Zero-dimensional molybdenum disulfide (MoS 2 ) quantum dots (QDs) have attracted remarkable interest due to their peculiar properties such as the quantum-confinement effect and high surface area. Exploring recombination dynamics in MoS 2 QDs is not only expected to gain a deeper insight into their fundamental physics, it is also important for potential applications in optoelectronics and energy-conversion technology. This study synthesized p-type MoS 2 QDs doped with diethylenetriamine (DETA) using pulsed laser ablation method. A hole concentration as high as 2.08 × 10 12 cm −2 has been demonstrated by gatedependent conductance measurements. A 110-fold enhancement of photoluminescence in the p-type MoS 2 QDs has been found after the introduction of DETA, and the dependence of the radiative and nonradiative recombination of MoS 2 QDs on carrier densities were studied. As the carrier density was increased, a decrease of the radiative lifetime was found, which is similar to the behavior of the radiative lifetime in monolayer MoS 2 . The Shockley-Read-Hall (SRH) and Auger recombination dominates the nonradiative recombination at low and high carrier densities, respectively. The SRH lifetime of MoS 2 QDs increases with the increased carrier density, suggesting that the recombination mechanism at the low carrier density is dominated by the SRH recombination. This study found that as the carrier densities exceeded 0.53 × 10 12 cm −2 , the Auger recombination was responsible for the reduction of PL. Furthermore, MoS 2 QDs was used as a fluorescent sensor for the detection of ammonium hydroxide (NH 4 OH). The PL intensity of MoS 2 QDs demonstrates a gradual decrease with increasing NH 4 OH concentration. By investigating the time-resolved PL (TRPL), the mechanism that leads to the decrease of PL in MoS 2 QDs is addressed. This investigation is expected to demonstrate a promising development of an effective and low-cost MoS 2 QDsbased fluorescent sensor with superior sensitivity for the rapid detection of ammonia in aqueous media.

Negative differential resistance (NDR) devices have attracted considerable interest due to their potential applications in switches, memory devices, and analog-to-digital converters.

Understanding the mechanism of the negative differential resistance (NDR) in transition metal dichalcogenides is essential for fundamental science and the development of electronic devices. Here, the NDR of the current–voltage characteristics was observed based on the glutamine-functionalized WS2 quantum dots (QDs). The NDR effect can be adjusted by varying the applied voltage range, air pressure, surrounding gases, and relative humidity. A peak-to-valley current ratio as high as 6.3 has been achieved at room temperature. Carrier trapping induced by water molecules was suggested to be responsible for the mechanism of the NDR in the glutamine-functionalized WS2 QDs. Investigating the NDR of WS2 QDs may promote the development of memory applications and emerging devices.

No abstract