Premade gold nanorods were etched in a graphene liquid cell and imaged using Transmission Electron Microscopy (TEM). An aqueous solution of gold nanorods, Tris Buffer-HCl, and FeCl₃ was encapsulated between graphene sheets. The final concentration of FeCl₃ was 38 mM. Through a combination of the electron beam-generated radiolysis products and the FeCl₃, the nanorods underwent non-equilibrium etching. See associated papers for more details. 

Text taken from the Methods section of the previously published paper investingating the effect of the electron beam dose rate on the oxidative etching of gold nanocrystals:

Matthew R. Hauwiller, Justin C. Ondry,  Cindy M. Chan,  Prachi Khandekar,  Jessica Yu,  and A. Paul Alivisatos. Gold Nanocrystal Etching as a Means of Probing the Dynamic Chemical Environment in Graphene Liquid Cell Electron Microscopy. JACS. 2019.

Gold Nanorod Synthesis: Synthesis followed previous literature precedent.¹ All water used was filtered by Millapore Water Filter. 125 µL of 10 mM HAuCl₄ (Sigma Aldrich) was mixed with 5 mL of 100 mM hexadecyltrimethylammonium bromide, CTAB, (TCI) before adding 300 µL of 10 mM ice cold NaBH₄ (Sigma Aldrich). After stirring for 1 minute, the solution was aged for 30 minutes. 24 µL of this solution was injected into 20 mL of 100 mM CTAB, 1mL of 10 mM HAuCl₄, 0.18 mL of 10 mM AgNO₃ (Sigma Aldrich), and 0.114 mL 100 mM Ascorbic Acid (Sigma Aldrich). This nanorod solution was centrifuged two times for 15 minutes at 8,000 rpm.

Graphene Liquid Cell Fabrication: Graphene liquid cells were fabricated following reported procedure.² Graphene (3-5 layer, ACS materials) was transferred onto holey amorphous carbon, gold quantifoil TEM grids (SPI Supplies, 300 Mesh, R1.2/1.3), and these grids were used to encapsulate a solution of 104 mM FeCl₃ (Sigma Aldrich) in 22 mM HCl (Fisher Chemical), 100 mM Tris(hydroxymethyl)aminomethane hydrochloride, Tris-HCl, (Fisher Biotech), and the nanocrystals of interest. The volumes of FeCl₃/HCl and Tris-HCl were modulated to yield the desired final FeCl₃ concentration. All videos were taken between 30 minutes and 3 hours after encapsulation.

TEM Imaging Conditions: All TEM imaging was performed on a FEI Tecnai T20 S-Twin TEM operating at 200 kV with a LaB₆ filament. Timeseries of TEM images were collected with a Gatan Orius SC200 camera using a custom digital micrograph script with a full 2048x2048 readout with a binning of 2 pixels in each direction, at a nominal magnification of 71 kx resulting in a pixel resolution of 1.5 Å/pixel. The exposure time was 0.5 s, with a readout time of 0.8 s, yielding a frame rate of 0.77 fps. For the TEM electron beam dose rate calibration script (See S1 for further details), a conversion value of 6.7 was used to convert CCD counts to electrons There may be systematic inaccuracy based on this conversion value; however, all of the data is self-consistent and the conclusions drawn are based on trends in the data and thus independent of the exact conversion value. Metadata including dose rate and frame rate are embedded in the dm3 files.

(1) Nikoobakht, B.; El-Sayed, M. A. Preparation and Growth Mechanism of Gold Nanorods (NRs) Using Seed-Mediated Growth Method. Chem. Mater. 2003, 15 (10), 1957–1962.

(2) Hauwiller, M. R.; Ondry, J. C.; Alivisatos, A. P. Using Graphene Liquid Cell Transmission Electron Microscopy to Study in Situ Nanocrystal Etching. J. Vis. Exp. 2018, No. 135, 1–9.