Inna Popov

Au Growth on Semiconductor Nanorods: Photoinduced versus Thermal Growth Mechanisms

Gold growth on CdS nanorods and on seeded CdSe/CdS nanorods with and without illumination at different temperatures was studied. Two competing mechanisms were identified: thermal and light-induced growth. The thermal mechanism leads to growth of small gold particles at defects along the rod body and can be suppressed at lower temperatures. This control is attributed to a phase transition of the alkyl chains of the surface amine ligands to a static phase at lower temperatures, blocking the Au precursors access to the nanorod surfaces. While a long-chain (C18) amine shows effective blocking at 293 K, a shorter chain (C12) amine shows the same result only at 273 K; however, in the case of a bulky trialkylamine, defect growth was observed even at 273 K. Light-induced growth leads to selective deposition of gold on one end of the rods. The tip was shown to grow on sulfur-rich facets of the nanorod, producing end-on and angled tip orientations. Growth under illumination with decreased temperature provides a highly selective synthesis of hybrid semiconductor nanorods with a single gold tip. Such anisotropic semiconductor-metal hybrids are of interest for self-assembly and photocatalysis and as building blocks in optoelectronic devices.

Hybrid nanoscale inorganic cages

Cage structures exhibit inherent high symmetry and beauty, and both naturally occurring and synthetic molecular-scale cages have been discovered. Their characteristic high surface area and voids have led to their use as catalysts and catalyst supports, filtration media and gas storage materials. Nanometre-scale cage structures have also been synthesized, notably noble-metal cube-shaped cages prepared by galvanic displacement with promising applications in drug delivery and catalysis. Further functionality for nanostructures in general is provided by the concept of hybrid nanoparticles combining two disparate materials on the same system to achieve synergistic properties stemming from unusual material combinations. We report the integration of the two powerful concepts of cages and hybrid nanoparticles. A previously unknown edge growth mechanism has led to a new type of cage-structured hybrid metal-semiconductor nanoparticle; a ruthenium cage was grown selectively on the edges of a faceted copper(I) sulphide nanocrystal, contrary to the more commonly observed facet and island growth modes of other hybrids. The cage motif was extended by exploiting the open frame to achieve empty cages and cages containing other semiconductors. Such previously unknown nano-inorganic cage structures with variable cores and metal frames manifest new chemical, optical and electronic properties and demonstrate possibilities for uses in electrocatalysis.

ZnSe Quantum Dots Within CdS Nanorods: A Seeded‐Growth Type‐II System

The sizeand shape-dependent optical properties of colloidal semiconductor nanocrystals can be enhanced significantly by the growth of heterostructures of at least two materials. The potential profile of the involved materials dictates the optical properties of the final structure, where the most common typeI alignment has been extensively used in spherical core/shell nanocrystals to achieve electron and hole confinement in the core leading to high photoluminescence quantum efficiencies and enhanced stability. Type-II alignment, where the potential profile leads to charge-carrier separation, has also been reported and leads to prolonged emission lifetimes, modified multiexciton behavior, and enhanced optical-gain characteristics. Anisotropic rod heterostructures are also of great interest, and previously advantageous optical-gain studies were reported for type-I core/shell rods. Heterostructures were also grown by combining different materials into the growing nanorod. In particular, type-II nanorod heterostructures of CdSe/CdTe showing light-induced charge separation were recently reported. Exceptional optical properties and uniformity were recently reported for CdS nanorods with CdSe seeds by Talapin and Manna. A seeded-growth approach was utilized, based on earlier work on this system, which has already yielded significant insight to the electronic structure and optical properties of type-I seeded dot–rod heterostructures. Here, we expand this synthetic approach and develop CdS nanorods with embedded ZnSe quantum dots, which constitute an example of a nanorod heterostructure with a seed of zinc blende crystal structure. This structure is of high interest because of the type-II potential profile characteristics of ZnSe and CdS (see Figure 1). According to this potential profile, a charge-carrier separation should occur in the excited state of

Merging of metal nanoparticles driven by selective wettability of silver nanostructures

The welding and sintering of nanomaterials is relevant, for example, to form electrical contacts between metallic particles in printed electronic devices. Usually the welding of nanoparticles is achieved at high temperatures. Here we find that merging of two different metals, silver and gold nanoparticles, occurs on contact at room temperature. The merging process was investigated by experimental and molecular dynamics simulations. We discovered that the merging of these particles is driven by selective wettability of silver nanoparticles, independent of their size and shape (spheres or rods); silver behaves as a soft matter, whereas gold as a hard surface being wetted and retaining its original morphology. During that process, the silver atoms move towards the surface of the Au nanoparticles and wrap the Au nanoparticles in a pulling up-like process, leading to the wetting of Au nanoparticles.

Development and metrological characterization of quantitative X-ray diffraction phase analysis for the mixtures of clopidogrel bisulphate polymorphs

Clopidogrel bisulphate (CLP) is a pharmaceutical compound with a novel mechanism of action for the reduction of atherosclerotic events. Only two crystalline forms (CLP I and CLP II) among the six known polymorphs of CLP have therapeutic activity. The structure of the CLP I polymorph is unknown and the structure of the CLP II polymorph is known only partially. Two techniques of X-ray diffraction quantitative phase analysis have been developed in this work for the quantification of CLP I and CLP II in their mixtures. The first technique is based on use of the whole powder pattern decomposition method (WPDM). WPDM was realized through Powder Cell for Windows v.2.4 (PCW) freeware. The second technique is based on the classical direct method. Metrological characterization and comparison of methods have been performed on the mixtures with known phase composition as well as on the real samples with varying phase content. Quantitative phase analyses of 120 specimens containing mixtures of forms I and II of CLP were performed using both developed techniques. Absolute and relative errors and reproducibility of both methods were found to be very similar. The statistical analysis of obtained results revealed that the WPDM gives higher accuracy. We found that the limit of quantification using both methods is 1.0-1.5wt.% of phase content in the mix.

X-ray diffraction and SEM study of kidney stones in Israel: quantitative analysis, crystallite size determination, and statistical characterization

Urinary calculi have been recognized as one of the most painful medical disorders. Tenable knowledge of the phase composition of the stones is very important to elucidate an underlying etiology of the stone disease. We report here the results of quantitative X-ray diffraction phase analysis performed on 278 kidney stones from the 275 patients treated at the Department of Urology of Hadassah Hebrew University Hospital (Jerusalem, Israel). Quantification of biominerals in multicomponent samples was performed using the normalized reference intensity ratio method. According to the observed phase compositions, all the tested stones were classified into five chemical groups: oxalates (43.2%), phosphates (7.7%), urates (10.3%), cystines (2.9%), and stones composed of a mixture of different minerals (35.9%). A detailed analysis of each allocated chemical group is presented along with the crystallite size calculations for all the observed crystalline phases. The obtained results have been compared with the published data originated from different geographical regions. Morphology and spatial distribution of the phases identified in the kidney stones were studied with scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). This type of detailed study of phase composition and structural characteristics of the kidney stones was performed in Israel for the first time.

Highly defective MgO nanosheets from colloidal self-assembly

Highly defective magnesium oxide nanosheets were synthesized using a colloidal synthesis in which magnesium ethoxide was thermally decomposed in high-boiling-point weakly coordinating solvents. The nanosheets were assembled of small nanocrystal building blocks by oriented attachment. This assembly could be inhibited by using a strongly coordinating surfactant, such as oleic acid. The 2–3 nm spaced extended defects formed at the grain boundaries make up a material with a record defect density which causes an increased conductivity and dielectric constant, strong luminescence and paramagnetism. The point defect type prevailing at those interfaces is apparently charged oxygen vacancies. In situTEM annealing experiments showed that the extended defects begin to anneal out at temperatures as low as 300 °C, but a high density of point defects apparently survives even at 750 °C.

Rhodium growth on Cu2S nanocrystals yielding hybrid nanoscale inorganic cages and their synergistic properties

Metal decoration on the edges of highly faceted Cu2S semiconductor nanocrystals yields a family of nano-inorganic caged (NICed) hybrid semiconductor–metal nanoparticles. We present the growth of rhodium and of ruthenium–rhodium mixture to give Rh–Cu2S and RuRh–Cu2S hybrid nanoparticle cages, respectively. Transmission electron microscopy affirms the growth of the metals selectively on the nanocrystal edges within a narrow temperature window. The oxidation level of the metal frame could also be controlled during the reaction stages as characterized by X-ray photoelectron spectroscopy, providing additional variation for the hybrid nanoparticle cages. The synergistic electronic properties of the hybrid nanocages were observed on a single particle level using scanning tunneling spectroscopy. The various cage nanoparticles are also of interest as possible catalysts for metal and metal-oxide catalyzed reactions.

CdSe quantum dots induce superoxide stress in engineered biosensor bacteria

A panel of genetically-engineered Escherichia coli biosensor bacteria, responsive to chemical stressors inducing heat shock, DNA damage, oxidative stress (peroxide- and superoxide-type) and fatty acid metabolism interference, was used to characterize the chemical effect of CdSe quantum dot exposure. Results implicate a primary mode of superoxide-type stress toxicity that is dependent upon quantum dot dose, size, and chain length of capping agent, and are consistent with results from other reports employing mammalian cell lines. Imaging studies confirm association of quantum dots with lipophilic regions of the biosensor bacteria (i.e., inner/outer membranes, cell wall, periplasmic space), and demonstrate intracellular alteration of the quantum dot lattice. Corroboratory experiments with superoxide stress mutants and antioxidant amendments confirm oxidative stress while also implicating destabilization of quantum dots.

Crystallization of carbamazepine pseudopolymorphs from nonionic microemulsions.

Crystallization of carbamazepine (CBZ), an antiepileptic drug, precipitated from confined spaces of nonionic microemulsions was investigated. The study was aimed to correlate the structure of the microemulsion [water-in-oil (W/O), bicontinuous, and oil-in-water (O/W)] with the crystalline structure and morphology of solid CBZ. The precipitated CBZ was studied by DSC, TGA, powder XRD, single-crystal XRD, SEM, and optical microscopy. The results suggest that the microstructure of the microemulsions influences the crystallization process and allows crystallizing polymorphs that exhibit different crystal structure and habits. W/O nanodroplets orient the crystallizing CBZ molecules to form a prismlike anhydrous polymorphic form with monoclinic unit cell and P21/n space group. Bicontinuous structures lead to platelike dihydrate crystals with orthorhombic unit cell and Cmca space group. The O/W nanodroplets cause the formation of needlelike dihydrate crystals with monoclinic unit cell and P21/c space group. The morphological features of solid CBZ remain predetermined by the basic symmetry and parameters of its unit cell. Precipitation of CBZ pseudopolymorphs from supersaturated microemulsion is discussed in terms of oriented attachment that provides perfect packing of numerous separately nucleated ordered nuclei of CBZ into microscale platelets and then into macroscopic crystals. Crystallization from microemulsion media enabling one to obtain the drug (CBZ) with predicted structure and morphology should be of great significance for pharmaceutical applications.