Crystalline Dots Research Articles

Properties of phosphorus-boron co-doped c-Si quantum dots/SiNx:H thin film prepared by PECVD in-situ deposition

Co-doping of phosphorus and boron elements into crystalline silicon quantum dot (c-Si QD) is an effective approach for enhancing the photoluminescence (PL) performance. In this paper, we report on the preparation of hydrogenated silicon nitride (SiNx:H) thin films embedded with phosphorus-boron co-doped c-Si QDs via plasma enhanced chemical vapor deposition route. Mixed dilution including hydrogen (H2) and argon (Ar) is applied in the in-situ deposition process for optimizing the deposition process. The P-B co-doped c-Si QD/SiNx:H thin films exhibit a wide range of PL spectra. The emission is greatly improved especially for the short-wavelength light when compared to the SiOx:H thin film containing P-B co-doped c-Si QDs. The effects of H2/Ar flow ratio on the structural and optical characteristics of thin films are systematically investigated through a series of characterizations. Experimental results show that various properties, such as crystallinity, QD size, optical band gap and doping concentrations, are effectively controlled by tuning H2/Ar flow ratio. Based on the red-shift of QCE-related PL peak, the successful P-B co-doping into Si QDs are verified. Finally, a comprehensive discussion has been made to analyze the influence of H2-Ar mixed dilution on the film growth and impurity doping in detail in this paper.

Versatile femtosecond laser interference patterning applied to high-precision nanostructuring of silicon

We present a high-precision nanostructuring technique based on beam interference from a commercial Ti:Sa femtosecond amplified laser (800 nm, 120 fs, 1 kHz, 1 mJ). Its potential and versatility is illustrated by applying the technique to the nanostructuring of silicon. Employing commercial and ad-hoc laser-fabricated diffractive optical elements together with standard optical components, periodic line gratings and spot arrays with tunable periods down to 650 nm can readily be fabricated. Moreover, fabrication of millimeter-size diffraction gratings via multipulse irradiation at processing speeds up to 0.5 mm/s is demonstrated. The variety of structures written in crystalline silicon feature amorphous fringes and dots with widths down to 300 nm. The corresponding complex topography profiles consist of surface elevations and depressions with sizes down to 120 nm that can be controlled by the laser fluence and fringe width, demonstrating the presence of several competing matter reorganization processes in the molten phase. The exceptional high-contrast ratio of the fringe intensity together with a near-Gaussian intensity envelope of the laser spot enable patterning with well-defined local fluences, paving the way for single-pulse fluence-dependent studies. The high-quality experimental data that can be obtained with this technique can prove critical for modelling attempts aimed at unravelling the underlying formation mechanisms of complex surface topographies in a wide range of materials. Furthermore, the technique presented here has outstanding potential for the rapid and versatile fabrication of high-precision metasurfaces.

Presumed Onchocerciasis Chorioretinitis Spilling over into North America, Europe and Middle East.

Newer generation ophthalmologists practicing in the developed world are not very familiar with some tropical ocular diseases due to the absence of reports in the ophthalmic literature over the past thirty years. Because of world globalization or due to influx of immigrants from sub-Saharan Africa, exotic retinal diseases are being encountered more often in ophthalmology clinics. A multicenter case series of chorioretinitis or optic neuritis with obscure etiology that used serial multimodal imaging. Four cases qualified with the diagnosis of presumed ocular onchocerciasis based on their residence near fast rivers in endemic areas, multimodal imaging, long term follow-up showing progressive disease and negative workup for other diseases. Characteristic findings include peripapillary choroiditis with optic neuritis or atrophy, subretinal tracts of the microfilaria, progressive RPE atrophy around heavily pigmented multifocal chorioretinal lesions of varying shapes, subretinal white or crystalline dots, and response to ivermectin. Typical skin findings are often absent in such patients with chorioretinitis rendering the diagnosis more challenging. Familiarity with the myriad ocular findings of onchocerciasis, and a high-degree of suspicion in subjects residing in endemic areas can help in the correct diagnosis and implementation of appropriate therapy. Onchocercal chorioretinitis is a slow, insidious, progressive, and prolonged polymorphous disease.

Synthesis of water-stable and highly luminescent graphite quantum dots

Highly stable and environmentally friendly nitrogen-doped graphite quantum dots consisting of ∼12 layers of graphene, average diameter of ∼7.3 nm, prepared by atmospheric pressure microplasma are reported to have blue emission due to surface states created by nitrogen doping (9 atomic%) and reaction with oxygen. The low-temperature synthesis method requires simple precursors in water, with no annealing or filtration, producing crystalline disc-shaped quantum dots with ∼68% photoluminescence emission quantum yield at 420 nm excitation and that have shown stability for more than one month after the synthesis. The nitrogen doping in the quantum dots mainly occurs in graphitic core as substituted type of doping (63–67 atomic%) and the amount of doping is sufficient to create emissive states without impacting the core structure. The optical and chemical properties do not undergo serious retardation even with re-dispersion suggesting easy applicability for cellular imaging or optoelectronics.

Thermal stability of AgCuCoNiFe high-entropy alloy

Equi-atomic AgCuCoNiFe high entropy alloy was synthesized via mechanical alloying and the milled powder sample was annealed at 770 °C for 60 min in an argon atmosphere. A solid solution of AgCuCoNiFe having two FCC phases was obtained after alloying. Broadening in X-ray diffraction (XRD) peaks was observed with progression of milling time indicating the formation of a solid solution. XRD graph of the annealed sample showed the re-emergence of FCC-Cu peaks thereby implying the decomposition of the HEA. High resolution transmission electron microscopy (HRTEM) showed as-milled crystallites having lattice fringes from 0.286 nm to 0.32 nm and possessing a ring diffraction pattern indexed to FCC phases. Its annealed counterpart had lattice fringes of 0.24 nm with crystalline dot diffraction pattern indexed to FCC phase.

In situ growth MoS2 quantum dots as promising interface materials for silicon solar cells

The carrier selectivity at interface is one key factor to improve the performance of silicon solar cells. Here, Molybdenum disulfide (MoS2) quantum dots were successfully synthesized by one-step in situ plasma enhanced atom layer deposition. A transmission electron microscope was employed to investigate nano-size scaled as well as growth mechanism of the crystalline MoS2 quantum dots. MoS2 quantum dots with additional molybdenum-oxygen (Mo–O) bonding were prepared by co-reactant plasma processing, which exhibited photo-generated carrier selectivity as promising interface materials for silicon heterojunction solar cells. Our results indicated their carrier selectivity of electron-blocking and hole-transporting at interface was attributable to unique quantum effects and tunneling effects. A photovoltaic conversion efficiency 23% was achieved by a sample silicon solar cell combined with MoS2 quantum dots interface materials. Because the interface engineering is well-defined, and the synthesis is low-cost, this bottom-up strategy provides a potential advance in design and construction of innovative and highly efficient photovoltaic devices.

Amino Acid Mediated Highly Ordered Carbon Dots as Phase Directing Agent for Synthesizing α-Ni(OH)2Decorated with Nitrogen Doped CD as an Electrode for an Efficient Symmetric Supercapacitor

The synthesis of the α-phase of layered Ni(OH)2 is desirable owing to its efficient charge storage applications. The hydrothermal route of synthesis usually leads to formation of mixed of α- and β-phases of Ni(OH)2. We present here a novel hydrothermal approach for synthesizing predominantly the α-phase of Ni(OH)2 using a nitrogen doped crystalline carbon dot ([N-CD]BA) as a phase directing agent. The reaction medium comprising [N-CD]BA led to the formation of a microflower-like structure denoted as Ni(OH)2/[N-CD]BA with more petal density than in pristine α/β mixed phases of Ni(OH)2. The structure, composition, texture, and morphology of the as-synthesized batches of Ni(OH)2/[N-CD]BA and pristine Ni(OH)2 are thoroughly characterized. The electrochemical studies recorded by cyclic voltammetry and galvanostatic charging–discharging measurements demonstrated a battery-type supercapacitor. The batch of Ni(OH)2 prepared with 12.5 vol % [N-CD]BA, denoted as Ni(OH)2/12.5%[N-CD]BA, exhibited an optimum specific capacity of 482 C g–1 recorded at 1.0 A g–1, which is 4.5 times higher than that of pristine Ni(OH)2. The enhanced charge storage and transport mechanism are explained from electrochemical impedance spectroscopy (EIS). The high power density is reflected from a small relaxation time (0.4 s), and the charging–discharging efficiency is also improved for α-Ni(OH)2/12.5%[N-CD]BA. The application of the materials as supercapacitors has been demonstrated by fabricating a symmetric supercapacitor (SSC) device, i.e., Ni(OH)2/[N-CD]BA//Ni(OH)2/[N-CD]BA, using 2 M KOH as the electrolyte. The SSC exhibited a maximum energy density of 24 Wh kg–1 and a power density of 1.5 kW kg–1. The real-time application of the symmetric supercapacitor device has been demonstrated by successfully illuminating red LED lamps and powering a motor driven 1.6 mW fan.

Electronic structure, growth and properties of hydrothermally derived crystalline Cu2MnSnS4 quantum dots: optimization of physiochemical parameters and electrochemical performance

Electronic structure, growth and properties of hydrothermally derived crystalline Cu2MnSnS4 quantum dots: optimization of physiochemical parameters and electrochemical performance

Efficient generation of highly crystalline carbon quantum dots via electrooxidation of ethanol for rapid photodegradation of organic dyes

Crystalline Carbon Quantum Dots (CQDs) simply obtained by the electrooxidation of ethanol on Ni foam used for fast and efficient photodegradation of organic dyes.

Co-doping of Phosphorous-Boron in-situ grown c-Si quantum dots/a-SiOx:H thin films on PET

Phosphorus-boron co-doped amorphous hydrogenated silicon oxide (a-SiOx:H) thin films containing crystalline silicon quantum dot (c-Si QD) were prepared via plasma enhanced chemical vapor deposition (PECVD) route on polyethylene terephthalate (PET) substrate. With the aim of optimizing the doping efficiency and effectively controlling the properties of the flexible thin films, the helium (He) and argon (Ar) mixed dilution was applied in the in-situ deposition process. A series of characterizations have been carried out for studying the variation in the properties of flexible P-B co-doped Si QD/a-SiOx:H thin films when tuning the He/Ar flow ratio. Successful P-B co-doping has been proved according to the redshift of photoluminescence (PL) peak. Experimental results also show that the QD size and the doping concentration are controllable when varying the He/Ar flow ratio, while the PL peaks are tunable with QD size. Furthermore, the mechanisms on film growth and impurity doping were illustrated in detail.

Unraveling the role of agro waste-derived graphene quantum dots on dielectric and mechanical property of the fly ash based polymer nanocomposite

In this study, crystalline graphene quantum dots (GQDs) is prepared using agro waste of paddy straw via hydrothermal route and GQDs reinforced fly ash polymer nanocomposites was prepared for the first time. HR-TEM and XRD investigations confirmed the formation of hexagonal GQDs with average diameter of 8 nm. Nanocomposite prepared with GQDs reinforcement in fly ash waste under epoxy system was fabricated through the compressive molding machine. Graphene quantum dots-fly ash polymer nanocomposites showed a substantial and concurrent increase in dielectric constant (ɛ') up to ~ 350 compared to fly ash based polymer composites (ɛ'~13). The GQDs-reinforced fly ash based nanocomposites possess the high flexural strength of 60 MPa, whereas pristine fly ash polymer hybrid composite exhibited flexural strength of 35 MPa. The unconventional dielectric enhancement and flexural strength of agro waste derived GQDs reinforced fly ash polymer nanocomposite is attributed to the sudden increase in the electric dipoles and improved interfacial and chemical bonding of crystalline GQDs with fly ash and epoxy.

Don’t dust off the dust! – A facile synthesis of graphene quantum dots derived from indoor dust towards their cytotoxicity and antibacterial activity

This study presents a feasible and sustainable way for producing crystalline graphene quantum dots derived from indoor dust particles using a simple eco-friendly hydrothermal procedure.

Insights into the Structure and Self‐Assembly of Organic‐Semiconductor/Quantum‐Dot Blends

AbstractControlling the dispersibility of crystalline inorganic quantum dots (QD) within organic‐QD nanocomposite films is critical for a wide range of optoelectronic devices. A promising way to control nanoscale structure in these nanocomposites is via the use of appropriate organic ligands on the QD, which help to compatibilize them with the organic host, both electronically and structurally. Here, using combined small‐angle X‐ray and neutron scattering, the authors demonstrate and quantify the incorporation of such a compatibilizing, electronically active, organic semiconductor ligand species into the native oleic acid ligand envelope of lead sulphide, QDs, and how this ligand loading may be easily controlled. Further more, in situ grazing incidence wide/small angle X‐ray scattering demonstrate how QD ligand surface chemistry has a pronounced effect on the self‐assembly of the nanocomposite film in terms of both small‐molecule crystallization and QD dispersion versus ordering/aggregation. The approach demonstrated here shows the important role which the degree of incorporation of an active ligand, closely related in chemical structure to the host small‐molecule organic matrix, plays in both the self‐assembly of the QD and small‐molecule components and in determining the final optoelectronic properties of the system.

Facile oxidation reaction to produce monolayered highly crystalline nitrogen-doped graphene quantum dots

Nitrogen-doped graphene quantum dots (NGQDs) made by standard hydrothermal synthesis route were found to produce non-uniform nanostructures that exhibit poor crystallinity and unstable optical properties. In this study, a simple post synthesis oxidation step was shown to significantly improve the overall crystallinity and stability of the nanostructures via removal of reaction by-products and oxidation of reactive functional groups, generating oxidized nitrogen-doped graphene quantum dots (Ox-NGQDs). Through transmission electron microscopy (TEM) and atomic force microscopy (AFM) the Ox-NGQDs were found to be uniform monolayered nanostructures with lateral size of 20–25 nm. The appearance of G and D bands in the Raman spectrum of the Ox-NGQDs sample confirmed that the reaction by-products had been removed, and indicated that the Ox-NGQDs were composed of a highly ordered graphitic structure. X-ray photoelectron spectroscopy (XPS) indicated that oxidation of the surface functional groups took place. The Ox-NGQDs produced in this work gained a significant increase in visible absorbance, which is important in a wide range of potential light harvesting applications and uses.

Ultrafast generation of highly crystalline graphene quantum dots from graphite paper via laser writing

Graphene quantum dots (GQDs) are attractive fluorescent nanoparticles that have wide applicability, are inexpensive, nontoxic, photostable, water-dispersible, biocompatible and environmental-friendly. Various strategies for the synthesis of GQDs have been reported. However, simple and efficient methods of producing GQDs with control over the size of the GQDs, and hence their optical properties, are sorely needed. Herein, an ultra-fast and efficient laser writing technique is presented as a means to produce GQDs with homogeneous size from graphene produced by the instantaneous photothermal gasification and recrystallization mechanism. Controlling the laser scan speed and output power, the yield of GQDs can reach to be about 31.458 mg/s, which shows promising potential for large-scale production. The entire process eliminates the need for chemical solvents or any other reagents. Notably, the prepared laser writing produced GQDs (LWP-GQDs) exhibit blue fluorescence under UV irradiation of 365 nm and the Commission Internationale de L’Eclairage (CIE) chromaticity coordinates is measured at (0.1721, 0.123). Overall, this method exhibits superior advantages over the complex procedures and low yields required by other existing methods, and thus has great potential for the commercial applications.

Room temperature driven highly crystalline fluorine-doped carbon quantum dots for sensitive tetracycline sensing

Carbon quantum dots (CQDs) with semiconductor-like properties have received considerable attention because of their unique photoelectric properties and electron transfer ability. However, the preparation of highly crystalline CQDs with strong fluorescence (FL) emission by the room temperature (RT) synthesis is a challenging task. Herein, we develop a highly-efficient RT synthesis strategy based on the Schiff base condensation reaction for preparing the fluorine-doped CQDs (F-CQDs) with good crystallinity. The as-prepared F-CQDs show strong blue FL emission with a high quantum yield of 39%, which is the highest values yet recorded for carbon dots prepared by RT synthesis. Moreover, the F-CQDs can be used for sensitive tetracycline sensing based on inner filter effect. The FL intensity ratio (F0/F) of the F-CQDs is proportional to the concentration of tetracycline in the range of 0.1–25 μM with the limit of detection of 85 nM. This sensitive assay has a good application prospect for tetracycline detection in the complex matrixes because of its simplicity and sensitivity.

Synthesis and size modulation of MoS2 quantum dots by pulsed laser ablation in liquid for viable hydrogen generation

In the present work, MoS2 quantum dots (QDs) were synthesized by chemical-free, single step photo-exfoliation of a solid MoS2 target using pulsed laser ablation in distilled water. MoS2 quantum dots (QDs) with average sizes of ∼4, 2.9, and 6.1 nm were synthesized by ablating an MoS2 target for ablation durations of 5, 10, and 20 min at a fixed laser energy of 40 mJ. Furthermore, quantum dots with average sizes of ∼2.9, 3.6, and 4.0 nm were also synthesized at laser energies of 10, 20, and 40 mJ, respectively, for a fixed ablation duration of 5 min. The quantum dots resulted in luminescence in the visible region. The as-synthesized colloidal solution of MoS2 quantum dots in distilled water showed excitation wavelength-dependent luminescence shifted to longer wavelength by varying excitation wavelength from 290 to 390 nm exhibiting the effect of wide size distribution. Energy dispersive x-ray spectroscopy, selected area electron diffraction pattern, and zeta potential analysis demonstrated the formation of stoichiometric, highly crystalline, and stable MoS2 quantum dots. Raman spectra of the samples showed two sharp and intense Raman active modes A1g and E2g1 of the MoS2 crystal, indicating crystalline MoS2 quantum dot formation. As an electrocatalytic activity, MoS2 quantum dots exhibited a high rate of hydrogen generation with a minimum Tafel slope of ∼57 mV/dec. High surface area with a large number of active edges makes MoS2 QDs an active catalyst for hydrogen production.

Crystalline borophene quantum dots and their derivative boron nanospheres

An efficient strategy was proposed to prepare crystalline borophene quantum dots with two-photo fluorescence and their derivative boron nanospheres.

Growth and properties of hydrothermally derived crystalline ZnSe quantum dots.

Chalcogenide nanostructures are the materials with diverse applications. Here, we report rapid hydrothermal synthesis of crystalline ZnSe quantum dots (QDs), avoiding the use of toxic chemicals. To the best of our knowledge, this is the first report on very rapid (5h) hydrothermal synthesis of pristine ZnSe QDs. Elemental selenium is used as a source for selenium. Structural, morphological, compositional, and optical properties of the semiconductor were studied. Structural properties (X-ray diffraction) demonstrate that the particles have grown in a single cubic phase. Morphological studies show formation of agglomerated QDs (4nm). The material possess stoichiometric ratio of the constituent elements that are uniformly distributed. Selected area electron diffraction (SAED) study indicated the material is polycrystalline in nature. Optical properties demonstrated that the QDs are suitable for optoelectronic devices exhibiting room temperature photoluminescence. Commission Internationale de l'Éclairage (CIE) chromaticity diagram shows the material exhibits violet emission and hence suitable for violet LEDs that have potential ability in clinical applications.

In-situ construction of a Mg-modified interface to guide uniform lithium deposition for stable all-solid-state batteries

Uniform lithium (Li) deposition in all-solid-state Li metal batteries is greatly influenced by the anode/electrolyte interface. Herein, a Mg-modified interface was constructed via the simple in-situ electrochemical reduction of Mg2+ from Mg(TFSI)2 in polyethylene oxide (PEO) and a Li bis(trifluoromethane)sulfonimide (LiTFSI) formulae. As confirmed by cryogenic transmission electron microscopy, the anode/electrolyte interface exhibited hybrids consisting of crystalline Mg, Li2O, and Li dots embedded in an amorphous polymer electrolyte. The crystalline Mg dots guided the uniform Li nucleation and growth, inducing a smoother anode/electrolyte interface compared with the pristine electrolyte. With 1 wt% Mg(TFSI)2 in the PEO-LiTFSI electrolyte, the Mg-modified electrolyte enabled the Li/Li symmetric cells with cycling performance of over 1700 and 1400 h at current densities of 0.1 and 0.2 mA cm−2, respectively. Moreover, the full LFP/Li cells using the novel Mg-modified electrolyte delivered a cycling lifespan of over 450 cycles with negligible capacity loss.