Implantation of organic matter through water onto solid substrates by a laser induced molecular jet
Introduction
The interaction of a laser beam with many kinds of materials leads to modification of a surface material, which plays a crucial role in many fields of material engineering [1]. During the last several years researchers have been continuously developing a new technique which would enable them to modify a material surface. One of the famous methods is Laser Molecular Implantation (LMI), and this is a technique used for molecular doping of a polymer surface with implanted dots at high-space resolution. The first report on laser-induced implantation of organic molecules onto a polymer surface [2] highlighted the fundamental aspects and possible practical application of this process. This technique involves interaction of laser pulses with source films doped with molecules, leading to the molecules' absorption of laser light, where the absorbed energy is converted into heat by a cycle of repetitive excitation and nonradiative decays [3]. Consequently, hot domains are generated and molecules are ejected from the source film to the target. The main drawback of this technique lies in the possibility of fixing molecules only onto the polymer surface within a range of several microns. In order to reduce the size of implanted dots, several Laser Induced Molecular Implantation Techniques (LIMIT) have been developed [4], [5]. For example, there has been a report on the technique of an ablative transfer of organic matter from a doped micro-pipette to a surface after its laser activation. The size of the doped molecular region obtained then was 600 nm [6], [7]. However, the problem of this technique is that, if applied on a larger area, the implanted dots show a rather sporadic distribution.
Another possible method for preparing patterns with organic molecules is photopolymerization process. For example, Müller and all, synthesized color-emitting polymers that can be cross-linked with a photopolymerization polymer, and demonstrated a three color OLED (organic light-emitting diodes) using a mixture of color-emitting polymers and photopolymerization polymer [8].
Organic molecules are also useful as functional components in microdevices. Micropatterning and nanopattering of organic molecules have been the subject of great importance in such fields as micro/nanotechnology, optics and electronics [8], [9], [10], [11], [12]. Those can be performed for preparing microdevices, microcolor displays, multifunctional optical devices, and so on. Unfortunately, organic molecules easily get damaged during their manipulation or preparation patterns due to strong laser light and high temperature. For this reason, another technique to achieve micropatterning was developed, namely a laser ablative transfer of matter from a doped polymer film to an un-doped one. In this case, the quality of implantation was highly reproducible [13], [14] but the size of implanted Coumarin 6 dots still remains in a region of several micrometers.
In order to decrease the size of an implanted area, we tried to control a molecular plume by means of a laser induced water jet. Thus, we filled the gap between a source film and the target with water. We found that this way it is indeed possible to decrease the size of implanted C6 molecules, and also that if we use a generated LIMJ, the water layer helps fixing organic matter not only onto a polymer target, but also onto a hard substrate, namely glass and ITO.
Section snippets
Experimental
The details of the experimental set-up were reported on before [15]. A pulsed dye laser (τ = 4 ns, λ = 440 nm) coupled with a microscope was used to implant organic molecules, such as Coumarin 6 (C6) and 5-(2′-ethyl-hexyloxy)-p-phenylene-venylene] (MEH-PPV) (Fig. 1a, b). The source films of C6/PBMA (poly (butyl methacrylate)) with a concentration of 4 wt.% and PPV films were prepared through dissolving the corresponding components (PBMA and C6) and MEH-PPV molecules in monochlorobenzene (from
Implantation of C6 molecules
In order to investigate the size and the shape of implanted C6 dots, we previously tried to implant Coumarin 6 molecules by LIMIT at different concentrations of source films [13]. It became clear that the size of the implanted dots strongly depends on the distance between interfaces, laser fluences, etc., when the gap between them is filled with air [14]. We also came to the conclusion that the best appropriate concentration of a source film to prepare is 4 wt.%. As a result, the implanted dots
Conclusions
We have shown that by means of using a laser induced molecular jet Coumarin 6 and MEH-PPV molecules can be implanted onto the surface of a borosilicate glass and indium tin oxide film in the form of dots at low laser fluence, and in the form of a ring at the highest laser fluences. Utilizing the mentioned technique we found a way to implant organic molecules on a submicron area. Recorded fluorescence spectra show that the C6 molecules were transferred from the source film to the target through
Acknowledgments
The present work is supported by the Grant-in-Aid for Scientific Research (KAKENHI) in Priority Area “Molecular Nano Dynamics” from the Ministry of Education, Culture, Sports, Science and Technology, and it is partly supported by NEDO.
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