Nanoislands

The Ru (and surrounding Pt) nanoislands need to develop independent CO populations—a condition realized by solution CO dosing to high CO coverage on both Pt and Ru of the Pt/Ru surface. 

Figure 12.21 BB-SFG spectra of CO on a mixed metal electrode (in a CO-saturated 0.1 M H2SO4 solution) made by depositing Ru nanoislands on Pt(lll) at a coverage of 0.35 ML. The electrolyte is a 25 p-m thick solution layer (see Fig. 12.1). The acquisition time was 40 s data were obtained at = 0.1 V. As in Fig. 12.11b(II), the BBIR pulses are tuned to optimize the multiply bonded spectra, suppressing the atop intensity.

In summary, in situ STM studies of CO titration on the oxygen precovered metal surfaces have demonstrated atomic details of CO oxidation on metal surfaces and have shown excellent agreement with macroscopic kinetic measurements. Moreover, in situ studies have revealed an interesting but not well-understood, nonlinear behavior of reaction kinetics. The accelerated reaction rate observed takes place only when surface oxygen islands, either compressed oxygen islands or surface oxide islands, are reduced to the nanometer size. The nonlinear reactivity of these nanoislands is in stark contrast with the large adsorbate layer and requires further investigations. 

Figure 17. AFM images of nanoisland arrays produced using natural lithography.

Figure 18. Range of resonance wavelengths achievable by varying nanoisland geometry.

Figure 19. Scanner image of pin-printed Cy5 dye spots on glass chip bearing nanoislands.

In a second experiment, Cy5-labelled antiBSA antibodies were immobilised on a silanised glass slide precoated with metallic nanoislands using a polydimethylsiloxane (PDMS) flow-cell. The antibody solution was left for 1 hour to attach and then the cell was flushed with deionised water. The slide was then dried with N2. For this experiment, a portion of the slide was not coated with metallic nanoislands, in order to act as a reference. Figure 20 shows the image recorded using the fluorescence laser scanner mentioned previously. The enhancement in fluorescence emission between those areas with and without nanoislands (B and A, respectively) is again evident. For both chips, an enhancement factor of approximately 8 was recorded. There is considerable interest in the elucidation and exploitation of plasmonic effects for fluorescence-based biosensors and other applications. 

Figure 20. Image of fluorescence recorded from Cy5-labelled antibodies attached to (A) plain glass surface (B) surface containing metallic nanoislands.

In Ref 13, a new approach toward the preparation of Au(lll) nanoisland-arrayed electrode based on fine colloidal nanolayer-directed seeding growth has been presented. 

Some Recent Studies on the Local Reactivity of O2 on Pt3 Nanoislands Supported on Mono- and Bi-Metallic Backgrounds... 

Schalkhammer, T., Aussenegg, F.R., Leitner, A., Brunner, H., Hawa, G., Lobmaier, C., and Pittner, F. (1997). Detection of fluorophore-labelled antibodies by surface-enhanced fluorescence on metal nanoislands. SPIE 2976 129-136. 

Semiconducting CrSi2 nanocrystallites (NCs) were grown by reactive deposition epitaxy (RDE) of 0.6 nm Cr at 500, 550 and 600 C. The NCs were covered by epitaxial silicon at 700 °C with different thickness. It was observed that CrSi2 is localized nearthe surface in the form of 20 nm 2D nanoislands and 40-80 nm 3D NCs. The 2D nanoisland concentration is found to be reduced by the Si cap growth, while the large 3D NCs appear at the depth of Cr deposition and they also appear at the surface. 

The samples prepared at 500 °C, 550 °C and at 600 °C by RDE of 0.6 nm Cr without Si cap layer were analyzed by AFM to characterize the CrSi2 nanoislands. Cr deposition at 500 °C silicide islands have bimodal size distribution (10-20 nm and 40-80 nm) as it is shown in Fig. la. The bimodal size distribution indicates that significant secondary nucleation occurs during Cr deposition at 500 C in parallel to the growth of the Islands. At 550 °C a narrow CrSii island size distribution was observed as it is shown in Fig. lb. Islands had the maximal density (4T0 cm ), minimal sizes (15-20 nm) and heights (2-4 nm). The silicon surface is 30-50% covered by nanoislands. 

THERMAL OXIDATION OF MOLECULAR BEAM EPITAXIAL DEPOSITED Sn NANOISLANDS... 

We report on formation of tin-dioxide nanoislands by molecular-beam deposition of Sn on Si/Si02 substrates followed by thennal oxidation. The microstructure and phase composition of Sn and SnO nanoislands wens studied by TEM. The formation of coreshell Sn02/Sn structures as well as holes in the SnO nanoislands is documented and found to correlate with the thickness of initial Sn layer and with the oxidation temperature. The results are discussed on the basis of the Kirkendall effect with an additional assumption that absorption of oxygen atoms on the oxide surface creates an electric field that promotes the diffusion of metal ions. 

In the present work, the oxidation behavior of Sn nanoparticles and the formation of core-shell SnO/Sn and of hollow Sn02 nanoislands are investigated by transmission electron microscopy (TEM). 

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