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Materials Today: Proceedings 18 (2019) 1803–1810 www.materialstoday.com/proceedings
2214-7853 © 2019 Elsevier Ltd. All rights reserved.
Selection and/or Peer-review under responsibility of INTERNATIONAL CONGRESS ON SEMICONDUCTOR MATERIALS AND DEVICES.
ICSMD-2017
Femtosecond Laser Ablation Synthesis of Nanoparticles and
Nano-Hybrides in Ethanol Medium
Yasemin Gündoğdu
a, Abdullah Kepceoğlu
a, Serap Yiğit Gezgin
a,
Hayrettin Küçükçelebi
a, Hamdi Şükür Kılıç
a,b,*aSelçuk University, Faculty of Science, Department of Physics, 42000, TURKEY bSelçuk University, High Technology Research and Application Center, 42000, TURKEY
Abstract
The nanoparticle production has a significant importance because of its unique optical properties in molecular biology and medicine. Plasmonic metallic nanoparticles are widely used in cancer monitoring studies as contrast agents on the account of their surface plasmon resonance (SPR) effect. Beside, silicon (Si) semiconductor nanoparticles can provide several beneficial properties that they are used commonly intensifying the detecting signals. Nanoalloys/Nanohybides/Nanocomposites are more functional materials than a single material structure and having many restrictions. At that point, the application of Pulsed Laser Ablation (PLA) technique has many advantages if applied in the liquid. Since no any chemical technique is applied, this procedure promises a clean synthesis process; it is a simple and economical technique in the production process. It provides some possibilities to generate particles in the desired size, shape and density, and these properties of nanoparticles produced can be controlled by controlling the laser parameters. In this work, we have focused on the production of nanoparticles to rid off chemical processes using femtosecond laser ablation technique, and this technique presents a process to reach the fast and reliable results for production of nanoshells, nanocomposites and all nanoforms of particles. We have produced Si@Au nanohybrids in ethanol medium using femtosecond laser ablation depending on laser pulse energy. Absorption spectra were recorded day by day to determine the optical characteristics of produced nanoparticles within these time durations, Transmission Electron Microscopy (TEM) images were obtained for monitoring and determining the size/structure of nanoparticles, energy dispersive spectroscopy (EDS) for material compositions were produced, these results obtained are presented in the scope of this paper.
© 2019 Elsevier Ltd. All rights reserved.
Selection and/or Peer-review under responsibility of INTERNATIONAL CONGRESS ON SEMICONDUCTOR MATERIALS AND DEVICES.
Keywords: Nanoparticle; ablation; femtosecond laser; silicon; gold
*Corresponding author. Tel.: +90-5333652174; fax: +90 332 241 24 99. E-mail address: hamdisukurkilic@gmail.com
1. Introduction
Pulse Laser Ablation in Liquids (PLAL) is a particular technique that allows the production of highly pure nanoparticles. Laser wavelength, pulse duration and also laser fluence can be adjusted to obtain nanoparticles in different sizes and shapes [1, 2]. There are many parameters which can be applied on material processing during the laser ablation in liquid and to produce nanoparticles, especially nanoparticles which are composed of organic, inorganic molecules and oxide nanoparticles for use as nanomarkers in medicine and also biomedical applications [3-6].
Metallic nanoparticles have a wide application range due to their optical, mechanical and electronic properties. The physical properties of the nanoparticles are also among the parameters that are effective in the areas where these particles are used [7]. Nanostructures may have several promising properties depending on the properties of the source bulk materials, but significantly different than that of bulk materials due to their chemical, optical, magnetic and electrical properties. Thus, new application areas for nanoparticles are emerged unlike bulk materials [8-11].
The production of nanoparticles by PLA is considered to be a new method as well as this method has become a widespread technique for several application fields [12]. Nano-sized core-shell, nanorods, nanocubes, nanocage structures are widely used in cancer diagnosis and targeted drug delivery [13]. In the direction of development in nanotechnology, the use of nanoscale structures in the cancer treatment is also developing. If cancer nanotechnology, the diagnosis, imaging, therapy can be made at the molecular level, these processes can become much faster [14].
PLAL method is known as eco-friendly and cheap method compared to other nanoparticle production methods. Actually, PLAL is an excellent technique to synthesize nanoforms with desired shape and size [15]. In the last few decades, Au nanoparticles has been used and their application fields widely covers from biomedical engineering to photovoltaics owing to advantages of the tunable optical properties of Au nanoparticles [16-18]. Among the great advantages of nanoparticles produced by PLAL is that particles formed in the nanostructures are not hazardous because nanoparticles are trapped in the liquid during the production process.
The nanoparticles formed by PLAL from the metals present some sophisticated and excellent properties quite different than their bulked forms, especially in the absorption properties. , Au nanoparticles are used intensively in cancer diagnosis and treatment due especially to their surface plasmonic resonance (SPR) effects [19]. It is also well known that the production and application of gold and silicon nanoparticles give an excellent usage in all fields from medicine to industry [16, 20-24]. The first publication for Au nanoparticles was given by Faraday in 1857 [25]. Then, in the 20th centuries, It has become easier to identify the features of nanoparticles produced in the course of important developments in microscope technology such as TEM and AFM (Atomic Force Microscopy), so that understand the nature of nanoparticles and their application areas become widespread and are among the topics studied extensively in the literature [14].
In this paper, Au, Si and Si@Au nanohybrides have been produced by using Femtosecond Pulsed Laser Ablation (fs-PLAL) in ethanol medium. Hence, all obtained nanoparticles were analysed and recorded by using TEM, EDS and their absorption spectra were recorded and plotted using UV-Vis spectrometer.
2. Materials and Methods
In this study, fs-PLA processes were carried out using a Ti:Sapphire pulsed laser system which provides ~90 fs laser pulses in width with up to a 3.5mJ energy per pulse at 1-3 kHz repetition rate (Quantronix, Integra-C-3.5, NY, USA) pumped by Kerr-Lens mode-locked Ti:Sapphire oscillator laser (Quantronix, Ti-Light, NY, USA) (with 330 mW pulse power). Ti:Light oscillator laser produces laser pulses that are ~90 fs laser pulses in duration with a 85.5 MHz repetition rate with ~3 nJ per pulse at a fundamental wavelength of 800 nm.
The laser output was controlled by using an oscilloscope (LeCroy Corporation, WaveRunner 64 Xi, NY, USA) and a PC system. 99.99% pure gold and silicon wafer targets were placed at the focal point of the laser beam using a micromachining system (Quantronix, QMark, USA) to scan targets. The laser wavelength used for all experimental work is 800 nm and laser beam was focused on target in micromachining system which has an 11 cm focal point f-theta lens.
Fig. 1. Schematic representation of pulsed laser ablation in liquid medium for gold and silicon nanoparticle production.
Fig. 1 shows the schematic diagram of PLAL for production of nanoparticles. Fs-LA were applied in pure ethanol medium using different laser intensities. Au and Si targets were placed at the bottom of glass vessel filled with 5mL volume ethanol which was added into glass vessel for all experiments and then targets were ablated in ethanol. Laser was tightly focused on the targets for only 30 minutes duration and experiment was repeated for different laser intensities. Ablation processes were carried out at the room temperature.
Laser pulse powers used were set at 750 mW, 550mW, 350mW, 150mW and 50 mW to produce Si@Au nanohybrids in ethanol medium to observe optimum laser ablation parameters and then it was determined that the most suitable laser pulse power was determined to be 350 mW.
Experimental works have been carried out in three steps.
In the first step: we have first produced Au nanoparticles in ethanol medium and then Si target ablated in this Au
dispersed solution for 30 min.
In the second step: Si target was first irradiated in ethanol medium and then Au target ablated in ethanol with Si
nanoparticles solution and
In the last step: the Si and Au targets were irradiated at the same time by fs laser ablation 30 min time duration.
The TEM images were recorded to display shapes, widths and sizes of nanoparticles produced using a TEM-JEOL JEM-2100 (UHR). EDS images were taken using EDS detector-Oxford X-MAX 80-T. Absorption spectra from all nanoparticles were recorded using a Hitachi-U4100 UV-Vis-NIR spectrophotometer for 3 consecutive days.
3. Results and Discussion
During the last decades, synthesize of nanoparticles has gained very high importance due to their capabilities. The PLAL nanoparticle production process accepts a pioneering growing research area which produced other nanoparticle production processes because of it promises unique properties such as clean, highly pure, safe and also repeatable.
We have studied a laser-based formation of Si@Au nanohybrids in ethanol medium at different laser intensities between 9.8×1013 W/cm2 and 9.8×1014 W/cm2.
Laser ablation was applied on Au and Si targets using different laser powers to determine optimum laser parameters. It has been observed from our results that if time is kept constant to produce nanoparticles, in the case of low laser powers (50mW-150mW) are used, longer time is required to produce enough nanoparticles, but if laser
powers are tuned to power values higher (750 mW-550mW) than optimum (350mW) laser power, larger nanoparticles were produced which is unwanted situation.
3.1 TEM images & EDS results
TEM images and EDS results for Au nanoparticles, which were synthesized in ethanol medium, are shown in the Fig. 2. TEM images shows particle sizes and shapes distribution clearly. There is a tiny Si peak, visible in EDS spectrum, shown in fig. 2(d), this is due to that we have used the same vessel to produce Si and Au nanoparticles to ablated them after a cleaning process. We have cleaned vessel using ethanol, however, it can still be detected and shown in fig. 2(d).
Fig. 2. (a), (b) and (c) are TEM images of produced Au nanoparticle at 800 nm wavelength using 90fs pulsed laser at 350mW laser power, (d) EDS result for Au nanoparticle.
We have investigated optimum conditions to produce nanoparticles by changing laser power. Hence, we have produced all nanoparticles at 350 mW laser power using 90 fs laser pulses. We have obtained nanoparticle from 5 nm to 50 nm in sizes shown in fig.2 (a) and fig. 2(b). Images show that we have obtained Au nanoparticles in spherical shapes in this work.
We have carried out the production of Si nanoparticles using fs laser system at 800 nm wavelength and 90 fs laser pulses with 350 mW power. It has been observed that the sizes of nanoparticles change from 10 nm to 200 nm. Spherical silicon nanoparticles in ethanol medium show very pure EDS peaks as presented in fig. 3(d).
TEM images shown in Fig.4. (a), (b) and (c) belong to Si@Au nanohybrids. When the Si and Au targets were irradiated together at the same time, it was noticed that Si nanoparticles are wrapped around Au nanoparticles as shown in fig. 4. According to the ratio of nanoparticles from our EDS results, the numerical density of Au nanoparticles is much larger than Si nanoparticles in the case of the same laser parameter used. This is due to the
fact that the ablation threshold of Au metal and Si semiconductors are dramatically different. However, since the Si nanoparticles can better coalescence by each other compared to other metallic structures, such as Au, Ag etc, the size of the Si nanoparticles is larger than the size of the Au nanoparticles.
Fig. 3. (a), (b) and (c) are TEM images of produced Si nanoparticles at 800 nm wavelength using 90fs pulsed laser, (d) EDS result for Si nanoparticle.
Fig. 4. (a), (b) and (c) are TEM images belong to Si@Au veya Au-Si nanohybrids which ablated at the same time at 800 nm wavelength at 350mWlaser power using 90fs pulsed laser, (d) EDS result for Si@Au nanohybrids.
3.2. UV-Vis Results
The absorption spectra of Au, Si and Si@Au nanohybrids were recorded for 3 consecutive days. This is important measurement since we wonder whether the nanoparticles produced in ethanol that coalescence day by day or not. As a result, we observed that there is no important change in the absorption peaks and the position of the absorption peaks for Si@Au obtained are shown in Table 1.
Table 1. Au @ silicon nanoparticles were obtained depending on laser power to optimize the producing conditions.
Day 750mW 550mW 350mW 150mW
1 529 nm 528 nm 528 nm 527 nm
2 539 nm 539 nm 528 nm 529 nm
3 539 nm 548 nm 531 nm 534 nm
Fig. 5 was recorded Si@Au nanohybrides when they were ablated at the same time in ethanol medium for 30 min. laser ablation time. It has been observed that there is no remarkable change for the Si@Au nanohyrids in the absorption peak compared to the days. As shown in Tauc plot graph, in fig. 5(a), Si@Au nanohyrids which has 1,7 eV band gap (Eg).
(a) (b)
Fig. 5. (a) Tauc plot spectrum shows the Si@Au naohyrids which the band gap (Eg) is 1,7 eV; (b)The absorption spectra were recorded Si@Au nanoparticles at 800nm, 90fs, 350 mW laser power day by day.
4. Conclusions
Si@Au nanoparticles were prepared by 90 fs laser pulses at 800 nm laser wavelengths with 350 mW laser power. It was focused on target by using 11 cm focal length f-theta lens to ablate Au and silicon targets using micromaching system as described in the experimental section. Time is kept constant at 30 minutes during when the ablation process was carried out in ethanol medium.
One of the most important advantages of PLAL method is to have a clean synthesis process because it is not exposed to any chemicals, being simple and economical, and capable of producing particles at the desired size depending on the laser parameters.
When the particle size increases due to aggregation, the SPR peak shifts towards the long wavelength region. As the days progresses, SPR peak stays in the same position in the spectral region, and therefore, the particle sizes can be kept the same without any aggregation. In addition, as the laser power increases, larger number of particles are
ablated, hence, as the particle density increases, the inter-particle interactions increase and the particle size grows. So, as the laser power increases, the SPR peak shifts to the long wavelength region.
We have observed in Si@Au nanohybrids when they are ablated in ethanol medium simultaneously. Si nanoparticles are much smaller when it is produced together with Au in ethanol medium and their sizes were measured to be about a few nm and covers Au nanoparticles.
Acknowledgements
We would kindly like to thank to (1) Selcuk University, Scientific Research Projects (BAP) Coordination Unit for financial supports, (2) İLTEK for giving opportunity to use Infrastructure to held this project.
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