88 research outputs found
Self-compensation in semiconductors: The Zn vacancy in Ga-doped ZnO
Self-compensation, the tendency of a crystal to lower its energy by forming point defects to counter the effects of a dopant, is here quantitatively proven. Based on a new theoretical formalism and several different experimental techniques, we demonstrate that the addition of 1.4 × 10 exp 21-cm exp −3 Ga donors in ZnO causes the lattice to form 1.7 × 10 exp 20-cm exp −3 Zn-vacancy acceptors. The calculated VZn formation energy of 0.2 eV is consistent with predictions from density functional theory. Our formalism is of general validity and can be used to investigate self-compensation in any degenerate semiconductor material.Peer reviewe
Genetic diversity and host alternation of the egg parasitoid Oencyrtus pityocampae between the pine processionary moth and caper bug
Research ArticleThe increased use of molecular tools for species identification in recent decades revealed
that each of many apparently generalist parasitoids are actually a complex of morphologically
similar congeners, most of which have a rather narrow host range. Ooencyrtus pityocampae
(OP), an important egg parasitoid of the pine processionary moth (PPM), is
considered a generalist parasitoid. OP emerges from PPM eggs after winter hibernation,
mainly in spring and early summer, long before the eggs of the next PPM generation occurs.
The occurrence of OP in eggs of the variegated caper bug (CB) Stenozygum coloratum in
spring and summer suggests that OP populations alternate seasonally between PPM and
CB. However, the identity of OP population on CB eggs seemed uncertain; unlike OP-PPM
populations, the former displayed apparently high male/female ratios and lack of attraction
to the PPM sex pheromone. We studied the molecular identities of the two populations
since the morphological identification of the genus Ooencyrtus, and OP in particular, is difficult.
Sequencing of COI and ITS2 DNA fragments and AFLP analysis of individuals from
both hosts revealed no apparent differences between the OP-PPM and the OP-CB populations
for both the Israeli and the Turkish OPs, which therefore supported the possibility of
host alternation. Sequencing data extended our knowledge of the genetic structure of OP
populations in the Mediterranean area, and revealed clear separation between East and
West Mediterranean populations. The overall level of genetic diversity was rather small,
with the Israeli population much less diverse than all others; possible explanations for this
finding are discussed. The findings support the possibility of utilizing the CB and other hosts
for enhancing biological control of the PPMinfo:eu-repo/semantics/publishedVersio
An interesting Encyrtid parasitic in the larvae of carpenter-bees (Hymenoptera: Encyrtidae)
Volume: 37Start Page: 195End Page: 19
Polarity-Related Asymetry At ZnO Surfaces and Metal interfaces
Clean ZnO (0001) Zn- and (000(/1)) O-polar surfaces and metal interfaces have been systematically studied by depth-resolved cathodoluminescence spectroscopy, photoluminescence, current-voltage and capacitance-voltage measurements, and deep level transient spectroscopy. Zn-face shows higher near band edge emission and lower near surface defect emission. Even with remote plasma decreases of the 2.5 eV near surface defect emission, (0001)-Zn face emission quality still exceeds that of (000(/1))-O face. The two polar surfaces and corresponding metal interfaces also present very different luminescence evolution under low-energy electron beam irradiation. Ultrahigh vacuum-deposited Au and Pd diodes on as-received and O2/He plasma-cleaned surfaces display not only a significant metal sensitivity but also a strong polarity dependence that correlates with defect emissions, traps, and interface chemistry. Pd diode is always more leaky than Au diode due to the diffusion of H, while Zn-face is better to form Schottky barrier for Au compared with O-face. A comprehensive model accounts for the metal-and polarity-dependent transport properties
Cage for observing and rearing small arthropods
Volume: 51Start Page: 256End Page: 25
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