PacSurf2014 Session NM-WeP: Nanomaterials Poster Session

Fluorescence materials are used for a broad range of industry and biomedical technology applications involving electroluminescent displays and fluorescent contrast dye of bioimaging. However, they are confronting some serious problems, such as complicated preparation techniques and low production yield. Therefore, it is necessary to develop new synthesis approaches for realization of facile preparation and large-scale production of fluorescence materials. We have prepared ammonium hexafluorosilicate ((NH₄)₂SiF₆) particles as one of the fluorescence materials using a chemical route with good productivity. These (NH₄)₂SiF₆ particles possess excellent advantages such as high-efficiency fluorescence and long-term photostability compared to the other silicon (Si)-based fluorescence materials. In this presentation, we propose a new way to fabricate (NH₄)₂SiF₆ particles by simplified procedures based on a chemical approach. The features of our synthesis technologies are to adopt the simplified synthesis system in which only Si powders and chemicals consisting of nitric hydrofluoric acid solution were hermetically sealed in polymeric container without any vacuum systems. The (NH₄)₂SiF₆ particles with mean diameter of approximately 700 nm were densely deposited on the Si substrate by using this novel synthesis system. The crystalline structures and the chemical compositions of (NH₄)₂SiF₆ particles were confirmed by X-ray diffraction (XRD) patterns and Fourier transform infrared (FTIR) spectroscopy. The XRD patterns were consistent with the sharp diffraction peaks derived from the cubic phase of crystalline (NH₄)₂SiF₆ with space group of Fm3m(225). For the FTIR characterization, the absorption peaks related to the SiF₆^2- and NH₄+ ions in addition to N-H mode were also observed. These results demonstrate that the (NH₄)₂SiF₆ particles are not only maintained high crystallinity but also composed of ammonium and silicon fluoride as major ingredients. Such (NH₄)₂SiF₆ particles exhibited bright reddish orange fluorescence with a peak wavelength at 630 nm under the irradiation of xenon lamp equipped with optical bandpass filter of 365 nm. The main advantages of (NH₄)₂SiF₆ particles are to attain the high fluorescence quantum yield of 34 %. Additionally, the fluorescence intensity was maintained about 80% of the initial maximum intensity even after aging beyond six months. Therefore, our suggested synthesis technologies can provide a new chemical route for the fabrication of high-brightness and stable fluorescence particles.

Recent research has shown that N-doping into TiO₂, Ta₂O₅, or LaTaO₄ is effective for narrowing the band-gap and attaining the visible-light photocatalysis. N-doped metal oxide powder is commonly synthesized by elevating metal oxide specimens temperature over 500^oC with flowing ammonia gas or nitrogen. In this study, we succeeded in synthesizing N-containing ZnO rods by hydrothermal process using ammine-hydroxo zinc complex solution at 100^oC.

10 ml of 2.5 M NaOH (aq) was added in drops to 15 ml of 0.5 M Zn (NO₃)₂･6H₂O aqueous solution over stirring vigorously. The resulting hydroxide slurry was centrifuged and the supernatant was removed. The hydrated precipitate was dissolved in 50 ml of 6.6 M NH₃ (aq) to form a stock solution. 30 ml of the solution was transferred into a 35 ml Teflon-lined stainless steel autoclave, followed by heating in an oven at 100^oC for 6-24 h. After the reaction, the precipitates were separated by centrifugation, and then washed with water.

TiO₂ is actively studied as photocatalyst with environmental applications effected on photocatalytic performance by adjusting many factors in the structure. Recently, TiO₂ monolith with unique three-dimensional structure has been reported. This is expected to various applications because the pore size and volume are able to control by the synthesis condition. The material, generally used as an adsorbent, extended the applications with visual light-sensitive. In this research, TiO₂ monolith was synthesized with various heating temperatures, and its photocatalytic activity was investigated under visible light.

Porous TiO₂ monolith was synthesized by sol-gel method. HCl, the aqueous solution of Polyethylen glycol (10000) in water and N-methyl formamide are added to Titanium propoxide stirring under ice-cooled condition. The gel is aged at 60^oC for 24 h and heat-treated at 200^oC for 2 h in stainless-steel autoclave with a Teflon inner liner. The wet gel plate thus obtained is washed by 1-propanol for 12 h, slowly drying for 1 week at room temperature and calcinated at 600, 700, 800 and 900^oC for 5 h. Each of temperature rising rates is 1.0 ^oC/min. Each sample is immersed in the CuCl₂ (moler rations of Cu/TiO₂ = 1.0 × 10^-3) aqueous solution at 90^oC for 3 h. After washing by water and drying at 80^oC, they are measured photocatalytic activity.

The samples heated at 600, 700, and 800^oC had monolith structure, and the pore size and primary particle size depend on calcination temperature. However, the sample heated at 900^oC did not maintain monolith structure. From the results of XRD patterns and Raman spectra, anatase was main phase at less than 700^oC while rutile started to be observed at more than 700^oC. It is expected that Cu(II)-grafted rutile monolith samples exhibit excellent photocatalytic activity under visiblelight. In addition, it was succeded that rutile nanotubes were formed on the surface of the monolith structures by solvothermal treatment. The monolith with nanotubes had very high specific surface area compared to the monolith without nanotubes. In detail, I will report the activity on the day.

CuO is a versatile p-type transition metal oxide semiconductor with a narrow band gap in the region 1.2-1.8 eV [1]. It is a naturally abundant, nontoxic and stable material and is commonly used as a component material in a wide range of applications such as gas sensing, catalysis and energy storage and conversion [2-4]. Three dimensional ellipsoidal shaped CuO nanostructures and two dimensional nanosheets have been successfully synthesized using surfactant free simple solution phase method. Synthesis of CuO nanostructures was followed by structural, morphological characterization using X-ray diffraction, Scanning Electron Microscopy and Transmission Electron Microscopy. We have demonstrated that morphology and dimensionality of nanostructures can be controlled by changing the initial reactant concentrations. It is observed that ordered aggregation and growth of smaller CuO subunits generates an ellipsoidal shaped morphology at lower reactant concentration, while at higher reactant concentration, sheet like structures are generated. Self-assembled structures provide an opportunity to investigate the formation mechanism and aggregation based growth of nano subunits as fundamental building blocks. This bottom-up method offers facile synthesis of nanostructures of controlled morphology and functionality. We have also observed a change in morphology as the nanostructures were thermally annealed. A morphological transformation from rod-like to plate-like structure was observed as the flake-like nanostructures were annealed at 400⁰C and 600⁰C respectively. The formation mechanism that plays behind the generation of different CuO nanostructures is explored. Optical properties are investigated using UV-Vis spectroscopy and Raman spectroscopy. We found that morphology of the nanostructure strongly reflect on the optical properties as band gap widening and the change in the position and width of Raman modes.

References

[1] M.A. Gondal, T.F. Qahtan, M.A. Dastageer, T.A. Saleh, Y.W. Maganda, D.H. Anjum, Appl. Surf. Sci. 286 (2013) 149.

[2] Z. Zhang, H. Che, Y. Wang, L. Song, Z. Zhong, F. Su, Catal. Sci. Technol. 2 (2012) 1953.

[3] M. Frietsch, F. Zudock, J. Goschnick, M. Bruns, Sens. Actuat. B 65 (2000) 379.

[4] X.P. Gao, J.L. Bao, G.L. Pan, H.Y. Zhu, P.X. Huang, F. Wu, D.Y. Song, J. Phys. Chem. B 108 (2004) 5547.

Low energy ion beam sputtering (IBS) induces a wide variety of surface morphology evolution with different shapes such as, ripples, dots and pyramidal pattern on semiconductor surfaces. Under off normal incidence beam ripple formation is developed. On other hand, hexagonal or square order dots were reported for normal incidence ion beam or off normal ion incidence with simultaneous sample rotation [1]. Patterned surfaces have a broad range of technological applications, such as lasers, solar cells, sensors, biomedical tags and light emitting diodes.

Temperature effect on the ripple pattern has not yet been broadly studied due to difficulties in their experimental conditions. However, several studies reports that target temperature has a strong influence on the wavelength of ripple pattern [2].

In this work, Ge surfaces were bombarded with low energy O₂ ions to conduce a modification in surface morphology. Different oxygen ion bombarding energies were used, such as, 250 eV, 500 eV, 1 keV and 2 keV. Simultaneously different angle of incidences at different target temperatures and different sputtering doses were utilized under ultra high vacuum (UHV) conditions inside a TOF-SIMS-5 (IonTof Co) time-of-flight secondary ion mass spectrometer. After varying the above conditions of IBS, we observed the evolution of surface roughness lead up to a formation of nano-patterned structures.

After ion irradiation, the surface morphology was investigated by atomic force microscopy (AFM) using a Solver Next instrument from NT-DMT. We used the so-called tapping mode to analyze 3-D surface relief; all measurements were conducted in the presence of air. The AFM measurements were performed for different scan sizes (from 0.5x0.5 microns to 50x50 microns) with a resolution of 512x512 pixels and we analyzed roughness statistics and characteristics of nano-pattern (wave length and amplitude). Later, the ion sputtered surfaces were compared with original surface at each case.

References:

[1] B. Ziberi, F. Frost, B. Rauschenbach. Pattern on Ge surfaces during low-energy ion beam erosion. Appl. Phys. Lett. 88, 173115 (2006).

[2] Makeev MA, Cuerno R, Bar´abasi AL (2002) Morphology of ion-sputtered surfaces. Nucl Instr and Meth B 97: 185-227.

We describe a device that has a resonant cavity for optical modes embedded inside an acoustic cavity. This double cavity structure is a resonator for acoustical waves and enhances the interaction between sound and light.

An acoustic cavity confines the phonon field in the same way that an optical microcavity confines the photon field, leading to strong changes in the wave-matter interaction. Optical microcavities also amplify the interaction between light and phonons [1-2]. Phonon engineering is relevant for the design of optimized phonon devices (mirrors, filters, and cavities) for coherent (single-wavelength) phonon generation and control, to attain phonon amplification and ‘‘lasing’’ [4], and to control the electron–phonon interaction in improved quantum electronic devices [5].

We report the theoretical calculations and the experimental demonstration of optical confinement in acoustic cavity structures based on porous silicon (PS). We designed and fabricated multilayer structures with acoustic cavity modes around 1.1 GHz and optical modes in the infrared range.

Spatial and spectral localization is demonstrated by calculations of acoustic and optical field distribution in samples. Theoretical calculations have been performed by using the Transfer Matrix Method for longitudinal acoustic waves in the continuum limit, in acoustic case, and for unpolarized light, in electromagnetic case. Localization is experimentally demonstrated by direct acoustic transmission and optical reflectivity measurements. And we present calculations of pump and probe time dependent optical reflectivity and acoustic transmission that evidence temporal behavior that derives from both the electromagnetic and acoustic confinement.

References:

[1] Trigo M, Bruchhausen A, Fainstein A, Jusserand B and Thierry-Mieg V, Phys. Rev. Lett.89 227402 (2002).

[2] N. D. Lanzillotti-Kimura, A. Fainstein, A. Huynh, B. Perrin, B. Jusserand, A. Miard, and A. Lemaître, Phys. Rev. Lett.99, 217405 (2007).

Zeolitic imidazolate frameworks (ZIFs) are a subclass of metal-organic frameworks (MOFs) and are comprised by metal ions and imidazoles. Pervaporation is a type of membrane separation process with a wide range of uses, such as in solvent dehydration and organic mixtures. Here, we want to control the particle sizes of ZIF-8 to optimize the effect on pervaporation by using Taguchi method and then dope it into polyvinyl alcohol (PVA) membrane to increase the separation performance of water/ethanol mixture. We also further changed the amounts of ZIF-8 to optimize the water and ethanol separation performance.

In recent years, ferrofluids have received special attention due to their interesting properties and various biomedical applications such as drug delivery, since it requires that the magnetic nanoparticles be suspended in colloidal or ferrofluid solutions to provide better stability and dispersion nanoparticles as to be administered via intravenous or intra arterial to the target site. Therefore, it is important to characterize their rheological properties in order to find a fluid with good stability.

In this work, magnetite particles were synthesized by Fast Injection Co-precipitation method and coated with chitosan (core-shell type). These nanoparticles were used to synthesize two ferrofluids (magnetite and magnetite-chitosan) using oleic acid as a surfactant. An study of the rheological properties of both fluids was carried out; with and without a magnetic field applied (0.02Teslas) for the two fluids. The fluid containing the uncoated nanoparticles showed Newtonian fluid properties and the fluid containing the coated nanoparticles (magnetite- chitosan Core / Shell type) showed Bingham fluid properties. When the magnetic field was applied, the ferrofluid containing the uncoated nanoparticles showed a non-Newtonian fluid behavior and in the case of the ferrofluid coated nanoparticles showed liquid-plastic behavior. Finally, viscosity was measured without/with an applied magnetic field, and for both fluids it was observed that without magnetic field they behave like Newtonian fluids and with magnetic field as a Bingham fluid.

Abstract

Suggestted potential applications in heterostructure material, due to band gap modulation result in the interface carrier pile-up, can be wildly used in Electro-Optical nanodevice and micro-electro-mechanical systems(MENS).

In this study, catalystic assisted chemical vapor deposition(CVD) method was used in the synthesis of Ⅲ- nitride heterostructure nano-materials on direct reactions of ammonia and source materials at elevated temperatures. By using nickel as metal catalyst, hexagonal wurtzite structure of GaN nanowires were successfully obtained on silicon substrate. The average diameters of the nanowires were 50 nm and the lengths were about tens of micrometers. The produced GaN nanowire was, in turn, placed in the CVD system, and covered by a layer of AlN, to synthesize a one-dimensional GaN/AlN core-shell heterostructure.

The morphology and heterostructure interface of nanowires was investigated by SEM (Scanning electron microscope) and TEM (Transmission electron microscopy)。EDS (Energy dispersion spectronscopy) and XRD (X-ray diffraction) were used to characterize its composition and lattice structure. The inspections show that CVD process was successfully demostrated to synthesize high-quality GaN/AlN core-shell nanowire with uniform surface and 148 nm diameter. The TEM inspection also shows the integrity of its structure. The oprtical preperties were inspected by PL (photoluminecence) as well.

Thanks to nanotechnology, new materials are being fabricated with special properties used in a variety of applications, such as the materials used as implants or bone substitute in the human body, these must be adapted to the changes that occur in the bone as it reconstructs constantly. The main bone component is the calcium phosphate denominated as hydroxyapatite. The human body is constantly reabsorbing this and reconstructing new bone. In this way the body adjusts the bone width in response to the change of weight distribution with the body. Synthetic nanostructured ceramics have been developed in order to react with the body fluids so apatite can be formed, which is the natural ceramic in the bone. But the idea is to go further. Not only pure mechanical zones, like articulations or extremities, can be replaced: to this day, corneal blindness can be treated using a cornea transplant. In the present work the employed technique was precipitation as a simple technique for the obtaining of nanocrystalline calcium phosphate with the goal of producing odonto keratoprosthesis and therefore avoid the canine tooth extraction surgery as it is an expensive operation, actually this synthesis route was used in order to save time and see how the results are affected by modifying the variables. No impurities were detected other than calcium phosphate as a result of the pH variation. In the infrared spectra shown a very small amount of the CTAB molecule incorporated in the calcium phosphate.

Hydrothermal Synthesis of Nickel hydroxide/Cobalt Hydroxide/Reduced graphene Oxide Composite for Electrochemical Capacitors

Sintayehu Nibret Tiruneh¹, Sung Ryul Mang­², Tran Ngoc Quang², Hyung Dae Lim², Bong Kyun Kang², Dae Ho Yoon^1,2*

¹ SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University,

2066 Seobu-ro, Jangan-gu, Suwon, Gyeonggi-do 440-746, Korea

²School of Advanced Materials Science & Engineering, Sungkyunkwan University,

2066 Seobu-ro, Jangan-gu, Suwon, Gyeonggi-do 440-746, Korea

Tel: +82-31-290-7388

E-mail:dhyoon@skku.edu [mailto:dhyoon@skku.edu]

Pseudocapacitive materials such as hydroxides, oxides, and polymers are being explored for producing supercapacitors with increased specific capacitances (Cs) and a high energy density. Metal hydroxides (MHs) (hydroxides of Co, Ni, Mn, Fe etc) deliver high specific capacitance and are renowned on their well-defined pseudocapacitance. Though they have high energy density, their importance is limited in Electrochemical Capacitors (ECs) application due to low power density which arises from their poor conductivity nature. In contrary, graphene is an ideal wonder substrate to render them electrochemically active and electrically conductive to the outside current collectors. Many researches have been done on MHs/Graphene composites. Recently, synthesizing of two or more MHs growing on graphene is getting much attention in increasing the conductivity while keeping high C_s and significant improvements were seen. Nevertheless, hydroxides/graphene composites synthesized in this way were poorly crystallized.

In this study, we report chemical precipitation of Co(OH)₂/Ni(OH)₂ on graphene followed by hydrothermal synthesis to boost crystallinity and uniform coating of the MHs on reduced graphene oxide(rGO) while maintaining the high C_s. Different MHs precursor ratios, MHs to rGO ratio, and hydrothermal synthesis temperature were used as a parameter.In addition, two methods of growing the precursors on rGO are reported. Morphology of the as-obtained samples was characterized by X-ray diffraction and scanning electron microscopy. Furthermore, electrochemical measurements were investigated.

Nano-sized diamond, such as nanocrystalline diamond (NCD), ultrananocrystalline diamond (UNCD), and diamondoids, is a new nanocarbon. Since it was reported that diamond exhibits strong photoluminescence due to nitrogen-vacancy center and generates defect-induced magnetization, the application of nanodiamonds to drag delivery has received much attention. In order to induce the novel functionalities in diamond, doping should be carried out precisely.

Nano-sized diamond powder has ever been fabricated by detonation, and the doping of foreign elements to the powder has been made mainly by ion implantation. In-situ doping during the formation should enable us to incorporate foreign element atoms into nano-sized diamond, effectively and simply. In this work, we employed a coaxial arc plasma gun for the formation of UNCD powder and demonstrated the in-situ doping of chromium during the formation. A coaxial arc plasma gun (ULVAC APG-1000) equipped with a chromium-blended graphite target was operated in vacuum and hydrogen atmospheres. The head of the gun was pointed at a quartz plate. The distance between the plate and gu head was 15 mm. Quartz plate’s temperatures are 550 ºC. Films that quickly and automatically exfoliated from the plate were gathered, and they were smashed into powder. The XRD pattern of 10 at% Cr doped powdered diamond nanoparticles, measured with 12 keV X-ray at beamline 15 of the SAGA-LS, exhibited obvious peaks due to diamond-111 and 220. The electron diffraction also exhibited the similar results. Chromium K-edge XAFS spectra were measured at beamline 6 of the SAGA-LS (: Kyushu University Beamline). The magnetic properties were measured by a vibrating sample magnetometer and superconducting quantum interference device. The details will be reported in the conference presentation.

Much attention has been paid on Magnesium alloys in electronics and automobiles industrial parts, due to lightweight and other excellent properties, such as low density, high specific strength, and good castability. However, due to the limited number of slip systems associated with their hexagonal close-packed crystal structure, both magnesium and its alloys show poor room-temperature formability. It is well-known that crystallographic texture plays an important role in both plastic deformation and macroscopic anisotropy of magnesium alloys. Therefore, many authors have been studied to understand the texture control of magnesium alloys, focusing on improvement of the room temperature formability in Magnesium alloy. However, despite having many excellent properties in magnesium alloys, the study for various properties of magnesium alloys have not been clarified enough.

It was well-known that magnesium alloys have a good damping capacity compared to the other alloys. Also, the damping properties of metals are generally recognized to be dependent on microstructural factors such as grain size and texture. However, there are very few studies on the relationship between the damping ability and texture of Mg alloys. Therefore, in this study, the AZ31 magnesium alloy which was carried out by heat treatment was experimentally investigated about the relationship between the texture and damping capacity.

A 60 mm × 60 mm × 40 mm rectangular plate was cut out by machining an ingot of AZ31 magnesium alloy (Mg-3Al-1Zn in mass%), and rolling was carried out at 673 K to a rolling reduction of 30%. Then, heat treatment was carried out at temperatures in the range of 573–723 K for durations in the range of 30–180 min. The samples were immediately quenched in oil after heat treatment to prevent any change in the microstructure. Specimens for damping capacity measurements were machined from the rolled specimen, to have a length of 120 mm, width of 20 mm, and thickness of 1 mm. The damping capacity was measured with a flexural internal friction measurement machine at room temperature. Texture was evaluated on the compression planes by the Schulz reflection method using nickel-filtered Cu Kα radiation. Electron backscatter diffraction measurements were conducted to observe the spatial distribution of various orientations. It was found that the damping capacity increases with both increasing heat-treatment temperature and time, due to grain growth and also, the pole densities of texture increase with increasing the internal friction.

[1] T. K. Kim, E. D. Jeong, C. Y. Oh, M. H. Hyun, M. S. Lee, H. K. Moon, J. P. Kim, O. S. Jung, F. N. Nawaz, J. S. Jin, Chem. Pap. 65(4), 2011, 495

Suggested topic: Nanomaterials (NM1-Nano Devices)