Supporting Information

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1 Supporting Information Anisotropic and Multi-Component Nanostructures by Controlled Symmetry Breaking of Metal Halide Intermediates Alexander E. Kossak,,^ Benjamin O. Stephens,,^ Yuan Tian,, Pan Liu, Mingwei Chen,, Thomas J. Kempa*,, Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore, Maryland 21218, United States Advanced Institute for Materials Research, Tohoku University, Sendai , Japan State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai , PR China ^ These authors contributed equally to this work. *Thomas J. Kempa (tkempa@jhu.edu) Supporting Information Content Page(s) Materials and Methods 2 3 Figure S1: FT-IR spectrum of oleate-stabilized AgBr particles. 4 Figure S2: Dimer size distributions as a function of ph. 5 Figure S3: Mean diameter of dimer phases as a function of ph. 6 Figure S4: Low-dose TEM imaging of Ag AgBr evolution. 7 1

2 Materials and Methods: 1. AgBr synthesis. All glassware and stir bars were thoroughly cleaned with aqua regia before use. All aqueous solutions were prepared with ultrapure water dispensed from an ELGA PURELAB Flex System. To prepare AgBr nanoparticles, 900 mg of Sodium Oleate (TCI, 97.0%) were added to 12 ml of ultrapure water. Ultrasonication (VWR, ) in a warm water bath (40 C) aided dissolution of the solid oleate. This solution was allowed to cool to room temperature and was added to a 25 ml round bottom flask containing a stir bar. The ph of the solution was adjusted to 9.4 through addition of a 2M Nitric Acid solution prepared from ACS grade Nitric Acid (BDH, ACS 68-70%). The ph was monitored using an Orion ROSS Sure-Flow ph electrode (8174BNWP) calibrated with ph = 4.00 ±0.01, ph = 7.00 ±0.01, and ph = ±0.01 standards on a VWR symphony Benchtop Meter (B10P). All experiments requiring ph adjustment involved the use of appropriate amounts of 2M Nitric Acid and ph monitoring as described above. While stirring the solution at 450 rpm, the round bottom flask was charged with 90 µl of a 1M Lithium Bromide (Sigma-Aldrich, 99.0%) solution and 90 µl of a 1M L-Ascorbic Acid (Sigma-Aldrich, 99.0%) solution. 180 µl of 1M Silver Nitrate (STREM, %) was then added and the reaction was allowed to stir continuously for 24 hours. The AgBr particles were purified via ultracentrifugation (Eppendorf 5810R) at 13,000 g for 60 minutes. The pellets were re-suspended in 12 ml of ultrapure water via ultrasonication. This washing step was repeated a total of 4 times. 2. Ag AgBr synthesis. To prepare Ag AgBr dimers, 7.2 ml of ultrapure water were added to a 25 ml round bottom flask along with a stir bar, all of which were cleaned by aqua regia. While stirring the water at 1500 rpm, 0.8 ml of purified silver bromide nanoparticle solution (see Section 1 above) and 10 µl of 1M L-Arginine (Sigma-Aldrich, BioUltra 99.5%) were added to the round bottom flask. The solution was irradiated with the 254 nm ultraviolet light output of a compact UV source (Analytik Jena Pen-Ray UV Lamp, ), which is powered by a UVP Pen-Ray Power Supply ( ). The lamp was allowed to warm up for 10 seconds after it was turned on, and was subsequently lowered into the round bottom above the cone of the vortex. The solution changed from gray-blue to purple after seven seconds and was immediately removed from the round bottom µl of Hydrogen Peroxide (VWR, 3% Solution, USP) was added to the round bottom flask. Ag AgBr colloidal solutions were stored in a refrigerator to prevent their thermal and photochemical degradation. 2

3 3. UV-visible spectroscopy sample preparation and characterization. AgBr nanoparticles and Ag AgBr dimers were diluted to a 1:6 ratio of nanostructure solution to ultrapure water and then added to a quartz cuvette. Ultraviolet-visible (UV-vis) spectra were collected on an Agilent Cary Win UV-visible spectrophotometer. The instrument was blanked with ultrapure water prior to sample measurement. Spectra were collected at wavelengths from 200 nm to 1000 nm. 4. XRD sample preparation and characterization. Nanostructures for X-ray diffraction (XRD) experiments were prepared by evaporating solvent from the purified colloidal solution (see Section 1 above). XRD patterns were collected using Cu Kα radiation (λ = Å) on a Bruker D8 Focus Diffractometer, which was equipped with a LynxEye detector. 5. TEM and EDS sample preparation and characterization. Nanostructures for transmission-electron microscopy (TEM) investigations were prepared by drop casting 5 µl of purified product onto TEM grids containing an ultrathin carbon on lacey carbon support film (Ted Pella, 01824). Grids were stored in an automatic desiccator (Bel-Art Dry-Keeper, H ). Bright-field TEM investigations were carried out on an FEI Talos F200C operating at an acceleration voltage of 200 kv. Images were collected using the built-in Ceta detector at 4k resolution and 1 s integration time. Low-dose images (Figure S2) were collected using the built-in Flu-Cam at condenser spot size 9. Detailed chemical and structural analyses were performed using a high-resolution TEM system (JEOL, JEM-ARM200F) equipped with a cold field-emission gun and double hexapole Cs correctors (CEOS GmbH, Heidelberg, Germany). Energy dispersive X-ray spectroscopy (EDS), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) observations were performed at an acceleration voltage of 200 kv. The spatial resolution of the STEM is below 0.1 nm. The collecting angle for HAADF- STEM was between 100 and 267 mrad. The image of the dimer interface was collected on a high-resolution TEM system (JEOL, JEM-2100F) operating under similar conditions. 3

4 Figure S1: Figure S1. FT-IR spectrum of oleate-stabilized AgBr particles. Fourier transform infrared spectroscopy data of AgBr particles (blue) and of a neat oleate powder (green). In the blue trace, the peaks at 1516 cm 1 and 1406 cm 1 can be ascribed to the asymmetric and symmetric, respectively, stretching modes of the COO group of the oleate ligand coordinated to the AgBr particles. 28 In the green trace, the peaks at 1559 cm 1 and 1423 cm 1 are ascribed to the asymmetric and symmetric, respectively, stretching modes of the COO group of the neat oleate powder. 28 In both traces, the peaks at 2920 cm 1 and 2849 cm 1 are ascribed to the asymmetric and symmetric, respectively, stretching modes of the CH2 groups in oleate. 28 We note that the asymmetric stretching mode associated with the oleate in the AgBr sample appears at a wavenumber, which is lower by 43 cm 1 relative to its value in the neat oleate sample. 4

5 Figure S2: Figure S2. Dimer size distributions as a function of ph. For each ph, TEM images at a magnification of 120,000 were collected to survey the size of the Ag AgBr dimers. Size distributions of the diameters of the Ag phase (orange bar charts) and AgBr phase (blue bar charts) are shown. A total of 1006 dimers was analyzed. 5

6 Figure S3: Figure S3. Mean diameter of dimer phases as a function of ph. The mean diameter of the Ag phase (orange trace) and AgBr phase (blue trace) at ph values between and including 8.4 and The vertical error bars are standard deviations about the mean. A total of 1006 dimers was analyzed. 6

7 Figure S4: Figure S4. Low-dose TEM imaging of Ag AgBr evolution. (a) TEM images of an AgBr particle taken every 1 s over a period of 18 s of irradiation with an electron flux of ~7 electrons s 1 Å 2 within the TEM; Scale bar: 20 nm. Budding and growth of the Ag nanophase is clearly visible, as is the contraction of the AgBr phase on the timescale of the measurement. (b) Plot of the cross-sectional area of the Ag nano-phase (orange points) and the AgBr nano-phase (blue points) as a function of time. Each point represents the average cross-sectional area of 10 individual dimers and the error bars correspond to standard deviations about the mean value. 7