Ordering Of Nanocrystals Research Articles

Composite polymer films with semiconductor nanocrystals for organic electronics and optoelectronics

Organic materials and, in particular, polymer films enhanced with certain nanocrystals have a potential for wide application in electronics and optoelectronics due to their organic flexibility, lightweight, simple integration, affordable manufacturing cost, and low environmental impact of their production. The purpose of this research is to investigate the electrical properties of polymer-based composite films containing Cd1–xCuxS nanocrystals in order to determine their prospects for use as conductive layers in organic electronics and optoelectronics. The paper contains a detailed description of the synthesis method of hybrid nanocomposite films based on peroxide reactive copolymer (PRC) with Cd1–xCuxS nanocrystals. The defect structure of the films is studied by analyzing the photoluminescence spectra. Current-voltage characteristics of the films with different Cd and Cu contents in the Cd1–xCuxS nanocrystals embedded into the polymer matrix, deposited on glass substrates are measured in the dark and under light illumination. The film conductivity is found to increase with the Cu content in the Cd1–xCuxS nanocrystals. The carrier transport corresponds to the Ohm law at low voltages and the space charge limited current (SCLC) or Poole–Frenkel mechanisms at higher ones. The conductivity of the polymer-based hybrid nanocomposite films has a weak dependence on the intensity of light illumination. The explanation of the obtained experimental results is proposed.

Tunable Unexplored Luminescence in Waveguides Based on D-A-D Benzoselenadiazoles Nanofibers.

A set of novel Donor-Acceptor-Donor (D-A-D) benzoselenadiazole derivatives has been synthesized and crystallized in nanocrystals in order to explore the correlation between their chemical structure and the waveguided luminescent properties. The findings reveal that all crystals exhibit luminescence and active optical waveguiding, demonstrating the ability to adjust their luminescence within a broad spectral range of 550-700 nm depending on the donor group attached to the benzoselenadiazole core. Notably, a clear relationship exists between the HOMO-LUMO energy gaps of each compound and the color emission of the corresponding optical waveguides. These outcomes affirm the feasibility of modifying the color emission of organic waveguides through suitable chemical functionalization. Importantly, this study marks the first utilization of benzoseleniadiazole derivatives for such purposes, underscoring the originality of this research. In addition, the obtention of nanocrystals is a key tool for the implementation of miniaturized photonic devices.

Lipid-Coated Nanocrystals as a Tool for Improving the Antioxidant Activity of Resveratrol

Trans-resveratrol, a polyphenolic phytoalexin found in various plant sources, has been the focus of increasing attention in recent years because of its role in the prevention of many human diseases, and particularly because of its antioxidant properties. However, the in vivo effect of trans-resveratrol after oral administration is negligible when compared to its efficacy in vitro, due to its low bioavailability. Moreover, it presents stability issues as it is an extremely photosensitive compound when exposed to light. This work aims to develop lipid-coated nanocrystals in order to improve the antioxidant activity and bioavailability of trans-resveratrol. Lipid-coated trans-resveratrol nanocrystals with sizes lower than 500 nm, spherical shapes and smooth surfaces were obtained via a milling method. They showed a faster dissolution rate than the coarse trans-resveratrol powder. The antioxidant properties of trans-resveratrol were not impaired by the milling process. The in vivo pharmacokinetics of lipid-coated trans-resveratrol nanocrystals were evaluated after oral administration to rats, with a commercial Phytosome® formulation being used for comparison purposes. An increase in the trans-resveratrol area under the curve was observed and the lipid-coated nanocrystal formulation led to an enhancement in the oral bioavailability of the compound.

Low-Threshold, Highly Stable Colloidal Quantum Dot Short-Wave Infrared Laser enabled by Suppression of Trap-Assisted Auger Recombination.

Pb-chalcogenide colloidal quantum dots (CQDs) are attractive materials to be used as tuneable laser media across the infrared spectrum. However, excessive nonradiative Auger recombination due to the presence of trap states outcompetes light amplification by rapidly annihilating the exciton population, leading to high gain thresholds. Here, a binary blend is employed of CQDs and ZnO nanocrystals in order to passivate the in-gap trap states of PbS-CQD gain medium. Using transient absorption, a fivefold increase is measured in Auger lifetime demonstrating the suppression of trap-assisted Auger recombination. By doing so, a twofold reduction is achieved in amplified spontaneous emission (ASE) threshold. Finally, by integrating the proposed binary blend to a distributed feedback (DFB) resonator, single-mode lasing emission is demonstrated at 1650nm with a linewidth of 1.23nm (0.62 meV), operating at a low lasing threshold of ≈385 μJ cm-2 . The Auger suppression in this system has allowed to achieve unprecedented lasing emission stability for a CQD laser with recorded continuous operation of 5 h at room temperature and ambient conditions.

Cyber-Physical System Enabled Digital Manufacturing of Nanocrystals: A Crystputer

Digital manufacturing of materials in a rational and designable strategy and is gaining popularity on the macro-scale . However, it is challenging to control the nanocrystal morphologies on a nano-scale. Herein, we introduce Crystputer as a state-of-the-art cyber- physical system , which will enable digital manufacture of nanocrystals through convergence of cyber and physical systems. In the cyber system, an all-programmable process with rational design including codes, working files, mathematic models, and databases is designed. In the physical system, controllable synthesis is achieved by synergistic coupling of robot-assisted synthesis and nanocrystal growth , which are benefited from the identified structure-directing agents on the macro-scale as triggers of the surface energy to control the morphology on the atomic-scale. Driven by the Crystputer efficiency, over 2,300 experiments are conducted autonomously together with in situ characterization to build up the Au nanocrystals genome. The genome architecture with logic gates is further designed for the Crystputer. It is demonstrated that the Crystputer can be trained as an experienced expert for retrosynthesis and scale-up synthesis of targeted Au nanorods by taking advantage of the machine learning prediction and logic computation. The sophisticated mechanism encompassing design-control-synthesis-characterization-computing-retrosynthesis enables this Crystputer to deliver unprecedented performance and efficiency for rational design, controllable synthesis, and retrosynthesis of target Au nanocrystals. The insights and new knowledge open an opportunity to enhance the feasibility of Crystputer for intelligent digital manufacturing of customized nanocrystals in order to facilitate the paradigm shift of data-driven materials innovation from ‘code’ to ‘nanocrystals’.

Energy level tuning of InP/ZnS nanocrystals by electronically delocalized dithiocarbamate derivatives

The nanocrystals have characteristics of varying the energy gap between the valence band and the conduction band depending on the size, and are attracting attention as light emitting materials due to the excellent in light stability. Since the bandgap of nanocrystals is determined by the size, it is very important to control the size of the nanocrystals in order to realize the red, green and blue primary color in a display. However, there are many difficulties in finely adjusting the nanocrystal bandgap to a size. In this study, the monodentate amine ligands coordinated on the surface of InP/ZnS nanocrystals are substituted with bidentate dithiocarbamate ligands having a strong coordination ability and electrically resonant structures, so that the nanocrystal can be finely tuned to control the emission spectrum. NMR analysis showed that some amine ligands on the surface of the nanocrystals were substituted with dithiocarbamate ligands. The PL spectra also show that the emission wavelength of the new nanocrystals is increased by about 20 nm (bathochromic shift), indicating that the active region of the exciton (an electron-hole pair) is extended to the delocalized dithiocarbamate ligands as well as the nanocrystals.

A combination of nanosystems for the delivery of cancer chemoimmunotherapeutic combinations: 1-Methyltryptophan nanocrystals and paclitaxel nanoparticles

IDO is an enzyme that tumors use to create a state of immunosupression. 1-d-methyltryptophan (1-MT) is an IDO pathway inhibitor. After being successfully evaluated in preclinical studies, current clinical trials are actually analyzing its efficacy as monotherapy or in combination with multiple chemotherapeutic agents such as paclitaxel. 1-MT very poor solubility in water and many other solvents precludes its ease parenteral administration. It is currently administered by oral route because high daily doses were well-tolerated and effectively inhibited the IDO activity although only 25% of dose was recovered in plasma.The present work describes the preparation and characterization of 1-MT nanocrystals in order to enhance its solubility, dissolution rate, biodisponibility as well as facilitate its administration by parenteral route. A bottom-down approach of nanoprecipitation with an antisolvent was used for the fabrication of the nanocrystals and the choice of stabilizers was critical for reducing the size. Thermal analysis and x-ray diffraction indicated modifications in the drug crystalline state by the process. Through the reduction size and crystalline state modifications the dissolution characteristics of raw material were significantly increased. In a Lewis Lung cancer mice model, the nanocrystals strategy facilitated the sc administration and its antitumoral activity was similar to that of i.v. paclitaxel. The best efficacy was achieved when sc 1-MT nanocrystals were administered in combination with oral paclitaxel loaded in poly(anhydride) nanoparticles. Take together, 1-MT nanocrystals delivery performs a nanotechnological strategy suitable to modify the current route and schedule for its administration.

The most active Cu facet for low-temperature water gas shift reaction

Identification of the active site is important in developing rational design strategies for solid catalysts but is seriously blocked by their structural complexity. Here, we use uniform Cu nanocrystals synthesized by a morphology-preserved reduction of corresponding uniform Cu2O nanocrystals in order to identify the most active Cu facet for low-temperature water gas shift (WGS) reaction. Cu cubes enclosed with {100} facets are very active in catalyzing the WGS reaction up to 548 K while Cu octahedra enclosed with {111} facets are inactive. The Cu–Cu suboxide (CuxO, x ≥ 10) interface of Cu(100) surface is the active site on which all elementary surface reactions within the catalytic cycle proceed smoothly. However, the formate intermediate was found stable at the Cu–CuxO interface of Cu(111) surface with consequent accumulation and poisoning of the surface at low temperatures. Thereafter, Cu cubes-supported ZnO catalysts are successfully developed with extremely high activity in low-temperature WGS reaction.

Kinetics and Mechanism of Methanol Conversion over Anatase Titania Nanoshapes

The kinetics and mechanism of methanol dehydration, redox, and oxidative coupling were investigated at 300 °C under dilute oxygen concentration over anatase TiO2 nanoplates and truncated-bipyramidal nanocrystals in order to understand the surface structure effect of TiO2. The two TiO2 nanoshapes displayed both (001) and (101) facets, with a higher fraction of the (001) facet exposed on the nanoplates, while truncated-bipyramidal nanocrystals were dominated by the (101) facet. A kinetic study using in situ titration with ammonia shows that the active sites for methanol dehydration are acidic and nonequivalent in comparison to redox and oxidative coupling. In situ FTIR spectroscopy reveals that adsorbed methoxy is the dominant surface species for all reactions, while the observed methanol dimer is found to be a spectator species through isotopic methanol exchange, supporting the dissociative mechanism for methanol dehydration via surface methoxy over TiO2 surfaces. Density functional theory calculations sho...

Excess of topological defects induced by confinement in vortex nanocrystals

We directly image individual vortex positions in nanocrystals in order to unveil the structural property that contributes to the depletion of the entropy-jump entailed at the first-order transition. On reducing the nanocrystal size the density of topological defects increases near the edges over a characteristic length. Within this "healing-length" distance from the sample edge vortex rows tend to bend while towards the center of the sample the positional order of the vortex structure is what is expected for the Bragg-glass phase. This suggests that the healing-length may be a key quantity to model the entropy-jump depletion in the first-order transition of extremely-layered vortex nanocrystals.

Cellular internalization of LiNbO3 nanocrystals for second harmonic imaging and the effects on stem cell differentiation.

Second harmonic generation (SHG) nanocrystals have recently been reported to label cancer cells and other functional cell lines due to their unique double-frequency property. In this paper, we report for the first time the use of lithium niobate (LiNbO3, LN) nanocrystals as SHG labels for imaging stem cells. Rat mesenchymal stem cells (rMSCs) were labeled with LN nanocrystals in order to study the cellular internalization of the nanocrystals and the influence on stem cell differentiation. The results showed that LN nanocrystals were endocytosed by the rMSCs and the distribution of the internalized nanoparticles demonstrated a high consistency with the orientation of the actin filaments. Besides, LN-labeled rMSCs showed a concentration-dependent viability. Most importantly, rMSCs labeled with 50 μg per mL of LN nanocrystals retained their ability to differentiate into both osteogenic and adipogenic lineages. The results prove that LN nanocrystals can be used as a cytocompatible, near-infrared (NIR) light driven cell label for long-term imaging, without hindering stem cell differentiation. This work will promote the use of LN nanocrystals to broader applications like deep-tissue tracking, remote drug delivery and stem cell therapy.

Oriented Metallic Nano-Objects on Crystalline Surfaces by Solution Epitaxial Growth.

Chemical methods offer the possibility to synthesize a large panel of nanostructures of various materials with promising properties. One of the main limitations to a mass market development of nanostructure based devices is the integration at a moderate cost of nano-objects into smart architectures. Here we develop a general approach by adapting the seed-mediated solution phase synthesis of nanocrystals in order to directly grow them on crystalline thin films. Using a Co precursor, single-crystalline Co nanowires are directly grown on metallic films and present different spatial orientations depending on the crystalline symmetry of the film used as a 2D seed for Co nucleation. Using films exposing 6-fold symmetry surfaces such as Pt(111), Au(111), and Co(0001), the Co heterogeneous nucleation and epitaxial growth leads to vertical nanowires self-organized in dense and large scale arrays. On the other hand, using films presenting 4-fold symmetry surfaces such as Pt(001) and Cu(001), the Co growth leads to slanted wires in discrete directions. The generality of the concept is demonstrated with the use of a Fe precursor which results in Fe nanostructures on metallic films with different growth orientations which depend on the 6-fold/4-fold symmetry of the film. This approach of solution epitaxial growth combines the advantages of chemistry in solution in producing shape-controlled and monodisperse metallic nanocrystals, and of seeded growth on an ad hoc metallic film that efficiently controls orientation through epitaxy. It opens attractive opportunities for the integration of nanocrystals in planar devices.

Thermo-responsive and aqueous dispersible ZnO/PNIPAM core/shell nanoparticles

In this work, we developed a new process to covalently graft a thermoresponsive polymer on the surface of fluorescent nanocrystals in order to synthesize materials that combine both responsive and fluorescent properties. For the first time, poly(N-isopropylacrylamide) (PNIPAM) was grown by activator regenerated by electron transfer–atom transfer radical polymerization (ARGET-ATRP) from ZnO quantum dots (QDs) by surface-initiated polymerization. This process allowed the formation of fluorescent and responsive ZnO/PNIPAM core/shell QDs while only requiring the use of a ppm amount of copper for the synthesis. The influence of the nature of the silanized layer and the polymerization time on the properties of the final nanomaterials were investigated. Results clearly evidence that both the PNIPAM layer thickness and the temperature affected the luminescence properties of the core/shell nanoparticles, but also that the PNIPAM layer, when it is thick enough, could stabilize the QDs’ optical properties.

Morphology-controlled self-assembly and synthesis of photocatalytic nanocrystals.

Abilities to control the size and shape of nanocrystals in order to tune functional properties are an important grand challenge. Here we report a surfactant self-assembly induced micelle encapsulation method to fabricate porphyrin nanocrystals using the optically active precursor zinc porphyrin (ZnTPP). Through confined noncovalent interactions of ZnTPP within surfactant micelles, nanocrystals with a series of morphologies including nanodisk, tetragonal rod, and hexagonal rod, as well as amorphous spherical particle are synthesized with controlled size and dimension. A phase diagram that describes morphology control is achieved via kinetically controlled nucleation and growth. Because of the spatial ordering of ZnTPP, the hierarchical nanocrystals exhibit both collective optical properties resulted from coupling of molecular ZnTPP and shape dependent photocatalytic activities in photo degradation of methyl orange pollutants. This simple ability to exert rational control over dimension and morphology provides new opportunities for practical applications in photocatalysis, sensing, and nanoelectronics.

Adsorptive removal of fluoride ions from aqueous solution by using sonochemically synthesized nanomagnesia/alumina adsorbents: An experimental and modeling study

Wet impregnation followed by sonochemical approach was applied to dope γ-Al2O3 with MgO nanocrystals in order to synthesize a new and more efficient fluoride nanosorbent (4–30nm). The effects of operating conditions such as pH, fluoride concentration, contact time and dosage were studied. The adsorbents were characterized by using the pHZPC measurement and FTIR, HR-SEM, XRD, EDAX, and BET analyses. The optimum fluoride removal (>85%), adsorption capacity of ∼5.6mg/g, was obtained at 140min, neutral pH range of 6.3–7.3, and adsorbent dosage of 0.5g/L. The isomorphic substitution of OH− of brucite in the nanosorbent with fluoride ions could be herein the dominant sorption mechanism. Furthermore, other ions (Cl−, SO42−, HCO3−, PO43−) in the solution had very little interference in the fluoride adsorption. However, PO43− was the greatest competitor for fluoride adsorption. Finally, the experimental adsorption equilibrium and kinetic data were closely followed the Langmuir adsorption isotherm and pseudo second order kinetic model respectively.

Correlation of structural and magnetic properties of Ni-doped ZnO nanocrystals

In order to gain insight into the magnetic behaviour of Ni-doped ZnO nanocrystals (NCs) the local structure was rigorously studied by extended x-ray absorption fine structure (EXAFS) along with the magnetic measurements. At low doping level of Ni, local structure remains identical to ZnO NCs with subtle increase in the bond length. EXAFS and the optical absorption measurements indicate valence of Ni to be +2. Undoped as well as Ni-doped ZnO NCs with very low Ni concentration are weakly ferromagnetic. Further increase in doping level yields paramagnetic NCs. The present studies clearly prove that ferromagnetic ordering in NCs is primarily a manifestation of point defects and incorporation of transition metal impurities plays a secondary role.

New Insights into the SnO2 Sensing Mechanism Based on the Properties of Shape Controlled Tin Oxide Nanoparticles

We report on the sensing behavior of SnO2 shape controlled nanocrystals in order to evaluate the role of their exposed crystal surfaces in the sensing mechanism. Octahedral (OCT), elongated dodecahedral (DOD), and nanobar shaped (NBA) nanocrystals were synthesized by previously reported procedures and their performances were evaluated in the sensing toward CO. Singly ionized oxygen vacancies (VO•) were detected by electron spin resonance (ESR), and their abundance and reactivity were associated to the exposed crystal faces and, in turn, to the sensing responses of the nanocrystals. Results indicated that the electrical properties and the formation/reactivity of the VO• centers are interconnected and are relatable to the nanoparticle specific surfaces. Two different temperature-dependent sensing mechanisms were proposed, depending on the prevalence of the surface structure or of the specific surface area on the sensing ability of shape controlled SnO2 nanoparticles.

Copper-Diffused AgInS2 Ternary Nanocrystals in Hybrid Bulk-Heterojunction Solar Cells: Near-Infrared Active Nanophotovoltaics

We have grown copper-diffused AgInS2 ternary nanocrystals in order to introduce the nanoparticles in organic/inorganic bulk-heterojunction devices for photovoltaic applications. Here, copper diffuses to vacant sites and improves conductivity of the nanocrystals. Upon use of such copper-diffused nanoparticles that led to a decrease in internal resistance of sandwiched devices based on the bulk-heterojunction, there has been a marked improvement in short-circuit current under white light illumination. Due to a red-shift in the optical absorption spectrum of the nanoparticles upon copper diffusion, the devices moreover acted as near-infrared (IR) active photovoltaic solar cells. From current-voltage characteristics and impedance spectroscopy of the devices, we optimized performance of the photovoltaic devices. To do so, we have varied the content of diffused copper in AgInS2 nanoparticles and also the weight-ratio between the polymer and the nanoparticles of the hybrid bulk-heterojunction devices.

Cooperative Spontaneous Emission from Nanocrystals to a Surface Plasmon Polariton in a Metallic Nanowire

We analyze the cooperative spontaneous emission of optically excited nanocrystals into surface plasmon polaritons propagating on the surface of a cylindrical metallic nanowire. The spontaneous emission probability of the nanocrystals is obtained by perturbative expansions with and without dipole-dipole interaction among nanocrystals in order to see the cooperative effects. The spontaneous emission probability depends on the radial and axial distributions, as well as on the dipolar orientation of nanocrystals. It is shown that the spontaneous emission probability is strongly influenced by dipole-dipole interaction, axial distribution, and dipolar orientation of nanocrystals for closely spaced nanocrystals.

DNA template driven CdSe nanowires and nanoparticles: Structure and optical properties

CdSe nanocrystals (NCs) with good crystallinity were successfully grown by an electrochemical deposition technique using two different single stranded (ss) DNA molecules, poly G (30) and poly C (30) as templates. A model describing the structural ordering in CdSe NCs using ssDNA and its conjugate is being proposed. TEM and GXRD measurements confirm the structural ordering in NC CdSe–DNA systems. FTIR measurements confirm the tagging of DNA to CdSe NC. Micro Raman scattering of structurally ordered CdSe NCs show strong phonon confinement.