Single Entity Behavior of CdSe Quantum Dot Aggregates During Photoelectrochemical Detection

Abstract

We demonstrate that colloidal quantum dots of CdSe and CdSe/ZnS are detected during the photooxidation of MeOH, under broad spectrum illumination (250 mW/cm2). The stepwise photocurrent vs. time response corresponds to single entities adsorbing to the Pt electrode surface irreversibly. The adsorption/desorption of the QDs and the nature of the single entities is discussed. In suspensions, the QDs behave differently depending on the solvent used to suspend the materials. For MeOH, CdSe is not as stable as CdSe/ZnS under constant illumination. The photocurrent expected for single QDs is discussed. The value of the observed photocurrents, > 1 pA is due to the formation of agglomerates consistent with the collision frequency and suspension stability. The observed frequency of collisions for the stepwise photocurrents is smaller than the diffusion-limited cases expected for single QDs colliding with the electrode surface. Dynamic light scattering and scanning electron microscopy studies support the detection of aggregates. The results indicate that the ZnS layer on the CdSe/ZnS material facilitates the detection of single entities by increasing the stability of the nanomaterial. The rate of hole transfer from the QD aggregates to MeOH outcompetes the dissolution of the CdSe core under certain conditions of electron injection to the Pt electrode and in colloidal suspensions of CdSe/ZnS.

Laser Induced Temperature Perturbation on Ultramicroelectrodes: Unsupported Solutions in Nonaqueous Methanol

“…Although here we propose that convection is negligible, based on the discussion below, it is possible that this regime includes some convection. 11 This would mean that the method overestimates our temperature for the data in Fig. 7.…”

“…In our previous work, we have investigated single entities under illumination to measure the stochastic photoelectrochemical currents from nanoparticles (NPs) suspended. [6][7][8][9][10][11] Other studies include single entity photoeletrochemistry of NPs with an emphasis on electron transport properties across a porous TiO2 film. 12,13 In addition, Mirkin et al, have studied two new types of photoelectrochemical nano-impacts in aqueous solutions.…”