This paper introduces the concept of continuous chaotic printing, i.e. the use of chaotic flows for deterministic and continuous extrusion of fibers with internal multilayered micro- or nanostructures. Two free-flowing materials are coextruded through a printhead containing a miniaturized Kenics static mixer (KSM) composed of multiple helicoidal elements. This produces a fiber with a well-defined internal multilayer microarchitecture at high-throughput (>1.0 m min−1). The number of mixing elements and the printhead diameter determine the number and thickness of the internal lamellae, which are generated according to successive bifurcations that yield a vast amount of inter-material surface area (∼102 cm2 cm−3) at high resolution (∼10 µm). This creates structures with extremely high surface area to volume ratio (SAV). Comparison of experimental and computational results demonstrates that continuous chaotic 3D printing is a robust process with predictable output. In an exciting new development, we demonstrate a method for scaling down these microstructures by 3 orders of magnitude, to the nanoscale level (∼150 nm), by feeding the output of a continuous chaotic 3D printhead into an electrospinner. The simplicity and high resolution of continuous chaotic printing strongly supports its potential use in novel applications, including—but not limited to—bioprinting of multi-scale layered biological structures such as bacterial communities, living tissues composed of organized multiple mammalian cell types, and fabrication of smart multi-material and multilayered constructs for biomedical applications.

Infrared photoinduced force microscopy (IR-PiFM) is a scanning probe spectroscopic technique that maps sample morphology and chemical properties on the nanometer (nm)-scale. Fabricated samples with nm periodicity such as self-assembly of block copolymer films can be chemically characterized by IR-PiFM with relative ease. Despite the success of IR-PiFM, the origin of spectroscopic contrast remains unclear, preventing the scientific community from conducting quantitative measurements. Here we experimentally investigate the contrast mechanism of IR-PiFM for recording vibrational resonances. We show that the measured spectroscopic information of a sample is directly related to the energy lost in the oscillating cantilever, which is a direct consequence of a molecule excited at its vibrational optical resonance—coined as opto-mechanical damping. The quality factor of the cantilever and the local sample polarizability can be mathematically correlated, enabling quantitative analysis. The basic theory for dissipative tip-sample interactions is introduced to model the observed opto-mechanical damping.

We numerically analyze PiFM's lateral and vertical (subsurface) imaging performance in the visible and IR regimes. The lateral spatial resolution and subsurface imaging capabilities are limited by the field spatial confinement near the tip apex, which is directly proportional to the excitation wavelength. In addition, we show that near-field optical force exerted on the tip due to sample molecular resonance is indeed in the detectable range. Moreover, driving sample on (off) resonance reveals high (low) contrast. The strength of the optical forces is assessed for metal (gold), polymers (Polystyrene and Polymethylmethacrylate), and solid (SiC). By increasing tip-coating thickness from 5 nm to 35 nm, the gap-field enhancement decreases to about 40%. In IR, force spectrum over an absorption band is predominantly following the real part of the polarizability, as predicted by dipole-dipole approximation.

A nanoscopy technique that can characterize light-matter interactions with ever increasing spatial resolution and signal-to-noise ratio (SNR) is desired for spectroscopy at molecular levels.Photoinduced force microscopy (PiFM) with Au-coated probe-tips has been demonstrated as an excellent solution for this purpose. However, its accuracy is limited by the asymmetric shape of the Au-coated tip resulting in tip-induced anisotropy. To overcome such deficiencies, we propose a Si tip-Au nanoparticle (NP) combination in PiFM. We map the near-field distribution of the Au NPs in various arrangements with an unprecedented SNR of up to 120, a more than 10-fold improvement compared to conventional optical near-field techniques, and a spatial resolution down to 5.8 nm, smaller than 1/100 of the wavelength, even surpassing the tip-curvature limitation. We also map the beam profile of an azimuthally polarized beam (APB) with an excellent symmetry. The proposed approach can lead to the promising single molecule spectroscopy.Recently the photoinduced force microscopy (PiFM) technique has been developed as a superior near-field optical imaging and spectroscopy technique with both high SNR and nanoscale spatial resolution based on a modified atomic force microscopy (AFM) system. 16 Compared to s-SNOM in which the excitation is in near field and the detection is in the far field, in PiFM both the excitation and detection take place in near field which effectively suppresses the background scattering photons from the far field. 17,18 As a result, PiFM has been widely used for stimulated Raman spectroscopy, 19,20 nanoscale mapping of tightly focused electromagnetic beams 21,22 and propagating surface plasmon polaritons, 23 enantioselectivity of chiral nanostructures, 24,25

This paper introduces the concept of continuous chaotic printing, i.e., the use of chaotic flows for deterministic and continuous fabrication of fibers with internal multilayered micro-or nanostructures. Two free-flowing materials are coextruded through a printhead containing a miniaturized Kenics static mixer (KSM) composed of multiple helicoidal elements. This produces a fiber with a well-defined internal multilayer microarchitecture at high speeds (>1.0 m min-1). The number of mixing elements and the printhead diameter determine the number and thickness of the internal lamellae, which are generated according to successive bifurcations that yield a vast amount of inter-material surface area (~102 cm2 cm-3) and high resolution features (~10 µm). In an exciting further development, we demonstrate a scale-down of the microstructure by 3 orders of magnitude, to the nanoscale level (~10 nm), by feeding the output of a continuous chaotic 3D printhead into an electrospinner. Comparison of experimental and computational results demonstrates the robust and predictable output and performance of continuous chaotic 3D printing. The simplicity and high resolution of continuous chaotic printing strongly supports its potential use in novel applications, including-but not limited to-bioprinting of multi-scale tissue-like structures, modeling of bacterial communities, and fabrication of smart multi-material and multilayered constructs.

Abstract:We demonstrate the measurement of laterally induced optical forces using an Atomic Force Microscope (AFM). The lateral electric field distribution between a gold coated AFM probe and a nano-aperture in a gold film is mapped by measuring the lateral optical force between the apex of the AFM probe and the nano-aperture. Torsional eigen-modes of an AFM cantilever probe were used to detect the laterally induced optical forces. We engineered the cantilever shape using a focused ion beam to enhance the torsional eigen-mode resonance. The measured lateral optical force agrees well with simulations. This technique can be extended to simultaneously detect both lateral and longitudinal optical forces at the nanoscale by using an AFM cantilever as a multi-channel detector. This will enable simultaneous Photon Induced Force Microscopy (PIFM) detection of molecular responses with different incident field polarizations. The technique can be implemented on both cantilever and tuning fork based AFM's. Lateral force AFM is a technique that is primarily used to differentiate nanoscale surface properties [1], [2].In Lateral force AFM, the frictional forces between the tip and sample creates a torsion of the cantilever which in turn is a function of the surface properties, and leads to chemical force microscopy [3], [4]. In this letter we demonstrate the detection of lateral optical forces using the torsion mode of cantilever thereby enhancing the capability of lateral force AFM to detect optical forces at the nanoscale. Photon Induced Force Microscopy (PIFM) is a promising new technique to study linear and non-linear optical properties measured only using photon induced forces [5] - [9]. PIFM uses an Atomic Force Microscope (AFM) to measure the optical forces between an optically induced dipole in the sample under measurement and another optically induced dipole formed at the tip of the gold coated AFM probe. Previously, PIFM was introduced to detect and image linear molecular resonances at nanometer level [5], [7], [8] and perform non-linear imaging and spectroscopy at the nanoscale [6], [9] as well as time-resolved imaging of non-linear optical properties [9] of molecules. Indeed, PIFM has been used to image molecular resonances over a wide range of wavelengths from the visible to mid-IR wavelength regimes [10]. In addition, optical forces between a gold coated AFM tip and its image on a glass substrate was used to image the focal field distributions of tightly focused laser beams with different polarizations [7]. The response of the tip to different polarizations was used to estimate the aspect ratio of the AFM probe tip making it a useful technique to estimate the quality of probes for sensitive experiments such as Tip Enhanced Raman Spectroscopy (TERS) [7]. The previous works used the AFM in the attractive mode to measure the component of optical force, along the tip axis.In this paper, we demonstrate the use of PIFM to measure the lateral optical force (perpendicular to the tip axis) between a gold coated AFM probe ...

Multi-material and multilayered micro-and nanostructures are prominently featured in nature and engineering and are recognized by their remarkable properties. Unfortunately, the fabrication of micro-and nanostructured materials through conventional processes is challenging and costly. Herein, we introduce a high-throughput, continuous, and versatile strategy for the fabrication of polymer fibers with complex multilayered nanostructures. Chaotic electrospinning (ChE) is based on the coupling of continuous chaotic printing (CCP) and electrospinning, which produces fibers with an internal multi-material microstructure. When a CCP printhead is used as an electrospinning nozzle, the diameter of the fibers is further scaled down by 3 orders of magnitude while preserving their internal structure. ChE enables the use of various polymer inks for the creation of nanofibers with a customizable number of internal nanolayers. Our results showcase the versatility and tunability of ChE to fabricate multilayered structures at the nanoscale at high throughput. We apply ChE to the synthesis of unique carbon textile electrodes composed of nanofibers with striations carved into their surface at regular intervals. These striated carbon electrodes with high surface areas exhibit 3-to 4-fold increases in specific capacitance compared to regular carbon nanofibers; ChE holds great promise for the cost-effective fabrication of electrodes for supercapacitors and other applications.

The contrast mechanism of infrared photoinduced force microscopy (IR-PiFM) for recording vibrational resonances is experimentally investigated. We show that spectroscopic contrast in IR-PiFM is mediated by opto-mechanical damping of the cantilever oscillation.