X-Ray Diffraction of Gold Nanoparticles in Solution

A. Mews1, T. Kipp1, A.-C. Dippel2, U. Rütt2, J. Strempfer2, D. Shukla2, O. Gutowski2, T. Redder1,

N. Bohn1, E. Huber1, J. Flügge1, D. Bonatz1

1Institute of Physical Chemistry, University of Hamburg, Grindelallee 117, D-20146 Hamburg,

Germany

2Deutsches Elektronen-Synchrotron (DESY), HASYLAB, Notkestrasse 85, D-22603 Hamburg,

Germany

The transition between defined goldclusters with distinct shapes and facets towards nanocrystals with preferred morphology is depending on several parameters like composition, crystal structure or surface ligands. Gaining a deep understanding of the growth pathway is the aim of our experiments. Therefore we want to use high energy x-ray scattering to observe the growth of nanoparticles on a short timescale. First preliminary studies were performed at beamline P02.1 to determine which parameters like particle size, concentration and solvent are necessary for suitable measurements. To study the nucleation and growth of gold nanoparticles in-situ measurements were performed. Nanoparticles with sizes of 1 nm to 3 nm were obtained by a synthesis route by Chen and Kimura[1]. Slightly larger nanoparticles with 10 nm in diameter were obtained by a synthesis route by Gao[2]. TEM measurements have been performed to determine particle size and size distribution of the gold particles.

Figure 2: Diffraction pattern of gold nanoparticle powder with a particle size of 1 nm to 3 nm compared to calculated diffraction pattern of different sizes. Measurements were performed at 60 keV. Simulations were performed with DISCUS.

Figure 1: in-situ measurements of gold nanoparticles during synthesis. The blue curve presents the obtained signal before the reaction was started. The green curve presents the diffraction pattern at the end of the reaction. Red curve is the difference. Measurements were performed at 60 keV and the exposure time was set to 8s

The software package DISCUS[3] was used to calculate diffraction pattern of gold nanoparticles of different sizes. By comparing the calculated diffraction patterns with the measured ones important information about the particle size and size distribution of the sample can be obtained. Further studies were carried out in a free liquid jet at beamline P09. The advantage of measurements in a free liquid jet is that a certain spatial position of the ejected stream corresponds to a distinct reaction duration if the reaction is started in the jet. The time resolution will therefore be determined by the flow velocity and the size of the x-ray beam.

References

[1] S. Chen and K. Kimura, Langmuir 15, 1075-1082 (1999).[2] H. Gao, H. Ding, S. Chen, L. Bao, J. Tian, C. Xiao, T. Yang, C. Hui, C. Shen, Chem. Mater. 20,

6939-6944 (2008).[3] Th. Proffen and R.B. Neder, J. Appl. Crystallogr. 32, 838 (1999).

Figure 4: Diffraction pattern of gold nanoparticles in a free liquid jet with a diameter of 100 µm. Particle size was 10 nm, measurements were performed at 20 keV.

Figure 3: Picture of the free liquid jet. The jet has a variable diameter of 6 µm to 100 µm. The fluid stream is disrupted after 0.5 cm. The speed of the liquid jet can be controlled by the pump flow and is between 4 m/s and 40 m/s.