Intense Femtosecond Laser-Mediated Electrical Discharge Enables

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Intense Femtosecond Laser Mediated Electrical Discharge Enables Preparation of Amorphous Nickel Phosphide Nanoparticles Zhuo-Chen Ma, Qi-Dai Chen, Bing Han, He-Long Li, Lei Wang, Yong-Lai Zhang, and Hong-Bo Sun Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b04190 • Publication Date (Web): 29 Apr 2018 Downloaded from http://pubs.acs.org on April 30, 2018

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Intense Femtosecond Laser Mediated Electrical Discharge Enables Preparation of Amorphous Nickel Phosphide Nanoparticles †

†

†

†

†

†

Zhuo-Chen Ma, Qi-Dai Chen,* Bing Han, He-Long Li, Lei Wang, Yong-Lai Zhang, and Hong-Bo Sun †

†

State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and

Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China.

ACS Paragon Plus Environment

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ABSTRACT: Reported here is a high-efficiency preparation method of amorphous nickel phosphide (Ni-P) nanoparticles by intense femtosecond laser irradiation of nickel sulfate and sodium hypophosphite aqueous solution. The underlying mechanism of the laser assisted preparation was discussed in terms of the breaking of chemical bond in reactants via highly intense electric field discharge generated by the intense femtosecond laser. The morphology and size of the nanoparticles can be tuned by varying the reaction parameters such as ions concentration, ions molar ratio, laser power, and irradiation time. XRD and TEM results demonstrated that the nanoparticles were amorphous. Finally, TG-DTA experiment verified that the as-synthesized non-crystalline Ni-P nanoparticles had an excellent catalytic capability towards thermal decomposition of ammonium perchlorate. This strategy of laser mediated electrical discharge under such an extremely intense field may create new opportunities for decomposition of molecules or chemical bonds that could further facilitate the recombination of new atoms or chemical groups, thus bringing about new possibilities for chemical reaction initiation and nanomaterial synthesis that may not be realized under normal conditions. KEYWORD: femtosecond laser, intense laser field, nonlinear optics, electrical discharge, nickel phosphide nanoparticles


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INTRODUCTION Nickel phosphide (Ni-P) nanoparticles have excellent electric, magnetic, and optical properties, which makes them ideal catalysts for various energy materials, e.g. thermal decomposition of ammonium perchlorate (a key energy material for rocket propellants),1,2 hydrodesulphurization (HDS),3 hydrodenitrogenation (HDN),4 hydrogen evolution reaction,5-7 magnetic storage,8,9 electrode materials for Li batteries,10-12 and water splitting.13-15 In addition, they are good conductors of heat and electricity and they also have high thermal and chemical stability.16 Triggered by these unique properties, great efforts have been devoted to the development of novel synthesis strategies for preparation of Ni-P nanoparticles, including vapor deposition,17,18 sol-gel methodology,19 and hydrothermal/solvothermal reactions.20-24 Although these approaches have been successfully adopted for the synthesis of Ni-P nanoparticles, some problems still need to be addressed. For instance, (i) as for the hydrothermal reactions, highly active and flammable phosphorus sources (usually red phosphorus or sodium phosphide) are always employed, which makes the synthesis process very dangerous; (ii) with regard to the solvothermal reactions, some organic agents like trioctylphosphane (TOP), trioctylphosphane oxide (TOPO), or triphenylphosphane (TPP) are used as the phosphorus source or organic solvent, which are not a “green chemistry” process; (iii) in most cases, nickel nanoparticles should be prepared beforehand, and then through a following phosphorization process the Ni-P nanoparticles could be finally obtained, hence the preparation procedure becomes very complex and time consuming. Besides, the reaction conditions are difficult to control, thus often bringing about other impurities. In this regard, a synthetic method that enables preparation of Ni-P nanoparticles in a green, facile, and high-efficiency manner is highly desired, but obviously, it remains currently challenging.


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To address the above-mentioned issues, intense femtosecond laser irradiation of aqueous solutions might provide an alternative approach to reach this end.25-33 The intensity inside the focused optical field could reach approximately 1013-1014 W/cm2,25,28,31 which is high enough to excite molecules into highly excited states by multiphoton excitation. Accordingly, it is expected that such an intense optical field will strongly interact with molecules and produce highly charged ions or free radicals and electrons, giving rise to a significant optical decomposition of molecules and succeeding formation of different molecules or particles.34-37 Since the generation of such an extremely intense optical field, the focused femtosecond laser irradiation of a liquid has the potential to be a novel method for efficient initiation of chemical reactions and preparation of nanomaterials that might be out of reach under normal conditions. Herein, in this work we demonstrated a green, facile, and high efficiency synthesis strategy for Ni-P nanoparticles preparation via focused femtosecond laser irradiation of the mixture aqueous solution containing only nickel sulfate and sodium hypophosphite. By varying the laser power, irradiation time, nickel ion concentration, and relative molar ratio of the reactants, well dispersed Ni-P nanoparticles with average sizes ranging from 30 nm to approximately 140 nm were successfully prepared. In addition, the dispersibility and homogeneity of the nanoparticles were greatly improved through the addition of polyvinylpyrrolidone (PVP) as a dispersant. The formation mechanism of the Ni-P nanoparticles was also discussed in terms of the breakdown of chemical bond in the reactant via the highly intense electric field discharge generated by focused femtosecond laser. Without the use of any organic reagents, this method is undoubtedly a green procedure. Moreover, size-controllable Ni-P nanoparticles can be prepared facilely and promptly in just several minutes once irradiated by femtosecond laser, this method is considered to be quite facile and high efficiency. The intense femtosecond laser mediated electrical discharge


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processing of solutions may open up a new door for a wide range of material synthesis and chemical reactions initiation.


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EXPERIMENTAL SECTION Materials and preparation procedures. A high intensity femtosecond laser irradiation method was used to prepare the Ni–P nanoparticles. The excitation source was a Spectra-Physics Ti: sapphire amplifier laser system. The laser output had a central wavelength of 800 nm and pulse duration of 100 fs at a repetition rate of 1 kHz. The schematic map of this one-step femtosecond laser irradiation setup is described in Figure 1. Two commercially available reagents, nickel–sulfate hexahydrate (NiSO4·6H2O) and sodium hypophosphite (NaH2PO2·H2O), were directly used without further purification. The preparation detail of the reaction solution is described as follows: firstly, 5.257 g of nickel–sulfate hexahydrate was dissolved into 100 mL deionized water to get the nickel–sulfate solution with concentration of 0.2 mol/L, and 6.3594 g of sodium hypophosphite was also dissolved into 100 mL deionized water to get the sodium hypophosphite solution with concentration of 0.6 mol/L. Prior to use, 10 ml of the nickel–sulfate solution and 10 ml of the sodium hypophosphite were mixed to get a 20 ml mixture solution of nickel–sulfate and sodium hypophosphite. Then, the mixture solution was stirred on a magnetic stirring. High intensity femtosecond laser pulses were generated from the amplified Ti: sapphire laser system. The laser beam was introduced in a direction normal to the surface of the liquid sample from up to down, and it was focused using a lens (f= 200 mm) to the interior of the solutions. The diameter of the laser spot before focusing was about 5 mm. After irradiation, the black Ni–P nanoparticles were separated and collected from the solution by centrifugation after the solution was washed by deionized water three times. Characterization methods. The nanoparticle size and morphology were characterized by the JEOL JSM-6700F field emission scanning electron microscope (SEM) operating at 5.0 kV, and the composition was measured by using energy-dispersive spectrometer (EDS) analysis with the


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AMETEK APOLLP-XL EDS system integrated in the SEM system. The XRD spectrum of Ni-P nanoparticles was collected at RigakuD / Max-2550 diffractometer with Cu Kα radiation (λ = 0.15418 nm). The UV-Vis spectra were obtained with the SHIMADZU UV-2550 ultraviolet and visible spectrophotometer. The transmission electron microscopy (TEM) images were taken with a HITACHI Mic-H-600 TEM system. Catalytic performance test. In order to characterize the catalytic capability of the as-prepared Ni-P nanoparticles, TG-DTA (Thermogravimetric- Differential Thermal Analysis) tests were conducted by using STA 449C over a temperature range of 50-600 ℃. The content of the Ni-P nanoparticles was 7.0 wt. % in the ammonium perchlorate (AP) and Ni-P composites. The heating rate was 10 ℃/min. The samples were sealed in an alumina sample cell, and the samples were swept by a nitrogen flow at a rate of 50 ml/min. The total masses were 10 mg.


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RESULTS AND DISCUSSION During the experimental procedure, after the focused femtosecond laser had been irradiated into the aqueous solution that was dark green originally for several minutes, its colour faded to light green quickly. With the proceeding of irradiation, the solution around the laser focus turned turbid and black, indicating the formation of Ni-P nanoparticles. The schematic formation process is exhibited in Figure 1.

Figure 1. Schematic illustration for the preparation of Ni-P nanoparticles via intense femtosecond laser irradiation. The left is the experimental setup demonstration, and the right side shows the proposed reaction procedure.

The experimental setup is shown on the left, and the right side demonstrates the proposed coreduction procedure of Ni and P caused by the intense laser induced breakdown of the P-H bond in sodium hypophosphite, details of which will be discussed later. In order to prepare Ni-P nanoparticles with different sizes and morphologies, various reaction conditions have been


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carried out, including nickel ion concentration, reactant molar ratio, laser power (measured before the lens) and irradiation time (Table 1).

Group

a

b

c

d

C(Ni2+)

Power

Time

(mol/L)

(W)

(min)

1:1

0.1

1

10

1:2

0.1

1

10

1:3

0.1

1

10

1:4

0.1

1

10

1:5

0.1

1

10

1:3

0.01

1

10

1:3

0.05

1

10

1:3

0.1

1

10

1:3

0.2

1

10

1:3

0.3

1

10

1:3

0.1

1.2

10

1:3

0.1

1.1

10

1:3

0.1

1.0

10

1:3

0.1

0.9

10

1:3

0.1

0.8

10

1:3

0.1

1

10

1:3

0.1

1

15

1:3

0.1

1

20

1:3

0.1

1

25

1:3

0.1

1

30

c(Ni2+)/c(H2PO2-)

Table 1. Different reaction parameters including the molar ratio between the nickel ion and the sodium hypophosphite, the nickel ion concentration, the laser power, and the irradiation time.


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Firstly, a series of samples with different molar ratios between the nickel ion and the sodium hypophosphite (1:1, 1:2, 1:3, 1:4, and 1:5 respectively) were adopted under the irradiation of femtosecond laser irradiation. The concentration of nickel ion was kept as 0.1 M, the excitation laser power was 1 W, and the irradiation time was 10 minutes. In all these conditions, the sample solutions turned turbid and black promptly in several minutes. The as-formed Ni-P nanoparticles are shown in Figure 2, from which it can be seen that the nanoparticles’ average sizes ranged from 80 nm to 55 nm when the reactant molar ratio varied from 1:1 to 1:5. This indicates that smaller Ni-P nanoparticles were formed in solutions with increasing content of sodium hypophosphite.


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Figure 2. Dependence of the Ni-P nanoparticle size distribution on the molar ratio between nickel ion and sodium hypophosphite (1:1, 1:2, 1:3, 1:4, and 1:5 respectively). Other factors that might influence the synthesis procedure were also studied in detail, including nickel ion concentration (Figure S1), excitation laser power (Figure S2) and irradiation


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time (Figure S3). Therefore, through the variation of different reaction conditions, nanoparticles with average sizes ranging from 30 nm to 140 nm could be adjusted facilely. This synthesis procedure was actually triggered by the highly intense optical field interaction with aqueous solution, which was a nonlinear optical effect that relies largely on the excitation laser intensity.25,28 That is, the reaction could only be initiated when the laser intensity was high enough. Hence, in our experiment, a range of laser intensity was tried from 1.59×1014 W/cm2 to 7.96×1014 W/cm2. As a result, only when the incident laser intensity was higher than 4.79×1014 W/cm2 could the reaction be observed. Figure 3 shows the UV absorption spectra of the samples after the irradiation of different laser intensity.

Figure 3. UV-Vis absorption spectra of the irradiated solutions with a series of laser intensities. From up to down: solutions irradiated with 7.96×1014 W/cm2, 6.37×1014 W/cm2, 4.79×1014 W/cm2, 3.18×1014 W/cm2, 1.59×1014 W/cm2, and without irradiation respectively. As can be seen, the samples processed with a laser intensity larger than 4.79×1014 W/cm2 depicted an evident absorption increase between the wavelength ranges of 300-900 nm owing to the formation of Ni-P nanoparticles. While those samples irradiated with a laser intensity below


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4.79×1014 W/cm2 demonstrated no color change, indicating the failure of reaction initiation. Accordingly, these samples’ absorption spectra exhibited no change compared with the sample kept in dark. Therefore, this highly intense femtosecond laser induced synthesis reaction greatly depends on the excitation laser intensity, revealing the nonlinear optical effect of this process. The detailed structure of the as-prepared Ni-P nanoparticles under the condition of d5 was characterized by TEM images as shown in Figure 4(a). It can be seen that the nanoparticle shapes are approximately spherical with diameters about 30-40 nm. Moreover, a high-resolution TEM (HRTEM) image was shown in Figure 4(b). Obviously, the atomic configuration of the nanoparticles is principally disordered, and there are no clear long-range ordered domains, suggesting that the nanoparticles should be in a noncrystalline state. The XRD spectrum of the particles was also presented in Figure 4(c), from which we can see that a relatively weak peak was centered at approximately 44.5° and a very broad but not too distinct peak spread over 70° to 80°, which further confirmed the amorphous nature of the as-prepared Ni-P nanoparticles. Figure 4(d) illustrates the EDS measurement result, in which four elements Ni, P, Si, and O were revealed. Si and O elements can be attributed to the substrate SiO2, therefore it can be concluded that the as-prepared nanoparticles were composed only of Ni and P. The inset of Figure 4(d) shows that the atomic ratio of phosphorus increases with increasing laser power, which demonstrates the flexibility of this synthesis method in controlling the nanoparticle composition. This kind of noncrystalline Ni-P nanoparticles are considered to be very interesting and valuable because of their potential applications in catalytic activity such as thermal decomposition of AP,1,2 hydrogen evolution reaction,5-7 or hydrodesulphurization reaction.3


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Figure 4. (a) The TEM photograph of the Ni-P nanoparticles. Scale bar: 20 nm; (b) HRTEM photograph of the nanoparticle. Scale bar: 5 nm; (c) XRD spectrum of the nanoparticles; (d) EDS result of the Ni-P nanoparticles, the inset shows the relationship between the atomic ratio of phosphorus and laser power.

In order to improve the homogeneity and dispersibility of the particles synthesized by femtosecond laser irradiation, polyvinylpyrrolidone (PVP), which is commonly used as a dispersant for metal colloids, was added to the sample liquid with nickel ion concentration 0.1 M and reactant ratio 1:3. The incident laser power was set to be 1 W, and the irradiation time was 10 minutes. By adding PVP with different concentrations (0.05 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M,


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and 1M) into the solution, it could be observed that the nanoparticles configuration and their dispersibility varied significantly, as shown in Figure 5. When the PVP concentration was relatively lower (from 0.05 M to 0.4 M), the homogeneity and dispersibility of the particles could be improved evidently, which were displayed in Figure 5(a)-(c). Whereas, if PVP solution with higher concentration was added, the particles had a tendency to merge together instead (Figure 5d-f). Note that as shown in Figure 5(g), particularly when 0.4 M PVP was adopted, the size distribution became narrower than the other distributions without adding PVP, and most of the particles were approximately 35 nm in diameter, besides their morphologies were improved prominently. Thus, the addition of 0.4 M PVP could drastically improve the morphology and homogeneity of the nanoparticles in our experiment.


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Figure 5. (a-f) SEM images of the prepared Ni-P nanoparticles using PVP as a dispersant with different concentrations: (a) 0.05 M PVP; (b) 0.2 M PVP; (c) 0.4 M PVP; (d) 0.6 M PVP; (e) 0.8 M PVP; (f) 1 M PVP. Scale bar: 300 nm; (g) Comparison of size distributions between the nanoparticles synthesized using 0.4 M PVP and those without using PVP, the red curves are their fitting results.

Additionally, the effect of femtosecond laser irradiation on PVP itself was examined by processing PVP aqueous solution with different concentrations (0.05 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, and 1M) using the same method as above. Consequently, after irradiation for several tens of minutes, not any black sediment was observed throughout the process for all these samples, demonstrating that no particles could be fabricated by the intense femtosecond laser irradiation of pure PVP solution. Therefore, PVP was considered to perform well as a dispersant in our experiment, without introducing any impurities. To better understand the formation procedure of the as-prepared nanoparticles, taking the underlying synthesis mechanism into consideration is extremely necessary. In previous studies, Tan et al. reported successful preparation of Ni-P nanoparticles via a liquid pulse discharge method.2,38,39 In their work, a peak voltage of 1200 V was applied between a pair of needle-like electrodes about 3 mm apart, which equaled approximately to an average electric field of 4×105 V/m assuming that this electric field between the electrodes was uniform. Actually, this electric field was not like this, meaning that relatively stronger regions and other relatively weaker regions existed simultaneously. The electric field in those strong regions could reach as high as 109 ~1010 V/m, which was strong enough and responsible for initiating the chemical reactions of Ni-P nanoparticles formation. While in our own experiment, for the focused femtosecond laser


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with an average power of 0.6 W and a focal length of 200 mm, the diameter of the focused laser spot could be estimated using the following formula:

d=

2λ f

πω0

(1)

where λ represents the laser wavelength, f represents focal length of the lens, and ω0 represents radius of the laser spot before focusing. Therefore, the diameter was approximately 40 µm after calculation. Then the laser intensity was calculated to be 4.79×1014 W/cm2, and thus the corresponding electric field was 5.21×1010 V/m (shown in Table 2). Whereas, as for the unfocused laser with the same average power of 0.6 W, the laser intensity was 3×1010 W/cm2, accordingly the electric field was only 4.13×108 V/m, which was about two orders of magnitude lower than that of focused femtosecond laser. The contrast of sample solutions under these two kinds of laser irradiation with their stock solutions that suffered no laser irradiation was shown in Figure S4, from which we can see that the solution under focused laser irradiation turned black in just ten minutes (Figure S4a), but the other solution under unfocused laser irradiation exhibited no color change even after one hour (Figure S4b). Therefore, it was very likely that in our experiment the synthesis procedure was triggered by the strong electric field discharge in the focused laser. In order to verify this explanation, several other kinds of lasers were adopted, such as 808 nm continuous wave (CW) laser (Figure S4c) and 405 nm CW laser (Figure S4d), the corresponding electric field intensities of which were displayed in Table 2. Consequently, these CW lasers both failed in the initiation of nanoparticles formation, which might be due to the much weaker electric field. All these phenomena demonstrated that the high intensity electric field discharge in incident lasers played a vital role in this synthesis process.


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Laser intensity (W/cm2)

Irradiation laser Focused 800 nm femtosecond laser (0.6 W)

4.79×10

14

Electric field (V/m) 5.21×1010

Unfocused 800 nm femtosecond laser (0.6 W)

3×1010

4.13×108

808 nm CW laser (0.2 W)

3.33

4.35×103

405 nm CW laser (0.2 W)

1.02

2.40×103

Pulsed discharge

−

4×105

Table 2. Comparison of their respective electric field values between pulsed discharge and various kinds of irradiation lasers. Further, for the focused femtosecond laser, such an intense electric field will strongly interact with molecules and might produce highly charged ions resulting in significant decomposition of molecules and succeeding formation of different molecules or particles.34-37 While in our experiment, nickel sulfate was used as the metal ion source, and sodium hypophosphite served as a reducing agent. As is well known, sodium hypophosphite has been traditionally employed as a reductant in electroless plating of nickel since its P-H chemical bond is able to be decomposed on the catalytic surface to be plated,40 thereafter forming the atomic hydrogen which has strong reducing capability and thus serves as the real reducing agent. Therefore, in our experiment, it is expected that the highly intense electric field in the focused femtosecond laser would provide strong energy for breaking down the P-H bond of sodium hypophosphite, enabling the release of atomic hydrogen H which was further responsible for the reduction of nickel ion and phosphorus. Then the as-formed Ni and P came into co-deposition and accordingly the amorphous Ni-P nanoparticles were produced as such. Meanwhile, the side reaction of the hydrogen gas formation also occurred as a consequence of the atomic hydrogen combination. The product of HPO2- is actually an unstable intermediate state, which is followed by further reactions.41 The main steps can be demonstrated briefly as follows:


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H2PO2- + nhv

HPO2- + H

HPO2- + OH-

H2PO3- + e

Ni2+ + 2H

Ni + 2H+

H2PO2- + H+ + H

2H

2H2O + P

H2

As is well known, AP is an important energy material for rocket technologies and thus has been widely adopted in rocket propellants. The thermal decomposition process of AP is crucial for the combustion of propellants. Previous studies have revealed that amorphous Ni-P nanoparticles possess prominent catalytic capability that can speed the decomposition procedure or decrease the decomposition temperature of AP.1,2,42 In our experiment, the thermal decomposition process of AP with the addition of the as-synthesized Ni-P nanoparticles was investigated by TG-DTA test. Figure 6 compares the catalytic performance results between AP mixed with and without the amorphous Ni-P nanoparticles.


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Figure 6. TG-DTA test results of pure AP (a) and AP mixed with the prepared amorphous Ni-P nanoparticles (b) towards catalytic thermal decomposition of AP. It can be seen that the DTA curve of pure AP exhibits three obvious peaks at 251.7, 313.1 and 417.2 ℃ (Figure 6a). The first peak is an endothermic feature centered at about 251.7 ℃, which corresponds to the transformation of AP from the orthorhombic to cubic form. The second peak is an exothermic feature centered at 313.1 ℃ , which corresponds to a low temperature decomposition (LTD) of AP. The third peak centered at 417.2 ℃ can be attributed to the high temperature decomposition (HTD) of AP. After the HTD process, the TG test result showed that the sample had a weight loss of about 99.69 %, demonstrating that nearly all AP had been decomposed adequately. When 7.0 wt% of the as- prepared amorphous Ni-P nanoparticles were mixed with AP, the three characteristic peaks on the DTA curve still existed, however, some


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changes appeared (shown in Figure 6b). The first endothermic peak position at 245.1 ℃ demonstrated only a little shift of 6.6 ℃ compared with the result of pure AP in Figure 6a, indicating that the presence of Ni-P nanoparticles had little effect on the crystallographic transition. The LTD peak at 307.9 ℃ became much weaker than the result of pure AP and almost disappeared. Whereas, the HTD peak at 369.7 ℃ demonstrated a significant decrease of approximately 47.5 ℃ compared with the peak at 417.2 ℃ of pure AP. Besides, the HTD peak became evidently sharper, indicating that owing to the addition of Ni-P nanoparticles the HTD process became much more intense. The TG curve in Figure 6b demonstrates that the final residue is about 7.1 wt. % of original composite samples, illustrating that nearly all the AP has been decomposed completely with only Ni-P nanoparticles left. From these experimental results, it can be verified that the as-prepared noncrystalline Ni-P nanoparticles have a distinct catalytic capability towards the thermal decomposition of AP, especially in the HTD process.


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CONCLUSIONS In this study, amorphous Ni-P nanoparticles were successfully prepared by using the technique of highly intense femtosecond laser irradiation of nickel sulfate and sodium hypophosphite aqueous solution. This proposed method is green, facile, and high-efficiency. The effects of reaction parameters such as reactant concentration, reactant molar ratio, irradiation laser power, and irradiation time have been studied to adjust the morphology and size distribution of the particles which consequently spread from approximately 30 nm to 140 nm. In addition, the noncrystalline Ni-P nanoparticles revealed high activity in catalytic thermal decomposition of AP. The synthesis mechanism of the nanoparticles was also discussed in terms of strong electric field discharge of the highly intense femtosecond laser induced break down of P-H bond in sodium hypophosphite, resulting in the formation of a strong reducing agent atomic hydrogen H. The processing strategy of laser induced electrical discharge under such an extremely intense field described here is considered to be very versatile, and it is likely to be applicable to the synthesis of other nanomaterials or initiation of chemical reactions that are not feasible under normal conditions as well, investigations into which are currently under way.

ASSOCIATED CONTENT Supporting Information Dependence of the morphologies of synthesized Ni-P nanoparticles on nickel ion concentration, excitation laser power, and irradiation time. The Supporting Information is available free of charge on the ACS Publications website at http://pubs.acs.org.


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AUTHOR INFORMATION Corresponding Author *

Email: [email protected]

Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS The authors gratefully acknowledge the financial support from National Natural Science Foundation of China (NSFC) under grants #91423102, #91323301, #61378053, #51335008, and #61590930. ABBREVIATIONS Ni-P, nickel phosphide; CW, continuous wave; LTD, low temperature decomposition; HTD, high temperature decomposition; SEM, scanning electron microscope; TEM, transmission electron microscopy; EDS, energy-dispersive spectrometer.


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A table of contents entry for

Intense Femtosecond Laser Mediated Electrical Discharge Enables Preparation of Amorphous Nickel Phosphide Nanoparticles Zhuo-Chen Ma, † Qi-Dai Chen,*† Bing Han,† He-Long Li,† Lei Wang,† Yong-Lai Zhang, † and Hong-Bo Sun†

We reported here femtosecond laser mediated electric field discharge processing of aqueous solutions for synthesis of amorphous nickel phosphide nanoparticles.


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Intense Femtosecond Laser-Mediated Electrical Discharge Enables

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