bluuebunny/crossref_metadata_2025 huggingface dataset:
Luminescence Properties of Europium-Doped Yttrium Oxides Derived from Their Dodecylsulfate-Templated Mesostructure and Nanotube Forms
Authors: Kijima Tsuyoshi , Iwanaga Kenichi , Hamasuna Tomomi , Mohri Shinji , Yada Mitsunori , Sekita Masami , Machida Masato
Published: June 2019

Europium-doped hexagonal-mesostructured and nanotubular yttrium oxides templated by dodecylsulfate species as well as surfactant free bulk oxides were synthesized by the homogeneous precipitation method. All the as grown nanostructured or bulk materials with amorphous or poorly crystalline frameworks showed weak luminescence bands at room temperature. On calcination at 1000°C these materials were converted into highly crystalline yttrium oxides, resulting in a total increase in intensity of all the bands by one order of magnitude. In the hexagonal-mesostructured system, the main band due to the 5D0-7F2 transition for the calcined phases showed a sharp but asymmetrical multiplet splitting indicating multiple Eu sites. Concentration quenching was found at a Eu content of 3 mol% or above for these phases. In contrast, the main emission for the calcined solids in the nanotubular system occurred as poorly resolved broad band and the intensity of the main band at higher Eu content was significantly enhanced compared with those for the other two systems.
Sol-gel Elaboration of Porous Oxide Coatings as Interphase in SiC/SiC Ceramic Matrix Composites
Authors: Verdenelli M. , Parola S. , Chassagneux F. , Jacques S. , Vincent H. , Dazord J. , Scharff J.P. , Bourgeat-Lami E.
Published: June 2019

Combinations of meso-, macro- and microporous coatings with a chemical composition of 90%Al2O3-10%SiO2were elaborated on SiC Hi-Nicalon fibers using the sol-gel process. They were evaluated as porous interphase for the reinforcement of CMC. The mesoporous oxide, in contact with the fiber, allows cracks deviation whereas the macroporous one, in contact with the matrix, avoids the gaseous infiltration of the mesopores during the SiC CVD matrix process. It also prevents from oxygen diffusion during high temperature under air. The characterization of the composites was performed by SEM (scanning electron microscopy), TEM (transmission electron microscopy), X-ray diffraction, and EDS (energy dispersive spectrometry). TEM evidenced the porosity gradient as expected. A tensile test on the composites revealed brittle behavior (fracture) and no fiber debonding was observed.
Encapsulation of Ibuprofen in Mesoporous Silica: Solid State NMR Characterization
Authors: Babonneau Florence , Camus Lydie , Steunou Nathalie , Ramila Ainhoa , Vallet-Regi Maria
Published: June 2019

Mesoporous silica materials have been studied for the time-dependent delivery of bioactive agents. It has already been shown that ibuprofen molecules can be encapsulated with loading as high as 30 wt% in MCM-41 silica, functionalized or not by amino groups. Interactions between the guest molecules and the host matrix have been investigated by 1H, 29Si and 13C solid state NMR spectroscopy. These experiments demonstrate an extremely high mobility of the ibuprofen molecules when the matrix is not functionalized, despite of the presence of a carboxylic function on the ibuprofen molecules. On the contrary, when the silica matrix is functionalized by amino groups, the 13C NMR response shows a strong restriction in mobility suggesting the existence of interactions between the amino groups and the carboxylic groups.
Vapor Treatments of Spin-On Mesostructured Silica Films for the Enhancement of Structural Stability
Authors: Tanaka Shunsuke , Nishiyama Norikazu , Egashira Yasuyuki , Oku Yoshiaki , Ueyama Korekazu
Published: June 2019

Organically functionalized mesoporous silica films were prepared by a novel synthesis procedure. The synthesis procedure involves a vapor infiltration technique for mesostructured silica films prepared through a spin-coating process. Organic-functional groups were incorporated into the mesochannel wall by the vapor infiltration treatment using organosiloxanes. The structural stability of spin-on mesostructured silica films is generally low, resulting in a structural shrinkage or a collapse of the mesostructure under calcination process. On the other hand, the treated films did not contract during calcination, indicating high structural stability. A contact angle of water on the treated film was large, showing high hydrophobicity. FTIR analysis suggested that the residual silanol groups were replaced with the organosilyl groups after vapor infiltration treatment. The increase in the film thickness was hardly observed under vapor infiltration, suggesting no deposition of organosiloxanes vapor on the surface of the film.
Nanowire and Nanotube Syntheses Through Self-assembled Nanoporous AAO Templates
Authors: Wang H. Hau , Han Catherine Y. , Willing Gerold A. , Xiao Zhili
Published: June 2019

Nanowires and nanotubes have attracted significant interest during recent years due to their novel electrical, magnetic, and photonic properties. Quantum confinement, proximity interaction, and surface plasmon enhancement effects are among a few unique phenomena associated with these materials. A convenient procedure to prepare these materials is through anodized aluminum oxide (AAO) template synthesis. Nanoporous AAO membranes with pore diameters ranging from 10 to 200 nm can be prepared with anodization in oxalic, sulfuric and phosphoric acids under various reaction conditions. With repeated anodization-etching cycles, highly ordered straight channels can be prepared through self-organization. With electro- and electroless deposition, a variety of nanowires and nanotubes such as Ni, Co, Au, Pb, Bi, etc. have been prepared. The synthesis, characterization, and physical properties of these materials are presented.
Bio-Inspired Submicron Electrodes
Authors: Stanish Ivan , Lowy Daniel A. , Singh Alok
Published: June 2019

Immobilized polymerized electroactive vesicles (IPEVs) are submicron biocapsules capable of storing charge in confined environments and chemisorbing on surfaces. Methods to immobilize stable submicron sized electroactive vesicles and the means to measure electroactivity of IPEVs at nanolevels have been demonstrated. IPEVs can withstand steep potential gradients applied across their membrane, maintain their structural integrity against surfaces poised at high/low electrical potentials, retain electroactive material over several days, and reversibly mediate (within the membrane) electron flow between the electrode surface and vesicle interior. IPEVs have strong potential to be used for charge storage and electron coupling applications that operate on the submicron scale and smaller.
Hygroscopic Growth of Self-Assembled Layered Surfactant Molecules at the Interface between Air and Organic salts
Authors: Shin Yongsoon , Wang Li-Qiong , Fryxell Glen E. , Exarhos Greg J.
Published: June 2019

In this paper, we report a self-assembly of surfactant molecules at the interface of air/hygroscopic quaternary ammonium salts such as tetrabutylammonium acetate (TBAAc), tetrabutylammonium bromide (TBAB), and tetrabutylammonium nitrate (TBAN), where they show different hygroscopicity, TBAAc > TBAB > TBAN. Homogeneously dissolved surfactants rearrange themselves when they contact air due to high moisture adsorption behavior of such organic salts. Highly ordered lamellar phases with different lattice spacings have been observed when surfactants with long alkyl chains were used. Alkylammonium halides form monolayers, while neutral alkylamines forms bilayers based upon basal spacings of their X-ray diffraction patterns. The change in basal spacings in lamellar patterns, the alkyl chain conformation of surfactants, and Hbonding property of neutral amine surfactants are discussed in detail.
Polymeric One-Dimensional Reflectors Based on Self-Organization of Comb-Shaped Supramolecules
Authors: Kosonen Harri , Valkama Sami , Ruokolainen Janne , Brinke Gerrit ten , Ikkala Olli
Published: June 2019

Polystyrene-block-poly(4-vinylpyridine) (PS-block-P4VP) diblock copolymer was complexed with dodecylbenzenesulfonic acid (DBSA), leading to comb-coil polymeric supramolecules PS-block-P4VP(DBSA)y(y= 1.0, 1.5, and 2.0). Complexes formed hierarchical lamellar structure with long period of ca. 1400 Å. Due to periodicity and refractive index contrast between the layers, transmission and reflectance measurements showed a relatively narrow incomplete bandgap at ca. 460 nm. The angular dependence of the bandgap was also studied using different angles (ø) relative to the surface normal. The mid-gap was blue-shifted when the incident angle was increased indicating that the lamellar structure was partly oriented by the surfaces of quartz glasses.
Spin-Coating Self-Assembly for Micropatterning of Ultrathin Multilayer Films
Authors: Jang Hongseok , Kim Sangcheol , Char Kookheon
Published: June 2019

A new approach to create layer-by-layer assembled multilayer ultrathin films with welldefined micropatterns in a short process time is introduced. To achieve such micropatterns with high line resolution in organic multilayer films, microfluidic channels were combined with the convective self-assembly process employing both hydrogen bonding and electrostatic intermolecular interactions. The channels were initially filled with polymer solution by capillary pressure and the residual solution was then removed by spinning process. The micropatterns with distinct line boundaries were obtained and the small ridges were also observed at the edges of the patterned lines. Spin self-assembled vertical heterostructural multilayer patterning using (PVP/PAA)5 micropatterns, which were prepared with microfluidic channels, as a template was also investigated.
Self-Organization of Gold Nanoparticles on Surface-Modified Conducting Polymer Films
Authors: Zhang Donghui , Klapman Sarah , Hanks Timothy W.
Published: June 2019

Thiol-coated gold nanoparticles with a diameter of approximately 7.5 nanometers and a narrow particle distribution were prepared from sodium tetrachloroaurate under phase transfer conditions. The thiols used were 1-mercaptododecane (1) and 1-mercapto-9,11-heptadecadiyne (4). The particles were cast onto thin films of polyaniline and poly (3,4-ethylenedioxythiophene), as well as onto thiol-coated versions of the same polymer. Surface modification of the polymers with long chain thiols encourages the spontaneous self-assembly of the particles into twodimensional arrays and may offer a unique method for stabilization of nanoparticle assemblies on polymer substrates.
Novel Conjugated Polymer/Silica Nanocomposites with Tunable Mesostructure Synthesized by a Robust Pd Catalyst
Authors: McCaughey Byron , Costello Chris , Hampsey J. Eric , Wang Donghai , Li Chaojun , Lu Yunfeng
Published: June 2019

Conjugated poly(2,5-thienylene ethynylene) (PTE)/silica nanocomposites with cubic and lamellar mesostructures have been synthesized. Surfactant directed assembly coorganized 2,5-diiodothiophene monomer and palladium-based catalyst within a silica matrix. Subsequent polymerization initiated by exposing the monomer/catalyst/silica nanostructures to acetylene gas resulted in the formation of an ordered, mesostructured poly(2,5-thienylene ethynylene)/silica nanocomposite as determined by XRD, UV-vis, FTIR, and TEM experiments. Mesostructured PTE with 287m2/g surface area is obtained after silica removal. Further polymerization of PTE oligomers occurs after exposure to acetylene gas due to active Pd catalyst attached to the polymer chains. This novel approach provides a unique route to synthesize mesostructured conjugated polymer/inorganic nanocomposites and porous mesostructured PTE.
One and Two-dimensional Semiconducting Nanostructures Self-assembly of Conjugated Oligomers
Authors: Leclère Ph. , Surin M. , Jonkheijm P. , Henze O. , Schenning A.P.H.J. , Biscarini F. , Grimsdale A.C. , Feast W.J. , Meijer E.W. , Müllen K. , Brédas J.L. , Lazzaroni R.
Published: June 2019

The properties of organic electronic materials in the solid-state are determined not only by those of individual molecules but also by those of ensembles of molecules. The ability to control the architectures of these ensembles is thus essential for optimising the properties of conjugated materials for use in electronic devices (light emitting diodes, field effect transistors, solar cells,…) and is primordial for potential technological applications in nanoelectronics.

Here, we report on the observation by atomic force microscopy (AFM) of 1D and 2D nanoscale architectures obtained in the solid-state from solutions of molecularly-dissolved conjugated block copolymers or oligomers, and demonstrate that the conjugated molecules can organize onto a surface over lengthscales from nanometers to several microns, forming semiconducting fibrils by π-stacking processes.
Characterization of Nano-size Indium Cluster in InGaN/GaN Multiple QuantumWells with High Indium Composition
Authors: Cho Hyung Koun , Lee Jeong Yong
Published: June 2019

We report the effect of strain-induced indium clustering on the emission properties of InGaN/GaN multiple quantum wells grown with high indium composition by MOCVD. Nanosize indium clustering confirmed by high-resolution transmission electron microscopy results in the redshift of the emission peak and the increase of the integrated photoluminescence (PL) intensity. We found that strong carrier localization in indium clustering induces the increases of the activation energy of PL integrated intensity and the temperature independence of PL decay profiles. All these observations suggest structurally and optically that the improved emission properties in the InGaN/GaN multiple quantum well with high indium composition are associated with the localized states in the nano-size indium cluster.
Nanopatterned Si(001) Substrates as Templates for Quantum Dot Growth
Authors: Ney A. , Pampuch C. , Schulz J. J. , Perepelittchenko L. , Koch R.
Published: June 2019

It has been shown recently, that the formation of GeSi quantum dots on Si(001) is strongly affected by the surface properties of the substrate. With an increasing number of missing dimer vacancies the growth mode can even change from a Stranski-Krastanow to a kinetic 3D island growth mode. Here we report on atomically resolved scanning tunneling microscopy images of Si(001) after different preparation procedures, namely the conventional high temperature procedure employed for commercial wafers, and Shiraki-type samples which require only low temperature treatment. The latter method yields an atomically flat Si(001) (2 × 1) surface, however, with a defect (ad- and missing dimers) concentration depending on the respective preparation conditions. Furthermore, repeated flashing occasionally yields a (2 × n) reconstructed surface consisting of well-ordered self-assembled trenches of missing dimers, similar to the ones discussed controversially in the previous literature. From our results we can clearly exclude contaminants to be involved.
Atomistic Simulation Study of Controlled Nanostructure Patterning
Authors: Lee Byeongchan , Cho Kyeongjae
Published: June 2019

We investigate the surface kinetics of Pt using the extended embedded-atom method, an extension of the embedded-atom method with additional degrees of freedom to include the nonbulk data from lower-coordinated systems as well as the bulk properties. The surface energies of the clean Pt (111) and Pt (100) surfaces are found to be 0.13 eV and 0.147 eV respectively, in excellent agreement with experiment. The Pt on Pt (111) adatom diffusion barrier is found to be 0.38 eV and predicted to be strongly strain-dependent, indicating that, in the compressive domain, adatoms are unstable and the diffusion barrier is lower; the nucleation occurs in the tensile domain. In addition, the dissociation barrier from the dimer configuration is found to be 0.82 eV. Therefore, we expect that atoms, once coalesced, are unlikely to dissociate into single adatoms. This essentially tells that by changing the applied strain, we can control the patterning of nanostructures on the metal surface.
Nanostructure of Surface Formed by Vacancy Clustering in FeAl
Authors: Yoshimi Kyosuke , Haraguchi Tomohide , Ogawa Tomohisa , Kobayashi Takayuki , Sung Min-Seok , Hanada Shuji
Published: June 2019

In B2-type FeAl, supersaturated vacancies retained upon rapidly quenching are absorbed near surface during an aging treatment, being agglomerated into nano- to meso-clusters through the absorption process. Eventually, surface morphology is self-patterned in nano-order by the vacancy clustering. If FeAl was not quenched from high temperature or plastic strain remained near surface, the surface self-patterning never occurs, indicating that the change in surface morphology is caused by the clustering of supersaturated vacancies. The clusters have specific shape with cluster surfaces faceted toward {100} planes. Thus, the shape of the clusters formed near surface is controllable by changing surface orientation. Vacancy cluster size and its distribution density can be also controlled by varying the concentration of supersaturated vacancies and/or the clustering condition. These indicate that the vacancy clustering is a unique process to efficiently pattern the surfaces of metals, alloys and intermetallics in nano-scale.
1.3 νm InAs/GaAs Quantum Dots Directly CappedWith GaAs Grown By Metal Organic Chemical Vapor Deposition
Authors: Huang K.F. , Hsieh T.P. , Yeh N.T. , Ho W.J. , Chyi J.I. , Wu M.C.
Published: June 2019

Systematic studies of the growth temperature and growth rate effect of the formation of InAs/GaAs quantum dots (QDs) have been demonstrated. These QDs are formed with large InAs coverage (3.0 MLs) and periodic growth interruption via Strnski-Krastonov (S-K) epitaxial growth mode by using metalorganic chemical vapor deposition (MOCVD). The room temperature photoluminescence (PL) spectra show red-shift of peak wavelength by decreasing the InAs growth temperature from 540°C to 500°C. As growth rate increases from 0.05 ML/s to 0.2 ML/s at growth temperature of 500°C, PL linewidth could be narrowed and emission intensity could be increased. These results could be correlated to the In clusters and uniformity of InAs/GaAs QDs observed by scanning electron microscopy (SEM) image. Finally, the room temperature photoluminescence spectra of InAs/GaAs QDs directly capped with GaAs shows peak wavelength of 1.35 μm with narrow linewidth of 30.8 meV is obtained.
Formation of Luminescent Si Nanocrystals by High-Temperature Annealing of Ion-Beam-Sputtered Si/SiO2 Multilayers
Authors: Choi Suk-Ho , Bae Jun Sung , Kim Kyung Jung , Moon Dae Won
Published: June 2019

Si/SiO2 multilayers (MLs) have been prepared under different deposition temperatures (TS) by ion beam sputtering. The annealing at 1200°C leads to the formation of Si nanocrystals in the Si layer of MLs. The high resolution transmission electron microscopy images clearly demonstrate the existence of Si nanocrystals, which exhibit photoluminescence (PL) in the visible range when TS is ≥ 300°C. This is attributed to well-separation of nanocrystals in the higher-TS samples, which is thought to be a major cause for reducing non-radiative recombination in the interface between Si nanocrystal and surface oxide. The visible PL spectra are enhanced in its intensity and are shifted to higher energy by increasing TS. These PL behaviours are consistent with the quantum confinement effect of Si nanocrystals.
Red shifted-Photoluminescence of Ensembles of GaN Nano-Crystallites
Authors: Bergman Leah , Chen Xiang-Bai , Feldmeier Joel , Purdy Andrew P.
Published: June 2019

We present optical analysis concerning the redshift of the photoluminescence (PL) of ensembles of GaN nano-crystals. We found that the extent of the redshift depends on the laser power as well as on the ensemble size. For ensemble of size ∼ 30 μm, the laser power in our experimental specification impacted the PL energy and caused a redshift of up to 120 meV. This phenomena was not observed for a small ensemble of ∼ 1 νm or less. For the small ensemble the PL redshift was negligible and depended weakly on the laser power; similar behavior was found in GaN thin film. The above findings were observed in the PL of GaN nano-crystalline of Wurtzite as well as cubic structure. Our results point to a laser heating event occurring in the large ensemble; the emitted and scattered light is confined among the nano-crystallites thus causing the heating. For a small ensemble the light has a higher probability of diffusing outside the enclosure, and thus no laser heating occurs.
Optical Properties and Local Structure of Cu(II) Dopant in ZnSe Nanoparticles
Authors: Norman Thaddeus J. , Magana Donny , Bridges Frank , Zhang Jin Z.
Published: June 2019

Cu(II) doped ZnSe nanoparticles were synthesized using molecular cluster precursors. The Cu(II) dopant had the effect of quenching the ZnSe band edge emission, yet only weak emission from Cu(II) centers was observed. An X-ray Absorption Fine Structure (XAFS) experiment was performed on the Cu(II) doped ZnSe nanoparticles. It was determined that the Cu(II) occupies a tetrahedral site in the lattice in an environment similar to that of Cu in bulk Cu2Se, and is likely to have substituted for Zn(II) in the lattice.
Formation, Patterning, and Polymerization of Surface Adlayers Using Self-Assembled Monolayers as Templates
Authors: Mosley David W. , Sellmyer Mark A. , Jacobson Joseph
Published: June 2019

Ordered surface adlayers of diacetylene-containing molecules were formed using amide hydrogen-bonding interactions with a pre-formed self-assembled monolayer on gold. Photopolymerization of the diacetylene molecules in the adlayer results in enhanced solvent and processing stability of the adlayer. Patterning of the base monolayer using soft lithography techniques allows patterning of the adlayer as well, and may lead to methods for templating soluble two-dimensional monolayer sheets.
Electric Field Induced Carbon Nanostructures for Electronics and High Surface Areaapplications
Authors: Lin Chao Hsun , Lee Shu Hsing , Hsu Chih Ming , Tsai Ming Her , Kuo Cheng Tzu
Published: June 2019

Strong influence of the applied or self-induced (i.e. self-biasing) electric field on the alignment, orientation and structures was found in the carbon nano-structure deposition process. This study applied microwave-plasma electron-cyclotron-resonance CVD (ECR-CVD) technique for carbon nano-structure deposition. The deposited structures and properties were characterized with SEM and field emission I–V measurements. The result shows that a negative dc bias applied on the substrate is a necessary condition. In this condition, all carbon nanostructures were well aligned and perpendicular to the substrate surfaces and independent to the plasma/gas flowing directions. Interestingly, when applied an additional electric field near the substrate surface by a guiding metal plate, the CNT growth direction could be manipulated from perpendicular to nearly parallel to the substrate surface. Moreover, a rattan-like CNT would form when prolonging the deposition time or increasing the plasma carbon concentration. These novel nanostructures are expected to have high potential in energy storage, field emission display, nanoelectronics and gas sensing applications accordingly.
Field Emission of Zinc Oxide Nanostructure
Authors: Lee Sang Hyun , Yu SeGi , Jeong Taewon , Heo Jungna , Kim Wonseok , Lee Chang Soo , Lee Jeonghee , Kim J. M. , Kim Tae Yun , Nahm Kee Suk
Published: June 2019

Field emission characteristics were investigated for zinc oxide nanostructures which were grown on NiO catalyzed silicon (100) substrate by chemical vapor deposition method. The asgrown zinc oxide showed needle-shaped nanostructures with tip diameters of 20∼40 nm and length of 3∼5 νm. The turn-on field was found to be about 6 V/νm at a current density of 1 νA/cm2. After several field emission measurements, the turn-on field was increased up to 8.5 V/νm and the magnitude of field enhancement factor was decreased from 1190 to 940. According to SEM, the tip diameter increase of the zinc oxide to 60 nm was observed after several emission measurements. Therefore, degradation of the field emission characteristic after measurements is attributed to this deformation of the tip shape.
Design and Characterization of Nanoarchitectures from Multifunctional Polyparaphenylenes
Authors: Ravindranath Renu , Valiyaveettil Suresh , Baskar Chinnapan , Putra Ananda , Fitrilawati Fitri , Knoll Wolfgang
Published: June 2019

Conducting polymers are interesting materials due to their wide range of applications in electronics, sensing, photonics and display applications. The present paper delineates the synthesis and characterization of the three functionalized poly (p-phenylene)s (PPP) (A-C) and solution properties of the polymers. The self-assembly of the polymers were investigated on various substrates and the optical/morphological properties of thin films of these polymers were also studied. The spontaneous self assembly of the modified PPP's lead to the formation of thin films on both hydrophilic and modified surfaces.
Synthesis of carbon-encapsulated magnetic nanoparticles by a grain-boundary-reaction
Authors: Wang Qixiang , Ning Guoqing , Wei Fei , Luo Guohua
Published: June 2019

Carbon-encapsulated ferric magnetic nanoparticles were prepared by the grain-boundary-reaction of ultrafine goethite particles. The mechanism of the grain-boundary-reaction was studied with high-resolution transmission electronic microscope, X-ray diffraction and thermo gravimetric analysis. The magnetic properties are measured with a vibrating sample magnetometer. The diameter of carbon-encapsulated ferric magnetic nanoparticles is 30~60 nm, and the coercive force and saturate magnetization are 315 Oe and 30 emu /(g powder), respectively. These composite particles are very stable in air.
Chalcogen Nanowires: Synthesis and Properties
Authors: Mayers Brian T. , Xia Younan
Published: June 2019

We have demonstrated a variety of solution-phase approaches for the synthesis of 1- dimensional nanostructures from chalcogens such as Se and Te. These nanostructures include uniform, single crystalline nanowires and nanorods (lateral dimensions from 10 to 1000 nm, and lengths ranging from 2 to >100 νm). These nanostructures grew via a solid-solution-solid transformation mechanism, in which Se and Te atoms were transported from the less stable source (amorphous colloids) into the more stable product (trigonal phase nanocrystallites). The nanocrystallites (or seeds) were formed either through temperature driven homogeneous nucleation or by sonochemical cavitation. As directed by the highly anisotropic crystal structure, the growth could be confined to one particular direction. These nanowires could be prepared both as dispersions in various solvents or as networked arrays on solid supports.
Dielectrophoretic Assembly of Switchable Two-Dimensional Photonic Crystals with Specific Orientation
Authors: Lumsdon Simon O. , Kaler Eric W. , Velev Orlin D.
Published: June 2019

One and two-dimensional colloidal crystals are assembled from aqueous suspensions of latex and silica microspheres in an alternating electric field. These crystals of size up to 25 mm2 are formed in the gap between two planar gold electrodes. They have specific axis orientation parallel to the direction of the applied field without the need for expensive micropatterned templates. The field gradient causes the particles to accumulate on the surface between the two electrodes, align into rows along the field direction, and then crystallize into hexagonal arrays. The lattice spacing can be controlled via electrostatic repulsion. The system can find application in switchable photonic devices.
Fabrication of Polymer Photonic Crystals by Two-Photon Nanolithography
Authors: Lee Tae-Woo , Mitrofanov Oleg , White Christopher A. , Hsu Julia W. P.
Published: June 2019

We use a two-photon laser-scanning microscope to fabricate two-dimensional (2D) photonic crystal structures in commercially available SU-8 polymer films, and successfully demonstrate making nanostructures beyond the diffraction limit with high aspect ratios. By varying the laser beam power, scanning speed, focal depth, line spacing and scanning angles, we obtain 2D photonic crystals with circular, elliptical, rectangular, or diamond-shape unit cells in a hexagonal or square lattice. An aspect ratio as high as 6.9 with 250 nm line width was achieved. In addition, we can controllably place defects of specific patterns, e.g. lines, dots, and Y-splitters, in the otherwise perfect photonic crystal. We also combine two-photon nanolithography with conventional UV photolithography to make 2D photonic crystals between waveguides. The combination of these two lithography methods was done on a single polymer film, suggesting potential for easy fabrication of complex photonic devices.
Fabrication and Characterization of Iron-Cobalt Alloy Magnetic NanoclusterWires by Thermal DecompositionMethod inMagnetic Fields
Authors: Moon Heesung , Nam Changhun , Kim Changwook , Kim Bongsoo , Lee Gangho
Published: June 2019

We present one-step synthetic method of magnetic alloy nanocluster wires. This process is simple, less expensive, and saves time. The gas is vaporized in a vacuum chamber from a solution of dicobalt octacarbonyl (Co2(CO)8) and iron pentacarbonyl (Fe(CO)5) mixture, and thermally decomposed by using a nichrome wire. The silicon substrate is placed in a homogeneous magnetic field which is produced by two permanent magnets (4000 gauss), so that the nanowires easily grow in the direction of the magnetic flux. From X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), we confirmed that these have a body-centered-cubic (BCC) structure with the magnetization easy axis of [110] direction, and a diameter in the range of 4 to 6 nm with a few micrometers in length. Also, we investigated that the squareness of the hysteresis loop is 61% for magnetic fields parallel to the wires and the coercivity along the easy axis is 670 oersteds by using vibrating scanning magnetometer (VSM).
Proton Beam Nano-Machining: End Station Design and Testing
Authors: Kan J.A. van , Bettiol A.A. , Watt F.
Published: June 2019

A new nuclear nanoprobe facility has been developed at the Centre for Ion Beam Applications (CIBA) in the Physics Department of the National University of Singapore. This facility is the first of its type dedicated to proton beam micromachining on a micron as well as a nano scale. The design and performance of the facility, which is optimized for 3D lithography with MeV protons, is discussed here. The system has been designed to be compatible with Si wafers up to 6”.

The production of good quality high aspect ratio microstructures requires a lithographic technique capable of producing microstructures with smooth vertical sidewalls. In proton beam micromachining, a high energy (e.g. 2 MeV) proton beam is focused to a sub-100 nm spot size and scanned over a resist material (e.g. SU-8 and polymethylmethacrylate (PMMA)). When a proton beam interacts with matter it follows an almost straight path, the depth of which is dependent on the proton beam energy. These features enable the production of nanometer sized polymer structures. Experiments have shown that post-bake and curing steps are not required in this SU-8 process, reducing the effects of cracking and internal stress in the resist. Since proton beam micromachining is a fast direct write lithographic technique it has high potential for the production of high-aspect-ratio nano-structures.
Thermal stability of Pt nanowires manufactured by Ga+ focused ion beam (FIB)
Authors: Inkson B.J. , Dehm G.
Published: June 2019

Pt nanowires have been produced by FIB deposition of Pt thin films in a commercial Ga+ focused ion beam (FIB) system, followed by cross-sectional sputtering to form electron transparent Pt nanowires. The thermal stability of amorphous FIB manufactured Pt wires has been investigated by in-situ thermal cycling in a TEM. The Pt wires are stable up to 580-650°C where partial crystallization is observed in vacuum. Facetted nanoparticles grow on the wire surface, growing into free space by surface diffusion and minimising contact area with the underlying wire. The particles are fcc Pt with some dissolved Ga. Continued heating results in particle spheroidization, coalescence and growth, retaining the fcc structure.
Magnetic Nanostructures Produced By Electron Beam Direct Writing
Authors: Wang J.P. , Zhao Y. , Zhou T.J. , Thong J.T.L. , Chong T.C.
Published: June 2019

We present a method of direct magnetic patterning of nonmagnetic CoC and CoTaC films by electron irradiation-induced nano-scale phase transition. CoxC1-x (0.4<X<0.8) films were prepared by co-sputtering. The as-deposited films with Co concentration less than 60% are amorphous and non-ferromagnetic. All films become ferromagnetic after annealing. Doping Ta into the CoC films can enhance the segregation of Co and C and therefore reduce the phase transition temperature. It is found that the magnetic properties of annealed (Co60C40)97Ta3 films are much better than that of annealed Co60C40 films at the same annealing condition. Magnetic nano-patterning (dot/line array) of the as-deposited CoC and Co(TaC) films was realized by subjecting them to electron irradiation using a focused 30keV electron beam with a current of 7.1 nA and dwell time per dot of 0.75 to 15.2 seconds. A 250nm magnetic dot/line array was produced by this method. It was also found that the time required to magnetically pattern non-magnetic (Co60C40)97Ta3 thin films (0.75 seconds) is much shorter than that required for Co60C40 films (3.8 seconds). The present method of magnetically patterning a nonmagnetic film has the potential application for nanoscale solid magnetic devices.
Electron beam induced effects in Cu/GeSe2amorphous films
Authors: Romero J.S. , Fitzgerald A.G.
Published: June 2019

Copper migration is observed in the SEM in amorphous GeSe2/Cu thin films when an electron beam is focused in pulsed or continuous operation on the surface of these thin films. The phenomenon can be explained using a simple model in which the population of D- centers is considered to increase upon electron irradiation. The increase in the D- center population is envisaged as due to the breaking of bonds by the electron radiation and by the constant presence of negative charge in irradiated regions. Changes in copper concentration of 20%-30% have been obtained. Additionally we have observed the local crystallization of amorphous GeSe2/Cu thin films in the TEM when the samples were subjected to intense electron bombardment. The crystalline product has been identified as Berzelianite (Cu2Se).
Magnetization dynamics of irradiation-fabricated perpendicularly magnetized dots inside a softer magnetic matrix
Authors: Devolder T. , Belmeguenai M. , Chappert C. , Bernas H. , Suzuki Y.
Published: June 2019

Global Helium ion irradiation can tune the magnetic properties of thin films, notably their magneto-crystalline anisotropy. Helium ion irradiation through nanofabricated masks can been used to produce sub-micron planar magnetic nanostructures of various types. Among these, perpendicularly magnetized dots in a matrix of weaker magnetic anisotropy are of special interest because their quasi-static magnetization reversal is nucleation-free and proceeds by a very specific domain wall injection from the magnetically “soft” matrix, which acts as a domain wall reservoir for the “hard” dot. This guarantees a remarkably weak coercivity dispersion. This new type of irradiation-fabricated magnetic device can also be designed to achieve high magnetic switching speeds, typically below 100 ps at a moderate applied field cost. The speed is obtained through the use of a very high effective magnetic field, and high resulting precession frequencies. During magnetization reversal, the effective field incorporates a significant exchange field, storing energy in the form of a domain wall surrounding a high magnetic anisotropy nanostructure's region of interest. The exchange field accelerates the reversal and lowers the cost in reversal field. Promising applications to magnetic storage are anticipated.
Ion Beam Stabilization of FePt Nanoparticle Arrays for Magnetic Storage Media
Authors: Baglin J.E.E. , Sun Shouheng , Kellock A.J. , Thomson T. , Toney M.F. , Terris B.D. , Murray C.B.
Published: June 2019

We describe the use of ion beam induced crosslinking to harden the organic matrix material of self-assembled arrays of monodisperse (4 nm) FePt nanoparticles, providing diamondlike carbon barriers to inhibit agglomeration of the nanoparticles under heat treatment. Such stabilization is necessary for the particles to survive the >500°C annealing required for growth of the fct L10 phase of FePt, whose magnetic anisotropy is necessary for application of such arrays for high density recording. Selective area irradiation of continuous nanoparticle coatings, using ion beams patterned over a full disk by stencil mask or with ion projection optics, followed by dissolution of the unexposed coating, is proposed as a means of fabricating extended bit patterns consisting of isolated “islands” of FePt nanoparticles, with characteristic dimensions of tens of nanometers.
A New Pathway for Si Nanocrystal Formation: Oxi-Reduction Induced by Impurity Implantation
Authors: Jacobsohn L.G. , Zanatta A.R. , Lee J.K. , Cooke D.W. , Bennett B.L. , Wetteland C.J. , Tesmer J.R. , Nastasi M.
Published: June 2019

In this work we show the feasibility of producing silicon nanocrystals by means of a new method based on the oxi-reduction of silicon dioxide induced by the presence of an impurity and annealing. The choice of magnesium as the impurity relies on its chemical properties of oxireducing the SiO2 matrix while avoiding the formation of Si-based compounds. The samples were obtained by 3×1016 and 1×1017 at/cm2 ion implantation into fused silicon dioxide followed by annealing in vacuum at 900 °C for 2 or 10 h. Rutherford backscattering spectrometry (RBS) characterized the chemical content and the Mg depth distribution. In all cases, photoluminescence measurements that showed a broad band starting around 1.8 eV with increasing emission intensity for lower energies, indicating the presence of Si nanocrystals. The analysis of the photoluminescence data in the framework of the quantum confinement theory suggests the existence of relatively large Si nanocrystals. The presence of these nanocrystals was also confirmed by Raman spectroscopy.
Luminescence of Silicon Nanocrystals in SiO2: Effects of Excitation Spectrum
Authors: Hryciw A. , White C.W. , Chow K.H. , Meldrum A.
Published: June 2019

Silicon nanocrystals formed by ion implantation and annealing of fused silica wafers show a strong, broad photoluminescence (PL) peak centered at a wavelength between 750 and 900 nm, depending on the processing conditions. This luminescence has been extensively investigated and trial device structures based on these materials have been built. However, relatively few studies also report the optical absorption spectra. In fact, the absorbance of these specimens is quite low (usually < 10%) at wavelengths greater than 450 nm (i.e., at the pump wavelengths typically used for PL studies). This suggests that in numerous studies of Si nanocrystals produced by ion implantation, only a small fraction of the nanocrystals is responsible for the observed PL at the typical pump wavelengths. In this study, we investigated how the PL spectrum and intensity depend on the power and wavelength of the pump laser. We find that the PL intensity approaches saturation at high pump fluences, and that the peak emission wavelength is sensitive to the excitation power. These observations can be attributed to the dynamics of the excitation/recombination processes at different energies, and indicate that considerable care must be taken when comparing the emission spectra of different specimens. Our data are uniformly consistent with a mechanism of light emission involving subgap states (i.e., radiative trap sites) and are not supportive of a “pure” quantum confinement model.
Gold clusters: the role of the ion energy in their formation
Authors: Thune Elsa , Carpene Ettore , Sauthoff Katharina , Seibt Michael , Reinke Petra
Published: June 2019

The rapidly growing interest in the deposition of size-selected nanoclusters on surfaces is motivated both by technology and by basic physical questions. Due to their finite size, small particles have totally different material properties compared to their bulk crystalline counterparts. Clusters have been deposited by a monoenergetic, mass-selected ion beam with low energies (10-500 eV) on amorphous carbon substrates, which are used to minimize the influence of surface crystallography and ion-induced structural changes. Gold clusters were deposited as a model system to study the ion energy dependence, the temporal evolution, and the influence of the temperature on the cluster distribution. For impact energies below 100 eV, surface processes dominate the cluster nucleation and growth. If higher energies are used, an increasing number of ions is implanted below the surface and different processes control the cluster formation. When the energy increases above 350 eV, the cluster size drastically drops below 5 nm. The clusters are analysed with different methods such as Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), and X-Ray Photoelectron Spectroscopy (XPS) to determine their size distribution, composition and structure.
Magnetite/Nickel andMagnetite/Cobalt Multilayer Nanostructures Obtained by Pulsed Laser Deposition
Authors: Sorescu Monica , Grabias Agnieszka , Diamandescu Lucian
Published: June 2019

Nanostructured magnetite/T multilayers, with T = Ni, Co, Cr, have been prepared by pulsed laser deposition. The thickness of individual magnetite and metal layers takes values in the range of 5 - 40 nm with a total multilayer thickness of 100 -120 nm. X-ray diffraction has been used to study the phase characteristics as a function of thermal treatment up to 550 °C. Small amounts of maghemite and hematite were identified together with prevailing magnetite phase after treatments at different temperatures. The mean grain size of magnetite phase increases with temperature from 12 nm at room temperature to 54 nm at 550 °C. The thermal behavior of magnetite in multilayers in comparison with powder magnetite is discussed.
Techniques for assessing the performance of circuit materials at microwave and millimetre-wave frequencies
Authors: Free Charles E
Published: June 2019

This paper discusses the techniques that are available for characterising circuit materials at microwave and millimetre wave frequencies. In particular, the paper focuses on a new technique for measuring the loss tangent of substrates at mm-wave frequencies using a circular resonant cavity. The benefits of the new technique are that it is simple, low cost, capable of good accuracy and has the potential to work at high mm-wave frequencies.
Synthesis, Characterization, Sintering and Leaching of Thorium – Uranium (IV) Phosphate Diphosphate Solid Solutions from Low-Temperature Precursors
Authors: Dacheux Nicolas , Clavier Nicolas , Podor Renaud , Coustumer Philippe Le
Published: June 2019

In the field of the immobilization of high level activity and long life radwaste for a deep underground repository, several phosphate matrices were already proposed to delay the release of actinides to the biosphere. Among them, Thorium Phosphate-Diphosphate (TPD) and associated solid solutions were considered. In order to improve the homogeneity of the samples prepared, a new way of preparation based on the precipitation in closed containers, at 150°C, of the Thorium-Phosphate HydrogenPhosphate hydrate (TPHP) or associated Thorium – Uranium (IV) Phosphate HydrogenPhosphate hydrate (TUPHP) was developed. Well crystallized and single phase TUPD solid solutions of general formula Th4−xUxP6O23 were prepared after heating above 950°C. Dense TUPD pellets were also obtained through a two-steps procedure involving a uniaxial pressing of the powder at room temperature then a heating treatment at 1250°C for 10 hours. Several properties of the pellets such as their chemical durability during leaching tests were considered carefully. All the normalized dissolution rates of powdered and sintered TUPD solid solutions remained low by comparison to that reported for several other ceramics studied in the same objective.
Strengthening Porous Skeletons by Metal Deposition from a Nanoparticle Suspension
Authors: Crane Nathan B. , Sachs Emanuel M. , Frank Andreas
Published: June 2019

Solid freeform fabrication (SFF) processes such as three-dimensional printing (3DP) and selective laser sintering (SLS) produce porous bodies that must be densified for many applications. New homogenous infiltration techniques can produce dense, homogenous parts of selected standard alloys, but the increased infiltration temperature dramatically increases creep deflection under self-weight. This paper reports on a method that improves dimensional stability by reducing creep deflection rates at high temperature. This method is applicable to all metal skeletons that must be strengthened without increasing shrinkage. In this method, the skeletons are reinforced by the addition of nanometer-sized particles dispersed in a liquid. The liquid is applied to the structure either during 3DP printing or after forming (3DP, SLS, pressing). The liquid is then evaporated, depositing the metal in the skeleton. The metal nanoparticles are sintered to density below the sintering temperature of the micron-scale skeleton particles. This concept is demonstrated using a suspension of 8–10 nm iron particles infiltrated into lightly sintered porous steel skeletons. When heated with an unsupported overhang to a typical infiltration temperature, creep deflection was reduced 50–80% with 0.5–1 wt% added metal.
SFF of Ceramic Parts: Literature Overview and Direct Experiments
Authors: Babini Gian N. , Fedele Andrea , Settineri Luca
Published: June 2019

The great development of Solid Freeform Fabrication (SFF) techniques from their introduction into the market, more than 20 years ago, has fueled their diffusion in the mechanical sector to the point that they are today an indispensable component of the process of designing, engineering and producing a mechanical parts.

At the same time, these techniques found application in different and even distant sectors, like biomedicine or architecture. This lead to the necessity of developing SFF processes suitable for materials different from those they were at the beginning thought for. Such techniques, taken from the original ones or entirely developed ex-novo, allowed for a surprising differentiation of the applications.

The fabrication of ceramic parts by SFF techniques is a relatively new field which is widening the role of such materials in sectors not traditionally covered.

The present paper reports a state of the art of the techniques that appear more effective for the production of ceramic goods, with representative or even functional properties.

Further, some results of 3D Printing experiments of alumina parts will be presented.
Three Dimensional Hydrogen Microscopy in Diamond
Authors: Dollinger Günther , Reichart Patrick , Bergmaier Andreas , Hauptner Andreas , Wild Christoph
Published: June 2019

We introduce proton-proton scattering at a microprobe of 17 MeV protons to quantitatively image three dimensional hydrogen distributions in polycrystalline diamond at a lateral resolution better than 1 μm and high sensitivity. The images show that most of the hydrogen of a <110>-textured undoped polycrystalline diamond film is located at grain boundaries. The average amount of hydrogen is (8.1±1.5)·1014 atoms/cm2 along the grain boundaries which corresponds to about a third of a monolayer. The content within the grain is below the detection limit of 1.4·1016 atoms/cm2 (0.08 at-ppm).