Phases of Gold-Based Nanocomposite

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Various Morphologies/phases of Au-Based Nanocomposite Particles Produced by Pulsed Laser Irradiation in Liquid Media – Insight in Physical Processes Involved in Particles Formation #aneta #wi#tkowska-Warkocka, Alexander Pyatenko, Kenji Koga, Kenji Kawaguchi, Hongqiang Wang, and Naoto Koshizaki J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b00187 • Publication Date (Web): 20 Mar 2017 Downloaded from http://pubs.acs.org on March 23, 2017

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The Journal of Physical Chemistry

Various Morphologies/Phases of Au-based Nanocomposite Particles Produced by Pulsed Laser Irradiation in Liquid Media – Insight in Physical Processes Involved in Particles Formation Z. Swiatkowska-Warkocka,1* A. Pyatenko,2 K. Koga,2 K. Kawaguchi,2 H. Wang,3 N. Koshizaki4. 1 Institute of Nuclear Physics Polish Academy of Sciences, PL-31342, Krakow, Poland 2 National Institute of Advanced Industrial Science and Technology, Tsukuba, 305-8565, Japan 3 Northwestern Polytechnical University, Xi’an, 710072, China 4 Hokkaido University, Sapporo, 060-8628, Japan

ABSTRACT

In this work taking Au/MxOy (M=Fe, Co, Ni) particles as examples, we investigate and discuss the physical processes involved in particles formation by laser irradiation of mixture of two different kinds of nanoparticles dispersed in liquids. We showed that this method is an efficient and universal way for synthesis and control a variety of composite particles with various morphology (core-shell, alloy) and compositions which are not only metals or oxides but also non-equilibrium bimetallic alloys (AuFe, AuCo, and AuNi). Additionally, fluence diagrams which were designed to show the relation between laser fluence and particle diameter plot based

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on the heating-melting-evaporation model are useful for better understanding of the mechanism of composite particles formation during pulsed laser irradiation. To the extent of our knowledge, this is the first explanation of the mechanism of Au-based composite particles formation during pulsed laser irradiation of mixture of two different raw nanomaterials dispersed in liquid based on experimental results and theoretical calculations. INTRODUCTION Harmonization and cooperative assemblance of different components into a single material remains one of the most recent achievements in material science. The novel composites thus accessed are characterized with improved or exciting unusual properties resulting from synergistic effects of reactions between different components.1–7 Especially, the possibility of controlled synthesis of novel nano/microstructured composites is still a challenge for researchers in materials science. Magnetic particles offer wide-ranging applications in the fields of magnetic recording, magnetic energy storage, magnetic separation, magnetic resonance imaging, hyperthermia treatments and drug delivery.8-14 Transition metal oxides have unusual and useful electronic, magnetic, and catalytic properties.15 While gold is widely used in in catalysis, electronics, spectroscopy and biomedical research.16-22 Combination of gold with magnetic component leading to a rich variety of optic, magnetic, and chemical properties. The connection of Au with transition metal oxides could give a new material for use in opto-chemical sensors.23 Different applications demand structures with specific morphologies and/or phase compositions. Morphology may also affect enhancing and/or tuning the properties of hybrid materials.


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Presently, efforts to manipulate the composition, size and morphology of particles constitute a part of methodical attempts to modify their chemical and physical attributes. Within this context, pulsed laser irradiation of colloidal nanoparticles in liquid has emerged a useful method for synthesis of a variety of hybrid metal or metal oxides composites from colloidal nanoparticles dispersed in liquid. This method represents an interesting strategy for the preparation of particles such as metal, metal oxides, metal oxides composites, noble-metal/metal oxides composite particles, and alloy particles via a bottom-up approach.24-32 The mechanism of particles interaction between laser pulse and nanoparticles dispersed in liquid are based on heatingmelting-evaporation model.33-34 During the past decade, laser-induced nanoparticles formation were intensively studied. Pulsed laser irradiation of colloidal noble metal nanoparticles causes their size reduction, shape and morphology changes.35-40 Experimental results and numerical simulations demonstrated that nanoparticle formation can be explained either due to photothermal mechanism or due to Coulomb explosion. Laser irradiation of metal films or metal nanoparticles deposited on surfaces (glass or SiO2/Si) is also widely used as a nanostructuring methods.41-43 Despite the great interest in laser-induced formation and modification of nanoparticles, current models are based on the laser beam interaction with nanoparticles showing a strong absorption in the visible region, like gold or silver. In our work we studied the evaluation of morphology and composite of obtained particles after laser irradiation of mixture of two different raw nanoparticles dispersed in liquid. In particular gold nanoparticles which show an extremely high absorption in the visible region with transition


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metal oxide nanoparticles characterized by the absorption efficiencies lower than the efficiency of gold nanoparticles (Fe3O4, Co3O4), or equal to zero (NiO). Here, we focus our attention on the better understanding of the physical processes involved in particles formation by laser irradiation in liquids. We try to find answer how morphology of obtained particles (core-shell, alloy) and their compositions depend on experimental conditions. To do that, a series of both experimental and theoretical studies were performed. In particular, by using different experimental parameters including laser fluence, laser irradiation time, starting material, molar ratio of raw nanoparticles, composite particles are obtained with different size, composition and morphology. EXPERIMENTAL SECTION Synthesis of Au nanoparticles Source gold (Au) nanoparticles were prepared by pulsed laser ablation in liquid (PLAL).56 Synthesis of MxOy nanoparticles Source magnetite (Fe3O4) nanoparticles were prepared by conventional co-precipitation from FeCl2.4H2O and FeCl3.6H2O.57 Co-oxides nanoparticles (nanopowder form, average size 22 nm, purity 99.5%) were purchased from Nano Tek, and NiO nanoparticles (nanopowder form, average size>y) alloy. Although the characteristic peak for the (111) plane of fcc Fe at 2θ = 44.5º were almost overlapped with those for the (200) plane of Au at 2θ = 44.4 the formation of AuxFey alloy nanoparticles could be confirmed from the fact that the characteristic peaks of AuxFey alloy nanocrystals were slightly broader than those of Au nanoparticles, suggesting their poorer crystallinity, which is the result of less ordered structures usually observed in alloys. In addition, it was noted that the Au main peaks slightly shift towards high angle, indicating a decrease in lattice constant arising out of replacing in the crystal lattice of Au by Fe. Based on the calculated lattice parameter (a=4.058 Å) we estimated the concentration of iron in the obtained particles as ∼10 at.%.47 b) Au/CoxOy As shown in Figure 4, the products with varied morphologies in different sizes are seen in the SEM and TEM images. When the molar ratios of Au:CoxOy were varied from 1:10 to 1:1, the shape of obtained particles changed from dumbbell-like particles, connected by liquid bridges to spherical (Figure 4 a, b). With further increase of the molar ratio of Au:CoxOy the large spherical particles as well as large amount of very small particles are produced and the radiuses of spherical particles are 1 µm and 20 nm, respectively (Figure 4 c).


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Figure 4. SEM, TEM images and XRD patterns of Au/CxOy particles synthesized by laser irradiation (100 mJ/pulse.cm2, 1h) with different molar ratio of Au:CoxOy: (a) 1:10, (b) 1:1, and (c) 10:1. #: Au, *:Au-Co alloy, &: Co. The XRD profiles as-synthesized Au/CoxOy particles are shown in Figure 4. When the molar ratios of Au:CoxOy is 1:10, the particles were confirmed to be a composite of Au, Au-Co alloy and Co phases. With increasing the molar ratio of Au:CoxOy, the Co phase disappears, the product is composed of Au and Au-Co alloy phases. Lattice constants of Au-Co alloy particles obtained for 1:10 and 1:1 molar ratios were calculated from XRD data as 3.989 and 3.972 Å, which allowed to estimate the concentration of cobalt in the alloy as 22 at.% and 27 at.%.44,45 Increasing the molar ratios of Au:CoxOy to 10:1 results in the formation of AuxCoy (ｘ>>ｙ), which appears phase pure by XRD. The refined Au lattice parameters for the 1:10, 1:1, and 10:1


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molar ratios give 4.063, 4.069, and 4.067 Å fcc lattice constants, which are slightly compressed compared with that of pure Au at 4.076 Å. c) Au/NixOy As shown in Figure 5, the morphology of Au/NixOy particles is similar to Au/CoxOy particles. When the molar ratios of Au:NiO is 1:10, the product shows large spherical and nonspherical particles. With increasing the molar ratio of Au:NiO only spherical particles are produced. As evident from the XRD data in Figure 5, the composition of obtained particles depends on molar ratio of Au:NiO. For the case with the molar ratio of Au:NiO equal to 1:10, the particles were confirmed to be a composite of Au, and NiO phases. Precise analysis of very broad diffraction peak in the 2θ range of 41-44° shows that peak is not single. This peak can be divided into four peaks and identified as peaks corresponded to Ni3C, NiO, AuxNiy (xy) alloy phases. Based on the calculated lattice parameters of these alloys (4.055 Å, 4.015 Å, and 3.927 Å) we estimated the concentration of nickel in AuxNiy as ∼5,15, and 40 at.%,48 respectively.


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Figure 5. SEM, TEM images and XRD patterns of Au/NiO particles synthetized by laser irradiation (100 mJ/pulse.cm2, 1h) with different molar ratio of Au:NiO: (a) 1:10, (b) 1:1, and (c) 10:1. #: Au, *:Au-Ni alloy, &: NiO, v: Ni, ^:Ni3C. Mechanism of formation of Au/FexOy, Au/CoxOy and Au/NixOy particles Composite spheres form by heating-melting-evaporation-cooling/solidification process during pulse laser irradiation. Optical absorption of the particles and their thermodynamics strongly influence on the process.33 The critical values of laser fluence for different phase transformation were calculated. As it was shown in ref 34, the typical characteristic times of particle cooling process last for about 10-4 -10-6 s and are shorter than being about 10-2 s interval between two consecutive pulses but longer than lasting 10-8 s pulse duration. It allows us to neglect the heat


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losses during the particle heating-melting interval and make the calculations for a single laser pulse. At the time, the laser energy absorbed by a particle can be written as equation 1 Eabs=Jσabsλ(dp) (1) where J is the laser fluence, dp is the diameter of the particle, and σabsλ is the particle absorption cross-section. We assume that all of the energy absorbed by the particle will be spent on heating, melting, and evaporation (Eq. 2) because the estimated possible heat losses are negligible compared to the energy absorbed by the particles from a laser pulse. The values of particle absorption cross section, or its relative analog, often called the absorption efficiency (Qabsλ=4σabsλ(dp)/πdp2), can be calculated using the classical Mie theory, if the optical constants of materials are known. Optical constants of Au can be found in the reference book,49 M-oxides were taken from original paper (Fe3O4,50 FeO,51 Co3O4,52 NiO42).


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Figure 6. Particle-size dependence of absorption efficiency obtained by Mie calculations for Au, Fe3O4, FeO, Co3O4, and NiO at 532 nm. Results of Mie calculation are presented in Figure 6, where absorption efficiencies for Au, Fe3O4, FeO, Co3O4, and NiO are shown as functions of particle diameter. For small particles (>y or y>>x we can assume that the properties of alloy is rather similar to the properties of appropriate component.


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Figure 7. Particle size dependence of the required laser fluence J for (a) Au, (b) Fe3O4, (c) Co3O4, (d) NiO systems to heat a particle to the melting point, to complete melting, to heat to the boiling point, and to complete evaporation, using 532 nm laser. Our calculations show very large differences between Au-FexOy, Au-CoxOy and Au-NiO systems. For the first one, the process of spherical particles formation is continuous because absorption of energy for Fe3O4 and FeO is nearly the same, so in the beginning Fe3O4 decomposes to FeO, then FeO decomposes to Fe. For Au-CoxOy first Co3O4 decomposes to CoO, but after that the CoO does not absorb enough energy and the process of spherical particle formation is continued due to the absorption of light by Au and heat transfer from Au to CoO. For last one, there is very small energy absorption by NiO, so the process of particle formation occurs due to energy absorption by Au and heat transfer from Au to NiO.


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a)

Laser fluence and irradiation time dependent size/phase evolution

We used the Au/CoxOy as an example to show qualitative discussion of the particle size change in accordance with the calculation result. Take into account that during the first estimation in the theoretical calculation no secondary effects (e.g. potential pyrolysis of liquid around a particle and interaction between pyrolyzed product and surface of particles) were considered. As visible in the calculation results presented in Figure 7a, the laser fluence equal to 100 mJ/pulse.cm2 is enough for complete evaporation of Au nanoparticles. The raw materials include Au (20 nm) and Co-oxides (20 nm) nanoparticles. Since both gold and oxides particles are very small, we can expect that they will be strongly agglomerated. There are several possibilities. Co-oxides nanoparticles may agglomerate with each other and/or with gold. In one individual pulse Au absorbs much more energy than Co-oxides and transfers some part of this energy to Co-oxides particles. As a results, both the gold and the cobalt oxide melt. Without transfer energy Au particles must be evaporated completely. Repeated particles agglomeration, laser energy absorption and melting-solidification processes lead to an increase of the particles size and form finally the spherical submicron particles (Figure 2a). When the laser fluence is increased from 100 to 177 mJ/pulse.cm2, average sizes of spherical particles increased (Figure 2 a, b). Explanation of the size increase can be found in Figure 7a, which shows that higher laser fluence can lead to complete melting of larger particles. Increasing of irradiation time from 1h to 2 h (Figure 2 b, c) brings the particle size increase owing to merging of melted nearby particles.


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During laser irradiation not only size and morphology are changed, but also phase changes are observed (Figure 2). Au absorbs energy and transfers this energy to Co-oxides particles, causing them to melt and reduce it to Co. Liquid Au and Co can form the Au-Co alloy. Therefore, it is possible to expect the full reduction of CoO and formation of Au-Co alloy during longer laser irradiation (Figure 2a). When the laser fluence is increased from 100 to 177 mJ/pulse.cm2 formation of Au-Co alloy could be faster. Additionally, the Au particles can start evaporate, what leads to formation of very small Au, or Au-Co nanoparticles agglomerated on the surface of large Au-Co particles (Figure 2 b). b)

Molar ratio dependent morphology/phase evolution on the example of Au/FexOy and

Au/NixOy As seen in the calculation results shown in Figure 7 a, the laser fluence equal to 100 mJ/pulse.cm2 is enough for complete evaporation of Au nanoparticles. Large Au particles (>100 nm) need high energy to melt or evaporated. In the case of Fe-O system (Figure 7 b), Fe3O4 particles will be melted at 100 mJ/pulse.cm2. It should be remembered that absorption cross section at 532 nm is completely different for Au and Fe3O4 nanoparticles, so in one laser pulse Au particles absorb tens of times more energy than Fe3O4 particles. The raw colloids include Au (20 nm) and Fe3O4 (5 nm) nanoparticles. As in the case of Au and cobalt oxide strong agglomeration of nanoparticles can be expected. In this case much smaller Fe3O4 nanoparticles probably attach onto larger Au nanoparticles and agglomerate with quasi core-shell structure. When the molar ratio of Au:Fe3O4 is 1:10, the magnetite particles must form several layers on the Au, and all these agglomerates must float in the ocean of Fe3O4 nanoparticles. The amount of energy that Au can transfer to Fe3O4 is very small, but at J = 100 mJ/pulse.cm2 Fe3O4 will be melted, so this small additional energy will promote decomposition of Fe3O4 to FeO. So we can


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expect after one laser pulse the formation of spherical core-shell particles with Au core and shell consisting of Fe3O4 and FeO. Due to the melting process, in next 1 h of laser irradiation experiment the particles will grow and form finally the spherical submicron particles, which is typically for selective pulse heating process.14 Au cores can can get closer to each other also fuse and grow. Between two consecutive pulses, some core-shell particles can get closer to each other and then fuse. Because the shell Fe oxide layer is relatively thick this time, not all the core Au particles can do that. As the result, we have multi core-shell particles, contained not only one but sometimes two or three Au cores inside one Fe oxide shell. In TEM picture (Figure 3 a) we can observe also small amount of particles consisted only from Fe oxide (without any Au cores). Existence of such particles can be explained by the fact that small initial Fe3O4 particles can be agglomerated not on the surfaces of large Au particles only, but sometimes form the agglomerates themselves. In such case the size of agglomerate will be not so large, therefore the finally grown Fe oxide particle will be smaller than the size of core-shell particles. Chemically the cores must be composed from Au and the shell must be composed from Fe3O4 and FeO. This corresponds to our experimental results (Figure 3 a). If the molar ratio of Au:Fe3O4 is 1:1 (Figure 3 b), the magnetite nanoparticles can form 1 - 2 layer on Au surface. Same as previous case Au transfers energy to Fe3O4, but at this time the energy is enough for Fe3O4 melting and complete decomposition to FeO. Therefore, after one laser pulse spherical Au core- FeO shell particles will be formed. Due to the repeated melting process, in next 1 h of laser irradiation experiment the particles will grow and form finally the spherical submicron particles, which is typically for selective pulse heating process. Due to the relatively small thickness of FeO shell layers, the Au cores will be fussed together during the short periods of time when the particles exist in liquid conditions. So, large Au core-


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FeO shell spherical particles will be formed. Also FeO will be reduced to Fe by liquid mediaethanol. Fe atoms produced in this reduction process can diffused through liquid FeO layer to Au core and form an AuxFey alloy with liquid Au. Au core itself can promote the reduction of FeO atoms to Fe. So finally, AuxFey alloy core- FeO shell particles will be formed. This result agrees with our experimental results. When molar ratio of Au:Fe3O4 increases to 10:1, the Fe3O4 nanoparticles can’t form one single layer around Au particles. In this case the energy which can transfer from Au to Fe3O4 is much higher than amount needed for melting, decomposition and full evaporation of Fe3O4. Therefore, in this case we have to suppose part evaporation of Au as well as Fe. Due to the high concentration of the particles into the colloid, evaporated atoms condensed immediately on the surfaces of neighbor particles. The particles will grow in the result of this consecutive melting and solidification processes. The results of XRD analysis of final chemical composition are in good correspondence with our theoretical consideration (Figure 3c). Because energy transferred to Fe3O4 is so large, we have full decomposition of Fe3O4 to FeO and complete reduction of FeO to Fe. Fe. So, we can not expect in final product any Fe oxides. And because the amount of Au is much higher than the amount of Fe, all Fe atoms will form an alloy with Au. Probably due to many evaporation processes, all Fe atoms can mix with Au atoms. As the result, we have only AuxFey alloy in final products. Final diameter of AuxFey particles are in a good coincidence with maximum size that can be obtained for pure Au particles (Figure 7 a) In the case of Ni-O system (Figure 7 c), 100 mJ/pulse.cm2 is not enough even for start melting NiO particles. When the molar ratio of Au:NiO is 1:10, the amount of energy that Au


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can transfer to NiO is too small and not enough even for melting of NiO nanoparticles. Therefore, we can expect only a melting of Au. Due to such melting, the particles could be grown, be-cause liquid Au can be leak through NiO particles, but we can’t expect of spherical particles formation. And inside on the outside surfaces of these nonspherical particles, large amount of NiO particles can be expected. Composition must be the same as initial one: 10% of Au and 90% of NiO. SEM picture (Figure 5 a) is very similar to that expectation. When the molar ratio of Au:NiO change to 1:1, the amount of energy transferred to NiO, is enough for complete melting and part decomposition to Ni. Due to the melting process the particle will grow and form finally the spherical submicron particles, which is typically for selective pulse heating process. So the main part of NiO can be reduced. Note that all calculations are made for one individual laser pulse. If some amount of NiO will not decompose in one pulse, it can be reduced in next pulses. Also, ethanol will promote NiO decomposition (reduction) process at the surface of agglomerates. Therefore, it is possible to expect the full decomposition of NiO during the 1 h of laser irradiation. During the melting process, when particle’s agglomerate is in liquid condition, Ni atoms will diffuse to the core and form the AuxNiy alloy. Because the mole ratio of Au to Ni is 1, it is possible to expect x close to y. In experiment we observe the formation of submicron spherical particles consisted of Au and AuxNiy alloy (Figure 5b). The fact that the large amount of Au was found in final product, can be explained by very short time when particle exists in liquid conditions (about 10-4 – 10-5s for one individual laser pulse) and when the Ni atoms can diffuse to Au core to form an alloy. In this case of molar ratio of Au:NiO is equal to 10:1, the energy which can transfer from Au to NiO is much higher than amount needed for melting, decomposition and full evaporation of NiO. Therefore, in this case we have to suppose part evaporation of Au as well as Ni. The results of


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XRD analysis of final chemical composition are in good correspondence with our theoretical consideration (Figure 5 c). Because energy transferred to NiO is so large, we have full decomposition of NiO to Ni. And because the amount of Au is much higher than the amount of Ni, all Ni will form an alloy with Au. Probably due to many evaporation processes, all Ni can mix with Au atoms. As the result, we have AuxNiy alloy, in which x is much larger than y. Optical and magnetic properties

Figure 8. (a) UV-vis absorption spectra Au/CoxOy particles with various molar ratios of Au:CoxOy. (b) Magnetic hysteresis loops at 300 K for Au/CoxOy obtained by laser irradiation with various laser fluence 100 mJ/pulse.cm2 (black solid line), and 177 mJ/pulse.cm2 (blue dotted line). The inset is the magnification around origin. By variation some experimental parameters, Au:MxOy ratio and/or laser fluence we can easy changing the optical and magnetic properties of the particles. Figure 8 a shows UV-vis absorption spectra of Au/CoxOy particles prepared by laser irradiation of mixture of Au and CoxOy with various molar ratios. As expected the characteristic absorption


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band of composite particles prepared with molar ratios 10:1 occurs at 521 nm, while particles prepared with molar ratios 1:1 and 1:10 did not exhibit any characteristic absorption bands. In addition, the absorbance decreases with decreasing Au:CoxOy molar ratios, exposing the atoms of cobalt disturb the electron cloud oscillation of surface gold atoms. To determine the coersivity, the saturation magnetization and remanent magnetization, the dependences between magnetic field and magnetization at 300 K for Au/CoxOy particles obtained by laser irradiation under different process conditions: 1h, 100 mJ/pulse.cm2, and 1h, 177 mJ/pulse.cm2 were measured, and are illustrated in Figure 8 b. It was found that with increasing laser fluence, the coersivity increases from 32 Oe to 38 Oe, while the saturation magnetization and remanent magnetization decrease. CONCLUSIONS In summary, taking Au/FexOy, Au/CoxOy and Au/NixOy particles as examples, we have demonstrated a facile bottom-up pulsed laser irradiation approach for fabricating composite particles with various morphology (core-shell, alloys) and compositions not only metallic, oxides but also non-equilibrium bimetallic alloys (AuFe, AuCo, and AuNi). The colloidal particles commonly achieved using chemical methods could be alternatively created in the process of laser irradiation in liquid. Using this method, we have shown that pulsed laser irradiation is versatile and flexible for designing composite particles with tunable composition and morphology. Our studies indicate that such experimental parameters including laser fluence, laser irradiation time, starting material, molar ratio of raw nanoparticles influence the formation of composite particles. Additionally, fluence diagrams which were designed to show the relation between laser fluence and particle diameter plot based on the heating-melting-evaporation model


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are useful for better understanding of the mechanism of composite particles formation during pulsed laser irradiation. However, we should remember that in the theoretical calculation some secondary effects like possible pyrolysis of solvent around a particle and interaction of this pyrolyzed product with particle surface were not considered. Moreover, by changing some experimental conditions, i.e. molar ratio of raw materials and/or laser fluence, the optical and magnetic properties of produced materials can be easily changed. These advantages cause that this method is an efficient and universal approach for synthesis of variety of multicomponent submicrometer particles. We hope that our investigation could help understand the processes involved in particles formation during pulsed laser irradiation of nanoparticles dispersed in liquid and better control of variety of bi- or multicomponent submicrometer particles. AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]. Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT


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This work was supported by KAKENHI 2008734, and the magnetization measurements were conducted at the Nano-Processing Facility, supported by IBEC Innovation Platform, AIST. REFERENCES 1. Cozzoli, P. D., Pellegrino, T., Manna, L. Synthesis, properties and perspectives of hybrid nanocrystal structures, Chem. Soc. Rev. 2006, 35, 1195-1208. 2. Zeng, H., Sun, S. Syntheses, Properties, and Potential Applications of Multicomponent Magnetic Nanoparticles, Adv. Funct. Mater. 2008, 18, 391-400. 3. Férey, G. Some suggested perspectives for multifunctional hybrid porous solids, Dalton Trans. 2009, 4400-4415. 4. Shi, W., Zeng, H., Sahoo, Y., Ohulchanskyy, T. Y., Ding, Y., Wang, Z. L., Swihart, M., Prasad, P. N. A General Approach to Binary and Ternary Hybrid Nanocrystals, Nano Lett. 2006, 6, 875–881. 5. Wang, M., Duan, X., Xu, Y., Duan, X. Functional Three-Dimensional Graphene/Polymer Composites, ACS Nano 2016, 10, 7231–7247. 6. Nambiar, S.,. Yeow, J. T. W. Polymer-Composite Materials for Radiation Protection, ACS Appl. Mater. Interfaces 2012, 4, 5717–5726. 7. Mahmood, N., Zhang, Ch., Yin, H., Hou, Y. Graphene-based nanocomposites for energy storage and conversion in lithium bat-teries, supercapacitors and fuel cells, J. Mater. Chem. A 2014, 2, 15-32 8. Willard, M. A., Kurihara, L. K., Carpenter, E. E., Calvin, S., Harris, V. G. Chemically prepared magnetic nanoparticles, Int. Mater. Rev. 2004, 49, 125–170. 9. Cushing, B. L., Kolesnichenko, V. L., O'Connor, Ch. J. Recent Advances in the Liquid-Phase Syntheses of Inorganic Nanoparticles, Chem. Rev. 2004, 104, 3893–3946.


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Figure 1. SEM images (left), XRD patterns (right) for raw (a) Au nanoparticles, (b) Fe3O4 nanoparticles, (c) Co-oxides nanoparticles (the hash (#) correspond to Co3O4 phase, the stars (*) denote the peaks corresponding to CoO phase), and (d) NiO nanoparticles. 142x134mm (300 x 300 DPI)


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Figure 2. SEM images, particle size distributions and XRD patterns for Au/CoxOy particles obtained by laser irradiation under different process conditions: (a) 1 h, 100 mJ/pulse.cm2, (b) 1h, 177 mJ/pulse.cm2, and (c) 2 h, 177 mJ/pulse.cm2, (molar ratio of Au:CoxOy=1:1). The corresponding average sizes are (a) 310±117 nm, (b), 590±105 nm, and (c) 700±181 nm. #: Au, *:Au-Co alloy, &: Co and/or CoCx. 183x102mm (300 x 300 DPI)



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Figure 3. SEM, TEM images and XRD patterns of Au/FexOy particles synthetized by laser irradiation (100 mJ/pulse.cm2, 1h) with different molar ratio of Au:Fe3O4: (a) 1:10, (b) 1:1, and (c) 10:1. #: Au, *:Au-Fe alloy, &: Fe3O4, v: FeO. 161x102mm (300 x 300 DPI)


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Figure 4. SEM, TEM images and XRD patterns of Au/CxOy particles synthesized by laser irradiation (100 mJ/pulse.cm2, 1h) with different molar ratio of Au:CoxOy: (a) 1:10, (b) 1:1, and (c) 10:1. #: Au, *:Au-Co alloy, &: Co. 161x102mm (300 x 300 DPI)



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Figure 5. SEM, TEM images and XRD patterns of Au/NiO particles synthetized by laser irradiation (100 mJ/pulse.cm2, 1h) with different molar ratio of Au:NiO: (a) 1:10, (b) 1:1, and (c) 10:1. #: Au, *:Au-Ni alloy, &: NiO, v: Ni, ^:Ni3C. 161x102mm (300 x 300 DPI)


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Figure 6. Particle-size dependence of absorption efficiency obtained by Mie calculations for Au, Fe3O4, FeO, Co3O4, and NiO at 532 nm. 287x199mm (300 x 300 DPI)



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Figure 7. Particle size dependence of the required laser fluence J for (a) Au, (b) Fe3O4, (c) Co3O4, (d) NiO systems to heat a particle to the melting point, to complete melting, to heat to the boiling point, and to complete evaporation, using 532 nm laser. 178x131mm (300 x 300 DPI)


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Figure 8. (a) UV-vis absorption spectra Au/CoxOy particles with various molar ratios of Au:CoxOy. (b) Magnetic hysteresis loops at 300 K for Au/CoxOy obtained by laser irradiation with various laser fluence 100 mJ/pulse.cm2 (black solid line), and 177 mJ/pulse.cm2 (blue dotted line). The inset is the magnification around origin. 70x27mm (300 x 300 DPI)



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TOC Graphic 95x95mm (300 x 300 DPI)


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Phases of Gold-Based Nanocomposite

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