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ABSTRACT: We provide evidence of nanopatterning-induced bending of an ultrathin tensile strained silicon layer directly on oxide. This strained layer is achieved through the epitaxial growth of silicon on a Si(0.84)Ge(0.16) virtual substrate and subsequent transfer onto a SiO(2)-capped silicon substrate by combining hydrophilic wafer bonding and the ion-cut process. Using high resolution transmission electron microscopy, we found that the upper face of the strained silicon nanostructures fabricated from the obtained heterostructure using electron beam lithography and dry reactive ion etching displays a concave shape. This bending results from the free-surface-induced strain relaxation, which implies lattice out-of-plane expansion near the edges and concomitant contraction at the center. For a ∼ 110 nm × 400 nm × 20 nm nanostructure, the bending is associated with an angle of 1.5° between the [Formula: see text] vertical atomic planes at the edges of the ∼ 110 nm side. No bending is, however, observed at the strained Si/SiO(2) interface. This phenomenon cannot be explained by the classical Stoney's formula or related formulations developed for nanoscale thin films. Here we employed a continuum mechanical approach to describe these observations using three-dimensional numerical calculations of relaxation-induced lattice displacements.
Nanotechnology 01/2011; 22(4):045701. · 3.98 Impact Factor
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ABSTRACT: Multilayer samples of the type (YSZ|Sc2O3) × n with layer thicknesses between 8 nm (n=100) and 250 nm (n=5) were prepared on (0001) sapphire substrates by pulsed laser deposition (PLD). The samples were characterised using X-ray diffraction (XRD), scanning electron microscopy (HRSEM) and transmission electron microscopy (TEM/HRTEM, SAED (selected-area electron diffraction) and quantitative EELS (electron energy-loss spectroscopy)). The polycrystalline layers show a columnar microstructure, which is typical for the used preparation technique. The layers are highly textured and only one axial orientation relation is found between yttria-stabilised zirconia (YSZ), scandium oxide and the substrate: (0001) Al2O3‖(111) Sc2O3‖(111) YSZ. A preferred orientation relationship also exists for the azimuthal rotation of the crystallites, which was demonstrated by SAED, XRD pole figure measurements and fast Fourier transformation (FFT) of HRTEM micrographs. The interfaces between YSZ, Sc2O3 and the substrate are sharp and do not contain diffuse transition regions. Dislocations appear not to be arranged in regular arrays. With increasing interface density (thinner individual layers in the multilayer), the conductivity of the multilayers decreases. We relate this to the negative nominal misfit present at the YSZ|Sc2O3 interfaces (compressive stress in YSZ at the phase boundaries). This observation agrees well with the previously investigated case of YSZ|Y2O3 (A. Peters et al., Phys. Chem. Chem. Phys., 2008, 10, 4623), where tensile misfit strain was present in YSZ at the phase boundaries, leading to a conductivity increase.
Physical Chemistry Chemical Physics 10/2010; 12(43):14596-608. · 3.57 Impact Factor
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ABSTRACT: Silicon (Si) nanoparticles (NPs) were synthesized by transforming a Si wafer surface to ammonium silicon hexafluoride (ASH) or (NH(4))(2)SiF(6) under acid vapor treatment. Si-NPs which were found to be embedded within the polycrystalline (ASH) layer exhibit a strong green-orange photoluminescence (PL). Differential PL measurements revealed a major double component spectrum consisting of a broad band associated with the ASH-Si wafer interfacial porous oxide layer and a high energy band attributable to Si-NPs embedded in the ASH. The origin of the latter emission can be explained in terms of quantum/spatial confinement effects probably mediated by oxygen related defects in or around Si-NPs. Although Si-NPs are derived from the interface they are much smaller in size than those embedded within the interfacial porous oxide layer (SiO(x), x > 1.5). Transmission electron microscopy (TEM) combined with Raman scattering and Fourier transformed infrared (FTIR) analysis confirmed the presence of Si-NP and Si-O bondings pointing to the role of oxygen related defects in a porous/amorphous structure. The presence of oxygen of up to 4.5 at.% in the (NH(4))(2)SiF(6) layer was confirmed by energy dispersive spectroscopy (EDS) analysis.
Nanotechnology 09/2010; 21(43):435701. · 3.98 Impact Factor
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ABSTRACT: Conformal atomic layer deposition of thin Sb(2)S(3) layers takes place epitaxially on suitable substrates at 90 degrees C. More elevated deposition temperatures increase the mobility of the solid and result in the diffusion of Sb(2)S(3) along surface energy gradients. On an Sb(2)Se(3) wire that presents the high-energy c facet at its extremity, this results in the axial elongation of the wire with a Sb(2)S(3) segment. When an Sb(2)S(3) wire whose c planes are exposed on the sides is used as the substrate, the homoepitaxy collects material laterally and yields a nano-object with a rectangular cross section.
Journal of the American Chemical Society 06/2010; 132(22):7592-4. · 9.91 Impact Factor
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ABSTRACT: Vertical epitaxial short (200-300 nm long) silicon nanowires (Si NWs) grown by molecular beam epitaxy on Si(111) substrates were separately doped p- and n-type ex situ by implanting with B, P and As ions respectively at room temperature. Multi-energy implantations were used for each case, with fluences of the order of 10(13)-10(14) cm(-2), and the NWs were subsequently annealed by rapid thermal annealing (RTA). Transmission electron microscopy showed no residual defect in the volume of the NWs. Electrical measurements of single NWs with a Pt/Ir tip inside a scanning electron microscope (SEM) showed significant increase of electrical conductivity of the implanted NWs compared to that of a nominally undoped NW. The p-type, i.e. B-implanted, NWs showed the conductivity expected from the intended doping level. However, the n-type NWs, i.e. P- and As-implanted ones, showed one to two orders of magnitude lower conductivity. We think that a stronger surface depletion is mainly responsible for this behavior of the n-type NWs.
Nanotechnology 05/2009; 20(16):165706. · 3.98 Impact Factor
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ABSTRACT: Epitaxial silicon nanowires (NWs) of short heights (∼280 nm ) on Si <111> substrate were grown and doped in situ with boron on a concentration range of 10<sup>15</sup>–10<sup>19</sup> cm <sup>-3</sup> by coevaporation of atomic Si and B by molecular beam epitaxy. Transmission electron microscopy revealed a single-crystalline structure of the NWs. Electrical measurements of the individual NWs confirmed the doping. However, the low doped (10<sup>15</sup> cm <sup>-3</sup>) and medium doped ( 3×10<sup>16</sup> and 1×10<sup>17</sup> cm <sup>-3</sup> ) NWs were heavily depleted by the surface states while the high doped ( 10<sup>18</sup> and 10<sup>19</sup> cm <sup>-3</sup> ) ones showed volume conductivities expected for the corresponding intended doping levels.
Applied Physics Letters 07/2008; · 3.84 Impact Factor
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ABSTRACT: Uniformly a-axis-oriented, epitaxially twinned La-substituted Bi4Ti3O12 (BLT) thin films having the major spontaneous polarization entirely along the film normal were grown by pulsed laser deposition on yttria-stabilized zirconia-buffered Si(100) substrates covered with very thin SrRuO3 bottom electrodes. Using SrRuO3 bottom electrodes of a specific low thickness in combination with a relatively high growth rate and a high oxygen pressure, the volume fraction of the BLT (100) orientation, which is competing with the BLT (118) orientation, was increased up to 99%. In this way the growth of fully a-axis-oriented BLT films was achieved, attaining a remanent polarization of 32 μC/cm2. Initial fatigue experiments indicated hardly any fatigue after 109 switching cycles. © 2003 American Institute of Physics.
Journal of Applied Physics 04/2003; 93(9):5592-5601. · 2.17 Impact Factor
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ABSTRACT: The use of bismuth-layered perovskite films for planar-type nonvolatile ferroelectric random-access memories requires films with spontaneous polarization normal to the plane of growth. Epitaxially twinned a axis-oriented La-substituted Bi4Ti3O12 (BLT) thin films whose spontaneous polarization is entirely along the film normal were grown by pulsed laser deposition on yttria-stabilized zirconia-buffered Si(100) substrates using SrRuO3 as bottom electrodes. Even though the (118) orientation competes with the (100) orientation, epitaxial films with almost pure (100) orientation were grown using very thin, strained SrRuO3 electrode layers and kinetic growth conditions, including high growth rates and high oxygen background pressures to facilitate oxygen incorporation into the growing film. Films with the a-axis orientation and having their polarization entirely along the direction normal to the film plane can achieve a remanent polarization of 32 microcoulombs per square centimeter.
Science 07/2002; 296(5575):2006-9. · 31.20 Impact Factor
