Ultrathin Gold Island Films on Silanized Glass. Morphology and Optical Properties

Abstract

Evaporated gold island films have been the subject of studies dealing with a variety of spectroscopic and sensing applications. Development of these and other applications requires film stability as well as tunability of the morphology and optical properties of the island films. In the present work, ultrathin, island-type gold films were prepared by evaporation of 1.0-15.0 nm (nominal thickness) gold at a rate of 0.005-0.012 nm s -1 onto glass substrates modified with 3-mercaptopropyl trimethoxysilane (MPTS), the latter used to improve the Au adhesion to the glass. The morphology of the films, either unannealed or annealed (20 h at 200 °C), was studied using atomic force microscopy (AFM) and high-resolution scanning electron microscopy (HR-SEM). The information provided by the two imaging techniques is complementary, giving a good estimate of the shape of the islands and its variation with film thickness and annealing. The optical properties of the films were examined using transmission UV-vis spectroscopy, showing a strong dependence of the localized Au surface plasmon (SP) band on the morphology of the island films. The imaging and spectroscopy indicate a gradual transition from isolated islands to a continuous film upon increasing the Au thickness.

Preparation of Gold Nanoisland Arrays from Layer-by-Layer Assembled Nanoparticle Multilayer Films

“…Different gold nanoisland films were generated from Au NPs-PAH multilayer films with two, five or eight layers of gold nanoparticles after annealing at ~ 500 o C. The optical properties of the films were examined using transmission UV-vis spectroscopy (Figure 3), showing strong SP bands around 533, 541, and 542 nm for nanoisland films generated from Au NPs-PAH 2-, 5-, and 8-nanoparticle layer films, respectively. Similar SP bands have been observed from Rubinstein's vacuum evaporated films after annealing at 200 -250 o C. 19,21 Their study showed that the increase in the optical intensity was observed upon increasing the nominal thickness of the evaporated island films. UV-vis spectra of our nanoisland films generated from Au NPs-PAH multilayer films with 2-, 5-, or 8-layers of gold nanoparticles also showed a strong dependence of the localized gold SP band intensity on the composition of gold island films.…”

“…The morphologies of these nanoisland film arrays were quite comparable to those of nanoisland films prepared by vacuum evaporation method. [15][16][17][18][19][20][21][22] As shown in Figure 5, the nanoisland films generated from 8-nanoparticle layer films had more grains and the peak of the distribution moved to a lower value. Density of grains for nanoisland films from 5-and 8-nanoparticle layer films was estimated to be ~ 500 grains/µm 2 and ~ 950 grains/µm 2 , respectively.…”

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] In LSPR sensing, the spot size can be minimized to a small number of individual sensing elements with an in-plane width of less than ~ 100 nm. Therefore, LSPR-based nanosensors can be extremely simple, small, and light.…”

“…In addition, the LSPR nanosensors can be used in both transmission mode and reflection mode. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] When UV-vis extinction spectroscopy in transmission geometry is used for sensing, it is known as transmission localized surface plasmon resonance (T-LSPR) sensing. The major advantage of T-LSPR sensing over conventional SPR sensing lies in the low-cost samples and simple experimental setup, which can be reduced to measurements at a single wavelength in a transmission configuration.…”

“…Rubinstein's method involves a preparation of ultrathin (less than 10 nm) semi-transparent gold island films by vacuum evaporation onto inert transparent substrates. [15][16][17][18][19][20][21][22] Van Duyne's nanosphere lithographic techniques involve the fabrication of arrays of triangular silver nanoparticles in the interstices between the elements of the nanosphere deposition mask. [8][9][10][11][12][13][14] The removal of the deposition mask following thermal deposition, pulsed laser deposition, or e-beam deposition of metal leaves triangular nanoisland arrays on the solid substrates.…”