Thickness-Controlled Synthesis of Colloidal PbS Nanosheets and Their Thickness-Dependent Energy Gaps

New ways to synthesize lead sulfide nanosheets—substituted alkanes direct the growth of 2D nanostructures

“…8,9,10,11,18,19 Here, we demonstrated that amines and aliphatic fluorides are also suitable for the growth of twodimensional lead sulfide shapes at reaction temperatures of 170 °C. By omitting the coligand, the only ligand left in the solution is oleic acid.…”

“…In case of PbS nanosheets, the synthesis was shown to be driven by the addition of chlorinated alkanes as coligands. 8,9,10,11 Recently, we could show that different chloroalkanes can lead to similar lead sulfide nanosheets and only the reaction temperature or the amount of the chloroalkane plays a role for the formation of two-dimensional nanocrystals. 10 An interplay between oleic acid/oleate and the chloroalkane with the crystal facets of lead sulfide was identified as the main reason for small lead sulfide nanocrystals to merge via oriented attachment rather than to form individual spherical or cubic nanoparticles.…”

Few-Atom-Thick Colloidal PbS/CdS Core/Shell Nanosheets

“…The data points are slightly above the fitting curve obtained previously. 29 The slightly-larger energy gap is likely due to the additional confinement in the width direction since the width of the nanosheets is about 20 nm which is close to the exciton Bohr radius of PbS. After cation exchange, the decrease of the PbS thickness results in a larger energy gap.…”

“…4,21 It will help to resolve a debated problem -the energy gap dependence on the thickness of the nanosheets -which is partially due to the difficulty in measuring the thickness accurately. 4,21,29 Photoluminescence lifetime of core/shell nanosheets is significantly longer than the core-only nanosheets, indicating a better surface passivation. The core/shell structures with improved surface properties are important for further multiple-exciton-generation study.…”

“…Further increase of the reaction temperature to 150 o C shifts the peak to 0.93 eV after additional 60 minutes cation exchange. (b) Comparison of the energy-gap of the nanosheets (solid dots), the nanosheet model developed earlier (solid line) 29 and PbS quantum dots (dashed line). 35 The arrow indicates the data from PbS/CdS core/shell nanosheets obtained through cation exchange from the 3.3 nm thick PbS nanosheets (the rightmost dot).…”