Question 1

Where is the plasmon resonance of aluminum nanoparticles?

Accepted Answer

In the ultraviolet. Aluminum's free electrons are dense, so small spheres resonate in the deep UV (below 200 nm in water). Larger particles red-shift strongly: about 212 nm at 30 nm, 252 nm at 50 nm, 332 nm at 80 nm and 394 nm at 100 nm, reaching the visible above about 120 nm (table above).

Question 2

Why use aluminum for plasmonics?

Accepted Answer

It is the only common metal with a strong plasmon in the UV, it is cheap and CMOS-compatible, and its few-nanometre native oxide makes it stable. It suits UV spectroscopy, UV-SERS, photocatalysis and full-colour structural printing.

Question 3

How does the native oxide change the spectrum?

Accepted Answer

Aluminum always carries 2–4 nm of Al2O3 (refractive index about 1.65–1.77). It red-shifts the resonance by several nanometres and slightly damps it. Add a shell of that thickness with a custom refractive index in the calculator to include it.

Question 4

Why do aluminum particles absorb near 800 nm?

Accepted Answer

Bulk aluminum has an interband transition at about 1.5 eV (around 800 nm). It shows up as a weak, broad absorption band in the spectra of larger particles, independent of the plasmon.

Question 5

Do aluminum nanoparticles scatter or absorb?

Accepted Answer

Above about 30 nm mostly scatter: 70 % of the extinction at 30 nm and 85–90 % from 50 nm up (table above). Their low absorption makes them good UV scatterers and poor heaters.

Question 6

Can I compute aluminum nanospheres, core–shell nanoparticles, arrays, near fields, heating or substrates?

Accepted Answer

Yes: aluminum nanospheres and core–shell nanoparticles (add a shell) are available in every calculator, from spectra to optical properties: near-field enhancement maps, dimers and hot spots, nanoparticle arrays and lattice resonances, particles on a substrate, emitters and the Purcell factor, nanorods and laser heating.

Diameter	Plasmon peak (dipole)	Molar extinction coefficient	Scattering share
5 nm	below 200 nm (deep UV)	6.85 × 10⁵ M⁻¹ cm⁻¹	< 1 %
10 nm	below 200 nm (deep UV)	5.72 × 10⁶ M⁻¹ cm⁻¹	2 %
20 nm	below 200 nm (deep UV)	5.68 × 10⁷ M⁻¹ cm⁻¹	13 %
30 nm	212 nm	2.05 × 10¹⁰ M⁻¹ cm⁻¹	70 %
40 nm	231 nm	2.83 × 10¹⁰ M⁻¹ cm⁻¹	80 %
50 nm	252 nm	3.59 × 10¹⁰ M⁻¹ cm⁻¹	85 %
60 nm	277 nm	4.39 × 10¹⁰ M⁻¹ cm⁻¹	88 %
80 nm	332 nm	6.21 × 10¹⁰ M⁻¹ cm⁻¹	90 %
100 nm	394 nm	8.40 × 10¹⁰ M⁻¹ cm⁻¹	91 %
150 nm	561 nm	1.56 × 10¹¹ M⁻¹ cm⁻¹	90 %
200 nm	752 nm	2.56 × 10¹¹ M⁻¹ cm⁻¹	86 %

Aluminum nanoparticle plasmon calculator

Questions & answers