Effect of X‐ray irradiation on the blinking of single silicon nanocrystals

Abstract

Photoluminescence (PL) intermittency (blinking) observed for single silicon nanocrystals (Si‐NCs) embedded in oxide is usually attributed to trapping/de‐trapping of carriers in the vicinity of the NC. Following this model, we propose that blinking could be modified by introducing new trap sites, for example, via X‐rays. In this work, we present a study of the effect of X‐ray irradiation (up to 65 kGy in SiO2) on the blinking of single Si‐NCs embedded in oxide nanowalls. We show that the luminescence characteristics, such as spectrum and life‐time, are unaffected by X‐rays. However, substantial changes in ON‐state PL intensity, switching frequency, and duty cycle emerge from the blinking traces, while the ON‐ and OFF‐ time distributions remain of mono‐exponential character. Although we do not observe a clear monotonic dependence of the blinking parameters on the absorbed dose, our study suggests that, in the future, Si‐NCs could be blinking‐engineered via X‐ray irradiation.

Probing silicon quantum dots by single-dot techniques

“…For example, ligand passivated Si nanocrystals in a liquid were reported to exhibit no blinking [104], suggesting the key role of defects in the oxide and at the SiNC/SiO 2 interface at charge capture. However, x-rays irradiation of thick oxide samples did not result in strong changes in Si NC blinking, possibly due to self-annealing of oxide traps at room temperature [101].…”

“…In general, one can distinguish two types of interval time distributions for this binary process. First, the exponential distribution, also known as 'random telegraph noise' [97][98][99][100][101], detected for thermally oxidized Si NCs. Second, the power-law distribution, typically observed for direct bandgap nanocrystals and porous silicon particles [74,102].…”

X-ray radiation hardness and influence on blinking in Si and CdSe quantum dots

“…Recently, we reported the effect of X-ray exposure on the PL of single Si/SiO 2 -QDs and we demonstrated that lifetime, emission energy, and linewidth were surprisingly unaffected up to the high dose of $65 kGy (SiO 2 ). 34 Although the preliminary study showed dot-to-dot variations of the blinking ON-and OFF-time constants as a function of X-ray dose, it was limited in terms of the number of samples/dots probed, blinking statistics, and maximum absorbed dose. In this letter, we analyze under identical conditions the irradiation effect for two types of core/shell QDs: CdSe/CdZnS and Si/SiO 2 .…”

“…1 show that the PL of Si-QDs is intense even at $270 kGy, thus confirming and extending our previous study, which was limited to 65 kGy. 34 However, if we focus our attention on single luminescent Si-QDs, we can visually notice that different dots vary in luminescence intensity as a result of irradiation. Consequently, the X-ray irradiation is clearly influencing their photophysical properties.…”

“…From the literature, the statistics of Dt ON and Dt OFF in Si-QDs exhibit a mono-exponential behavior with respective time constants s ON and s OFF . 34,37,41 3 shows s ON and s OFF of different single Si/SiO 2 -QDs (colour-coded) versus the cumulative absorbed dose. Both ON-and OFF-time distributions retained their monoexponential character over all the radiation range.…”