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Government of India | Department of Atomic Energy
Raja Ramanna Centre for Advanced Technology
Laser Materials Processing Division

DENSELY PACKED PALSMONIC NANOPARTICLE FILMS OF TUNABLE OPTICAL RESPONSE

Pulsed laser deposition based controlled growth of plasmonic nanoparticle films

  • Film synthesis method: Pulsed laser deposition (PLD)
  • Potential applications: Metal nanoparticle films of tunable localized surface plasmon resonance (LSPR) characteristics are required for different studies to evaluate their role in various applications like surface enhanced Raman scattering, photo-voltaics, light harvesting at nanoscale etc.

Study1: Synthesis of Gold films of Controllable Plasmon Resonance Characteristics

Highlights:

  • Deposition of densely packed gold nanoparticle films (Fig. 1)
    • Fig. 1 AFM images of PLD-grown gold nanoparticle films with TSD of (a) 4.5 cm; (b) 6.0 cm and (c) 7.5 cm.
    Fig. 1 AFM images of PLD-grown gold nanoparticle films with TSD of (a) 4.5 cm; (b) 6.0 cm and (c) 7.5 cm.

  • Surface plasmon resonance response of gold film was controlled by suitably varying substrate temperature, target-to-substrate distance (TSD), laser fluence and number of pulses.
  • Gold films of different mass thicknesses but with same plasmon resonance wavelength were synthesized (Fig. 2).
    • Fig. 2 Transmission spectra of densely packed gold nanoparticle films (left) grown at different target-to-substrate distances and (right) of different mass thickness but with same plasmon resonance.
    Fig. 2 Transmission spectra of densely packed gold nanoparticle films (left) grown at different target-to-substrate distances and (right) of different mass thickness but with same plasmon resonance.

Publications:

  1. Shweta Verma, B.T. Rao et al., Applied Surface Science, 258(11), 2012, 4898-4905.
  2. L.M. Kukreja, Shweta Verma et al, Journal of Physics D: Applied Physics, 47, 2014, 034015.

Study2: Synthesis of Silver Nanoparticle (SNP) Films of Stable and Controllable Plasmon Resonance Characteristics

Highlights:

  • Silver films grown at room temperature with small target-to-substrate distance (TSD) did not show plasmon response due to percolation.
  • Films grown in helium ambience displayed slight red shifted LSPR wavelength and overall increased transmission compared to that of vacuum.

    • Fig. 3 AFM images of silver nanoparticle films grown in (a) vacuum and (b) helium ambience.
    Fig. 3 AFM images of silver nanoparticle films grown in (a) vacuum and (b) helium ambience.

  • Alumina-capping of SNPs nanoparticle films produced:
    1. Red shifted and stronger localized surface plasmon resonance (LSPR) response.
    2. Significant improvement in the stability of plasmon resonance characteristics (Fig. 4).

    Fig. 4 Transmission spectra of uncapped and alumina-capped SNPs grown with (a) 2,500 and (b) 5,000 number of pulses. Solid, dashed and dotted curves present the spectra of the films after few minutes, two and four months respectively.
    Fig. 4 Transmission spectra of uncapped and alumina-capped SNPs grown with (a) 2,500 and (b) 5,000 number of pulses. Solid, dashed and dotted curves present the spectra of the films after few minutes, two and four months respectively.

Publications:

  1. B. Tirumala Rao et al., Journal of Nanoscience Letters, 3(17), 2013.
  2. Shweta Verma, B. Tirumala Rao et al, Proc. DAE BRNS 6th National Symposium on Pulsed Laser Deposition of Thin Films and Nanostructured Materials (PLD), Nov. 14-16, 2013, West Bengal.

Study3: Ag-Au alloy Plasmonic Nanoparticle Films by Sequential Laser Ablation

Highlights:

  • Single step growth of Ag-Au alloy nanoparticle films of tunable alloy composition (Fig. 5)
  • Localized surface plasmon resonance (LSPR) wavelength tuning in the range of 450-900 nm was achieved by varying alloy composition and film thickness.

    • Fig. 5 AFM images of silver-gold alloy nanoparticle films grown at 300ºC substrate temperature with (left) 2000 and (right) 4000 total number of pulses (Ag/Au pulses ratio 1:1).
    Fig. 5 AFM images of silver-gold alloy nanoparticle films grown at 300ºC substrate temperature with (left) 2000 and (right) 4000 total number of pulses (Ag/Au pulses ratio 1:1).

  • The optical response predicted by three different dielectric functions of Ag-Au alloy has been compared using modified Yamaguchi effective medium theory (Fig. 6).

    • Fig. 6 (Left) Optical transmission spectra of silver-gold bimetallic films grown at substrate temperatures of 300ºC and room temperature (RT) and (right) calculated variation of LSPR wavelength with Ag composition in the film.
    Fig. 6 (Left) Optical transmission spectra of silver-gold bimetallic films grown at substrate temperatures of 300ºC and room temperature (RT) and (right) calculated variation of LSPR wavelength with Ag composition in the film.

Publications:Shweta Verma, B.T. Rao et al., J. Appl. Phys. 117, 2015, 133105.


Study4: Realization of Gradient Thickness Gold Films of Varied Plasmonic Characteristics

Highlights:

  • PLD being a directional film growth methodology endowed with many controllable process parameters is found to be highly effective for localized surface plasmon resonance (LSPR) related studies based on gradient thickness nanoparticle films (Fig. 7).

    • Fig. 7 SEM images of a typical gradient film in (left) top and (right) bottom regions.
    Fig. 7 SEM images of a typical gradient film in (left) top and (right) bottom regions.

  • The thickness gradient was obtained in the range of 0.15 - 0.65 nm/mm.
  • Small target-to-substrate distance (TSD) and high substrate temperature resulted in ~ 100 nm tuning of LSPR wavelength across 20 mm length of the substrate (Fig. 8).

    • Fig. 8 Variation of SPR wavelength in gradient thickness Au films grown with different number of pulses.
    Fig. 8 Variation of SPR wavelength in gradient thickness Au films grown with different number of pulses.

Publications:B. Tirumala Rao, Shweta Verma et al, Proc. DAE BRNS 6th National Symposium on Pulsed Laser Deposition of Thin Films and Nanostructured Materials (PLD), Nov. 14-16, 2013, West Bengal.
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