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AuFePt Ternary Homogeneous Alloy Nanoparticles with Magnetic and Plasmonic Properties Priyank Mohan, Mari Takahashi, Koichi Higashimine, Derrick Mott, and Shinya Maenosono Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b04363 • Publication Date (Web): 23 Jan 2017 Downloaded from http://pubs.acs.org on January 27, 2017

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AuFePt Ternary Homogeneous Alloy Nanoparticles with Magnetic and Plasmonic Properties Priyank Mohan, Mari Takahashi, Koichi Higashimine, Derrick Mott, Shinya Maenosono* School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan

ABSTRACT Combining Au and Fe into a single nanoparticle is an attractive way to engineer a system possessing both plasmonic and magnetic properties simultaneously. However, the formation of the AuFe alloy is challenging due to the wide miscibility gap for these elements. In this study, we synthesized AuFePt ternary alloy nanoparticles as an alternative to AuFe alloy nanoparticles, where Pt is used as a mediator which facilitates alloying between Au and Fe in order to form ternary alloy nanoparticles. The relationship between composition, structure and function is investigated and it was found that at an optimized composition (Au52Fe30Pt18), ternary alloy NPs exhibit both magnetic and plasmonic properties simultaneously. The plasmonic properties are investigated in detail using a theoretical Mie model and found that it is governed by the dielectric constant of the resulting materials.

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Introduction Multimetallic nanoparticles (NPs) hold abundant opportunities to create systems having an extended range of physico-chemical properties in comparison to their monometallic counterparts. This concept has been greatly exploited by mixing more than one metallic element into a single nanoparticle where the synthetic strategy used can lead to alloys, heterostructures or intermetallics.1-4 Manipulation of the NP structure opens up wide opportunities to tune the particle properties, either (i) by producing synergistic effects in the chemical and physical properties possessed in the case of alloys5 and intermetallics or (ii) by producing multifunctionality through incorporation of multiple pure metals as in the case of core-shell,6 janus7 and several other types of heterostructured particles. Therefore, multimetallic NPs have become a promising candidate for various applications in the fields of catalysis, electronics, magnetics, plasmonics, biomedicine, and so on.8 Alloy NPs also have unique characteristics where the constituent elements can often become easier to form metastable phases even though those elements are immiscible, and thus it enables us to explore novel materials consisting of metastable phases.9,10 Obtaining new alloy compositions in nanomaterials that are typically immiscible could lead to the discovery of new and unique properties due to synergistic effects which are not possible at bulk scale. Ag-Rh and Pd-Ru alloy NPs which exhibit superior electronic and/or catalytic properties have been reported as such examples.2 Integration of magnetic elements such as Fe, Co and Ni and plasmonic noble metals such as Au and Ag into alloy NPs is an interesting endeavor to explore a novel class of magneticplasmonic multifunctional NPs, for example, AuFe,11 AuNi,12 AuCo,13 AgCo,14 or AgNi,15 which are potentially useful for various applications in the fields of sensing (plasmonics and SERS),11 biotechnology,12 catalysis,13-15 etc. It has been well known that both Au and Fe show


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extraordinary properties at the nanoscale.16-18 However, alloying Au with Fe is challenging, because of the large miscibility gap in the binary Au-Fe system for the bulk scale. The AuFe alloy is thermodynamically unstable when the Fe concentration is more than 2.5 atm% at room temperature.19 A metastable AuFe alloy can be obtained only by kinetically-controlled sudden cooling of the molten metals20 or radiofrequency sputtering.21 Recently, AuFe alloy NPs have been synthesized either by physical methods including sequential ion implantation of Fe atoms in Au NPs embedded in a silica matrix,22 pulsed laser deposition,23 laser ablation of bulk alloy target in a liquid medium,19,24 or by wet-chemical synthesis methods.25-28 Despite these efforts, there are many controversial issues in the AuFe NP system in terms of structural and physical properties. For example, in many cases, the structural characterization is insufficient to definitively conclude that AuFe alloy NPs were formed without any phase segregation.25,26 In another example, some papers reported that the peak wavelength of the localized surface plasmon resonance (LSPR) band of the AuFe alloy NPs was redshifted compared to that of Au NPs with the same size and shape,25,26 while the LSPR peak of AuFe alloy NPs was reported to blueshift in some other papers.11,23 Among the existing literature with respect to AuFe alloy NPs, Amendola and coworkers have recently shown relatively reliable results in a series of experiments.11,19,24,29 They succeeded in synthesizing AuFe alloy NPs in which the maximum Fe concentration is 15 atm% by laser ablation of a bulk alloy target in a liquid medium. Even though much effort has been made to create AuFe alloy NPs as described above, there still remain several limitations in terms of ease of synthesis and physical properties of the resulting NPs. On the other hand, either Au or Ag has traditionally been incorporated in FePt NPs as an “impurity” by chemical synthetic methods to lower the phase transition temperature from


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chemically-disordered fcc FePt phase to chemically-ordered fct FePt phase.30,31 In addition, alloying Au with Pt is known to be relatively easy in the nanoscale structure and thus AuPt alloy NPs have also been successfully synthesized,9 even though those elements are immiscible. Being inspired by these facts, we conceived an idea to chemically synthesize AuFePt ternary alloy NPs in lieu of AuFe binary alloy NPs using Pt as a mediating element for alloying Au and Fe. To the best of our knowledge, no study has been reported with respect to an in-depth investigation of the structural and physical properties of chemically-synthesized AuFePt ternary alloy NPs. With this in mind, AuxFeyPt100-x-y ternary alloy NPs with systematically controlled composition were synthesized and it was found that Au52Fe30Pt18 NPs simultaneously exhibit both superparamagnetic and LSPR properties. Because it is well known that alloying Au with Pt leads to significant damping of the LSPR extinction, the structure and physical properties of the resulting NPs were thoroughly investigated using various analytical techniques to elucidate the expression of the multifunctionality observed in Au52Fe30Pt18 NPs.

Experimental Section Chemicals Gold(III) chloride trihydrate (HAuCl4·3H2O, purity ≥99.9%), iron(III) acetylacetonate [Fe(acac)3, purity ≥99.9%), platinum(II) acetylacetonate [Pt(acac)2, purity ≥97.0%) and oleylamine (OAM, purity 70%) were purchased from Sigma-Aldrich and used as received. Toluene, acetone and methanol were purchased from Kanto chemicals. Synthesis of AuxFeyPt100-x-y NPs AuxFeyPt100-x-y alloy NPs were synthesized by the hot injection method as shown in Scheme 1. In a typical synthesis, firstly α mmol (0 ≤ α ≤ 0.5) of Pt(acac)2 and 20 mL of OAM were put into


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a three-necked flask. Then, the reaction mixture was vigorously stirred for 10 min with Ar bubbling at room temperature. Subsequently, the reaction temperature was raised to 300 °C with Ar bubbling. During increasing the temperature, 0.5 mmol of Fe(acac)3 and β mmol (α + β = 0.5 ≡ const) of HAuCl4·3H2O dissolved in a mixture of 0.5 mL of OAM and 3.5 mL of toluene (stock solution) was quickly injected into the reaction mixture when the temperature reached 190 °C.

Scheme 1. Schematic illustration of the synthesis of AuxFeyPt100-x-y ternary alloy NPs.

After the injection of the stock solution, the reaction temperature was elevated to 300 °C and then the reaction was continued for 1 hour at 300 °C. After the reaction, the mixture was allowed to cool down to room temperature naturally. Finally, the resulting NPs were washed several times by centrifuging with a mixture of toluene, acetone and methanol. A summary of the reaction conditions is summarized in Table 1. Characterization of AuxFeyPt100-x-y NPs The resulting NPs were characterized by transmission electron microscopy (TEM), a scanning TEM (STEM) equipped with a high-angle annular dark-field (HAADF) detector, energydispersive X-ray spectroscopy (EDS) elemental mapping, inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), superconducting quantum interference device (SQUID) magnetometry and ultraviolet5 ACS Paragon Plus Environment

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visible spectroscopy (UV-vis). TEM analysis was performed on a Hitachi H-7650 microscope operated at 100 kV. STEM-HAADF imaging and EDS elemental mapping were performed on a JEOL JEM-ARM200F microscope operated at 200 kV with a spherical aberration corrector, and a nominal resolution of 0.8 Å. ICP-OES analysis was performed on a Shimadzu ICPS-7000. XRD patterns were collected on an X-ray diffractometer (Rigaku MiniFlex600) operated in reflection geometry at room temperature with Cu Kα radiation (1.5418 Å). XPS analysis was performed on a high-performance XPS system (Shimadzu Kratos AXIS-ULTRA DLD). Photoelectrons were excited by monochromated Al Kα radiation. The SQUID analysis was performed on a Quantum Design MPMS. UV-vis spectra were recorded on a JASCO V-670 spectrophotometer.

Table 1. Input moles of Pt(acac)2 (α) and HAuCl4·3H2O (β) and their ratios. Sample

Pt(acac)2, α, (mmol)

HAuCl4·3H2O, β, (mmol)

α : β (%)

A B C D E F G

0.5 0.4375 0.375 0.3125 0.25 0.125 0

0 0.0625 0.125 0.1875 0.25 0.375 0.5

100 : 0 87.5 : 12.5 75 : 25 62.5 : 37.5 50 : 50 25 : 75 0 : 100

Results Structure and composition Figure 1 shows TEM images of AuxFeyPt100-x-y NPs synthesized with different conditions (samples A-G) as shown in Table 1. As can be seen in Fig. 1, NPs were well-separated on a TEM grid in all samples indicating that the NPs were well dispersed in a solvent without aggregation.


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With increasing Au/Pt input molar ratio, the mean size of NPs increased and the shape of the NPs changed from irregular to spherical. More specifically, the seed-like shaped NPs are mainly observed in the case of sample A (β = 0) (Fig. 1a), and worm-like shaped NPs are distinct in the cases of samples B (β = 0.0625) and C (β = 0.125) (Fig. 1b and 1c), while spherical NPs become dominant in the cases of samples D-G (Fig. 1d-1g). The mean spherical diameters of NPs were calculated to be 5.5 ± 0.7, 8.1 ± 1.9, 7.0 ± 1.4, 7.9 ± 1.2, 8.9 ± 1.1, 10.2 ± 1.7 and 17.0 ± 2.7 nm for samples A-G, respectively, as shown in Fig. S1a-S1g (Supporting Information). In the inset of Fig. 1f, as a typical example, a high resolution TEM image of a single NP in sample F is shown. As can be seen, well defined lattice fringes with interplanar distance of 2.3 Å which corresponds to the (111) plane are clearly observed. This lattice spacing is found to be in between those of fcc FePt(111) (2.2 Å) and fcc Au(111) (2.4 Å)32 indicating the formation of fcc AuFePt alloy NPs.

Figure 1. TEM images of AuxFeyPt100-x-y alloy NPs, from (a) to (g), corresponding to samples AG (see Table 2). The scale bars are 50 nm. The inset in panel (f) shows a high resolution TEM image of a single NP in sample F. (h) The mean size of NPs plotted versus the input moles of Au precursor, β.


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Figure 2a shows the STEM-HAADF image of two individual NPs in sample F (β = 0.375). The contrast of the NPs is uniform throughout the entire area of the NPs also indicating the successful formation of homogeneous alloy NPs. Figure 2b-2e shows the EDS elemental mapping images for Au, Fe and Pt, and overlaid image, respectively. All three elements were uniformly distributed within the NPs supporting the formation of homogeneous alloy NPs. STEM-HAADF and EDS elemental mapping images of other samples are shown in Figs. S2-S7 (Supporting Information). By taking a close look at the EDS mapping images, Fe is found to be slightly rich at the surface of the NPs, nevertheless the alloying of the three metals is likely to occur in samples B-F. In the case of sample G, however, only trace amounts of Fe is present on the surface of the NPs (Fig. S7, Supporting Information) without forming AuFe alloy NPs. These results strongly suggest that Pt plays an important role in the formation of AuxFeyPt100-x-y ternary alloy NPs.

Figure 2. (a) STEM-HAADF and (b-e) EDS elemental mapping images of two distinct NPs in sample F (upper and lower panels): (b) Au L edge, (c) Fe K edge, (d) Pt L edge, and (e) overlay.

The atomic compositions of sample A-G determined by ICP-OES, XPS and EDS are shown in Table 2. By taking the average of atomic compositions determined by different analytical 8 ACS Paragon Plus Environment

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techniques, we determined the compositions of samples A-G as listed in Table 2. It is worth noting that the actual compositions of samples B-G are different from the input molar ratio of the metallic precursors.

Table 2. Atomic composition of AuxFeyPt100-x-y alloy NPs. Sample A B C D E F G

ICP-OES x 0 6 15 29 36 56 100

XPS

y 48 45 41 35 33 25 0

x 0 5 12 24 28 47 97

EDS Y 47 46 47 39 42 34 3

X 0 4 11 21 33 52 95

y 53 51 47 43 40 32 5

Composition Fe49±3Pt51±3 Au5±1Fe47±3Pt48±2 Au13±2Fe45±3Pt42±2 Au25±4Fe39±4Pt36±1 Au33±4Fe38±5Pt29±2 Au52±5Fe30±5Pt18±2 Au97±3Fe3±3

XRD patterns of samples A-G are shown in Fig. 3. In the case of sample A, the XRD pattern is typical of chemically-disordered fcc FePt phase (Fig. 3A). The XRD pattern of sample B is almost identical to that of sample A as shown in Fig. 3. With increase in the content of Au and corresponding decrease in Pt (moving from sample C to G), the (111) peak systematically shifted toward lower angle indicating that AuxFeyPt100-x-y alloy NPs with different compositions were successfully formed. This result is consistent with the results of STEM-HAADF and EDS elemental mapping images (Fig. 2). Magnetic properties Magnetic properties of as-synthesized NPs were measured by SQUID magnetometer. Figure 4 shows magnetization (M-H) curves of samples A-F taken at 300 K and 5 K. All samples are found to be superparamagnetic at 300 K, while they exhibit ferromagnetic behavior at 5 K. Note that sample G (Au97Fe3) exhibited a diamagnetic response which is typical of Au (data not 9 ACS Paragon Plus Environment

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shown). In Table 3, the saturation magnetization (MS) values of samples A-F are summarized. The value of MS of alloy NPs is basically dependent on the atomic fraction and oxidation state of Fe. In fact, the value of MS is approximately proportional to the atomic fraction of Fe in the NPs.

Figure 3. XRD patterns of as-synthesized alloy NPs, from top to bottom, corresponding to samples A-G listed in Table 2, respectively. The reference patterns shown in the figure are fcc Au (blue line, JCPDS PDF No. 01-071-4615), bcc Fe (red line, No. 01-071-4410), fcc Pt (green line, No. 00-004-0802) and fcc FePt (purple line, No. 03-065-9122).


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Figure 4. M-H curves of as-synthesized alloy NPs, from (a) to (f), corresponding to samples A-F listed in Table 2, respectively. Black and red lines represent M-H curves measured at 5 K and 300 K, respectively.

Table 3. The values of MS of samples A-F. Sample A B C D E F

MS at 300 K (emu/g) 23.6 28.5 26.1 15.7 16.3 7.8

MS at 5 K (emu/g) 33.6 35.9 33.5 23.3 23.1 12.7


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Plasmonic properties Figure 5 shows UV-vis spectra of samples A-G. Since the LSPR extinction spectrum is known to highly depend on the size, shape and concentration of NPs,33,34 the LSPR extinction spectra in the present study were normalized with respect to the number of NPs (i.e. the concentration of NPs). Because the difference in the mean sizes of NPs in all samples is too small to have significant effect on the LSPR properties,19 the contribution of the difference in size and shape to the LSPR extinction spectra was omitted. Because Fe and Pt are known to have no LSPR band within the visible range, sample A (Fe49Pt51) naturally exhibits no LSPR band within the visible range. In addition, samples B-E also did not show any LSPR feature mainly because of the damping effect of Pt on the LSPR property of Au.35 Interestingly, however, sample F (Au52Fe30Pt18) clearly exhibited an LSPR band in the extinction spectrum. The LSPR peak wavelength is 513 nm which is significantly blueshifted from the LSPR peak (526 nm) of Au NPs (sample G).

Figure 5. UV-vis spectra of toluene dispersions of as synthesized AuFePt ternary alloy NPs. 12 ACS Paragon Plus Environment

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Discussion Formation mechanism of AuFePt alloy NPs The reduction potential of Au3+/Au (1.5 V versus SHE)36 is highest among the three elements (Au, Fe and Pt). Therefore Au would be separately reduced first in the early stage of reaction, and thus the creation of a homogeneous alloy NPs is likely to fail when all metal precursors are put into the flask from the beginning. On the other hand, it is known that Pt nucleates first and then Fe deposits on the surface of Pt nuclei followed by atomic interdiffusion of those elements during the synthesis of FePt NPs,37 because the reduction potential of Pt2+/Pt (1.18 V versus SHE)36 is much higher than that of Fe3+/Fe (-0.047 V versus SHE).36 In the present study, in order to synthesize AuFePt ternary alloy NPs, Pt precursor was first heated to 190 °C. When the reaction temperature reaches 190 °C at which the onset of Pt reduction was observed, Au and Fe precursors were simultaneously injected into the reaction solution. By doing so, AuPt seeds were immediately formed, and then Pt sites on the surface of AuPt seeds act as a catalyst to reduce Fe cations. As a result, AuFePt ternary alloy NPs were formed by the same mechanism as the case of FePt NPs. As summarized in Table 2, the atomic fraction of Fe in the resulting NPs seems to be pulled down along with Pt atomic fraction even though the input mole of Fe precursor was kept constant. This trend is most obvious in sample G. This result clearly suggests that Au seeds do not facilitate the reduction of Fe cations, while Pt and AuPt seeds do. Alternatively or simultaneously, alloying Au with Pt would enhance the solubility of Fe in a AuPt alloy. Therefore, it can be concluded that Pt plays several critical roles in the formation of AuFePt alloy NPs.


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It is also worth noting that AuxFeyPt100-x-y NPs with low Au atomic composition (0 < x ≤ 15: samples B and C) exhibit worm-like morphology as mentioned earlier (Fig. 1b and 1c). In general, the growth behaviour of NPs in colloidal synthesis depends upon the balance between the attractive van der Waals forces between the NPs and repulsive force due to the surfactant capping on the NPs surface, which is element specific. In addition, due to the different adsorption energies of surfactant on the different facets of the crystal, this leads to anisotropic growth of the NPs and therefore in the case of alloy with different compositions can show varying growth behaviour. Composition dependent morphologies in sample B and C have been observed previously in Pt-based alloy NPs and are attributed to the oriented attachment mechanism of small seed NPs along specific crystal planes.38,39

For instance, Peng and

coworkers demonstrated the unusual growth formation of Pt53Ag47 alloy nanowires due to the oriented attachment of the primary NPs along the (111) crystal plane, while other Pt-rich and Agrich PtAg alloy NPs formed sphere-like or faceted shape NPs under the same reaction conditions.38 When, OAM is used as capping ligand on the Pt and Pt-based crystals, the OAM adsorption energy is on the order of (110) > (100) > (111),38,40 which leads to growth of the NPs along the (111) direction resulting in the formation of nanowire type structures. Formation of the worm-like structures in sample B and C is attributed to the same growth mechanism. Magnetic properties As mentioned earlier, the value of MS is approximately proportional to the atomic fraction of Fe in the NPs as shown in Table 3. To compare the values of MS among different samples more precisely, the value of MS was normalized to the total mass of Fe atoms in the AuxFeyPt100-x-y alloy NPs. Figure 6 shows the normalized values of MS plotted versus the atomic fraction of Fe. If there is no difference in the state of Fe atoms, the curve plotted in Fig. 6 should be flat.


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However, the normalized value of MS of sample F (y = 30) appears to be significantly lower. To clarify the reason of the reduction in MS, XPS spectra were recorded for samples A-F as shown in Fig. S8 (Supporting Information). As can be seen in Fig. S8f and Table S6, the fraction of Fe0 component in sample F is found to be significantly lower than those in other samples. These results suggest that the oxidation of Fe atoms segregated to the surface of NPs could not be effectively suppressed presumably due to significantly lower Pt atomic fraction in sample F than other samples resulting in the formation of thicker iron oxide layer in the case of sample F which effectively reduces the value of MS of the NPs.

Figure 6. Plot of Ms normalized to the total mass of Fe atoms versus the atomic fraction of Fe, y.

Plasmonic properties As shown in Fig. 5, sample F (Au52±5Fe30±5Pt18±2) clearly exhibited an LSPR band in the extinction spectrum, while other ternary alloy NPs did not. It has been reported that the LSPR band was completely damped in the case of bimetallic Au50Pt50 alloy NPs.35 For comparison, we 15 ACS Paragon Plus Environment

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synthesized AuPt binary alloy NPs keeping the reaction scheme the same. The resulting NPs were characterized by TEM, XRD, EDS, etc., and it was confirmed that they are homogeneous Au47±9Pt53±9 alloy NPs of mean diameter of 6.9±1.1 nm (Fig. S9, Supporting Information). As shown in Fig. S10 (Supporting Information), the LSPR band is found to be completely damped in the UV-vis spectrum of equiatomic AuPt NPs. This result indicates that Fe has less damping effect on the LSPR property of Au than Pt. To further investigate the mechanisms underlying the lower damping effect of Fe on the LSPR property than Pt, the extinction spectra of alloy NPs were simulated by Mie theory calculation. According to Mie theory, optical extinction cross-section, σ ext , can be calculated as41

σ ext =

3/ 2 18πε m

λ

V

ε 2 (λ )

[ε1 (λ ) + 2ε m ]2 + [ε 2 (λ )]2

(1)

where V is the volume of a single NP, λ is the wavelength of light, ε m is the dielectric constant of the surrounding medium. Here ε1 (λ ) and ε 2 (λ ) are the real and imaginary parts of the dielectric function of the NP, respectively. Because the difference in the mean sizes of NPs in all samples is too small to have significant effect on the LSPR properties,19 the contribution of the difference in size to the LSPR extinction spectra can be neglected. The surrounding medium was toluene for all samples, and thus ε m is constant. Therefore, the determining factors for the LSPR property are ε1 (λ ) and ε 2 (λ ) which depend on the atomic composition of alloy NPs. Since the values of ε1 (λ ) and ε 2 (λ ) for AuxFeyPt100-x-y alloy are not available in the literature, and due to the lack of any generalized formula for the calculation of dielectric constants in the case of alloy NPs, the composition-weighted linear average of the elemental components have been used for 16 ACS Paragon Plus Environment

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the estimation of effective dielectric constant of the alloy NPs. Thus we estimated ε1 (λ ) and

ε 2 (λ ) by the linear average of the real and imaginary parts of the dielectric function of the components weighted by their atomic fractions given as

ε 1alloy , 2 (λ ) =

x Au y Fe 100 − x − y Pt ε 1, 2 (λ ) + ε 1,2 (λ ) + ε 1,2 (λ ) 100 100 100

(2)

Fe Pt where ε1Au , 2 (λ ) , ε1, 2 ( λ ) and ε1, 2 ( λ ) denote the real and imaginary parts of the dielectric

function of Au, Fe and Pt, respectively. The values of each dielectric function were taken from the existing literature (see Fig. S11 in the Supporting Information).36,42 Figure S12 (Supporting Information) shows the calculated extinction spectra of Au, Fe and Pt monometallic NPs. Then, the extinction spectrum of Au52±5Fe30±5Pt18±2 ternary alloy NPs (sample F) was fitted based on Eq. (1) by varying the atomic fractions of components, i.e. x and y, within the range of composition variation. In consequence, the composition of ternary alloy NPs which gives a bestfit was determined to be Au51Fe30Pt19 as shown in Fig. 7. Figure 8 shows ε1 (λ ) and ε 2 (λ ) in the cases of Au51Fe30Pt19 and AuPt. The reason why Au51Fe30Pt19 ternary alloy NPs show a distinct LSPR band while the LSPR band is completely damped in the case of equiatomic AuPt binary alloy NPs is mainly due to relatively smaller ε 2 (λ ) of Au51Fe30Pt19 than that of AuPt, which was caused by the incorporation of Fe. Based on this analysis, we can conclude that the alloying of AuPt with a third element which has lower ε 2 (λ ) than Pt can dilute the damping effect of Pt.


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Figure 7. (a) Calculated extinction spectra corresponding to AuPt NPs (black) and sample F (red). (b) Actual UV-vis spectra of AuPt NPs (black) and sample F (red).

Figure 8. Calculated dielectric functions corresponding to AuPt NPs (black) and sample F (red).


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Conclusion AuxFeyPt100-x-y ternary alloy NPs with different atomic compositions were successfully synthesized and the composition-structure-property relation was investigated. In consequence, it is found that Pt and Fe play crucial roles in the formation of ternary alloy NPs and their physical properties. More specifically, Pt acts as a mediator of integration between Au and Fe to create homogeneous AuxFeyPt100-x-y ternary alloy NPs, and Fe acts as a dilution agent to counteract the damping effect of Pt on the LSPR band as well as a source of magnetism. It is demonstrated that both superparamagnetic and LSPR properties were simultaneously expressed in AuxFeyPt100-x-y alloy NPs with an optimal composition (Au52Fe30Pt18). Base on Mie calculation, it is revealed that the alloying of AuPt with a third element (such as Fe) which has a lower imaginary part of the dielectric function than Pt can dilute the damping effect of Pt on the LSPR property of the ternary alloy NPs. The present study will open a new avenue to design a novel class of magneticplasmonic multimetallic alloy NPs. In addition, it will give insight into the creation of multielement nanocrystals with new compositions that are typically immiscible.

ASSOCIATED CONTENT Supporting Information Size distributions of as-synthesized AuxFeyPt100-x-y ternary alloy NPs (samples A-G), STEMHAADF and EDS elemental mapping images of samples A-G (except for F), Fe 2p XPS spectra of samples A-F and corresponding peak parameters, TEM image and XRD pattern of assynthesized Au47Pt53 binary alloy NPs, UV-vis spectrum of a toluene dispersion of Au47Pt53 alloy NPs, the real and imaginary parts of the dielectric function of Au, Fe and Pt, and calculated


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extinction spectra of Au, Fe and Pt monometallic NPs. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *(Word Style “FA_Corresponding_Author_Footnote”). * (Word Style “FA_Corresponding_Author_Footnote”). Give contact information for the author(s) to whom correspondence should be addressed. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by a Grant-in-Aid for Scientific Research, Grant no. 26600053 (S.M.).

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TOC GRAPHIC and SYNOPSIS Magnetic-plasmonic dual-functional AuFePt ternary alloy nanoparticles are created using Pt as a mediating element for alloying Au and Fe.


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Figure 1 88x43mm (300 x 300 DPI)

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Figure 4 125x90mm (300 x 300 DPI)


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Figure 8 114x155mm (300 x 300 DPI)


AuFePt Ternary Homogeneous Alloy ... - ACS Publications

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