the mobility which dominates the uni-modal growth, in which the lateral growth rate can be two orders of magnitude higher than the vertical growth rate. As a consequence, the abnormal grain growth has been converted from bi-modal to uni-modal.

Зависимость скорости роста и структуры III-V нитевидных нанокристаллов от площади сбора адатомов на поверхности подложки

A theoretical analysis is presented for the growth rate and structure of III-V nanowires depending on the collection area of group III adatoms on the substrate surface. An expression for the maximum possible nanowire vertical growth rate is obtained and different reasons are analyzed for its suppression in different technologies. It is shown that the maximum growth rate is proportional to the collection area and inversely proportional to the squared nanowire radius. It is demonstrated that self-catalyzed GaAs nanowires grow or shrink radially at large or small adatom collection areas, respectively, having the zincblende crystal phase in both cases. The wurtzite phase forms in GaAs nanowires growing only axially at the intermediate adatom collection areas.

Facet-control in selective area growth (SAG) of a-plane GaN by MOVPE

Selective area growth (SAG) of a-plane GaN grown on r-plane sapphire with a stripe orientation along <1-100> was investigated. The key technology of facet-control is optimizing the growth temperature and the reactor pressure. Our experiments reveal that the growth temperature determined facet form: in samples grown at 1000 °C, the structure consists of {11-22}and (000-1); with increasing growth temperature to 1050 °C, the area of {11-22} facet gradually decreases, and two new planes, (0001) and {11-20} facets form; eventually, in samples grown at 1000 oC, the {11-22} facet completely disappears, (0001) and {11-20} facet continue to increase to form a rectangle cross-section. The reactor pressure determines the ratio of the lateral growth rate and the vertical growth rate: with reactor pressure decreasing from 500 torr to 100 torr, the rectangle structure gradually decreases the height and increases the width, and the volume nearly keeps constant.

Growth and Carbon Metabolism of Tall Fescue and Zoysiagrass as Affected by Deficit Irrigation

Understanding turfgrass physiological responses to deficit irrigation will help explain potential effects of this practice on turf quality and subsequent stresses. The objective of this study was to investigate the influence of deficit irrigation growth and physiology of ‘Falcon II’ tall fescue (Festuca arundinacea Schreb) and ‘Meyer’ zoysiagrass (Zoysia japonica Steud). Turf was subjected to deficit irrigation levels of 20%, 40%, 60%, 80%, and 100% of actual evapotranspiration (ET) from June to Sept. 2001 and 2002 in Manhattan, Kans. In an earlier study, minimum deficit irrigation levels required to maintain acceptable quality (MDIL) were determined. We compared growth and physiological parameters at these MDIL with turf irrigated at 100% ET. Tall fescue had a lower canopy vertical growth rate (30% lower), canopy net photosynthesis (Pn, 14% lower), and whole-plant respiration (Rw, 11% lower) in 1 of 2 years when irrigated at the MDIL compared with 100% ET; tiller number was not reduced at the MDIL. Water use efficiency (μmol CO2 per mmol H2O) in tall fescue increased by 15% at the MDIL relative to turf receiving 100% ET in 1 of 2 years. In zoysiagrass, the MDIL had no effect on any of the growth or physiological parameters measured. Reductions in canopy vertical growth rate at the MDIL in tall fescue during deficit irrigation would likely reduce mowing requirements. Across all deficit irrigation levels, Pn was more sensitive to deficit irrigation in both grasses than was Rw, which could potentially contribute to declines in canopy vertical growth rate, tiller number, and turf quality. Zoysiagrass exhibited higher water use efficiency than tall fescue, particularly at irrigation levels 60% or more ET.

WITHIN-TREE VARIATION IN GROWTH RATE AND CELL DIMENSIONS IN THE WOOD OF BLACK LOCUST (ROBINIA PSEUDOACACIA)

Black locust (Robinia pseudoacacia L.) is regarded as an important natural resource almost throughout the world but relatively little is known about the within-tree variability of the anatomical characteristics of its wood. Discs 2 cm thick were cut at 2.25 m intervals, from the ground level to the top from ten black locust trees, 18–37-years-old, from the University Forest of Taxiarchi, Chalkidiki, Greece. The discs were used for the determination of growth rate and cell dimensions (fiber length and vessel member length and diameter) and their withintree variability (radial, oblique, vertical). Growth rate increased within the first 5–9 growth rings from the pith and then gradually decreased. Oblique variation of growth rate did not exhibit any clear tendency but a decrease at the top. In the case of vertical variation, growth rate decreased gradually with the year of cambium formation. Radial variability curves were found to be typical for the dimensions of cells (fibers, vessel members) especially for the fiber length. A rapid increase in cell dimensions was observed in the first 7–11 growth rings, the juvenile zone. Oblique and vertical variation of cell dimensions did not exhibit any clear tendencies.

Surface Instability and Associated Roughness of Pendeo-epitaxy GaN (0001) Films Grown via Metalorganic Vapor Phase Epitaxy

A growth process route that results in thin film GaN templates with a smooth surface morphology at the optimum temperature of 1020°C has been developed. Atomic force microscopy (AFM) reveals hillocks on films grown above 1020°C. Hillocks resulted from the rotation of heterogeneous steps formed at pure screw or mixed dislocations which terminated on the (0001) surface. Growth of the latter feature was controlled kinetically by temperature through adatom diffusion. The 106 cm-2 density of the hillocks was reduced through growth on thick GaN templates and regions of pendeo-epitaxy (PE) overgrowth with lower pure screw or mixed dislocations. Smooth PE surfaces were obtained at temperatures that reduced the lateral to vertical growth rate but also retarded hillock growth that originated in the stripe regions. The (1120 ) PE sidewall surface was atomically smooth, with a root mean square roughness value of 0.17 nm which was the noise limited resolution of the AFM measurements.