Transition from Five-Fold Symmetric to Twinned FCC Gold Particles by Thermally Induced Growth

Abstract

Stable gold clusters around 1 nm in size have been prepared by evaporation of the metal into an organosilicon polymer solution. A controlled particle growth of the entrapped gold particles was achieved by annealing in helium at ∼410 °C. Above 460 °C the growth rate is dramatically increased, concurrent with the onset of pyrolysis of polysilazane to form a porous solid. X-ray diffraction and simulation calculations using Debye functions of model clusters of different sizes and both crystallographic and noncrystallographic symmetry were used to characterize these particles. The exclusive presence of noncrystallographic (decahedral and icosahedral) multiply twinned particles (MTPs) in the as-prepared material is confirmed by EXAFS. The high precision of the XRD experiments and theoretical data fits gives detailed insight into the thermally induced growth process, during which the MTPs progressively disappear and are replaced by singly twinned fcc particles of larger size. This transition occurs in the range ∼2−3 nm. This analysis requires the introduction of a size-dependent contraction for the Au−Au distance in the order of 1−3% compared to bulk gold. This is discussed in the context of theoretical predictions.

Nanoparticle size distribution estimation by a full-pattern powder diffraction analysis

“…(7,8,9) can be approximated by the h 0 -th term of the RHS sum, neglecting terms of O(2πqR) −4 . Furthermore, in general,S(∆q) =S(0) + O(∆q 2 ).…”

“…In fact, nanoparticles (NPs hereafter) present unique analytical challenges. In the most complex cases, non-crystallographic structures 2,3,4,5,6,7,8,9,10,11 may occur. Surface-related deformation fields 12,13,14 are another challenge.…”

Microstrain and Residual Stress in Thin-Films Made from Silver Nanoparticles Deposited by Inkjet-Printing Technology

“…The results show that the contribution from thermal ramp and sintering time is almost negligible since the stress variation is comprised within a range of 10 MPa (see Table 1). The low stress (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) MPa) observable in such printed structures after annealing has to be emphasized because of its great difference with the expected behavior of conventional thin films during thermal cycles. If the low impact of sintering time complies with a stabilization of microstructure observed after 15 min of curing, the reason of the limited impact of thermal ramp remains unclear.…”

“…The values and the evolution of β are consistent with literature for multiply twinned particles. Previous experiments reported on gold nanoparticles (very close to Ag crystallographic structure) of 5 nm and 10 nm diameter led to values of 3.6 % and 6.5 %, respectively [21,22]. Regarding crystallite size, this is quite stable up to 150°C and is the result of the solid-state sintering mechanism through interparticle neck growth.…”

Performances of Enzymatic Glucose/O2 Biofuel Cells

“…An X-ray diffraction study (Fig. 10) based on Warren's treatment of defective metals and previously described (Vogel et al, 1998;Vogel et al, 1983) combined with high resolution transmission electron microscopy (HRTEM) measurements allowed to exhibit the peculiar structure of high gold content catalysts (Habrioux et al, 2009b). …”