Single-lens dynamic [Formula: see text]-scanning for simultaneous in situ position detection and laser processing focus control

Existing auto-focusing methods in laser processing typically include two independent modules, one for surface detection and another for [Formula: see text]-axis adjustment. The latter is mostly implemented by mechanical [Formula: see text] stage motion, which is up to three orders of magnitude slower than the lateral processing speed. To alleviate this processing bottleneck, we developed a single-lens approach, using only one high-speed [Formula: see text]-scanning optical element, to accomplish both in situ surface detection and focus control quasi-simultaneously in a dual-beam setup. The probing beam scans the surface along the [Formula: see text]-axis continuously, and its reflection is detected by a set of confocal optics. Based on the temporal response of the detected signal, we have developed and experimentally demonstrated a dynamic surface detection method at 140-350 kHz, with a controlled detection range, high repeatability, and minimum linearity error of 1.10%. Sequentially, by synchronizing at a corresponding oscillation phase of the [Formula: see text]-scanning lens, the fabrication beam is directed to the probed [Formula: see text] position for precise focus alignment. Overall, our approach provides instantaneous surface tracking by collecting position information and executing focal control both at 140-350 kHz, which significantly accelerates the axial alignment process and offers great potential for enhancing the speed of advanced manufacturing processes in three-dimensional space.

Anisotropic material depletion in epitaxial polymer crystallization

The physical properties of a semicrystalline polymer thin film are intimately related to the morphology of its crystalline domains. While the mechanisms underlying crystallization of flat-on oriented polymer crystals are well known, similar mechanisms remain elusive for edge-on oriented thin films due to the propensity of substantially thin films to adopt flat-on orientations. Here, we employ an epitaxial polymer-substrate relationship to enforce edge-on crystallization in thin films. Using matrix-assisted pulsed laser evaporation (MAPLE), we deposit films in which crystal nucleation is spatially separated from subsequent epitaxial crystallization. These experiments, together with phase-field simulations, demonstrate a highly anisotropic and localized material depletion during edge-on crystallization. These results provide deeper insight into the physics of polymer crystallization under confinement and introduce a processing motif in the crystallization of ultrathin structured films.

Liquid-liquid phase separation within fibrillar networks

Complex fibrillar networks mediate liquid-liquid phase separation of biomolecular condensates within the cell. Mechanical interactions between these condensates and the surrounding networks are increasingly implicated in the physiology of the condensates and yet, the physical principles underlying phase separation within intracellular media remain poorly understood. Here, we elucidate the dynamics and mechanics of liquid-liquid phase separation within fibrillar networks by condensing oil droplets within biopolymer gels. We find that condensates constrained within the network pore space grow in abrupt temporal bursts. The subsequent restructuring of condensates and concomitant network deformation is contingent on the fracture of network fibrils, which is determined by a competition between condensate capillarity and network strength. As a synthetic analog to intracellular phase separation, these results further our understanding of the mechanical interactions between biomolecular condensates and fibrillar networks in the cell.

Micro-dispenser-based optical packaging scheme for grating couplers

Due to their sub-millimeter spatial resolution, ink-based additive manufacturing tools are typically considered less attractive than nanophotonics. Among these tools, precision micro-dispensers with sub-nanoliter volumetric control offer the finest spatial resolution: down to 50 µm. Within a sub-second, a flawless, surface-tension-driven spherical shape of the dielectric dot is formed as a self-assembled µlens. When combined with dispersive nanophotonic structures defined on a silicon-on-insulator substrate, we show that the dispensed dielectric µlenses [numerical aperture (NA) = 0.36] engineer the angular field distribution of vertically coupled nanostructures. The µlenses improve the angular tolerance for the input and reduces the angular spread of the output beam in the far field. The micro-dispenser is fast, scalable, and back-end-of-line compatible, allowing geometric-offset-caused efficiency reductions and center wavelength drift to be easily fixed. The design concept is experimentally verified by comparing several exemplary grating couplers with and without a µlens on top. A difference of less than 1 dB between incident angles of 7° and 14° is observed in the index-matched µlens, while the reference grating coupler shows around 5 dB contrast.

Observation of electron orbital signatures of single atoms within metal-phthalocyanines using atomic force microscopy

Resolving the electronic structure of a single atom within a molecule is of fundamental importance for understanding and predicting chemical and physical properties of functional molecules such as molecular catalysts. However, the observation of the orbital signature of an individual atom is challenging. We report here the direct identification of two adjacent transition-metal atoms, Fe and Co, within phthalocyanine molecules using high-resolution noncontact atomic force microscopy (HR-AFM). HR-AFM imaging reveals that the Co atom is brighter and presents four distinct lobes on the horizontal plane whereas the Fe atom displays a "square" morphology. Pico-force spectroscopy measurements show a larger repulsion force of about 5 pN on the tip exerted by Co in comparison to Fe. Our combined experimental and theoretical results demonstrate that both the distinguishable features in AFM images and the variation in the measured forces arise from Co's higher electron orbital occupation above the molecular plane. The ability to directly observe orbital signatures using HR-AFM should provide a promising approach to characterizing the electronic structure of an individual atom in a molecular species and to understand mechanisms of certain chemical reactions.

Unlocking High Capacity and Fast Na+ Diffusion of Hx CrS2 by Proton-Exchange Pretreatment

This study presents a new material, "H_x CrS₂ " (denotes approximate composition) formed by proton-exchange of NaCrS₂ which has a measured capacity of 728 mAh g^-1 with significant improvements to capacity retention, sustaining over 700 mAh g^-1 during cycling experiments. This is the highest reported capacity for a transition metal sulfide electrode and outperforms the most promising proposed sodium anodes to date. H_x CrS₂ exhibits a biphasic structure featuring alternating crystalline and amorphous lamella on the scale of a few nanometers. This unique structural motif enables reversible access to Cr redox in the material resulting in higher capacities than seen in the parent structure which features only S redox. Pretreatment by proton-exchange offers a route to materials such as H_x CrS₂ which provide fast diffusion and high capacities for sodium-ion batteries.

Hysteresis in the thermally induced phase transition of cellulose ethers

Functionalized cellulosics have shown promise as naturally derived thermoresponsive gelling agents. However, the dynamics of thermally induced phase transitions of these polymers at the lower critical solution temperature (LCST) are not fully understood. Here, with experiments and theoretical considerations, we address how molecular architecture dictates the mechanisms and dynamics of phase transitions for cellulose ethers. Above the LCST, we show that hydroxypropyl substituents favor the spontaneous formation of liquid droplets, whereas methyl substituents induce fibril formation through diffusive growth. In celluloses which contain both methyl and hydroxypropyl substituents, fibrillation initiates after liquid droplet formation, suppressing the fibril growth to a sub-diffusive rate. Unlike for liquid droplets, the dissolution of fibrils back into the solvated state occurs with significant thermal hysteresis. We tune this hysteresis by altering the content of substituted hydroxypropyl moieties. This work provides a systematic study to decouple competing mechanisms during the phase transition of multi-functionalized macromolecules.

Multi-focal laser processing in transparent materials using an ultrafast tunable acoustic lens

Fast and versatile alteration of focal positions is critical for applications including selective volumetric modification and parallel laser processing. In this Letter, we implement and characterize an ultrafast, variable focal system using a tunable acoustic gradient of index lens to achieve multi-focal laser processing. We apply our method to the femtosecond laser-induced intra-volumetric modification in glass to show the flexibility in controlling focal positions. Based on this understanding, we exploit the multi-focal nature of the system to demonstrate laser machining on both surfaces of a transparent glass slide in a single lateral scan.

The Effect of Mechanical Frequency on Piezoelectrochemical Energy Harvesters

Microenergy harvesters such as piezoelectro-chemical (PEC) devices allow the extraction of low-frequency mechanical energy, which might otherwise be lost. Recent literature on PEC harvesters has noted that the input mechanical frequency affects the device current outputs, but this effect is not well understood. Mechanical energy sources often have variable frequencies, so understanding PEC harvester performance as a function of frequency is vital for the optimization of these devices. Using a commercially available lithium ion pouch cell as a test system, this work finds that applying a square-wave frequency with the fastest strain rate and longest hold time maximizes PEC current output. There is a monotonic increase in peak power, maximum half-cycle energy, and energy conversion efficiency as the input mechanical frequency approaches zero. This indicates that PEC harvesters have more flexibility in operating frequency than piezoelectric harvesters, as PEC harvesters do not have resonance or antiresonance frequencies.

Breaking a dative bond with mechanical forces

Bond breaking and forming are essential components of chemical reactions. Recently, the structure and formation of covalent bonds in single molecules have been studied by non-contact atomic force microscopy (AFM). Here, we report the details of a single dative bond breaking process using non-contact AFM. The dative bond between carbon monoxide and ferrous phthalocyanine was ruptured via mechanical forces applied by atomic force microscope tips; the process was quantitatively measured and characterized both experimentally and via quantum-based simulations. Our results show that the bond can be ruptured either by applying an attractive force of ~150 pN or by a repulsive force of ~220 pN with a significant contribution of shear forces, accompanied by changes of the spin state of the system. Our combined experimental and computational studies provide a deeper understanding of the chemical bond breaking process.

Evolution of Polymer Colloid Structure During Precipitation and Phase Separation

Polymer colloids arise in a variety of contexts ranging from synthetic to natural systems. The structure of polymeric colloids is crucial to their function and application. Hence, understanding the mechanism of structure formation in polymer colloids is important to enabling advances in their production and subsequent use as enabling materials in new technologies. Here, we demonstrate how the specific pathway from precipitation to vitrification dictates the resulting morphology of colloids fabricated from polymer blends. Through continuum simulations, free energy calculations, and experiments, we reveal how colloid structure changes with the trajectory taken through the phase diagram. We demonstrate that during solvent exchange, polymer-solvent phase separation of a homogeneous condensate can precede polymer-polymer phase separation for blends of polymers that possess some degree of miscibility. For less-miscible, higher-molecular-weight blends, phase separation and kinetic arrest compete to determine the final morphology. Such an understanding of the pathways from precipitation to vitrification is critical to designing functional structured polymer colloids.

A Bioinspired Elastic Hydrogel for Solar-Driven Water Purification

The global demand for clean and safe water will continue to grow well into the 21st century. Moving forward, the lack of access to clean water, which threatens human health and strains precious energy resources, will worsen as the climate changes. Therefore, future innovations that produce potable water from contaminated sources must be sustainable. Inspired by nature, a solar absorber gel (SAG) is developed to purify water from contaminated sources using only natural sunlight. The SAG is composed of an elastic thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) hydrogel, a photothermal polydopamine (PDA) layer, and a sodium alginate (SA) network. Production of the SAG is facile; all processing is aqueous-based and occurs at room temperature. Remarkably, the SAG can purify water from various harmful reservoirs containing small molecules, oils, metals, and pathogens, using only sunlight. The SAG relies on solar energy to drive a hydrophilic/hydrophobic phase transformation at the lower critical solution temperature. Since the purification mechanism does not require water evaporation, an energy-intensive process, the passive solar water-purification rate is the highest reported. This discovery can be transformative in the sustainable production of clean water to improve the quality of human life.

Interfacial Engineering to Tailor the Properties of Multifunctional Ultralight Weight hBN-Polymer Composite Aerogels

A common feature of aerogels is that they are brittle and suffer from poor mechanical properties. The development of high-performance, lightweight, and mechanically robust polymer composite aerogels may find use in a broad range of applications such as packaging, transportation, construction, electronics, and aerospace. Most aerogels are made of ceramic materials, such as silica, alumina, and carbide. These aerogels are dense and brittle. Two-dimensional (2D) layered nanostructures such as graphene, graphene oxide and hexagonal boron nitride (hBN) have promising potential in emerging technologies including those involved in extreme environmental conditions because they can withstand high temperatures, harsh chemical environments, and corrosion. Here, we report the development of highly porous, ultralightweight, and flexible aerogel composites made by the infiltration of various polymers into 2D hBN aerogels. The 2D hBN aerogels in which pore size could be controlled were fabricated using a unique self-assembly approach involving polystyrene nanoparticles as templates for ammonia borane into desired structures. We have shown that the physical, mechanical, and thermal properties of hBN-polymer composite aerogels can be tuned by the infiltration of different additives. We also performed theoretical calculations to gain insight into the interfacial interactions between the hBN-polymer structure, as the interface is critical in determining key material properties.

Crystalline Nature of Colloids in Methylammonium Lead Halide Perovskite Precursor Inks Revealed by Cryo-Electron Microscopy

Metal halide perovskites have generated interest across many fields for the impressive optoelectronic properties achievable in films produced using facile solution-processing techniques. Previous research has revealed the colloidal nature of perovskite precursor inks and established a relationship between the colloid distribution and the film optoelectronic quality. Yet, the identity of colloids remains unknown, hindering our understanding of their role in perovskite crystallization. Here, we investigate precursor inks of the prototypical methylammonium lead triiodide perovskite using cryo-electron microscopy (cryo-EM) and show, for the first time, that the colloids are neither amorphous nor undissolved lead iodide, as previously speculated, but are a crystalline, non-perovskite material. We identify this as a perovskite precursor phase and discuss this as a potential means to understanding the role of chloride in processing. This work establishes cryo-EM as a viable technique to elucidate the nature of colloids in perovskite inks, a vital step toward a fundamental understanding of thin-film crystallization.

Effects of disorder on two-photon absorption in amorphous semiconductors

Structural disorder inherent to amorphous materials affords them unique, tailorable properties desirable for diverse applications, but our ability to exploit these phenomena is limited by a lack of understanding of complex structure-property relationships. Here we focus on nonlinear optical absorption and derive a relationship between disorder and the two-photon absorption (2PA) coefficient. We employ an open-aperture Z-scan to measure the 2PA spectra of arsenic (III) sulfide (As₂S₃) chalcogenide glass films processed with two solvents that impart different levels of structural disorder. We find that the effect of solvent choice on 2PA depends on the energy of the exciting photons and explain this as a consequence of bonding disorder and electron state localization. Our results demonstrate how optical nonlinearities in As₂S₃ can be enhanced through informed processing and present a fundamental relationship between disorder and 2PA for a generalized amorphous solid.

Controlling the Surface Chemistry of a Hydrogel for Spatially Defined Cell Adhesion

A two-step synthesis is described for activating the surface of a fully hydrated hydrogel that is of interest as a possible scaffold for neural regeneration devices. The first step exploits the water content of the hydrogel and the hydrophobicity of the reaction solvent to create a thin oxide layer on the hydrogel surface using a common titanium or zirconium alkoxide. This layer serves as a reactive interface that enables rapid transformation of the hydrophilic, cell-nonadhesive hydrogel into either a highly hydrophobic surface by reaction with an alkylphosphonic acid, or into a cell-adhesive one using a (α,ω-diphosphono)alkane. Physically imprinting a mask ("debossing") into the hydrogel, followed by a two-step surface modification with a phosphonate, allows for patterning its surface to create spatially defined, cell-adhesive regions.

Ultrafast z-scanning for high-efficiency laser micro-machining

High-throughput laser micro-machining demands precise control of the laser beam position to achieve optimal efficiency, but existing methods can be both time-consuming and cost-prohibitive. In this paper, we demonstrate a new high-throughput micro-machining technique based on rapidly scanning the laser focal point along the optical axis using an acoustically driven variable focal length lens. Our results show that this scanning method enables higher machining rates over a range of defocus distances and that the effect becomes more significant as the laser energy is increased. In a specific example of silicon, we achieve a nearly threefold increase in the machining rate, while maintaining sharp side walls and a small spot size. This method has great potential for improving the micro-machining efficiency of conventional systems and also opens the door to applying laser machining to workpieces with uneven topography that have been traditionally difficult to process.

Concentration dependence of As2S3 chalcogenide glass cluster size in amine solution

Solution processing chalcogenide glasses is a common and effective first step in optoelectronic device fabrication. Arsenic(iii) sulfide (As₂S₃) is believed to take on a nanoscale cluster structure in n-propylamine and n-butylamine, which affects the morphology and properties of the deposited material; however, the size of these clusters and the mechanism of size determination are poorly understood. We combine experimental and analytical techniques to investigate As₂S₃ cluster size in n-propylamine and its dependence on solution concentration. We find that the cluster size increases with concentration and show that this trend is consistent across independent experimental techniques. We then explain these results by proposing a simplified dissolution mechanism and deriving cluster size through a free energy argument. Our findings enable informed control of chalcogenide glass cluster size during solution processing and improved property control in optoelectronic device fabrication.

A mechanism for cluster size determination in solution-processed chalcogenide glasses is proposed, enabling improved property control in optoelectronic device fabrication.

Perforation Does Not Compromise Patterned Two-Dimensional Substrates for Cell Attachment and Aligned Spreading

Polymeric sheets were perforated by laser ablation and were uncompromised by a debris field when first treated with a thin layer of photoresist. Polymer sheets perforated with holes comprising 5, 10, and 20% of the nominal surface area were then patterned in stripes by photolithography, which was followed by synthesis in exposed regions of a cell-attractive zirconium oxide-1,4-butanediphosphonic acid interface. Microscopic and scanning electron microscopy analyses following removal of unexposed photoresist show well-aligned stripes for all levels of these perforations. NIH 3T3 fibroblasts plated on each of these perforated surfaces attached to the interface and spread in alignment with pattern fidelity in every case that is as high as that measured on a nonperforated, patterned substrate.

Photoluminescence of Functionalized Germanium Nanocrystals Embedded in Arsenic Sulfide Glass

Embedding metallic and semiconductor nanoparticles in a chalcogenide glass matrix effectively modifies the photonic properties. Such nanostructured materials could play an important role in optoelectronic devices, catalysis, and imaging applications. In this work, we fabricate and characterize germanium nanocrystals (Ge NCs) embedded in arsenic sulfide thin films by pulsed laser ablation in aliphatic amine solutions. Unstable surface termination of aliphatic groups and stable termination by amine on Ge NCs are indicated by Raman and Fourier-transform infrared spectroscopy measurements. A broad-band photoluminescence in the visible range is observed for the amine functionalized Ge NCs. A noticeable enhancement of fluorescence is observed for Ge NCs in arsenic sulfide, after annealing to remove the residual solvent of the glass matrix.

Irreversible Adsorption Controls Crystallization in Vapor-Deposited Polymer Thin Films

Matrix-assisted pulsed laser evaporation (MAPLE) provides a gentle means for the quasi-vapor deposition of macromolecules. It offers a unique opportunity for the bottom-up control of polymer crystallization as film growth and crystallization occur simultaneously. Surprisingly, with increasing deposition time, it has been shown that crystallization becomes prohibited despite the availability of polymer via continuous deposition. In this Letter, we investigate the molecular origins of suppressed crystallization in poly(ethylene oxide) films deposited by MAPLE atop silicon substrates. We find that suppressed crystallization results from the formation of an irreversibly adsorbed polymer nanolayer at the substrate that forms during deposition. Substrate temperature is shown to influence the stability of the irreversibly adsorbed nanolayer and, hence, polymer thin film crystallization. Our investigation offers new insight into how temperature and interfacial interactions can serve as a new toolbox to tune polymer film morphology in bottom-up deposition.

Selectable light-sheet uniformity using tuned axial scanning

Light-sheet fluorescence microscopy (LSFM) is an optical sectioning technique capable of rapid three-dimensional (3D) imaging of a wide range of specimens with reduced phototoxicity and superior background rejection. However, traditional light-sheet generation approaches based on elliptical or circular Gaussian beams suffer an inherent trade-off between light-sheet thickness and area over which this thickness is preserved. Recently, an increase in light-sheet uniformity was demonstrated using rapid biaxial Gaussian beam scanning along the lateral and beam propagation directions. Here we apply a similar scanning concept to an elliptical beam generated by a cylindrical lens. In this case, only z-scanning of the elliptical beam is required and hence experimental implementation of the setup can be simplified. We introduce a simple dimensionless uniformity statistic to better characterize scanned light-sheets and experimentally demonstrate custom tailored uniformities up to a factor of 5 higher than those of unscanned elliptical beams. This technique offers a straightforward way to generate and characterize a custom illumination profile that provides enhanced utilization of the detector dynamic range and field of view, opening the door to faster and more efficient 2D and 3D imaging.

Three-dimensional particle tracking via tunable color-encoded multiplexing

We present a novel 3D tracking approach capable of locating single particles with nanometric precision over wide axial ranges. Our method uses a fast acousto-optic liquid lens implemented in a bright field microscope to multiplex light based on color into different and selectable focal planes. By separating the red, green, and blue channels from an image captured with a color camera, information from up to three focal planes can be retrieved. Multiplane information from the particle diffraction rings enables precisely locating and tracking individual objects up to an axial range about 5 times larger than conventional single-plane approaches. We apply our method to the 3D visualization of the well-known coffee-stain phenomenon in evaporating water droplets.

Toward Low-Frequency Mechanical Energy Harvesting Using Energy-Dense Piezoelectrochemical Materials

The piezoelectrochemical coupling between mechanical stress and electrochemical potential is explored in the context of mechanical energy harvesting and shown to have promise in developing high-energy-density harvesters for low-frequency applications (e.g., human locomotion). This novel concept is demonstrated experimentally by cyclically compressing an off-the-shelf lithium-ion battery and measuring the generated electric power output.

Improved efficiency of hybrid organic photovoltaics by pulsed laser sintering of silver nanowire network transparent electrode

In this Research Article, we demonstrate pulsed laser processing of a silver nanowire network transparent conductor on top of an otherwise complete solar cell. The macroscopic pulsed laser irradiation serves to sinter nanowire-nanowire junctions on the nanoscale, leading to a much more conductive electrode. We fabricate hybrid silicon/organic heterojunction photovoltaic devices, which have ITO-free, solution processed, and laser processed transparent electrodes. Furthermore, devices which have high resistive losses show up to a 35% increase in power conversion efficiency after laser processing. We perform this study over a range of laser fluences, and a range of nanowire area coverage to investigate the sintering mechanism of nanowires inside of a device stack. The increase in device performance is modeled using a simple photovoltaic diode approach and compares favorably to the experimental data.

Transport and Stability of Laser-Deposited Amorphous Polymer Nanoglobules

We characterized the transport, i.e., time-of-flight, and nanoscale thermal properties of amorphous polymer nanoglobules fabricated via a laser-deposition technique, Matrix-Assisted Pulsed Laser Deposition (MAPLE). Here, we report the first experimental measurement of the velocity of polymer during MAPLE processing and its connection to nanostructured film formation. A nanoscale dilatometry technique using atomic force microscopy was employed to directly measure the thermal properties of MAPLE-deposited polymer nanoglobules. Similarly to bulk stable polymer glasses deposited by MAPLE, polymer nanoglobules were found to exhibit enhanced thermal stability and low density despite containing only thousands of molecules. By directly connecting the exceptional properties of the nanostructured building blocks to those of bulk stable glasses, we gain insight into the physics of glassy polymeric materials formed via vapor-assisted techniques.

Non-spherical particles for optical trap assisted nanopatterning

Optical trap assisted nanopatterning is a laser direct-write technique that uses an optically trapped microsphere as a near-field objective. The type of feature that one can create with this technique depends on several factors, one of which is the shape of the microbead. In this paper, we examine how the geometry of the bead affects the focus of the light through a combination of experiments and simulations. We realize nanopatterning using non-spherical dielectric particles to shape the light-material interaction. We model the resulting nanoscale features with a finite difference time domain simulation and obtain very good agreement with the experiments. This work opens the way to systematic engineering of the microparticle geometry in order to tailor the near-field focus to specific nanopatterning applications.

Simultaneous imaging of multiple focal planes for three-dimensional microscopy using ultra-high-speed adaptive optics

Traditional white-light and fluorescent imaging techniques provide powerful methods to extract high-resolution information from two-dimensional (2-D) sections, but to retrieve information from a three-dimensional (3-D) volume they require relatively slow scanning methods that result in increased acquisition time. Using an ultra-high speed liquid lens, we circumvent this problem by simultaneously acquiring images from multiple focal planes. We demonstrate this method by imaging microparticles and cells flowing in 3-D microfluidic channels.

Parallel optical trap assisted nanopatterning on rough surfaces

There exist many optical lithography techniques for generating nanostructures on hard, flat surfaces over large areas. However, few techniques are able to create such patterns on soft materials or surfaces with pre-existing structure. To address this need, we demonstrate the use of parallel optical trap assisted nanopatterning (OTAN) to provide an efficient and robust direct-write method of producing nanoscale features without the need for focal plane adjustment. Parallel patterning on model surfaces of polyimide with vertical steps greater than 1.5 µm shows a feature size uncertainty better than 4% across the step and lateral positional accuracy of 25 nm. A Brownian motion model is used to describe the positional accuracy enabling one to predict how variation in system parameters will affect the nanopatterning results. These combined results suggest that OTAN is a viable technique for massively parallel direct-write nanolithography on non-traditional surfaces.

Ultrastable nanostructured polymer glasses

Owing to the kinetic nature of the glass transition, the ability to significantly alter the properties of amorphous solids by the typical routes to the vitreous state is restricted. For instance, an order of magnitude change in the cooling rate merely modifies the value of the glass transition temperature (T(g)) by a few degrees. Here we show that matrix-assisted pulsed laser evaporation (MAPLE) can be used to form ultrastable and nanostructured glassy polymer films which, relative to the standard poly(methyl methacrylate) glass formed on cooling at standard rates, are 40% less dense, have a 40 K higher T(g), and exhibit a two orders of magnitude enhancement in kinetic stability at high temperatures. The unique set of properties of MAPLE-deposited glasses may make them attractive in technologies where weight and stability are central design issues.

Chalcogenide glass microlenses by inkjet printing

We demonstrate micrometer scale mid-IR lenses for integrated optics, using solution-based inkjet printing techniques and subsequent processing. Arsenic sulfide spherical microlenses with diameters of 10-350 μm and focal lengths of 10-700 μm have been fabricated. The baking conditions can be used to tune the precise focal length.

Synthesis of platinum dendrites and nanowires via directed electrochemical nanowire assembly

Directed electrochemical nanowire assembly is a promising high growth rate technique for synthesizing electrically connected nanowires and dendrites at desired locations. Here we demonstrate the directed growth and morphological control of edge-supported platinum nanostructures by applying an alternating electric field across a chloroplatinic acid solution. The dendrite structure is characterized with respect to the driving frequency, amplitude, offset, and salt concentration and is well-explained by classical models. Control over the tip diameter, side branch spacing, and amplitude is demonstrated, opening the door to novel device architectures for sensing and catalytic applications.

Solution-processed chalcogenide glass for integrated single-mode mid-infrared waveguides

Chalcogenide glass materials exhibit a variety of optical properties that make them desirable for near- and mid-infrared communications and sensing applications. However, processing limitations for these photorefractive materials have made the direct integration of waveguides with sources or detectors challenging. Here we demonstrate the viability of two complementary soft lithography methods for patterning and integrating chalcogenide glass waveguides from solution. One method, micro-molding in capillaries (MIMIC), is shown to fabricate multi-mode As(2)S(3) waveguides which are directly integrated with quantum cascade lasers (QCLs). In a second method, we demonstrate the ability of micro-transfer molding (µTM), to produce arrays of single mode rib waveguides (2.5 µm wide and 4.5 µm high) over areas larger than 6 cm(2) while maintaining edge roughness below 5.1 nm. These methods form a suite of processes that can be applied to chalcogenide solutions to create a diverse array of mid-IR optical and photonic structures ranging from <5 to 10's of µm in dimension.

Wafer-scale nanopatterning and translation into high-performance piezoelectric nanowires

The development of a facile method for fabricating one-dimensional, precisely positioned nanostructures over large areas offers exciting opportunities in fundamental research and innovative applications. Large-scale nanofabrication methods have been restricted in accessibility due to their complexity and cost. Likewise, bottom-up synthesis of nanowires has been limited in methods to assemble these structures at precisely defined locations. Nanomaterials such as PbZr(x)Ti(1-x)O(3) (PZT) nanowires (NWs)--which may be useful for nonvolatile memory storage (FeRAM), nanoactuation, and nanoscale power generation--are difficult to synthesize without suffering from polycrystallinity or poor stoichiometric control. Here, we report a novel fabrication method which requires only low-resolution photolithography and electrochemical etching to generate ultrasmooth NWs over wafer scales. These nanostructures are subsequently used as patterning templates to generate PZT nanowires with the highest reported piezoelectric performance (d(eff) ∼ 145 pm/V). The combined large-scale nanopatterning with hierarchical assembly of functional nanomaterials could yield breakthroughs in areas ranging from nanodevice arrays to nanodevice powering.

Chalcogenide glass waveguides integrated with quantum cascade lasers for on-chip mid-IR photonic circuits

We demonstrate on-chip hybrid integration of chalcogenide glass waveguides and quantum cascade lasers (QCLs). Integration is achieved using an additive solution-casting and molding method to directly form As(2)S(3) strip waveguides on an existing QCL chip. Integrated As(2)S(3) strip waveguides constructed in this manner display strong optical confinement and guiding around 90° bends, with a NA of 0.24 and bend loss of 12.9dB at a 1mm radius (λ=4.8μm).

Low-loss chalcogenide waveguides on lithium niobate for the mid-infrared

We demonstrate low-loss chalcogenide (As(2)S(3)) waveguides on a LiNbO(3) substrate for the mid-IR wavelength (4.8 μm). Designed for single-mode propagation, they are fabricated through photolithography and dry-etching technology and characterized on a mid-IR measurement setup with a quantum cascade laser. For straight waveguides, propagation loss as low as 0.33 dB/cm is measured and low-loss bends on the order of 100 μm are simulated, with measurement results showing <3 dB for a 250 μm bend radius. The coupling efficiency is estimated to be 81%. In addition, the influences of variations in width and bend radius are also investigated.

Mid-infrared characterization of solution-processed As2S3 chalcogenide glass waveguides

An etch-free and cost-effective deposition and patterning method to fabricate mid-infrared chalcogenide glass waveguides for chemical sensing applications is introduced. As(2)S(3) raised strip optical waveguides are produced by casting a liquid solution of As(2)S(3) glass in capillary channel molds formed by soft lithography. Mid-IR transmission is characterized by coupling the output of a quantum cascade (QC) laser (lambda = 4.8 microm) into the 40 microm wide by 10 microm thick multi-mode waveguides. Loss as low as 4.5 dB/cm is achieved using suitable substrate materials and post-processing. Optical absorption and surface roughness measurements indicate that the solution-processed films are of sufficient quality for optical devices and are promising for further development of waveguide-based mid-IR elements.

Influence of annealing conditions on the optical and structural properties of spin-coated As(2)S(3) chalcogenide glass thin films

Spin-coating of chalcogenide glass is a low-cost, scalable method to create optical grade thin films, which are ideal for visible and infrared applications. In this paper, we study the influence of annealing on optical parameters of As(2)S(3) films by examining UV-visible and infrared spectroscopy and correlating the results to changes in the physical properties associated with solvent removal. Evaporation of excess solvent results in a more highly coordinated, denser glass network with higher index and lower absorption. Depending on the annealing temperature and time, index values ranging from n = 2.1 to the bulk value (n = 2.4) can be obtained, enabling a pathway to materials optimization.

Two-photon microscopy with simultaneous standard and extended depth of field using a tunable acoustic gradient-index lens

We describe a simple setup that allows depth of field switching at kilohertz rates in a nonlinear microscope. Beam profile and/or divergence are modulated using a tunable, acoustically driven gradient-index fluid lens. We demonstrate two modulation strategies, one based on fast varifocus scanning during each pixel and the other based on pseudo-Bessel beam excitation. Average beam shape is switched every line during scanning, resulting in the interlaced acquisition of two different images. We apply this approach to the simultaneous standard and 4.5x-extended depth-of-field imaging of developing embryos.

Array-based optical nanolithography using optically trapped microlenses

Current demands on optical nanolithography require the ability to rapidly and cost-effectively write arbitrary patterns over large areas with sub-diffraction limit feature sizes. The challenge in accomplishing this with arrays of near-field probes is maintaining equal separations between the substrate and each probe, even over non-planar substrates. Here we demonstrate array-based laser nanolithography where each probe is a microsphere capable of fabricating 100 nm structures using 355 nm light when self-positioned near a surface by Bessel beam optical trapping. We achieve both a feature size uniformity and relative positioning accuracy better than 15 nm, which agrees well with our model. Further improvements are possible using higher power and/or narrower Bessel beam optical traps.

High-speed varifocal imaging with a tunable acoustic gradient index of refraction lens

Fluidic lenses allow for varifocal optical elements, but current approaches are limited by the speed at which focal length can be changed. Here we demonstrate the use of a tunable acoustic gradient (TAG) index of refraction lens as a fast varifocal element. The optical power of the TAG lens varies continuously, allowing for rapid selection and modification of the effective focal length at time scales of 1 mus and shorter. The wavefront curvature applied to the incident light is experimentally quantified as a function of time, and single-frame imaging is demonstrated. Results indicate that the TAG lens can successfully be employed to perform high-rate imaging at multiple locations.

Optical analysis of time-averaged multiscale Bessel beams generated by a tunable acoustic gradient index of refraction lens

Current methods for generating Bessel beams are limited to fixed beam sizes or, in the case of conventional adaptive optics, relatively long switching times between beam shapes. We analyze the multiscale Bessel beams created using an alternative rapidly switchable device: a tunable acoustic gradient index (TAG) lens. The shape of the beams and their nondiffracting, self-healing characteristics are studied experimentally and explained theoretically using both geometric and Fourier optics. By adjusting the electrical driving signal, we can tune the ring spacings, the size of the central spot, and the working distance of the lens. The results presented here will enable researchers to employ dynamic Bessel beams generated by TAG lenses.