We study the influence of nitrogen, a potential acceptor in ZnO, on the lattice dynamics of ZnO. A series of samples grown by chemical vapor deposition ͑CVD͒ containing different nitrogen concentrations, as determined by secondary ion mass spectroscopy ͑SIMS͒, was investigated. The Raman spectra revealed vibrational modes at 275, 510, 582, 643, and 856 cm Ϫ1 in addition to the host phonons of ZnO. The intensity of these additional modes correlates linearly with the nitrogen concentration and can be used as a quantitative measure of nitrogen in ZnO. These modes are interpreted as local vibrational modes. Furthermore, SIMS showed a correlation between the concentration of incorporated nitrogen and unintentional hydrogen, similar to the incorporation of the p-dopant magnesium and hydrogen in GaN during metalorganic CVD.There is increasing interest in investigating the properties of ZnO epitaxial films with a direct gap of 3.37 eV at room temperature. 1 The material is a potential competitor for GaN-based light-emitting devices in the ultraviolet and blue spectral range. There are reports of superior ZnO properties such as a high exciton binding energy combined with a low lasing threshold density 2 and a good resistance to bombardment with high-energy particles. 3,4 For other wide-band-gap semiconductors as GaN ͑Ref. 5͒ and ZnSe ͑Ref. 6͒ controlled p-type doping is problematic. As-grown ZnO typically has n-type conductivity with background concentrations between 10 16 and 10 17 cm Ϫ3 . However, there have been reports on the synthesis of p-conducting ZnO doped with As ͑Ref. 7͒ and a Ga/N codoping 8 as well as the fabrication of a p-n-junction by excimer-laser doping. 9 In this letter, we report on doping experiments with nitrogen as a potential acceptor and its influence on the lattice dynamics of ZnO.The ZnO thin films under investigation were grown by chemical vapor deposition ͑CVD͒ using a home built epitaxy system which consists of a horizontal quartz reactor and a resistance heating with different temperature zones. Metallic zinc was kept in one zone at a temperature of 470°C the growth temperature was 650°C. We used NO 2 as oxygen precursor and NH 3 as nitrogen source for the doping experiments. The epitaxial films were deposited on GaN/sapphire templates which offers the advantage of a lattice parameter similar to ZnO. We investigated samples containing different nitrogen concentrations. Secondary ion mass spectroscopy ͑SIMS͒ was applied to determine the concentration of nitrogen and unintentional dopants such as hydrogen. The primary ion species was cesium. Nitrogen was detected as 14 N 16 O Ϫ and hydrogen as 64 Zn 1 H Ϫ clusters. The given abso-lute concentrations are accurate to within half an order of magnitude. Despite this accuracy the relative error is less than 10%. The Raman-scattering experiments were carried out in backscattering geometry with a triple-grating spectrometer equipped with a cooled charge-coupled device detector. The lines at 488 and 514.5 nm of an Ar ϩ /Kr ϩ mixedgas laser were used...

We report on GaN n-type doping using silane, germane, and isobutylgermane as Si and Ge dopants, respectively. A significant increase in tensile stress during growth is observed for Si doped samples while this is not the case for Ge doping. In addition, Ge can be doped up to 2.9 Â 10 20 cm À3 , while Si doping leads to 3-D growth already at concentrations around 1.9 Â 10 19 cm À3. The free carrier concentration was determined by Hall-effect measurements, crystal quality, and structural properties by x-ray diffraction measurements. Additionally, secondary ion mass spectroscopy and Raman measurements were performed demonstrating the high material quality of Ge doped samples. V

SummaryUsing plants as production factories for therapeutic proteins requires modification of their N -glycosylation pattern because of the immunogenicity of plant-specific sugar residues. In an attempt towards such humanization, we disrupted the genes for α 1,3-fucosyltransferase and β 1,2-xylosyltransferase in Physcomitrella patens by homologous recombination. The single ∆ fuc-t and ∆ xyl-t plants, as well as the double knockout, lacked transcripts of the corresponding genes, but did not differ from the wild-type moss in morphology, growth, development, and ability to secrete a recombinant protein, the human vascular endothelial growth factor VEGF 121 , into the culture medium. N -Glycan analysis, however, revealed the absence of 1,3-fucosyl and / or 1,2-xylosyl residues, respectively. Therefore, the modifications described here represent the key step towards the generation of moss lines suitable for the production of plant-made glycosylated biopharmaceuticals with nonallergenic N -glycans.

We report the phonon deformation potentials of wurtzite GaN and ZnO for all zone center optical phonon modes determined by Raman measurements as a function of uniaxial pressure. Despite all the structural and optical similarities between these two material systems, the pressure dependency of their vibrational spectra exhibits fundamental distinctions, which is attributed to their different bond ionicities. In addition, the LO-TO splitting of the A 1 and E 1 phonon modes is analyzed which yields insight into the uniaxial pressure dependency of Born's transverse effective charge e T ‫ء‬ .

The magnetic behavior of Fe lines on top of a continuous FeF 2 antiferromagnetic layer was investigated as a function of the orientation of the lines with respect to the applied magnetic field and a unidirectional anisotropy established by field cooling. The orientational dependence of the asymmetric loop shift, called exchange bias, shows that the competition between shape and unidirectional anisotropies modifies the exchange bias and the coercivity. Remarkably, in certain cases, exchange bias can be observed even when the applied field is perpendicular to the unidirectional anisotropy. Numerical simulations with a coherent rotation model illustrate a rich phase diagram, which originates from the noncollinearity of the involved anisotropies. Using this phase diagram, exchange bias and coercivity can be predictably tailored. In particular, different preferred magnetization directions can be designed in separately patterned structures of the same sample with identical preparation and magnetic history.