Formation Of Island Structures Research Articles

Effect of formulation and process on morphology and electrical conductivity of Ag-graphene hybrid inks

Conductive inks are considered very promising for device fabrication on flexible substrates and large areas. Silver (Ag)-graphene hybrid inks offer many opportunities, including cost/conductivity optimization for different applications. In this work, several conductive hybrid ink formulations containing Ag nanostructures and graphene derivatives were prepared using different processing strategies and thoroughly characterized. SEM and morphological studies were used to explore the probable reasons for the difference in electrical conductivity of various inks. Strong interaction between Ag nanoparticles and graphene layers prevented the formation of island structures in films, especially at high temperatures. While Ag nanowires and graphene layers formed a uniform, dense three-dimensional network, offering high electrical conductivity. Additionally, an improvement of electrical conductivity by using graphene quantum dots as a graphene component in hybrid inks was observed, which was related to creating new conductive bridges. The highest conductivity of prepared inks varied in the range of 2.67 × 102 S/cm to 4.0 × 104 S/cm. Finally, formulation guidelines were offered to be used for inks by several printing methods.

Formation of Island Structures during Melting Process of Tin Films on Amorphous Carbon Substrate

Formation of Island Structures during Melting Process of Tin Films on Amorphous Carbon Substrate

Stochastic approach to simulation of evaporation-triggered multiple self-assembly of mixed metal nanoparticles and their variable superradiance

We developed a design principle for the evaporation-triggered heterogeneous assembly of different kinds of metal nanoparticles in a two-dimensional environment. A dynamic Monte Carlo simulation shows the formation of island structures of gold nanoparticles (gold islands) surrounded by smaller silver nanoparticles (silver matrix) during the evaporation of organic solvent from the dispersion liquid on the water surface. Our developed principle revealed the spontaneous change in multiple interactions between gold and silver nanoparticles owing to the presence or the absence of solvation repulsion, which plays a crucial role in the formation of gold islands in the silver matrix. Not only the randomly arranged gold islands, but also the surrounding silver matrix phase contributed to the wavelength-tunable light scattering enhanced by a factor of 102 due to the superradiance effect. These results will pave the way for the design of multicolored optical devices based on random plasmonics via controlled interparticle interactions.

Enhanced Sensitivity for Electrochemical Detection Using Screen-Printed Diamond Electrodes via the Random Microelectrode Array Effect.

The electrochemical properties of screen-printed diamond electrodes with various insulating polyester (PES) resin binder/boron-doped diamond powder (BDDP) ratios were investigated for high sensitivity electrochemical detection. For PES/BDDP weight ratios in the range of 0.3-0.5, the BDDP-printed electrodes exhibited cyclic voltammetry (CV) characteristics for Fe(CN)6(3-/4-) that are typical of a planar electrode, whereas microelectrode-like characteristics with sigmoidal CV curves were observed for PES/BDDP ratios of 1.0-2.0. Cu elemental mapping images of copper-electrodeposited BDDP-printed electrodes indicated the formation of island structures with conductive BDDP domains surrounded by an insulating PES matrix for large PES/BDDP ratios. The electrochemical detection of ascorbic acid (AA) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) was also investigated using polycrystalline BDD thin-film and BDDP-printed electrodes (PES/BDDP ratio = 0.3 and 1.0). As a result, the signal-to-background (S/B) ratios for the voltammetric detection of AA and 8-OHdG were in the order BDDP-printed electrode (PES/BDDP = 1.0) > BDDP-printed electrode (PES/BDDP = 0.3) > polycrystalline BDD thin film electrode, based on the large faradaic current with respect to the background current. Therefore, the BDDP-printed electrode with a large insulating binder/BDDP ratio has the potential for use as a disposable electrode for electrochemical detection. The electrode is cheaper, lighter and more sensitive than conventional BDD electrodes.

Effect of compressive strain relaxation on surface morphology in GaAsP growth on GaP substrate

Surface morphology change of GaAs0.6P0.4 and GaAs layer grown on GaP substrate during growth was investigated by an Atomic Force Microscope. The compressive strain in the GaAsP layer was relaxed by {111} plane slips while that in the GaAs layer was relaxed by formation of island structures. During growth, the GaAs layer showed much flatter surface morphology. It was found that the mechanism of the strain relaxation largely affects the surface morphology. Finally, we compared the critical thickness for the {111} plane slip and the transition thickness in which the layer growth mode transits from a layer growth to an island growth to explain the different strain relaxation mechanisms.

MgO(100) 기판 위에 증착된 Ag/CoFeB 박막의 스퍼터링 조건에 따른 미세성장구조 변화 연구

본 연구에서는 DC 마그네트론 스퍼터링을 이용해 MgO 단결정 기판 위에 성장된 Ag/CoFeB 박막의 스퍼터링 조건에 따른 박막 미세구조의 변화를 연구하였다. Ag 박막의 결정성 및 표면 거칠기는 인가전력(sputtering power) 및 증착온도의 변화에 따라 증착온도가 증가하는 경우 (200) 방향의 결정성이 향상되는 것을 확인하였으며, 인가전력이 증가되는 경우 표면 거칠기가 감소하는 것을 확인하였다. 또한 고분해능 TEM(transmission electron microscopy) 및 XRR(X-ray reflectivity) 측정을 통해 MgO 기판 위 Ag층의 켜쌓기 성장 및 MgO 기판과 Ag층 사이에 산화층에 해당하는 계면층이 존재하는 것을 알 수 있었으며, 증착온도의 증가에 따른 Ag의 섬상구조 형성 및 intermixing 효과에 의한 Ag/CoFeB 계면층의 변화 및 자기적 특성의 변화를 연구하였다. In this study, we have systematically investigated the effect of sputtering conditions on the microstructural properties of Ag/CoFeB thin film on MgO substrate. It was found that the crystallinity and surface roughness of the Ag film strongly depends on the Ar sputtering pressure and sputtering power. Epitaxial growth of Ag(100) film on MgO(100) substrate was achieved under the sputtering conditions of high sputtering power and elevated temperature. XRR (X-ray reflectivity) and high-resolution TEM (transmission electron microscopy) measurements also revealed the interfacial roughening in the Ag/CoFeB interface due to the island structure formation and intermixing between Ag and CoFeB.

Mixed homopolymer brushes grafted onto a nanosphere

Microphase separation of mixed A∕B polymer brushes grafted onto a nanosphere with its radius comparable to the size of polymers is investigated by numerical implementation of the self-consistent field theory. The idea is to embed the sphere within a larger cubic computational cell and use a "masking" technique to treat the spherical boundary. The partial differential equations for the chain propagator on the sphere can thus be readily solved with an efficient and high-order accurate pseudospectral method involving fast Fourier transform on a cubic cell. This numerical technique can circumvent the "pole problem" due to the use of a spherical coordinate system in conventional finite difference or finite element grid. We systematically investigate the effect of the total grafting density, composition, chain length asymmetry between two grafted homopolymers as well as spherical radius, i.e., substrate curvature on the formation of island structure with specific arrangement in a regular lattice. A series of island structures with different island numbers representing specific structure symmetry ranging from 2 to 12 except for 11 are found, in contrast to conventional hexagonal arrangement for polymer brushes on a planar substrate. Among these parameters, the spherical radius plays a significant role in determining the type of island structures, i.e., the morphology formed on the sphere.

Thin film semiconductor islands and numerical experiment

The distribution functions of island nuclei of germanium melt drops on Si(100) substrate over lateral sizes and heights in the presence of a surface linear defect are obtained in a numerical experiment simulating the initial stage of the first-order phase transition. A similar model of heterogeneous condensation of silicon carbide vapor is discussed. Quasi-linear kinetic partial differential equations are solved by the efficient numerical method of stochastic analogue of nonequilibrium processes. The Volmer-Weber mechanism of cluster formation from melt islands, their crystallization, and island structure formation on the substrate are considered.

Alkyl chain grafting on silica–zirconia mixed oxides: preparation and characterization

Silica–zirconia mixed oxide substrates were prepared and grafted with C18 alkyl chains using n-octadecyltrichlorosilane. Si : Zr molar ratios in the mixed oxide samples before and after alkyl chain modification were determined by X-ray photoelectron spectroscopy (XPS). Nitrogen sorption measurements provided the porous features of these materials. By means of solid-state 29Si nuclear magnetic resonance (NMR) the amounts of the silanol groups present in the as-prepared, humidified and grafted mixed oxide systems as well as the degree of cross-linking of the silanes were obtained. 13C NMR spectroscopy was used to examine the conformational order of the n-octadecyl chains grafted on the silica–zirconia mixed oxide substrates. Similar information was available from variable temperature Fourier transform infrared (FTIR) investigations. Scanning electron microscopy (SEM) measurements and energy dispersive X-ray (EDX) analyses yielded the morphological features of the solid substrates and information about the distribution of the alkyl chains on the oxide surfaces. The annealing temperature for the preparation of the mixed oxides and the elemental composition of the samples, i.e. relative amount of the oxide components, were found to determine the surface properties and in turn the alkyl chain assembly on the mixed oxide surfaces. FTIR and solid-state 13C NMR data gave evidence for an unusual high conformational order of the grafted C18 alkyl chains in all samples, irrespective of the low surface coverage, which exceeds comparable C18 and C30 grafted silica and metal oxide systems. This finding was attributed to the formation of island structures with aggregated octadecyl chains of high conformational order due to strong intermolecular interactions. Differences in the conformational order of the various samples most likely arise from vertical polymerization which varies with the actual sample.

In-situ ellipsometric monitor with layer-by-layer analysis for precise thickness control of EUV multilayer optics

Ion beam sputtering fabrications of Mo/Si multilayers for soft X-ray mirrors were studied using an automatic null ellipsometer. The ellipsometric growth curves plotted on the complex plane showed island structure formation for every Mo layer grown on Si when deposition was performed with a 1400 V Ar ion beam. The ellipsometric growth curves indicated that the multilayers fabricated with 900 V ions had sharper and smoother interfaces compared to those fabricated with 1400 V ions. Quantitative layer-by-layer analysis showed that the Si layers deposited at 1400 V became optically isotropic as thin as 1 nm. These data depict the usefulness of our in-situ ellipsometer in controlling layer thickness and also optimizing the deposition condition to form homogeneous and optically isotropic layer structures.

Fabrication and microstructure of high coercivity FePt thin films at 400 °C

L 1 0 phase FePt thin films deposited on MgO (100) single-crystal substrate with good (001) texture were investigated. Epitaxial growth of the FePt (001) films was observed with a deposition temperature of 400 °C. With ultrathin Ag intermediate layers deposited between FePt layers, the film structures changed from an interconnection network to an isolated-island character. The perpendicular coercivity of the FePt film dramatically increased from 6.5 to 32.5 kOe. The improvement of the magnetic properties may be attributed to the formation of island structures by the additive Ag in the FePt films.

High coercivity FePt thin films with Ag intermediate Layers deposited at 400/spl deg/C

L1/sub 0/ phase FePt thin films deposited on amorphous Corning glasses and single crystal MgO (100) substrates were investigated. Epitaxial growth of the FePt [001] films was observed on MgO substrate at a deposition temperature of 400/spl deg/C. With ultrathin Ag intermediate layers deposited between FePt layers, the film structure changed from interconnection network to isolated-island character. The perpendicular coercivity of the FePt film increased to about 32 kOe with intermediate layers inserted. The improvement of the magnetic properties may be attributed to the formation of island structures by the additive Ag layers in the FePt films.

Metal-induced crystallization of amorphous Si 1− xGe x by rapid thermal annealing

Metal-induced crystallization (MIC) of amorphous Si 1− x Ge x ( x=0.2 and 0.3) thin films on SiO 2 by rapid thermal annealing (RTA) at 300–600 °C has been investigated. At low annealing temperature, Ni reacted with a-Si 1− x Ge x films to form Ni germanosilicides. The crystallization temperature of a-Si 0.7Ge 0.3 and a-Si 0.8Ge 0.2 was lowered from 500 to 400 °C and 600 to 500 °C, respectively, with capping Ni. The Ni germanosilicide grains were observed to form in the annealed Ni/a-Si 0.7Ge 0.3 and Ni/a-Si 0.8Ge 0.2 samples after annealing at 500 °C. The formation of island structure containing a small amount of Ge at the bottom of polycrystalline Si 1− x Ge x films is attributed to the preferential reactions of Ni with Si to Ge.

デュアルイオンビームスパッタ法を用いたＡｕ超薄膜の作製とその紫外域透明電極への応用

Technologies of fabricating resent semiconductor devices such as electro-luminescence (EL) devices, LED, laser sources and solar cells require conductive films with high transparency to ultraviolet light. Ultrathin Au film is a good candidate for this application, wherein the transparency goes up with a decrease of film thickness. However, it has been known that ultrathin Au films deposited by several methods such as evaporation and conventional sputtering are not conductive due to the formation of island structure at the initial growth stage. In this study, the initial island growth was controlled by Ar bombardment using an ion source, and ultrathin conductive Au films were deposited by dual ion beam sputtering [DIBS]. The optimum condition for the sputtering and Ar bombardment was studied. Again, the two kinds of Au films, without Ar bombardment [IBS], and with Ar bombardment [DIBS], were deposited as a function of thickness (tF). The tF dependence of the morphology and the resistivity (ρ) and the transmittance (T) was investigated. The films deposited by IBS and DIBS transformed from island structure to layer structure at tF of 8.0 and 2.8 nm, respectively. The films showed conductive properties above these critical tF. T of the films was higher than 62% for IBS and 75% for DIBS at a wavelength between 200 and 400 nm. It was found that the technique of Ar bombardment was useful to suppress the initial growth of island structure.

Formation of island structures in the course of deposition of weakly supersaturated aluminum vapors

The formation of island structures in the course of deposition of weakly supersaturated aluminum vapors is investigated by transmission electron (TEM) and scanning electron (SEM) microscopies and electron microdiffraction. The aluminum layers are prepared by dc magnetron sputtering in a high-purity Ar atmosphere. The conditions of formation of statistically homogeneous nanocrystalline layers depend on the deposition temperature and the partial pressures of Ar and reactive gases. The wetting angle between islands and the substrate is calculated from the derived relationships as a function of the condensation temperature.

PEEM AND SXES CHARACTERIZATION ON THE SURFACE AND INTERFACE OF THE TRANSITION-METAL/SiC SYSTEM

The Si L2,3 and C K soft X-ray emission spectra of the interface of the Ti(50 nm)/4H-SiC(substrate) system, thermally annealed from 800°C to 1000°C and characterized by soft X-ray emission spectroscopy (SXES), revealed the formation of a reacted region composed of silicides with Ti 5 Si 3 as the majority formed species and carbides in TiC-like bonding. Also, the photoemission electron microscopy (PEEM) imaging of Ti(10 nm) film on 3C-SiC surface during in situ heat treatment showed the formation of island structures (in ring clusters) at ~ 800°C.

Nucleation and growth behavior of epitaxial Pb(Zr,Ti)O3/MgO(100) observed by atomic force microscopy

Nucleation and growth of epitaxially grown lead zirconium titanate (PZT) thin films on as-cleaved MgO(100) substrate were studied with X-ray diffraction and atomic force microscopy using a tapping mode. The films were grown by MOCVD at different deposition times from 10 to 1800 s at 650°C. At the initial stage of the film deposition, the growth of layer-like PZT thin film was observed up to thickness of 1.0–1.2 nm, which corresponds to 5–6 monolayers (ML) of PZT. The chemical composition of initial layer was stoichiometric PZT. Over the thickness, formation of island structure was observed at thickness of around 2 nm. Then coalescence of three dimensional nuclei to form monodispersed grain size distribution via bimodal distribution and grain growth proceeds not only perpendicular but also horizontal to the substrate with increasing deposition time. This indicates that the growth mechanism coincides with Stranski–Krastanov (SK) growth mode. It was also clarified that the grain size distribution corresponds to the root mean square (rms) roughness on the preparation of thin film. The critical thickness of PZT thin film on MgO(100) substrate was 1.0–1.2 nm in good agreement with other reported epitaxial grown thin films.

Reconnection: Space plasma simulations for multi-spacecraft satellite observations in the ISTP Era

In the ISTP era multi-spacecraft measurements have not only become a tool for phenomenological and correlative studies of the solar- terrestrial coupling. They also open new opportunities to test, verify or falsify basic physical concepts. For the use of multi-spacecraft measurements in this sense numerical modelling and simulations are becoming more and more a necessary tool for interpreting the observations correctly. We take the reconnection process as an example. Reconnection is supposed to release magnetic field energy from the sun, to couple the Earth's magnetosphere to the solar wind and to suddenly release previously stored magnetic energy in the course of magnetospheric substorms. Hence, reconnection is a key concept in the solar-terrestrial relationship. On the other hand it is difficult to theoretically grasp collisionless reconnection in space plasmas. This complicates its experimental verification.In this paper we present some selected essentially kinetic features of spontaneous reconnection through collisionless thin current sheets in two and three dimensions: These should be observable, e.g., at the onset of magnetospheric substorm. The kinetic approach is necessary due to the cross-scale coupling, inherent to collisionless reconnection. We demonstrate that microscopic magnetic islands of the Debye length scale are always present through thin current sheets. They are, however, reversible and occur at the level of thermal fluctuations. Macroscopic reconnection and island structure formation starts with irreversible energy transfer from fields to plasma. We demonstrate the different routes to macroscopic merging in two and three dimensions. In two dimensions Landau damping in the potential wells of magnetic islands causes the classical slow tearing mode instability. In three dimensions a sausage mode bulk current instability accelerates the transition to macroscopic reconnection. As a result three-dimensional magnetic islands are formed, which are limited in all three spatial directions. We, finally, demonstrate how multi-spacecraft observations of the ISTP era together with well posed computer simulations can help to understand col lisionless reconnection by means of in situ measurements in the Earth's magnetosphere.

Focused ion beam etching of resist/Ni multilayer films and applications to metal island structure formation

A new method to fabricate single-electron tunneling structures with magnetic materials using focused ion beam (FIB) sputtering and lithography techniques is proposed. By using this method, a small metal island with a size comparable to or smaller than the FIB diameter, connected with source and drain electrodes via tunnel junctions, can be fabricated. In the present article, some important parameters in this method, such as sputtering yields of the photoresist (AZ 1350) and nickel (Ni) layers, were measured and cross-sectional images of the grooves delineated on a AZ/Ni/SiO2 substrate, which is the basic structure in this method, were observed. At present, a 0.4-μm-wide groove is obtained. However, this width is limited not by a fundamental process but by noise in the scan signal and stage vibration.

Synthesis and Behavior of the Polymer Covering on a Solid Surface. 3. Morphology and Mechanism of Formation of Grafted Polystyrene Layers on the Glass Surface

Polystyrene films have been grafted by radical polymerization in situ on the surface of glass slides. The morphology of these films resulting from different grafting temperatures has been investigated by both the contact angle method and scanning probe microscopy with respect to the grafting time. At a grafting density regime where the theory proposes the existence of a homogeneous layer, the formation of island structures of grafted polymer with a size substantially higher than expected by the theory has been observed. Overshot polymer structures of large sizes are created. The amount of grafted polymer is substantially higher than that predicted from the conception of monolayer covering. The grafting layer becomes impermeable for water only at a high amount of grafted polymer, which corresponds to the multilayer structure of the coating. We suggested a mechanism for the grafting process that included at least three stages: (a) first, a brushlike polymer layer is formed; (b) subsequently, a second layer of ungrafted chains is created in the regime when excess chains are forced out from the first layer; (c) big polymer clusters, with an average size of 100−200 nm due to gel polymerization in the clusters, formed in the force out regime.