Tetrafluoro-and tetrachloro-4-pyridylnitrenes are formed on matrix photolysis of the corresponding azides and are found to be highly photostable in low-temperature matrices in contrast to nonhalogenated 4-pyridylnitrene. Matrix photolysis of 3,5-dichloro-or 3-chloro-5-cyano-2,4,6-triazidopyridines leads in rapid succession to mono-, di-, and trinitrenopyridines. The corresponding 3,5-dicyano-2,4,6-triazidopyridine does not produce an identifiable trinitrene. All the above species were identified by evaluation of the temporal evolution of the Ar matrix IR spectra and excellent agreement with DFT-calculated data.

The small-signal equivalent circuit of AlGaN/GaN HEMT is discussed It is shown that an extremely high gate voltage has to be applied to correctly determine series resistances. Effects appearing at high forward gate voltages are discussed. Good agreement between measured and simulated data has been achieved.

The algebraic quantification of nonclassicality, which naturally arises from the quantum superposition principle, is related to properties of regular nonclassicality quasiprobabilities. The latter are obtained by non-Gaussian filtering of the Glauber-Sudarshan P function. They yield lower bounds for the degree of nonclassicality. We also derive bounds for convex combinations of Gaussian states for certifying quantum non-Gaussianity directly from the experimentally accessible nonclassicality quasiprobabilities. Other quantum-state representations, such as s-parametrized quasiprobabilities, insufficiently indicate or even fail to directly uncover detailed information on the properties of quantum states. As an example, our approach is applied to multi-photon-added squeezed vacuum states.

We report on the application of infrared spectroscopic ellipsometry (IR-SE) for wavenumbers from 333cm -1 to 1200cm -1 as a novel approach to non-destructive optical characterization of free-carrier and optical phonon properties of group III-nitride heterostructures. Undoped α -GaN, α -AlN, α -Al x Ga 1-x N ( x = 0.17, 0.28, 0.5), and n -type silicon (Si) doped α -GaN layers were grown by metalorganic vapor phase epitaxy (MOVPE) on c -plane sapphire ( α -Al 2 O 3 ). The four-parameter semiquantum (FPSQ) dielectric lattice-dispersion model and the Drude model for free-carrier response are employed for analysis of the IR-SE data. Model calculations for the ordinary ( ∈ ⊥ ) and extraordinary ( ∈ || ) dielectric functions of the heterostructure components provide sensitivity to IRactive phonon frequencies and free-carrier parameters. We observe that the α -Al x Ga 1-x N layers are unintentionally doped with a back ground free-carrier concentration of 1-4 10 18 cm -3 . The ternary compounds reveal a two-mode behavior in ∈ ⊥ , whereas a one-mode behavior is sufficient to explain the optical response for ∈ || . We further provide a precise set of model parameters for calculation of the sapphire infrared dielectric functions which are prerequisites for analysis of infrared spectra of III-nitride heterostructures grown on α -Al 2 O 3 .

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