Amine-Assisted Facetted Etching of CdSe Nanocrystals

Abstract

The treatment of CdSe nanocrystals (NCs) in a 3-amino-1-propanol (APOL)/water (v/v = 10:1) mixture at 80 degrees C in the presence of O(2) causes them to undergo a slow chemical etching process, as evidenced by spectroscopic and structural investigations. Instead of the continuous blue shift expected from a gradual decrease in NC dimensions, a bottleneck behavior was observed with distinct plateaus in the peak position of photoluminescence (PL) and corresponding maxima in PL quantum yield (i.e., 34 +/-7%). It is presently argued that such etching behavior is a result of two competitive processes taking place on the surface of these CdSe NCs: (i) oxidation of the exposed Se-sites to acidic SeO(x)() entities, which are readily solubilized in the basic APOL/H(2)O mixture, and (ii) coordination of the underlying Cd-sites with both amines and hydroxyl moieties to temporally impede NC dissolution. This is consistent with the HRTEM results, which suggest that the etched NCs adopt pyramidal morphologies with Cd-terminated facets (i.e., (0001) bases and either {011} or {21} sides) and account for the apparent resistance to etching at the plateau regions.

An investigation into the effective surface passivation of quantum dots by a photo-assisted chemical method

“…19 The blue shift observed in the PL emission is related to a decrease in the size of the QDs due to surface etching by the APOL/H 2 O solutions and is a demonstration of the quantum confinement effect. This result is in good agreement with the previous study by Li et al 17 However, the blue shift of the PL emission peak in this study is observed to be gradual. This differs from previous studies which have reported a stepwise blue shift.…”

“…The etching time-dependent PL emission spectra with the corresponding absorption spectra are shown in Figure 2(b). The maximum PL emission intensity peak of the as-synthesized QDs observed a wavelength of around 590 nm which is slightly lower than that of the previous samples but much closer to those of the previous study by Li et al 17 The maximum intensity peak also exhibited a clear blue shift with increasing time however the FWHM showed only a slight increase (after 1 h).…”

“…Talapin et al successfully replaced the surface ligand from TOPO with dodecylamine, which significantly increased the photoluminescence (PL) QY% of the QDs. 11,17 Bullen et al, found that the chain length of the amine had no effect on the QY%. However, due to surface etching of the cadmium carboxylate groups, the PL emission peak exhibited a blue shift.…”

“…However, due to surface etching of the cadmium carboxylate groups, the PL emission peak exhibited a blue shift. 18 Using etching methods, Li et al have investigated size-tunable processes on CdSe QDs using a 3-amino-1-propanol (APOL)/water mixture solution at 80 • C. 17 Despite the etching ability of the amine solution, the PL spectra, which corresponds to the size of the QDs, shows a stepwise blue shift after the etching process. For example, although the PL emission maximum peak remained at a constant wavelength during etching, the QY% exhibited both increase and decrease compared with the initial QY%.…”

The Role of Halogens in the Synthesis of Semiconductor Nanocrystals

“…The presence of halogen compounds in the synthesis of semiconductor nanocrystals (NCs) produced by hot injection [1] drastically influences their capping ligand sphere and/or their chemical reactivity [2][3][4][5], allowing for the growth of hybrid systems [6], including composites of NCs decorating carbon sp 2 surfaces [7]. Several works have reported on chemical and photochemical processes taking place during the growth of semiconductor NCs in the presence of halide or acetate anions [8].…”