The ability to respond to injury with tissue repair is a fundamental property of all multicellular organisms. The extracellular matrix (ECM), composed of fibrillar collagens as well as a number of ...other components is dis-regulated during repair in many organs. In many tissues, scaring results when the balance is lost between ECM synthesis and degradation. Investigating what disrupts this balance and what effect this can have on tissue function remains an active area of research. Recent advances in the imaging of fibrillar collagen using second harmonic generation (SHG) imaging have proven useful in enhancing our understanding of the supramolecular changes that occur during scar formation and disease progression. Here, we review the physical properties of SHG, and the current nonlinear optical microscopy imaging (NLOM) systems that are used for SHG imaging. We provide an extensive review of studies that have used SHG in skin, lung, cardiovascular, tendon and ligaments, and eye tissue to understand alterations in fibrillar collagens in scar tissue. Lastly, we review the current methods of image analysis that are used to extract important information about the role of fibrillar collagens in scar formation.
The ability to perform nanometer‐scale optical imaging and spectroscopy is key to deciphering the low‐energy effects in quantum materials, as well as vibrational fingerprints in planetary and ...extraterrestrial particles, catalytic substances, and aqueous biological samples. These tasks can be accomplished by the scattering‐type scanning near‐field optical microscopy (s‐SNOM) technique that has recently spread to many research fields and enabled notable discoveries. Herein, it is shown that the s‐SNOM, together with scanning probe research in general, can benefit in many ways from artificial‐intelligence (AI) and machine‐learning (ML) algorithms. Augmented with AI‐ and ML‐enhanced data acquisition and analysis, scanning probe optical nanoscopy is poised to become more efficient, accurate, and intelligent.
Three main paradigms of machine learning—supervised learning, unsupervised learning, and reinforcement learning—can be applied to optical scanning probe techniques in future instrumentation and data analysis to solve unique problems.
State‐of‐the‐art 3D two‐photon laser printing systems already use pre‐compensation algorithms to reduce systematic deviations between the printed and the targeted structures. Nevertheless, the ...remaining deviations are often still larger than the uncontrollable or “statistical” deviations. In principle, it is straightforward to correct for systematic deviations by measuring the difference between printed structure and target and by subtracting the difference from the first target to obtain the next‐iteration target. However, in reality, one faces several issues such as noise and systematic errors of the characterization measurement itself, as well as unwanted translations and rotations between the coordinate systems of the characterization setup and the printer, respectively. Two examples of printed structures requiring sub‐micrometer accuracy are considered, a large 1D micro‐lens array and a specific diffractive optical element. For both, the device performance before the pre‐compensation workflow described herein is insufficient for the targeted application and has become sufficient after this workflow. The workflow involving optimizations using cross‐correlations with confocal‐optical‐microscopy data is documented by an open‐access program (available via GitLab). This program includes an easy‐to‐use graphical user interface so that other researchers can immediately profit from it.
In multi‐photon 3D‐laser‐nano printing, several systematic factors like shrinkage or stitching lead to deviations between the printing result and the required designed structure. Fortunately, these errors can be corrected by modifying the design before printing. A method is presented to measure the systematic deviations using confocal‐optical microscopy and provide a flexible user‐friendly program to calculate a pre‐compensated design from them.
As a new member of 2D materials, GeSe has attracted considerable attention recently due to its fascinating in‐plane anisotropic vibrational, electrical, and optical properties originating from the ...low‐symmetry crystal structure. Among these anisotropic properties, the anisotropic optical property, as a new degree of freedom to manipulate optoelectronic properties in 2D materials, is of great importance for practical applications. However, the fundamental understanding of the optical anisotropy of GeSe is still under exploration, severely restricting its utility in polarization‐sensitive optical systems. Here, a systematic study about the in‐plane optical anisotropy of GeSe is reported, including its anisotropic optical absorption, reflection, extinction, and refraction. The anisotropic band structure of GeSe is experimentally observed for the first time through angle‐resolved photoemission spectroscopy, explaining the origin of the optical anisotropy. The anisotropic reflection and refraction of GeSe are further directly visualized through the angle‐dependent optical contrast of GeSe flakes by azimuth‐dependent reflectance difference microscopy and polarization‐resolved optical microscopy, respectively. Finally, GeSe‐based photodetectors exhibit a polarization‐sensitive photoresponsivity due to the intrinsic linear dichroism. This study provides fundamental information for the optical anisotropy of GeSe, forcefully stimulating the exploration of novel GeSe‐based optical and optoelectronic applications.
In‐plane optical anisotropy of GeSe is systematically studied by angle‐resolved photoemission spectroscopy, azimuth‐dependent reflectance difference microscopy, and polarization‐resolved optical microscopy, thus providing fundamental information for the optical anisotropy of GeSe and stimulating the exploration of novel GeSe‐based optical and optoelectronic applications.
Resistive switching devices based on metal oxides are candidates for nonvolatile memory storage. They often rely on the valence change mechanism, the field‐induced movement of donor ions leading to ...nanoscale conductive paths in filamentary‐type devices. Devices usually consist of a transition metal oxide like Ta2O5 sandwiched between two metal electrodes. Critical parameters of the devices, such as cycle‐to‐cycle variability, Roff/Ron ratio, and endurance depend on the morphology and composition of the filaments. However, investigating filaments on the nanoscale is cumbersome, and commonly applied techniques such as conductive atomic force or transmission electron microscopy require delaminating the metal top electrode, inhibiting in operando investigations over many switching cycles. Here, the authors use infrared scattering‐type scanning near‐field optical microscopy (s‐SNOM) to investigate resistive switching in Ta2O5 films with a graphene top electrode in operando and reveal individual filaments on the device level. By selecting an appropriate illumination frequency, the authors can trace the evolution of filaments and the joule heating‐induced retraction of the top electrode until device failure. s‐SNOM promises a deeper understanding of resistive switching devices’ microscopic switching behavior and applies to a wide range of resistive switching oxides, such as HfO2, SrTiO3, and SiO2.
Infrared scattering‐type scanning near‐field optical microscopy (s‐SNOM) is used to investigate resistive switching in Ta2O5 films and reveals individual filaments on the device level of resistive random‐access memories (ReRAMs). By selecting an appropriate illumination frequency, the simultaneous tracing of the evolution of filaments and the joule heating‐induced retraction of the top electrode until device failure is possible.
Polarized‐light optical microscopy (POM) is applied for investigation of homogeneous crystal nucleation in polymers, using the advantage of precise control of the nucleation pathway by application of ...fast scanning chip calorimetry (FSC). In the first part of this paper, homogeneous crystal nucleation in glassy poly (l‐lactic acid) (PLLA) employing Tammann's two‐stage crystal nuclei‐development method is highlighted. PLLA samples of different nucleation history are prepared in an FSC, and then POM micrographs are studied regarding the effect of time and temperature of annealing the glass on the number of spherulites, which developed in the growth‐stage at higher temperature. The obtained images provide ultimate evidence about the validity of Tammann's approach for obtaining information about the kinetics of homogeneous crystal nucleation using calorimetry, when quantifying the number of nuclei by the enthalpy of crystallization during their growth to crystals in the development stage. In the second part of this study, information about the semicrystalline morphology of samples of poly(butylene terephthalate) and polyamide 66 crystallized at different supercooling using FSC is presented. POM analysis confirms the origin of the frequently observed bimodal temperature‐dependence of the crystallization rate as being caused by different mechanisms of crystal nucleation, resulting in qualitatively different structures.
The combination of fast scanning chip calorimetry (FSC) and polarized‐light optical microscopy (POM) is advantageous for gaining additional information about structure formation in semicrystalline polymers beyond the specific capabilities of the individual methods. FSC offers the opportunity to precisely control thermal profiles for generation of different structures identified by POM.
Scanning‐probe microscopy (SPM) is the method of choice for high‐resolution imaging of surfaces in science and industry. However, SPM systems are still considered as rather complex and costly ...scientific instruments, realized by delicate combinations of microscopic cantilevers, nanoscopic tips, and macroscopic read‐out units that require high‐precision alignment prior to use. This study introduces a concept of ultra‐compact SPM engines that combine cantilevers, tips, and a wide variety of actuator and read‐out elements into one single monolithic structure. The devices are fabricated by multiphoton laser lithography as it is a particularly flexible and accurate additive nanofabrication technique. The resulting SPM engines are operated by optical actuation and read‐out without manual alignment of individual components. The viability of the concept is demonstrated in a series of experiments that range from atomic‐force microscopy engines offering atomic step height resolution, their operation in fluids, and to 3D printed scanning near‐field optical microscopy. The presented approach is amenable to wafer‐scale mass fabrication of SPM arrays and capable to unlock a wide range of novel applications that are inaccessible by current approaches to build SPMs.
3D‐printed scanning‐probe microscopy (SPM) engines offer a tremendous freedom of design allowing the integration of several measurement principles in one monolithic structure, which includes excitation and read‐out already. Atomic force microscopy with atomic‐scale step‐height resolution as well as scanning near‐field optical microscopy characterizing active and passive optical elements is demonstrated. Wafer‐level fabrication of massively SPM arrays is possible.
Among the novel materials for electronic applications and novel device concepts beyond classical Si‐based CMOS technology, SrTiO3 represents a prototype role model for functional oxide materials: It ...enables resistive switching, but can also form a 2D electron gas at its interface and thus enables tunable transistors. However, the interplay between charge carriers and defects in SrTiO3 is still under debate. Infrared spectroscopy offers the possibility to characterize structural and electronic properties of SrTiO3 in operando, but is hampered by the diffraction‐limited resolution. To overcome this limitation and obtain nanoscale IR spectra of donor‐doped Sr1‐xLaxTiO3 ceramics, scattering‐type scanning near‐field optical microscopy is applied. By exploiting plasmon–phonon coupling, the local electronic properties of doped SrTiO3 are quantified from a detailed spectroscopic analysis in the spectral range of the near‐field ‘phonon resonance’. Single crystal‐like mobility, an increase in charge carrier density N and an increase in ε∞ at grain boundaries (µ≈ 5.7 cm2 V−1s−1, N = 7.1 × 1019 cm−3, and ε∞ = 7.7) and local defects (µ≈ 5.4 cm2 V−1s−1, N = 1.3 × 1020 cm−3, and ε∞ = 8.8) are found. In future, subsurface quantification of defects and free charge carriers at interfaces and filaments in SrTiO3 can be envisioned.
Infrared near‐field optical microscopy is used to non‐destructively quantify the electronic properties of doped SrTiO3 on the nm scale. This is enabled by exploiting plasmon–phonon coupling and a detailed analysis of the near‐field optical phonon resonance. Thus, the accumulation of electrons at grain boundaries in donor‐doped ceramics is revealed and as a proof of principle resistively switched spots are identified.
Super‐resolution optical imaging techniques can break the optical diffraction limit, thus providing unique opportunities to visualize the microscopic world at the nanoscale. Although near‐field ...optical microscopy techniques have been proven to achieve significantly improved imaging resolution, most near‐field approaches still suffer from a narrow field of view (FOV) or difficulty in obtaining wide‐field images in real time, which may limit their widespread and diverse applications. Here, the authors experimentally demonstrate an optical microscope magnification and image enhancement approach by using a submillimeter‐sized solid immersion lens (SIL) assembled by densely‐packed 15 nm TiO2 nanoparticles through a silicone oil two‐step dehydration method. This TiO2 nanoparticle‐assembled SIL can achieve both high transparency and high refractive index, as well as sufficient mechanical strength and easy‐to‐handle size, thus providing a fast, wide‐field, real‐time, non‐destructive, and low‐cost solution for improving the quality of optical microscopic observation of a variety of samples, including nanomaterials, cancer cells, and living cells or bacteria under conventional optical microscopes. This study provides an attractive alternative to simplify the fabrication and applications of high‐performance SILs.
By using a self‐developed silicone oil two‐step dehydration method, 15 nm TiO2 nanoparticles can be spontaneously assembled into a submillimeter‐sized solid immersion lens (SIL) with both high transparency and a high refractive index. This TiO2 nanoparticle‐assembled SIL has been successfully used to visualize microscopic structures with improved image magnification, resolution, and contrast under a conventional light microscope.
Quasi-one-dimensional (quasi-1D) materials enjoy growing interest due to their unusual physical properties and promise for miniature electronic devices. However, the mechanical exfoliation of ...quasi-1D materials into thin flakes and nanoribbons received considerably less attention from researchers than the exfoliation of conventional layered crystals. In this study, we investigated the micromechanical exfoliation of representative quasi-1D crystals, TiS
whiskers, and demonstrate that they typically split into narrow nanoribbons with very smooth, straight edges and clear signatures of 1D TiS
chains. Theoretical calculations show that the energies required for breaking weak interactions between the two-dimensional (2D) layers and between 1D chains within the layers are comparable and, in turn, are considerably lower than those required for breaking the covalent bonds within the chains. We also emulated macroscopic exfoliation experiments on the nanoscale by applying a local shear force to TiS
crystals in different crystallographic directions using a tip of an atomic force microscopy (AFM) probe. In the AFM experiments, it was possible to slide the 2D TiS
layers relative to each other as well as to remove selected 1D chains from the layers. We systematically studied the exfoliated TiS
crystals by Raman spectroscopy and identified the Raman peaks whose spectral positions were most dependent on the crystals' thickness. These results could be used to distinguish between TiS
crystals with thickness ranging from one to about seven monolayers. The conclusions established in this study for the exfoliated TiS
crystals can be extended to a variety of transition metal trichalcogenide materials as well as other quasi-1D crystals. The possibility of exfoliation of TiS
into narrow (few-nm wide) crystals with smooth edges could be important for the future realization of miniature device channels with reduced edge scattering of charge carriers.
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