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Powder additive pulsed Nd:YAG laser (wavelength 1064 nm), with the aim of preparing AM of such material. The influence of oxygen content in the initial silicon powders on the continuous tracks morphology was investigated. It was found that the initial oxygen content of the processed powders must be lower than 0.1 wt% to produce a smooth silicon melted track. This result is explained as due to the formation of gaseous manufacturing (AM) of materials is affected by the oxygen present in the raw material, especially if they possess a native oxide. The latter influences the properties of the laser molten track. We carried out a study on the interactions between silicon fine powder (

This study unleashes the potential of nanoporous connected networks as excellent oil reservoirs for reducing friction and wear in Al2O3-Al2O3 tribo-pairs. Alumina were fabricated via slip casting and sintering to generate wide-ranging densifications (70–99.5%) and slid in a reciprocating flat-on-flat configuration. Friction coefficients (FCs) lie between 0.025 and 0.37 which decreased with an increase in normal load (10–220 N), lubricant’s viscosity (19, 289 mPa·s) and sliding frequency (6, 12, 24 Hz). A central finding is that FCs of infused specimens are smaller than those of surface lubricated. Wear rates decreased from 10−5 to

Additive manufacturing (AM) of brittle materials remains challenging, as they are prone to cracking due to the steep thermal gradients present during melting and cooling after laser exposition. Silicon is an ideal brittle material for study since most of the physical properties of single-element materials can be found in the literature and high-purity silicon powders are readily available. Direct laser melting (DLM) of silicon powder was performed to establish the conditions under which cracks occur and to understand how the solidification front impacts the final microstructure. Through careful control of process conditions, paying special attention to thermal gradients and the growth velocity, epitaxial pillars free of cracks could be grown to a length of several millimeters.

Visible-light photocatalyst titanium dioxide (TiO2) was successfully prepared via a novel and facile single-mode microwave assisted synthesis process. In this one-step synthesis, Ti as target material selectively oxidizes in magnetic field throughout rapid heating, whose process requires less energy consumption and short time. In obtained TiO2, self-doping of Ti3+ was confirmed, which makes TiO2 perform sufficient light absorption in visible region with wavelength above 400 nm. Such Ti3+ self-doped TiO2 exhibits much narrower optical bandgap (2.14 eV) with compared stoichiometric TiO2 (3.0–3.2 eV). The synthesized TiO2 also shows superior photocatalytic activity to commercially available TiO2 towards the degradation of Rhodamine B under visible light irradiation.

Mesoporous submicron α−Al2O3 green compacts were fabricated using slip casting of ultrafine alumina powders. The pre-sintered samples were sintered in air atmosphere at 1300 °C, 1350 °C, 1400 °C, and 1500 °C to obtain a variety of grain morphologies namely submicron equiaxed and micro rod structures. The resulting grain diameters lie between ∼ 270 nm and ∼ 1590 nm and total porosity fraction between 0.05% and 13%. The room temperature flexural strength (σ) evaluations and fractography analyses of sintered alumina samples were performed. It was observed that the total porosity fraction dictates the flexural strength as compared to grain diameter. Further, it was found that the flexural strength exhibited a decreasing trend for an increase in the total porosity fraction, and proved to be a better effective parameter than open porosity fraction. The fractography analyses suggest that samples sintered at 1300 °C and 1350 °C predominantly underwent intergranular fracture, while those sintered at 1400 °C and 1500 °C underwent a mixture of intergranular and transgranular fracture.

The purpose of this work was to investigate the effects of different texture patterns and orientations on the wear and failure mechanisms of grey cast iron sliding against 42CrMo6 steel. Reciprocating tests were performed on 16 different micro-textures under starved lubrication conditions. The textures were designed using a design of experiments (DoE) approach and produced by a nanosecond-laser. Under starved lubrication conditions, the non-textured samples always failed catastrophically by scuffing, which is a sudden and catastrophic failure. However, textured samples showed two different wear and failure mechanisms. It is revealed that the sudden and catastrophic failure due to scuffing can be avoided by surface texturing. Choosing the right distance between the micro-textures can change the surface damage mode from scuffing to a more gradual oxidative wear mechanism. For the studied tribo-system, it was shown that if the distance of micro-textures in the direction of sliding (DMS) is less than 3 mm, samples will fail by an oxidation mechanism. For textured samples with DMS greater than 3.5 mm, the failure mechanism is scuffing, the same as for the non-textured cast iron.

High temperature and prolonged thermal annealing for the crystallization of cathode in thin-film batteries (TFBs) restricts the choice of current collector and substrates and causes lithium loss in the cathode. This work explores photonic-based alternatives for cathode crystallization, specifically xenon flash-lamp annealing (FLA), ultra-violet excimer laser irradiation (UV-laser), and infrared laser (IR) annealing. The effect of these methods is systematically compared to that of thermal annealing in terms of processing time, crystal structure and electrochemical performance of the LiMn2O4 model thin-film cathode. FLA and UV excimer laser can crystallize LMO cathode in short periods of 6 min and 25 min, respectively, compared to the reference (ref.) thermal processing time of 60 min at 600 °C. The performance of the FLA-processed LMO cathodes (crystallinity, capacity, diffusion coefficient) is comparable to that of the thermal ref. with a capacity of 6 μAh cm−2 and 5 μAh/cm−2 at 15 C for FLA and thermal ref. respectively, with the practical limit of the 150 nm LMO film being 9.5 μAh cm−2. A thin-film FTO/LMO/Li3POxNy/Li solid-state battery was assembled and cycled at a high rate of 10 C with only a negligible capacity fade of 3.6% after 200 cycles. FLA can be used as an effective alternative for fast crystallization of thin-film cathodes on temperature-sensitive substrates and is suitable for upscaling processes.

The failure mechanism known as scuffing is a major problem in lubricated sliding mechanical components, specifically for those tribological systems working under starved lubrication conditions. It occurs suddenly and often results in loss of component functionality, and thus high repair costs. Despite the extensive studies on scuffing over the past 80 years, the basic mechanism of scuffing is not yet well understood. In the present study, a cast iron-steel tribo-system working under starved lubrication conditions, which resembles a semi journal bearing used in a cutting machine, with the dominant scuffing failure mechanism is investigated. Based on the experimental observations in this work, a new theory is proposed for initiation of scuffing in this cast iron-steel tribo-system. According to the proposed theory, scuffing initiates when the tribo-film iron oxide reduces to α-iron providing metal-metal contact and, consequently, strong adhesion between the sliding surfaces. The reduction of the oxide takes place due to a temperature increase at the contacting asperities together with the presence of carbon, coming from either the lubricant or graphite flakes of cast iron, as the reducing agent. Keywords: Scuffing, Starved lubrication, Friction, Wear mechanism, Cast iron

Many interfacial properties are governed by both their surface chemistries and topologies. In particular, surface patterning is gaining rapid momentum since last decade to aid in the extenuation of bacterial fouling for biomedical applications. The materials of catheters, contact lenses, endotracheal tubes, prosthetic devices, drug delivery devices, stents, and many implants comprise a variety of polymers, ceramics, and metals, whose surfaces are attached by gram-negative and gram-positive bacteria. In this chapter, we emphasize on the recent developments of surface texturing for lowering the adhesion of bacterial fouling species. A variety of surface topological features such as Sharklet, square pillars, circular pillars, cones, dimples, pores, lines, and hatches were utilized as inspired from the concepts of lotus leaf, shark skin, rice leaves, and Nepenthes pitcher plant. Innovative fabrication technology developments on colloidal lithography, additive manufacturing, replication technologies, hot embossing, and laser surface patterning as learnt from other research domains will be put forth owing to their robustness and large-scale feasibility.

In this article, an optical method to control the break-up of high-speed liquid jets is proposed. The method consists of focusing the light of a pulsed laser source into the jet behaving as a waveguide. Experiments were performed with the help of a Q-switched frequency doubled Nd:Yag laser (λ=532 nm). The jet diameter was 48 µm and jet velocities from 100 to 200 m/s. To study the laser-induced water jet break-up, observations of the jet coupled with the high power laser were performed for variable coupling and jet velocity conditions. Experimentally determined wavelength and growth rate of the laser-generated disturbance were also compared with the ones predicted by linear stability theory of free jets.

In atomic layer deposition processes (ALD), surface reactions of adsorbed precursor species lead to the formation of thin films. In order to achieve a well-controlled, self-limiting process, the substrate is sequentially exposed to different precursor molecules, each one until the surface is completely saturated. The necessary time of exposure depends on precursor transport and on surface kinetics of which the latter are determined by the respective activation energies for the surface reactions. In this contribution, we apply a surface kinetic model and surface reaction rates to describe the ALD process for the deposition of titanium dioxide utilizing titanium isopropoxide and water as reactive precursor combination. We examine in detail precursor surface coverages and investigate the influence of substrate temperature and exposure time on the hydrolytic decomposition of the adsorbed titanium precursor. In this way, we can quantify the deposition rate in each deposition cycle and examine the contribution ...

This study investigates the effect of laser surface texturing on the friction behavior and the lifetime of grey cast iron reciprocating under starved lubrication conditions. Five geometrical texture parameters (feature depth, diameter, length, area fraction and sliding direction) were studied using a design of experiments (DoE) approach by developing a fractional factorial design. Reciprocal sliding tests were carried out for the cast iron-steel tribo-pair at a pressure of 24 MPa and a frequency of 6 Hz. DoE results revealed that the geometrical parameters of micro-textures interact in a complex manner. Hence, for better understanding the effect of surface texturing on the tribological performance, the interactions between geometrical parameters need to be considered. It is found that except the following main factors: diameter and area fraction, mainly interactions of geometrical parameters have significant impact on the coefficient of friction. It is also observed that micro-textures could increase the lifetime of tribo-systems sliding under starved conditions. Based on the DoE analysis, an optimum micro-texture having a relatively low coefficient of friction and a long lifetime are achieved with the following (geometrical) parameters: a depth of 50 μm, a diameter of 100 μm, a length of 500 μm, an area fraction of 5%, and the sliding direction perpendicular to the micro-textures.

The typical foreign body response (FBR) to synthetic implants is characterized by local inflammation and tissue fibrosis. Silicone implants have been associated with the development of adverse capsular contraction (ACC); a form of excessive FBR to the material that often requires the replacement of the implant. It has been shown that surface roughening of silicone can reduce the prevalence of ACC, but the mechanisms remain poorly understood. Macrophages are key cells in FBR. They exert their control mainly by polarizing into pro-inflammatory (M1) or pro-healing (M2) cells. It is postulated that surface topography can reduce M1 polarization by limiting cell spreading and cytoskeleton organization. To test this hypothesis, we used KrF Excimer laser ablation with half-tone masks to produce convex and concave topographies with controlled surface dimensional parameters. Cells in convex and concave topographies were compared to cells in planar surfaces, with or without chemical polarization. We show that chemical polarization induced specific changes in the cell shape on planar substrates. Macrophage shape and size was different in concave and convex surfaces, but no correlation was found with the cell polarization state. The results highlight that chemical polarization of macrophages is associated with changes in the cell shape; however, topography-induced changes in macrophage shape could not be linked with a shift in macrophage polarization. Thus, the sole manipulation of cell shape does not seem to be the mechanism by which macrophage function could be controlled.

Understanding the surface kinetics of precursor decomposition during thin film formation represents a key aspect in the understanding and engineering of chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes. The determination of activation energies of the surface reaction steps, however, is often challenging because it requires precise knowledge of precursor impinging rates. Afterward, the kinetics can be investigated by comparing the amount of deposited material with the absolute precursor flow. Ideally, the experimental equipment allows a distinction between gas phase and surface reactions. Both are difficult to achieve in conventional CVD processes. A high vacuum environment, however, enables the quantitative prediction of precursor impinging rates due to the ballistic nature of precursor transport; additionally precursor gas phase reactions do not occur. We investigated the surface reaction kinetics of titanium isopropoxide (TTIP) in the high vacuum CVD of titanium dioxide. Addit...

The combinatorial characterization of the growth kinetics in chemical vapor deposition processes is challenging because precise information about the local precursor flow is usually difficult to access. In consequence, combinatorial chemical vapor deposition techniques are utilized more to study functional properties of thin films as a function of chemical composition, growth rate or crystallinity than to study the growth process itself. We present an experimental procedure which allows the combinatorial study of precursor surface kinetics during the film growth using high vacuum chemical vapor deposition. As consequence of the high vacuum environment, the precursor transport takes place in the molecular flow regime, which allows predicting and modifying precursor impinging rates on the substrate with comparatively little experimental effort. In this contribution, we study the surface kinetics of titanium dioxide formation using titanium tetraisopropoxide as precursor molecule over a large parameter range. We discuss precursor flux and temperature dependent morphology, crystallinity, growth rates, and precursor deposition efficiency. We conclude that the surface reaction of the adsorbed precursor molecules comprises a higher order reaction component with respect to precursor surface coverage.

Barium titanate is a very promising material for the integration of optical communication into electronic integrated circuits. For a successful integration into CMOS compatible technology, a growth process has to be found which allows forming crystalline BaTiO3 at sufficiently low temperatures. We describe the combinatorial analysis of BaTiO3 formation by high vacuum chemical vapor deposition using barium triisopropyl cyclopentadienyl and titanium tetraisopropoxide as metal sources; water, oxygen, or ozone are used as oxidizing agents. We analyzed the impact of these oxidizing agents on the interaction of the precursor molecules on the substrate surface. Furthermore, we characterized the films concerning chemical composition and identified growth conditions leading to deposit composition corresponding to the stoichiometric BaTiO3 formation. XRD analysis confirms the formation of crystalline BaTiO3 phases for deposition temperatures as low as 370 °C.

A key factor in engineering integrated optical devices such as electro-optic switches or waveguides is the patterning of thin films into specific geometries. In particular for functional oxides, etching processes are usually developed to a much lower extent than for silicon or silicon dioxide; therefore, selective area deposition techniques are of high interest for these materials. We report the selective area deposition of titanium dioxide using titanium isopropoxide and water in a high-vacuum chemical vapor deposition (HV-CVD) process at a substrate temperature of 225 °C. Here—contrary to conventional thermal CVD processes—only hydrolysis of the precursor on the surface drives the film growth as the thermal energy is not sufficient to thermally decompose the precursor. Local modification of the substrate surface energy by perfluoroalkylsilanization leads to a reduced surface residence time of the precursors and, consequently, to lower reaction rate and a prolonged incubation period before nucleation occurs, hence, enabling selective area growth. We discuss the dependence of the incubation time and the selectivity of the deposition process on the presence of the perfluoroalkylsilanization layer and on the precursor impinging rates—with selectivity, we refer to the difference of desired material deposition, before nucleation occurs in the undesired regions. The highest measured selectivity reached (99 ± 5) nm, a factor of 3 superior than previously reported in an atomic layer deposition process using the same chemistry. Furthermore, resolution of the obtained patterns will be discussed and illustrated.

Novel glazing with embedded micro-mirrors can significantly reduce the energy consumption due to cooling and lighting in buildings. Especially promising are large arrays of periodic micro compound-parabolic-concentrators (CPCs) with angular-selected transmittance. For the production of micro CPCs, curved sidewall grooves with a controlled optical surface and an aspect ratio of about 2.3 are fabricated on polycarbonate substrates by scanning nanosecond 248-nm excimer laser ablation. The likewise obtained microstructures can be used as master mold for replication. The cross-sections of the micro grooves are characterized by confocal microscopy, and the extracted morphologies are used for the ray-tracing simulation of the optical devices. Prior to the scanning ablation using a suitable mask in the optical path, the depth profiles under static ablation are investigated to identify ablation rate, imaging resolution and produced surface. Interestingly for the width of the mask opening being less than 6 μm, the ablation rate is increased due to optical interference and /or less shielding by debris. Concerning the scanning ablation, the depth of the curved sidewall grooves ranges from 48 μm to 114 μm, corresponding to the width of the groove opening being in the range from 20 μm to 50 μm. The observed final shapes in cross-sections are in good agreement with the design of the mask. For both theoretical and fabricated groove shapes, the angular-selected transmittance profiles predicted from ray-tracing simulations are highly similar. Scanning nanosecond excimer laser ablation is therefore a promising approach for the realization of high-quality micro CPCs.

Chemical vapor deposition (CVD) techniques rely on high temperatures to activate the chemical decomposition of precursors on the substrate surface. Lower temperatures are applied in atomic layer deposition (ALD), where deliberate pyrolysis of the precursor is avoided to favor self-saturating surface reactions between two or more reactive partners. In ALD the substrate is exposed sequentially to two properly separated reactive precursors that interact on the surface, which is detrimental to the growth rate but offers exceptional conformality of the obtained films. We demonstrate the adaption of an ALD type reaction to a high vacuum CVD process; i.e., we deposited homogeneous titanium dioxide thin films on flat substrates by exposing simultaneously substrates with titanium isopropoxide and water at ALD typical temperatures (175–225 °C) in a high vacuum environment obtaining growth rates of up to 2 nm·min–1. We identified different growth regimes as a function of precursor impinging rates and substrate tempe...

Accomplishing mechanically robust omniphobic surfaces is a long-existing challenge, and can potentially find applications in bioengineering, tribology and paint industries. Slippery liquid impregnated mesoporous α-Al2O3 interfaces are achieved with water, alkanes, water based and oil based high viscosity acrylic paints. Incredibly high abrasion-resistance (wear coefficients ≤10-8 mm3 N-1 m-1) and ultra-low friction coefficients (≥0.025) are attained, attributing to the hard alumina matrix and continuous replenishment of perfluoropolyether aided by capillarity and surface diffusion processes. A variety of impregnating liquids employed suggest that large molecules, faster surface diffusion and lowest evaporation rate generate the rare combination of high wear-resistance and omniphobicity. It is noteworthy that these novel liquid impregnated Al2O3 composites exhibit outstanding load bearing capacity up to 350 MPa; three orders of magnitude higher than achievable by the state of the art omniphobic surfaces. Further, our developed thermodynamic calculations suggest that the relative thermodynamic stability of liquid impregnated composites is linearly proportional to the spreading coefficient (S) of the impregnating liquid with the matrix material and is an important tool for the selection of an appropriate matrix material for a given liquid.

Currently, Additive Manufacturing (AM) is limited to three classes of materials: ceramics, polymers and metals. Even within these classes, only a small number of materials can be processed by AM, either in a powder bed approach or in a direct energy deposition approach.

A key factor in engineering integrated devices such as electro-optic switches or waveguides is the patterning of high quality crystalline thin films into specific geometries. In this contribution high vacuum chemical vapor deposition (HV-CVD) was employed to grow titanium dioxide (TiO2) patterns onto silicon. The directed nature of precursor transport - which originates from the high vacuum environment during the process - allows shading certain regions on the substrate by shadow masks and thus depositing patterned thin films. While the use of such masks is an emerging field in stencil or shadow mask lithography, their use for structuring thin films within HV-CVD has not been reported so far. The advantage of the employed technique is the precise control of lateral spacing and of the distance between shading mask and substrate surface which is achieved by manufacturing them directly on the substrate. As precursor transport takes place in the molecular flow regime, the precursor impinging rates (and therefore the film growth rates) on the surface can be simulated as function of the reactor and shading mask geometry using a comparatively simple mathematical model. In the current contribution such a mathematical model, which predicts impinging rates on plain or shadow mask structured substrates, is presented. Its validity is confirmed by TiO2-deposition on plain silicon substrates (450 degrees C) using titanium tetra isopropoxide as precursor. Limitations of the patterning process are investigated by the deposition of TiO2 on structured substrates and subsequent shadow mask lift-off. The geometry of the deposits is according to the mathematical model. Shading effects due to the growing film enables to fabricate deposits with predetermined variations in topography and non-flat top deposits which are complicated to obtain by classical clean room processes. As a result of the enhanced residual pressure of decomposition products and titanium precursors and the corresponding surface coverage of them, growth conditions differ in proximity of the shadowed areas compared to the case of plain substrates and the obtained film thickness differs significantly from predictions. (C) 2014 Elsevier B.V. All rights reserved.

The bipotent nature of the HepaRG cell line is a unique property among human hepatoma-derived cells. Cell treatment with specific differentiation inducers results in a mixture of hepatocyte- and biliary-like cells, accompanied by upregulation of liver-specific proteins, drug metabolizing enzymes, transcription regulators, membrane receptors or innate immune response effectors. These features make the HepaRG cells a suitable and handy replacement for primary hepatocytes, to study hepatic functions in vitro. However, cell differentiation is a long, variable process, requiring special culture conditions, while the resulting mixed cell populations is usually a major drawback. This process can potentially be controlled by interface characteristics, such as substrate topography. To screen for such novel substrates, we have first developed a new HepaRG cell line, designated as HepaRGDsRed, expressing the reporter gene DsRed. The fluorescent protein was expressed in hepatocyte- and not biliary-like cells, in a differentiation dependent-manner. We have further used replicated microstructured gradients of polydimethylsiloxane (PDMS) that allow three-dimensional manipulation in vitro, to monitor HepaRGDsRed differentiation in real time. We demonstrate that this approach enables the controlled assembly of viable hepatocyte-like cells for functional studies, which can be maintained in culture without loss of differentiation. The regulated expression of the DsRed reporter proved a valuable tool not only for rapid screening of novel cell growth substrates favoring cell differentiation, but also, to enrich the hepatocyte-like cell population by fluorescence-activated cell sorting to investigate liver-specific processes in vitro.

Significant progress has been made in integrating novel materials into silicon photonic structures in order to extend the functionality of photonic circuits. One of these promising optical materials is BaTiO

Combinatorial high-vacuum chemical vapor deposition (HV-CVD) was used to identify the conditions required to obtain hafnium-doped lithium niobate thin films on sapphire {001} substrates. Niobium tetraethoxydimethylaminoethoxide (Nb(OEt)(4)(dmae)), lithium tert-butoxide (Li(OBut)), and hafnium tert-butoxide (Hf(OBut)(4)) were used as precursors. X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that a single phase of textured {001} Hf-doped lithium niobate film was obtained under certain precursor flux conditions. The lithium content ([Li]/([Li] + [Nb])) of the textured film was estimated using Raman spectroscopy to be about 49 mol %. The presence of hafnium inside the films was confirmed by X-ray photoelectron spectroscopy (XPS) measurements, and the hafnium content of the textured film ([Hf]/([Hf] + [Nb])) was estimated to be about 3 mol %. XPS data confirmed that Hf and Nb, respectively, are in the +4 and +5 oxidation states inside the film. The film consists of nearly parallel {001} hafnium-doped lithium niobate columns with different in-plane orientations.

The deposition of amorphous alumina (Al2O3) films on four inch wafers with high deposition rate (up to 50 nm/min) by an advanced HV-CVD technique is discussed. Amorphous nature of the films is confirmed by X-ray diffraction. Refractive index of the deposited alumina can be adjusted in the large range (1.3-1.62@633 nm) by varying the substrate temperate during the deposition. The films are highly transparent. The density and stoichiometry of the deposits are also influenced by deposition conditions. Presence of -OH groups is observed in some cases.

A laser or electron beam assisted deposition in HV-CVD conditions was used in order to achieve structured amorphous alumina (Al2O3) deposits. Selective deposition of Al2O3 in the irradiated regions has been demonstrated. We investigate the influence of irradiation parameters on the deposition rate and composition of the deposits. The technique is aimed to be used on full wafer substrates.

High-k films of CaCu3Ti4O12 are of interest for industrial multifunctional electronics. For oriented flow High Vacuum CVD processes, precursors are needed that they can be safely transported in the gas phase without carrier gas. We investigated the vapor pressure, and transport rate and temporal stability of a potential Ca precursor [Ca(hfa)2tgte] (hfa: hexafluoroacetylacetonate, tgte: tetraethylene glycol dimethyl ether) under HV conditions by varying the evaporation temperature. At 115{degree sign}C, the transport rate for the Ca(hfa)2tgte precursor of 4.3 mmol per hour was achieved allowing for high film deposition rates.

Erbium-doped amorphous aluminum oxide layers deposited on Si or oxidized silicon substrates are promising construction pieces for future monolytic integrated optoelectronics devices. In a novel high-vacuum chemical vapor deposition setup the alumina films are grown with high homogeneity on 4 in. wafers with well controlled growth rate, chemical composition, and high deposition rates of up to 20 nm/min. The HV-CVD applies thermal decomposition of aluminum-isopropoxide with or without additional oxygen as reactive partner gas. Arbitrarily chosen values for different parameters show that deposition works in a wide parameter range and that the chemical composition, the roughness, growth rate, and the resulting index of refraction and optical guiding properties need a systematic study of the working window of the process. Nevertheless optical guiding at 670 nm wavelength-is demonstrated and addition of erbium tetramethyl-heptanedionate as erbium precursor results in co-deposition of erbium in the alumina layers. (C) 2007 Elsevier B.V. All rights reserved.

High temperature nanoimprinting of viscous polymers which are glassy at room temperature is usually performed using brittle and expensive molds made of inorganic materials. As a replacement, soft molds made of plastics or elastomers have been used because of their low cost and ease of fabrication. However, the deformation of polymer molds under pressure remains a major issue which limits their resolution in high temperature nanoimprinting. Moreover, the replicated structures are often broken or lack definition due to sticking of the embossed polymer to the mold. We report a method for imprinting fine, densely packed nanostructures down to 12 nm into a wide range of technologically important polymers using a flexible and robust mold made from ethylene(tetrafluoroethylene) (ETFE). The high resolution achieved is due to the mold's mechanical stability and resistance to distortion at high pressures and high temperatures. The flexibility and low surface energy of ETFE provide a clean mold release without fracture or deformation of the embossed structures. Multiple imprinting and patterning on large areas is also made possible because of the good conformal contact and low-adhesion of the ETFE mold. Finally, this simple and inexpensive method allows reproduction of the stamps from one single master, thus providing an economical alternative to expensive and brittle inorganic materials.

Novel approaches to achieve uniform deposition, in particular for dielectric oxides, are highly desirable in the fields of electronics and optics. We succeeded to deposit thin films of alumina (Al2O3) with high uniformity on 150 mm diameter Si wafers. We use thermal decomposition in oxygen atmosphere of Aluminum isopropoxide, under molecular flow regime, in a High Vacuum Chemical Vapor Deposition (HV–CVD) reactor. © 2006 Elsevier B.V. All rights reserved.

The performance of micro- and nanoelectromechanical systems depends on the surface properties of the substrate material, such as chemical composition, roughness, friction, adhesion, and wear. Substrates of aluminum deposited onto Si (Al/Si) have been chemically reacted with perfluorodecyldimethylchlorosilane (PFMS), octadecylphosphonic acid (ODP), decylphosphonic acid (DP), octylphosphonic acid (OP), and perfluorodecylphosphonic acid (PFDP) and then characterized by X-ray photoelectron spectroscopy (XPS), contact angle measurements, and atomic force microscopy (AFM). PFMS/Al self-assembled monolayers (SAMs) were studied by friction force microscopy, a derivative of AFM, to better understand their micro- and nanotribological properties. The adhesion forces for PFMS/Al SAMs were found to be lower when compared to those of bare Al/Si; however, the coefficient of friction for both was comparable. XPS analysis revealed the presence of the corresponding alkyl chain molecules on PFMS/Al, ODP/Al, DP/Al, OP/Al, an...

Superhydrophobicity is obtained on photolithographically structured silicon surfaces consisting of flat-top pillars after a perfluorosilanization treatment. Systematic static contact angle measurements were carried out on these surfaces as a function of pillar parameters that geometrically determine the surface roughness, including pillar height, diameter, top perimeter, overall filling factor, and disposition. In line with thermodynamics models, two regimes of static contact angles are observed varying each parameter independently: the "Cassie" regime, in which the water drop sits suspended on top of the pillars (referred to as composite), corresponding to experimental contact angles greater than 140-150 degrees, and the "Wenzel" regime, in which water completely wets the asperities (referred to as wetted), corresponding to lower experimental contact angles. A transition between the Cassie and Wenzel regimes corresponds to a set of well-defined parameters. By smoothly depositing water drops on the surfaces, this transition is observed for surface parameter values far from the calculated ones for the thermodynamic transition, therefore offering evidence for the existence of metastable composite states. For all studied parameters, the position of the experimental transition correlates well with a rough estimation of the energy barrier to be overcome from a composite metastable state in order to reach the thermodynamically favored Wenzel state. This energy barrier is estimated as the surface energy variation between the Cassie state and the hypothetical composite state with complete filling of the surface asperities by water, keeping the contact angle constant.

Ceramic surface microstructuring is a rapidly growing field with a variety of applications in tribology, wetting, biology, and so on. However, there are limitations to large-area microstructuring and fabrication of three-dimensional (3D) micro free forms. Here, we present a route to obtain intricate surface structures through in situ slip casting using polydimethylsiloxane (PDMS) negative molds which are replicated from excimer laser ablated polycarbonate (PC) master molds. PC sheets are ablated with a nanosecond KrF (λ = 248 nm) excimer laser mask projection system to obtain micron-scale 3D surface features over a large area of up to 3 m(2). Complex surface structures that include 3D free forms such as 3D topography of Switzerland, shallow structures such as diffractive optical elements (60 nm step) and conical micropillars have been obtained. The samples are defect-free produced with thicknesses of up to 10 mm and 120 mm diameter. The drying process of the slip cast alumina slurry takes place as a one-dimensional process, through surface evaporation and water permeation through the PDMS membrane. This allows homogeneous one-dimensional shrinkage during the drying process, independent of the sample's lateral dimensions. A linear mass diffusion model has been proposed to predict and explain the drying process of these ceramic colloidal suspensions. The calculated drying time is linearly proportional to the height of the slurry and the thickness of the negatively structured PDMS and is validated by the experimental results. An experimentally observed optimum Sylgard PDMS thickness range of ∼400 μm to 1 mm has achieved the best quality microstructured green compacts. Further, the model predicts that the drying time is independent of the microstructured areas and was validated using experimental observations carried out with microstructured areas of 300 mm(2), 1200 mm(2), and 120 cm(2). Therefore, in principle, the structures can be further replicated in areas up to 3 m(2) with the same drying time for the same slurry height. The surface-structured ceramics display interesting wetting properties, for example, eicosane-coated mesoporous microstructured alumina shows superhydrophobic behavior. Additionally, ceramic bulk samples could be further used as second-generation very hard and low-wear molds for further microfabrication.

We present a new method based on B-spline snakes (active contours) for measuring high-accuracy contact angles. In this approach, we avoid making physical assumptions by defining the contour of the drop as a versatile B-spline curve. When useful, we extend this curve by mirror symmetry so that we can take advantage of the reflection of the drop onto the substrate to detect the position of the contact points. To keep a wide range of applicability, we refrain from discretizing the contour of the drop, and we choose to optimize an advanced image-energy term to drive the evolution of the curve. This term has directional gradient and region-based components; additionally, another term—an internal energy—is responsible for the snake elasticity and constrains the parameterization of the spline. While preserving precision at the contact points, we limit the computational complexity by constraining a non-uniform repartition of the control points. The elasticity property of the snake links the local nature of the contact angle to the global contour of the drop. A global knowledge of the drop contour allows us to use the reflection of the drop on the substrate to automatically and precisely detect a line of contact points (vertical position and tilt). We apply cubic-spline interpolation over the image of the drop; then, the evolution procedure takes part in this continuous domain to avoid the inaccuracies introduced by pixelization and discretization. We have programmed our method as a Java software and we make it freely available [A.F. Stalder, DropSnake, Biomedical Imaging Group, EPFL, [ON LINE] visited 2005. http://bigwww.epfl.ch/demo/dropanalysis ]. Our experiments result in good accuracy thanks to our high-quality image-interpolation model, while they show applicability to a variety of images thanks to our advanced image-energy term.

The fabrication of interdigitated titanium nanoelectrode arrays of 50 nm in width and spacing is described in this work. The nanoarrays have been realized using a Ga+ focused ion beam (FIB). FIB milling is typically accompanied by redeposition of removed material, which represents an important hindrance for milling closely spaced nanostructures. Redeposition effects have been reduced by means of XeF2 gas assistance, which increases the etch yield by a factor of seven compared with pure ion milling. Furthermore, we used a simple adsorption model, which led to the conclusion that dwell time and refresh time should be 30 ms, respectively, for optimized XeF2 assisted Ti milling. The measured resistance R of the electrodes is higher than 1 G ohm.

Aluminum-coated silicon substrates are commonly used for various micro/nanooptoelectromechanical systems (MOEMS/NOEMS) including Digital Micromirror Devices (DMD®). For efficient and failure proof operation of these devices, ultra-thin lubricant films of self-assembled monolayers (SAMs) are increasingly being employed. Fluorinated molecules are known to exhibit low surface energy, adhesion, and friction, desirable for tribological applications. In this study, we investigate contact angle, surface energy, friction, adhesion, and wear properties of a perfluoroalkylphosphonate SAM and compare them with those of alkylphosphonate SAMs. The influence of relative humidity, temperature, and sliding velocity on the friction and adhesion behavior is studied. Failure mechanisms of SAMs are investigated by wear tests. These studies are expected to aid in the design and selection of proper lubricants for MOEMS/NOEMS.

The distribution of metal-precursors supplied via a gas injection system to the substrate inside a focused electron beam (FEB) induced deposition system is investigated for the first time. The impinging precursor molecules are thermally decomposed using a heating stage. Resulting deposit thickness profiles obtained from [(PF"3)"2RhCl]"2, Co"2(CO)"8, and (hfac)CuVTMS precursors are determined optically by interference colors or by profilometry. FEB access to the precursor flux peak and the flux peak value itself depend on tube tilt and vertical tube distance to the substrate. Monte Carlo simulation match best the experiments when assuming molecular flow conditions.

This paper presents experimental studies of the enhanced light transmission through metallic films pierced by subwavelength annular apertures. Two different methods (e-beam lithography and focused ion beam) have been used to build the nano-structures. We have experimentally recorded their far-field spectral response in the visible range and the optical near-field above the nano-structures when they are excited at 633 nm. The spectral response exhibits a transmission peak at 700 nm with maximum efficiency around 16%. The near-field exhibits a characteristic two-lobe structure just above the aperture. Finite difference time domain (FDTD) simulations reproduce quite well the experimental results.

Polished copper (Cu) surfaces modified with 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTS) have been shown to be very hydrophobic and stable. Mechanically polished, oxidized, and PFTS-reacted Cu surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy, which confirmed the presence of perfluorinated alkyl chains. For a PFTS-modified Cu surface (PFTS/Cu), the sessile drop static contact angle of pure water at ambient temperature and high relative humidity (RH) was measured to be more than 125° and the Zisman critical surface energy to be typically less than 16 mN/m. Ellipsometry showed the thickness of the PFTS/Cu film to be typically less than 25 nm. Stability tests indicated that the PFTS/Cu film could survive in pure boiling water for one hour, boiling nitric acid (pH 1.5 or 1.8) for 30 min, sodium hydroxide solution (pH 12, 70 °C) for 30 min, and autoclave conditions (steam at 134 °C and 3 atm) for 15 min. The more commonly used self-assembled monolayer (SAM) modifications of Cu surfaces, e.g. thiol compounds, are significantly less stable than PFTS/Cu. The extremely hydrophobic and stable PFTS/Cu could be a very good candidate for corrosion inhibition and/or heat exchangers exploiting condensation. Copyright © 2005 John Wiley & Sons, Ltd.

Recent investigations have revealed the profound influence of stiction/adhesion, friction and wear on the reliability of micro/nanoelectromechanical systems (MEMS/NEMS). Studies have shown that the so-called self-assembled monolayers (SAMs) can be potential anti-stiction lubricants for MEMS/NEMS. Understanding the molecular tribological mechanisms of SAMs is a key to successfully designing and preparing super lubricants for MEMS/NEMS. For this purpose, perfluoroalkylsilane and alkylsilane SAMs have been deposited by a vapor deposition process on silicon with a native oxide layer and silica substrates. The surface roughness, adhesion, friction and wear properties of these coatings have been extensively studied by atomic force microscopy (AFM). Tribological properties on the macroscale have also been investigated for comparison.

An auger electron spectroscopy study was carried out on Rh-containing micro-structures grown by electron beam induced deposition (EBID) of the iso-structural and iso-electronic precursors [RhCl(PF3)2]2 and [RhCl(CO)2]2. A material containing between 55 and 60 at.% Rh was obtained from both precursors. The chemical composition of structures grown from the two different precursors indicates a similar decomposition mechanism. Deposits grown from [RhCl(PF3)2]2 showed a chemical composition independent of electron energy and electron dose in the investigated range of conditions.

We present evidence that during focused electron beam induced deposition of 3D micro- and nanostructures, different growth rates are obtained when scanning the beam towards different directions, as well as on different sides of a growing structure. The effects of electron scattering are taken into account and shown to account only partially for this observation. We propose an interpretation in terms of gas dynamics around the deposits. Our observation and description of this effect could serve the future design of complex shapes.

We have screened several organic precursors for focused electron beam induced deposition of carbon. The growth rates are found to be higher with the light carboxylic acid series than with styrene. The deposits obtained are analyzed by several micro-characterization methods. They have close compositions and structures, quite independently on the nature of the precursor. Besides C, the deposits contain only O and H. The compositions of the deposits are shown to be close to C"9H"2O"1. The C fraction is amorphous carbon, more than 90% sp^2. Two electron-induced processes occur: electron-induced precursor fixation and desorption of volatile elements.

Titanium dioxide thin films are obtained by CVD on low temperature substrates (60-210 °C) using perpendicular irradiation from a long pulse 308 nm excimer laser. Titanium tetra-isopropoxide is used as the precursor in an oxygen-containing atmosphere with a total pressure in the chamber of 10 mbar. An empirical law describing the growth rate as a function of the experimental parameters (substrate temperature and laser fluence) is derived. The deposited thickness is proportional to the number of photons and has an Arrhenius dependence on the substrate temperature. Low growth rates per pulse (less than 0.1 nm per pulse) obtained allow a good control of the deposited thickness, while the use of high laser repetition rates leads to high temporal growth rates (up to 100 nm min -1 ).