Strong Lateral Growth Research Articles

Quasi-2D Growth of Aluminum Nitride Film on Graphene for Boosting Deep Ultraviolet Light-Emitting Diodes.

Efficient and low‐cost production of high‐quality aluminum nitride (AlN) films during heteroepitaxy is the key for the development of deep ultraviolet light‐emitting diodes (DUV‐LEDs). Here, the quasi‐2D growth of high‐quality AlN film with low strain and low dislocation density on graphene (Gr) is presented and a high‐performance 272 nm DUV‐LED is demonstrated. Guided by first‐principles calculations, it is found that AlN grown on Gr prefers lateral growth both energetically and kinetically, thereby resulting in a Gr‐driven quasi‐2D growth mode. The strong lateral growth mode enables most of dislocations to annihilate each other at the AlN/Gr interface, and therefore the AlN epilayer can quickly coalesce and flatten the nanopatterned sapphire substrate. Based on the high quality and low strain of AlN film grown on Gr, the as‐fabricated 272 nm DUV‐LED shows a 22% enhancement of output power than that with low‐temperature AlN buffer, following a negligible wavelength shift under high current. This facile strategy opens a pathway to drastically improve the performance of DUV‐LEDs.

Genetic variation within a dominant shrub structures green and brown community assemblages

Two rising challenges in ecology are understanding the linkages between above- and belowground components of terrestrial ecosystems and connecting genes to their ecological consequences. Here, we blend these emerging perspectives using a long-term common-garden experiment in a coastal dune ecosystem, whose dominant shrub species, Baccharis pilularis, exists as erect or prostrate architectural morphotypes. We explored variation in green (foliage-based) and brown (detritus-based) community assemblages, local ecosystem processes, and understory microclimate between the two morphs. Prostrate morphs supported more individuals, species, and different compositions of foliage arthropods, litter microarthropods, and soil bacteria than erect morphs. The magnitude of community compositional differences was maintained from crown to litter to soil. Despite showing strikingly similar responses, green and brown assemblages were associated with different underlying mechanisms. Differences in estimated shrub biomass best explained variation in the green assemblage, while understory abiotic conditions accounted for variation in the brown assemblage. Prostrate morphs produced more biomass and litter, which corresponded with their strong lateral growth in a windy environment. Compared to erect morphs, the denser canopy and thicker litter layer of prostrate morphs helped create more humid understory conditions. As a result, decomposition rates were higher under prostrate shrubs, despite prostrate litter being of poorer quality. Together, our results support the hypothesis that intraspecific genetic variation in primary producers is a key mediator of above- and belowground linkages, and that integrating the two perspectives can lead to new insights into how terrestrial communities are linked with ecosystem pools and processes.

Evaluation of the initial growth of electroless deposited Co(W,P) diffusion barrier thin film for Cu metallization

The formation mechanism of electroless deposited Co(W,P) films is investigated. Co(W,P) films, containing 88–90 at% of Co and 10–12 at% of W and P, are deposited directly onto p-type Si(100) substrate via Pd wet activation. Co(W,P) initially nucleates around Pd activation sites and this is followed by a strong lateral growth. Uniform Co(W,P) thin films can be obtained after 2 min deposition. Fast immersion measurement shows that the mixed potential of Co(W,P) is −0.78 V versus Ag/AgCl electrode. XRD examination shows that the Pd layer has a domination of (111) texture and the principle microstructure of the as-deposited Co(W,P) film is the hcp phase of nano-sized ε-Co. The inelastic mean free path of diffused Cu in Co(W,P) is determined to be 7.37 Å which is significantly smaller than that (9.9 Å) in pure Co, indicating that Co(W,P) is a very effective barrier layer.

Strong lateral growth and crystallization via two-dimensional allotropic transformation of semi-metal Bi film

Two-dimensional (2D) nano-objects, such as metallic nanofilms are the most fundamental building blocks for nanoelectronics devices. However, the fabrication of highly ordered nanofilms has been difficult because of well known Stranski–Krastanov growth, which results in rough growth front and high density grains. Here we report on the unusual high-quality film growth of Bi on a Si surface with atomic-level surface/interface smoothness and high film crystallinity. The formation of a newly discovered 2D allotrope was clarified to initiate its strong 2D growth. Above several-monolayer thickness, the 2D allotrope transforms into a single-crystalline film with bulk-like layered structure. Our study unveils the atomistic growth process of nano-sized Bi, and the obtained knowledge here will be generally applicable for the fabrication of various nano-devices using this intriguing material that shows rich thermal, magnetic, electronic properties in nanometer scale.

Optical and Structural Characterization of Silicon Microstructures Fabricated by Laser Interference Crystallization

ABSTRACTUniform gratings of sharply defined polycrystalline silicon lines with micrometer-sized periods were created by laser interference crystallization of amorphous silicon. Atomic force microscopy (AFM) reveals that lines fabricated with high pulse energies (380 mJ/cm2) contain large grains (dimensions up to 1.5 μm), growing in a direction perpendicular to the lines. We assign this strong lateral growth to the melting of the material in the center of the lines combined with the presence of small grains, which act as nuclei, at the interfaces with the amorphous regions. Spatially resolved Raman spectroscopy shows that size effects dominate the Raman line shape at the edge of the line, confirming the AFM results, while stress increases towards the center of the line. The spectra measured in the middle of lines created with high energies show doping effects caused by the diffusion of boron atoms from the substrate upon exposure.

Systemic Diseases on Hosts with Different Growth Patterns

To date, several reviews and books have focused on fungal pathogens in natural plant populations (Burdon 1987, Augspurger 1988, Alexander 1990). All stress the importance of fungal pathogens in shaping plant populations, since they have the potential to cause high mortality in adult plants (Paul and Ayres 1986), seedlings (Augspurger 1984) and seeds (Hendrix and Campbell 1973). Despite the awareness of the importance of pathogens, we still know very little about the general nature of host-pathogen interactions in natural populations. At present, we have no good way of predicting the immediate outcome of any interaction between a given fungus and its host plant, i.e. the effects of pathogens on the survival, biomass, and reproduction of individual hosts. Not surprisingly then, we cannot predict the likely long-term consequences of a given interaction at the population level. One reason why predictions about host-pathogen systems are few, may be a consequence of treating pathogens as if they belong to a single homogeneous group (but see Burdon 1991, 1993). However, a large number of fungal genera and families are known to include pathogenic species. Studying them closely reveals that elements of life history strategies, such as longevity, reproduction, host specificity and growth pattern, vary considerably between species of pathogens. One important life history trait is whether the fungus is non-systemic or systemic. The former group consists of fungal pathogens that are not able to grow away from the site of infection, while the latter group consists of those pathogens that are able grow internally from the site of infection to other parts of the plant, and may produce pustules along the way. Many species of rusts and smuts are systemic and important pathogens of herbs, grasses and trees (Wilson and Henderson 1966, Lindeberg 1959). Systemic fungal diseases often form a perennial mycelium within the plant. They often form confluent pustules that strongly deform the diseased part, e.g. stems can be severely twisted (Parker 1987, Wennstrdm and Ericson 1992). Disease symptoms may be seen on the entire plant (Bryzgalova 1928), but more commonly, pustules are only seen on specific parts of the plants such as leaves (e.g. Puccinia pulsatillae on Pulsatilla pratensis, Wennstrbm and Ericson 1991) or flowers (e.g. Microbotryum (Ustilago) violaceum on Silene dioica, Carlsson and Elmqvist 1992). The extent of damage caused to the host plants varies considerably between systemic diseases. For example, the systemic Puccinia pulsatillae enhances growth and increases survival of its host, Pulsatilla pratensis (Wennstrom and Ericson 1991), while the systemic Urocystis trientalis reduces survival and growth of its host, Trientalis europaea (Wennstrom and Ericson 1990). One way to understand and hopefully also develop a predictive theory of how fungal pathogens behave in plant populations and communities is to incorporate studies of the life-history of the pathogen (cf. Andrews and Rouse 1982). Life history studies should, however, also include the life-history strategies of the host, e.g. host longevity, reproduction and growth pattern. The growth pattern, and especially variation in the lateral growth of the host, may prove to be important in host-pathogen interactions, as incomplete transmission of systemic diseases has been reported for host plants with a strong lateral growth (e.g. Pady 1939, van den Ende et al. 1987, Wennstr6m and Ericson 1992). Although about 70% of all plant species in temperate zones of the world are clonal, the exact growth pattern varies considerably from species to species (van Groenendael and de Kroon 1990). For example, ramets can be formed close to the parent (hereafter called plants with weak lateral growth) or on lateral shoots or roots at some distance from the parent (hereafter called plants with a strong lateral growth). In this paper, I concentrate on perennial systemic rusts and smuts on host plants with different growth patterns. I compare characteristics of disease expression (disease levels, infection rate), and host response between hosts with weak lateral growth, and those with strong lateral growth.

The effect and transmission of one isolate of the rust Puccinia minussensis on five clones of Lactuca sibirica.

In a greenhouse experiment, one isolate of the systemic rust fungus Puccinia minussensis was applied to the host clone from which it was collected and to four other clones of the host Lactuca sibirica. The plants were grown in fertilized potting compost (N+) to promote growth and in peat (N-) to hamper growth, for three growing periods during one year. The results show that the expression of host plant resistance could not be determined visually, but there were differences in effects on the clones. The rust isolate was found to produce a significantly higher percentage of diseased shoots on clone A (the clone it was taken from). Furthermore, the rust also had the strongest effect on both biomass and shoot production on clone A compared to the other four clones. The data suggest that the rust isolate is highly adapted to the clone from which it originated. We suggest that selection in this system has not favoured a benign pathogen and that similar patterns are likely to occur for plants that (i) rarely establish by seeds; (ii) have strong lateral growth; and (iii) may persist for long periods once established.

Plate translocation in spatangoid echinoids: its morphological, functional and phylogenetic significance

Analysis of relative changes in plate position during ontogeny was made on a number of Cenozoic spatangoid echinoids: species ofBreynia, Lovenia, ProtenasterandEchinocardium. Contrary to the generally held view that adjacent ambulacral and interambulacral columns in echinoids always remain in a fixed relative position during ontogeny, many spatangoids show great fluidity in plate growth, with adjacent columns ‘sliding past’ one another during ontogeny. Furthermore, in many genera plates from one column may undergo strong lateral growth and bisect pairs of plates in adjacent rows. This phenomenon of relative plate movement, both meridional and equatorial, is herein termed ‘plate translocation’. It is considered to occur by localized resorption and redeposition in a narrow zone along adjacent plate boundaries. Plate translocation has been of considerable phylogenetic significance to spatangoids and, combined with an increase in differential allometries between plates, has been one of the most important factors in the evolution of the Spatangoida. Furthermore, the initiation of plate translocation in the apical system in certain Jurassic echinoids may have been the trigger for the migration of the periproct out of the apical system, and a major factor in the evolution of irregular echinoids. Heterochrony in plate growth has been critical in controlling the course of evolution in many lineages of spatangoid echinoids.