3D Nanolithography Research Articles

3D Nanolithography via Holographic Multi‐Focus Metalens

Abstract3D nanolithography based on two‐photon polymerization (TPP) allows for the high‐precision fabrication of nearly arbitrary 3D micro/nanostructures, finding extensive applications in areas such as micro‐optics, micro‐mechanics, and biomedicine. However, the large size, complexity of optical systems, and high costs have significantly constrained the widespread adoption of 3D nanolithography technology in both scientific research and industry. In this study, a metasurface is introduced, for the first time, into 3D nanolithography resulting in the construction of a miniaturized and simplified TPP system that achieved efficient multi‐focus parallel processing with high uniformity. A microlens array is fabricated, showcasing the system's application capacity to generate an array of devices with high consistency and quality. It is believed that the utilization of metasurface devices will provide a novel TPP operating platform, enabling richer and more flexible printing functionalities while maintaining system miniaturization and low cost.

Subdiffraction 3D Nanolithography by Two‐Photon Two‐Step Absorption and Photoinhibition

AbstractImproving the 3D resolution is a decisive step in the transition of direct laser writing from being limited to research use to being a powerful tool. Three‐color (3CL) lithography is expected to result in significantly higher resolution with two‐color lasers initiating polymerization in two steps and one‐color laser inhibiting polymerization. However, the 3CL process increases the complexity of the system and makes the influence of chromatic aberration worse which leads to non‐ideal writing results, which is ≈80 nm linewidth (≈λ/10) at present. In this study, the 3CL lithography is improved by introducing almost one color (1CL) instead of three colors to achieve subdiffraction 3D nanolithography based on two‐photon two‐step absorption and photoinhibition (T2A‐PI). Using benzil as a photoinitiator, a sub‐30 nm (<λ/17.5) lateral feature size, minimum 80 nm lateral, and 160 nm axial pitches are achieved, which, to our knowledge, is the best to be fabricated using the laser in the visible region. 3D woodpile photonic crystals and other high‐quality nanostructures are fabricated, demonstrating the unique advantages over existing direct laser writing technologies.

X-photon laser direct write 3D nanolithography

ABSTRACT Multiphoton photopolymerisation (MPP), also known as 3D nanoprinting, was studied using a wavelength-tunable femtosecond laser. The possibility of using any colour of the spectrum from 500 to 1200 nm with a fixed pulse width of 100 fs revealed an interplay of photophysical mechanisms more delicate than just two-photon photopolymerisation. An effective order of absorption, i.e. the X-photon absorption, as well as optimal exposure conditions were assessed for photosensitised and pure SZ2080 pre-polymer. The tunability of wavelength greatly influenced the dynamic fabrication window (DFW), optimised conditions resulting in a 10-fold increase. Furthermore, a non-trivial energy deposition by X-photon absorption was noted with an onset of a strong lateral size increase at longer wavelengths and can be understood as due to reaching epsilon-near-zero conditions. Such a control over the voxel aspect ratio and, consequently, the photopolymerised volume, may boost 3D nanoprinting efficiency. Overall, the results reveal wavelength being an important degree of freedom to tailor the MPP process and, if optimised, benefiting broad applications in areas of micro-optics, nanophotonic devices, metamaterials and tissue engineering.

Single‐Step 3D Printing of Micro‐Optics with Adjustable Refractive Index by Ultrafast Laser Nanolithography

AbstractLaser exposure defines voxel's dimensions as essential building blocks in direct write 3D nanolithography. However, the exposure conditions not only influence the size of the produced features but also their optical properties. This empowers the realization of an adjustable refractive index out of single material by varying the writing strategy while preserving laser 3D nanolithography's flexibility in geometry and high resolution. Here, the refractive index for the 450–1600 nm spectral range of the micro‐optics out of SZ2080 hybrid polymer is systematically studied by applying ray and wave optics approaches followed by optical resolution analysis. It reveals the exact value of the laser‐printed components instead of the determination assessed by other techniques measuring thin films or bulky volumes of the investigated substance. The studied micro‐lenses are of below 100 µm in dimensions and a clear distinction in their performance on low and high exposure doses is found by analyzing it in all different approaches and validating using different lithography setups. Findings reveal the complexity of the refractive index of the 3D micro‐optics which is influenced by the material density and morphology. A route for freedom in 3D printing shape and refractive index can be realized by the technological optimization of delicate exposure control in ultrafast laser nanolithography.

3D Nanolithography by Means of Lipid Ink Spreading Inhibition (Small 10/2023)

Lipid Ink Spreading Inhibition In article number 2205590, Eider Berganza, Michael Hirtz, and co-workers utilize dip-pen nanolithography to print lipid patches layer-by-layer forming 3D structures on a surface coated with serum albumin stabilizing the structures. The lipid molecules transfer from the probe to the substrate through a water meniscus. To further improve their stability, lipid-structures get covered with a few nanometers of gold through physical vapor deposition.

Circularly symmetric nanopores in 3D femtosecond laser nanolithography with burst control and the role of energy dose

Abstract The fabrication of three-dimensional (3D) nanostructures within optical materials is currently a highly sought-after capability. Achieving nanoscale structuring of media within its inner volume in 3D and with free design flexibility, high accuracy and precision is a development yet to be demonstrated. In this work, a 3D laser nanolithography technique is developed which allows producing mm-long hollow nanopores inside solid-state laser crystals and with a high degree of control of pore cross-sectional aspect ratio and size. We report an in-depth study on the formation of pores both within the non-thermal regime at which temperature is fast dissipated after each laser pulse, and for a thermally controlled regime using pulse-bursts which facilitate the formation of pores with highly circular shapes down to 1.1. We demonstrate this process for a wide range of speeds, pulse repetition rates and pulse energies, thus opening the door to a much more useful nanofabrication technique for nanophotonics. Finally, we also report the change in index of refraction that is produced at the nanoscale obtaining a positive index contrast of ∼3%. The work therefore provides a promising path towards reliable 3D nanostructuring of solid-state laser media for the flexible fabrication of large and complex structures with features sizes from the nanoscale up to the mm-scale. Moreover, due to the embedded, seamless, and monolithic nature of this technology, and since YAG crystals can sustain temperatures of up to 1900 °C and are highly chemically inert and erosion resistant, we anticipate its direct application in harsh environments.

3D Nanolithography by Means of Lipid Ink Spreading Inhibition.

While patterning 2D metallic nanostructures are well established through different techniques, 3D printing still constitutes a major bottleneck on the way to device miniaturization. In this work a fluid phase phospholipid ink is used as a building block for structuring with dip-pen nanolithography. Following a bioinspired approach that relies on ink-spreading inhibition, two processes are presented to build 2D and 3D metallic structures. Serum albumin, a widely used protein with an innate capability to bind to lipids, is the key in both processes. Covering the sample surface with it prior to lipid writing, anchors lipids on the substrate, which ultimately allows the creation of highly stable 3D lipid-based scaffolds to build metallic structures.

High‐Speed One‐Photon 3D Nanolithography Using Controlled Initiator Depletion and Inhibitor Transport

AbstractAdditive manufacturing of sophisticated 3D nanoscale objects commonly uses femtosecond lasers to photopolymerize a light‐sensitive resin using multi‐photon absorption. This nonlinear process provides high accuracy and flexibility in advanced 3D fabrication; however, it typically has limited throughput and high cost. This work makes use of a one‐photon‐based dosage‐nonlinearity to fabricate 3D nanostructures, demonstrating a cost‐effective method for 3D nanolithography using a low‐cost 405 nm continuous‐wave diode laser. This dosage‐nonlinearity is achieved by using controlled depletion of photo‐initiation species in an environment containing inhibiting species. By controlling multiple competing processes, the undesired dose accumulation outside the writing voxel is stopped, and thereby this method creates a confined writing voxel in space. A multiphysics model is developed to numerically study the one‐photon nonlinear photopolymerization process, which is compared with experimental results.

Advanced Technology for 3D Nanoprinting

Today, additive manufacturing research and development rely heavily on 3D printing. While there is a wide choice of commercial 3D printers, few reach nanometer resolution and feature size. The difficulties arise from special high precision required for materials delivery and registry among layers in the printing process. Scanning probe microscopy (SPM) has been widely used by the research and development community to visualize specimens with unprecedented resolution: reaching nanometer levels routinely and atomic and molecular levels on occasion. , The localization of SPM at atomic and molecular scale, has been harnessed to control interactions of molecules toward 2D and 3D nanolithography. Combining SPM’s spatial precision with advanced local delivery methodologies, including microfluidics, this presentation demonstrates feasibility and examples to reach 3D nanoprinting as well as new materials chemistry. Potential applications will also be discussed.

Hybrid multi-chip assembly of optical communication engines by in situ 3D nano-lithography

Three-dimensional (3D) nano-printing of freeform optical waveguides, also referred to as photonic wire bonding, allows for efficient coupling between photonic chips and can greatly simplify optical system assembly. As a key advantage, the shape and the trajectory of photonic wire bonds can be adapted to the mode-field profiles and the positions of the chips, thereby offering an attractive alternative to conventional optical assembly techniques that rely on technically complex and costly high-precision alignment. However, while the fundamental advantages of the photonic wire bonding concept have been shown in proof-of-concept experiments, it has so far been unclear whether the technique can also be leveraged for practically relevant use cases with stringent reproducibility and reliability requirements. In this paper, we demonstrate optical communication engines that rely on photonic wire bonding for connecting arrays of silicon photonic modulators to InP lasers and single-mode fibres. In a first experiment, we show an eight-channel transmitter offering an aggregate line rate of 448 Gbit/s by low-complexity intensity modulation. A second experiment is dedicated to a four-channel coherent transmitter, operating at a net data rate of 732.7 Gbit/s – a record for coherent silicon photonic transmitters with co-packaged lasers. Using dedicated test chips, we further demonstrate automated mass production of photonic wire bonds with insertion losses of (0.7 ± 0.15) dB, and we show their resilience in environmental-stability tests and at high optical power. These results might form the basis for simplified assembly of advanced photonic multi-chip systems that combine the distinct advantages of different integration platforms.

Stitchless support-free 3D printing of free-form micromechanical structures with feature size on-demand

Femtosecond laser based 3D nanolithography is a powerful tool for fabricating various functional micro- and nano-objects. In this work we present several advances needed to push it from the laboratory level use to the industrial production lines. First, linear stage and galvo-scanners synchronization is employed to produce stitch-free mm-sized structures. Furthermore, it is shown that by varying objective numerical apertures (NA) from 1.4 NA to 0.45 NA, voxel size can be tuned in the range from sub μm to tens of mm, resulting in structuring rates between 1809 μm3/s and 313312 μm3/s at 1 cm/s translation velocity achieved via simultaneous movement of linear stages and scanners. Discovered voxel/throughput scaling peculiarities show good agreement to ones acquired with numerical modeling. Furthermore, support-free 3D printing of complex structures is demonstrated. It is achieved by choosing pre-polymer that is in hard gel form during laser writing and acts as a dissolvable support during manufacturing. All of this is combined to fabricate micromechanical structures. First, 1:40 aspect ratio cantilever and 1.5 mm diameter single-helix spring capable of sustaining extreme deformations for prolonged movement times (up to 10000 deformation cycles) are shown. Then, free-movable highly articulated intertwined micromechanical spider and squids (overall size up to 10 mm) are printed and their movement is tested. The presented results are discussed in the broader sense, touching on the stitching/throughput dilemma and comparing it to the standard microstereolithography. It is shown where multiphoton polymerization can outpace standard stereolithography in terms of throughput while still maintaining superior resolution and higher degree of freedom in terms of printable geometries.

Three-dimensional colloidal interference lithography

Light interactions with colloidal particles can generate a variety of complex three-dimensional (3D) intensity patterns, which can be utilized for nanolithography. The study of particle–light interactions can add more types of intensity patterns by manipulating key factors. Here we investigate a novel 3D nanolithography technique using colloidal particles under two-beam coherent illuminations. The fabricated 3D nanostructures are hollow, nested within periodic structures, and possess multiple chamber geometry. The effects of incident angles and particle size on the fabricated nanostructures were examined. The relative phase shift between particle position and interference pattern is identified as another significant parameter influencing the resultant nanostructures. A numerical model has been developed to show the evolution of nanostructure geometry with phase shifts, and experimental studies confirm the simulation results. Through the introduction of single colloidal particles, the fabrication capability of Lloyd’s mirror interference can now be extended to fabrication of 3D nanostructure with complex shell geometry. The fabricated hollow nanostructures with grating background could find potential applications in the area of photonics, drug delivery, and nanofluidics.

Ordered 3D Thin‐Shell Nanolattice Materials with Near‐Unity Refractive Indices

The refractive indices of naturally occurring materials are limited, and there exists an index gap between indices of air and available solid materials. With many photonics and electronics applications, there has been considerable effort in creating artificial materials with optical and dielectric properties similar to air while simultaneously being mechanically stable to bear load. Here, a class of ordered nanolattice materials consisting of periodic thin‐shell structures with near‐unity refractive index and high stiffness is demonstrated. Using a combination of 3D nanolithography and atomic layer deposition, these ordered nanostructured materials have reduced optical scattering and improved mechanical stability compared to existing randomly porous materials. Using ZnO and Al2O3 as the building materials, refractive indices from 1.3 down to 1.025 are achieved. The experimental data can be accurately described by Maxwell Garnett effective media theory, which can provide a guide for index design. The demonstrated low‐index, low‐scattering, and high‐stiffness materials can serve as high‐quality optical films in multilayer photonic structures, waveguides, resonators, and ultra‐low‐k dielectrics.

Direct-write 3D nanolithography at cryogenic temperatures

Direct-write three-dimensional nanolithography is demonstrated using cryogenic electron beam-induced deposition (EBID). Cryogenic cooling and an electron beam were used to condense and expose the precursor methylcyclopentadienyl(trimethyl)platinum (MeCpPtMe3). The exposure process was modeled by Monte Carlo simulations of electron–condensate interactions, which were used to develop two approaches for the fabrication of three-dimensional self-supporting structures with incorporated gaps. Vertical and lateral resolutions of approximately 150 and 22 nm are demonstrated, and underlying mechanisms that limit resolution and throughput are identified. Resolution can be traded off for condensate exposure efficiency, which is shown to be up to four orders of magnitude greater than that of conventional, room temperature EBID.

From Two-Dimensional Colloidal Self-Assembly to Three-Dimensional Nanolithography

A number of "top-down" lithographic and "bottom-up" self-assembly methods have been developed to fabricate three-dimensional (3D) nanostructures to support the recent advances in nanotechnology. But they are limited by a number of factors such as fabrication cost, pattern resolution, and/or flexibility of geometry. Here we present a 3D nanolithography process that utilizes self-assembled nanospheres to create a periodic array of focal spots, which are then replicated across multiple depth in a transparent medium according to the Talbot effect. The Talbot field then exposes a pattern onto the underlying photoresist, recording the 3D intensity distribution. We have demonstrated designable complex 3D periodic structures with 80 nm minimum feature size, roughly one-fourth of the operating wavelength. This approach combines 2D colloidal self-assembly and 3D phase lithography, is robust, cost-effective, and widely applicable to nanoscale research and manufacturing.

Template-Assisted Three-Dimensional Nanolithography via Geometrically Irreversible Processing

An innovative and versatile nanofabrication technique based on template assisted three-dimensional (3D) nanolithography is presented that takes advantage of the irreversibility of conformal growth and conformal etching at locations with negative surface curvatures in 3D templates. Using colloidal crystals as templates, nanoring particles are generated with quantity much higher than conventional methods. Relying on the same principle, metallodielectric photonic crystals with discrete metal elements are fabricated that show strong absorption in the near-IR and transmission at longer wavelengths.