Eur. Phys. J. D 31, 69–76 (2004) DOI: 10.1140/epjd/e2004-00129-8 T HE EUROPEAN P HYSICAL JOURNAL D Structural, compositional, optical and colorimetric characterization of TiN-nanoparticles A. Reinholdt 1, a , R. Pecenka 1 , A. Pinchuk 1, 2 , S. Runte 1 , A.L. Stepanov 1, 3 , Th.E. Weirich 4 , and U. Kreibig 1 1 I. Physikalisches Institut 1A, RWTH Aachen, Postfach, 52056 Aachen, Germany 2 Institute of Surface Chemistry of NASU, General Naumov Str. 17, 03164 Kyiv, Ukraine 3 Institut f¨ ur Experimentalphysik, Karl-Franzens-Universit¨at, Universit¨atsplatz 5, 8010 Graz, Austria 4 Gemeinschaftslabor f¨ ur Elektronenmikroskopie, RWTH Aachen, Ahornstrasse 55, 52074 Aachen, Germany Received 3 June 2004 / Received in final form 23 August 2004 Published online 28 September 2004 – c  EDP Sciences, Societ`a Italiana di Fisica, Springer-Verlag 2004 Abstract. We present results of an investigation of TiN nanoparticles, which were produced by laser abla- tion/evaporation and adiabatic expansion with the nanoparticle beam apparatus LUCAS. Compositional and structural characterization, using secondary ion mass spectrometry (SIMS), electron energy loss spec- troscopy (EELS), X-ray diffraction (XRD) and selected area electron diffraction (SAED), revealed that crystalline and almost stoichiometric particles were formed and that they are susceptible to oxidation. Fur- thermore, transmission electron microscopy (TEM) analysis showed that TiN nanoparticles exhibit cuboid shapes. The size distributions were obtained using the edge length as parameter. They are fairly broad and the mean particle diameter depends on the seeding gas flow (the pressure) that is applied to the ablation chamber during production. In situ optical transmission spectra of the TiN nanoparticles deposited on a quartz substrate indicate a pronounced single Mie resonance at around 1.7 eV and an absorption flank starting at approximately 3.0 eV. The experimental optical extinction spectra of different samples were fitted using Mie theory calculations. The dielectric function of bulk TiN was modified to account for size and interface damping of the Mie resonance. Due to the distinct absorption band, TiN may be used as a color pigment. The dependence of the color stimulus on the extinction cross-section as well as on the product of the particle concentration and the sample thickness were examined. Chromaticity coordinates were derived according to the CIE 1976 (L ∗ a ∗ b ∗ ) color space from the in situ optical transmission spectra. PACS. 42.66.Ne Color vision: color detection, adaptation, and discrimination – 78.67.Bf Nanocrystals and nanoparticles – 81.07.Bc Nanocrystalline materials 1 Introduction TiN and the other nitrides of the Ti-group gained much importance in the past, because of their special physi- cal and chemical properties. They exhibit high hardness and abrasion resistance as well as high thermal stability and good conductivity. Today, they are used for example as hard and protective coatings for tools or in electronic devices. Since the dielectric function is similar to a Drude-like metal, TiN also became interesting in nano-optics re- cently, because a pronounced Mie resonance should show up in the optical spectrum. This has been predicted by Quinten [1], who calculated nanoparticle spectra based on Mie’s theory for monodisperse spherical particles. But to the best of our knowledge no experimental data has been published yet. There is a constant search of new and stable color pig- ments for applications, because the widely used organic a e-mail: reinholdt@physik.rwth-aachen.de dyes tend to disintegrate in time or due to irradiation by UV light. Anorganic nanoparticles with distinct absorp- tion bands can act as an alternative, because they often do not degrade in time. TiN in particular is suited for this application. Besides the compositional and structural characteriza- tion, we focus in this article on the analysis and discussion of the optical and colorimetric properties. We present ex- perimental extinction spectra and show, that they can be modeled by Mie theory calculations using a modified bulk dielectric function. In addition, the applicability of TiN as color pigment and the dependence of the color on different experimental parameters is discussed. 2 Experimental The ablation target was produced from pressed TiN pow- der (Alpha Aesar, 99.8% purity). The powder was moist- ened with a few droplets of pure propanol and pressed for