3D-Printed Scanning-Probe Microscopes with Integrated Optical Actuation and Read-Out

Ultra-Large Scale Stitchless AFM: Advancing Nanoscale Characterization and Manipulation with Zero Stitching Error and High Throughput

The atomic force microscopy (AFM) is an important tool capable of characterization, measurement, and manipulation at the nanoscale with a vertical resolution of less than 0.1 nm. However, the conventional AFMs' scanning range is around 100 µm, which limits their capability for processing cross-scale samples. In this study, it proposes a novel approach to overcome this limitation with an ultra-large scale stitchless AFM (ULSS-AFM) that allows for the high-throughput characterization of an area of up to 1 × 1 mm2 through a synergistic integration with a compliant nano-manipulator (CNM). Specifically, the compact CNM provides planar motion with nanoscale precision and millimeter range for the sample, while the probe of the ULSS-AFM interacts with the sample. Experimental results show that the proposed ULSS-AFM performs effectively in different scanning ranges under various scanning modes, resolutions, and frequencies. Compared with the conventional AFMs, the approach enables high-throughput characterization of ultra-large scale samples without stitching or bow errors, expanding the scanning area of conventional AFMs by two orders of magnitude. This advancement opens up important avenues for cross-scale scientific research and industrial applications in nano- and microscale.

3D nanoprinting for fiber-integrated achromatic diffractive lens

Achromatic performance is crucial for numerous multi-wavelength optical fiber applications, including endoscopic imaging and fiber sensing. This paper presents the design and nanoprinting of a fiber-integrated achromatic diffractive lens within the visible spectrum (450-650 nm). The 3D nanoprinting is achieved by a high-resolution direct laser writing technology, overcoming limitations in the optical performance caused by the lack of an arbitrary 3D structure writing capability and an insufficient feature resolution in the current manufacturing technology for visible light broadband achromatic diffractive lenses. A three-step optimization algorithm is proposed to effectively balance optical performance with writing difficulty. The characterization results demonstrate excellent achromatic focusing performance, paving the way towards the development of nanoprinted flat optical devices for applications such as optical fiber traps, miniature illumination systems, and integrated photonic chips.

Adjustment-free two-sided 3D direct laser writing for aligned micro-optics on both substrate sides

3D direct laser writing is a powerful and widely used tool to create complex micro-optics. The fabrication method offers two different writing modes. During the immersion mode, an immersion medium is applied between the objective and the substrate while the photoresist is exposed on its back side. Alternatively, when using the dip-in mode, the objective is in direct contact with the photoresist and the structure is fabricated on the objective facing side of the substrate. In this Letter, we demonstrate the combination of dip-in and photoresist immersion printing, by using the photoresist itself as immersion medium. This way, two parts of a doublet objective can be fabricated on the front and back sides of a substrate, using it as a spacer with a lateral registration below 1 µm and without the need of additional alignment. This approach also enables the alignment free combination of different photoresists on the back and front sides. We use this benefit by printing a black aperture on the back of the substrate, while the objective lens is printed on the front.

Stress-induced birefringence in 3D direct laser written micro-optics

3D direct laser writing is a widely used technology to create different nano- and micro-optical devices for various purposes. However, one big issue is the shrinking of the structures during polymerization, which results in deviations from the design and in internal stress. While the deviations can be compensated by adapting the design, the internal stress remains and induces birefringence. In this Letter, we successfully demonstrate the quantitative analysis of stress-induced birefringence in 3D direct laser written structures. After presenting the measurement setup based on a rotating polarizer and an elliptical analyzer, we characterize the birefringence of different structures and writing modes. We further investigate different photoresists and the implications for 3D direct laser written optics.

Resonant-Opto-Thermomechanical Oscillator (ROTMO): A Low-Power, Large Displacement, High-Frequency Optically Driven Microactuator

A light-driven micromechanical oscillator is presented, which can be operated by a low optical power (in the mW, or even the µW range), can produce large mechanical displacements (>5-100 µm), and can be designed to operate at frequencies from sub-kHz up to more than 200 kHz. The actuation of the oscillator is achieved by an asymmetrically metal-coated optical microwire configured into a silica micromechanical oscillator. The metalized optical microwire confines and absorbs the light strongly over a short distance, which results in a controlled optical power conversion into heat, and, consequently, into mechanical actuation through the temperature rise and the difference in thermal expansions of the silica microwire and the asymmetrically applied metal layer. Mechanical displacements are amplified further by the resonance operation of the oscillator, which is driven by a low-power, harmonic optical excitation signal generated by a current-modulated laser diode. Proper selection of the micromechanical oscillator's geometrical configuration and materials allows for a high-frequency operation at large mechanical displacements of the oscillator, while relying on low excitation optical power. The presented concept of a fully optically driven micromechanical oscillator may, thus, present a basis for realization of new classes of actuated micro-opto-mechanical Systems and similar photonics microdevices.

3D printed hybrid refractive/diffractive achromat and apochromat for the visible wavelength range

Three-dimensional (3D) direct laser writing is a powerful technology to create nano- and microscopic optical devices. While the design freedom of this technology offers the possibility to reduce different monochromatic aberrations, reducing chromatic aberrations is often neglected. In this Letter, we successfully demonstrate the combination of refractive and diffractive surfaces to create a refractive/diffractive achromat and show, to the best of our knowledge, the first refractive/diffractive apochromat by using DOEs and simultaneously combining two different photoresists, namely IP-S and IP-n162. These combinations drastically reduce chromatic aberrations in 3D printed micro-optics for the visible wavelength range. The optical properties, as well as the substantial reduction of chromatic aberrations, are characterized, and we outline the benefits of 3D direct laser written achromats and apochromats for micro-optics.

Photothermal Optical Beam Steering Using Large Deformation Multi-Layer Thin Film Structures

Photothermal actuation of microstructures remains an active area of research for microsystems that demand electrically isolated, remote, on-chip manipulation. In this study, large-deformation structures constructed from thin films traditional to microsystems were explored through both simulation and experiment as a rudimentary means to both steer and shape an incident light beam through photothermal actuation. A series of unit step infrared laser exposures were applied at increasing power levels to both uniformly symmetric and deliberately asymmetric absorptive structures with the intent of characterizing the photothermal tilt response. The results indicate that a small angle (<4° at ~74 W/cm²) mechanical tilt can be instantiated through central placement of an infrared beam, although directional control appears highly sensitive to initial beam placement. Greater responsivity (up to ~9° mechanical tilt at ~54 W/cm²) and gross directional control was demonstrated with an asymmetrical absorptive design, although this response was accompanied by a large amount (~5–10°) of mechanical tilt burn-in and drift. Rigorous device cycling remains to be explored, but the results suggest that these structures, and those similar in construction, can be further matured to achieve controllable photoactuation suitable for optical beam control or other applications.

3D-printed optical probes for wafer-level testing of photonic integrated circuits

Wafer-level probing of photonic integrated circuits is key to reliable process control and efficient performance assessment in advanced production workflows. In recent years, optical probing of surface-coupled devices such as vertical-cavity lasers, top-illuminated photodiodes, or silicon photonic circuits with surface-emitting grating couplers has seen great progress. In contrast to that, wafer-level probing of edge-emitting devices with hard-to-access vertical facets at the sidewalls of deep-etched dicing trenches still represents a major challenge. In this paper, we address this challenge by introducing a novel concept of optical probes based on 3D-printed freeform coupling elements that fit into deep-etched dicing trenches on the wafer surface. Exploiting the design freedom and the precision of two-photon laser lithography, the coupling elements can be adapted to a wide variety of mode-field sizes. We experimentally demonstrate the viability of the approach by coupling light to edge-emitting waveguides on different integration platforms such as silicon photonics (SiP), silicon nitride (TriPleX), and indium phosphide (InP). Achieving losses down to 1.9 dB per coupling interface, we believe that 3D-printed coupling elements represent a key step towards highly reproducible wafer-level testing of edge-coupled photonic integrated circuits.

3D-printed cellular tips for tuning fork atomic force microscopy in shear mode

Conventional atomic force microscopy (AFM) tips have remained largely unchanged in nanomachining processes, constituent materials, and microstructural constructions for decades, which limits the measurement performance based on force-sensing feedbacks. In order to save the scanning images from distortions due to excessive mechanical interactions in the intermittent shear-mode contact between scanning tips and sample, we propose the application of controlled microstructural architectured material to construct AFM tips by exploiting material-related energy-absorbing behavior in response to the tip–sample impact, leading to visual promotions of imaging quality. Evidenced by numerical analysis of compressive responses and practical scanning tests on various samples, the essential scanning functionality and the unique contribution of the cellular buffer layer to imaging optimization are strongly proved. This approach opens new avenues towards the specific applications of cellular solids in the energy-absorption field and sheds light on novel AFM studies based on 3D-printed tips possessing exotic properties.

The authors investigate 3D-printed tips, based on controlled microstructural architectured materials, as probes for shear-mode atomic force microscopy. They demonstrate that the tailored stiffness and energy-absorbing behaviour of the material are beneficial for improving image quality.

Distortion-free multi-element Hypergon wide-angle micro-objective obtained by femtosecond 3D printing

In this Letter, we present a 3D-printed complex wide-angle multi-element Hypergon micro-objective, composed of aspherical lenses smaller than 1 mm, which exhibits distortion-free imaging performance. The objective is fabricated by a multi-step femtosecond two-photon lithography process. To realize the design, we apply a novel (to the best of our knowledge) approach using shadow evaporation to create highly non-transparent aperture stops, which are crucial components in many optical systems. We achieve a field-of-view (FOV) of 70°, at a resolution of 12.4 µm, and distortion-free imaging over the entire FOV. In the future, such objectives can be directly printed onto complementary metal-oxide-semiconductor (CMOS) imaging chips to produce extremely compact, high-quality image sensors to yield integrated sensor devices used in industry.

O-FIB: far-field-induced near-field breakdown for direct nanowriting in an atmospheric environment

Nanoscale surface texturing, drilling, cutting, and spatial sculpturing, which are essential for applications, including thin-film solar cells, photonic chips, antireflection, wettability, and friction drag reduction, require not only high accuracy in material processing, but also the capability of manufacturing in an atmospheric environment. Widely used focused ion beam (FIB) technology offers nanoscale precision, but is limited by the vacuum-working conditions; therefore, it is not applicable to industrial-scale samples such as ship hulls or biomaterials, e.g., cells and tissues. Here, we report an optical far-field-induced near-field breakdown (O-FIB) approach as an optical version of the conventional FIB technique, which allows direct nanowriting in air. The writing is initiated from nanoholes created by femtosecond-laser-induced multiphoton absorption, and its cutting "knife edge" is sharpened by the far-field-regulated enhancement of the optical near field. A spatial resolution of less than 20 nm (λ/40, with λ being the light wavelength) is readily achieved. O-FIB is empowered by the utilization of simple polarization control of the incident light to steer the nanogroove writing along the designed pattern. The universality of near-field enhancement and localization makes O-FIB applicable to various materials, and enables a large-area printing mode that is superior to conventional FIB processing.