The structural and piezoresponse properties of c-axis-oriented Aurivillius phase Bi5Ti3FeO15 thin films deposited by atomic vapor deposition

The deposition by atomic vapor deposition of highly c-axis-oriented Aurivillius phase Bi 5Ti 3FeO 15 (BTFO) thin films on (100) Si substrates is reported. Partially crystallized BTFO films with c-axis perpendicular to the substrate surface were first deposited at 610°C (8 excess Bi), and subsequently annealed at 820°C to get stoichiometric composition. After annealing, the films were highly c-axis-oriented, showing only (00l) peaks in x-ray diffraction (XRD), up to (0024). Transmission electron microscopy (TEM) confirms the BTFO film has a clear layered structure, and the bismuth oxide layer interleaves the four-block pseudoperovskite layer, indicating the n 4 Aurivillius phase structure. Piezoresponse force microscopy measurements indicate strong in-plane piezoelectric response, consistent with the c-axis layered structure, shown by XRD and TEM.

High Precision Plasma Etch for Pattern Transfer: Towards Fluorocarbon Based Atomic Layer Etching

A basic requirement of a plasma etching process is fidelity of the patterned organic materials. In photolithography, a He plasma pretreatment (PPT) based on high ultraviolet and vacuum ultraviolet (UV/VUV) exposure was shown to be successful for roughness reduction of 193nm photoresist (PR). Typical multilayer masks consist of many other organic masking materials in addition to 193nm PR. These materials vary significantly in UV/VUV sensitivity and show, therefore, a different response to the He PPT. A delamination of the nanometer-thin, ion-induced dense amorphous carbon (DAC) layer was observed. Extensive He PPT exposure produces volatile species through UV/VUV induced scissioning. These species are trapped underneath the DAC layer in a subsequent plasma etch (PE), causing a loss of adhesion. Next to stabilizing organic materials, the major goals of this work included to establish and evaluate a cyclic fluorocarbon (FC) based approach for atomic layer etching (ALE) of SiO2 and Si; to characterize the mechanisms involved; and to evaluate the impact of processing parameters. Periodic, short precursor injections allow precise deposition of thin FC films. These films limit the amount of available chemical etchant during subsequent low energy, plasma-based Ar+ ion bombardment, resulting in strongly time-dependent etch rates. In situ ellipsometry showcased the self-limited etching. X-ray photoelectron spectroscopy (XPS) confirms FC film deposition and mixing with the substrate. The cyclic ALE approach is also able to precisely etch Si substrates. A reduced time-dependent etching is seen for Si, likely based on a lower physical sputtering energy threshold. A fluorinated, oxidized surface layer is present during ALE of Si and greatly influences the etch behavior. A reaction of the precursor with the fluorinated substrate upon precursor injection was observed and characterized. The cyclic ALE approach is transferred to a manufacturing scale reactor at IBM Research. Ensuring the transferability to industrial device patterning is crucial for the application of ALE. In addition to device patterning, the cyclic ALE process is employed for oxide removal from Si and SiGe surfaces with the goal of minimal substrate damage and surface residues. The ALE process developed for SiO2 and Si etching did not remove native oxide at the level required. Optimizing the process enabled strong O removal from the surface. Subsequent 90% H2/Ar plasma allow for removal of C and F residues.

Atomic layer-by-layer Co3O4/graphene composite for high performance lithium-ion batteries

An "atomic layer-by-layer" structure of Co3O4/graphene is developed as an anode material for lithium-ion batteries. Due to the atomic thickness of both the Co3O4 nanosheets and the graphene, the composite exhibits an ultrahigh specific capacity of 1134.4 mAh g-1 and an ultralong life up to 2000 cycles at 2.25 C, far beyond the performances of previously reported Co3O4/C composites.

Dye-sensitized solar cells based on a single layer deposition of TiO 2 from a new formulation paste and their photovoltaic performance

A new strategy for enhancing the efficiency and reducing the production cost of TiO 2 solar cells by design of a new formulated TiO 2 paste with tailored crystal structure and morphology is reported. The conventional three- or four-fold layer deposition process was eliminated and replaced by a single layer deposition of TiO 2 compound. Different TiO 2 pastes with various crystal structures, morphologies and crystallite sizes were prepared by an aqueous particulate sol-gel process. Based on simultaneous differential thermal (SDT) analysis the minimum annealing temperature to obtain organic-free TiO 2 paste was determined at 400°C, being one of the lowest crystallization temperatures of TiO 2 photoanode electrodes for solar cell application. Photovoltaic measurements showed that TiO 2 solar cell with pure anatase crystal structure had higher power conversion efficiency (PCE) than that made of pure rutile-TiO 2. However, the PCE of solar cells depends on the anatase to rutile weight ratio, reaching a maximum at a specific value due to the synergic effect between anatase and rutile TiO 2 nanoparticles. Moreover, it was found that the PCE of solar cells made of crystalline TiO 2 powders was much higher, increasing in the range 32-84% depending on anatase to rutile weight ratio, than that of prepared by amorphous powders. TiO 2 solar cell with the morphology of mixtures of nanoparticles and microparticles had higher PCE than the solar cell with the same phase composition containing TiO 2 nanoparticles due to the role of TiO 2 microparticles as light scattering particles. The presented strategy would open up new insight into fabrication and structural design of low-cost TiO 2 solar cells with high power conversion efficiency. © 2012 Elsevier Ltd.

Precursor adsorption on copper surfaces as the first step during the deposition of copper: a density functional study with van der Waals correction

Copper dimethylamino-2-propoxide [Cu(dmap)2] is used as a precursor for low-temperature atomic layer deposition (ALD) of copper thin films. Chemisorption of the precursor is the necessary first step of ALD, but it is not known in this case whether there is selectivity for adsorption sites, defects, or islands on the substrate. Therefore, we study the adsorption of the Cu(dmap)2 molecule on the different sites on flat and rough Cu surfaces using PBE, PBE-D3, optB88-vdW, and vdW-DF2 methods. We found the relative order of adsorption energies for Cu(dmap)2 on Cu surfaces is Eads (PBE-D3) > Eads (optB88-vdW) > Eads (vdW-DF2) > Eads (PBE). The PBE and vdW-DF2 methods predict one chemisorption structure, while optB88-vdW predicts three chemisorption structures for Cu(dmap)2 adsorption among four possible adsorption configurations, whereas PBE-D3 predicts a chemisorbed structure for all the adsorption sites on Cu(111). All the methods with and without van der Waals corrections yield a chemisorbed molecule on the Cu(332) step and Cu(643) kink because of less steric hindrance on the vicinal surfaces. Strong distortion of the molecule and significant elongation of Cu–N bonds are predicted in the chemisorbed structures, indicating that the ligand–Cu bonds break during the ALD of Cu from Cu(dmap)2. The molecule loses its initial square-planar structure and gains linear O–Cu–O bonding as these atoms attach to the surface. As a result, the ligands become unstable and the precursor becomes more reactive to the coreagent. Charge redistribution mainly occurs between the adsorbate O–Cu–O bond and the surface. Bader charge analysis shows that electrons are donated from the surface to the molecule in the chemisorbed structures, so that the Cu center in the molecule is partially reduced.

ZnO based nanowires grown by chemical vapour deposition for selective hydrogenation of acetylene alcohols

Vertically aligned ZnO nanowires (NWs) with a length of 1.5-10 mu m and a mean diameter of ca. 150 nm were grown by chemical vapour deposition onto a c-oriented ZnO seed layer which was deposited by atomic layer deposition on Si substrates. The substrates were then spin-coated with an ethanol solution containing Pd nanoparticles with an average size of 2.7 and 4.5 nm. A homogeneous distribution of the Pd nanoparticles on ZnO NWs has been obtained using both Pd particle series. The catalytic activity of the ZnO NWs and Pd/ZnO NWs catalysts was measured in the semihydrogenation of 2-methyl-3-butyn-2-ol at 303-343 K and a pressure of 2-10 bar. The effect of the solvent used on the catalytic performance of the Pd/ZnO NWs catalyst was studied. The Pd/ZnO catalysts showed alkene selectivity of up to 95% at an alkyne conversion of 99%. A kinetic model is proposed to explain the activity and selectivity of the ZnO support and Pd/ZnO catalysts.

Method for the in situ preparation of a single layer of zeolite Beta crystals on a molybdenum substrate for microreactor applications

A method for the hydrothermal synthesis of a single layer of zeolite Beta crystals on a molybdenum substrate for microreactor applications has been developed. Before the hydrothermal synthesis, the surface of the substrate was modified by an etching procedure that increases the roughness at the nanoscale level without completely eliminating the surface lay structure. Then, thin films of Al2O3 (170 nm) and TiO2 (50 nm) were successively deposited by atomic layer deposition (ALD) on the substrate. The internal Al2O3 film protects the Mo substrate from oxidation up to 550 degrees C in an oxidative environment. The high wettability of the external TiO2 film after UV irradiation increases zeolite nucleation on its surface. The role of the metal precursor (TiCl4 vs TiI4), deposition temperature (300 vs 500 degrees C), and film thickness (50 vs 100 nm) was investigated to obtain titania films with the slowest decay in the superhydrophilic behavior after UV irradiation. Zeolite Beta coatings with a Si/Al ratio of 23 were grown at 140 degrees C for 48 It. After ion exchange with a 10(-4) M cobalt acetate solution, the activity of the coatings was determined in the ammoxidation of ethylene to acetonitrile in a microstructured reactor. A maximum reaction rate of 220 mu mol C2H3N g(-1) s(-1) was obtained at 500 degrees C, with 42% carbon selectivity to acetonitrile. (C) 2007 Elsevier Inc. All rights reserved.

Layer-by-layer deposition of praseodymium oxide on tin-doped indium oxide (ITO) surface

Praseodymium oxide as a thin film of controllable layer is known to display many unique physiochemical properties, which can be useful to ceramic, semiconductive and sensor industries. Here in this short paper, we describe a new chemical method of depositing praseodymium oxide on tin-doped indium oxide (ITO) surface using a layer-by-layer approach. The process is carried out by dipping the ITO in solutions of adsorbable polycationic chitosan and alkaline praseodymium hydroxide Pr(OH)(3) alternatively in order to build up the well-defined multi-layers. XRD suggests that the predominant form of the oxide is Pr6O11, obtained after heat treatment of the deposited ITO in static air at 500 degrees C. Microscopic studies including AFM, TEM and SEM indicate that the deposited oxide particles are uniform in size and shape (cylindrical), mesoporous and the thickness of the film can be controlled. AC impedance measurements of the deposited materials also reveal that the oxide layers display a high electrical conductivity hence suitable for sensor uses. (c) 2006 Elsevier B.V. All rights reserved.

Hydrogen-bonding-driven self-assembly of PEGylated organosilica nanoparticles with poly(acrylic acid) in aqueous solutions and in layer-by-layer deposition at solid surfaces

PEGylated organosilica nanoparticles have been synthesized through self-condensation of (3-mercaptopropyl)trimethoxysilane in dimethyl sulfoxide into thiolated nanoparticles with their subsequent reaction with methoxypoly(ethylene glycol) maleimide. The PEGylated nanoparticles showed excellent colloidal stability over a wide range of pH in contrast to the parent thiolated nanoparticles, which have a tendency to aggregate irreversibly under acidic conditions (pH < 3.0). Due to the presence of a poly(ethylene glycol)-based corona, the PEGylated nanoparticles are capable of forming hydrogen-bonded interpolymer complexes with poly(acrylic acid) in aqueous solutions under acidic conditions, resulting in larger aggregates. The use of hydrogen-bonding interactions allows more efficient attachment of the nanoparticles to surfaces. The alternating deposition of PEGylated nanoparticles and poly(acrylic acid) on silicon wafer surfaces in a layer-by-layer fashion leads to multilayered coatings. The self-assembly of PEGylated nanoparticles with poly(acrylic acid) in aqueous solutions and at solid surfaces was compared to the behavior of linear poly(ethylene glycol). The nanoparticle system creates thicker layers than the poly(ethylene glycol), and a thicker layer is obtained on a poly(acrylic acid) surface than on a silica surface, because of the effects of hydrogen bonding. Some implications of these hydrogen-bonding-driven interactions between PEGylated nanoparticles and poly(acrylic acid) for pharmaceutical formulations are discussed.

Optimizing layer-by-layer deposition of interpolymer complexes on solid substrates using Biacore

The layer-by-layer deposition of polymers onto surfaces allows the fabrication of multilayered materials for a wide range of applications, from drug delivery to biosensors. This work describes the analysis of complex formation between poly(acrylic acid) and methylcellulose in aqueous solutions using Biacore, a surface plasmon resonance analytical technique, traditionally used to examine biological interactions. This technique characterized the layer-by-layer deposition of these polymers on the surface of a Biacore sensor chip. The results were subsequently used to optimize the experimental conditions for sequential layer deposition on glass slides. The role of the solution pH and poly(acrylic acid) molecular weight on the formation of interpolymer multilayered coatings was researched, and showed that the optimal deposition of the polymer complexes was achieved at pHs ≤2.5 with a poly(acrylic acid) molecular weight of 450 kDa.

A blank slate? Layer-by-layer deposition of hyaluronic acid and chitosan onto various surfaces

Although poly(alpha-hydroxy esters), especially the PLGA family of lactic acid/glycolic acid copolymers, have many properties which make them promising materials for tissue engineering, the inherent chemistry of surfaces made from these particular polymers is problematic. In vivo, they promote a strong foreign-body response as a result of nonspecific adsorption and denaturation of serum proteins, which generally results in the formation of a nonfunctional fibrous capsule. Surface modification post-production of the scaffolds is an often-utilized approach to solving this problem, conceptually allowing the formation of a scaffold with mechanical properties defined by the bulk material and molecular-level interactions defined by the modified surface properties. A promising concept is the so-called blank slate: essentially a surface that is rendered resistant to nonspecific protein adsorption but can be readily activated to covalently bind bio-functional molecules such as extracellular matrix proteins, growth factors or polysaccharides. This study focuses on the use of the quartz crystal microbalance (QCM) to follow the layer-by-layer (LbL) electrostatic deposition of high molecular weight hyaluronic acid and chitosan onto PLGA surfaces rendered positively charged by aminolysis, to form a robust, protein-resistant coating. We further show that this surface may be further functionalized via the covalent attachment of collagen IV, which may then be used as a template for the self-assembly of basement membrane components from dilute Matrigel. The response of NIH-3T3 fibroblasts to these surfaces was also followed and shown to closely parallel the results observed in the QCM.

Atomic layer structure of vanadium oxide nanotubes grown on nanourchin structures

We report the detailed characterization of high quality vanadium oxide (VOx) nanotubes (NTs) and highlight the zipping of adjacent vanadate layers in such NTs formed on remarkable nanourchin structures. These nanostructures consist of high-density spherical radial arrays of NTs. The results evidence vanadate NTs with unprecedented uniformity and evidences the first report of vanadate atomic layer zipping. The NTs are ∼2 μm in length with inner diameters of 20-30 nm. The tube walls comprise scrolled triplet-layers of vanadate intercalated with organic surfactant. Such high-volume structures might be useful as open-access electrolyte scaffolds for lithium insertion-based charge storage devices.