Fabrication of Nano-Structured Hemispheres and Pillars Using Laterally Migrating Polymer Templates
J. Nanosci. Nanotechnol. 2009, Vol. 9, No. 5
We report herein a reliable method of fabricating 2D periodic gold nanopillars with well-defined anisotropic shapes by the combinational actions of colloidal crystals and gold evaporation. The deposition of gold on a polymer template produced dual functional Janus-like nanopillars up to 633 nm in height as well as hemispherical shells with 120 nm. The thermal-induced active migration of the nanopillars from the pristine position in the lateral direction occurred at the colloidal defects while some cavity space was formed inside the gold pillars. The nano-structured gold pillars exhibited a strong surface plasmon resonance at 598 nm, as compared to that of the solid gold nanospheres at 520 nm, and a noticeable red shift to 640 nm was induced by the removal of the polymer template.
Selective Deposition of Iron Oxides Thin Layers on Si(100) from Aqueous Solutions
Bull. Korean Chem. Soc. 2009, Vol. 30, No. 6
micrometer scale patterns of two types of iron oxide layers were obtained successfully using microcontact
printing of OTS on Si. The iron oxide thin layers were formed on the OTS printed area, which was assigned to the catalytic etching of OTS under the acidic experimental conditions, or to the heterogeneous nucleation on OTS layer. It was also found that the high ionic strength of the reaction media helped increase the edge-resolution of the thin film patterns during pattern formation, particularly at low pH. Overall, this patterning method can be applied to other solution deposition processes.
Silica Effect on Coloration of Hematite Nanoparticles for Red Pigments
Chemistry Letters Vol. 38, No. 8 (2009)
A novel red pigment displaying consistent properties up to a heating temperature of 1000 C was synthesized, which indicates that the multilayer silica coating actually minimizes the agglomeration of the nanoparticles.
Surface Selective Deposition of PMMA on Layered Double Hydroxide Nanocrystals Immobilized on Solid Substrates
Adv. Mater. 2009, 21, 546–549
we demonstrated a novel method of optimizing the coverage of monolayer MgAl-LDH nanocrystals on solid
substrates with maximum face-to-face contact by changing the solvent systems at room temperature without using any additional molecular linker. The LDH nanocrystals could be readily assembled on polymer and gold substrates by simple ultrasonification. PMMA nanostructures with a high-graft density were successfully generated on an immobilized LDH monolayer by employing UV-induced polymerization, which makes it possible not only to control the reaction kinetics, but also the grafting polymer density by adjusting the coverage values of the MgAl-LDH monolayer.
Three-dimensional Iron Glutarate with Five- and Six-coordinated Iron(II)–Oxygen Networks
Chemistry Letters Vol. 38, No. 1 (2009)
A novel open framework iron(II)–carboxylate was synthesized and characterized. Four crystallographically different iron atoms have five- and six-coordinated geometry giving rise to 1D double metal–oxygen layers. The glutarate ligands link inorganic chains to give an interlocked 3D structure containing water. Magnetic measurement of iron–carboxylate compound shows canted antiferromagnetism around 4 K.
Two-dimensional nanopatterning by PDMS relief structures of polymeric colloidal crystals
Applied Surface Science 254 (2008) 5134–5140
A new constructive method of fabricating a nanoparticle self-assembly on the patterned surface of a poly(dimethylsiloxane) (PDMS) relief nanostructure was demonstrated. Patterned PDMS templates with close-packed microwells were fabricated by molding against a self-assembled monolayer of polystyrene spheres. Alkanethiol-functionalized gold nanoparticles with an average particle size of 2.5 nm were selectively deposited onto a hydrophobic self-assembled monolayer printed on the substrate by the micro-contact printing (mCP) of the prepared PDMS microwell, in which the patterned gold nanoparticles consisted of close-packed hexagons with an average diameter of 370 nm. In addition, twodimensional colloidal crystals derived from PMMA microspheres with a diameter of 380 nm and a negative surface charge were successfully formed on the hemispherical microwells by electrostatic force using positively charged PAH-coated PDMS as a template to produce multidimensional nanostructures.
Selective MOCVD of titanium oxide and zirconium oxide thin films using single molecular precursors on Si(1 0 0) substrates
Journal of Physics and Chemistry of Solids 69 (2008) 128–132
Titanium oxide (TiO2) and zirconium oxide (ZrO2) thin films have been deposited on modified Si(1 0 0) substrates selectively by metalorganic chemical vapor deposition (MOCVD) method using new single molecular precursor of [M(OiPr)2(tbaoac)2](M = Ti, Zr; tbaoac = tertiarybutyl-acetoacetate). For changing the characteristic of the Si(1 0 0) surface, micro-contact printing (mCP) method was adapted to make self-assembled monolayers (SAMs) using an octadecyltrichlorosilane (OTS) organic molecule which has –CH3 terminal group. The single molecular precursors were prepared using metal (Ti, Zr) isopropoxide andtert-butylacetoacetate (tbaoacH) by modifying standard synthetic procedures. Selective depositions of TiO2and ZrO2were achieved in a home-built horizontal MOCVD reactor in the temperature range of 300–5001C and deposition pressure of 1x10*-3–3x10*-2 Torr. N2gas (5 sccm) was used as a carrier gas during film depositions. TiO2and ZrO2thin films were able to deposit on the hydrophilic area selectively. The difference in surface characteristics (hydrophobic/hydrophilic) between the OTS SAMs area and the SiO2or Si–OH layer on the Si(1 0 0) substrate led to the site-selectivity of oxide thin film growth.
Hybrid Assembly of Layered Double Hydroxide Nanocrystals with Inorganic, Polymeric and Biomaterials from Micro- to Nanometer Scales
Eur. J. Inorg. Chem. 2008, 5573–5578
We demonstrated a novel method of assembling electrostatically charged particles on a monolayer of LDH nanocrystals that act as a stable inorganic particulate interface, due to their plate-like particle shape and surface charges. In the case of the zeolite/LDH bilayer system, the zeolite microcrystals were tightly attached onto the LDH monolayer, where the zeolite monolayer has a preferred orientation. Most significantly, this assembly strategy provided the necessary compatibility between the hydrophobic polymers and hydrophilic LDHs, resulting in the formation of homogeneous PMMA-LDH nanocomposites with a structure consisting of PMMA nanobeads uniformly embedded into the LDH nanocrystals, thanks to their nanometer-sizes and charged surfaces. We anticipate that conformal polymer films induced by thermal treatment can act as active membranes in controlling the release properties of the interlayer anions.
Fabrication of Textured Silicon Solar Cell using Microlens as Anti-Reflection Layer
This paper presents facile, reproducible softlithographic technique for fabricating textured crystalline silicon
solar cell with hexagonally close-packed hemispherical arrays using ordered polymeric microspheres. Close-packed monolayers of polymer microspheres were deposited on flat cleaned glass substrate using spin-casting technique. The relief structure of highly ordered microspheres successfully generated their negative replica of elastomers. Hemispherical microlens arrays were molded by dispensing and curing liquid ultraviolet-curable photopolymers into the negative replica on crystalline silicon solar cell module. Sub-micrometer scaled microlens with uniform, cleaned surface morphology were easily reproduced by using the prepared molds, without multi-step engineering processes. The microlens-coated crystalline silicon solar cell showed additional increment of 1% in solar cell efficiency, compared to that of SiNx anti-reflection coated one, as well as remarkable decrease of reflectance in SiNx-uncoated solar cell.
Fabrication of polydimethylsiloxane shadow masks for chemical solution deposition of CdS thin-film transistors
Thin solid Films 516 (2008) 6492–6498
PDMS (polydimethylsiloxane) shadow masks were fabricated by replica molding using laser-patterned metal shadow masks as primary templates, which were applied to solution as well as vapor deposition to prepare patterned thin films on solid substrates. We demonstrated a method of fabricating cadmium sulfide (CdS) thin-film transistors (TFTs) using the prepared PDMS shadow masks thanks to their solution-tight, free-standing and elastic characteristics. The patterned CdS thin films were deposited by chemical solution deposition in aqueous solution and aluminum metal electrodes were deposited by thermal evaporation. The electrical characteristics of the CdS/SiO2/n-Si transistors consisted of a field effect mobility of ~0.5 cm2/Vs, a threshold voltage of ~14 V and an on/off ratio of ~10*7.
Fabrication of poly(methyl methacrylate) colloidal monolayer on chemically modified silicon surface and hemispherical platinum nanoshell
Applied Surface Science 255 (2008) 3400–3406
A dip-coating technique was used to deposit self-assembled monolayer arrays of PMMA colloidal particles with a diameter of 125 nm onto a silicon surface coated with (3-aminopropyl)-triethoxysilane (APTES), exploiting the electrostatic interaction between the negative particle and the positive substrate. The PMMA colloidal arrangement was controlled efficiently by the dipping time and temperature, concentration and pH of the colloidal solutions. A non-close-packed monolayer assembly was prepared without the need for pre-patterned templates. The deposition of platinum metal on the 2D PMMA arrays and subsequent thermal treatment produced ordered hemispherical Pt nanoshells, 74 nm in height, as soft-lithographic templates and biological sensor materials.
A Three-dimensional MOF Assembled by Metal-organic Tapes Comprising of Copper(II) Tetranuclear Clusters and 5-Sulfoisophthalates
Bull. Korean Chem. Soc. 2008, Vol. 29, No. 12
We have presented a facile synthesis of a three-dimensional MOF assembled by 1D metal0organic tapes. The unique copper(II) tetranuclea cluster is anticipated to play a role as a versatile building block in forming other MOFs with different network types from that shown in this work.
A new series of isophthalate-based electrochromic materials were prepared. The functional groups at the 5-position of isophthalate have a significant influence on the observed color. In particular, an electrochemically active nitro group induced a multi-color display, indicating that further electrochromic properties could be manipulated using more diverse 5-substituted isophthalate derivatives.
Selective Layer Reaction of Layer-by-Layer Assembled Layered Double-Hydroxide Nanocrystals
J. AM. CHEM. SOC. 2007, 129, 3522–3523
In summary, we demonstrated the layer-by-layer assembly and selective layer expansion of MgAl-LDH on Si using 2-carboxyethylphosphonic acid. By considering the relative affinity for the incorporation and adsorption of guests on the host layers, this edgegrafting mechanism and on-off control of the crystalline edge sites can be extended to the adjustment of the release properties of guest molecules and the catalytic ability of layered composite materials. Multilayer MgAl-LDH nanocomposites can be designed by surface treatment, thus making them useful to fabricate functional nanosensors, catalysts, ion-selective electrodes, optical coatings, and nanosized containers for biomolecules.
A Porous and Interpenetrated Metal–Organic Framework Comprising Tetranuclear Iron III –Oxo Clusters and Tripodal Organic Carboxylates and Its Implications for (3,8)-Coordinated Networks
Crystal Growth & Design, Vol. 7, No. 11, 2007
A porous metal–organic framework (MOF), Fe4(µ3O)2(BTB)8/3(DMF)2(H2O)2·(DMF)10(H2O)2(1) (BTB = benzene-1,3,5-tribenzoate, DMF)N,N-dimethylformamide) has two interpenetrating 3D frameworks composed of fused cages and shows a stronger affinity for CO2than most other known highly porous MOFs. The unique tetranuclear iron–oxo clusters act as 8-connectors, which are linked by 3-connecting BTBs, to give a partially augmentedthe net (using the symbolism of O’Keeffe and co-workers). The underlying implications for (3,8)-coordinated networks are also discussed in relation to the framework structure of1.
Two-dimensional carboxylate bridged network of europium(III)–transition metal(II) glutarate compounds
Dalton Trans., 2005, 2603–2609
Four new heterometallic glutarate coordination polymers, [Eu2M(H2O)4][O2C(CH2)3CO2]4·2H2O(M=Mn (1), Fe
(2), Co (3) and Ni (4)) have been obtained under hydrothermal synthesis. The single-crystal X-ray diffraction analyses showed that they have two-dimensional frameworks based on the linear polyhedral chains consisting of two nine-coordinated Eu(III)O9 and a six-coordinated M(II)O6.These1-DMO6–Eu2O16 chains are cross-linked by glutarate ligands as an interchain pillared architecture, whose conformations vary depending upon the transition metals. The magnetic behavior of the compounds show a weak antiferromagnetic interaction, in which shielding of the 4f electrons by the outer shell electrons effectively precludes significant coupling interactions between the Eu-4f electrons and transition metal (M)-3d electrons.
Structural and optical properties of 6,13-pentacenequinone film
Applied Surface Science 244 (2005) 615–618
We report on the structural and optical properties of 6,13-pentacenequinone film deposited onn-Si by thermal evaporation at room temperature. According to X-ray diffraction, films were found to have good crystallinity and also to have two crystalline phases mixed. Photoluminescence (PL) spectra exhibited double peaks at 1.97 and 2.09 eV while the corresponding (double) peaks related to highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) transition were observed from direct absorption spectra at 2.94 and 3.11 eV. The PL intensity was very strong under a UV illumination. It also seems that such a large Stokes shift as 1 eV exist in this organic crystal system. Au/organic/n-Si structures using 6,13-pentacenequinone films onn-Si showed rectifying behavior but with a relatively high level of leakage current due to many traps in the organic film.
Step-wise Anion-Exchange in Layered Double Hydroxide Using Solvothermal Treatment
Bull. Korea Chem. Soc. 2005, Vol. 26, No. 2
Synthetic layered double hydroxides (LDHs), [Mg4Al2(OH)12]CO3·nH2O, were prepared in the submicron size
of plate-like polycrystals. Anion-exchange reactions with various lineardicarboxylic acids were performed to produce LDH/organic hybrid materials by solvothermal treatment in toluene. X-ray powder diffraction spectra for the products indicated that the interlayer spacings of LDHs remarkably changed, up to 20 Å when 1,10-decanedicarboxylic acid anions were intercalated as an organic guest. Dicarboxylates-LDHs samples could be also re-exchanged consecutively with other dicarboxylic acids or carbonate without serious destruction of layer structure under the scanning electron microscopic observation.
Crystal Packing of Two Different Tetranuclear Iron(III) Clusters, [(tacn)4Fe4O2(OH)4]2·8Br·9H2O (tacn = 1,4,7-triazacyclononane)
Bull. Korean Chem. Soc. 2005, Vol. 26, No.2
[(tacn)4Fe4O2(OH)4]2·8Br·9H2O (tacn = 1,4,7-triazacyclononane), a tetranuclear iron(III) complex was synthesized by the hydrolysis of (tacn)FeCl3 and crystallizes in the orthorhombic space group, Pca2(1), with cell parameters, a = 37.574(3) Å, b = 16.9245(12) Å, c = 14.2830(11) Å, V = 9082.9(12) Å3. [(tacn)4Fe4O2(OH)4]4+ cations approach S4 point symmetry containing an adamantane skeleton. Four Fe(III) atoms have distorted
octahedral environments with two hydroxo and an oxo bridges. Two [(tacn)4Fe4O2(OH)4]4+ clusters having
different Fe…Fe distances are connected to each other by the networked hydrogen bonds. The electrochemical behavior reveals irreversible three cathodic and two anodic peaks. Magnetic properties are characterized by antiferromagnetic (AF) interactions between Fe(III) ion spins. However, the low-lying states are still magnetic and exhibit a blocking behavior and a magnetic hysteresis at low temperatures.
Transverse anisotropy of the single-molecule magnet Mn12-PrCl
Journal of Magnetism and Magnetic Materials 272–276 (2004)
We present magnetization measurements in the single-molecule magnet Mn12-PrCl. Both powdered and single crystalline samples have been characterized by measuring the magnetization as functions of temperature, magnetic field, and the angle between the easy axis of magnetization and the magnetic field. From the analyses of magnetization data, we found the second-order transverse anisotropy of E = 0.15 K in Mn12-PrCl.
Synthesis and Magnetic Relaxation of [Mn12O12(O2CCH2CH2CH2Cl)16(H2O)4] Complex
Bull. Korean Chem. Soc. 2004, Vol. 25, No. 7
Mn12O12(O2CCH2CH2CH2Cl)16(H2O)4] (noted as Mn12-BuCl), a new polynuclear complex of manganese chlorobutyrate has been successfully prepared by substitution of acetate with 4-chlorobutyric acid. The Mn12-BuCl crystallizes into triclinic space group P-1 with a= 14.5560(11) Å, b= 14.5819(11) Å, c= 27.265(2) Å, α= 84.1140(10)°, β= 88.805(2)°, γ= 89.8820(10)°, and Z= 2. The local environments of manganese 3+ and 4+ ions of the title compound are close to those of other Mn12compounds. The electrochemical data for Mn12-BuCl involve reversible reactions of two-electron reductions. The Mn12-BuCl also presents magnetic relaxation below 10 K implying that each molecule behaves as a single molecule magnet.
Solvothermal Ion Exchange of Aliphatic Dicarboxylates into the Gallery Space of Layered Double Hydroxides Immobilized on Si Substrates
Chem. Mater. 2004, 16, 3774–3779
Highly ordered Mg/Al-based layered double hydroxide (LDH) nanocrystals on Si substrates were successfully obtained by ultrasonic treatment in organic solvents. LDHs intercalated with aliphaticR,ω-dicarboxylate were prepared through anion exchange by solvothermal treatment at around 100 °C. Binary solvent mixtures of alcohol and toluene prevent dissolution of the LDH and preserve the layered crystal structure of the LDH during the anion-exchange reaction. Atomic force microscopy results present conservation of lateral positions and morphologies of the LDH crystals on Si before and after anion exchange. The interlayer spacings of LDH crystals intercalated with dicarboxylates vary directly with the chain length of the dicarboxylates, and reaction stepwise anion exchanges are possible. The results gave an original example of the direct measurement of the anisotropic nanomorphological change of the selected LDH crystals in the intercalation reaction, which opens a wide range of applications.
Journal of Magnetism and Magnetic Materials 272–276 (2004)
The electronic structure of Mn12-Ac has been investigated using photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS). The PES spectrum indicates that Mn 3d states are located near the top of the valence band, and the Mn 2p XAS spectrum provides clear evidence for the Mn3+–Mn4+ mixed-valent states.
Magnetization relaxation of Mn12-Ac in the presence of crystal imperfections
Journal of Magnetism and Magnetic Materials 272–276 (2004)
Effects of crystal imperfection on the magnetic properties of Mn12-Ac have been studied. Crystal defects were
introduced in the lattices of Mn12-Ac by a novel heat-treatment process. The magnetization relaxation associated with quantum tunneling of magnetization is strongly influenced by the existence of crystal defects. Experimental data are explained qualitatively in terms of the distribution of transverse anisotropy induced by the crystal imperfection.
A novel hybrid of high-Tc cuprate and paramagnetic organic radical
Solid State Communications 130 (2004) 287–291
We have found a heterostructured spin-system consisting of superconducting and paramagnetic sub-systems, where free radicals (S = 1/2) are stabilized between Bi-based cuprate layers. The superconducting-paramagnetic dual magnetism observed in this work may provide a useful probe for investigating the mechanism of high transition temperature (high-Tc) superconductivity. The stabilization of solid-state free radicals in-between (super) conductive layers is expected to provide a new class of magnetic heterostructures with unusual functionalities, which may find applications as magneto-electronic
A Novel 3-D Network of Fe(II) Glutarate: 2-D Honeycomb-type Edge-shared FeO6Layers and Isolated Interlayer FeO6Octahedra
Chemistry Letters Vol.33, No.3 (2004)
The 3-D structure of Fe(II) glutarate is built up from 2-D honeycomb layers of 12-membered FeO6 polyhedra and pillarlike interlayer FeO6 interconnected by Fe–O–C–O–Fe bridging modes, presenting ferrimagnetic coupling below 5 K.