Shape and internal structure of silver nanoparticles embedded in glass
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M. Dubiel Department of Physics, University of Halle-Wittenberg, D-06108 Halle, Germany (Received 19 November 2004; accepted 21 March 2005)
The structural characteristics of silver nanoparticles embedded in glass by various routes of fabrication were studied in detail using high-resolution electron microscopy to find out if they are influenced by interaction with the surrounding glass matrix. Besides the formation conditions, the strength of the interaction between metal and glass governs the size-dependent changes of lattice spacings in such nanoparticles. However, determination of these changes is not straightforward because of complicated particle configurations and the interference nature of the lattice imaging technique. Imaging of lattice plane fringes and careful diffractogram analysis allowed the exclusion of any kind of tetragonal lattice distortion or transformation to hexagonal lattice type that may be deduced at first sight. Instead, the formation of twin faults in these nanoparticles turned out to be the essential structural feature and the main source of confusion about the lattice structure observed. The variety of particle forms is comparable to particles supported on oxide carriers. It is composed of single-crystalline particles of nearly cuboctahedron shape, particles containing single twin faults, multiple twinned particles containing parallel twin lamellae, and multiple twinned particles composed of cyclic twinned segments arranged around axes of 5-fold symmetry. The more twin planes involved in the particle composition, the more complicated is the interpretation of lattice spacings and lattice fringe patterns due to superposition of several twin segments.
I. INTRODUCTION
The structural characteristics of metal nanoparticles become more important the more they are used in structure-sensitive processes such as heterogeneous catalysis1 or applications such as selective optical absorbance.2 For the latter purpose, incorporation of the nanoparticles in a transparent and durable host is required. Nearly spherical metal particles of nanometer dimensions embedded in soda-lime silicate glass can be fabricated by several means. Their optical properties, promising for potential applications, depend on concentration, size, shape, spatial arrangement and configuration of the nanoparticles.3,4 Conventional experimental routes of synthesis like Na+/Ag+ ion exchange plus thermal
a)
Address all correspondence to this author. e-mail: [email protected] b) Present address: Materials Science Department, University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA 19104. DOI: 10.1557/JMR.2005.0197 J. Mater. Res., Vol. 20, No. 6, Jun 2005
processing enable only minor variations of these structural characteristics.5 Large volume fractions of nanoparticles arranged in a near-surface region of glassy hosts may be obtained by high-energy ion implantation plus thermal processing.6 The formation of metal nanoparticles in glass may be accompanied by the generation of tensile or compressive stresses due to therm
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