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We have demonstrated the effect of gradients in phase composition and microstructure of p-type CeFe4Sb12 melt-spun ribbons on Seebeck coefficient by using a thermoelectric (TE) screening tool in conjunction with x-ray diffraction. The spatial Seebeck coefficient variation was found to correlate with the changes in the phase composition and microstructure. The observed gradient was the result of a postannealing effect caused by the thermal lag between the contact surface with the roller and the free surface. Our results illustrate the application of our screening tool to the three-dimensional variation in Seebeck coefficient in a model TE material. [ABSTRACT FROM AUTHOR]

Efficient crystalline silicon heterojunction solar cells are fabricated on p-type wafers using amorphous silicon emitter and back contact layers. The independently confirmed AM1.5 conversion efficiencies are 19.3% on a float-zone wafer and 18.8% on a Czochralski wafer; conversion efficiencies show no significant light-induced degradation. The best open-circuit voltage is above 700 mV. Surface cleaning and passivation play important roles in heterojunction solar cell performance. [ABSTRACT FROM AUTHOR]

Uniaxial tensile measurements have been performed on [0001]-oriented zinc oxide nanowires (NWs) with diameters ranging from 18 to 204 nm using a homemade in situ mechanical testing system. Diameter dependence of tensile modulus (TM) is further compared with that of bending modulus (BM, shown earlier). With diameters of NWs decreasing in an intermediate range (about 30–120 nm), TM increases slower than BM, while it gets close to the latter with diameters decreasing below 30 nm; for rather large diameters, they both tend to the bulk modulus. A core-shell model is developed based on diameter-dependent and radial-distributed elastic stiffening in NWs and well explains our experimental results. [ABSTRACT FROM AUTHOR]

The chemical and electronic surface structure of ZnO:Zn3N2 (ZnO:N) thin films with different N contents was investigated by soft x-ray emission spectroscopy. Upon exposure to ambient air (in contrast to storage in vacuum), the chemical and electronic surface structure of the ZnO:N films changes substantially. In particular, we find that the Zn3N2/(Zn3N2+ZnO) ratio decreases with exposure time and that this change depends on the initial N content. We suggest a degradation mechanism based on the reaction of the Zn3N2 content with atmospheric humidity. [ABSTRACT FROM AUTHOR]

Transmission electron microscopy observations, cathodoluminescence spectroscopy and spectrum imaging are combined to investigate the emission spectrum in Cu(In,Ga)Se[sub 2] (CIGS) thin films with improved spatial resolution. We report direct evidence for a surface layer of wider band gap, which forms spontaneously in CIGS films. The existence of such a surface layer is critical for attaining high efficiency in solar cells based on these chalcopyrite semiconductor compounds. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In most Cu(In,Ga)Se[sub 2] thin films used for solar cells, there usually exist interfaces lying about 0.1 to 0.2 µm below surfaces. We report on convergent-beam electron diffraction and energy-dispersive x-ray spectroscopy study of the microstructure and chemical composition of the surface region in Cu(In,Ga)Se[sub 2] thin films. We find that the surface region and the bulk are structurally similar, with no ordered defect chalcopyrite structure observed. However, their composition is slightly different, indicating that they can have different point defect physics. Our results suggest that the subinterfaces and the bulk absorber may form homojunctions. [ABSTRACT FROM AUTHOR]

Examines the structures of high angle boundaries in the (BiPb)[sub 2]Sr[sub 2]Ca[sub 2]Cu[sub 3]O[sub x] grains by high resolution electron microscopy. Tendency of compositional variable boundaries to facet onto the (001) plane; Formation of weak link at high angle boundaries; Types of boundary structures.

Bi-based superconducting phases have been studied by transmission electron microscopy. The strong one-dimensional modulations in undoped and Ce-doped monoclinic Bi2 Sr2 CuO6 (2201) samples are different from one another. We have found a new 2201 phase containing Pb and Ca with orthorhombic symmetry in nominal (Bi0.90 Pb0.10 )2 Sr2 CaCu2 O8 crystals. Its structure with space group Bbmb and two-dimensional modulation are analogous to those of the Pb-doped higher members of the structural series Bi2 Sr2 Can-1 Cun O2n+4 . Hence, this new orthorhombic rather than the monoclinic 2201 phase should be the first member of the structural series. [ABSTRACT FROM AUTHOR]

Pb-doped Bi[sub 2] Sr[sub 2] Ca[sub 2] Cu[sub 3] O[sub 10] (2223) and Bi[sub 2] Sr[sub 2] Ca[sub 3] Cu[sub 4] O[sub 12] (2234) superconducting phases have been identified by convergent beam electron diffraction. The c parameters of the 2223 and 2234 phases are 37.6 and 44 Å, respectively. The two phases trove the same symmetry; their common point group is mmm. Both phases are modulated, but the modulations are different from and considerably weaker than that in the unleaded Bi[sub 2] Sr[sub 2] CaCu[sub 2]O[sub 8]. This work confirms for the first time the existence of the 2234 phase. [ABSTRACT FROM AUTHOR]

The magnetic anisotropy energy (MAE) of bulk D022-Mn3X (X = Ga, Ge), Mn3X/MgO, and Mn3X/STiO3(STO) heterostructures is calculated from first principles calculations. The main source of the large perpendicular magnetic anisotropy (PMA) of bulk Mn3X is identified as Mn atoms in the Mn-Mn layer. In the four heterostructures, the magnetic moment of interfacial Mn atoms was reversed when Mn3X was epitaxially grown on MgO and STO substrates. More importantly, a large in-plane tensile strain induced by lattice mismatch between Mn3X and MgO significantly changes the MAE, explaining the difficulty in experiments to obtain PMA in epitaxial Mn3X/MgO. Furthermore, interface and surface Mn atoms also help to enhance the PMA of Mn3X/STO (MgO) heterostructures due to dxy and d z 2 states changing from occupied states in bulk Mn3X to unoccupied states in the interface (surface) Mn of the heterostructures. These results suggest that the PMA of manganese compound heterostructures can be produced by decreasing the lattice mismatch with substrates and will guide the search for ultrathin manganese compound films with high PMA epitaxially grown on substrates for the application of spintronic devices. [ABSTRACT FROM AUTHOR]

Atomic-resolution Z-contrast images demonstrate unambiguously that the annealed, metalorganic chemical vapor deposition derived transparent In[sub 2]O[sub 3]–ZnO films have a polytypoid microstructure, consisting of ZnO slabs of variable width separated by single In–O octahedral layers. These In–O layers induce a polarity inversion in the two adjacent ZnO layers, which is reversed again by a mirror domain boundary inside each ZnO slab. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The atomic structure of ordered domains in Ba(Mg[sub 1/3]Nb[sub 2/3])O[sub 3] and La-doped and undoped Pb(Mg[sub 1/3]Nb[sub 2/3])O[sub 3] is studied by high-resolution Z-contrast imaging. The ordered domain structure in both doped and undoped Pb(Mg[sub 1/3]Nb[sub 2/3])O[sub 3] is determined to be in agreement with the charge balanced random-layer model and inconsistent with the space-charge model. It is shown that La doping in Pb(Mg[sub 1/3]Nb[sub 2/3])O[sub 3] enhances not only the domain size but also the degree of ordering. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]