ISSN 10876596, Glass Physics and Chemistry, 2015, Vol. 41, No. 6, pp. 593–596. © Pleiades Publishing, Ltd., 2015. Original Russian Text © G.A. Sycheva, V.A. Tsekhomskii, 2015, published in Fizika i Khimiya Stekla.
Optical and Crystallization Properties of Photostructured Lithium Silicate Glass with Different Contents of Gold Nanoparticles G. A. Sychevaa and V. A. Tsekhomskiib a
Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences, St. Petersburg, 199034 Russia email:
[email protected] bSt. Petersburg National Research University of Information Technologies, Mechanics and Optics, St. Petersburg, 197101 Russia Received October 12, 2014
Abstract—A study has been performed, in which the crystallization and optical properties of glass of the sto ichiometric composition of lithium disilicate 33.5Li2O · 66.5SiO2 mol % has been studied on the same sam ples of photostructured glass with additives of the photosensitive gold impurity of 0.03 and 0.003 wt % above 100%. It was shown that the same amount of the crystal phase in glass with different amounts of the photo sensitive gold impurity can be obtained by varying the Xray irradiation time. The position of the surface plas mon resonance does not change. Keywords: gold nanoparticles, surface plasmon resonance, heterogeneous crystallization, photostructured glass DOI: 10.1134/S1087659615060164
INTRODUCTION In glass containing photosensitive impurities (e.g., gold), the free electrons reduce the ions’ impurity under the action of Xray radiation, transferring them into the atomic state and creating a latent image in the irradiated places. Such glass is called photostructured. At the increased temperature, gold atoms form nano particles, which serve as the crystallization centers of the main nonmetal phase of the used glass. The nucle ation rate of the crystals in the regions subjected to the preliminary irradiation is by an order of magnitude higher than in the nonirradiated glass. The crystalliza tion of the photostructured regions of the glass leads to the development of a latent image. The surface plas mon resonance (SPR) of nanoparticles (NPs) of met als arises during the interaction between the electro magnetic radiation and metal nanoparticles, which are formed under the action of the Xray radiation and thermal processing of such glass. A sharp increase in the intensity of absorption and scattering occurs on a certain wavelength of the incident light being in reso nance with the intrinsic frequency of the vibrations of electrons on the surface of the particles. A series of investigations dealing with the study of different stages of the creation of the latent and devel oped images in glass of different compositions was performed in [1–3]. The ways of the synthesis of pho tostructured glass and their effect on the nucleation parameters of crystals of the main crystal phase formed in this glass are studied in detail in [4, 5]. In [6, 7] the mechanisms of the heterogeneous and
homogeneous crystallization in glass of the tium sili cate system with the Li2O content ranging from 23.40 to 46.00 mol % without additives and with photosensitive gold and silver additives and under the action of the Xray irradiation were compared, the nucleation rates of the crystals were determined in a wide range of compositions, and their temperature dependences were plotted. All these studies [6, 7] were performed on glass with the photosensitive impurity content of 0.03 wt % above 100%. This work is aimed at studying and comparing the crystallization and optical proper ties of glass of the lithium disilicate composition with gold additives of 0.03 and 0.003 wt % above 100%. OBJECTS AND METHODS OF STUDIES The charge for the synthesis of glass was prepared in the way described in [8]. Glass was synthesized in a smelting furnace with carbide heaters and worked out by casting on a massive metal plate. According to the results of the chemical analysis, both types of glass had the composition 33.5Li2O · 66.5SiO2 mol % with an accuracy of ±0.5% for each oxide. Glass 1 contained Au 0.03 wt %, was transparent with a ruby color, glass 2 with Au content of 0.003 wt % had only a weak pink hue. Thermal processing was performed in an electric shaft furnace of the resistive shaft processing labora tory type, the accuracy of temperature maintenance was ±1.5°C. The irradiation of glass and the Xray phase analysis (XPA) of the samples wasa performed on a DRON2.0 diffractometer, CuKαradiation; at a
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(b)
(c)
(d)
Fig. 1. External view of the initial (a, b), irradiated and crystallized glass (c, d). Mode of thermal processing of samples c, d: nucle ation of crystals at 450°C for 24 h, development of crystals at 600°C, 10 min. The diameter of the irradiated spot is 0.86 cm.
working voltage of 30 kV and current of 20 mA; the counter rotation rate was 2 degrees/min. The absorp tion of the Xray radiation was taken into account by calculating the thickness of the layer of the halfvalue attenuation of radiation Δ. For the glass of the given composition Δ is 0.1 mm. The crystallization kinetics of lithium disilicate were studied by the development method. The main parameter describing the nucleation kinetics of crys tals in glass, independent of whether it is homoge neous or heterogeneous, is the stationary nucleation rate of crystals Ist = dn/dt, where n is the number of nucleated crystals and t is the time in which they orig inated. The number of nucleated crystals n was deter mined by calculating the number of particles in the sample on a Jenaval microscope (Carl Zeiss, Ger many) optical microscope of transmitted light. Plates with the thickness of 0.2 mm were used for calculating the number of crystals. The position of the plate was strictly fixed with respect to the external surface of the irradiated sample. Samples with the linear dimensions of 10 × 10 mm and thickness 2 mm were prepared for studies of their optical properties. Samples were ground on a diamond disk and a steel disk with a cloth material coating (cerium(IV) oxide as an abrasive) was used for polish ing. The optical absorption spectra of the samples was measured on a Perkin Elmer Lambda 650 spectropho
Optical density
2.5 2.0 3
1.5
2 1
EXPERIMENTAL RESULTS AND THEIR DISCUSSION Samples of glass 1 were irradiated for 10, 20, 30, 40, 50, and 64 min; glass 2, for 30, 64, 120, 150, and 240 min. Then the samples were exposed in a muffle furnace at the temperatures of 100, 200, 300, 350, 400, and 450°C for 1 h. In order to study the crystallization properties, the samples were subjected to a twostage thermal processing. First they were exposed in the temperature interval of the nucleation of lithium disil icate crystals (400–520°C) with the step of 10°C for the time necessary for achieving the stationary nucle ation rates of crystals [7]. Then the samples were developed (grown to dimensions visible in the optical microscope) at the temperature of 600°C for 10 min. It should be noted that according to the XPA data, lithium disilicate crystallizes in the specified tempera turetime mode. Figure 1 shows the external view of the initial, irra diated, and crystallized glass. The nucleation of the crystals on the irradiated regions of the samples (Figs. 1c, 1d) occurred according to the heteroge neous mechanism with the high values of the station ary nucleation rates. In [1–7, 9] an explanation of this process is given. In the irradiated zone, the Au nano particles are formed according to the scheme
Au + + e − → Au 0; x Au 0 → Au 0x .
1.0 0.5 0 250 300 350 400 450 500 550 600 650 700 λ, nm Fig. 2. Absorption spectra of samples of glass 1 after Xray irradiation for 10 (1), 30 (2) and 64 min (3).
tometer at room temperature in the interval of 250– 900 nm. The measurement step was 1 nm. The inte gration time of the measurement step was 0.1 s. Elec tron microscopy was performed on an EM125 trans mission electron microscope at the accelerating volt age of 75 kV. We used the method of celluloidcarbon replicas. In this method the electron beam passes not through the sample but through a replica of its surface.
(1)
The nucleation of lithium disilicate crystals takes place on Au nanoparticles as heterogeneous crystalli zation centers. The nonirradiated regions remain transparent and the nucleation of lithium disilicate crystals in them occurs according to the slow homoge neous mechanism. Optical absorption of glass 1. Variation of the size of the nanoparticles under the action of the Xray radia
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OPTICAL AND CRYSTALLIZATION PROPERTIES OF PHOTOSTRUCTURED LITHIUM (а)
(b)
(c)
0.5 μm
0.3 μm
0.7 μm
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(d)
1 μm
Fig. 3. Electronmicroscopy pictures of samples of glass 1 subjected to CuKα irradiation for 10 (a), 30 (b), 40 (c), 64 min (d).
tion and temperature. Figure 2 shows the absorption spectra of samples of glass 1 subjected to Xray irradi ation for 10, 30, and 64 min. It can be seen in Fig. 2 that for all samples, the SPR maximum is detected in the region of 530 nm, which indicates the presence of colloid gold nanoparticles in the glass [9–11]. According to the quasistatic mode of the Mie theory, the position of the absorption max imum if the surface plasmon resonance of the spheri cal NPs with a diameter of less than 20 nm does not depend on the size and is determined by factors such as the refractive indices of the surrounding medium and the particle itself [9]. The full width at the half maximum (FWHM), according to this theory [10], depends on the NP size according to the expression
d = 2v F Δ ω1 2 .
(2)
Here d is the diameter NP, vF is the Fermi velocity in metal (for Au it is 1.39 × 108 cm/s) and Δω1/2 is the FWHM of the absorption band in the angular units ω = c/λ, where c is the speed of light 3 × 1011 cm/s and λ is the wavelength in cm. 5.5
d, nm
5.0 4.5 4.0 3.5 50 100 150 200 250 300 350 400 450 500 T, °C
Using expression (2), we calculated the variation of the NP Au size with the increase in the duration of the Xray irradiation. It is +15% (from 4.25 nm for the irradiation time tirr = 10 min to 4.9 nm for tirr = 64 min). This result (the tendency to an increase in the NP size with the increase in the duration of the Xray radiation) is also confirmed by electronmicroscopy data (Fig. 3). The NP Au size decreases monotonically with the increase in the processing temperature from 100 to 400°C of samples of glass 1irradiated for 10 min (Fig. 4). Optical absorption of glass 2. Figure 5 shows the absorption spectra of samples of glass 2 subjected to Xray irradiation for 10, 30, 64, 90, 120, and 240 min. The gold peak in the region of 530 nm characteristic for colloid nanoparticles at a low irradiation duration is expressed very weakly; it is not noticeable until after irradiation for 120 min, and after 240 min, it is com parable to the peak for glass 1 irradiated by the CuKα radiation for tirr = 10 min. Comparison of the crystallization properties of glass 1 and 2. Figure 6 shows the dependence of the number of crystals n on the irradiation time tirr by Xray for glass 1 and 2. The number of crystals in both types of glass was calculated on the same depth of the sample (0.5 mm from the irradiated surface). It is important to take this into account in order to compare the number of crystals in the regions that got the same irradiation dose. It is seen in Fig. 6 (curve 1) that a tendency to sat uration for glass 1 is revealed already after the irradia tion time on the order of 10 min. In glass 2 with the lower gold content, saturation is achieved only after 240 min of irradiation (Fig. 6, curve 2), which is in agreement with the data on studies of the optical den sity. The presence of saturation on the dependences of the crystallization degree n(t) of photostructured glass is a consequence of the complete action of gold nano particles as the crystallization catalyst. CONCLUSIONS
Fig. 4. Temperature dependence of the NP Au size in glass 1 irradiated by CuKα for 10 min. The size of the particles was calculated from the FWHM of the plasmon resonance peak. GLASS PHYSICS AND CHEMISTRY
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recommended for the preparation of glass substrates used as biochips and biosensors (nanostructures of noble metals). Being plasmon concentrators, they increase the local amplitude of the field of the electro magnetic wave that leads to an increase in the lumi nescence of the studied objects. In addition, the nucleation of the crystals on the gold nanoparticles being an independent problem of the heterogeneous nucleation is of direct relevance to the problem of glass formation on the whole.
Optical density
4 3 2 3 6
2
1
5 4
1
0 250
350
450
550 λ, nm
650
750
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Fig. 5. Absorption spectra of samples of glass 2 after the Xray irradiation for 10 (1), 30 (2), 64 (3), 90 (4), 120 (5) and 240 (6) min.
1
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REFERENCES
n × 10–6, mm–3
10 8 2
6 4 2 0
50
100
ACKNOWLEDGMENTS We are grateful to I.A. Drozdova (Laboratory of structural chemistry of oxides, Grebenshchikov Insti tute of Silicate Chemistry, Russian Academy of Sci ences) for providing the electronmicroscopy pictures.
150 200 tirr, min
250
300
Fig. 6. Dependence of the number of crystals n on the Xray irradiation time tirr for glass 1 (1) and 2 (2). Prelim inary thermal processing at 460°C for 5 h, development at 600°C for 10 min.
ties was studied on the same photostructured glass of a lithium disilicate composition with gold additives of 0.03 and 0.003 wt % above 100%. It was shown that the same amount of the crystal phase in glass with differ ent amounts of the photosensitive gold impurity can be obtained by varying the time of the Xray irradiation. The saturation effect was found in the process of irra diation, which affects the amount of crystals originat ing per volume unit of the sample for the glass with the gold content of 0.03 wt % Au and for the glass with the gold content of 0.003 wt % Au. It can be explained by the complete action of the gold impurity as a catalyst of the nucleation of lithium disilicate crystals. In practice, the obtained results are of interest for the elaboration of new photostructured materials based on lithium disilicate. This composition can be
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