Structural and magnetic characterizations of Mn2CrO4 and MnCr2O4 films on MgO(001) and SrTiO3(001) substrates by molecular beam epitaxy J. Appl. Phys. 109, 07D714 (2011); 10.1063/1.3545802Structural characteristics and magnetic properties of λ-MnO 2 films grown by plasma-assisted molecular beam epitaxyThe phase and orientation of manganese nitride grown on MgO͑001͒ using molecular beam epitaxy are shown to be controllable by the manganese/nitrogen flux ratio as well as the substrate temperature. The most N-rich phase, phase ͑MnN͒, is obtained at very low Mn/N flux ratio. At increased Mn/N flux ratio, the next most N-rich phase, the phase ͑Mn 3 N 2 ͒, is obtained having its c axis normal to the surface plane. Further increasing the Mn/N flux ratio, the phase ͑Mn 3 N 2 ͒ having its c axis in the surface plane is obtained. Finally, the phase ͑Mn 4 N͒ is obtained at yet higher Mn/N flux ratio. The structural phase variation with Mn/N flux ratio is due to the kinetic control of the surface chemical composition, which determines the energetically most favorable phase. For a given Mn/N flux ratio, the phase is also found to be a function of the substrate temperature, with the less N-rich phase occurring at the higher substrate temperature. The change of phase with temperature is attributed to the change in the chemical composition resulting from the diffusion of N vacancies. Since the magnetic properties of Mn x N y depend on the phase, the Mn/N flux ratio provides a way of directly controlling the magnetic properties. A phase diagram for molecular beam epitaxial growth is presented.

Atomic-scale spin-polarized scanning tunneling microscopy is demonstrated in the case of the unique surface spin structure of Mn3N2(010) at 300 K. We find that the surface spin structure is manifested as a modulation of the normal atomic row height profile. The atomic-scale spin-polarized image is thus shown to contain two components, one the normal, nonpolarized part, and the other the magnetic, spin-polarized part. A method is presented for separating these two spatially correlated components, and the results are compared with simulations based on integrated local spin density of states calculated from first principles.

Face-centered tetragonal (fct) η-phase manganese nitride films have been grown on magnesium oxide (001) substrates by molecular-beam epitaxy. For growth conditions described here, reflection high energy electron diffraction and neutron scattering show primarily two types of domains rotated by 90° to each other with their c axes in the surface plane. Scanning tunneling microscopy images reveal surface domains consisting of row structures which correspond directly to the bulk domains. Neutron diffraction data confirm that the Mn moments are aligned in a layered antiferromagnetic structure. The data are consistent with the fct model of G. Kreiner and H. Jacobs for bulk Mn3N2 [J. Alloys Compd. 183, 345 (1992)].

The effect of the Ga/N flux ratio on the Mn incorporation, surface morphology, and lattice polarity during growth by rf molecular beam epitaxy of (Ga,Mn)N at a sample temperature of 550 °C is presented. Three regimes of growth, N-rich, metal-rich, and Ga-rich, are clearly distinguished by reflection high-energy electron diffraction and atomic force microscopy. Using energy dispersive x-ray spectroscopy, it is found that Mn incorporation occurs only for N-rich and metal-rich conditions. For these conditions, although x-ray diffraction in third order does not reveal any significant peak splitting or broadening, Rutherford backscattering clearly shows that Mn is not only incorporated but also substitutional on the Ga sites. Hence, we conclude that a MnxGa1−xN alloy is formed (in this case x∼5%), but there is no observable change in the c-axis lattice constant. We also find that the surface morphology is dramatically improved when growth is just slightly metal rich. When growth is highly metal-rich, but not Ga-rich, we find that Ga polarity flips to N polarity. It is concluded that the optimal growth of Ga-polar MnGaN by rf N-plasma molecular beam epitaxy occurs in the slightly metal-rich regime.

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Articles you may be interested inCarbon doping of GaN with CBr 4 in radio-frequency plasma-assisted molecular beam epitaxy J. Appl. Phys. 95, 8456 (2004); 10.1063/1.1755431 Ga/N flux ratio influence on Mn incorporation, surface morphology, and lattice polarity during radio frequency molecular beam epitaxy of (Ga,Mn)N

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In this paper, a series of novel acridine derived bisbenzimidazolium macrocyclic fluorescent sensors were designed and synthesized. X-ray crystal structures demonstrated the self-assembly behavior of these cyclophanes in the solid state driven by hydrogen bond and π-π interactions. Anion binding studies of these sensors revealed a significant effect of the macrocyclic size and rigidity for H2PO4(-) sensing via the obvious turn-on as well as bathochromic-shift in fluorescence emission. Different cavity size or rigidity of the sensors showed different bathochromic-shifts (from 36 to 126 nm) in fluorescence emission induced by H2PO4(-), which resulted in significant color changes of fluorescence from blue to orange red, orange, green and blue-green respectively. The unique fluorescence response toward H2PO4(-) may be attributed to H2PO4(-)-induced assembly of sensors forming the excimer between two acridine rings to a different extent.