Patterning of light-emitting conjugated polymer nanofibres

This review concentrates on the applications of nanoimprint lithography (NIL) and hot embossing for the fabrications of nanolectronic devices, nanophotonic metamaterials and other nanostructures. Technical challenges and solutions in NIL such as nanofabrication of templates, removal of residual resist, pattern displacement in thermal NIL arising from thermal expansion are first discussed. In the nanofabrication of templates, dry etch in plasma for the formation of multi-step structures and ultra-sharp tip arrays in silicon, nanophotonic chiral structures with high aspect ratio in SiC are demonstrated. A bilayer technique for nondestructive removal of residual resist in thermal NIL is described. This process is successfully applied for the fabrication of T-shape gates and functional high electron mobility transistors. However, pattern displacement intrinsically existing in thermal NIL/hot embossing owing to different thermal expansions in the template and substrate, respectively, limits its further development and scale-up. Low temperature even room temperature NIL (RTNIL) was then proposed on HSQ, trying to eliminate the pattern distortion by avoiding a thermal loop in the imprint. But, considerable pressure needed in RTNIL turned the major attentions to the development of UV-curing NIL in UV-curable monomers at low temperature. A big variety of applications by low-temperature UV-curing NIL in SU-8 are described, including high-aspect-ratio phase gratings, tagging technology by nanobarcode for DNA sequencing, nanofluidic channels, nanophotonic metamaterials and biosensors. Hot embossing, as a parallel technique to NIL, was also developed, and its applications on ferroelectric polymers as well as metals are reviewed. Therefore, it is necessary to emphasize that this review is mainly attempted to review the applications of NIL/embossing instead of NIL technique advances.

We implemented and developed a number of different mechanical patterning methods, including soft hot embossing, rapid prototyping, sub-μm fluidics, high-temperature and room-temperature nanoimprinting lithography, to fabricate planar periodic structures based on organic materials. Patterns were faithfully transferred to many different organic compounds, including polymers, low-molar-mass compounds, and blends, up to 100-nm scale resolution. Lithography does not reduce the emission yields of light-emitting organic compounds, thus opening the way to the one-step realization of organic-based confined optoelectronic devices. We carefully investigated the possible changes in the optical properties (absorbance, luminescence, and quantum yield) of light-emitting species, thus ruling out any possible degradation of the active materials after patterning. In particular, the observed increase in the external luminescence yield is ascribed to the reduced self-absorption within the dielectric slab of the organic film, as a consequence of the pattern-induced enhanced forward scattering. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Room-temperature nanoimprint lithography (RT-NIL) technology has been developed to overcome critical dimensions and pattern placement errors caused by thermal expansion in the conventional nanoimprint lithography (NIL) process. We propose RT-NIL using hydrogen silsequioxane (HSQ) instead of the poly(methylmethacrylate) used in conventional NIL. We demonstrate HSQ-replicated patterns with a 90 nm diameter hole and 50 nm linewidth for room-temperature replications. Furthermore, we have developed new nanotransfer printing technology utilizing the adhesion characteristics of HSQ. We also demonstrate the transfer of photoresist and Au patterns from a mold to a substrate.

Room-temperature nanoimprint lithography in air is used in order to pattern a nonthermoplastic, low-molar-mass thiophene-based pentamer with excellent gain properties. No degradation of the luminescence efficiency of the active medium was observed after patterning. In this way, we fabricated single-mode emission distributed feedback lasers having a threshold excitation fluence of 140 μJ/cm2. The lasing line is peaked at 637 nm and exhibits a linewidth of less than 0.7 nm and a well-behaved input-output characteristic in the whole range of pump fluences. These results demonstrate room-temperature nanoimprint lithography as powerful and straightforward fabrication technique for oligomer-based nanostructured optoelectronic devices.

A room-temperature nanoimprint lithography (RT-NIL) is presented to fabricate subwavelength phase retarders by combining high-refractive-index TiO2 material, which shows some unique advantages in terms of lower cost, higher efficiency and better performances. The TiO2 subwavelength phase retarders are designed and analyzed by the rigorous coupled wave analysis, where the phase retardations of 130° to 60° from 370 to 780 nm are achieved. The phase retarders are fabricated by the RT-NIL, where the fabrication process is described in details, and SEM images of fabricated gratings are shown. Further, phase retardations and transmittances of the fabricated phase retarders are measured, which shows that the transmittances of TE polarization and TM polarization are stronger than 76 % and 85 % in visible region respectively, and the measured phase retardations agree well with the theoretical results, and the proposed RT-NIL technique is expected to find wide applications in fabrication of subwavelength optical devices in future.

When nanoimprint serves as a lithography process, it is most attractive for the ability to overcome the typical residual layer remaining without the need for etching. Then, ‘partial cavity filling’ is an efficient strategy to provide a negligible residual layer. However, this strategy requires an adequate choice of the initial layer thickness to work without defects. To promote the application of this strategy we provide a ‘guiding chart’ for initial layer choice. Due to volume conservation of the imprint polymer this guiding chart has to consider the geometric parameters of the stamp, where the polymer fills the cavities only up to a certain height, building a meniscus at its top. Furthermore, defects that may develop during the imprint due to some instability of the polymer within the cavity have to be avoided; with nanoimprint, the main instabilities are caused by van der Waals forces, temperature gradients, and electrostatic fields. Moreover, practical aspects such as a minimum polymer height required for a subsequent etching of the substrate come into play. With periodic stamp structures the guiding chart provided will indicate a window for defect-free processing considering all these limitations. As some of the relevant factors are system-specific, the user has to construct his own guiding chart in praxis, tailor-made to his particular imprint situation. To facilitate this task, all theoretical results required are presented in a graphical form, so that the quantities required can simply be read from these graphs. By means of examples, the implications of the guiding chart with respect to the choice of the initial layer are discussed with typical imprint scenarios, nanoimprint at room temperature, at elevated temperature, and under electrostatic forces. With periodic structures, the guiding chart represents a powerful and straightforward tool to avoid defects in praxis, without in-depth knowledge of the underlying physics.

Nanoimprint Lithography (NIL) has demonstrated its value in manufacturing nanostructures with extremely tight tolerances for the optics industry. Doing NIL process on single samples in the lab has been displayed for a long time in industry and academia. Scaling up from one good sample to full wafer and wafer to wafer uniformity for many wafers in a row, has some obstacles to overcome. In this paper, we discuss the process repeatability of manufacturing nanostructures starting from basic line/space through various other periodic and meta structures. Demonstrating the manufacturing capability using NIL for pattering also includes the other related process steps such as thin films and etching. We discuss key metrology, process control characterization, and process stability which include thin film RI uniformity, master to print replication uniformity, and post etch structural critical dimensions uniformity (CDU). Our NIL process has achieved 1.0nm σ on line widths at 45nm. This precision of replication includes all variation introduced from multiple stamps, wafer to wafer prints, and multiple sites within the wafer. This level of process control at the masking layer needs to be maintained for the finished structure.

: Our research on electron-phonon and phonon-phonon processes in low-dimensional semiconductor nanostructures has been focused on the effects of a surfaces and interfaces on the electron energy momentum relaxation rates due to acoustic phonon emission, new specific mechanism of electron interaction with acoustic phonons in semiconductor heterostructures, and phonon-induced processes of charge can loosing phase coherence in heterostructures. Our research provides the necessary basis for the control of 1 dissipation and for the design of nanodevices with electron-phonon relaxation and dephasing rates required specific applications. .

The integration of organic materials into electrode batteries, specifically lithium-ion batteries, has shown significant potential in enhancing battery performance. Organic materials offer several advantages, including abundant availability, environmental friendliness, and tunable properties, making them attractive alternatives to traditional inorganic materials. Research has demonstrated that organic compounds can improve the energy density, cycling stability, and overall efficiency of lithium-ion batteries. These materials contribute to better electrode flexibility, higher capacity retention, and faster charge-discharge rates. Innovations in the synthesis and design of organic electrode materials have led to the development of high-performance batteries with increased lifespan and reduced environmental impact. Challenges remain, such as ensuring long-term stability and addressing issues related to material degradation. However, ongoing advancements continue to drive the optimization of organic materials for lithium-ion batteries, promising a future with more sustainable and efficient energy storage solutions. This abstract highlights the transformative potential of organic materials in revolutionizing lithium-ion battery technology.

The authors report on the fabrication and characterization of an organic distributed feedback laser operating in the near infrared. The device, fabricated by room-temperature nanoimprint lithography, is based on an organic dye hosted by a poly(methylmethacrylate) matrix. The laser emission from an imprinted 620nm period grating is peaked at 918nm with a linewidth of 8Å and a pumping threshold of 37μJ∕cm2, and it is strongly polarized with a polarization contrast as high as 0.99. The lasing wavelength is tunable in the range of 890–930nm by adjusting the grating period, and the operational lifetime is up to 6×103 excitation pulses in vacuum environment. These results demonstrate the possibility of realizing imprinted organic-based near-infrared lasers, thus approaching spectral regions relevant for optical communication applications.

Since the beginning of this millennium, there has been an increasing interest in nanofiber-based sorbents for extraction due to their accessibility, scalability, ease of handling, high surface area, variety of chemistries available, and applications in miniaturized methods. Organic and inorganic materials have been converted into nanofibers using various techniques to obtain sorbents for use in analytical chemistry, such as sensors, filter membranes, sorptive phases, and extraction media. Polymer nanofibers are mainly prepared by electrospinning of polystyrene, polyamides, and polyacrylonitrile. In contrast, this review aims to survey other polymers, including biopolymers and biodegradable polymers. In addition, the possibilities of innovative alternative fabrication techniques leading to fiber materials with unique mechanical properties are described. We also focus on unexplored extraction formats using polymer nanofibers. Examples of recent applications benefiting from desorption with minimal solvent volume and on-line hyphenation to chromatographic methods are reported. Finally, the future prospects of these nanosorbents are discussed.

Synthesis and characterization of a new organic semiconductor material

We have demonstrated multi-step room-temperature nanoimprint lithography (RTNIL) using polystyrene (PS, average molecular weight 97 kg/mol) as the polymer layer for imprinting complex patterns. In separate experiments, single, double, and multiple (up to 10) sequential imprint steps were performed at imprint pressures between 1 to 30 MPa. To accomplish this demonstration, we designed and built a tool that controllably and repeatedly translated and pressed a sample into a stationary mold. The demonstrated inter-step alignment accuracy of this tool was ∼500 nm. Results of these experiments revealed the polymer deformation that results when nanoimprint is used to further deform a previously structured surface. The molds used in these experiments consisted of 400-nm-period diffraction gratings, as well as of rectangular structures of varying aspect ratios, ranging from 150 to 300 nm wide.

Ultrafast all-optical modulation with optically resonant nanostructures is an essential technology for high-speed signal processing on a compact optical chip. Key challenges that exist in this field are relatively low and slow modulations in the visible range as well as the use of expensive materials. Here we develop an ultrafast all-optical modulator based on MAPbBr3 perovskite metasurface supporting exciton-polariton states with exceptional points. The additional angular and spectral filtering of the modulated light transmitted through the designed metasurface allows us to achieve 2500% optical signal modulation with the shortest modulation time of 440 fs at the pump fluence of ∼40 μJ/cm2. Such a value of the modulation depth is record-high among the existing modulators in the visible range, while the main physical effect behind it is polariton condensation. Scalable and cheap metasurface fabrication via nanoimprint lithography along with the simplicity of perovskite synthesis and deposition make the developed approach promising for real-life applications.

Surface‐enhanced Raman spectroscopy (SERS) is a highly sensitive and noninvasive molecular fingerprinting technique already making an impact in fields such as medical diagnosis and environmental monitoring. However, challenges persist in the fabrication of SERS substrates, which delays the adoption of SERS as a standard analytical tool. Here, we experimentally demonstrate and compare two methods for achieving reproducible SERS substrates on a 150 mm wafer scale. In the first approach, we use nanoimprint lithography (NIL) to create highly periodic structures with subwavelength dimensions (< 300 nm). These periodic structures offer high signal uniformity, with a spatial variation of just 7.7% over a 20 × 20 µm area. In the second approach, we use a maskless reactive ion etching (RIE) process to create statistically distributed spikes in silicon wafers. Compared to the periodic structures, the statistical structures offer five times greater signal enhancement and twice the signal‐to‐background ratio at the cost of increased spatial variation. Both substrate types perform similarly or better than commercially available SERS substrates. In addition, we demonstrate spatially selective Raman mapping via microarray templating by photolithography, with potential for multimodal detection of analytes or use in quality control.