Site symmetry analysis of the 738 nm defect in diamond

Based on a detailed analysis of polarized Raman and luminescence measurements of a ‘‘mosaic’’ diamond film, symmetry properties of a ubiquitous point defect observed in diamond films are determined. Specifically, the defect, which gives rise to emission at 738 nm, is determined unequivocally to be a 〈110〉‐oriented defect with the transition dipole moment of the center oriented along the 〈110〉 symmetry axis. These results represent the first analysis of the symmetry properties of this point defect and aid in the development of structural model of the center. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69825/2/JAPIAU-78-6-4069-1.pd

If cooperation is likely punish mildly: Insights from economic experiments based on the snowdrift game

Punishment may deter antisocial behavior. Yet to punish is costly, and the costs often do not offset the gains that are due to elevated levels of cooperation. However, the effectiveness of punishment depends not only on how costly it is, but also on the circumstances defining the social dilemma. Using the snowdrift game as the basis, we have conducted a series of economic experiments to determine whether severe punishment is more effective than mild punishment. We have observed that severe punishment is not necessarily more effective, even if the cost of punishment is identical in both cases. The benefits of severe punishment become evident only under extremely adverse conditions, when to cooperate is highly improbable in the absence of sanctions. If cooperation is likely, mild punishment is not less effective and leads to higher average payoffs, and is thus the much preferred alternative. Presented results suggest that the positive effects of punishment stem not only from imposed fines, but may also have a psychological background. Small fines can do wonders in motivating us to chose cooperation over defection, but without the paralyzing effect that may be brought about by large fines. The later should be utilized only when absolutely necessary.Comment: 15 pages, 6 figures; accepted for publication in PLoS ON

Photoluminescence investigation of GaN films grown by metalorganic chemical vapor deposition on (100) GaAs

GaN films were grown on (100) GaAs substrates by metalorganic chemical vapor deposition and were found to be of (200) cubic or (111) cubic/(0002) hexagonal phase. Their photoluminescence characteristics remained invariant with material phase. We report assignment of band‐edge photoluminescence near 3.36 eV and 3.15–3.31 eV in apparently cubic GaN to intrinsic/bound excitons and phonon‐assisted, donor‐acceptor pair recombination respectively, on the basis of observed temperature and intensity dependences. A free exciton energy of 3.375 eV is deduced at 6.5 K. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69757/2/JAPIAU-77-4-1705-1.pd

Observation of near‐band‐gap luminescence from boron nitride films

We report results from cathodoluminescence spectroscopy of boron nitride films grown on Si(100) substrates by ion‐source‐assisted magnetron sputtering of a hexagonal BN target. Three main peaks are observed in the near‐band‐gap region for hexagonal boron nitride films at energies of 4.90, 5.31, and 5.50 eV. We also report deep‐level emission spectra of predominantly cubic boron nitride films which are correlated with sample growth conditions. In particular we show that the emission intensity, position, and linewidth are strongly dependent on the substrate bias voltage used during sample growth.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69948/2/APPLAB-65-10-1251-1.pd

Site symmetry analysis of the 738 nm defect in diamond

Based on a detailed analysis of polarized Raman and luminescence measurements of a "mosaic" diamond film, symmetry properties of a ubiquitous point defect observed in diamond films are determined. Specifically, the defect, which gives rise to emission at 738 nm, is determined unequivocally to be a (1 lO)-oriented defect with the transition dipole moment of the center oriented along the (110) symmetry axis. These results represent the first analysis of the symmetry properties of this point defect and aid in the development of structural model of the center. 0 199.5 American Institute of Physics