Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Deposition of gold nano-particles and nano-layers on polyethylene modified by plasma discharge and chemical treatment
Introduction
Metal–polymer composites are attractive for many applications, especially in microelectronics [1]. Mutual interaction between metal and polymers is generally very weak but it can be increased if the polymer surface is modified prior to metal deposition. Several modification techniques, physical, chemical or their combination, have been suggested for enhancing metal adhesion [2], [3]. Gold nano-particles, due to their unique electrical, optical and photophysical properties, are expected to provide variety of potential applications as electronic and sensor materials [4], [5], [6], [7]. The well known stability, non-reactivity and bioinertness of gold is used with advantage in medical diagnostics [8], Raman spectroscopy [9], biological imaging [10] and biosensors [11]. Gold nano-particles are promising structures for biomedical applications, structures combining gold nano-particles with polymers [12], [13], [14]. Since gold is the most inert metal the adhesion between gold particles and polymers is expected to be very poor. However, gold can easily react with thiol (–SH) groups, which can be fixed on the polymer surface modified beforehand in a proper manner. The polymer surface can efficiently be modified by irradiation with plasma, ultraviolet light from an excimer lamp or by ion irradiation [15], [16], [17].
In this work the polyethylene (PE) surface was modified by plasma discharge and subsequently grafted with 1,2-ethanedithiol to introduce thiol (–SH) groups. Short dithiol is expected to be fixed via one of –SH groups to radicals created by the preceding plasma treatment. Next, the free –SH group are allowed to interact either with gold nano-particles or with gold atoms from sputtered Au nano-layer. The main goal of this study is to examine the effect of the plasma treatment and dithiol grafting on the binding of gold nano-particles and on the adhesion of sputtered gold layer on the PE surface.
Section snippets
Materials, plasma modification, grafting and sputtering
Oriented, high density polyethylene (PE, ρ = 0.952 g cm−3) in the form of 40 μm thick foils (supplied by Granitol Ltd., Czech Republic) was used in the present experiments. The samples were modified in diode plasma discharge on Balzers SCD 050 device for 240 s. DC Ar plasma was obtained under following conditions: Ar gas purity 99.997%, discharge power of 8.6 W, Ar flow ∼0.3 l s−1, working pressure of 10 Pa, distance between the electrode (48 cm2 in area) and the sample of 50 mm, chamber volume about 1000 cm
Results and discussion
Radical concentration (R), determined from EPR measurement on the plasma modified PE (PE/plasma) and plasma modified and dithiol grafted PE (PE/plasma/SH), is shown in Table 1 as a function of the time from the plasma treatment. Plasma treatment results in scission of C–H and C–C bonds and production of free radicals (unpaired electrons). As could be expected, the radical concentration declines with increasing time from the treatment due to radical recombination [21]. Grafting of plasma treated
Conclusion
It was shown that the plasma treatment results in degradation of the PE macromolecular chain, creation of free radicals and conjugated double bonds. After grafting from methanol solution of 1,2-ethanedithiol the concentration of free radicals declines but the concentration of double bonds remains unchanged. This finding shows that most of the grafted dithiol molecules are bound onto radicals produced by the plasma treatment. The presence of Au and S (from dithiol) on the surface of the plasma
Acknowledgements
This work was supported by the Ministry of Education of the Czech Republic under programs 6046137302, 6046137305, 1M6837805002 and LC 06041, GAAS CR under the projects KAN 400480701 and KAN 200100801 and GACR under the Project 106/09/0125.
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SH) with good affinity to Au. The plasma treatment was used to activate the glass surface to react with the BPD and create a strong bond. Nanoindentation and scratch tests were performed on the thin Au layers deposited on pristine and treated glass. The results show the plasma treatment leads to improvements of the adhesion by itself with the BPD grafting not having a positive effect in this matter. Scanning electron microscopy showed the substrate modification has influence on the microstructure of the subsequently grown Au layers which leads to change of their optical properties as well.