82 research outputs found
Symmetry and structure of carbon-nitrogen complexes in gallium arsenide from infrared spectroscopy and first-principles calculations
Molecular-like carbon-nitrogen complexes in GaAs are investigated both
experimentally and theoretically. Two characteristic high-frequency stretching
modes at \num{1973} and \SI{2060}{cm^{-1}}, detected by Fourier transform
infrared absorption (FTIR) spectroscopy, appear in carbon- and
nitrogen-implanted and annealed layers. From isotopic substitution it is
deduced that the chemical composition of the underlying complexes is CN and
CN, respectively. Piezospectroscopic FTIR measurements reveal that both
centers have tetragonal symmetry. For density functional theory (DFT)
calculations linear entities are substituted for the As anion, with the axis
oriented along the \hkl direction, in accordance with the experimentally
ascertained symmetry. The DFT calculations support the stability of linear
N-C-N and C-C-N complexes in the GaAs host crystal in the charge states ranging
from to . The valence bonds of the complexes are analyzed using
molecular-like orbitals from DFT. It turns out that internal bonds and bonds to
the lattice are essentially independent of the charge state. The calculated
vibrational mode frequencies are close to the experimental values and reproduce
precisely the isotopic mass splitting from FTIR experiments. Finally, the
formation energies show that under thermodynamic equilibrium CN is more
stable than CN
Amphiphilic Zwitterionic Bioderived Block Copolymers from Glutamic Acid and Cholesterol : Ability to Form Nanoparticles and Serve as Vectors for the Delivery of 6-Mercaptopurine
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