RESUMEN
The recently commercialized helium ion microscope (HIM) has already demonstrated its outstanding imaging capabilities in terms of resolution, surface sensitivity, depth of field and ease of charge compensation. Here, we show its exceptional patterning capabilities by fabricating dense lines and three-dimensional (3D) nanostructures on a Si substrate. Small focusing spot size and confined ion-Si interaction volume of a high-energy helium ion beam account for the high resolution in HIM patterning. We demonstrate that a set of resolvable parallel lines with a half pitch as small as 3.5 nm can be achieved. During helium ion bombardment of the Si surface, implantation outperforms milling due to the small mass of the helium ions, which produces tumefaction instead of depression in the Si surface. The Si surface tumefaction is the result of different kinetic processes including diffusion, coalescence and nanobubble formation of the implanted ions, and is found to be very stable structurally at room temperature. Under appropriate conditions, a linear dependence of the surface swollen height on the ion doses can be observed. This relation has enabled us to fabricate nanopyramids and nanocones, thus demonstrating that HIM patterning provides a new 'bottom-up' approach to fabricate 3D nanostructures. This surface tumefaction method is direct, both positioning and height accurate, and free of resist, etch, mode and precursor, and it promises new applications in nanoimprint mold fabrication and photomask clear defect reparation.
RESUMEN
Pulsed laser deposition was used to grow Sr(2)FeMoO(6) films of different thicknesses on MgO(100), SrTiO(3)(100), and LaAlO(3)(100) with respective lattice mismatches of +6.2%, -1.2%, and -4.3%. Surface roughness and morphology, and film crystal quality and epitaxy were determined by atomic force microscopy and x-ray diffraction, respectively. Two-dimensional layer-by-layer growth was evident for the Sr(2)FeMoO(6) grown on MgO and SrTiO(3) with the film becoming smoother with increasing thickness. The Sr(2)FeMoO(6) films had more nucleation sites on MgO than SrTiO(3). On LaAlO(3), however, three-dimensional progressive growth of flakelike Sr(2)FeMoO(6) nanostructures was observed for all film thicknesses. High-resolution x-ray diffraction measurements indicated that the Sr(2)FeMoO(6) films are near-epitaxial and c-axis oriented on all the substrates. Reciprocal space maps further revealed that Sr(2)FeMoO(6) grows on MgO with relatively constant lattice parameters with increasing film thickness. For films thicker than 120 nm, the formation of a second phase was observed on SrTiO(3) and LaAlO(3) but not on MgO, suggesting that the formation of a second phase provides an effective strain relief in the former. These results suggested a different growth mechanism for the Sr(2)FeMoO(6) films on MgO compared to the SrTiO(3) and LaAlO(3) substrates.
RESUMEN
Monoshaped and monosized copper nanostructured particles have been prepared by potentiostatic electrochemical deposition on an ultrathin polypyrrole (PPY) film, electrochemically grown on a Si(100) substrate sputter-coated with a thin gold film or gold-film electrode (GFE). The crystal size and the number density of the copper nanocrystals have been examined by varying several deposition parameters, including the thickness of the gold film, the PPY film thickness, the applied potential, and the Cu2+ and the electrolyte concentrations for copper deposition. Optimal conditions for uniform growth ofnanocrystals well-dispersed on the GFE have been determined, along with insight into the mechanism of crystal growth. A minimum gold film thickness of 80 nm is required to eliminate the effects of the gold-silicon interface. The PPY film thickness and homogeneity principally affect the shape uniformity of the nanocrystals, while the copper deposition potential could be used to regulate the size and number density of the nanocrystals. Both the Cu2+ and electrolyte concentrations are also found to play important roles in controlling the electrodeposition of nanocrystal growth.