Ž . Materials Science and Engineering C 19 2002 67–71 www.elsevier.comrlocatermsec Properties of PbS nanocrystals embedded in zirconia sol–gel film A. Sashchiuk a, ) , E. Lifshitz a , R. Reisfeld b , T. Saraidarov b a Department of Chemistry, Technion, 32000 Haifa, Israel b Department of Inorganic and Analytical Chemistry, Hebrew UniÕersity of Jerusalem, 91940 Jerusalem, Israel Abstract Ž . The PbS nanocrystals NCs embedded in amorphous zirconia sol–gel films were grown at a temperature ranging from 200 to 350 8C. The size of PbS NCs was determined both by TEM and by the blue shift of the absorption edge, which increased with an increase of the Ž . synthesis temperature and PbS concentration in the range of 5–30 mol%. Any further increase of the PbS concentration 40–50 mol% at 200 8C caused the separation of a thin continuous layer of bulk PbS on top of the PbS NC zirconia sol–gel film. The optical and electrical Ž . properties of the PbS NCs in the zirconia film were investigated by utilizing absorption, photoluminescence PL and current–voltage Ž . I – V measurement. The PL spectra were Stokes-shifted from the corresponding absorption edge by about 0.8 eV. The latter can be Ž . associated with the recombination processes of surface states. The I – V curves of an indium tin oxide ITO rPbS NCs–zirconiarAu structure exhibit nearly symmetric nonlinear behavior, while ITOrPbS NCs–zirconiarPbS bulkrAu heterostructures at room temperature exhibit a rectifying behavior with two distinct peaks, which are attributed to a resonant tunneling process via the NCs’ film. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Nanocrystals; Zirconia oxide films; PbS; Optical and electrical measurements 1. Introduction Ž . Semiconductor nanocrystals NCs in transparent media have received recently a large attention due to their promising applications in nonlinear optics and optical w x switches 1,2 . Compared to the well-known II–VI and Ž III–V materials, PbS has a larger exciton radius a s 18 B . nm and a small fraction of atoms at the surface at the same carrier confinement regime. The absorption edges of PbS NCs cover the 0.5–2.5-mm wavelength region, which are important for telecommunication. More recent reports discuss the incorporation of PbS NCs in glasses and w x wx polymers 3,4 , including a sol–gel procedure 5 . The sol–gel process extends the conventional glass-melting methods, as it allows the incorporation of semiconductor NCs at low temperatures and at predetermined concentra- tion and size. Furthermore, the sol–gel technology has advantages in the formation of films with controllable thickness, three-dimensional protection of the NCs, pre- vention of NC growth, aggregation and oxidation. This paper presents a synthetic procedure, optical and electrical properties of various sizes and concentration of PbS NCs in a zirconia sol–gel film. It will be shown below that the ) Corresponding author. Ž . E-mail address: chaldona@techunix.technion.ac.il A. Sashchiuk . observed optical and electrical properties of PbS NCs– zirconia film provide strong evidence for carrier confine- ment. 2. Experiment The preparation of the zirconia film doped with differ- wx ent PbS NCs was described in detail in Ref. 6 . PbS NCs were synthesized by reacting lead acetate with ammonium thiocyanate in the precursor solutions for sol–gel forma- tion. The sol matrices for zirconia oxide films were ob- tained from zirconia tetrapropoxide in propanol, and acetic acid was used as chelating agent to stabilize the zirconia precursor. The sizes of the NCs were controlled by the Ž . concentration of PbS 5–50 mol% in the final solution and by the temperature treatment ranging from 200 to 350 Ž . 8C. The films were prepared by dipping one or two times Ž . microscope glass slides or indium tin oxide ITO -coated glass substrate into the final solution while the annealing process completes the chemical reaction between lead and sulfur. Finally, gold electrodes were deposited on the top of the films by photolithography technique. Reference sample of the pure zirconia film deposited between ITO and gold contacts was prepared under identical conditions as discussed above. 0928-4931r02r$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. Ž . PII: S0928-4931 01 00444-1