AVS2008 Session NS-TuP: Poster Session
Tuesday, October 21, 2008 6:30 PM in Room Hall D
Tuesday Evening
Time Period TuP Sessions | Topic NS Sessions | Time Periods | Topics | AVS2008 Schedule
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NS-TuP-1 Kinetic Control of Self-catalyzed Indium Phosphide Nanostructures
R.L. Woo, L. Gao, S. Kodambaka (University of California, Los Angeles); N. Goel, M.K. Hudait (Intel Corporation); K.L. Wang, R.F. Hicks (University of California, Los Angeles) Nanowire research has gained tremendous momentum due to its potential applications in nano-electronics, photonics, solar cells, and thermoelectrics. Precise control of size, morphology, density, and uniformity is essential for realizing these commercial opportunities. Most indium phosphide nanowire research is prepared by vapor-liquid-solid (VLS) growth using gold catalysts. However, gold incorporation into the InP is unavoidable and can adversely affect optoelectronic properties. As an alternative, we have investigated the self-catalyzed growth of InP using liquid indium droplets in a metalorganic vapor-phase epitaxy (MOVPE) process. In this study, three distinct shapes were obtained depending on the growth conditions: nano- wires, cones, and pillars. The shape of nanostructures is determined by the relative rates of indium phosphide deposition via vapor-liquid-solid and vapor-phase epitaxial growth processes. At the meeting, we will discuss more details on the underlying mechanisms of the crystal growth process and the relationship between the deposition mechanism and the resultant shape of the nanostructure. |
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NS-TuP-2 Polymer Transfer Printing for Chemical Patterns and its Application on Colloidal Assembly
Y.H. Kim (Furukawa Electric Co. Ltd., Japan); B.S. Kim, P.T. Hammond (Massachusetts Institute of Technology) A new approach to directly organize colloidal particles into patterned arrays using templates coated with a layer-by-layer assembled polyelectrolyte multilayer was introduced. In this approach, a template using a UV-curable photo polymer was coated with polyelectrolyte multilayers, followed by a contact printing of an oppositely charged polyelectrolyte monolayer. The resultant topological template with both positive and negative charges provided a finely defined chemical nano-pattern to guide selective deposition of colloidal particles onto the patterned surface upon Coulombic attraction. For example, when negatively charged dilute colloidal suspensions were placed on the template, the particles were selectively adsorbed within positively charged grooves or holes. Additionally, we have demonstrated development of uniform PEG copolymer chemical patterns via polymer transfer printing and their applications on direct assembly of two different sets of particles to different surface regions. This effective method provides a flexible and versatile route to the development of composite colloidal structures which will present interesting technological applications in photonics, electronics and sensors. |
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NS-TuP-3 Low-energy Electron Beam Calcination to Obtain Well-ordered Mesopores in Titanium dioxide Film
A. Hozumi, H. Taoda (AIST, Japan) Mesoporous materials fabricated using organic surfactant molecules or block copolymers as structural directing agents has attracted much attention not only catalysts and adsorbents, but also insulating layers, chemical and gas sensors, and optical and electrical devices. In order to fabricate microdevices based on such well-ordered mesoporous materials, the control of morphologies and geometries in nano ~ micrometer scale is one of the key technologies for practical uses. In this study, we report on a facile and rapid template removal method at low temperature to obtain mesoporous titania film without cracking. Our approach demonstrated here, named “low-energy electron beam (LEEB) calcination,” is a novel calcination technique based on the decomposition and oxidation of organic fractions such as surfactants or block copolymers by LEEB irradiation under vacuum. Organic templates can rapidly be eliminated from precursor mesocomposite film within 30 min without distorting periodic mesostructure, resulting in the successful conversion to crack-free ordered mesoporous titania film. Our best rate by LEEB calcination is ~14 times faster than the result obtained by photocalcination using 172 nm vacuum UV light. |
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NS-TuP-4 Structural and Morphological Evolution of Gallium Nitride Nanorods Grown by Chemical Beam Epitaxy
S.-Y. Kuo (Chang Gung University, Taiwan); F.-I. Lai (Yuan-Ze University, Taiwan); W.-C. Chen, C.-N. Hsiao (National Applied Research Laboratories, Taiwan) The morphological and structural evolution is presented for GaN grown by chemical beam epitaxy on (0001) Al2O3 substrates. Their structural and optical properties are investigated by x-ray diffraction, scanning and transmission electron microscopy, and temperature-dependent photoluminescence measurements. While increasing the growth temperature and the flow rate of radio-frequency nitrogen radical, the three-dimensional growth mode will be enhanced to form the one-dimensional nanostructures. The high density of well-aligned nanorods with a diameter of 30–50 nm formed uniformly over the entire sapphire substrate. The x-ray diffraction patterns and transmission electron microscopic images indicate that the self-assembled GaN nanorods are a pure single crystal and preferentially oriented in the c-axis direction. In addition, the enhanced A1(LO) intensity of micro-Raman spectrum confirms the formation of strain-free GaN nanorods in consistent with XRD and HRTEM results. Particularly, the “S-shape” behavior observed in the temperature-dependent photoluminescence might be ascribed to the fluctuation in crystallographic defects and composition. Neither catalyst nor template is required in our epitaxial system make this technique feasible to develop nanodevices based on strain-free III-nitride nanorods. |
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NS-TuP-7 Synthesis and Field Emission Properties of W18O49 Nanorods
K. Yong, S. Jeon (POSTECH, Korea) In recent years, the assembly of 1-D nanostructures in the fabrication of transition metal oxides has received increasing attention due to their interesting potential applications. Among these metal oxide nanomaterials, the fabrication of tungsten oxide nanostructures have been intensively studied due to their promising physical and chemical properties. In current study, we report for the first time the synthesis of tungsten oxide nanorods from tungsten-compound material using a simple annealing of the W2N/Si substrate. W2N film was deposited on Si(100) substrate by chemical vapor deposition at 450 °C and then heating of the film at 600 ~ 700 °C produces a high density of tungsten oxide nanorods. The morphology, structure, composition and chemical binding states of the prepared nanorods were characterized by SEM, XRD, XPS, EDX and TEM measurements. XRD and TEM analysis showed that the grown nanorods were single-crystalline W18O49. According to XPS analysis, the W18O49 nanorods contained ~62% of W6+, ~28% of W5+, and ~10% of W4+. Field emission measurements showed a low turn-on field of 9.5 V/μm for the W18O49 nanorods, indicating that they can be used as potential field emitters. |
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NS-TuP-9 Fabrication of Three-Dimensionally Periodic Macroporous TiO2 Thin Film for Photovoltaic Application
S.B. Yoon, Y.H. Kim, K. Kim, B.-C. Woo (Korea Research Institute of Standards and Science); S.J. Chung (Korea Research Institute of Biosience and Biotechnology); W.S. Yun (Korea Research Institute of Standards and Science) Three-dimensionally (3D) periodic macroporous TiO2 thin film was fabricated by using polystyrene sulfonate (PSS) nanoparticle as an organic template and titanium alkoxide as a TiO2 precursor on fluorine-doped tin oxide (FTO) glass. Close-packed colloidal crystalline thin film composed of PSS nanoparticles was prepared by using 2D deposition technique. The TiO2 precursor was immersed into the void space between PSS nanoparticles and subsequently in-situ hydrolysis and condensation were performed. The nanocomposite of PSS nanoparticles and amorphous TiO2 was calcined to remove the organic materials and to crystallize the amorphous TiO2 to anatase type at 450℃ under air flowing. Resultant anatase TiO2 thin film was exhibited the 3D periodic macroporous framework with connecting windows. Photovoltaic cells composed of the Ru-dye coated 3D periodic macroporous anatase TiO2 thin film were fabricated and their energy conversion efficiency was also investigated. |
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NS-TuP-10 Vapour Phase Deposition of Aromatic Self-Assembled Monolayers
L. Kankate, H. Muzik, A. Turchanin, A. Gölzhäuser (University of Bielefeld, Germany) Self-assembled monolayers (SAMs) with aromatic moieties recently caused a particular interest due to their applications in molecular electronics,1 nanolithography2,3 and biotechnology.4 For high quality SAM-based devices and nanostructures, a reproducible fabrication of high quality SAMs is necessary. The traditional “wet” preparation of SAMs may suffer from solvent, ambient and substrate contaminations resulting in poor quality and degradation of the molecular assemblies. On the contrary, the preparation of SAMs in UHV can provide a high degree of control over the experimental parameters. We have studied the formation of 1,1’-biphenyl-4-thiol (BPT) and 4’-nitro-1,1’-biphenyl-4-thiol (NBPT) SAMs on gold surfaces by vapour deposition in UHV. The vapour deposited monolayers were characterized by mass spectrometry, X-ray photoelectron spectroscopy (XPS). and scanning tunnelling microscopy (STM). Based on this data, the deposition parameters were optimized. A comparison of vapor deposited SAMs with monolayers prepared from solution is presented. |
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NS-TuP-11 Characteristics of La-substituted Bismuth Titanate Ferroelectric Nanofibers by Electrospinning
K.T. Kim (University at Buffalo, the State University of New York); C.I. Kim (Chung-Ang University, Korea); Y.K. Yoon (University at Buffalo, the State University of New York) The bismuth layer-structured ferroelectrics have been known as high dielectric materials with attractive properties such as environmentally friendly lead-free composition and fatigue free characteristic. Specially, the La-substituted Bismuth Titanate (Bi3.25La0.75 Ti3 O12 :BLT) has received the intensive attention for their excellent ferroelectric, crystalline properties as a promising dielectric for capacitors and memory devices.1 Recently, there has been an intense research effort on one dimensional nano materials such as nanotube and nanofiber due to their unique structure and properties, such as high aspect ratio, large specific surface area and chemical/mechanical stabilities.2 In this study, BLT nanofiber synthesis has been demonstrated using electrospinning and subsequent sintering. A composite solution consisting of a metal-organic decomposition solution of BLT and a binder of poly(vinylpyrrolidone) (PVP) has been electrospun in an electric field of 3 x105 V/m to form nanofiber with a diameter of 120 nm. The BLT/PVP composite nanofiber has been calcined in air for 1 h at 500, 600, 700, 750, and 800 °C, respectively. The characteristics by X-ray diffraction, FT-IR, SEM and HR-TEM of the BLT/PVP composite nanofibers are reported. |
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NS-TuP-12 Nanostructured Glassy Carbon Supported GC/Pt Electrodes for Model Studies of Fuel Cell Relevant Electrocatalytic Reactions
Y.E. Seidel, A. Schneider, L. Colmenares, Z. Jusys, R.J. Behm (Ulm University, Germany); B. Wickmann, B. Kasemo (Chalmers University of Technology, Sweden) In this contribution, we discuss the potential of nanostructured planar electrodes for model studies of electrocatalytic reactions relevant for Polymer Electrolyte Fuel Cell (PEFCs). The model electrodes consist of catalytically active Pt nanostructures of well-defined size and separation, which are supported on planar glassy carbon substrates.1,2 They are fabricated employing colloidal lithography (CL)1 or Hole-mask Colloidal Lithography (HCL),2 or by micellar techniques, via deposition of metal loaded micelles and the subsequent removal of the polymer stabilizer.3 Both techniques allow us to independently vary size and separation of the catalytically active nanostructures/particles. The resulting particle sizes are ca. 3-15 nm (micellar techniques) and 70-150 nm (CL, HCL), respectively. These nanostructured model electrodes allow direct and quantitative access to an important aspect of electrocatalytic reactions which so far has been largely neglected, to the influence of mesoscopic transport effects on the characteristics of electrocatalytic reactions. Using the reduction of O2 and the oxidation of formaldehyde as examples it will be shown that mass transport effects not only modify the overall rate, but have significant effect also on the product distribution, e.g., on H2O2 formation. Possible contributions of the reactant transport to the overall reaction process will be discussed in a molecular picture. |
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NS-TuP-13 Dimer Ordering of M-TtertBuPc on Graphite
T. Takami, C. Carrizales, K.W. Hipps (Washington State University) The growth and ordering of metal complexes of 2,9,16,23-tetra-tert-butyl-phthalocyanines (TtertBuPc) on graphite surface have been studied by scanning tunneling microscopy. A well-ordered molecular layer having the molecular plane lying parallel to the graphite substrate was obtained at the solution - graphite interface at room temperature. For Cu-TtertBuPc, dimer ordering similar to that reported previously on the Si(111)-r3Xr3-Ag surface1 was partly observed. We will also discuss the effects of changing the center metal and/or the phthalocyanine to naphthalocyanine, and imaging and orbital mediated tunneling spectroscopy in ultrahigh vacuum (UHV). |
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NS-TuP-14 Optical Performance of EUV Lithography Mask with Silver Doped Zinc Oxide Absorber
H.Y. Kang, M.K. Kim, C.K. Hwangbo (Inha University, Republic of Korea) The lithography performance of extreme ultraviolet lithography (EUVL) mask depends on the correct choice of absorber materials because it is directly related to imaging contrast, shadowing effect, focus shift effect, and thermal effect.1 The optical constant of the absorber materials in the EUV region should have higher extinction coefficient for higher attenuation. Also, the absorber material should exhibit good conductivity, which can alleviate the charging effect during electron-beam patterning. In the past, a wide range of materials (Ti, TiN, Al–Cu, TaSi, Ta, TaN, Cr, etc) has been evaluated as possible conductive absorbing materials for EUVL mask.2,3 The total thickness of the absorber stack by using the materials used to be greater than 80 nm because the available absorbing materials are limited and an anti-reflection coating is necessary to maximize pattern inspection efficiency at deep ultraviolet wavelength. It is reported that the large thickness of the absorber stack may cause a geometric shadow effect in an exposure step and as a result, the printed patterns are shifted and biased.4 In this study, we propose a new absorber stack with a silver doped zinc oxide absorber layer. The optical constants of ZnO layers with various concentration of Ag at 13.5 nm are calculated. It is found that the optical constants of ZnO layers with high concentration of Ag show lower refractive index and higher extinction coefficient at 13.5 nm than those of TaN layer. Thus ZnO layers doped with Ag enables EUVL masks to be designed to have very small height difference between high reflecting and absorbing stacks, suggesting that the geometric shadow effect can be significantly reduced. |
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NS-TuP-15 Actinide Powder Characterization for Nuclear Forensics
W.S. Duncan, A.D. Neuman, C.C. Davis, T.A. Nothwang (Los Alamos National Laboratory) Half of the Department of Energy’s nuclear forensics scientists are expected to retire within the next 15 years but there continue to be around 10 confirmed cases of nuclear material trafficking each year.1,2 The Interfacial Science team of LANL’s Materials Science & Technology division is addressing this need for new nuclear forensics expertise by helping to create a database of actinide powder characteristics. This poster addresses physical characterization on a nanoscale level via microscopy and other methods in order to obtain microstructural and elemental composition as well as crystal structure of known powders. |
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NS-TuP-16 Template-Free Synthesis and Characterization of Copper Oxide Nanostructures
K.-R. Lo, C.-C. Chang (National Taiwan University) As a relatively non-toxic p-type semiconductor and a classical example of excitonic solid, cuprous oxide may play an important role in the electronics industry as the dimensions of electronic devices continue to shrink. For example, devices made of nanometer-scale cuprous oxide are expected to be small and fast because the electrical signal can resonantly tunnel through the nanoscale cuprous oxide layers. In addition, cuprous oxide structures fabricated in the nanoscale may exhibit better antifouling and algicide effects, increase its overall water splitting capability for solar energy applications, and enhance its photocatalytic activity for degradation of organic pollutants under visible light. Nanoscale cuprous oxide structures were prepared in this study via a template-free synthetic approach in the ethylene glycol solution using different copper compounds as the precursor. SEM images and Auger spectra revealed that, instead of forming spherical particles, micro- to nano-sized aggregates of well-defined geometric shapes were obtained. These aggregates were made of nanocrystalline particles, as revealed in high-resolution TEM and diffraction studies, which self-assembled into organized solids. XPS spectra suggested that the crystallization and the self-assembling may take place via cuprophilic attraction. The shape and the dimensionality of the assemblage obtained can be controlled by adjusting reaction temperature and/or by using different surfactants. Chemical conversion of cuprous oxide to cupric oxide impaired the cuprophilic interaction, leading to dismantling of the assemblage at extended reaction time. The chemical process and the mechanism involved in the assembling and dismantling of the polycrystalline assemblage will be discussed. |
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NS-TuP-17 Preferred Diameter Growth of Single-Walled Carbon Nanotube by using Sapphire Substrates
K.-Y. Shin (National Tsing Hua University, Taiwan); J.-S. Kao (National Applied Research Laboratories, Taiwan); K.-C. Leou, C.-H. Tsai (National Tsing Hua University, Taiwan) Single-walled carbon nanotube (SWCNT) has been considered as an alternative material for nano-devices, such as carbon nanotube field-effect-transistor or nano-sensor. It has been found that the characteristics of the SWCNT-based device are affected by the band gap of the tube, which depends on its diameter and chirality. Preferred diameter growth of single-walled carbon nanotube (SWCNT) by using single crystal sapphire (0001) and sapphire (110-2) substrates is reported. The carbon nanotubes were grown by mono-layered iron catalyst from sapphire substrate and a mixture of methane and hydrogen at 900°C by chemical vapor deposition. Atomic force microscopy revealed that the particle size distribution of catalyst was varied with different orientation sapphire substrate. The micro-Raman spectra exhibited that the radial-breathing mode signals of SWCNTs grown by Fe (1nm) catalyst were shifted with different orientation sapphire substrates. A growth model based on minimum strain theory (i.e. O-lattice theory) and surface tension theory is proposed. |
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NS-TuP-19 Fabrication of Porous Si Using Anodic Aluminum Oxide
N.Y. Kwon, K.H. Kim, J.M. Kwon, I.S. Chung (Sungkyunkwan University, Korea) Porous Si templates with various pore patterns were obtained by etching underlying Si using an anodic aluminum oxide (AAO) mask. Si3N4 imprint stamps with a nano size matrix pillar (height : 50 nm) pattern were indented into Al film grown on Si wafer using an oil press method with the force of 5kN·cm-2. After indenting on Al thin film (thickness : 200 nm), we found that the periodic array with 30 nm depth was formed on Al thin film using scanning probe microscopy. The indented Al film was then anodized using two different anodizing conditions, namely, 0.3M oxalic acid of 4°C at 50V and 0.3M sulfuric acid of 10°C at 25V, and these conditions were suitable to define the matrix pore pattern. As pore's size and interval were decided by anodizing conditions, pre-patterning must set to anodizing condition to get regular pattern. We can control the size of pore and the interval of pore by modifying the aforementioned anodizing conditions. Thus, we can achieve a well organized Si porous template by transferring AAO pattern using ICP etcher with 30 W of rf power, 30 mTorr total pressure, 30 SCCM of CF4, and 4 SCCM of O2. |
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NS-TuP-20 Fabrication and Characterization of One-Dimensional Semiconducting Nanowire That Use AAO
K.H. Kim, N.Y. Kwon, J.K. Hong, I.S. Chung (Sungkyunkwan University, Korea) In this study, we attempted to fabricate and characterize one dimensional semiconducting nanowire(CdSe, Polypyrrole). It is well known that CdSe is n-type material, whereas polypyrrole is p-type material. The template used in the nanowire growth was AAO(Anodic Aluminum Oxide) template. After forming AAO template on Al foil, the oxidized underlying barrier layer was removed using a cathodic polarization method based on KCL(0.5mol, -5V, 4℃) solution. Then, nanowires with 50nm diameter and 300nm height were grown using the electroplating method. Finally, the nanowires were characterized using SPM(Seiko Instruments, SPA 300HV) by proving the conductive cantilever. I-V characteristics as a function of the temperature gives an activation energy which is useful to understand the conduction mechanism of semiconducting nanowires. |
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NS-TuP-22 Nanopatterning by Near-Field Photodeprotection of 2-Nitrophenylpropyloxycarbonyl-Protected Aminosiloxane Monolayers on Glass
S. Alang Ahmad (University of Sheffield, UK); L.-S. Wong (University of Manchester, UK); E. Haq, J. Hobbs, G. Leggett (University of Sheffield, UK); J. Micklefield (University of Manchester, UK) Nanometre scale control of chemical reactivity is key for many applications of nanotechnology in biology, electronics, materials science, etc. Currently there are few methods for the selective initiation of chemical transformations with nanometre precision. Here we report a novel approach to nanopatterning in which a scanning near-field optical microscope coupled to a near-UV laser is used to selectively deprotect 2-nitrophenylpropyloxycarbonyl (NPPOC) protected aminosiloxane monolayers on glass. Initially, UV deprotection was studied for unpatterned samples using X-ray photoelectron spectroscopy and contact angle measurements. The resulting amine-terminated surfaces were activated with glutaraldehyde and then derivatized using a fluorinated adsorbate and aldehyde polymer nanoparticles. Contact angle and XPS measurements indicate extensive surface functionalisation. Next, micrometre-scale patterns were fabricated using mask-based exposure to light from a He-Cd (325 nm) or Ar-ion (364 nm) laser, and characterised by friction force microscopy. Nanoparticle patterns were formed by covalent attachment methods. Nanometre scale patterns were fabricated using near-field exposure, and characterised by FFM. The nanopatterns were derivatised with functionalised molecules, showing that high spatial resolution (ca 100 nm) was readily achievable, and also that extensive functionalisation of the patterns could also be accomplished. |