New single photon sources by optoelectronic tailoring of 2D materials using low energy ion implantation

Monolayer thick transition metal dichalcogenides (TMDCs) with the chemical formula MX2 (M=Mo, W; X=S, Se), constitute a new class of direct bandgap semiconductors. Their remarkable physical properties resulting from their two dimensional (2D) geometry and lattice symmetry make them an exciting platform for developing photonic devices with new functionalities [1]. Monolayer TMDCs can be easily incorporated into electrically driven devices, which in turn can be coupled to optical microcavities or photonic circuits [2]. This work constitutes a proof-of-principle study to incorporate implanted TMDCs into non-classical single photon emitting diodes [3]. The development of such devices has far-reaching implications for emerging technologies such as quantum cryptography and quantum metrology. In order to make such devices a reality, methods of material modification for these materials, such as ultra-low energy (10-25 eV) ion implantation, must be developed [4,5]. Post-growth doping [6] of TMDCs offers an expanded selection of possible dopants compared to the popular method of doping via CVD growth. The technique allows for highly pure, clean and selective substitutional incorporation of dopants [7] and is also compatible with standard semiconductor processing. Ultra-low energy ion implantation is carried out using the ADONIS mass-selected ion beam deposition system at the University of Gottingen [8]

Understanding the Role of Single Molecular ZnS Precursors in the Synthesis of In(Zn)P/ZnS Nanocrystals

Environmentally friendly nanocrystals (NCs) such as InP are in demand for various applications, such as biomedical labeling, solar cells, sensors, and light-emitting diodes (LEDs). To fulfill their potential applications, the synthesis of such high-quality “green” InP NCs required further improvement so as to achieve better stability, higher brightness NCs, and also to have a more robust synthesis route. The present study addresses our efforts on the synthesis of high-quality In­(Zn)­P/ZnS core–shell NCs using an air- and moisture-stable ZnS single molecular precursor (SMP) and In­(Zn)P cores. The SMP method has recently emerged as a promising route for the surface overcoating of NCs due to its simplicity, high reproducibility, low reaction temperature, and flexibility in controlling the reaction. The synthesis involved heating the In­(Zn)P core solution and Zn­(S₂CNR₂) (where R = methyl, ethyl, butyl, or benzyl and referred to as ZDMT, ZDET, ZDBT, or ZDBzT, respectively) in oleylamine (OLA) to 90–250 °C for 0.5–2.5 h. In this work, we systematically studied the influence of different SMP end groups, the complex formation and stability between the SMP and oleylamine (OLA), the reaction temperature, and the amount of SMP on the synthesis of high-quality In­(Zn)­P/ZnS NCs. We found that thiocarbamate end groups are an important factor contributing to the low-temperature growth of high-quality In­(Zn)­P/ZnS NCs, as the end groups affect the polarity of the molecules and result in a different steric arrangement. We found that use of SMP with bulky end groups (ZDBzT) results in nanocrystals with higher photoluminescence quantum yield (PL QY) and better dispersibility than those synthesized with SMPs with the shorter alkyl chain groups (ZDMT, ZDET, or ZDBT). At the optimal conditions, the PL QY of red emission In­(Zn)­P/ZnS NCs is 55 ± 4%, which is one of the highest values reported. On the basis of structural (XAS, XPS, XRD, TEM) and optical characterization, we propose a mechanism for the growth of a ZnS shell on an In­(Zn)­P core