X-Ray-Assisted Formation of Gold Nanoparticles in Soda Lime Silicate Glass: Suppressed Ostwald Ripening D. Tatchev, 1, * A. Hoell, 2 M. Eichelbaum, 3,† and K. Rademann 3 1 Helmholtz-Zentrum Berlin, Institut fuer Angewandte Materialforschung, Albert-Einstein-Strasse 15, D-12489 Berlin, Germany and Institute of Physical Chemistry – Bulgarian Academy of Sciences, Acad. G. Bonchev Str. Bl. 11, 1113 Sofia, Bulgaria 2 Helmholtz-Zentrum Berlin, Institut fuer Angewandte Materialforschung, Albert-Einstein-Strasse 15, D-12489 Berlin, Germany 3 Institute of Chemistry, Humboldt-Universita ¨t zu Berlin, Brook-Taylor-Strasse 2, D-12489 Berlin, Germany (Received 26 March 2010; revised manuscript received 27 January 2011; published 23 February 2011) The in situ formation of gold nanoparticles in soda lime silicate glass under constant x-ray irradiation is compared with the ex situ formation in preirradiated glasses. The ASAXS measurements confirm that pure Au particles are formed. The comparison shows that the number of particles nucleated under irradiation is about an order of magnitude higher than of those nucleated with preirradiation. The radius, R, remains slightly below 1 nm under in situ conditions and the Ostwald ripening stage is slowed down. Under ex situ conditions Ostwald ripening is clearly observed and R grows up to 3 nm. DOI: 10.1103/PhysRevLett.106.085702 PACS numbers: 64.60.Q, 81.07.b, 87.85.Qr Metallic nanoparticles and nanostructures have excep- tional magnetic, optical or catalytic size dependent prop- erties that promise wide industrial applications [1–3]. Nanoparticles can be produced by various chemical [1] and physical [4] methods on surfaces or in a great variety of matrices. Nanoclusters grown in solution need a kind of charge or steric stabilization to avoid coalescence or agglomeration, for which, e.g., microemulsions, inverse micelles or organic layers are used. Current research is focusing on exploring the mechanisms of nanoparticle formation in solution [5–8] and in glassy matrices [9]. Glass is generally the perfect matrix for many optical devices. Outstanding future applications like cloaking de- vices as well as other photonic applications require precise control of the position, size and shape of metallic nano- particles, for example, of gold in glass [10,11]. Especially gold nanoparticles encapsulated in glass can be produced by doping the glass with Au ions first, reducing the ions to atoms and subsequent precipitation at elevated tempera- ture. Such a procedure has been used to produce colorful glass since antiquity [10,12]. However, it is generally not straightforward to control the size and spatial arrangement of nanoparticles in glassy matrices. The classic process of gold particle formation in glass requires elevated tempera- tures and annealing times of 20 or more hours. Very recently it was reported, that x-ray irradiation of the glass at room temperature prior to the annealing step signifi- cantly shortens the time (to 20 minutes or less) necessary for the precipitation and leads to a larger number density of particles with much smaller sizes [13] down to dimers or even neutral atoms [14]. This provides a unique opportu- nity for additional control over the precipitation process. Applying also lithographic techniques, even patterns of areas of nanoparticles can be produced [15]. An initially supersaturated solution is unstable and sep- arates a phase containing the solute whenever the kinetic conditions allow it. The separation proceeds by nucleation and growth processes that normally occur simultaneously at the beginning. If the growth is diffusion limited, then the average radius of the particles grows proportionally to t 1=2 , with t being the time. Both, the number density of nuclei and the volume fraction increase. Usually, the nucleation rate drops fast with decreasing supersaturation, but the growth continues until the critical particle size becomes comparable with the largest clusters in the system. The equilibrium solubility of the solute with a curved surface of the newly formed phase depends on the radius of curvature; the higher the curvature the higher the solubility. This difference makes the smaller, compared to some criti- cal cluster size, particles dissolve and the larger one’s grow. The volume fraction of the precipitating phase remains constant; the average radius continues to increase while the number of nuclei decreases. This process is called Ostwald ripening. In its asymptotic stage, the average radii of the particles will increase proportionally to t 1=3 (diffu- sional limitation). Depending on the kinetic parameters a transition period between the nucleation-growth regime and the 1=3 power law may exist during which the average radius does not increase significantly and reshaping of the size distribution occurs, see Figs. 4 and 6 in Ref. [16]. Here we show that the number and size of gold nano- particles in soda lime silicate glass can be controlled by x-ray irradiation and annealing. We compare two types of glass sample irradiation treatments; preliminary x-ray irradiation and subsequent annealing (ex situ) and x-ray irradiation during annealing (in situ). As a result we show that the in situ annealing process affects the growth mecha- nism in the ripening stage of gold cluster formation. Mobile gold atoms, generated by irradiation, are needed for both faster initial growth of the particles and for delay of the Ostwald ripening [17,18], both of which are observed in the in situ experiments. PRL 106, 085702 (2011) PHYSICAL REVIEW LETTERS week ending 25 FEBRUARY 2011 0031-9007= 11=106(8)=085702(4) 085702-1 Ó 2011 American Physical Society