Query: MQDs

title: White Photoluminescent Ti3C2 MXene Quantum Dots with Two Photon Fluorescence
abstract: A recently created class of inorganic 2D materials, MXenes, has become a subject of intensive research. Reducing their dimensionality from 2D to 0D quantum dots (QDs) could result in extremely useful properties and functions. However, this type of research is scarce, and the reported Ti3C2 MXene QDs (MQDs) have only shown blue fluorescence emission. This work demonstrates a facile, high output method for preparing bright white emitting Ti3C2 MQDs. The resulting product is two layers thick with a lateral dimension of 13.1 nm. Importantly, the as prepared Ti3C2 MQDs present strong two photon white fluorescence. Their fluorescence under high pressure is also investigated and it is found that the white emission is very stable and the pressure makes it possible to change from cool white emission to warm white emission. Hybrid nanocomposites are then fabricated by polymerizing Ti3C2 MQDs in polydimethylsiloxane (PDMS) solution, and the bright white emitting hybrid materials in white light emitting diodes are used. This work provides a facile and general approach to modulate various nanoscale MXene materials, and could further aid the wide development of applications for MXene materials in various optical related fields.

title: Many body effects in doped WS2 monolayer quantum disks at room temperature
abstract: Due to strong Coulomb interactions, reduced screening effects, and quantum confinement, transition metal dichalcogenide (TMD) monolayer quantum disks (MQDs) are expected to exhibit large exciton binding energy, which is beneficial for the investigation of many body physics at room temperature. Here, we report the first observations of room temperature many body effects in tungsten disulfide (WS2) MQDs by both optical measurements and theoretical studies. The band gap renormalization in WS2 MQDs was about 250 15 meV as the carrier density was increased from 0.6( 0.2) x 1012 to 8.3( 0.2) x 1012 cm 2. We observed a striking exciton binding energy as large as 990 30 meV at the lowest carrier density, which is larger than that in WS2 monolayers. The huge exciton binding energy in WS2 MQDs is attributed to the extra quantum confinement in the lateral dimension. The band gap renormalization and exciton binding energies are explained using efficient reduced screening. On the basis of the Debye screening formula, the Mott density in WS2 MQDs was estimated to be ~3.95 x 1013 cm 2. Understanding and manipulation of the many body effects in two dimensional materials may open up new possibilities for developing exciton based optoelectronic devices.

title: Investigation of GaN nanowires containing AlN/GaN multiple quantum discs by EBIC and CL techniques.
abstract: In this work, nanoscale electrical and optical properties of n GaN nanowires (NWs) containing GaN/AlN multiple quantum discs (MQDs) grown by molecular beam epitaxy are investigated by means of single wire I(V) measurements, electron beam induced current microscopy (EBIC) and cathodoluminescence (CL) analysis. A strong impact of non intentional AlN and GaN shells on the electrical resistance of individual NWs is put in evidence. The EBIC mappings reveal the presence of two regions with internal electric fields oriented in opposite directions: one in the MQDs region and the other in the adjacent bottom GaN segment. These fields are found to co exist under zero bias, while under an external bias either one or the other dominates the current collection. In this way EBIC maps allow us to locate the current generation within the wire under different bias conditions and to give the first direct evidence of carrier collection from AlN/GaN MQDs. The NWs have been further investigated by photoluminescence and CL analyses at low temperature. CL mappings show that the near band edge emission of GaN from the bottom part of the NW is blue shifted due to the presence of the radial shell. In addition, it is observed that CL intensity drops in the central part of the NWs. Comparing the CL and EBIC maps, this decrease of the luminescence intensity is attributed to an efficient charge splitting effect due to the electric fields in the MQDs region and in the GaN base.

title: Confinement effect of monolayer MoS2 quantum dots on conjugated polyimide and promotion of solar driven photocatalytic hydrogen generation.
abstract: A monolayer MoS2 quantum dot confined polyimide (MQDs/PI) photocatalyst was synthesized by using a facile immersion hydrothermal method. The investigations on the optical and electronic properties of MQDs/PI composites reveal that the strong quantum confinement effect of MQDs results in a blue shift of the absorption band edge of PI, and the interfacial electronic interaction between MQDs and PI improves the charge transfer rate of MQDs/PI. The ultra small size of 3.0 nm and perfect crystals of MQDs endow MQDs/PI composites with plenty of active sites and fast charge transfer, thus resulting in a 360% enhancement in photocatalytic hydrogen production compared with that of Pt/PI at the same loading amount of Pt. This discovery provides a new clue for the development of an efficient and sustainable non noble metal photocatalyst.

title: Colloidal Single Layer Quantum Dots with Lateral Confinement Effects on 2D Exciton.
abstract: Controlled lateral quantum confinement in single layer transition metal chalcogenides (TMCs) can potentially combine the unique properties of two dimensional (2D) exciton with the size tunability of exciton energy, creating the single layer quantum dots (SQDs) of 2D TMC materials. However, exploring such opportunities has been challenging due to the limited ability to produce well defined SQDs with sufficiently high quality and size control, in conjunction with the commonly observed inconsistency in the optical properties. Here, we report an effective method to synthesize high quality and size controlled SQDs of WSe2 via multilayer quantum dots (MQDs) precursors, which enables grasping a clear picture of the role of lateral confinement on the optical properties of the 2D exciton. From the single particle optical spectra and polarization anisotropy of WSe2 SQDs of varying sizes in addition to their ensemble data, we reveal how the properties of 2D exciton in single layer TMCs evolve with increasing lateral quantum confinement.

title: Quantum Dots and Fluorescent and Magnetic Nanocomposites: Recent Investigations and Applications in Biology and Medicine
abstract: This chapter presents a comprehensive and updated review on the ongoing research area of nanostructures with a focus on quantum dots (QDs) fluorescent and magnetic nanocomposites, and their applications in biological and medical field. The study includes the essential characteristics of QDs and fluorescent and magnetic nanocomposites, their structure, properties, and methods that are utilized for their characterization. Some interesting qualities of CdSe/ZnS QDs with reference to the research of the microorganism are emphasized. The bioimaging applications of QDs and fluorescent and magnetic nanocomposites and their role as nanoprobes and as contrast enhancing agents are discussed. So, in this work, an overview is exhibited including the case of the most commonly studied QD based hybrid NPs, which are called MQDs, such as a dual "two in one" fluorescent magnetic nanocomposite materials, that blend both fluorescent and magnetic properties in a unique concept and show the feasibility for clinical diagnostics, drug delivery, and therapy.

title: Quasi Dilemmas for Artificial Moral Agents
abstract: In this paper we describe moral quasi dilemmas (MQDs) situations similar to moral dilemmas, but in which an agent is unsure whether exploring the plan space or the world may reveal a course of action that satisfies all moral requirements. We argue that artificial moral agents (AMAs) should be built to handle MQDs (in particular, by exploring the plan space rather than immediately accepting the inevitability of the moral dilemma) and that MQDs may be useful for evaluating AMA architectures.

title: A magnetic fluorescence molecularly imprinted polymer sensor with selectivity for dibutyl phthalate via Mn doped ZnS quantum dots
abstract: In this work, magnetic quantum dots molecularly imprinted polymers were synthesized, which were based on ZnS and magnetic Fe3O4. The polymers had a spherical shape and a core shell structure and exhibited a magnetic strength of 17.20 emu g 1 and optical stability. After the experimental conditions were optimized, the fluorescence intensity showed a linear dependence with concentration from 5.0 mmol L 1 to 50 mmol L 1, with R2 0.9960. Upon optimizing the experimental conditions, the linear dependence of fluorescence intensity with concentration ranged from 5.0 mmol L 1 to 50 mmol L 1, with a detection limit of 0.08 mmol L 1. Furthermore, the MQDs MIPs were successfully used for the detection of a tap water sample. With three spiking concentration levels, the recovery rate of each experiment was from 99.45 to 103.4% with a relative standard deviation from 1.97 to 3.37% This study provides a promising strategy for fabricating magnetic fluorescence molecular imprinted polymers with highly selective recognition ability.

title: Fe Doped CdTeS Magnetic Quantum Dots for Bioimaging.
abstract: A facile synthesis of 3 6 nm, water dispersible, near infrared (NIR) emitting, quantum dots (QDs) magnetically doped with Fe is presented. Doping of alloyed CdTeS nanocrystals with Fe was achieved in situ using a simple hydrothermal method. The magnetic quantum dots (MQDs) were capped with NAcetyl Cysteine (NAC) ligands, containing thiol and carboxylic acid functional groups to provide stable aqueous dispersion. The optical and magnetic properties of the Fe doped MQDs were characterized using several techniques. The synthesized MQDs are tuned to emit in the Vis NIR (530 738 nm) wavelength regime and have high quantum yields (67.5 10% NIR emitting (738 nm) MQDs having 5.6 atomic% Fe content exhibited saturation magnetization of 85 emu/gm[Fe] at room temperature. Proton transverse relaxivity of the Fe doped MQDs (738 nm) at 4.7 T was determined to be 3.6 mM 1s 1. The functional evaluation of NIR MQDs has been demonstrated using phantom and in vitro studies. These water dispersible, NIR emitting and MR contrast producing Fe doped CdTeS MQDs, in unagglomerated form, have the potential to act as multimodal contrast agents for tracking live cells.

title: Electronic and magnetic properties of graphite quantum dots
abstract: We study the electronic and magnetic properties of multilayer quantum dots (MQDs) of graphite in the nearest neighbor approximation of tight binding model. We calculate the electronic density of states and orbital susceptibility of the system as function of the Fermi level location. We demonstrate that properties of MQD depend strongly on the shape of the system, on the parity of the layer number and on the form of the cluster edge. The special emphasis is given to reveal the new properties with respect to the monolayer graphene quantum dots. The most interesting results are obtained for the triangular MQD with zig zag edge at near zero energies. The asymmetrically smeared multipeak feature is observed at Dirac point within the size quantized energy gap region, where monolayer graphene flakes demonstrate the highly degenerate zero energy state. This feature, provided by the edge localized electronic states results in the splash wavelet behavior in diamagnetic orbital susceptibility as function of energy.