Low energy ion induced effects on TOPO capped CdSe nanocrystals probed by XPS depth profiling and optical measurements

Low energy ions have been used as a probe to determine the chemical composition and structure of CdSe nanocrystals along the depth. Semiconducting CdSe nanoparticles of 5–7 nm in size are synthesized using CdO precursor and capped with TOP/TOPO using different starting precursor ratios of Cd:Se. At an optimum ratio of Cd/Se ∼ 2:1, highly luminescent and monodispersed 5 nm nanoparticles are obtained. At other Cd/Se precursor ratios (1:1 and 3:1), signatures of polydispersity are visible. The PL peak positions of CdSe nanocrystals are significantly blue-shifted compared to the bulk band gap of CdSe. The damage caused by the bombardment of low energy 4 keV argon ions erodes the CdSe nanoparticles layer by layer. In conjunction with this sputtering, XPS studies were performed to chemical composition of the nanoparticles as the function of the depth. The results are supported by absorbance, PL and XRD studies as well. The nanoparticles formed by the different routes are modeled, based on the observations of several complementary techniques.