Physics

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We discuss several PT -symmetric deformations of superderivatives. Based on these various possibilities, we propose new families of complex PT -symmetric deformations of the supersymmetric Korteweg-de Vries equation. Some of these new models are mere fermionic extensions of the former in the sense that they are formulated in terms of superspace-valued superfields containing bosonic and fermionic fields, breaking however the supersymmetry invariance. Nonetheless, we also find extensions, which may be viewed as new supersymmetric Korteweg-de Vries equation. Moreover, we show that these deformations allow for a non-Hermitian Hamiltonian formulation. © 2008 IOP Publishing Ltd.

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Journal of Physics A: Mathematical and Theoretical

PT -symmetric extensions of the supersymmetric Korteweg-de Vries equation

We report here the synthesis, characterization, and organic thin-film transistor (OTFT) mobilities of 4,7-bis(5-(5-hexylthiophen-2-yl)thiophen-2-yl) benzo[1,2,5]thiadiazole (DH-BTZ-4T). DH-BTZ-4T was prepared in one high-yield step from commercially available materials using Suzuki chemistry and purified by column chromatography. OTFTs with hole mobilities of 0.17 cm2/(Vs) and on/off current ratios of 1 × 105 were prepared from DH-BTZ-4T active layers deposited by vacuum deposition. As DH-BTZ-4T is soluble in common solvents, solution processed devices were also prepared by spin coating yielding preliminary mobilities of 6.0 × 10-3 cm 2/(Vs). The promising mobilities and low band gap (1.90 eV) coupled with solution processability and ambient stability makes this material an excellent candidate for application in organic electronics. © 2008 American Chemical Society.

Chemistry of Materials

High-mobility organic thin film transistors based on benzothiadiazole- sandwiched dihexylquaterthiophenes

We have synthesized Mn-doped CdS nanocrystals (NCs) with size ranging from 1.8-3 nm. Photo-luminescence (PL) spectra of the doped NCs differ from that of the undoped NCs with an additional peak due to Mn d-d transitions. Electron paramagnetic resonance spectra along with X-ray absorption spectroscopy and PL spectra confirm the incorporation of Mn in the CdS lattice. The fact that emissions from surface states and the Mn d levels occur at two different energies, allowed us to study the PL lifetime decay behaviour of both kinds of emissions. {\textcopyright} Indian Academy of Sciences.

Bulletin of Materials Science

Luminescence in Mn-doped CdS nanocrystals

We show that the complex -symmetric periodic potential V(x) = -(iξsin 2x + N)2, where ξ is real and N is a positive integer, is quasi-exactly solvable. For odd values of N ≥ 3, it may lead to exceptional points depending upon the strength of the coupling parameter ξ. The corresponding Schrödinger equation is also shown to go over to the Mathieu equation asymptotically. The limiting value of the exceptional points derived in our scheme is consistent with known branch-point singularities of the Mathieu equation. © 2008 IOP Publishing Ltd.

A complex periodic QES potential and exceptional points

We study theoretically the spin reorientation transition in thin epitaxial films of NiO grown on Ag and MgO. Experimentally, the Ni spins point out-of-plane for films grown on the MgO substrate and in-plane for those on the Ag substrate. We successfully explain these opposite trends in the ground state moments for the two cases and simulate the isotropic x-ray absorption spectrum (XAS) for bulk NiO, in good agreement with experiments, on the basis of cluster configuration interaction calculations based on a NiO6 cluster. {\textcopyright} 2008 American Institute of Physics.

AIP Conference Proceedings

Theoretical investigation of the spin reorientation transition in epitaxial films of NiO

The strong blue and red electroluminescence from Eu-implanted Si O2 layers were investigated as a function of implantation and annealing conditions. It is shown that the red electroluminescence assigned to Eu3+ ions is favored by low Eu concentrations, low annealing temperatures, and short annealing times. Based on a more quantitative analysis of the electroluminescence spectra this preference is explained by a shorter supply of oxygen for higher Eu concentrations and the growth of Europium or Europium oxide clusters with increasing annealing temperatures and annealing times. The correlation between electroluminescence and microstructure is supported by transmission electron microscopy investigations and demonstrates that the electroluminescence of Eu-implanted Si O2 layers can serve as a probe for the microstructural development in the active layer of the light emitter. © 2008 American Institute of Physics.

Applied Physics Letters

Blue and red electroluminescence of Europium-implanted metal-oxide- semiconductor structures as a probe for the dynamics of microstructure

The effectiveness of AlN/BN and graphite annealing caps for ion implanted SiC was examined morphologically, structurally, chemically, and electrically. The AlN/BN cap more effectively blocks the out-diffusion of silicon because it is essentially inert. Relatively small amounts of silicon from the SiC diffuse out into the graphite cap and react with it. This has the effect of lowering the Si vapor pressure so that it does not create blow holes in this relatively weak structure. The graphite cap can be removed easily with an oxygen plasma, while warm KOH has to be used to remove the nitride cap, and not all of it can be removed after an 1800°C anneal. The out-diffusion of silicon through the graphite cap is most severe at 1800°C, where it roughens the SiC surface and forms reaction products when the Si reacts with the graphite at a significant rate. At lower temperatures these reaction products form small particulates on the surface that are visible only at higher magnifications. In those regions where the graphite cap crystallized, isolated morphological damage on the SiC surface was also detected, appearing to be in the vicinity of the grain boundaries. Scratches on the substrate surface were not affected even at temperatures as high as 1800°C. © 2008 TMS.

Journal of Electronic Materials

Structural and chemical comparison of graphite and BN/AlN caps used for annealing ion implanted SiC

Physical Review B

Ab initio Wannier-function-based correlated calculations of Born effective charges of crystalline Li 2 O and LiCl

The impact of rapid thermal annealing (RTA) in producing samples by sequential implantation of Si and Er ions into a 200 nm SiO2 layer combined with different annealing cycles as well as the corresponding roomerature visible and infrared photoluminescence (PL) have been studied. The Er-related PL intensity at 1533 nm for the samples prepared by implanting Si with subsequent annealing, followed by Er implantation, and final annealing (type I) was found to be stronger than the one produced similarly but without the first annealing step (type II). In fact, the 1533 nm peak intensity in the optimized RTA processed sample is comparable to the PL yield of the furnace-annealed sample. Moreover, the excitation wavelength (405 nm) was found to be suitable for exciting the Si=O related point defects in the SiO2 layer and can provide a PL band with a maximum at ∼580 nm. While this band was further intensified in the presence of Si nanocrystals (Si NCs), it became weaker by introducing additional Er3+ ions with a concomitant rise of the 1533 nm Er PL, confirming the visible range pumping of Er3+. The detailed spectral analyses suggest that the 580 nm band is the result of the excitation/deexcitation mechanism in molecule such as states in the Si=O or the Si=O state mediated recombination of carriers in Si NCs according to the model proposed by [Wolkin, Phys. Rev. Lett. 82, 197 (1999)]. The samples were further characterized by transmission electron microscopy and Fourier-transform infrared spectroscopy. The time-resolved PL measurements and a modeling by rate equations were also performed to determine and justify the energy migration mechanism from Si NC to the neighboring Er3+. © 2008 American Institute of Physics.

Journal of Applied Physics

Influence of annealing on the Er luminescence in Si-rich SiO2 layers coimplanted with Er ions

Hexagonal and cubic MgxZn1-xO thin films corresponding to optical band gaps of 3.52 eV, 4 eV and 6.42 eV for x = 0.15, 0.28 and 0.85 compositions were grown by pulsed laser deposition technique. The crystalline quality of the films was investigated by X-ray diffraction-rocking curve measurements and indicated a high degree of crystallinity with narrow FWHM's of 0.21°-0.59°. Rutherford back scattering-channeling spectroscopy provides channeling yields of 7-14% indicating the good crystalline quality of the thin films. X-Ray photoelectron spectroscopy measurements clearly indicated different level of oxidation states of Mg and Zn. © 2007 Elsevier B.V. All rights reserved.