Nonlinear Optical Properties of Silicon Carbide (SiC ... · SiC is known as a wide bandgap semiconductor with excellent electronic characteristics that allow this material to be used

Nonlinear Optical Properties of Silicon Carbide (SiC)Nanoparticles by Carbothermal Reduction

A. Rogov,(a) I. Tishchenko,(b) C. Joulaud,(h) A. Pastushenko,(c) Yu. Ryabchikov,(d) A.Kyrychenko,(b) D. Mishchuk,(b) A. Kharin,(e) V. Timoshenko,(f,g) Y. Mugnier,(h) R. Le

Dantec,(h) A. Geloen,(e) Jean-Pierre Wolf(a), V. Lysenko,(d,f) and L. Bonacina(a)

(a) GAP-Biophotonics, Universite de Geneve, 22 chemin de Pinchat, 1211 Geneve 4,Switzerland

(b) 1 KM Labs LLC, R&D Department, 1-3 Severo-Syretskaya str., 04136, Ukraine, Kyiv

(c) Apollon Solar SAS, 66 Course Charlemagne, 69002 Lyon, France

(d) University of Lyon, Nanotechnology Institute of Lyon (INL) UMR 5270, CNRS, INSALyon, Villeurbanne, F-69621, France

(e) University of Lyon, CarMeN Laboratory, UMR INSERM 1060, INSA de Lyon, Universityof Lyon, France

(f) Bio-Nanophotonic Laboratory, National Research Nuclear University MEPhI, 115409Moscow, Russia

(g) Moscow State Lomonosov University, Physics Department, Leninskie Gory 1, 119991,Moscow, Russia

(h) Univ. Savoie Mont Blanc, SYMME, F-74000 Annecy, France

ABSTRACT

SiC nanoparticles by carbothermal reduction show promising properties in terms of second harmonic and mul-tiphoton excited luminescence. In particular, we estimate a nonlinear efficiency < d > = 17 pm/V, as obtainedby Hyper Rayleigh Scattering. We also present results of cell labelling to demonstrate the potential use of SiCnanoparticles for nonlinear bioimaging by simultaneous detection of second harmonic and luminescence.

Keywords: Semiconductor Nanoparticles; Multiphoton Microscopy; Second Harmonic Generation; Cell La-belling

1. INTRODUCTION

In this paper we investigate Silicon Carbide (SiC) nanoparticles as potential biomarkers for multiphoton imaging.SiC is known as a wide bandgap semiconductor with excellent electronic characteristics that allow this materialto be used in high-temperature, high frequency, and high-power electronic devices. Very conveniently, in view ofapplications, both silicon and carbon are abundant elements and SiC can be produced cost efficiently, a significantadvantage compared to materials composed of noble metals and rare earths.1

The original optical properties of SiC nanostructures have led to various promising applications as light-emitting agents.1,2 Contrary to bulk SiC materials, in the case of low-dimensional SiC NPs, the relatively highquantum efficiency of luminescent SiC NPs is mainly due to quantum confinement of photo-generated excitons innanometer-scale crystalline structures. T. Serdiuk et al. have shown that small SiC NPs(≤ 5nm) easily penetrateinside cells membranes and can be used for one photon excited fluorescence bioimaging.3 Measurements of the

Send correspondence to Luigi Bonacina: E-mail: [email protected], Telephone: +41 22 3790508

Invited Paper

Colloidal Nanoparticles for Biomedical Applications XI, edited by Wolfgang J. Parak, Marek Osinski, Xing-Jie LiangProc. of SPIE Vol. 9722, 972213 · © 2015 SPIE · CCC code: 0277-786X/15/$18 · doi: 10.1117/12.2203133

Proc. of SPIE Vol. 9722 972213-1

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Figure 1. SiC NPs characterization. A. SEM image. B. Raman spectrum C. X-ray diffraction profile. D. Linear absorptionand emission spectra.

nonlinear efficiency of bulk SiC suggest relatively high nonlinear SHG coefficients (≈ 10 pm/V).4 and commercialSiC NPs with size between 50-80 nm were first tested as multiphoton labels by the Fraser group.5

In this paper, we investigate Second Harmonic Generation (SHG) and Two-Photon Excited Fluorescence(TPEF) from SiC nanocrystals by carbothermal reduction in order to describe their multimodal response. Theresults presented in this paper show that SiC nanoparticles have high optical nonlinear efficiency and are suitableimaging probes for SH imaging and benefits from the advantages related to this approach: signal photostability,wavelength flexibility, and narrow-band emission.6

2. METHODS AND RESULTS

2.1 Synthesis

SiC NPs samples were obtained by carbothermal reduction from amorphous silica, sucrose, and citric acid (onlyfor water quantity reduction). All the raw materials have been mixed in deionized water for 1 hour and driedto form white pellets which have then been carbonized at 240◦ C. As a result of the carbonization step, a darkbrown powder was obtained. Finally, white nanostructured SiC nanopowder constituted by sub-micrometricNPs has been synthesised in a furnace after high temperature treatment of the carbonised powder at 1420◦ C inmid vacuum under Ar flow and continuous mixing.



2.2 Nanoparticles characterization

The X-Ray Diffraction and Raman spectra in Fig. 1 unambiguously associate to the sample a 3C crystal structure,which is associated with noncentrosymmetric 43m symmetry and therefore to a non vanishing second ordersusceptibility, χ(2). Dynamic light scattering (DLS) shows that the mean size by number is approximately 160nm.

Having a size larger than one hundred nanometers, the SiC nanoparticles used here are much larger thanthose NPs used before by T.Serdiuk et al.3 Contrary to TPEF from small(< 10nm) SiC nanoparticles whichis ascribed to quantum confinement7 and SH from <30 nm particles, which could be dominated by surfacecontributions,8 the SH and TPEF emission of this sample is expected to come essentially from bulk.

Figure 1D shows the linear absorbance and photoluminescence spectra of SiC nanoparticles in eV. For areference, the maximum of one-photon absorption is at 300 nm, while the photoluminescence peak is located at800 nm.

2.3 Determination of nonlinear efficiency on colloidal ensembles

Hyper Rayleigh Scattering is an experimental technique which has been recently used to characterize the secondorder nonlinear efficiency of several nanomaterials. Following the procedure described in references,9–12 HRSmeasurements were performed on SiC nanoparticles colloidal suspensions. The experimental set-up10 is basedon a vertically polarized YAG laser (λ=1064nm) focused on the suspension. SHG intensity is collected at 90◦

from the excitation beam with a photomultiplier. For this set of measurement, a vertical polarizer is placed infront of the detector.

HRS results from the incoherent second harmonic signal emitted by each nanocrystal and is proportionalto the nanoparticles concentration N . Moreover, in this analysis we assume that the second harmonic signaloriginates from the nanocrystal bulk contribution given their comparatively large size. As a result, HRS intensityis proportional to the squared nanoparticle volume, V 2

np.

IHRS ∝ N〈d2〉V 2npI

2ω (1)

Knowing the mean particle size and suspension concentration from DLS and weighing measurements, theaveraged SHG coefficient 〈d〉 was estimated at 17 pm/V. 3C SiC (43m point group) has only one nonzerononlinear coefficient d14. The average SHG experimental coefficient〈d〉 is related to d14 by

〈d〉 =

√12

35× d14 (2)

Thus, we can estimate the nanoparticle value at d14 = 29 pm/V pointing to a relatively strong SHG efficiencycompared to other nanomaterials.13

Two-photon microscopy of SiC HNPs

The imaging set-up we employed is based on a Nikon A1R-MultiPhoton inverted microscope coupled witha Spectra-Physics Mai-Tai tunable laser oscillator (100 fs, 80 MHz, 700-1100 nm). Four independent non-descanned detectors acquire in parallel the epi-collected signal spectrally filtered by four tailored pairs of dichroicmirrors and interference filters. In general, SiC nanoparticles show a strong nonlinear optical response. Figure 2demonstrates that SiC nanoparticles simultaneously emit SHG and TPEF upon 720 nm excitation. Notice that,as SH emission is a non-resonant process, variable excitation wavelength can be used. The spectral density SHGat 485nm is approximately two orders of magnitude larger than that of TPEF (for a multiphoton excitation at720 nm). Please note that according to the one-photon absorbance spectrum(Fig. 1D) 720 nm laser excitationis not the most efficient for TPEF generation of SiC. Practically, by adjusting the microscope detectors’ settingsit is straightforward to simultaneously record the second harmonic signal and two-photon excited fluorescence ofSiC nanoparticles. The possibility of emitting two spectrally different signals allow SiC nanoparticles to be usedas correlative probes for multiphoton microscopy increasing selectivity against background.14,15



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c) d)Figure 2. Nonlinear microscopy image of SiC nanoparticles on a bare substrate. Excitation: 720 nm. A) blue (SH): 360/12nm; b) green (TPEF): 485/20 nm; c) yellow (TPEF): 525/50 nm; d) red (TPEF): 607/70 nm

Figure 3 demonstrates the possibility of using SiC nanoparticles for cell labelling. For this assessment, weused 3T3-L1 fibroblast cells and SiC NPs at 0.25 mg/ml concentration. In this case laser excitation was set to 790nm. In the images, blue corresponds to SHG (detected at 395 nm), and three combined colours(green - 485 nm,yellow - 525 nm, and red - 607 nm) correspond to TPEF from SiC nanoparticles and cells. The morphology ofcells can be seen by their autofluorescence, in green. The fact that some SiC nanoparticles can be detected only



a) b)Figure 3. Cells labelled with SiC P5 nanoparticles. Excitation 790nm. Blue correponds to SHG signal(395 nm), othercolors correspond to the two-photon luminescence. Cell autofluorescence in green.

by their TPEF signal can be explained by size dependence of second harmonic emission. As SHG is proportionalto V 2 ∝ R6 and the TPEF signal is proportional to V ∝ R3 the smaller particles might yield a stronger TPEFthan SHG. In addition, the SH signal strongly depends on individual HNPs orientation in space.16

3. CONCLUSIONS

SiC nanoparticles show promising properties in terms of SHG and TPEF. SiC has a high nonlinear efficiency< d > = 17 pm/V, as obtained by Hyper Rayleigh Scattering measurements. The first tests of cell labellingshow the potential use of SiC nanoparticles for nonlinear bioimaging.

Further studies should address biocompatibility of SiC nanoparticles, obtained by carbothermal reductionmethod. Recent studies indicated that while SiC nanoparticles, obtained by laser pyrolysis or solgel methods donot exert cytotoxic effects, they can lead to proinflammatory response and/or oxidative stress.17,18 Such effectsare related most probably to physicochemical features of the SiC NPs with size < 10 nm, which are known tointeract differently than large ones with cell membranes. In fact, contrary to > 50nm NPs which are activelyuptaken by endocytosis small NPs can penetrate directly through the membrane. Interestingly, T. Serdiuk et.al.have shown that SiC NPs with size < 10nm can be selectively located in the nucleus or cytoplasm by modifyingits surface charge.3

3.1 Acknowledgments

We acknowledge the financial support by Swiss SEFRI (project C15.0041, Multi Harmonic Nanoparticles), theFrench-Switzerland Interreg programme (project NANOFIMT), and European FP7 project NAMDIATREAM(NMP4-LA-2010-246479). This study was performed in the context of the European COST Action MP1302Nanospectroscopy.

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Nonlinear Optical Properties of Silicon Carbide (SiC ... · SiC is known as a wide bandgap semiconductor with excellent electronic characteristics that allow this material to be used