(Color online) Illustration of an incoming electric field polarizing a nanoparticle. As indicated in the figure, due to retardation, the electrons are not in phase with the applied electrical field.
(Color online) Illustration of the fabrication process for the nanoparticle preparation directly on glass. The relatively thick PMMA layer left the patterned trench with some undercut (not shown in the figure), ensuring a good lift-off without risk of detaching nanoparticles during this step.
SEM micrographs of gold nanoparticles on an ITO coated glass substrate, (a) showing an overview of a small section of the arrays of nanoparticles, and (b) showing a close-up image of four individual gold nanoparticles. The particle diameter and spacing were measured to be 149 ± 2 nm and 451 ± 2 nm, respectively.
SEM micrographs of gold nanoparticles on a borosilicate substrate. (a) and (b) show the uncoated nanoparticles, and in (c) and (d), the particles are shown after depositing a thin layer of AuPd. The effect of charging, causing the interparticle spacing as well as the individual particle size to appear smaller than they are, is evident.
(Color online) AFM image of nanoparticles on ITO is shown in (a). Brighter areas indicates more topography. In (b), a line scan from (a) (line in image) is presented. The scan shows the height information, revealing sharp and step edges on the nanoparticles. We show the uncorrected data, and it can be seen that the sample was mounted at an angle, leading to a sloping image.
(Color online) Illustration of the set-up used for measuring the extinction spectra from large arrays of nanoparticles. As can be seen, the set-up has the capability of detecting the reflected spectrum as well, but this was not exploited in this work.
(Color online) (a) Extinction spectra from three different samples of large nanoparticle arrays deposited on glass are shown. All samples have the same fabrication parameters (diameter of 150 nm and interparticle distance of 450 nm). Apart from a slight difference in intensity (particularly, sample 3), which we contribute to contamination effects, the overall agreement is excellent. In (b), the extinction spectra of gold nanoparticles, with similar size and interparticle distance, on an ITO coated glass substrate are shown. The ITO affects the LSPR peak. See discussion in main text.
(Color online) Extinction spectra of two different small size Au nanoparticles on glass. Sample 6 has particle diameters of 60610 nm and peak extinction at 59466 nm (top line), where as sample 7 has particle diameter of 4463 nm and peak extinction at about 570620 nm (bottom line). The intensity of the extinction peak appears lower compared to samples 1–5, but this is due to the fact that the interparticle distance is 450 nm as for the other samples leading to a much lower surface coverage, and hence much lower signal to noise.
(Color online) (a) Extinction spectra of nanoparticles coated with a 40 nm layer of SiO2 (right peak, sample 8) compared to the uncoated sample (left peak, sample 1). The peak is shifted 60 nm, to longer wavelengths. The increase in extinction is due to the additional layer of SiO2. In (b), the extinction spectra of aluminum nanoparticles is shown, and again compared to sample 1. Measured diameter of the aluminum nanoparticles was 135 ± 4 nm.
(Color online) Plot of the result listed in Table I . Our findings are shown with blue triangles. The error-bars are noticeably large, and this is because the values were collected from graphs presented in the respective work.
Experimental results for extinction maximum (LSPR position) of other research groups from similar studies on Au and Al nanoparticles of different sizes. The samples are produced by EBL or HCL. Interparticle distances are kept above two particle diameters to prevent near-field coupling, in order to measure the LSPR position of isolated particles.
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