It is known that increasing the size of the nanoparticle, increases the wavelength at which surface plasmon resonance occurs? But can anyone let me know what is the reason behind this? And how does size and shape of the nanoparticle affect the intensity and broadness of the peak formed?
Can any other spectroscopic techniques be used for characterizing the nanoparticles formed?
Are we talking about Ag, Au and Cu particles here?
What is your goal? Determining shape and size from optical spectra?
There is a size dependence of the resonance frequency in spherical particles, but afaik it is not a very strong one and will probably not help too much in discriminating particle sizes.
The width of the plasmon peak has two contributions, the "homogeneous" one and the "inhomogeneous one". The homogeneous width relates to the lifetime (or damping) of the oscillation. The other one results from the fact that (in most experiments) not all particles have the same spectra and therefore you observe a superposition (mixture). If now, by size or other effects the plasmon resonances do not coincide, the total spectrum will exhibit some extra broadening.
Smaller particles frequently have broader spectra than larger ones. In the older literature (U. Kreibig and coworkers have publiished a lot on this subject, there is also a book he coauthored) this has been phenomenologically attributed to the notion that due to an increased surface to volume ratio the oscillating electrons possess a higher probability of being scattered at the particle surface. This enhanced scattering reduces the lifetime of the oscillation and hence increases its spectral width.
If your particles are not spherical but ellipsoidal or rod shaped, then the resonances for oscillations along the different axes will be different. A typical result are plasmon spectra with two peaks. (See e.g. publications by Liz-Marzan et al., and I am sure there are many others)
Concerning other spectroscopies: people have used Mößbauer spectroscopy to characterize certain properties of Au nanoparticles. And one could name many others. We first need to know which property or properties you wish to gain information about.
Are we talking about Ag, Au and Cu particles here?
What is your goal? Determining shape and size from optical spectra?
There is a size dependence of the resonance frequency in spherical particles, but afaik it is not a very strong one and will probably not help too much in discriminating particle sizes.
The width of the plasmon peak has two contributions, the "homogeneous" one and the "inhomogeneous one". The homogeneous width relates to the lifetime (or damping) of the oscillation. The other one results from the fact that (in most experiments) not all particles have the same spectra and therefore you observe a superposition (mixture). If now, by size or other effects the plasmon resonances do not coincide, the total spectrum will exhibit some extra broadening.
Smaller particles frequently have broader spectra than larger ones. In the older literature (U. Kreibig and coworkers have publiished a lot on this subject, there is also a book he coauthored) this has been phenomenologically attributed to the notion that due to an increased surface to volume ratio the oscillating electrons possess a higher probability of being scattered at the particle surface. This enhanced scattering reduces the lifetime of the oscillation and hence increases its spectral width.
If your particles are not spherical but ellipsoidal or rod shaped, then the resonances for oscillations along the different axes will be different. A typical result are plasmon spectra with two peaks. (See e.g. publications by Liz-Marzan et al., and I am sure there are many others)
Concerning other spectroscopies: people have used Mößbauer spectroscopy to characterize certain properties of Au nanoparticles. And one could name many others. We first need to know which property or properties you wish to gain information about.
Bhubesh,
By increasing the size of nanopartciles the band gap decrease which result in the red shift (lower wave number ) in the UV-VIS spectrum. This can be explain by particle in 1D box quantum theory which give the formula (E is inversely proportional to the Length of the box ). therefore as we decrease the particle size the SPR wavelength decrease. If you have homogeneous particles then you will get one single peak in SPR, but the inhomogeneous size distribution of the particles size will result in the broadness of the peak.
you can use powder XRD and SEM or TEM to characterise the particle size and shape. SEM will give you the surface morphology of the particle whereas TEM will give the high resolved image of the particles. For SPR you use UV-VIS spectroscopy.
you can go through this article where effect of size of indium nanoparticle on SPR has been discussed.
http://pubs.rsc.org/en/content/articlehtml/2015/cp/c4cp05743k
Article Synthesis, Characterization and Optical Properties of Ligand...
Harish,
your answer touches about a point I asked to the OP. The physics of the metalic surface plasmon (-polariton) is an entirely different animal then the quantum confinement physics e.g. in particles of semiconductor materials (you are referring to band gaps in your answer). Bhubesh referred to the "surface plasmon", though, which is why I gave my answer above.
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nanostructured Materials
- Nanoparticles