Search

Although, poly(dimethylsiloxane) (PDMS) is a widely used material in numerous applications, such as micro- or nanofabrication, the method of its selective etching has not been known up to now. In this work authors present two methods of etching the pure, additive-free and cured PDMS as a positive resist material. To achieve the chemical modification of the polymer necessary for selective etching, energetic ions were used. We created 7 μm and 45 μm thick PDMS layers and patterned them by a focused proton microbeam with various, relatively large fluences. In this paper authors demonstrate that 30 wt% Potassium Hydroxide (KOH) or 30 wt% sodium hydroxide (NaOH) at 70 °C temperature etch proton irradiated PDMS selectively, and remove the chemically sufficiently modified areas. In case of KOH development, the maximum etching rate was approximately 3.5 μm/min and it occurs at about 7.5 × 1015 ion × cm−2. In case of NaOH etching the maximum etching rate is slightly lower, 1.75 μm/min and can be found at the slightly higher fluence of 8.75 × 1015 ion × cm−2. These results are of high importance since up to this time it has not been known how to develop the additive-free, cross-linked poly(dimethylsiloxane) in lithography as a positive tone resist material.

In this work authors present for the first time how to apply the additive-free, cured PDMS as a negative tone resist material, demonstrate the creation of PDMS microstructures and test the solvent resistivity of the created microstructures. The PDMS layers were 45 um and 100 um thick, the irradiations were done with a focused proton microbeam with various fluences. After irradiation, the samples were etched with sulfuric acid that removed the unirradiated PDMS completely but left those structures intact that received high enough fluences. The etching rate of the unirradiated PDMS was also determined. Those structures that received at least 7.5*10^15 ion*cm-2 fluence did not show any signs of degradation even after 19 hours of etching. As a demonstration, 45 um and 100 um tall, high aspect ratio, good quality, undistorted microstructures were created with smooth and vertical sidewalls. The created microstructures were immersed into numerous solvents and some acids to test their compatibility. It was found that the unirradiated PDMS cannot, while the irradiated PDMS microstructures can resist to chloroform, n-hexane, toluene and sulfuric acid. Hydrogen fluoride etches both the unirradiated and the irradiated PDMS., Comment: full paper

Oxidation Scanning Probe Lithography (o-SPL) is an established method employed for device patterning at the nanometer scale. It represents a feasible and inexpensive alternative to standard lithographic techniques such as electron beam lithography (EBL) and nanoimprint lithography (NIL). In this work we applied non-contact o-SPL to an engineered class of molecular resists in order to obtain crosslinking by electrochemical driven oxidation. By patterning and developing various resist formulas we were able to obtain a reliable negative tone resist behavior based on local oxidation. Under optimal conditions, directly written patterns can routinely reach sub-30 nm lateral resolution, while the final developed features result wider, approaching 50 nm width.

A multifunctional alternate current electroluminescent device (ACEL) was achieved by compositing ZnS:Cu particles in polyvinyl butyral (PVB) with two layers of percolated silver nanowire (AgNW) electrodes. The strong hydrogen bonding interactions and entanglement of PVB chains considerably strengthened the PVB, and thus, the cured mixture of ZnS:Cu particles and freestanding PVB required no additional support. The device was fabricated by embedding AgNWs on both sides of the ZnS:Cu-PVB composite film using an inverted layer process and intense-pulsed-light treatment. The strong affinity of PVB to the polyvinyl pyrrolidone (PVP) layer, which capped the AgNWs, mechanically stabilized the device to such an extent that it could resist 10,000 bending cycles under a curvature radius of 500 μm. Using AgNW networks in both the top and bottom electrodes made a double-sided light-emitting device that could be applied to wearable lightings or flexible digital signage. The capacitance formed in the device sensitively varied with the applied bending and unfolding, thus demonstrating that the device can also be used as a deformation sensor.

Polymer thin films are generally employed as coatings on implants to prevent protein adsorption. Polymer chain mobility and surface softness have been found to contribute to the protein resistance, but also bring film instability in a liquid protein medium. We investigated the protein resistance ability of three low-T g polymers, including hydrophobic polymers polyisoprene (PI), poly( n -butyl methacrylate) (PnBMA) and hydrophilic polyethylene oxide (PEO), by overcoming the instability issue with crosslinking. We found that the T g s of PI and PEO can be increased to around 0 °C after crosslinking. The remained strong chain mobility of both films can still resist protein adsorption regardless the hydrophobicity, yet greatly increases the film stability under an aqueous circumstance. The PnBMA film increased its T g to around room temperature after crosslinking, which deteriorated the protein-resistance ability having the surface covered by BSA molecules. Our results support that the chain mobility of a polymer film plays an important role in resisting protein adsorption due to the increased entropy associated with more mobile polymer chains. By tune the degree of crosslinking, the stability of polymer in aqueous environment can be increased while the protein resistant ability can be remained. Our results provide a new strategy to design polymer materials for effective antifouling.

To construct a lithiophilic-lithiophobic gradient collector has been regarded as an effective strategy to address the challenge of lithium dendrite growth in Li metal anode. However, it was also found that the uneven stress accumulation, induced by the directional deposition, would cause fatigue-like failure in the gradient structure. In this work, a hybrid carbon nano fiber (CNF) structure, consisting of a gradient nitrogen doping CNF layer and a Cu doped CNF layer, was fabricated. The Cu-decorated carbon nanofibers not only provide a deposits-free (lithiophilic) surface, but also act as “reinforcing rib” to resist the fatigue stress. The unique hybrid structure delivered a high Coulomb efficiency and resistance to repeat stress application.

The ubiquitous presence of hydrocarbon contamination on solid surfaces alters their inherent physical properties and complicates the surface analyses. An irradiation of sample surface with electron beam can lead to the chemical transformation of the hydrocarbon layer to carbon films, which are flexible and capable of acting as a barrier for chemical etching of an underlying material. The growth of these foils is limited by supply of hydrocarbons to the writing beam position rather than the electron dose or electron beam current. The prepared films can find their applications in fabrication of surface nanostructures without a need of an electron sensitive resist material.

Superhydrophobicity of polymers is easily destroyed by careless touching due to the softness of microstructures. In this study, based on a well-constructed polyvinylidene fluoride (PVDF) surface, a novel superhydrophobic PVDF/SiO2 composite film was fabricated by adding hydrophobic SiO2 nanoparticle and solvent into a coagulation bath. The water contact angle of the composite film reached 162.3° and the sliding angle was as low as 1.5°. More importantly, the composite film could be regenerated only through immersing the composite film in the designed regeneration agent. The composition of the designed regeneration agent ensured that SiO2 nanoparticles were firmly adhered on the film surface even under the ultrasonic cleaning. Hence, the superhydrophobicity and self-cleaing property could be regenerated and maintained effectively, and moreover, these propeties could resist a proper pressure. In addition, after many rubbing-regenerating cycles, the regeneration method was still valid.

Molybdenum ditelluride (MoTe2) is an excellent building block for assembling switching devices owing to its appropriate band gap, tunable p- and n-type conduction. Electron beam lithography (EBL) as a powerful method for electronic device fabrication, generally involves thermal process for resist solidification and electron beam writing. Herein, we find that thermal processing in air and electron beam irradiation result in significant p- and n-doping in multilayer MoTe2, respectively. The p- and n-doping levels can be precisely controlled by the annealing temperature (time) and injection Cullen density, respectively. Both p-doping by annealing and n-doping using irradiation are reversible and can realize degenerate-like conduction behavior. The annealing-induced adsorption of molecules as electron acceptors (e.g. O2, H2O) on the surface MoTe2 accounts for the p-doping, whereas irradiation-induced desorption and interface charging are probably responsible for the n-doping. Polymethyl methacrylate (PMMA) coating does not completely hinder but mitigate the p-doping by annealing. In contrast, PMMA coating is invalid in inhibition of the n-doping by irradiation. These findings would promote understanding of the transport properties of intrinsic MoTe2. Besides, the facile, reversible and controllable p- and n-doping methods are helpful for assembling novel electronics with diverse functionality.

Amorphous solid water (ASW) formed by vapor deposition at cryogenic temperatures acts as an emerging competitive electron resist with virtues like direct patterning and easy removal. In this work, we systematically study the properties of the ASW resist and assess its performance for lithographic applications. Dose curves show that ASW has a low contrast of ~1.6 and it is barely affected by the incident electron energy. Ice elimination is almost linear to applied electron doses. The calculated rate is around 30 μm3/μC at 10 kV, implying approximately seven electrons remove one water molecule in this case. The minimum linewidth of 12 nm is obtained on a 120-nm-thick ASW film and refined nanostructures such as ice nanodots and “micro-snowflakes” are also presented. Finally, we perform e-beam exposure on a bilayer configuration of ASW/PMMA resist and provide an alternative way to regulate lithographic properties of conventional electron resists.

Photoresist (PR) nanopatterning using extreme-ultraviolet-lithography (EUVL) drives significant advances in integrated-circuit downsizing; however, sub-10 nm nodes severely suffer from collapse in the rinsing process (structural rigidity ↓, capillary force ↑ in denser line patterns). To mitigate collapse, we propose a new type of photoresist, hybrid material, with delicate polymer microstructure across the exposure boundary; a blend of linear chains for exposed domain and crosslinked network for masked area. This hybrid system is synthesized in a computational model through exposure-bake-curing process that generates a steep chemical gradient at the exposure boundary of polymer and triggers selective crosslinking reaction on the protected functional groups. The crosslinked structure is formed exclusively for the protection group-rich unexposed region; thus, the chemical joints tightly anchor the masked chains in aqueous solution, leading to nanoscale smoothing on the interfacial surface. Moreover, chemical linkage on the residual chains contributes to force delivery on the polymer matrix under macroscopic strain. Among the candidate materials, the hybrid resist incorporating a bicyclic crosslinker exhibits the best load transfer efficiency (E 101.4% ↑) and uniform interfacial surface (roughness 26.4% ↓), which significantly alleviates mechanical deformation and extends the critical aspect ratio of the pattern over the neat system.

Random nanohole morphologies on a photoresist surface were produced spontaneously by ion bombardment, from normal to near-normal incidence. At an optimized ion energy, the critical parameters (diameter and depth) and uniformity of these nanoholes can be tailored with multi-ion parameters, including ion fluence (i.e. bombardment time), ion flux, and incidence angle. The temporal evolution of the nanohole structures, at normal incidence, showed growth and stabilization regimes. The mass redistribution effect and the distribution of energy deposition led to the transition from nanoholes to nanoripples, which were deduced from the crater shape evolution at low incidence angles. The incidence angle-dependent evolution of the crater shape (or rim) on the resist surface is consistent with the crater function simulation, and confirms the ion bombardment-induced surface atomic currents and mass redistribution. Finally, X-ray photoelectron spectroscopy characterization confirmed ion bombardment-induced decomposition, in particular, graphitization in the surface layer of the resist.

Patterning of diamond-like carbon (DLC) and DLC:metal nanocomposites is of interest for an increasing number of applications. We demonstrate a nanoimprint lithography process based on silicon containing thermoplastic resist combined with plasma etching for straightforward patterning of such films. A variety of different structures with few hundred nanometer feature size and moderate aspect ratios were successfully realized. The quality of produced patterns was directly investigated by the means of optical and scanning electron microscopy (SEM). Such structures were further assessed by employing them in the development of gratings for guided mode resonance (GMR) effect. Optical characterization of such leaky waveguide was compared with numerical simulations based on rigorous coupled wave analysis method with good agreement. The use of such structures as refractive index variation sensors is demonstrated with sensitivity up to 319 nm/RIU, achieving an improvement close to 450% in sensitivity compared to previously reported similar sensors. This pronounced GMR signal fully validates the employed DLC material, the technology to pattern it and the possibility to develop DLC based gratings as corrosion and wear resistant refractometry sensors that are able to operate under harsh conditions providing great value and versatility., 24 pages, 9 figures

Solution processed multilayer organic light-emitting diodes (OLEDs) present challenges, especially regarding dissolution of the first layer during deposition of a second layer. In this work, we first demonstrated a plasma cross-linking technology to produce a solution processed OLED. The surfaces of organic films can be cross-linked after mixed acetylene and Ar plasma treatment for several tens of seconds and resist corrosion of organic solvent. The film thickness and surface morphology of emissive layers (EMLs) with plasma treatment and subsequently spin-rinsed with chlorobenzene are nearly unchanged. The solution processed triple-layer OLED is successfully fabricated and the current efficiency increases 50% than that of the double-layer OLED. Fluorescent characteristics of EMLs are also observed to investigate factors influencing the efficiency of the triple-layer OLED. Plasma cross-linking technology may open up a new pathway towards fabrication of all-solution processed multilayer OLEDs and other soft electronic devices.

Mechanical durability is always a significant challenge in the application and research of superhydrophobic surfaces. In this work, a mechanical durable ceria (CeO2) superhydrophobic surface was fabricated by a facile hot press sintering process of CeO2 powders on the Cu substrate. Combustion synthesis is firstly adopted to fabricate CeO2 powders because powders with suitable micro-roughness for superhydrophobicity could be obtained by this method. In order to achieve hierarchical microstructures, stainless steel mesh is used to be the template in the hot press sintering process. After 90-day storage in air, the surfaces maintain superhydrophobic performance, indicating that the coating exhibits good long-term durability. The as-obtained superhydrophobic surface shows excellent mechanical stability after ultrasonic treatments of 120 min. The morphologies of the coatings before and after ultrasonic are observed. It is found that the microstructure is stable enough to resist severe mechanical damage, indicating the strong binding force between superhydrophobic coating and the substrate. This hot-press method has also been used to prepare superhydrophobic CeO2 surfaces on other different metal substrates, which shows broad application prospects.

The energy dependence of nanostructures on a photoresist produced by ion bombardment (IB) under normal incidence is studied through atomic force microscopy and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The energy-dependent morphology evolved from weak islands via nanoholes to a smooth surface on the resist; in particular, nanoholes were produced for a broad energy range of 300–550 eV. The enrichment of light components in the surface layer of the irradiated resist was illustrated owing to the strong decomposition of the photoresist by IB. The energy dependence of the morphologies is explained according to the ToF-SIMS characterization and the existing theoretical models of IB, which is an IB-induced synergy of chemical variation and sputtering. This study extends the IB in inorganic materials into an organic-multicomponent photoresist and provides new insights into the experimental evidence for nanoholes and possible parameters to improve the relevant theoretical model.

Thermal lithography is an alternative technique that can fabricate patterns beyond the diffraction limit. In thermal lithography, it is hard to obtain morphology on demand due to the difficulty in controlling thermal diffusion caused by the long laser pulses. To address this issue, enhanced thermal lithography with multiple femtosecond laser pulse exposure is proposed in this paper. C-Sb2Te3 (CST), a fine-tunable phase change material, is used as a negative heat-mode resist for the first time. The resolution and steepness of the microstructure prepared by this method are obviously enhanced compared with the conventional way. The height of the wet-etched microstructures can be preciously adjusted by tuning the exposure dose of femtosecond laser pulses. Microstructure and thermal field analysis results reveal the origin of the high resolution and fine-tuning. CST-based phase-change memory cell arrays were fabricated with this method to confirm the feasibility and advantage. This work provides an effective way to achieve enhanced thermal lithography in the manufacturing of micro/nanostructure-based electronic and photonic devices.

This study proposes two atomic force microscope (AFM) tip-based direct nanoscratching methods including single-pass scratching and multi-pass scratching compared with a vibration-assisted scratching method to fabricate nano-grooves on the surface of the polymethylmethacrylate (PMMA) thin-film resist. In order to protect the AFM tip from wearing and optimize the subsequent etching process, the machined depth is expected slightly less than the PMMA thickness to prevent the tip directly contacting with the silicon substrate and obtain better process results. First, single-pass scratching tests are performed on films with different thickness employing varied normal loads. Results show that the machined depths of the grooves cannot be obtained slightly less than the thickness of the film very easily when scratching with single-pass method, 50–120 nm in the present study, which may not be very suitable for the following etching process. Multi-pass and vibration-assisted methods are then utilized to solve this limitation of the machined depth in single-pass process. The machined depths using the multi-pass method are dependent on scratching times and the applied normal loads. Moreover, the depth closed to the thickness of the film can be obtained by enlarging the number of the scratching cycles. However, with a longer scratching time, large tip wear can be found. For vibration assisted method, the machined depths are controlled by the vibration amplitude and the applied normal load. With the vibration in z direction increasing, the machined depth can be enlarged comparing with the single-pass, which makes the fabrication process be feasible. In addition, the vibration-assisted method contributes to less tip wear during the machining process.

The oxidation behaviour of Mo–W doped carbon-based coating (Mo–W–C) is investigated in elevated temperature (400–1000 °C). Strong metallurgical bond between Mo–W–C coating and substrate prevents any sort of delamination during heat-treatment. Isothermal oxidation tests show initial growth of metal oxides at 500 °C, however graphitic nature of the as-deposited coating is preserved. The oxidation progresses with further rise in temperature and the substrate is eventually exposed at 700 °C. The performance of Mo–W–C coating is compared with a state-of-the-art DLC(Cr/Cr–WC/W:C–H/a:C–H) coating, which shows preliminary oxidation at 400 °C and local delamination of the coating at 500 °C leading to substrate exposure. The graphitisation starts at 400 °C and the diamond-like structure is completely converted into the graphite-like structure at 500 °C. Dynamic oxidation behaviour of both the coatings is investigated using Thermo-gravimetric analysis carried out with a slow heating rate of 1 °C/min from ambient temperature to 1000 °C. Mo–W–C coating resists oxidation up to ∼800 °C whereas delamination of DLC(Cr/Cr–WC/W:C–H/a:C–H) coating is observed beyond ∼380 °C. In summary, Mo–W–C coating provides improved oxidation resistance at elevated temperature compared to DLC(Cr/Cr–WC/W:C–H/a:C–H) coating.

Nanoparticles play an important role in scientific and technological fields, because they significantly affect the polymer matrix and lead to new properties. A combination of PMMA (poly-methylmethacrylate) with metal nanoparticles can offer very wide application field in medicine, because metals may act on a broad range of microbial targets, and many mutations may occur for microorganisms to resist their antimicrobial activity. Usually metal and other nanoparticles are coated onto surfaces of substrates. Unfortunately, the durability of such nanocomposites normally is very poor, because coatings are quite sensitive to different damages. Therefore the main target of this research was to apply nanoparticles on the surface of PMMA substrate and to affect them with microwave heating that nanoparticles intervene into the polymer matrix and form permanent damage resistance metal nanolayer. It was determined that the application of the metal nanolayer on the PMMA and the partial insertion of nanoparticles into the polymer were successful. Although Cu nanoparticles mostly formed deep elements than Ag nanoparticles in the nanocomposites, they both molded grains on the surface of nanocomposites. The incorporation of metal nanoparticles into the PMMA allowed expanding the application field of nanocomposites with more durable metal nanolayers.

Proton beam writing (PBW) is a lithographic technique that has been developed since the mid 1990s, initially in Singapore followed by several groups around the world. MeV protons while penetrating materials will maintain a practically straight path. During the continued slowing down of a proton in material it will mainly interact with substrate electrons and transfer a small amount of energy to each electron, the induced secondary electrons will modify the molecular structure of resist within a few nanometers around the proton track. The recent demonstration of high aspect ratio sub 20 nm lithography in HSQ shows the potential of PBW. To explore the full capabilities of PBW, the understanding of the interaction of fast protons with different resist materials is important. Here we give an update of the growing number of resist materials that have been evaluated for PBW. In particular we evaluate the exposure and development strategies for the most promising resist materials like PMMA, HSQ, SU-8 and AR-P and compare their characteristics with respect to properties such as contrast and sensitivity. Besides an updated literature survey we also present new findings on AR-P and PMGI resists. Since PBW is a direct write technology it is important to look for fast ways to replicate micro and nanostructures. In this respect we will discuss the suitability and performance of several resists for Ni electroplating for mold fabrication in nano imprint technologies. We will summarize with an overview of proton resist characteristics like sensitivity, contrast, aspect ratio and suitability for electroplating.

A molecular dynamics (MD) study was performed to examine the effect of mold–substrate material composition on the pattern transferring and defects of the resist polymer in a thermal Nano Imprint Lithography (NIL) process. As candidate materials, single crystalline nickel (Ni), silicon (Si) and silica (SiO2, α-quartz) for the rigid mold substrate, and amorphous poly-(methylmethacrylate) (PMMA) thin film for the resist were considered for common applications in NIL processes. Three different material compositions of Si mold–Ni substrate, Ni mold–Si substrate, and quartz mold–Ni substrate were considered. In accordance with a real NIL process, a sequence of indentation–relaxation–release processes was quasi-statically simulated using isothermal ensemble simulation on tri-layer molecular structures consisting of a mold, resist, and substrate. To correlate the deformed shape and delamination of PMMA resist from the substrate in indentation and release processes, non-bond interaction energy between a rigid mold and resist was calculated for each combination of mold and substrate materials. The Si mold–Ni substrate combination shows successful pattern transfer to the resist polymer even without an anti-sticking layer as a result of the desirable balance of surface free energy for mold and substrate materials. However, Ni mold–Si substrate combination shows a critical delamination of the resist in the release process due to strong van der Waals adhesion between the resist and Ni mold. Similarly, the quartz mold–Ni substrate combination shows the same delamination in pattern transfer, but the adhesion of the resist to the quartz mold is attributed to electrostatic interaction. In order to provide guidelines for material selection in imprint-like processes where surface adsorption and wetting characteristics are critical design parameters, a simple PMMA-rigid plate model is proposed, with which consistent surface interaction characteristics in the full model NIL process simulation can be obtained.

Single-pulse femtosecond laser patterning of nitrobiphenylthiol monolayers on Au-coated Si substrates at λ = 800 nm, τ 2 . Minimum structure sizes at a 1/e laser spot diameter of about 1 μm are close to 300 nm, i.e. sub-wavelength processing is demonstrated. Noteworthy, however, no indications for negative-tone resist properties of processed monolayers are evident, that is, cross-linking of the biphenyl moieties, if at all, is marginal. Also, complementary labeling experiments provide no evidence for chemical transformation of the nitro end groups into amine functionalities. Perspectives of resonant fs-laser processing in exploiting the particular prospects of nitrobiphenylthiol monolayers as negative-tone resists and chemically patternable platforms are discussed.

High density honeycombed nanostructures of porous alumina template (PAT) have been widely used to the fabrication of various electronic, optoelectronic, magnetic, and energy storage devices. However, patterning structures at sub-100 nm feature size with large area and low cost is of great importance and hardness on which semiconductor manufacture technology depends. In this paper, soft UV nanoimprint lithography (SUNIL) by using PAT as the initial mold is studied in detail. The results reveal a significant incompatibility between these two candidates. The native nonflatness of the PAT surface is about 100 nm in the range of 2–5 μm. Resist detaches from the substrate because of the mold deformation in the nonflat SUNIL. A two-inch similar porous alumina silicon (Si) template with nanopore size of 50–100 nm is fabricated. I – t curve conducted anodization and subsequent inductive coupled plasma (ICP) dry etching are applied to ensure the uniformity of the fabricated template. The surface flatness of the similar porous alumina Si template is the same as the polished Si wafer, which perfectly matches NIL.

Nanoimprint lithography (NIL) possesses the advantages of sub-10-nm feature and low cost. Nanoimprint lithography patterns the resist with physical deformation using a mold, which can easily reproduce the required nano-scale pattern. However, the variation of environmental conditions and process parameters seriously affect reproduction quality. How to ensure the quality of imprinted pattern is essential for industry. In this study, we used the surface plasmon resonance (SPR) to estimate filling defects, including incomplete mold filling and trapped air bubble. A novel mold structure is fabricated for exciting surface plasmon and a measuring system is set up for defects measurement. Both simulation and experiment demonstrate that the SPR behavior, including the measurable reflectivity change and resonance angle shift, can be affected dramatically by filling defects. Namely, the change of reflective spectrum curve and resonance angle can be used to evaluate the quality of the imprinted pattern. This method sheds light on the problems of detecting imprinting defect and can improve the yield of NIL.

We propose a simple method to elaborate a filler-free stretchable PDMS surface strong enough to resist to successive elongation/retraction cycles even at high degree of stretching. It consists in creating free radicals on a filler-containing PDMS surface by argon plasma exposure and reacting them with a filler-free PDMS resin during the crosslinking step. Changes of physical and chemical properties upon plasma modification are monitored by FTIR and XPS spectroscopies, contact angle measurements and atomic force microscopy. Electron spin resonance (ESR) is used to identify the nature of radicals involved in interfacial bonding. Although a brittle silica-like layer is created on the filler-containing PDMS surface after plasma treatment, an increase in the PDMS/PDMS interfacial strength is observed and a high interfacial resistance has been found under elongation/retraction (stretching/relaxation) cycles.

This work presents the fabrication of hollow-core metallic structures with a complete laser interference lithography (LIL) process. A negative photoresist is used as sacrificial layer. It is exposed to the pattern resulting from the interference of two laser beams, which produces a structure of photoresist lines with a period of 600 nm. After development of the resist, platinum is deposited on the samples by DC sputtering and the resist is removed with acetone. The resulting metallic structures consist in a continuous platinum film that replicates the photoresist relief with a hollow core. The cross section of the channels is up to 0.1 μm 2 . The fabricated samples are characterized by FESEM and FIB. This last tool helps to provide a clear picture of the shape and size of the channels. Conveniently dimensioned, this array of metallic submicrometric channels can be used in microfluidic or IC cooling applications.

Proton beam writing is a maskless lithographic technique for the fabrication of 3D micro and nano structures in polymers. The fabricated structures find application in micro fluidics, optics, biosensors, etc. We use proton beam writing for micro-patterning in polymers which will facilitate fabrication of test structures for micro-components of micro-fluidic devices, organic thin film transistors (OTFT) and organic light emitting diodes (OLED). In this paper we report fabrication of varying width micro channels in PMMA and SU-8 films used as positive and negative resists respectively. The patterns were written using 2 MeV proton beam focused down to around 1 micron. We have achieved clean periodic micro-channels of width varying from few micrometers to wider ones in both the resists. Being a mask less lithography it provides an efficient way of reducing turnaround time for test structures with several channel widths and patterns being conveniently written at the same development cycle. Possible applications of the patterned structures in OLED/TFT are discussed. Additional structures like checkered board are also fabricated. Optimized fluence for both the resist has been determined.

In this paper, we present the results of resist evaluation for the fabrication of metallic stamps used in the injection moulding of micro/nano fluidic devices. The resist was evaluated in terms of its suitability to combine direct proton beam writing (PBW) and UV lithography techniques for incorporating few tens of micron and micron- to millimeter sized features respectively. In a first step PBW is used to generate the fine features with smooth sidewall profiles in AR-P 3250, here the resist shows negative behavior. Following PBW, masked i-line UV lithography was used to create larger features to complete the device design, here the AR-P 3250 acts as a positive resist. After developing, the resist was used to generate the final mould through Ni electroplating, resulting in a high quality metallic stamp.

Demolding, the process to separate stamp from molded resist, is most critical to the success of ultraviolet nanoimprint lithography (UV-NIL). In the present study we investigated adhesion and demolding force in UV-NIL for different compositions of a model UV-curable resist system containing a base (either tripropyleneglycol diacrylate with shorter oligomer length or polypropyleneglycol diacrylate with longer oligomer length), a cross-linking agent (trimethylolpropane triacrylate) and a photoinitiator (Irgacure 651). The demolding force was measured using a tensile test machine with homemade fixtures after imprinting the UV resist on a silicon stamp. While decreasing the cross-linking agent content from 49 to 0 wt% has little effect on the resist surface energy, it reduces the resist's elastic modulus drastically. The decrease in elastic modulus results in a decreased adhesion force at the resist/stamp interface thereby facilitating the demolding. The decrease in elastic modulus and, therefore, demolding force by lowering the cross-linking agent content was markedly less pronounced in tripropyleneglycol diacrylate-based resists due to its shorter oligomer length. These general findings will be useful in designing new resists for UV-NIL process.

By ultraviolet (UV)-assisted synthetic procedure, we have successfully prepared several UV curable organic/inorganic hybrid nanocomposites with excellent gas barrier capabilities, moderate hardness, and good adhesive strength. The experimental results reveal that the physical properties of nanocomposites depend on their chemical structures. Therefore, introduction of silicone and polyurethane (PU) into the Acrylics backbone dramatically raises the adhesive strength as well as refractive index and lowers the gas penetration. Furthermore, we have also applied lab-made nanocomposite g for the encapsulation of organic optoelectronic devices such as OLEDs, flexible OLEDs, and organic solar cells. With the package of lab-made nanocomposite g, the organic optoelectronic devices effectively resist the entry of moisture and oxygen in the air, extending the lifetimes.

A model of CF3 etching Si (2 × 4) surface has been developed based on density functional theory. We find that the reconstruction Si surface tends to be fully F-terminated. Meanwhile, C–C chain forms spontaneously on the top of the surface to resist further F–Si interacting. Over-saturated Si bonds could still be stable as well due to the strong F–Si bonding, however, it needs to overcome an energy barrier of 1.85 eV to achieve this doubly saturated bonding. Two reaction paths are found to investigate chemical reaction of CF3 with the full F-terminated Si surface. The first path displays that all fully saturated F–Si bonds could be over-saturated and thus produce F–Si–F bonds with an energy barrier of ∼1.85 eV. For this path, there is no product of SiF4; the second path indicates a formation of SiF4 with a much lower surface energy than the first path. The formation of SiF4 shows the possible etching mechanism.

Three-dimensional (3-D) structures are used in many applications, including the fabrication of opto-electronic and bio-MEMS devices. Among the various fabrication techniques available for 3-D structures, nano imprint lithography (NIL) is preferred for producing nanoscale 3-D patterns because of its simplicity, relatively short processing time, and high manufacturing precision. For efficient replication in NIL, a precise 3-D stamp must be used as an imprinting tool. Hence, we attempted the fabrication of original 3-D master molds by low-voltage electron beam lithography (EBL). We then fabricated polydimethylsiloxane (PDMS) stamps from the original 3-D mold via replica molding with ultrasonic vibration.First, we experimentally analyzed the characteristics of low-voltage EBL in terms of various parameters such as resist thickness, acceleration voltage, aperture size, and baking temperature. From these e-beam exposure experiments, we found that the exposure depth and width were almost saturated at 3 kV or lesser, even when the electron dosage was increased. This allowed for the fabrication of various stepped 3-D nanostructures at a low voltage. In addition, by using line-dose EBL, V-groove patterns could be fabricated on a cured electron resist (ER) at a low voltage and low baking temperature. Finally, the depth variation could be controlled to within 10 nm through superposition exposure at 1 kV. From these results, we determined the optimum electron beam exposure conditions for the fabrication of various 3-D structures on ERs by low-voltage EBL. We then fabricated PDMS stamps via the replica molding process.

Microlens arrays of high-refractive-index glass GeO 2 -SiO 2 were fabricated by femtosecond laser lithography assisted micromachining. GeO 2 -SiO 2 thin glass films, which were deposited by plasma-enhanced chemical vapor deposition, have a refractive index of 1.4902 and exhibit high transparency at wavelengths longer than 320 nm. Using a femtosecond laser, three-dimensional patterns were written inside resists on GeO 2 -SiO 2 films, and then the patterns were transferred to the underlying films by CHF 3 and O 2 plasma treatments. This combined process enabled us to obtain uniform microlens structures with a diameter of 38 μm. The heights of the transferred lenses were approximately one-quarter the height of the resist patterns, due to differences in the plasma etching rates between GeO 2 -SiO 2 and the resist. The lens surfaces were smooth. When 632.8-nm-wavelength He-Ne laser light was normally coupled to the lenses, focal spots with a diameter of 3.0 μm were uniformly observed. The combined process was effective in fabricating three-dimensional surfaces of inorganic optical materials.

Maskless photolithographic methods have been developed using digital micromirror devices (DMDs) and grating light valves (GLVs), which are spatial light modulators (SLMs), because liquid crystal display (LCD) panel industries spend huge amounts of money for the cost of TFT (thin film resist)-LCD photomasks. The technology has been developed for implementing 2 μm bitmap resolutions, which is a requirement for the lithographic process, though the process time is still slow for mass-production system. A DMD-based maskless exposure uses 405 nm-wavelength semiconductor lasers as an illumination source and optical engines that contain DMDs, micro lens arrays (MLAs), and projection lenses. A GLV-based system consists of UV lasers and optical write engines, which are constructed with the GLV, grating optics, and imaging lenses. Since many companies have been trying to overcome the time limitations, the maskless technology will be realized in the LCD industry in near future.

High throughput and low cost fabrication techniques in the sub-micrometer scale are attractive for the industry. Laser interference lithography (LIL) is a promising technique that can produce one, two and three-dimensional periodical patterns over large areas. In this work, two- and four-beam laser interference lithography systems are implemented to produce respectively one- and two-dimensional periodical patterns. A high-power single pulse of ∼8 ns is used as exposure process. The optimum exposure dose for a good feature patterning in a 600 nm layer of AZ-1505 photoresist deposited on silicon wafers is studied. The best aspect ratio is found for a laser fluence of 20 mJ/cm2. A method to control the width of the sub-micrometer structures based on controlling the resist thickness and the laser fluence is proposed.

In nanoimprint lithography process, resist adhesion to the mold was usually self-assembled and a release agent on the mold surface to detach easily from the imprinted resist. In the paper, the commercially available silane, 1 H ,1 H ,2 H ,2 H -perfluorodecyltrichlorosilane (CF 3 –(CF 2 ) 7 –(CH 2 ) 2 –SiCl 3 or FDTS) was used to investigate the anti-adhesion for UV-nanoimprint lithography. A water contact angle as high as 113.11 was achieved by self-assembled monolayer (SAM) deposited on the quarter mold by vapor evaporation, which is desirable for a good anti-adhesion agent between the fused silica and the curing resist. The homogeneous monolayer was also evaluated by AFM and XPS. UV-NIL using FDTS-coated fused silica process good pattern transfer fidelity. It is shown that the FDTS is an excellent and promising release agent material for UV-nanoimprint lithography.

This paper describes an initial evaluation of the use of aliphatic dithiocarboxylic acids (ADTCAs) as transient protecting agents in soft lithographic patterning, also known as microcontact printing (μCP). Surfaces micropatterned using ADTCA-based inks (C10–C16) were compared to that patterned using a standard hexadecanethiol ink. The patterns were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Etch-removal studies of SAM-coated gold substrates found that the longer chain-length ADTCAs (C13–C16) provide better protection against etching than the shorter chain-length ADTCAs (C10–C12). These studies demonstrate that ADTCA-derived SAMs can be used as effective resists for soft lithographic applications.

Nanoimprint lithography (NIL), as a low-cost and mass production technique, has played an important role in micro/nano fabrication. However, the sticking problem between the stamp and resist blocks its further application. In order to modify the contact surface, a molecular dynamics (MD) method was used to choose the proper material to coat on the surface of the stamp. According to the MD analysis, CF2 was found to be a good choice for this purpose. It was applied to the nanoimprint stamp by using the gases in reactive ion etching (RIE). A self-assembly monolayer (SAM) layer was also used in the experiment to release the contact surface energy. Both dry and wet methods were demonstrated as excellent anti-sticking approaches by measuring the contact angles and calculating the surface energy. Both the stamps after anti-sticking treatment can be used more times than the untreated stamps.

The effect of polymer matrix on laser processing of Au nanoparticles dispersed polymer resist was reported. Au nanoparticles dispersed polymer is a resist in which Au nanoparticles with average diameter of around 3 nm was dispersed. Since the resist has a strong absorption at the wavelength of around 530 nm, it can be micromachined using focused low power Nd:YVO4-SHG laser (CW, wavelength of 532 nm). From the evaluation of a dispersibility of Au nanoparticle in the different polymer using X-ray diffraction and visible ray absorbance, it was confirmed that the dispersibility of Au nanoparticle induced by the kind of polymer matrix influenced laser-processed shape. Moreover, from thermal properties and the calculation of temperature rise distribution by laser beam in polymer resist, it was predicted that the processing mechanism for thermoplastic polymer resist was related with melt and grain growth of Au nanoparticle.

Interactions between a bottom anti-reflective coating (BARC) and a photoresist can critically impact lithographic patterns. For example, a lithographic pattern can shrink or spread near a BARC interface, a process called undercutting or footing respectively, due to incompatibility between the two materials. Experiments were conducted on two industrial BARC coatings in an effort to determine the impact of BARC surface chemistry on the footing and undercutting phenomena. The BARC coatings were characterized by near edge X-ray absorption fine structure (NEXAFS), contact angle measurements, and neutron and X-ray reflectivity. Contact angle measurement using a variety of fluids showed that the fluid contact angles were independent of the type of BARC coating or the BARC processing temperature. NEXAFS measurements showed that the surface chemistry of each BARC was also independent of the processing temperature. These results suggest that acid-base interactions at the BARC-resist interface are not the cause of the footing-undercutting phenomena encountered in lithographic patterns.

A new technique called “infrared laser-assisted nanoimprint lithography” was utilised to soften the thermoplastic polymer material mR-I 8020 during nanoimprint lithography. A laser setup and a sample holder with pressure and temperature control were designed for the imprint experiments. The polymer was spin coated onto crystalline Si substrates. A prepatterned Si substrate, which is transparent for the CO 2 laser irradiation, was used as an imprint stamp as well. It was shown, that the thermoplastic resist mR-I 8020 could be successfully imprinted using the infrared CW CO 2 laser irradiation ( λ = 10.6 μm). The etching rate of the CO 2 laser beam irradiated mR-I 8020 resist film under O 2 RF (13.56 MHz) plasma treatment and during O 2 reactive ion beam etching was investigated as well.

The production of high aspect ratio microstructures is a potential growth area. The combination of deep X-ray lithography with electroforming and micromolding (i.e. LIGA) is one of the main techniques used to produce 3D microstructures. The new technique of proton micromachining employs focused MeV protons in a direct write process which is complementary to LIGA. During ion exposure of positive photoresist like PMMA, scission of molecular chains occurs. These degraded polymer chains are removed by the developer. The aim of this paper is to investigate the capabilities of proton micromachining as a lithographic technique. We show the realization of sub-surface channels, or microtunnels, which have been fabricated in only one exposure and without cutting or resurfacing the material. Using our Van-de-Graaff accelerator, the resist (PMMA) has been exposed with high-energy protons (2.5 MeV). The range of charged particles in matter is well-defined and depends on the energy. Therefore, it is possible to obtain a dose which is sufficient to develop the bottom part of the ion paths but not the top part. Thus, by selecting the energy and the exposure time, a big variety of microtunnels can be realized.

Various clean complicated micro-pattern designs based on n-octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) on silicon substrates have been realized in large area by using vacuum ultraviolet (VUV) light irradiation at the wavelength of 172 nm. The degradation process of the alkylsilane SAM with irradiation time evolution has been traced by using ellipsometry, water contact angle measurement and X-ray photoelectron spectroscopy (XPS) techniques in detail. The results indicate that the SAM can be completely removed in several minutes by the irradiation of the shorter wavelength vacuum ultraviolet light. Furthermore, the ability of the OTS-SAM as resist for chemical etching has also been demonstrated.

A conductive tip is essential for probing the electrical characterization in scanning probe microscopy (SPM). This study investigates the efficiency of W and AuPd as coating materials in a silicon cantilever for application to conductive SPM. The results show that the two self-coated probes could both be used in SCM and SPO modes. However, they were not appropriate for use in CAFM mode because the conductive films do not strongly resist wear. The presented AuPd probe outperforms the W probe because it more strongly resists the oxide formation at the end of tip.

A new tip insulating process for active metal tips allowing atomic resolution ECSTM imaging has been developed. This new method using cathodic cataphoretic paint deposition has been tested successfully. The insulating deposited film appears homogeneous under optical microscopy and it has been characterised by infra red and SEM analysis. The depositing layer of the paint is sufficiently dense to effectively resist electrolyte ion penetration and resists corrosion in various acidic, basic aqueous or non-aqueous media. The coating film does not reduce the imaging capability of the ECSTM even to atomic resolution. This new insulating method adds to the approaches available to those preparing tips for ECSTM. This approach would also be of great utility for the preparation of microelectrodes using active metals.