Successive Layer Deposition Research Articles

Successive Deposition of Metals in Solid Freeform Fabrication Processes, Part 1: Thermomechanical Models of Layers and Droplet Columns

Solid Freeform Fabrication (SFF) processes allow the automated building of three-dimensional shapes by successively depositing material in layers. Residual stress-induced tolerance losses are principal concerns in using these processes to create functional parts. Thermomechanical models of temperatures and stresses are presented, which are relevant to controlling residual stress effects in SFF processes. Models are applied to a particular SFF process; however, insights and conclusions are applicable to a large number of related processes. The temporal evolution of temperatures and stresses is investigated at two levels of detail. The successive deposition of layers of material is investigated first using one-dimensional simulations, approximating the build-up of residual stress in a multi-layered part. The successive deposition of a column of molten metal droplets (a technique used to create thick layers) is then modeled using two-dimensional axisymmetric simulations. Insights are given into process changes that can minimize residual stress-related effects in manufactured parts, including part constraint and localized preheating near the point of deposition. Results for thermomechanical interactions between droplets deposited in a column provide the foundation for studying interactions between adjacently deposited droplets, which is addressed in Part 2.

Investigation into the dielectric behavior of ferroelectric superlattices formed by pulsed laser deposition

In an attempt to reproduce the functional properties associated with relaxor electroceramics, pulsed laser deposition has been used to fabricate thin-film capacitor structures in which the dielectric layer is composed of a superlattice of Ba0.8Sr0.2TiO3 and Ba0.2Sr0.8TiO3. The properties of the capacitors were investigated as a function of superlattice periodicity. The dielectric constant was enhanced at stacking periodicities of a few unit cells, consistent with relaxor behavior. However, enhancement of the dielectric constant was found to be associated with high dielectric loss. Analysis of the imaginary permittivity as a function of frequency shows that fine-scale superlattices conform to Maxwell–Wagner behavior. This suggests that the observed enhancement of the real part of the dielectric constant is an artefact produced by carrier migration. A comparison of this data with that already published on dielectric superlattices suggests that previous claims of an enhancement in dielectric constant may also be due to the Maxwell–Wagner effect. The onset of Maxwell–Wagner behavior was attributed to increasing density of defect zones associated with discontinuities in the superlattice structures. In an attempt to exaggerate the influence of such zones, deliberate delays between deposition of successive dielectric layers were introduced. This resulted in reproduction of several features normally associated with relaxors: enhancement of dielectric constants by over an order of magnitude; strong frequency dispersion around and below Tm; migration of Tm with frequency. However, these features were again associated with relatively high loss.

In situ atomic force microscopy studies of surface morphology, growth kinetics, defect structure and dissolution in macromolecular crystallization

Surface morphologies of thaumatin, catalase, lysozyme and xylanase crystals were investigated using in situ atomic force microscopy. For thaumatin, lysozyme and xylanase crystals, growth steps having a height equal to the unit cell parameter were produced both by screw dislocations and two-dimensional nuclei. Growth of catalase crystals proceeded in alternating patterns exclusively by two-dimensional nucleation and the successive deposition of distinctive growth layers, each having a step height equal to half the unit cell parameter. The shapes of islands on successive layers were related by 2-fold rotation axes along the 〈0 0 1〉 direction. Experiments revealed that step bunching on crystalline surfaces occurred either due to two- or three-dimensional nucleation on the terraces of vicinal slopes or as a result of uneven step generation by complex dislocation sources. Growth kinetics for thaumatin and catalase crystals were investigated over wide supersaturation ranges. Strong directional kinetic anisotropy in the tangential step growth rates in different directions was seen. From the supersaturation dependencies of tangential step rates and the rates of two-dimensional nucleation, the kinetic coefficients of the steps and the surface free energy of the step edge were calculated. Adsorption of impurities which formed filaments on the surfaces of catalase and thaumatin crystals was recorded. Cessation of growth of xylanase and lysozyme crystals was also observed and appeared to be a consequence of the formation of dense impurity adsorption layers. Crystal growth resumed upon scarring of the impurity adsorption layer and clearing of the crystal surface with the AFM tip. Adsorption of three-dimensional clusters, which consequently developed into either properly aligned multilayer stacks or misaligned microcrystals was recorded. For catalase crystals, incorporation of misoriented microcrystals as large as 50×3×0.1 μm 3 produced elastic deformations in growth layers of ≈0.6%, but did not result in the defect formation. Etching experiments on catalase crystals revealed high defect densities.

Layered assemblies and electroluminescence in poly(arylenevinylene)-type conjugated polymers

In this review we describe some of our recent research in Jerusalem concerning electroluminescence phenomena from conjugated polymers with emphasis on poly(arylenevinylene) polymers and copolymers as the active emitting polymers. Electroluminescence (EL) is described in both simple spin-cast thin films and multilayers produced by a layer-by-layer deposition technique. Newly synthesized copolymers and polymer heterostructures especially designed and useful for organic light-emitting diodes (OLEDs) were prepared by a two-step polymerization of α,α-bis-sulfonium salt of a p-xylene derivative. Copolymerization of different monomers allows one to control the HOMO—LUMO energy gap of the copolymer, and thus to tune the color of the emitted light. This notion of the color of light emitted in EL by performing relatively simple modifications has been termed chemical tuning and is an important part of the research carried out in the field of electroluminescence from conjugated polymers. Although most commonly thin film OLED devices are prepared by spin-casting, we have also developed a novel method of layer-by-layer (self-)assembly for device fabrication by which heterostructures containing active luminescent layers are formed by successive deposition of charged layers of an insulating polymer and conjugated polymer by a simple dipping procedure. We have shown that heterostructures prepared in this manner are structurally modulated and are ordered perpendicular to the substrate. The polymer/polymer interface roughness at the active layer/spacer layer interface is of the order of 10 A . Heterostructures prepared by the layer-by-layer technique showed increased stability in OLED devices. Furthermore, the luminescence in these multilayers is blue-shifted relative to spin-cast films provided that the thickness of the spacer layer is large in comparison to the thickness of the emitting conjugated polymer layer. We attribute this phenomenon to confinement effects. An additional emphasis in this review is given to recent studies on transient EL from poly(phenylenevinylene) in the presence of strong electrical pulses. We have demonstrated that at high fields an additional UV-violet EL emission, in addition to the typical green-yellow EL emission, is observed. We have proposed that the UV-violet emission is due to the formation of hot carriers in the strong electric field.

Properties of periodic α-Si:H/a-SiNx:H structures obtained by nitridization of amorphoussilicon layers

The kinetics of nitridization of a-Si:H layers, the properties of the structures that are formed and a-Si:H in them have been investigated. The changes occurring in the resistance of the a-Si:H layers in the course of nitridization are described in terms of the competition between doping, transport, and change in the thickness of the remaining a-Si:H layer. The experimental data on the band spectrum of superlattices with a-Si:H and a-SiNx:H layer thicknesses ∼35 A and ∼5 A, respectively, are in agreement with calculations in a model of interacting quantum wells with m*=(0.36±0.1)m0. Comparison of the properties of superlattices obtained by deposition of successive layers and nitridization of the a-Si:H layers showed that the latter can have a higher “structural perfection.”

Initial Stages of MOCVD Growth of Gallium Nitride Using a Multi-Step Growth Approach

ABSTRACTA multilayer buffer layer approach to GaN growth has been developed in which the thermal desorption and mass transport of low temperature buffer layer are minimized by deposition of successive layers at increased temperatures. High quality GaN with featureless surface morphology has been grown on (0001) sapphire substrate by metalorganic chemical vapor deposition using this multilayer buffer layer approach. The lateral growth and coalescence of truncated 3D islands (TTIs) nucleated on low temperature buffer layers at the initial stage of overlayer growth is affected by the thickness of the final buffer layer on which nucleation of TTIs takes place. The effect of the thickness of this buffer layer on the quality of GaN is studied by using scanning electron microscopy, van der Pauw geometry Hall measurements and cathodoluminescence and an optimum value of 400Å is obtained.

Solidification of aluminium spray-formed billets

A critical part of the billet spray-forming process is the successive intermittent deposition of thin layers of semi-solid aluminium alloy at different points on the top surface of the billet. Each thin layer is made up of a large number of impacted semi-solid spray droplets. As successive layers of alloy are deposited significant re-melting and re-freezing of underlying layers can occur. If the layers become too dry, high porosity will result; if they are too wet, fluid dynamic surface instabilities are possible. In extreme cases no billet will form. The process is essentially incremental, so that heat fluxes within the deposit very close to the top surface play a major role in determining the final deposit microstructure.

Residual stress-driven delamination in deposited multi-layers

An analysis is presented of the problem of residual stress-driven delamination in materials or parts manufactured by successive layer deposition. A direct application of this work is to parts that are built using rapid prototyping-based layered manufacturing methods. A two-dimensional model is presented that allows calculation of steady-state energy release rates for delamination cracks. Results from a finite element model of the problem are also presented. The results verify the steady-state analysis and show that it is applicable over a wide range of part dimensions. Crack displacement modes are also extracted from the finite element model. Results are presented for two- and four-layer bi-material configurations, over a large range of material mismatches. Examples are given of how this work can be used to identify critical interfaces where delamination is most likely to occur and thus to predict the susceptibility of multi-layers to delamination.

Self-assembled aromatic oligoazomethines on polar surfaces

The reaction between aromatic dialdehydes and diamines is studied by differential scanning calorimetry-thermal gravimetric analysis (DSC-TGA) measurements. It can be shown that the condensation reaction starts at temperatures below 100 °C. Thus, the high rate and the high conversions of this reaction lead to a new technique of thin-film growth on polar substrates, by successive deposition of monomer layers under high vacuum. Gravimetric measurements show that the first step is a bonding between the organic molecules and the surface. This leads to an oriented prime layer of deposited monomers. In the following steps reactive partners are deposited successively on the surface, layer by layer. Thin films grown by this technique are studied by UV-Vis spectroscopy. These well-ordered films can be applied as interfaces between organic and inorganic layers in solid-state optoelectronic devices.

Successive Deposition of Alternate Layers of Polyelectrolytes and a Charged Virus

Successive Deposition of Alternate Layers of Polyelectrolytes and a Charged Virus

Assembly of thin films by means of successive deposition of alternate layers of DNA and poly(allylamine)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAssembly of thin films by means of successive deposition of alternate layers of DNA and poly(allylamine)Yu. Lvov, G. Decher, and G. SukhorukovCite this: Macromolecules 1993, 26, 20, 5396–5399Publication Date (Print):September 1, 1993Publication History Published online1 May 2002Published inissue 1 September 1993https://doi.org/10.1021/ma00072a016RIGHTS & PERMISSIONSArticle Views1354Altmetric-Citations421LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Preparation of PbTiO3 Thin Film on Si by ArF Excimer Laser Ablation

Deposition behavior of PbTiO3 thin films on Si substrates having native oxide has been investigated by the laser ablation method using an ArF excimer laser. Atomic ratio Pb/Ti in the film decreases with increase of substrate temperature and laser shot period, but only changes slightly with increase of laser fluence. Preferentially c-axis-oriented film on Si substrate is obtained during the deposition in O2 gas of 13 Pa at the substrate temperature of 500°C and low laser repetition rate. The change of Pb/Ti and the origin of the preferential orientation are explained by Pb reevaporation from the substrate and successive deposition of Pb and Ti layers. Dielectric constant and the remanent polarization are about 130 and 30 µC/cm2, respectively.

Multiple coating of titanium-boron oxide sol-gel on glass

TiO 2/1b B 2 O 3 composite thin films have been coated on microscope slides by a multiple dip-coating technique. Films produced with heating steps between the deposition of successive layers exhibit a better optical quality than those without. The former have a smaller grain size, less than 30 nm as measured by SEM, and therefore result in less transmittance loss at the short wavelength region. X-ray diffraction studies show that these films are amorphous even after 500° C calcination, while films produced without intermediate heating become slightly crystallized after the same treatment. The thickness of the coated film is proportional to the number of layers applied. A film about 200 nm in thickness can be produced by just four coatings. The refractive index of the film is 2.23 as evaluated from the transmission spectrum.

Preliminary Studies of GaAs Deposition on Au(100), (110), and (111) Surfaces by Electrochemical Atomic Layer Epitaxy

The development of a new method for epitaxial growth of compound semiconductors is briefly described: electrochemical atomic layer epitaxy (ECALE). ECALE is based on the successive underpotential deposition (UPD) of atomic layers of different elements to form a compound. Preliminary studies of the ECALE deposition of were performed in a thin‐layer electrochemical cell with a polycrystalline Au electrode. Potentials required for oxidative UPD of As and reductive UPD of Ga were evaluated with different solution concentrations and pH's. Subsequent studies were performed in an ultrahigh vacuum surface analysis instrument interfaced to an electrochemical cell. A gold single crystal supporting the three low‐index planes was used in these studies. Auger electron spectroscopy (AES) and coulometry were used for surface composition analysis, while low energy electron diffraction (LEED) was used for structural analysis. Arsenic electrodeposition from solutions resulted in a succession of LEED patterns as the coverage increased on each face. Low coverage structures, corresponding to less than one monolayer of As, were observed only on the (100) and (110) faces: a at coverage and a at coverage. Oxidative UPD of As from was observed only on the (100) and (110) faces, resulting in low coverage ordered structures analogous to those formed during deposition from at low As coverages. Ga UPD from solutions was observed on all three faces, although it resulted in disordered layers of Ga oxide upon removal of the substrate from solution, due to partial oxidation of the Ga in contact with water in the absence of potential control. UPD of Ga on As‐covered surfaces ( and ) resulted in stoichiometric coverages of Ga and As on both. Structures displaying and LEED patterns were formed on the (100) and (110) faces, respectively. The stability of in aqueous solutions was evaluated. Potentials vs.pH plots were calculated for several concentrations of dissolved Ga and As species.

Cell surface interactions between sorghum roots and the parasitic weed Striga hermonthica: cytochemical aspects of cellulose distribution in resistant and susceptible host tissues

Cell surface interactions between sorghum roots and the parasitic weed Striga hermonthica were investigated using light and electron microscopy. An exoglucanase–gold complex was used to study the distribution of cellulose in host tissues of resistant and susceptible cultivars. In the susceptible cultivar, intrusive cells of S. hermonthica could reach xylem elements, whereas in the resistant cultivar, development occurred mainly in the outer cortex. Invasion of the susceptible cultivar was accompanied by wall alterations and by the release of cellulose-rich fragments likely detached from host walls through the action of lytic enzymes. The occurrence of wall alterations at a short distance from the point of parasite penetration provided indirect evidence for extracellular diffusion of cellulolytic enzymes. Tylose formation and accumulation of coating material along secondary thickenings of some xylem vessels were late responses observed in the susceptible cultivar. In the resistant cultivar, heavy deposition of successive layers of cellulosic material occurred in outer tissues. Accumulation of this material may constitute a defense reaction against penetration. Electron-dense coating material was noticeable in cortical cells and occasionally in xylem vessels. Defense reactions observed in both sorghum cultivars upon parasite attack differed in their temporal and spatial distribution. Key words: Striga, sorghum, haustorium, root anatomy, gold cytochemistry, cellulose, resistance.

Solitons in a ring superlattice

We consider the propagation of electromagnetic solitons in a ring superlattice formed by the successive deposition of coaxial ring-shaped layers lying in parallel planes. In contrast to a rectilinear (infinite) superlattice, in which either one soliton (a single solution) or an infinite number of solitons (fluxon solution), any finite number of equidistant solitons is possible in a ring superlattice. We calculate the constant component of the electric field along the axis of the superlattice and the density of the current of electron drag by solitons (“solitonelectric current”).

Magnetic and Magneto-Optical Properties of Mn(Sb1-xBix) Thin Films

Mn(Sb-Bi) alloy films with an NiAs-type structure were prepared by successive deposition of Mn layers onto Sb-Bi alloy layers, followed by annealing at temperatures up to 500oC. A single NiAs-type phase was obtained over the wide composition range 52≦Mn≦62 at%, 35≦Sb≦48 at%, 0≦Bi≦5 at%. Systematic experimental investigations of the magnetic and magneto-optical properties of these films were carried out. These investigations clarified (1) the dependences of M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> , H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> on composition, and (2) the dependence of θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</sub> on the composition and the wavelength λ (0.4 to 1.1 μm). The magnitudes of M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> and θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</sub> were found to depend on the Mn content. Maximum values of M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> and θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</sub> were 600 emu/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and 0.7° (at λ=0.633 μm) respectively for films containing 52 at% Mn. The maximum (positive) value of K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> (=1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> erg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) was obtained for films containing about 62 at% Mn.

A self-alignment process for amorphous silicon thin film transistors

A new method of fabricating amorphous Si thin film transistors (a-Si TFT's) has been developed. This method uses the self-alignment process, which also includes the successive deposition of gate insulator and active amorphous Si layers in one-pumpdown time in an RF glow discharge apparatus. This method greatly simplifies the fabrication process and results in stable device performance. The practicability of this method was confirmed by experimentally fabricated devices.

Vitreous asteroid bodies. Ultrastructural characteristics and composition.

Ultrastructural studies were performed on five cases of asteroid hyalosis of the human vitreous. The large asteroid bodies were composed if intertwined ribbons of multilaminar membranes with a 6-nm periodicity characteristic of complex lipids, especially phospholipids, lying in a homogeneous background matrix. Clumps of dense material were interspersed throughout the asteroids, and swirls of thin membranous strands often surrounded them. The structure of small asteroid bodies suggested that the lipid ribbons resulted from deposition of successive lipid layers on the thin membranes, so that bodies with variable degrees of lipidization occur. By energy-dispersive x-ray analysis, calcium and phosphorus were the main elements detectable in asteroid bodies of all sizes. Electron-diffraction structural analysis showed that calcium hydroxyapatite and, possibly, other forms of calcium phosphate crystals were present in the focal densities. Calcium may also be bound to phosphate groups in the phospholipids. The large quantity of complex lipids and calcium in asteroids bodies suggests a derivation from sources exogenous to the vitreous.

Problémes posés par la synthése et la réalisation de filtres spectraux multidiélectriques

Many spectral filtering problems require the use of assemblies of layers having thicknesses which bear no obvious relationship to each other. This is often the case when precisely defined properties are required over a wide spectral range. Two major problems arise when such filters are to be realized. The first ofthem concerns the design of a stack best satisfying filtering requirements (synthesis). This design must be performed by successive iterations and since the number of unknown parameters is very large it is necessary to use fast procedures for the computation. We describe here a new procedure based on a Fourier transform method. With recent progress in this field, it is now possible to derive theoretical designs to satisfy almost any filtering requirement. The second problem to be solved regards the production of the multilayers so defined. For optical monitoring of non-quarter wave multilayer stacks it is necessary to use large bandwidth control systems. Such a monitoring method is described and its advantages over methods using one single wavelength are pointed out. Finally, we note that it may be interesting to compensate residual thickness errors by using a minicomputer working in real time during the deposition of successive layers. Such a procedure avoids the cumulative effects of successive errors.