Laser-assisted fabrication of gold nanoparticle-composed structures embedded in borosilicate glass

Abstract

We present results on laser-assisted formation of two- and three-dimensional structures comprised of gold nanoparticles in glass. The sample material was gold-ion-doped borosilicate glass prepared by conventional melt quenching. The nanoparticle growth technique consisted of two steps - laser-induced defect formation and annealing. The first step was realized by irradiating the glass by nanosecond and femtosecond laser pulses over a wide range of fluences and number of applied pulses. The irradiation by nanosecond laser pulses (emitted by a Nd:YAG laser system) induced defect formation, expressed by brown coloration of the glass sample, only at a wavelength of 266 nm. At 355, 532 and 1064 nm, no coloration of the sample was observed. The femtosecond laser irradiation at 800 nm also induced defects, again observed as brown coloration. The absorbance spectra indicated that this coloration was related to the formation of oxygen deficiency defects. After annealing, the color of the irradiated areas changed to pink, with a corresponding well-defined peak in the absorbance spectrum. We relate this effect to the formation of gold nanoparticles with optical properties defined by plasmon excitation. Their presence was confirmed by high-resolution TEM analysis. No nanoparticle formation was observed in the samples irradiated by nanosecond pulses at 355, 532 and 1064 nm. The optical properties of the irradiated areas were found to depend on the laser processing parameters; these properties were studied based on Mie theory, which was also used to correlate the experimental optical spectra and the characteristics of the nanoparticles formed. We also discuss the influence of the processing conditions on the characteristics of the particles formed and the mechanism of their formation and demonstrate the fabrication of structures composed of nanoparticles inside the glass sample. This technique can be used for the preparation of 3D nanoparticle systems embedded in transparent materials with potential applications in the design of new optical components, such as metamaterials and in plasmonics.

Keywords: 2D and 3D nanoparticle fabrication; gold nanoparticles in glass; laser nanostructuring; optical properties of composite materials.

Figure 1

Optical absorbance spectrum of the as-prepared borosilicate glass.

Figure 2

Absorbance spectra of borosilicate glass samples annealed at 650 °C (blue curve) and at 700 °C (red curve) for 30 min.

Figure 3

TEM image of the glass sample annealed at 700 °C. The inset shows an SEAD image taken from one of the darker spots in the image.

Figure 4

Absorbance spectra of glass samples after irradiation by nanosecond laser pulses at 266 nm. a) Varying laser fluence with pulse number fixed at 600, and b) varying pulse number at a fixed laser fluence of 1.9 J/cm².

Figure 5

Absorbance spectra of samples irradiated by 600 ns laser pulses at a wavelength of 266 nm with different laser fluences and subsequently annealed at 600 °C for 30 min.

Figure 6

Absorbance spectra of glass samples irradiated by femtosecond laser pulses at 0.2 J/cm², 200 pulses (black), 0.2 J/cm², 1000 pulses (blue), and 0.8 J/cm², 1000 pulses (red). The inset shows an optical microscope image of the edge of the irradiated area at a fluence of 0.8 J/cm² after 1000 laser pulses.

Figure 7

Absorbance spectrum of a laser-irradiated zone whose optical microscope image is presented in the inset (top right). The zone was obtained by moving the sample at a speed ensuring the overlap of 1000 femtosecond pulses at a fluence of 0.8 J/cm². The high-resolution TEM image shows the structure of the material in the modified zone (bottom right). The zone marked by a circle indicates an area where the cubic structure of gold could be detected.

Figure 8

Absorbance spectra of glass samples irradiated by 10,000 pulses with laser fluences of 0.6 J/cm² (black line), 1 J/cm² (green line), 1.4 J/cm² (blue line), and 2 J/cm² (red line). The samples were then annealed at 600 °C for 30 min.

Figure 9

Dependence of the position of the plasmon resonance extinction band maximum on the gold nanoparticle diameter obtained from Equation 1.

Figure 10

Optical microscope image of a structure fabricated 1.5 mm below the surface of a gold-doped glass sample by focusing femtosecond laser radiation using a microscope objective followed by annealing at 600 °C for 30 min. The laser fluence was 1 J/cm² and the sample was moved during irradiation at a speed allowing for the overlap of 1000 laser pulses.