Surfaces,thin films and patterning of spin crossover compounds

Spin crossover compounds are multifunctional switching materials that change their spin state and many other physical properties, such as colour, magnetic susceptibility, electric conductivity, dielectric constant and mechanical properties, upon external stimuli. Spin crossover materials have been proposed for a variety of technological applications that require the elaboration of highly controlled thin films and patterns. Here, we present a brief overview of the most diffused approaches for thin film growth and patterning, showing both conventional and unconventional approaches and the most recent advancement in their applications, highlighting the most promising cases and the most critical problems.     

Status and perspectives in thin films and patterning of spin crossover compounds

Spin crossover compounds are a class of functional materials able to switch their spin state upon external stimuli. They were proposed as potential candidates for several technological applications that require highly controlled thin films and patterns. Here we present a critical overview of the most important approaches for thin film growth and patterning of spin-crossover compounds, giving special attention to Fe(ii) based molecules, which are the most studied materials. We present both conventional approaches to thin film growth (Langmuir-Blodgett, constructive chemical approach, spin coating, drop casting and vacuum sublimation) and patterning (combined top-down/bottom-up method, soft and unconventional lithography). We critically discuss the application of thin film growth and fabrication techniques highlighting the most critical aspects and the perspectives opened by the recent progress.     

Effects of molecular structure and interfacial ligation on the precision of Cu-bound alpha,omega-mercaptoalkanoic acid "molecular ruler" stacks

Nanolithography processes based on designed, precision thickness multilayer thin films (molecular rulers) have been reported that enable patterning of features on surfaces from a few to the hundred nanometer range. These strategies are unique in their potential ability to enable wafer scale patterning of features of just a few nanometers. If these techniques could be developed to be sufficiently precise and generally applicable, they would fill a long-standing need in nanoscience. In this study a systematic and detailed analysis of the growth mechanisms and molecular layer structures has been carried out for the mercaptoalkanoic acid-copper ion multilayer thin film system currently used as the standard nanolithography resist. Our results show these films form via a redox reaction of thiol groups with surface-ligated Cu(II) ions to form adlayers at only approximately 50% coverage with islanding of the alkyl chains, thereby leading to rough topographies and less than theoretical thicknesses based on a 1:1 ideal adlayer. Strategies are suggested to help overcome these issues for molecular resist applications in nanolithographic processing.     

Programmable modification of cell adhesion and zeta potential in silica microchips

Spatial patterning of thin polyacrylamide films bonded to self-assembled monolayers on silica microchannels is described as a means for manipulating cell-adhesion and electroosmotic properties in microchips. Streaming potential measurements indicate that the zeta potential is reduced by at least two orders of magnitude at biological pH, and the adhesion of several kinds of cells is reduced by 80-100%. Results are shown for cover slides and in wet-etched silica microchannels. Because the polyacrylamide film is thin and transparent, this film is consistent with optical manipulation of cells and detection of cell contents. The spatial patterning technique is straightforward and has the potential to aid on-chip analysis of single adherent cells.     

Control of wettability of molecularly thin liquid films by nanostructures

The patterning of liquid thin films on solid surfaces is very important in various fields of science and engineering related to surfaces and interfaces. A method of nanometer-scale patterning of a molecularly thin liquid film on a silicon substrate using the lyophobicity of the oxide nanostructures has recently been reported (Fukuzawa, K.; Deguchi, T.; Kawamura, J.; Mitsuya, Y.; Muramatsu, T.; Zhang, H. Appl. Phys. Lett. 2005, 87, 203108). However, the origin of the lyophobicity of the nanostructure with a height of around 1 nm, which was fabricated by probe oxidation, has not yet been clarified. In the present study, the change in thickness of the liquid film on mesa-shaped nanostructures and the wettability for the various combinations of the thickness of the liquid films and the height of ridge-shaped nanostructures were investigated. These revealed that lyophobicity is caused by a lowering of the intermolecular interaction between the liquid and silicon surfaces by the nanostructure and enables the patterning of a liquid film along it. The tendency of the wettability for a given liquid film and nanostructure size can be predicted by estimating the contributions of the intermolecular interaction and capillary pressure. In this method, the height of the nanostructure can control the wettability. These results can provide a novel method of nanoscale patterning of liquid thin films, which will be very useful in creating new functional surfaces.     

Microfabrication and imaging XPS analysis of ITO thin films

In this paper the microfabrication of ITO (tin‐doped indium oxide) films by the sol–gel process combined with chemical modification is presented. The microfabricated ITO thin film could be obtained through a one‐step process that combines film patterning with film leaching. The morphology and chemical components of the patterned ITO thin films were assessed by microscopy and XPS, respectively. Imaging XPS analysis is an effective way to evaluate the quality of the fine patterning. Copyright © 2007 John Wiley & Sons, Ltd.     

Rupture of thin films with resonant substrate patterning

We study the stability and rupture of thin liquid films on patterned substrates. It is shown that striped patterning on a length scale comparable to that of the spinodal instability leads to a resonance effect and an imperfect bifurcation of equilibrium film shapes. Weakly nonlinear analysis gives predictions for film shapes, stability, growth rates, and rupture times, which are confirmed by numerical solution of the thin-film equation. Film behavior is qualitatively different in the resonant patterning regime, but with sufficiently large domains rupture occurs on a spinodal length scale regardless of patterning. Instabilities transverse to the patterning are examined and shown to behave similarly as disturbances to films on uniform substrates. We explain some previously reported effects in terms of the imperfect bifurcation.     

Large-area patterning of coinage-metal thin films using decal transfer lithography

We describe two new procedures that appear to hold significant promise as means for patterning thin-film microstructures of the coinage metals (Cu, Ag, Au). A feature central to both is the modification of their surfaces to promote the adhesive transfer of PDMS thin-film microstructures, a material suitable for use as resist layers in large-area patterning, using Decal Transfer Lithography (DTL). The present work provides a significant extension of the capabilities of DTL patterning, providing general protocols that can be used to transfer decal resists to essentially any substrate surface. The first method involves the functionalization of a surface, specifically those of gold and silver films with a thiol-terminated silane coupling agent, (mercaptopropyl)trimethoxysilane. This self-assembled monolayer, when hydrolyzed to its silanol form, provides a robust adhesion-promoting layer suitable for use in DTL patterning. The second method exploits the surface chemistry provided by the deposition of a nanoscale silicon dioxide thin-film capping layer using e-beam evaporation. This procedure provides an exceptional method for patterning large-area, thin-film microstructures of Cu-one compatible with micrometer-scale design rules-that are essentially defect free. Both surface modification strategies enable high-quality poly(dimethylsiloxane) decal transfers, and as the current work shows, these structures are suitable for large-area micrometer-sized patterning of gold, silver, and copper thin films via both wet-etching and lift-off procedures.     

Interfacial chemistries for nanoscale transfer printing

We describe a patterning technique that uses self-assembled monolayers and other surface chemistries for guiding the transfer of material from relief features on a stamp to a substrate. This purely additive contact printing technique is capable of nanometer resolution. Pattern transfer is fast and it occurs at ambient conditions. We illustrate the versatility of this method by printing single-layer metal patterns with feature sizes from a few tens of microns to a few tens of nanometers. We also demonstrate its use for patterning, in a single step, metal/dielectric/metal multilayers for functional thin film capacitors on plastic substrates.     

喷墨打印图案化高分子薄膜及其在有机电子器件加工中的应用

喷墨打印技术由于在图案化加工方面的高效、低成本、非接触形式及柔性的加工过程等特点而被应用于有机电子器件的加工中.通过打印功能性高分子溶液,喷墨打印实现了功能高分子薄膜的沉积和图案化,并实现了有机发光二极管、有机薄膜晶体管及其集成器件的加工.对喷墨打印在有机电子器件加工中取得的成果进行了总结,同时综述了高分子溶液喷墨打印过程中存在的基本科学问题和研究现状.     

Fabrication of surface-patterned ZnO thin films using sol–gel methods and nanoimprint lithography

Surface-patterned ZnO thin films were fabricated by direct imprinting on ZnO sol and subsequent annealing process. The polymer-based ZnO sols were deposited on various substrates for the nanoimprint lithography and converted to surface-patterned ZnO gel films during the thermal curing nanoimprint process. Finally, crystalline ZnO films were obtained by subsequent annealing of the patterned ZnO gel films. The optical characterization indicates that the surface patterning of ZnO thin films can lead to an enhanced transmittance. Large-scale ZnO thin films with different patterns can be fabricated by various easy-made ordered templates using this combination of sol–gel and nanoimprint lithography techniques.     

Controlled wrinkling as a novel method for the fabrication of patterned surfaces

This article reviews recent applications of controlled wrinkling for creating structured and/or patterned interfaces, and its use in metrology. We discuss how wrinkles develop as a result of in-plane compression of thin sheets. As the wavelength of wrinkles is only dependent on elastic properties and thickness of the sheets, the phenomenon can be used in metrology for determination of elastic properties. The second aspect is its use for patterning and topographical structuring of surfaces. If mechanical properties and thickness are well controlled, wrinkle orientation and geometry can be tailored. Wavelengths between fractions of a micron and many micrometers are feasible. This process is based on a macroscopic deformation and upscaling to larger areas is possible which provides an attractive alternative to bottom-up or top-down approaches for surface patterning. We describe the formation of stable surface wrinkles in thin sheets of different materials having different surface chemistries, report on applications, and discuss the usefulness of wrinkles for building hierarchical structures.     

A new patterning method using photocatalytic lithography and selective atomic layer deposition

We report a new patterning method using photocatalytic lithography of alkylsiloxane self-assembled monolayers and selective atomic layer deposition of thin films. The photocatalytic lithography is based on the fact that the decomposition rate of the alkylsiloxane monolayers in contact with TiO2 is much faster than that with SiO2 under UV irradiation in air. The photocatalytic lithography, using a quartz plate coated with patterned TiO2 thin films, was done to prepare patterned monolayers of the alkylsiloxane on Si substrates. A ZrO2 thin film was selectively deposited onto the monolayer-patterned Si substrate by atomic layer deposition.     

A new seeding and electroless approach to alloying,direct patterning,and self-forming barriers for Cu thin-film nanostructures

In contrast to the previous studies involving sputter deposition to form Cu-alloy thin films with several atomic percentages of incorporated metallic solutes, this work examines the feasibility of using electroless deposition in conjunction with a new site-selective seeding process for the alloying and direct patterning of Cu thin-film nanostructures on dielectric layers. Very minute amounts (0.4 at.%) of manganese can be incorporated into the constituting Cu and segregated to form an interfacial layer at the SiO₂/Cu interface upon annealing in an Ar–H₂ atmosphere. The interfacial layer made up of only a few atomic layers is identified based on synchrotron X-ray spectroscopy and serves as a barrier for advanced technology nodes.     

Masterless soft lithography: patterning UV/ozone-induced adhesion on poly(dimethylsiloxane) surfaces

A novel microreactor-based photomask capable of effecting high resolution, large area patterning of UV/ozone (UVO) treatments of poly(dimethylsiloxane) (PDMS) surfaces is described. This tool forms the basis of two new soft lithographic patterning techniques that significantly extend the design rules of decal transfer lithography (DTL). The first technique, photodefined cohesive mechanical failure, fuses the design rules of photolithography with the contact-based adhesive transfer of PDMS in DTL. In a second powerful variation, the UVO masks described in this work enable a masterless soft lithographic patterning process. This latter method, UVO-patterned adhesive transfer, allows the direct transfer of PDMS-based polymer microstructures from a slab of polymer to silicon and other material surfaces. Both methods exploit the improved process qualities that result from the use of a deuterium discharge lamp to affect the UVO treatment to pattern complex, large area PDMS patterns with limiting feature sizes extending well below 1 microm (> or = 0.3 microm). The use of these structures as resists is demonstrated for the patterning of metal thin films. A time-of-flight secondary ion mass spectroscopy study of the process provides new insights into the mechanisms that contribute to the chemistry responsible for the interfacial adhesion of DTL transfers.     

Thin deposits and patterning of room-temperature-switchable one-dimensional spin-crossover compounds

We present a study on thin deposits and patterning of 1-D spin-crossover compounds Fe(II)-(L)(2)H](ClO(4))(3)·MeOH [L = 4'-(4'-pyridyl)-1,2':6'1'-bis- (pyrazolyl) pyridine] (1) that exhibit a reversible, thermally driven spin transition at room temperature. Micrometric rodlike crystals of 1 on silicon surfaces are achieved by drop casting and solvent annealing. We observed that the crystallinity of thin deposits and spin-transition properties critically depends on the deposition procedure. Furthermore, we proved processability and patterning using unconventional wet lithography that reduces the crystallite formation time by 1 order of magnitude. Thin deposits of 1 were characterized by atomic force microscopy, polarized optical microscopy and X-rays, and the switching properties were characterized by Raman spectroscopy.     

Novel, highly selective gold nanoparticle patterning on surfaces using pure water

We present a simple, novel procedure to selectively deposit gold nanoparticles using pure water. It enables patterning of nanoparticle monolayers with a remarkably high degree of selectivity on flat as well as microstructured oxide surfaces. We demonstrate that water molecules form a thin "capping" layer on exposed thiol molecules within the mercaptan self-assembled layer. This reversible capping of water molecules locally "deactivates" the thiol groups, therewith inhibiting the binding of metallic gold nanoparticles to these specific areas. This amazing role of water molecules can be used as a tool to pattern flat as well as structured surfaces with gold nanoparticles.     

Self‐Rolled Polymer Tubes: Novel Tools for Microfluidics,Microbiology, and Drug‐Delivery Systems

Recent work on the fabrication of tubular microstructures via self‐rolling of thin, bilayer polymer films is reviewed. A bending moment in the films arises due to the swelling of one component of the bilayer in a selective solvent. The inner diameters of the tubes vary from hundreds of nanometers to dozens of micrometers. The position of the tubes on the substrate and their length can be preset by photolithographic patterning of the bilayer. Prior to rolling, the bilayers can be exposed to different methods of surface functionalization, providing opportunities for engineering the microtube inner surfaces for use in microfluidic circuits and “microbiological” applications. The self‐rolling approach is promising for the development of novel drug‐ and cell‐delivery systems, as well as for tissue engineering.     

Control of doctor‐blade coated poly (3,4‐ethylenedioxythiophene)/poly(styrenesulfonate) electrodes shape on prepatterned substrates via microflow control in a drying droplet

We demonstrated a simple patterning method for the deposition of polymer electrodes such as poly(3,4‐ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS). We made use of the difference in wettability between hydrophobic surfaces and hydrophilic surfaces to make the patterns. However, the patterns made with our patterning method created undesirable ring‐like stains, which were caused by the outward flow of the solute within the PEDOT/PSS solution drop. To achieve homogenous device performance, we proposed a simple process for removing this ring‐like stain by making the surface tension gradient with dual solvent system in the PEDOT/PSS solution drop. Because this surface tension gradient causes the inward flow of the solute within the PEDOT/PSS solution drop, the ring‐like stain is removed. Finally, we confirmed the potential of our patterning method for polymer electrodes such as the PEDOT/PSS by fabricating pentacene thin‐film transistors (TFTs) and measuring the electrical properties of the pentacene TFTs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1590–1596, 2011