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PbS quantum dots were made following the protocol of Hines and Scholes.43 For ~4.5 nm particles, a mixture of 6 mL oleic acid (90%), 18 mL of octadecene (90%), and 560 mg PbO were heated under vacuum to 125 °C and held for 1 hour. To tune the size of the quantum dots, the oleic acid: octadecene ratio was adjusted without changing the total volume of the reaction. For smaller particles, a 2:1 stoichiometric ratio of oleic acid: PbO

was used; for larger particles, the vessel was loaded with pure oleic acid. Separately, an injection solution of 240 μL of bis(trimethylsilyl)sulfide was loaded mixed with 12 mL of dried and degassed octadecene. After the reaction vessel was evacuated it was placed under nitrogen and the injection solution swiftly added. The heating source was immediately removed from the flask and it was allowed to cool for purification. Washing was normally achieved by precipitations with butanol/ethanol (1) and hexanes/ethanol (2). Particles were dispersed in hexanes and at least 1 day allowed for ripening, which is reported in the literature.

PbSe nanocrystal synthesis followed literature procedures.44,141 For 5.5 nm PbSe nanocrystals, 2.67 g PbO was dissolved in 9 mL oleic acid and 60 mL octadecene at 120°C under vacuum for 1 hour. After turning clear, the solution was heated to 180 °C whereupon 24 mL of 1 M TOPSe solution (prepared by mixing Se pellets in TOP overnight) mixed with 207 μL of diphenylphosphine (DPP, 97%) was rapidly injected. The reaction temperature was maintained at 160°C for 20 minutes, then cooled by removing the heating mantle. The reaction product was precipitated with ethanol and washed two more times with hexanes/ethanol mixtures. Significant batch-dependence was observed for the phosphines in the synthesis and the protocol was re-optimized for different sizes. To obtain larger PbSe nanocrystals, typically smaller amounts of DPP were added to the injection solution to suppress nucleation and the reaction was run for longer times. To obtain smaller PbSe nanocrystals, the amount of DPP in the injection was increased, the temperature of the injection and growth also typically was decreased by 20 °C, and the reaction time was decreased (e.g. 3 minutes).

PbTe quantum dots and cuboctahedra were produced following a literature protocol with modifications.45 A stock solution of 0.75 M Te in TOP was prepared by mixing tellurium shot (99.999%) in TOP (90%) overnight. A three-neck flask was loaded with 670 mg Pb oxide (99.99%), 2.0 mL oleic acid (90%), and 20.0 mL octadecene (90%) and heated under vacuum to 125 °C and held 1 hour, turning clear. To synthesize larger cuboctahedra, the flask was heated under nitrogen to 195 °C and 4.0 mL of Te solution rapidly injected into the flask. The temperature was maintained at 175-180 °C

for 2 minutes and 30 seconds, then cooled with a water bath. The reaction product was purified as with PbSe.

A literature recipe67 was followed to obtain undulated nanowires of PbSe, but arrested by cooling the reaction flask after injection. To synthesize nanowires two reaction pots were prepared. The first was loaded with 2.0 mL oleic acid, 10 mL diphenyl ether (97%), and 760 mg lead acetate trihydrate (99.99%), cycled with nitrogen and vacuum three times, then heated under nitrogen to 150 °C for 30 minutes, then cooled to 60 °C. A vent needle was used to allow elimination of water and acetic acid. In the second pot was 15 mL diphenyl ether, heated under nitrogen to 250 °C for 30 minutes. To the first solution was slowly added 4 mL of 0.167 M Se in TOP solution (prepared by diluting a 1 M solution). Then, the contents of the first solution were taken up into a syringe and rapidly injected into the second reaction flask which was held at 240 °C. The temperature dropped rapidly to ~170 °C and the heating mantle was removed after 1 minute. The reaction product contained both nanowires and cubes of PbSe. The cubes were isolated by dispersing the reaction products in hexanes and centrifuging twice at 4000 rpm for 3 minutes to remove insoluble nanowires. The cubes were subsequently precipitated with isopropanol.

PbSe nanorods were prepared somewhat differently than the above. First, a solution of 1 M Se in tris(diethylamino)phosphine (TDP, 97%) was prepared from distilled TDP. Before distillation, which was carried out under mild vacuum, the TDP was heated to 210 °C and held 2 hours, forming a brownish-yellow liquid. The distilled product was clear. Second, 40 mL of octadecene (90%) and 30 mL of oleic acid (90%) were combined with 10.0 g PbO (99.999%) and heated under vacuum at 130 °C for 2 hours, becoming clear. The contents of the flask were transferred to a nitrogen-filled glovebox and allowed to solidify overnight. A white solid was formed and the product centrifuged at 8000 rpm for 5 minutes to isolate the pellet. The pellet was subsequently washed with anhydrous acetone, carefully breaking up the pellet before centrifuging again to precipitate. This was repeated 6 times. After the last three times, the white pellet was dried under vacuum for 1 hour and ground into a fine powder.

The reaction to synthesize PbSe nanorods was performed in a Schlenck tube heated with an oil bath to 130-145 °C. Typically, 5.4 mL dried and degassed octadecene (90%) and 770 mg lead oleate powder were loaded into a Schlenck tube under nitrogen. The tube was heated to 140 °C and allowed to stabilize, then 3 mL of 1 M Se in TDP solution was rapidly injected, the temperature adjusted to 130 °C and the reaction allowed to proceed for 8-15 minutes. The precise time of the reaction depends on the purity of the oleate precursor; insufficient washing led to shorter reaction times and more branching of the nanorods. Purification was performed with isopropanol precipitation followed by size-selective purification with isopropanol to obtain even more monodisperse products.