Showing papers in "Nanoscience and Nanotechnology Letters in 2011"

Deagglomeration of Detonation Nanodiamonds

Abstract: Ioffe Physical Technical Institute, 26 Polytechnicheskaya st. 194021, St. Petersburg, RussiaIt is well known that a commercial powder of detonation nanodiamonds (DND) and their aqueoussuspensions consist of agglomerates of 4 5 nm crystalline diamond grains. We have submitteda method for production of stable mono-disperse hydrosol of 4 nm isolated DND particles. Themethod includes deep puri“cation commercial DND from metal impurities and appropriate controlof its residual amount by electronic spin resonance, annealing of puri“ed DND in air and centrifu-gation. The main result of the study demonstrates that centrifuging of a DND hydrosol of particleswith a high negative zeta potential produced by deep puri“cation and air annealing results intobreakup of the agglomerates. A model explained high strength of the DND agglomerates has beendiscussed.

Blocking layer effect on dye-sensitized solar cells assembled with TiO2 nanorods prepared by dc reactive magnetron sputtering

Abstract: Three different thickness dense tio2 (150 nm, 300 nm and 450 nm respectively) films were deposited on ito substrates by dc reactive magnetron sputtering technique. these dense tio2 films were used as the blocking layers. after that, tio2 nanorod films were deposited on these dense tio2 films by same technique. both the dense and nanorod tio2 films have an anatase phase. the dense tio2 films have an orientation along the [101] direction and the tio2 nanorod films show a very strong orientation along the [110] direction. these tio2 materials were sensitized by n719 dye and the dsscs were assembled using them as photoelectrode. the effect of the blocking layer on the efficiency of the dsscs is discussed. the dssc assembled using tio2 nanorod film with 300 nm thickness blocking layer shows a high efficiency of 2.07%.

Fabrication of TiO 2 Aggregates by Electrospraying and Their Application in Dye-Sensitized Solar Cells

Abstract: Junting Xi1 2, Qifeng Zhang1, Shuhong Xie3 4, Supan Yodyingyong1, Kwangsuk Park1, Yueming Sun2, Jiangyu Li3, and Guozhong Cao1 ∗ 1Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA 2School of Chemistry and Chemical Engineering, Southeast University, Jiangsu 211189, People’s Republic of China 3Department of Mechanical Engineering, University of Washington, Seattle, WA 98195, USA 4Faculty of Materials, Optoelectronics and Physics, Xiangtan University, Hunan 411105, People’s Republic of China

Identification of substitutional nitrogen and surface paramagnetic centers in nanodiamond of dynamic synthesis by electron paramagnetic resonance

Abstract: Production of nanodiamond particles containing substitutional nitrogen is important for a wide variety of advanced applications. In the current work nanodiamond particles synthesized from a mixture of graphite and hexogen were analyzed to determine the presence of substitutional nitrogen using pulsed electron paramagnetic resonance (EPR) spectroscopy. Nitrogen paramagnetic centers in the amount of 1.2 ppm have been identified. The spin relaxation characteristics for both nitrogen and surface defects are also reported. A new approach for efficient depletion of the strong nonnitrogen EPR signal in nanodiamond material by immersing nanodiamond particles into ice matrix is suggested. This approach allows an essential decrease of the spin relaxation time of the dominant non-nitrogen defects, while preserving the substitutional nitrogen spin relaxation time.

Cell Growth in a Porous Microcellular Structure: Influence of Surface Modification and Nanostructures

Abstract: : This study investigates the growth, morphology and cell viability of bone cells (osteoblasts) inside microcellular graphitic foam having an interconnected porosity. This type of substrate can be useful as a scaffolding material for tissue growth, but has not been adequately investigated. The influence of various surface treatments was studied: an inorganic hydrophilic coating (silica), an organic coating (collagen), and grafting of carbon nanotubes (CNT) have been reported. It is seen that all foams have acceptable biocompatibility. Silica and collagen coatings tend to have more cell growth along pore walls but do not have any significant influence on overall nuclear density or cell viability. On the other hand, nanotube attachment results in simultaneous increase of cell proliferation, density and viability. These results indicate that attaching carbon nanotubes on surfaces of future implants may provide a hierarchical nanostructure with increased biocompatible surface area for improved cell attachment.

Electron Spin Resonance Study of α -Cr 2 O 3 and Cr 2 O 3 · n H 2 O Quasi-Spherical Nanoparticles

Abstract: The quasi-spherical nanoparticles of hydrated Cr2O3 · nH2O, and crystalline α-Cr2O3, have been synthesized by reduction of the first row (3d) transition metal complex of K2Cr2O7. The temperaturedependence of electron spin resonance (ESR) spectrum was studied in terms of g-factor, line width and intensity. ESR of both Cr2O3 · nH2O and α-Cr2O3 has been studied at X-band (9.61 GHz) in the temperature range of 292–420K. An anomalous thermal hysteresis was observed in the ESR intensity and linewidth (∆Hpp of Cr2O3 · nH2O. This study shows that there could be a dominant water loss/gain during the heating-cooling cycles which is influencing the thermal relaxation time of Cr2O3 · nH2O. A similar hysteresis was observed in the differential scanning calorimetry (DSC) data which correlates well with that of ESR indicating possible surface dehydration/rehydration of Cr2O3 ·nH2O nanoparticles during the heating–cooling cycles of ESR measurements.

Assessment of Human Lung Macrophages After Exposure to Multi-Walled Carbon Nanotubes. Part 1. Cytotoxicity

Abstract: Due to the widespread production and use of carbon nanotubes in almost every area of science (i.e., drug delivery, biosensors, fuel cells and thermal management systems), they are receiving considerable attention for their novel mechanical, electrical and chemical properties. At this time of high exposure potential, it is critical to ascertain the biological impact of these materials on likely target organs, tissues and cells, such as those of the lung. The aim of this study was to evaluate the degree of cytotoxicity to human lung macrophage (U937) cells after exposure to unpurified or acidpurified multi-walled carbon nanotubes. Cells were incubated with multi-walled carbon nanotubes and assessed for cytotoxicity, generation of reactive oxygen species, morphological changes and uptake. The results demonstrate that multi-walled carbon nanotubes can accumulate in human lung macrophage cells to different degrees based on their surface chemistry. MWNT-COOH reduces cell viability in a dose-dependent manner under these experimental conditions (5–50 g/ml, 2–24 h). However, images of individual cells demonstrate morphological changes at low concentrations. Therefore, before nanomaterials are fully accepted and integrated into biological systems, they will continue to undergo further scrutiny at various stages of their processing (i.e., before and after purification) and with models ranging from simple to complex (i.e., cells vs. whole animals) to gain a better understanding between their physicochemical properties and bio-effects.

Driving Ge Island ordering on nanostructured Si surfaces

Abstract: Semiconductor epitaxial nanostructures have been recently proposed as the key building blocks of many innovative applications in materials science and technology. To bring their tremendous potential to fruition, a fine control of nanostructure size and placement is necessary. We present a detailed investigation of the self-ordering process in the prototype case of Ge/Si heteroepitaxy. Starting from a bottom-up strategy (step-bunching instabilities), our analysis moves to lithographic techniques (scanning tunneling lithography, nanomechanical stamping, focused ion beam patterning) with the aim of developing a hybrid approach in which the exogenous intervention is specifically designed to suit and harness the natural self-organization dynamics of the system.

A Microbridge Method in Tensile Testing of Substrate for Fracture Toughness of Thin Films

Abstract: A new microbridge method is introduced in this paper in tensile testing of substrate for fracture toughness of thin films. Measurement of fracture toughness for bulk materials is a routine but extremely difficult and still not standardized for thin films (or coatings). The difficulties in clamping a freestanding thin film and the requirement of a critical delicate loading system are the main obstacles. In this paper, the film to be tested is deposited on a rectangular silicon wafer on which an edge crack is fabricated beforehand. The film is patterned and made into microbridges perpendicular to and ahead of the initial substrate crack. A displacement controlled tensile force is applied to propagate the substrate crack and fracture the microbridges. The critical fracture strain of the microbridge is measured through measuring that of the substrate at the respective location of the bridge. The fracture toughness of the film is thus obtained. This method successfully turned the tensile testing of the film into tensile loading of the substrate, avoided the delicate clamping and loading on the film itself. Two case studies are also presented.

Study of Silicon Dioxide Nanowires Grown via Rapid Thermal Annealing of Sputtered Amorphous Carbon Films Doped with Si

Abstract: Silica nanowires are usually synthesized by means of vapor liquid solid method with metal catalyst introduced at the top which will unambiguously affect the excellent light emission properties of silica nanowires in optoelectronic devices an optical sign l sensors. In this study, silicon dioxide nanowires without traces of catal st are grown via rapid thermal annealing of magnetron sputtered amorphous carbon film doped with silicon. These high density silicon dioxide nanowires were amorphous with a length longer than 20 m and a diameter of 30–140 nm. Detailed morphology and microstructure analysis are conducted with field emission scanning electron microscopy and high resolution transmission electron microscopy. Graphitization of carbon and oxidation of silicon during rapid thermal annealing were revealed by Raman and X-ray photoelectron spectroscopy. This study indicates that high growth rate of >6 m/min of high purity silicon dioxide nanowire is possible simply by sputtering followed by rapid thermal annealing and an additional heating treatment.

ESR Microscopy for Biological and Biomedical Applications

Abstract: We report on electron-spin resonance microscopy (ESRM) providing sub-micron resolution (~700nm) with a high spin concentration sample, i.e. lithium phthalocyanine (LiPc) crystal. For biomedical applications of our ESRM, we have imaged samples containing rat basophilic leukemia (RBL) cells as well as cancerous tissue samples with a resolution of several microns using a water soluble spin probe, Trityl_OX063_d24. Phantom samples with the nitroxide spin label, (15)N PDT, were also imaged to demonstrate that nitroxides, which are commonly used as spin labels, may also be used for ESRM applications. ESRM tissue imaging would therefore be valuable for diagnostic or therapeutic purposes. Also, ESRM can be used to study the motility or the metabolism of cells in various environments. With further modification and/or improvement of imaging probe and spectrometer instrumentation sub-micron biological images should be obtainable, thereby providing a useful tool for various biomedical applications.