Pulsed laser deposition nanostructures

L.M. Kukreja et al., Variable band gap ZnO nanostructures grown by pulsed laser deposition. J. Cryst. Growth 268, 531-535 (2004)... 

This scale effect indicates that the electrical conductivity is nearly constant for the films varying in thickness from 60 to 2,000 nm. The measured resistance, however, decreased when the film thickness further reduced. Both DC and AC conductivity measurements indicated that there was an enhanced conductivity for film thickness of <60 nm. They further proposed three orders of magnitude larger conductivity in 1.6-nm-thick films than lattice conductivity. Since the grain size was not provided, it is unknown whether only the grain size plays a role when a film s thickness is less than 60 nm. Guo et al. deposited YSZ thin films by pulsed laser deposition on MgO substrates with thicknesses of 12 and 25 nm. The electrical conductivity was measured in both dry and humid O2. The electrical conductivity in thin films, however, was found to be four times lower than ionic conductivity in microcrystalline specimens, as shown in figure 10.8. Furthermore, they found that there is not any remarkable proton conduction in the nanostructured films when annealed in water vapor. 

Guo et al. " proposed that there exists a de-doping effect in nanometer-thick YSZ films, which results in a lower bulk conductivity in nanocrystalline YSZ (grain size 80 nm, thickness = 12 and 25 nm) than in the microcrystalline specimen. They predicted that the conductivity of nanostructured YSZ (e.g., <5 nm) will be even smaller, analyzing from a space charge model. Because XRD results were not provided, neither the crystallinity nor the existence of the second phase is known in YSZ films grown by Pulsed Laser Deposition (PLD). However, electrical measurements were carefully carried out in both dry and wet O2, and the overall conductivity in their YSZ films is lower than that of bulk YSZ (grain size > 15 pm) by a factor of 4 (figure 10.8). 

For their rich potential in various applications described in the previous section, the synthesis and assembly of various ZnO micro and nanostructures have been extensively explored using both gas-phase and solution-based approaches. The most commonly used gas-phase growth approaches for synthesizing ZnO structures at the nanometer and micrometer scale include physical vapor deposition (40, 41), pulsed laser deposition (42), chemical vapor deposition (43), metal-organic chemical vapor deposition (44), vapor-liquid-solid epitaxial mechanisms (24, 28, 29, 45), and epitaxial electrodeposition (46). In solution-based synthesis approaches, growth methods such as hydrothermal decomposition processes (47, 48) and homogeneous precipitation of ZnO in aqueous solutions (49-51) were pursued. 

Choy KL (2000) Vapour processing of nanostructured materials. In Nelwa HS (ed) Handbook of nanostructured materials and nanotechnology, vol 1. Academic, San Diego, CA, pp 533-577 Choy KL (2003) Chemical vapour deposition of coatings. Prog Mater Sci 48(2) 57-170 Chrisey D, Hubler G (eds) (1994) Pulsed laser deposition of thin films. Wiley, New York, NY Christen HM, Eres G (2008) Recent advances in pulsed-laser deposition of complex oxides. J Phys Condens Matter 20 264005... 

Many techniques have been used to prepare ZnO-based thin films and nanostructures, such as CVD, electron beam evaporation (EBE), MBE, pulsed laser deposition (PLD), sol-gel, spray pyrolysis, sputtering, and vapor phase growth. To prepare ZnO films or nanostructures, thermal oxidation of Zn and ZnS in air has also been used [124]. However, as for ZnS nanocrystals, wet methods, in this case wet oxidation, are still important techniques for SC processing [112]. 

These ZnO nanostructures are synthesized by a variety of methods including ch ical vapor deposition, sputtering, thermal evaporation, pulsed laser deposition, vapor-phase techniques, as well as ECD. ... 

The last problem of this series concerns femtosecond laser ablation from gold nanoparticles [87]. In this process, solid material transforms into a volatile phase initiated by rapid deposition of energy. This ablation is nonthermal in nature. Material ejection is induced by the enhancement of the electric field close to the curved nanoparticle surface. This ablation is achievable for laser excitation powers far below the onset of general catastrophic material deterioration, such as plasma formation or laser-induced explosive boiling. Anisotropy in the ablation pattern was observed. It coincides with a reduction of the surface barrier from water vaporization and particle melting. This effect limits any high-power manipulation of nanostructured surfaces such as surface-enhanced Raman measurements or plasmonics with femtosecond pulses. 

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