Abstract

Heat transport through nanomaterials such as quantum dots (QDs) is essential for engineering their use in applications such as LEDs and TVs. Vibrational spectroscopy techniques such as Raman spectroscopy can be used to study heat transport in these materials; however, the Raman scattering process is very weak, which limits the signal. One way to solve this issue is to enhance the Raman scattering by the use silver nanoparticles resonant at Raman laser wavelength, through a process called Surface Enhanced Raman Spectroscopy (SERS). In this work, different methods for silver nanoparticles synthesis were explored, and the resulting nanoparticles were used for SERS with crystal violet as a test analyte. As a result, the Raman signal was enhanced significantly, by at least a factor of 90. For future work, we want to extend the use of the Ag NPs for SERS with QDs to study heat transport in these materials.

Background

AcknowledgementsWe thank the MIT MSRP program for funding this research.

Conclusion

References

Motivation

Future work

Methods and Results

Synthesis of Silver Nanoparticles with Plasmonic Resonance at 785 nmThibault Joseph Twahirwa1, Jolene Mork2, William A. Tisdale2

1Department of Physics & Dual-Degree Engineerings, Morehouse College2Department of Chemical Engineering, Massachusetts Institute of Technology

Why nanoparticles? They have unique optical properties

Localized Surface Plasmon resonance ( LSPR)Why silver nanoparticles? Silver has the highest quality factor ( the surface

plasmon strength) across the spectrum from 300 to 1200 nm.

Silver also exhibits the highest thermal and electrical conductivity of all metals.

Silver is relatively cheap

Continue SERS optimization to achieve specific sizes and shapes Use Ag NPs to enhance Raman scattering from QDs

Reproducible synthesis of silver nanoparticles with defined size. Synthesis of silver nanoparticles of define shapes. Use synthesized Silver nanoparticles to enhance Raman signals( SERS).

• Successfully synthesized Ag NPs of different sizes• Achieved triangular (prism) shapes• Best method for synthesis was the no light exposure method by Aherne, et al.• Demonstrated successful surface enhancement of Raman signal

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Crystal violet + AgNPs( Spheres)

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Synthesis using Silver Nitrate (AgNO3) 1

Reagents• Na3C6H5O7 (0.3mM) • AgNO3 (100ml of 0.1mM) • NaBH4 (1ml of 50mM) • PSSS (Polysodium

styrenesulphonate) 5mM/2ml

Conditions:light exposure 70hours

Synthesis without light exposure 3

Reagents• Na3C6H5O7 5ml of 2.5mM• AgNO3 5ml of 0.5mM• NaBH4 0.3ml of 10mM• PSSS 2.5mM/5ml• Ascorbic Acid 75μl/10mM

Synthesis using Silver perchlorate (AgClO4 ) 2

Reagents• AgClO4 (1ml/0.01M) at 0 °C• 99 mL of an ice cold

solution of 1 mM NaBH4 and 0.30 mM Na3C6H5O7 water.

• Conditions : light exposure 100hours

1. “Photoinduced Conversion of silver Nanopheres to Nanoprisms” Jin, et al. (Science) 2001.

2. “Optical Properties and Growth Aspects of Silver Nanoprisms Produced by a Highly Reproducible and Rapid Synthesis at Room Temperature. ” Domian Aherne et al. (Advanced functional Materials) 2008.

3. “Spectral Control of Plasmonic Emission Enhancement from Quantum Dots near Single Silver Nanoprisms.” Keiko Munechika et al, 98195-1700.Nano Lett., 2010, 10 (7), pp 2598–2603.

4. “Localized Surface Plasmon Resonance Spectroscopy and Sensing.” Willets and Van Duyne. (Annu. Rev. Phys. Chem) 2007.

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SERS (Surface-enhanced Raman spectroscopy)

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B.C. UV-Vis spectrum (A)

shows little change with illumination time.TEM images (C) show only spherical nanoparticles even after 96 hours.

Samples illuminated for 96 hrs. with fluorescent light

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Seed solutions ( L) and Illuminated solution(R) with fluorescent light

UV-Vis spectrum (A) demonstrates changes with illumination time.TEM images (C) show triangle nanoparticles are formed.

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Silver Nanoparticle synthesis

SERS sample preparation

Figure –  A surface plasmon is characterized as a surface charge density wave at a metal surface. 4

UV-Vis spectrum (A) shows changes with different amount of seeds solution. Set up (B) was used to control the silver amount injected into a seed solution. Image (C) shows color shift as the seed amount decrease. TEM images (D) and (E) show silver nanoprisms synthesized using this method.

Crystal violet molecule

Raman Signal was enhanced by the factor of >90 using silver nanoprism.

T = 148hrs

C.