Ultrafast large-area micropattern generation in nonabsorbing polymer thin films by pulsed laser diffraction

An ultrafast, parallel, and beyond-the-master micropatterning technique for ultrathin (30-400 nm) nonabsorbing polymer films by diffraction of laser light through a 2D periodic aperture is reported. The redistribution of laser energy absorbed by the substrate causes self-organization of polymer thin films in the form of wrinklelike surface relief structures caused by localized melting and freezing of the thin film. Unlike conventional laser ablation and laser writing processes, low laser fluence is employed to only passively swell the polymer as a pre-ablative process without loss of material, and without absorption/reaction with incident radiation. Self-organization in the thin polymer film, aided by the diffraction pattern, produces microstructures made up of thin raised lines. These regular microstructures have far more complex morphologies than the mask geometry and very narrow line widths that can be an order of magnitude smaller than the openings in the mask. The microstructure morphology is easily modulated by changing the film thickness, aperture size, and geometry, and by changing the diffraction pattern.     

Bragg gratings printed upon thin glass films by excimer laser irradiation and selective chemical etching

Photon-induced property changes of sputter-deposited GeO(2)-SiO(2) thin glass films were investigated. Irradiation with ArF laser pulses induced the changes in refractive index of -10% and volume of +30% in the film without ablation. A Bragg grating with a positive sinusoid wave pattern was printed upon the film by irradiation with ArF excimer laser pulses through a phase mask. The irradiated area could be quickly etched by a HF solution. The ratio of etching rate of irradiated area to unirradiated area was higher than 30. A Bragg grating with a surface relief pattern was successfully formed on the film by irradiation with excimer laser pulses followed by chemical etching. Diffraction efficiency of the gratings increased by 25 times with the etching.     

Self‐Organization of Thin Polymer Films Guided by Electrostatic Charges on the Substrate

The self‐organization of thin polymer films into functional patterns is important both scientifically and technologically. Electric fields have been exploited as an efficient and powerful means to induce the destabilization and self‐organization of soft materials. Previous attention, however, has mainly focused on externally applied electric fields. It is shown herein that the internal electric field is strong enough to guide the self‐organization of thin polymer films as well. Patterns of electrostatic charges with micrometer resolution are first introduced on a dielectric substrate. A thin polymer film is then spin‐coated onto the topographically flat substrate. Upon thermal annealing, the thin polymer film destabilizes due to a lateral gradient of electrostatic stress and flows away from the electroneutral regime to the charged area, resembling the patterns of charges on the substrate. Theoretical and numerical modeling based on the electrohydrodynamic instability shows excellent agreement with experimental observations both qualitatively and quantitatively. It is also demonstrated that the interplay between charge‐driven instability with spinodal dewetting and Rayleigh instabilities can generate finer and hierarchical polymeric patterns that are completely different from the charge patterns preintroduced on the substrate. This study provides direct evidence that the internal electric field caused by charges on the substrate is strong enough to destabilize thin polymeric films and generate patterns. This study also demonstrates new strategies for bottom‐up fabrication of structured functional materials.     

Patterning of TiO2 particles on poly(dimethyl siloxane) films by using proton irradiation and liquid-phase deposition process

Micropatterning of titanium dioxide (TiO2) on the surface of thin poly(dimethyl siloxane) (PDMS) films was described by means of proton irradiation and liquid-phase deposition (LPD) techniques. The surface of thin PDMS films was irradiated with accelerated proton ions through a pattern mask in the absence or presence of oxygen in order to create hydrophilically/hydrophobically patterned surfaces. The results of the surface analysis revealed that the PDMS films irradiated at the fluence of 1 x 10(15) ions cm-2 in the presence of oxygen showed the highest hydrophilicity. The LPD of TiO2 particles on the patterned PDMS film surface showed a selective deposition of TiO2 on the irradiated regions, leading to well defined TiO2 micropatterns. The crystal structure of the formed TiO2 films was found to be in an anatase phase by X-ray diffraction analysis. This process can be applied for patterning various metal and metal oxide particles on a polymer substrate.     

Selective laser sintering of barium titanate–polymer composite films

A selective laser sintering process has been used to consolidate electro-ceramic thin films on silicon substrates. Methods of forming pre-positioned layers of barium titanate were investigated by spin-coating the feedstock powder mixed with a commercial polymer photo-resist. The ceramic–polymer composite was deposited directly onto a nickel film which was evaporated onto a silicon substrate, pre-oxidised to form an electrically insulating layer. A range of laser processing parameters was identified in which consolidated barium titanate layers could be formed. The laser power was found to be more influential in forming sintered microstructures than laser exposure time. The microstructure of barium titanate films is sensitive to the SLS laser-processing conditions, with the optimum laser powers for the processing of the BaTiO₃–polymer found to be in the range 17–20 W. This article highlights the possibility of using ‘direct write’ techniques to produce piezoelectric materials upon silicon substrates.     

Microthermoforming of flexible, not-buried hollow microstructures for chip-based life sciences applications

A new method is presented for the manufacturing of flexible, not buried and thin-walled hollow microstructures from polymer films. This low-cost method seems to be especially suited for the fabrication of plastic microstructures for fluidic one-way applications in the field of life sciences. It is based on a thermoforming process adapted to microstructure technology and is called 'microthermoforming'. Inside a hot embossing press, a heated thin thermoplastic film is formed into the evacuated microcavities of a plate-shaped metal mould using a compressed gas. The film may be heat-sealed on to a thicker plastic film substrate inside the same press without demoulding the thermoformed film. To demonstrate the performance of the new manufacturing method, flexible capillary electrophoresis and cell culture chips from polystyrene, polycarbonate and a cyclo-olefin polymer with 16 and 625 parallel microstructures each, respectively, have been fabricated.     

Structural characterization of CdS thin film on quartz formed by femtosecond pulsed laser deposition at high temperature

CdS thin films have been grown on quartz substrates using femtosecond pulsed laser deposition. The structural and optical properties of the CdS thin films were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The results indicate that the compositional segregation of the CdS films could be drawn from the selective evaporation of sulfur from the film surface as a result of heating up the substrates. Growth temperature played an important role on changing crystal structure and optical properties of the CdS films.     

Microstructure of pulsed laser irradiated Sn and Ge-50 at.%Sn thin films on Ge single crystal substrates

The microstructures produced from pulsed laser irradiation of evaporated thin films of Sn and Ge-50 at.%Sn on single-crystal Ge substrates have been investigated as a function of laser energy density and film thickness. In general, the irradiated samples exhibit a trilayer morphology consisting of an overlayer of equiaxed β-Sn and/or -Ge in a β-Sn matrix, and epitaxial cellular and segregated-free -Ge(Sn) alloy layers. The overlayer thickness decreases and the cellular layer thickness and the cell size both increase with increasing laser energy density. The maximum Sn content in the segregation-free -Ge(Sn) alloy layers remains below 2 at.%Sn, but the maximum Sn content in the cellular -Ge(Sn) alloy layers can reach up to 55 at.%Sn, estimated from the selected area diffraction pattern.     

Depth profiling by confocal Raman microspectroscopy: semi-empirical modeling of the Raman response

It has been well documented that the use of dry optics in depth profiling by confocal Raman microspectroscopy significantly distorts the laser focal volume, thus negatively affecting the spatial resolution of the measurements. In that case, the resulting in-depth confocal profile is an outcome of several contributions: the broadening of the laser spot due to instrumental factors and diffraction, the spreading of the illuminated region due to refraction of the laser beam at the sample surface, and the influence of the confocal aperture in the collection path of the laser beam. Everall and Batchelder et al. developed simple models that describe the effect of the last two factors, i.e., laser refraction and the diameter of the pinhole aperture, on the confocal profile. In this work, we compare these theoretical predictions with experimental data obtained on a series of well-defined planar interfaces, generated by contact between thin polyethylene (PE) films (35, 53, 75, and 105 microm thickness) and a much thicker poly(methyl methacrylate) (PMMA) piece. We included two refinements in the above-mentioned models: the broadening of the laser spot due to instrumental factors and diffraction and a correction for the overestimation in the decay rate of collection efficiency predicted by Batchelder et al. These refinements were included through a semiempirical approach, consisting of independently measuring the Raman step-response in the absence of refraction by using a silicon wafer and the actual intensity decay of a thick and transparent polymer film. With these improvements, the model reliably reproduces fine features of the confocal profiles for both PE films and PMMA substrates. The results of this work show that these simple models can not only be used to assist data interpretation, but can also be used to quantitatively predict in-depth confocal profiles in experiments carried out with dry optics.     

Study of the characteristics and corrosion behavior for the Zr-based metallic glass thin film fabricated by pulse magnetron sputtering process

Two sets of source target which consist of ZrCuAlNiV and ZrTiAlNiV, respectively were selected as the target materials for preparing a series of thin film coatings on the 304 stainless steel substrate by DC pulse magnetron sputtering process. The microstructures of these as-prepared ZrCuAlNiV and ZrTiAlNiV thin films were examined by X-ray diffraction and TEM observation. In parallel, the characteristic analysis of these ZrCuAlNiV and ZrTiAlNiV alloy thin films including surface roughness, and corrosion resistance were analyzed by atomic force microscopy (AFM), and tested by electrochemical method as well as salt spray testing, respectively. The results showed that the ZrCuAlNiV thin film exhibits a typical amorphous microstructure and smooth surface with average roughness about 1 nm. The ZrCuAlNiV thin film performs similar corrosion resistance to 304 stainless steel according to the result of salt spray testing in 5% NaCl solution. Additionally, the AC impedance value of ZrCuAlNiV is 20 times than 316L stainless steel and 4 times than ZrTiAlNiV, implying that the ZrCuAlNiV thin film has better corrosion resistance than the others owing to its amorphous state.     

A growth rate, structure and surface morphology study of Si1-x-yGexCy films deposited by ArF-LCVD in tilted geometry

Ge, SiGe, SiC and SiGeC films were grown by ArF-Excimer laser induced chemical vapor deposition. The results demonstrate that in ArF-LCVD a fine and effective control of both the deposition rate, film properties and surface morphology is possible without altering the gas composition and pressure, by changing exclusively the distance between laser beam and substrate surface or by the fact of irradiating or not the films. Different distances have been achieved by tilting the sample 30° with respect to the beam, a geometry simultaneously producing both, an irradiated and a no irradiated zone in the same film.The extensive characterisation of these films was carried out through different techniques in order to see the influence of the irradiation geometry on composition, microstructure and roughness. The evaluation of the deposition rate and the XPS results revealed different growth rate behaviour along the film without considerable variations in composition. AFM proved the small roughness of the films and its strong dependence on the laser beam to substrate distance. Raman spectroscopy and XRD were used to determine the main structural properties. Additional information about surface morphology was also obtained through SEM.For pure Ge, some more studies have been performed due to the tendency of these films to show significant changes, especially in growth rate and roughness, both when the laser irradiated the samples and when temperature, pressure and laser power were varied.     

Wettability control of micropore-array films by altering the surface nanostructures

By controlling the surface nanostructure, the wettability of films with similar pore-array microstructure can be tuned from hydrophilic to nearly superhydrophobic without variation of the chemical composition. PA1 pore-array film consisting of the horizontal ZnO nanosheets was nearly superhydrophobic. PA2 pore-array film consisting of growth-hindered vertically-aligned ZnO nanorods was hydrophilic. The influences of the nanostructure shape, orientation and the micropore size on the contact angle of the PA1 films were studied. This study provides a new approach to control the wettability of films with similar pore-array structure at the micro-scale by changing their surface nanostructure. PA1 films exhibited irradiation induced reversible wettability transition. The feasibility of creating a wetted radial pattern by selective UV irradiation of PA1 film through a mask with radial pattern and water vapor condensation was also evaluated.     

Friction and adhesion properties of fluorocarbon polymer thin films prepared by magnetron sputtering

Fluorocarbon polymer thin films were deposited onto a SUS302 substrate with a poly(tetrafluoroethylene) (PTFE) target by three different types of r.f. magnetron sputtering systems with strong, weak and unbalanced magnetic fields. Friction and adhesion properties of these polymer thin films were evaluated.Friction coefficient of polymer thin films prepared with strong magnetic field, unbalanced magnetron and without magnetron (r.f. sputtering) was almost the same level, however, that prepared with the weak magnetic field was slightly lower than those of other thin films. Wear durability of polymer thin film increased with increase of the magnetic field.Adhesion strength between these thin films and SUS302 substrate and shear stress were measured by SAICAS. Both of the adhesion strength and shear stress of polymer thin films prepared with r.f. sputtering (without magnetron) were slightly higher than those prepared by magnetron sputtering systems.     

Structural characterization of Langmuir–Blodgett films by X-ray diffraction in transmission geometry

In this paper, we present a method which employs X-ray diffraction in transmission geometry for structural determination of Langmuir–Blodgett (LB) films. The LB multilayers are deposited on the outer surface of a thin glass capillary and diffraction pattern was recorded using a pin-hole flat camera. The remarkable advantage of this method is that both the multilayer reflections and in-plane reflections are recorded in one diffraction pattern which provides the following information about the film: layer thickness, electron density profile normal to the layers, in-plane packing of molecules and tilt angle of molecular chains with respect to the plane. As an example, we have determined the lattice parameters and the electron density profile of a lead stearate LB film according to one diffraction pattern where 15 orders of layer reflections and three in-plane reflections were recorded.     

HIGH Tc SUPERCONDUCTING THIN FILM DEPOSITION BY LASER INDUCED FORWARD TRANSFER

We review in this paper the basic mechanisms and potential applications of the Laser Induced Forward Transfer (LIFT) for the rapid deposition and patterning in a clean environment, of high Tc superconducting thin films. A stoichiometric oxide superconductor compound is initially deposited, in a thin layer, on an optically transparent support. By irradiating, under vacuum or in air, this precoated layer with a strongly absorbed single laser pulse through the transparent support, the film is removed from its support to be transferred onto a selected target substrate, held in contact or close to the original film. The mechanisms for transferring YBaCuO and BiSrCaCuO thin films, with a pulsed UV excimer laser are described using a thermal melting model based on the resolution of the heat flow equation. The various possibilities given by the LIFT technique for patterning high Tc films (mask and direct patterning) are also examined.     

Periodically structured glancing angle deposition thin films

Thin films fabricated using the glancing angle deposition technique have a porous microstructure consisting of freestanding columns. Many promising applications of such thin films require that the columns be arranged in periodic arrays using substrate topographies-so-called seed layers-that enforce controlled film nucleation. In this paper, we present the optimized design, fabrication, and characteristics of periodically structured thin films, achieving highly uniform periodic film morphologies. We derive geometrical rules for designing substrate seed layers, and explain how to fabricate large area seed patterns with submicrometer features. Using negative-resist electron-beam lithography and laser direct write lithography, we have reached extremely high pattern densities. An experimental analysis is provided of seed-enforced nucleation and thin-film growth, showing that the elimination of film growth between seeds is crucial, and that the substrate seed layer geometry must match the intended film microstructure. Finally, we discuss the enhanced properties of periodically structured oblique angle thin films and their applications.     

Directional Solution Coating by the Chinese Brush: A Facile Approach to Improving Molecular Alignment for High‐Performance Polymer TFTs

Directional solution coating by the Chinese brush provides a facile approach to fabricate highly oriented polymer thin films by finely controlling the wetting and dewetting processes under directional stress. The biggest advantage of the Chinese brush over the normal western brush is the freshly emergent hairs used, whose unique tapered structure renders a dynamic balance of the liquid within the brush by multiple forces when interacting with the liquid. Consequently, the liquid is steadily held within the brush without any unexpected leakage, making the liquid transfer proceed in a well‐controllable manner. It is demonstrated that the Chinese brush coating enables the crystallization of the polymer and the self‐assembly of conjugated backbones to proceed in a quasi‐steady state via a certain direction, which is attributed to the controllable receding of the three‐phase contact line during the dewetting process by the multiple parallel freshly emergent hairs. The as‐prepared polymer thin films exhibit over six times higher charge‐carrier mobility compared to the spin‐coated films, which therefore provides a general approach for high‐performance organic thin‐film transistors.     

退火温度对硅基溅射铜膜应力的影响

采用光学相移法 ,对Si基片上Cu膜应力随退火温度的变化进行了研究。研究表明 :随退火温度的升高 ,Cu膜应力减小 ,2 0 0℃时平均应力减小为 - 0 2 6 1× 10 8Pa,且应力分布均匀 ,在选区范围内应力差仅为 2 2 4 4× 10 8Pa。同时用X射线衍射技术测量分析了Cu膜经过不同退火温度热处理后的微结构组织 ,研究了Cu膜的微结构对其应力的影响     

Laser tunable Toraldo superresolution with a uniform nonlinear pupil filter

We demonstrate that it is possible to reduce the focal spot size by inserting a uniform nonlinear thin film at the aperture of a focusing lens. The reduction of spot size is tunable by adjusting the incoming laser power. In comparison with the original diffraction spot, the transverse spot size can be reduced 0.65 times. The nonlinear thin film acts effectively as a Toraldo filter, and the phase and amplitude modulation stems from the laser-induced variances in the transmission of the thin film. The proposed technique removes the need of fabricating annular pupil filters.     

Pulsed laser deposition of NiTi shape memory alloy thin films with optimum parameters

A series of experiments was carried out to optimize the pulsed laser deposition parameters for the fabrication of high quality NiTi shape memory alloy thin films. Smooth NiTi shape memory alloy thin films were deposited at high growth rate with optimum deposition parameters based on the analysis of the relationships among the morphology of the target surface and the deposited thin film, the laser energy, the target–substrate distance, the thin film composition and its growth rate. Crystal structures and phase transformation temperatures of the annealed Ni_49.7Ti_50.3 thin film were characterized by using X-ray diffraction and differential scanning calorimetry, respectively. The martensitic transformation temperature of the crystallized Ni_49.7Ti_50.3 thin film is found to be lower than room temperature and 27°C lower than that of the NiTi target material. These results are attributed to the refined grain size of the thin film and its composition, which deviates slightly from Ni₅₀Ti₅₀.