Incorporation of silver nanoparticles in DLC matrix and surface plasmon resonance effect

https://doi.org/10.1016/j.matchemphys.2005.11.008Get rights and content

Abstract

Silver nanoparticles were embedded in diamond-like carbon (DLC) matrix by using electrochemical technique on SnO2-coated glass substrates. Particle size and metal volume fraction were tailored by varying the amount of silver containing salt (silver acetate) in the electrolyte. Reduction in size of the metal particles culminated in red-shift of the surface plasmon resonance peak in the optical absorbance spectra of the films. Experimental absorbance spectra were theoretically simulated by Mie scattering theory and Maxwell-Garnett (M-G) effective medium theory. It was observed that Mie theory described the experimental observation more faithfully than the MG model.

Introduction

Studies on the low dimensional structures have become the subject of various experimental and theoretical research activities [1], [2] in recent times due to the extraordinary properties exhibited by them. A special interest in the study of granular metal of submicron sizes embedded in a dielectric matrix was witnessed in recent times. In these systems, the metal particles were dispersed in the dielectric medium with different inter-grain distances by changing the number density of the ultra-fine metal particles. Resonance frequency of the surface plasmon was seen to depend on the size and shape of the metal nanoparticles and the dielectric properties of local environment in which the metal nanocrystallites are embedded. These systems would exhibit a large third-order nonlinear susceptibility and fast time response [3], [4] near the surface plasmon resonance frequency leading towards the fruitful exploitation of the materials for photonic devices [5], [6]. Information on the metal nanoparticles embedded in dielectric matrix could be obtained from the studies on these systems. Recently, several researchers [7], [8], [9], [10] have reported their studies on optical properties of gold or silver nanoparticles embedded in dielectric matrix and the choice of the dielectric matrix was limited mainly to SiO2 and ZnO.

Although metal doping in diamond-like carbon (DLC) films prepared by chemical/physical vapour deposition techniques had been the issue of obtaining a new class of materials [11], [12], [13], [14] but the difficulty of dispersing the metal particles homogeneously in the DLC matrix by the techniques used by the researchers was found to be difficult. The key issue was to reduce the internal stresses in DLC films via incorporation of elements that form carbides (like Si and Ti) as well as elements that do not from carbides (like Cu and Ag). The metal particles were found to form clusters in the DLC matrix and formed carbide clusters in case of carbide forming metals. DLC–silver nanocomposites have also been shown to posses antimicrobial properties. Since the DLC films are large band gap material, metal inclusion in nanocrystalline form should also reveal interesting optical properties like surface plasmon resonance in these class of composite materials which have not been explored yet systematically.

In this communication, we present our studies on the optical properties of composite materials composed of ultra-fine silver particles having different grain sizes as well as inter-grain distances embedded in diamond-like carbon matrix. The composite films were prepared by simple electrodeposition technique which is a cheap and scalable technique besides being capable of depositing films on irregular surfaces.

Section snippets

Experimental details

Recently, we have demonstrated that DLC films could be deposited onto SnO2 coated glass substrates by electrodeposition technique using CH3COOH and deionized water as electrolyte [15] by applying significantly lower voltage than those reported [16], [17], [18], [19], [20]. Incorporation of different amount of silver nanoparticles was carried out by using different amount of silver acetate (CH3COO)Ag in the electrolytic bath. Films were deposited at a fixed volume percent of acetic acid (1%,

Results and discussion

The composite films of nanocrystalline silver embedded in DLC matrix deposited as above were found to be extremely adherent to the substrates and the colour of the films varied from greenish blue to reddish yellow as the size and volume fraction of silver nanoparticles changed. Generally, the transmittance of the composite films decreased with the incorporation of silver nanocrystallites in the DLC matrix beyond the surface plasmon resonance domain. Films composed of ultra-fine metal particles

Conclusions

Nanocrystalline silver/DLC composite films with various volume fractions of silver were prepared by electrodeposition technique. Silver nanocrystallite size varied between 1 and 4 nm and electron diffraction pattern indicated that the nanocrystalline silver particles were preferentially oriented in (1 1 1), (2 0 0) and (2 2 0) directions. The optical absorption peak corresponding to the surface plasmon resonance showed a red-shift with reduction in particle volume fraction and decrease in particle

Acknowledgements

The authors like to thank Dr. A.K. Jain, Institute of Pathology, New Delhi, India and Dr. P.V. Satyam, Electron Microscope Facility of Institute of Physics, Bhubaneswar, India for their assistance in recording the TEM images. One of the authors (R.K. Roy) wishes to thank the Council of Scientific and Industrial Research (CSIR), Government of India, for extending senior research fellowship in carrying out this programme.

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