Continuous flow liquid helium cryostat

Photoluminescence
measurements were performed on an Edinburgh Instruments FLS920 spectrometer
equipped with a TMS300 monochromator, 450 W Xe lamp, thermoelectrically
cooled Hamamatsu R928 PMT detector, and a liquid N₂ cooled
R5509-72 NIR PMT for wavelengths beyond 825 nm. The recorded emission
spectra were corrected for the spectral responsivity of the detectors
and monochromators. Photoluminescence decay curves were recorded with
a pulsed Coherent 45 mW OBIS LX 445 nm laser (modulated with an Agilent
function generator) and an R5509-72 NIR PMT. Cryogenic measurements
were performed in a continuous-flow liquid helium cryostat from Oxford
Instruments. UV/Vis absorption spectra were measured on a PerkinElmer
950 UV/vis/NIR spectrophotometer. Transmission electron microscopy
(TEM) samples were made by drop-casting a diluted dispersion of NCs
on carbon-coated TEM copper grids. Bright-field (BF-TEM) and high-angle
annular dark-field scanning transmission electron microscopy (HAADF-STEM)
images were taken on a Talos F200X from FEI operating at 200 keV.
High-resolution HAADF-STEM imaging was performed on an aberration-corrected
Titan electron microscope from Thermofisher operating at 300 keV.
To minimize structural changes of NCs during imaging, a low beam current
of ∼5 pA was used with relatively low magnifications.

The EPR spectra of 0.1 mM Mrp_{ORP_}CT, in 100 mM Tris-HCl, 500 mM NaCl, 3 mM DTT pH 8.1, were recorded on a X-band Bruker EMX spectrometer equipped with a rectangular cavity (model ER 4102 T) and an Oxford Instruments continuous liquid helium flow cryostat. The EPR sample was reduced with a solution of sodium dithionite prepared in 100 mM Tris-HCl pH 7.6. The experimental conditions used for spectral acquisition are described in the Figure legend. The EPR samples were prepared under anoxic conditions either inside a COY or a Mbraun anaerobic chamber.