103 research outputs found
Unusually strong space-charge-limited current in thin wires
The current-voltage characteristics of thin wires are often observed to be
nonlinear, and this behavior has been ascribed to Schottky barriers at the
contacts. We present electronic transport measurements on GaN nanorods and
demonstrate that the nonlinear behavior originates instead from
space-charge-limited current. A theory of space-charge-limited current in thin
wires corroborates the experiments, and shows that poor screening in high
aspect ratio materials leads to a dramatic enhancement of space-charge limited
current, resulting in new scaling in terms of the aspect ratio.Comment: 4 pages, 3 figures, to appear in Physical Review Letter
Critical aspects of substrate nanopatterning for the ordered growth of GaN nanocolumns
Precise and reproducible surface nanopatterning is the key for a successful ordered growth of GaN nanocolumns. In this work, we point out the main technological issues related to the patterning process, mainly surface roughness and cleaning, and mask adhesion to the substrate. We found that each of these factors, process-related, has a dramatic impact on the subsequent selective growth of the columns inside the patterned holes. We compare the performance of e-beam lithography, colloidal lithography, and focused ion beam in the fabrication of hole-patterned masks for ordered columnar growth. These results are applicable to the ordered growth of nanocolumns of different materials
Wafer-scale selective area growth of GaN hexagonal prismatic nanostructures on c-sapphire substrate
Selective area growth of GaN nanostructures has been performed on full 2"
c-sapphire substrates using Si3N4 mask patterned by nanoimprint lithography
(array of 400 nm diameter circular holes). A new process has been developed to
improve the homogeneity of the nucleation selectivity of c-oriented hexagonal
prismatic nanostructures at high temperature (1040\circ C). It consists of an
initial GaN nucleation step at 950 \circ C followed by ammonia annealing before
high temperature growth. Structural analyses show that GaN nanostructures are
grown in epitaxy with c-sapphire with lateral overgrowths on the mask. Strain
and dislocations are observed at the interface due to the large GaN/sapphire
lattice mismatch in contrast with the high quality of the relaxed crystals in
the lateral overgrowth area. A cathodoluminescence study as a function of the
GaN nanostructure size confirms these observations: the lateral overgrowth of
GaN nanostructures has a low defect density and exhibits a stronger near band
edge (NBE) emission than the crystal in direct epitaxy with sapphire. The shift
of the NBE positions versus nanostructure size can be mainly attributed to a
combination of compressive strain and silicon doping coming from surface mask
diffusion
Allergen specificity of early peanut consumption and effect on development of allergic disease in the Learning Early About Peanut Allergy study cohort
BACKGROUND: Early introduction of dietary peanut in high-risk infants with severe eczema, egg allergy, or both prevented peanut allergy at 5 years of age in the Learning Early About Peanut Allergy (LEAP) study. The protective effect persisted after 12 months of avoiding peanuts in the 12-month extension of the LEAP study (LEAP-On). It is unclear whether this benefit is allergen and allergic disease specific. Objective: We sought to assess the effect of early introduction of peanut on the development of allergic disease, food sensitization, and aeroallergen sensitization. METHODS: Asthma, eczema, and rhinoconjunctivitis were diagnosed based on clinical assessment. Reported allergic reactions and consumption of tree nuts and sesame were recorded by questionnaire. Sensitization to food allergens and aeroallergens was determined by means of skin prick testing and specific IgE measurement. RESULTS: A high and increasing burden of food allergen and aeroallergen sensitization and allergic disease was noted across study time points; 76% of LEAP participants had at least 1 allergic disease at 60 months of age. There were no differences in allergic disease between LEAP groups. There were small differences in sensitization and reported allergic reactions for select tree nuts, with levels being higher in the LEAP consumption group. Significant resolution of eczema and sensitization to egg and milk occurred in LEAP participants and was not affected by peanut consumption. CONCLUSION: Early consumption of peanut in infants at high risk of peanut allergy is allergen specific and does not prevent the development of other allergic disease, sensitization to other food allergens and aeroallergens, or reported allergic reactions to tree nuts and sesame. Furthermore, peanut consumption does not hasten the resolution of eczema or egg allergy
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