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