Distributed feedback lasers produced using soft lithography

Carbon Nanotubes In article number 2400303, Xiaojun Wei, Feibing Xiong, Huaping Liu, and co-workers developed a surfactant micelle-driven, high-efficiency, and high-resolution method for length separation of carbon nanotubes. Long carbon nanotubes can spontaneously precipitate for binary-surfactant system. This technique is perfectly compatible with surfactant-based methods for structure separations of carbon nanotubes and is significant for fabrication of high-performance optoelectronic devices.

Photodetector based on 2H-WSe2 grown by physical vapor deposition method

Summary form only given. A stagnation point flow (SPF) setup was used to directly observe deposition kinetics of colloidal particles onto micropatterned glass surfaces with well-defined surface charge heterogeneity features. The SPF system consists of a microscope focused on a small collector surface area, with an automated computer controlled image-capturing device comprising a CCD camera. Surface charge heterogeneity was microfabricated onto glass surfaces by chemically modifying well-controlled fractions of glass surface with aminosilane using a soft lithographic technique. Particle deposition was observed for a wide range of flow rates (Peclet numbers) and solution ionic strengths. The observed experimental particle deposition rates at various physicochemical conditions were compared to predictions based on a patchwise charge-heterogeneity model. Comparisons revealed that (1) deviation from patch model occurs at high flow rates (or Peclet numbers), (2) patch model approximates deposition rate at lower Peclet numbers, and (3) deviation from patch model predictions occurs at a lower flow velocity for lower ionic strength runs. The particle deposition behavior and breakdown of patch model are attributed to coupling between hydrodynamic and electrostatic double layer interactions. A mechanistic model which we term the bump effect is used to describe deposition behavior on micropatterned glass surfaces.

A static platelet adhesion test using whole human blood was employed to assess the affinity of various bare polymer (sulfonated polystyrene, acetal resin, Teflon FEP, polystyrene) surfaces as well as various surfaces of glass and polymers that were coated with plasma proteins. Platelet adhesion to the bare polymer surfaces was found to increase with increasing solid surface tension of the substrate. With protein‐coated glass and polymer surfaces, however, platelet adhesion did not follow the above pattern; more platelets adhered to the fibrinogen‐coated surfaces than to albumin‐coated surfaces. The solid surface tension of the underlying substrate also influenced the adhesion of platelets to the protein‐coated surfaces; platelet adhesion to the proteincoated high‐energy sulfonated polystyrene substrates was found to be greater than to the corresponding protein‐coated lower‐energy substrates of acetal resin and Teflon FEP.

Long-range spatial coherence can be induced in incoherent thermal emitters by embedding a periodic grating within a material supporting propagating polaritons or dielectric modes. However, only a single spatially coherent mode is supported by purely periodic thermal emitters. While various designs have been proposed for the purpose of allowing arbitrary emission profiles, the limitations associated with the partial spatial coherence of thermal emitters are not known. Here, we explore superstructure gratings (SSGs) to control the spatial and spectral properties of thermal emitters. SSGs have long-range periodicity but employ a unit cell that provides multiple Bragg vectors to interact with light. These Bragg vectors allow simultaneous launching of polaritons with different frequencies/wavevectors in a single grating, manifesting as additional spatial and spectral modes in the thermal emission profile. However, SSGs still have a well-defined period, which allows us to assess the role that finite spatial coherence plays in thermal emitters. We find that the spatial coherence length defines the maximum possible SSG period that can be used. This provides a fundamental limit on the degree of spatial coherence that can be induced in a thermal emitter and has broader implications for the use of techniques such as inverse design for structure optimization.

Elastomeric stamps and molds provide a great opportunity to eliminate some of the disadvantages of photolithograpy, which is currently the leading technology for fabricating small structures. In the case of "soft lithography" there is no need for complex laboratory facilities and high-energy radiation. Therefore, this process is simple, inexpensive, and accessible even to molecular chemists. The current state of development in this promising area of research is presented here.

The evolutions of the spectrum and spatial-coherence of light in optical resonators are investigated theoretically in detail on the basis of coherence theory in the space-frequency domain. The initial light in the resonator is assumed to be polychromatic and spatially incoherent with a certain spectral width. By considering the effects of the edge diffraction and phase modulation, the evolutions of the spectrum and coherence are clearly demonstrated for different types of resonator. The results show that the spectral evolution is affected not only by the g-factor of the resonator (the type of resonator), but also by the edge diffraction and phase modulation. We introduce a new parameter, called the global degree of spatial coherence, to characterize the spatial coherence on each mirror. The spatial-coherence evolution is also affected by g-factor of the resonator, edge diffraction, and phase modulation. The physical mechanism of these phenomena is explained and discussed.

We demonstrate enhanced light extraction in organic light-emitting devices (OLEDs) by using microlens arrays fabricated by a soft lithography technique. A large-area and close-packed polystyrene (PS) monolayer was formed on the SiO2 substrate using a convective-capillary assembly method, and a polydimethylsiloxane polymer was used to obtain a concave template, from which microlens arrays were fabricated from a photopolymerizable transparent optical adhesive. The microlens contact angle and array fill factor both depend on the size of PS microspheres, and nearly close-packed, hemispherical microlens arrays with microlens contact angle of (85 ± 5 deg) and array fill factor of (85 ± 3)% were obtained with 100-μm PS microspheres. The enhancement in the light-extraction efficiency in OLEDs when such fabricated microlens arrays were attached to the light-emitting surface depends on the contact angle of microlens, device size, and detailed multilayer structure of the OLED. For a large-area (12 × 12 mm) fluorescent OLED with a near close-packed hemispherical microlens array, a maximum enhancement of (70 ± 7)% in the light-extraction efficiency was achieved.

Photolithography and soft lithography are two common methods for fabrication of microfluidic cell culture devices. Well-defined microstructures are created by exposing a photoresist to UV-light under a photolithographic mask in which the intended patterns are transparent. The subsequent cross-linking of UV-exposed photoresist generates a reusable master that serves as a template for an elastomer, commonly polydimethylsiloxane (PDMS), that reciprocally recaptures the structures of the master in an optically clear and oxygen-permeable rubber-like material. Connections to the cell culture-containing channels of the device for perfusion of culture medium can be established by inserting tubing through the elastomer. In this protocol, the basic steps for making a standard microfluidic device for cell-based assays from photolithography and soft lithography techniques are outlined.

Three-dimensional (3D) organoid engineering aims to steer cell aggregates toward physiological mimicking of human tissue and organ systems at the cellular level, essentially serving as tissue and organ proxies that recapitulate biological parameters (e.g., spatial organization of heterogenous tissue-specific cells, cell-cell interactions, etc.). Currently, attempts at generation of brain organoids do not mature beyond the prenatal brain equivalent, the major obstacle being the lack of vascularization in the initial embryoid bodies that ultimately limit the growth and maturation of the organoids. Thus, attention is turned toward generation of a brain-on-a-chip model that can serve as a relevant model of the human brain in its recapitulation of the neuronal circuit (i.e., organoid-on-chip or “OOC”; brain-on-chip or “BOC”). In this study, soft lithography techniques using polydimethylsiloxane (PDMS) elastomers were implemented to fabricate a microfluidic chip to serve as a BOC/OOC. A mold was fabricated using 3D printing for performing soft lithography of the BOC (followed by bonding on to a glass slide). Neural organoids (spheroids) were dispensed into the BOC using a pipette. The BOC was designed for the organoids to be captured at specific locations using micro-pillars that are located strategically within the microchannel network. Copper microelectrodes were manually inserted into the device through specially designed ports to serve as probes (as electrical sensors) and were mounted strategically for detection of electrical response from the organoids. Experiments were conducted to acquire and analyze the electrical response of the organoids when subjected to a variety of conditions (and stimuli). Two sets of organoids were tested in these experiments: organoids that are light responsive (LR) and organoids that are not light responsive (NLR). The set of experiments performed in this study include: control experiments using pure media (exposed to light), control experiments performed using media decanted from organoid suspensions (with and without exposure to light for both LR and NLR), baseline tests using organoids not exposed to light (control experiments for both LR and NLR), and experiments involving organoids exposed to variety of stimuli (light exposure, saline solution, etc. for both LR and NLR).

Fabrication of artificial super-hydrophobic lotus-leaf-like bamboo surfaces through soft lithography

We have proposed an easy method for growth of well-aligned patterned CNTs arrays using 3D cubic ordered mesoporous silica films as the catalyst support combined with the soft-lithography technique....

Coherent light sources have been demonstrated based on a wide range of nanostructures, however, little effort has been devoted to probing their underlying coherence properties. Here, we report long-range spatial coherence of lattice plasmon lasers constructed from a periodic array of gold nanoparticles and a liquid gain medium at room temperature. By combining spatial and temporal interferometry, we demonstrate millimeter-scale (∼1 mm) spatial coherence and picosecond (∼2 ps) temporal coherence. The long-range spatial coherence occurs even without the presence of strong coupling with the lattice plasmon mode extending over macroscopic distances in the lasing regime. This plasmonic lasing system thus provides a platform for understanding the emergence of long-range coherence from collections of nanoscale resonators and points toward novel types of distributed lasing sources.

AFM-Based nanofabrication and quality inspection of three-dimensional nanotemplates for soft lithography

The controlled patterning of polymeric surfaces at the micro- and nanoscale offers potential in the technological development of small-scale devices, particularly within the fields of photovoltaics, micro-optics and lab- and organ-on-chip, where the topological arrangement of the surface can influence a system's power generation, optical properties or biological function - such as, in the latter case, biomimicking surfaces or topological control of cellular differentiation.One of the most promising approaches in reducing manufacturing costs and complexity is by exploitation of the self-assembling properties of colloidal particles. Self-assembly techniques can be used to produce colloidal crystals onto surfaces, which can act as replicative masks, as has previously been demonstrated with colloidal lithography, or templates in mold-replication methods with resolutions dependent on particle size. Within this context, a particular emerging interest is focused on the use of self-assembled colloidal crystal surfaces in polymer replication methods such as soft lithography, hot and soft embossing and nano-imprint lithography, offering low-cost and high-resolution alternatives to conventional lithographic techniques.However, there are still challenges to overcome for this surface patterning approach to reach a manufacturing reliability and process robustness comparable to competitive technologies already available in the market, as self-assembly processes are not always 100% effective in organizing colloids within a structural pattern onto the surface. Defects often occur during template fabrication. Furthermore, issues often arise mainly at the interface between colloidal crystals and other surfaces and substrates. Particularly when utilized in high-temperature pattern replication processes, poor adhesion of colloidal particles onto the substrate results in degradation of the patterning template. These effects can render difficulties in creating stable structures with little defect that are well controlled such that a large variety of shapes can be reproduced reliably.This review presents an overview of available self-assembly methods for the creation of colloidal crystals, organized by the type of forces governing the self-assembly process: fluidic, physical, external fields, and chemical. The main focus lies on the use of spherical particles, which are favorable due to their high commercial availability and ease of synthesis. However, also shape-anisotropic particle self-assembly will be introduced, since it has recently been gaining research momentum, offering a greater flexibility in terms of patterning. Finally, an overview is provided of recent research on the fabrication of polymer nano- and microstructures by making use of colloidal self-assembled templates.