Super‐Resolution Nonlinear Photothermal Microscopy

Super‐resolution fluorescence microscopy enables imaging of fluorescent structures beyond the diffraction limit. However, this technique cannot be applied to weakly fluorescent cellular components or labels. As an alternative, photothermal microscopy based on nonradiative transformation of absorbed energy into heat has demonstrated imaging of nonfluorescent structures including single molecules and ~1‐nm gold nanoparticles. However, previously photothermal imaging has been performed with a diffraction‐limited resolution only. Herein, super‐resolution, far‐field photothermal microscopy based on nonlinear signal dependence on the laser energy is introduced. Among various nonlinear phenomena, including absorption saturation, multiphoton absorption, and signal temperature dependence, signal amplification by laser‐induced nanobubbles around overheated nano‐objects is explored. A Gaussian laser beam profile is used to demonstrate the image spatial sharpening for calibrated 260‐nm metal strips, resolving of a plasmonic nanoassembly, visualization of 10‐nm gold nanoparticles in graphene, and hemoglobin nanoclusters in live erythrocytes with resolution down to 50 nm. These nonlinear phenomena can be used for 3D imaging with improved lateral and axial resolution in most photothermal methods, including photoacoustic microscopy.     

Position-, size-, and shape-controlled highly crystalline ZnO nanostructures

Highly ordered ZnO nanoboxes and nanowire structures with a width of ～ 20 nm have been successfully fabricated by the combination of nanoimprint lithography and pulsed laser deposition utilizing a glancing angle deposition (GLAD) technique. The periodicity, size, and shape of the ZnO nanoboxes and nanobelts can be easily controlled over a large area by changing the molds and deposition conditions. At the initial stage of growth by GLAD, nanonucleation led to nanopillar structures, which agglomerated to form nanobox and nanobelt structures at room temperature (RT). The ZnO nanostructures have a c-axis orientation along the nanopillar direction after postannealing and exhibit an intense cathodoluminescence peak around 380 nm at RT.     

Polarization-dependent photothermal beam deflection for the determination of the order parameter C(2) in a laser-oriented polymer system

We demonstrate polarization-dependent photothermal beam deflection as a powerful tool for analyzing quasi-two-dimensional molecular orientation. As examples we used two laser-beam-oriented polymer systems: DR1 in poly(methyl methacrylate) (PMMA) and PMMA with covalently bound DR1 and for comparison Phenol Blue in PMMA. Different order parameters C(2), for these systems have been found. It was also possible to orient by laser beam the DR1 chromophores cyclically by changing the polarization direction of the orienting laser beam and following these chromophore reorientations. The long-term stability of the orientation was investigated as well. The irreversible bleaching that is due to this laser treatment could be determined. Angular hole burning could easily be detected in these systems.     

Biradical-Featured Stable Organic-Small-Molecule Photothermal Materials for Highly Efficient Solar-Driven Water Evaporation

With recent progress in photothermal materials, organic small molecules featured with flexibility, diverse structures, and tunable properties exhibit unique advantages but have been rarely applied in solar-driven water evaporation owing to limited sunlight absorption resulting in low solar–thermal conversion. Herein, a stable croconium derivative, named CR-TPE-T, is designed to exhibit the unique biradical property and strong π–π stacking in the solid state, which facilitate not only a broad absorption spectrum from 300 to 1600 nm for effective sunlight harvesting, but also highly efficient photothermal conversion by boosting nonradiative decay. The photothermal efficiency is evaluated to be 72.7% under 808 nm laser irradiation. Based on this, an interfacial-heating evaporation system based on CR-TPE-T is established successfully, using which a high solar-energy-to-vapor efficiency of 87.2% and water evaporation rate of 1.272 kg m⁻² h⁻¹ under 1 sun irradiation are obtained, thus making an important step toward the application of organic-small-molecule photothermal materials in solar energy utilization.     

Supramolecular Nanodiscs Self-Assembled from Non-Ionic Heptamethine Cyanine for Imaging-Guided Cancer Photothermal Therapy

Supramolecular nanomedicines, which use supramolecular design to improve the precision and effectiveness of pharmaceutical practice and optimize pharmacokinetic profiles, have gathered momentum to battle cancer and other incurable diseases, for which traditional small-molecular and macromolecular drugs are less effective. However, the lack of clinical approval of supramolecular assembly-based medicine underscores the challenges facing this field. A 2D nanodisc-based supramolecular structure is formed by a non-ionic heptamethine cyanine (Cy7) dye, which generates fluorescence self-quenching but unique photothermal and photoacoustic properties. These Cy7-based supramolecular nanodiscs exhibit passive tumor-targeting properties to not only visualize the tumor by near-infrared fluorescence imaging and photoacoustic tomography but also induce photothermal tumor ablation under irradiation. Due to the nature of organic small molecule, they induce undetectable acute toxicity in mice and can be eliminated by the liver without extrahepatic metabolism. These findings suggest that the self-assembling cyanine discs represent a new paradigm in drug delivery as single-component supramolecular nanomedicines that are self-delivering and self-formulating, and provide a platform technology for synergistic clinical cancer imaging and therapy.     

Multifunctional Au@mSiO2/Rhodamine B Isothiocyanate Nanocomposites: Cell Imaging,Photocontrolled Drug Release,and Photothermal Therapy for Cancer Cells

The synthesis of Au@mesoporous SiO₂/rhodamine B isothiocyanate (Au@mSiO₂/RBITC) composite nanoparticles (NPs) is presented and their unique biofunctional properties are studied. The structure and morphology of the NPs are characterized by X‐ray powder diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy. These NPs can not only be functionalized for fluorescence imaging, but also possess well‐defined mesopore structures for drug loading and strong infrared surface plasmon absorption for light‐controlled drug release and photothermal therapy for cancer cells. In the biological experiments, one 808 nm laser is coupled to a confocal laser scanning microscopy (CLSM) system to monitor the photothermal therapy, drug release, and cell position and viability in real time by using the multichannel function of CLSM for the first time. Such novel nanomaterials offer a new chemotherapeutic route for cancer treatment by combining cell imaging and hyperthermia in a synergistic way.     

Bioinspired supramolecular liquid crystals

A brief account on the historical events leading to the discovery of self-assembling dendrons that generate self-organizable supramolecular dendrimers, or supramolecular polymers, and self-organizable dendronized polymers is provided. These building blocks were accessed by an accelerated design strategy that involves structural and retrostructural analysis of periodic and quasi-periodic assemblies. This design strategy mediated the discovery of porous helical supramolecular structures that self-assembled from dendritic dipeptides. Helical porous columns are the closest mimics of biologically related structures, such as tobacco mosaic virus coat, porous transmembrane proteins, porous pathogens and antibiotics. It is expected that this concept will allow one to investigate the structural origin of functions in synthetic supramolecular materials.     

Regular Aligned 1D Single‐Crystalline Supramolecular Arrays for Photodetectors

Solution‐processed semiconductor single‐crystal patterns possess unique advantages of large scale and low cost, leading to potential applications toward high‐performance optoelectronic devices. To integrate organic semiconductor micro/nanostructures into devices, various patterning techniques have been developed. However, previous patterning techniques suffer from trade‐offs between precision, scalability, crystallinity, and orientation. Herein, a patterning method is reported based on an asymmetric‐wettability micropillar‐structured template. Large‐scale 1D single‐crystalline supramolecular arrays with strict alignment, pure crystallographic orientation, and precise position can be obtained. The wettability difference between tops and sidewalls of micropillars gives rise to the confinement of organic solutions in discrete capillary tubes followed by dewetting and formation of capillary trailing. The capillary trailing enables unidirectional dewetting, regulated mass transport, and confined crystal growth. Owing to the high crystallinity and pure crystallographic orientation with Pt atomic chains parallel to the substrate, the photodetectors based on the 1D arrays exhibit improved responsivity. The work not only provides fundamental understanding on the patterning and crystallization of supramolecular structures but also develops a large‐scale assembly technique for patterning single‐crystalline micro/nanostructures.     

Large-scale orientation dependent heating from a single irradiated gold nanorod

We quantify the extreme heating associated with resonant irradiation of individual gold nanorods by using a novel assay based on partitioning of lipophilic dyes between membrane phases. The temperature increase is sensitively dependent on the angle between the laser polarization and the orientation of the nanorod. A dramatic and irreversible decrease in the heating of a nanorod occurs at high-illumination intensities; this effect is attributed to surface melting of the nanorod causing it to restructure into a more spherical shape and lose its extreme photothermal properties.     

Formation of porous niobium films by oblique angle deposition: Influence of substrate morphology

The present work demonstrates the formation of porous niobium films with separated columnar structures by oblique angle magnetron sputtering for capacitor application. The niobium films deposited on textured aluminium substrates, which had concave cell structures with the cell sizes ranging from 125 nm to 550 nm, consist of isolated columns of niobium with wider gaps between columns developing on the substrates with larger cell sizes. The surface areas of the deposited films, evaluated by the capacitance of the anodic films formed at several voltages, increased with an increase in the cell size of substrate. The surface area decreases with an increase in the formation potential of anodic films from 2 V to 10 V vs Ag/AgCl, because the gaps are filled with anodic oxide as a consequence of the large Pilling-Bedworth ratio of 2.6 for the Nb/Nb₂O₅ system. The reduction of the surface area is suppressed when the substrate with larger cell size is used, due to the formation of niobium columns with wider gaps, which are not filled with anodic oxide. The high surface area even at higher formation voltages of the anodic films is a requisite for capacitor application.     

Large-area pattern transfer of metallic nanostructures on glass substrates via interference lithography

In this paper, we report a simple and effective nanofabrication method for the pattern transfer of metallic nanostructures over a large surface area on a glass substrate. Photoresist (PR) nano-patterns, defined by laser interference lithography, are used as template structures where a metal film of controlled thickness is directly deposited and then transferred onto a glass substrate by the sacrificial etching of the PR inter-layer. The laser interference lithography, capable of creating periodic nano-patterns with good control of their dimensions and shapes over a relatively large area, allows the wafer-scale pattern transfer of metallic nanostructures in a very convenient way. By using the approach, we have successfully fabricated on a glass substrate uniform arrays of hole, grating, and pillar patterns of Ti, Al, and Au in varying pattern periodicities (200 nm-1 μm) over a surface area of up to several cm(2) with little mechanical crack and delamination. Such robust metallic nanostructures defined well on a transparent glass substrate with large pattern coverage will lead to advanced scientific and engineering applications such as microfluidics and nanophotonics.     

Investigation on fabrication of nanoscale patterns using laser interference lithography

Nanoscale patterns are fabricated by laser interference lithography (LIL) using Lloyd's mirror interferometer. LIL provides a patterning technology with simple, quick process over a large area without the usage of a mask. Effects of various key parameters for LIL, with 257 nm wavelength laser, are investigated, such as the exposure dosage, the half angle of two incident beams at the intersection, and the power of the light source for generating one or two dimensional (line and dot) nanoscale structures. The uniform dot patterns over an area of 20 mm x 20 mm with the half pitch sizes of around 190, 250, and 370 nm are achieved and by increasing the beam power up to 0.600 mW/cm2, the exposure process time was reduced down to 12/12 sec for the positive photoresist DHK-BF424 (DongJin) over a bare silicon substrate. In addition, bottom anti-reflective coating (DUV-30J, Brewer Science) is applied to confirm improvements for line structures. The advantages and limitations of LIL are highlighted for generating nanoscale patterns.     

Analysis of the enhancement of backscattering by nonspherical particles with flat surfaces

We examine backscattering by analyzing large nonspherical particles with flat surfaces for which where the size is much larger than the wavelength, using ray optics and diffraction theory. We show that the backscattering cross section for rectangles can be 1 order of magnitude larger than that for spheres with same geometrical cross sections, depending on the orientation of the particles. Then we show that there is a difficulty in estimating the backscattering cross section for hexagonal columns with the available solutions but that it is possible to estimate the integration of the differential scattering cross section over small solid angles in backward directions. The integral values for hexagonal columns are found to be more than 1 order of magnitude larger than that for spheres with the same volume. As an application, the use of power from hexagonal columns for lidar observations is analyzed. Unlike for spherical particles with their dependence on Z(-2) (where Z is the distance between the particle and the detector), for nonspherical particles such dependence varies with the particles' nonsphericity, such as shape and orientation: Z(0) for a hexagonal plate randomly oriented in the horizontal plane; Z(-1) for a hexagonal column randomly oriented in the horizontal plane.     

Supramolecular Two-Dimensional Systems and Their Biological Applications

Various biological systems rely on the supramolecular assembly of biomolecules through noncovalent bonds for performing sophisticated functions. In particular, cell membranes, which are 2D structures in biological systems, have various characteristics such as a large surface, flexibility, and molecule-recognition ability. Supramolecular 2D materials based on biological systems provide a novel perspective for the development of functional 2D materials. The physical and chemical properties of 2D structures, attributed to their large surface area, can enhance the sensitivity of the detection of target molecules, molecular loading, and bioconjugation efficiency, suggesting the potential utility of functional 2D materials as candidates for biological systems. Although several types of studies on supramolecular 2D materials have been reported, supramolecular biofunctional 2D materials have not been reviewed previously. In this regard, the current advances in 2D material development using molecular assembly are discussed with respect to the rational design of self-assembling aromatic amphiphiles, the formation of 2D structures, and the biological applications of functional 2D materials.     

Study on the Spatial Resolution of Imaging Technique for Absorption Loss Measurement of Optical Coatings

The uniformity of optical coatings becomes more and more important as large diameter optical devices are widely used. Absorption loss in optical components, particularly in optical coatings, is a limiting factor in high-power laser applications. This article analyzes the main factors, which affect the spatial resolution of three techniques for surface absorption loss measurement, including the photothermal deflection technique, the surface thermal lens technique, and the photothermal detuning technique. The influence of the size of the heating and probe beam on the photothermal detuning technique is studied in detail. Experiments are conducted to study the photothermal signal of the photothermal detuning technique for absorption measurement of the optical coating point by point. The results show that the main factors, which affect the spatial resolution of imaging measurements for absorption loss of coatings, are the heating beam size and the step accuracy of the sample translation stage. The heating and probe beam sizes has a significant impact on the application of the photothermal detuning technique. Experimental result shows that the photothermal detuning technique can be used for imaging of absorption loss measurements of optical coatings. The results provide theoretical and experimental supports for further application of the photothermal detuning technique.     

Supramolecular Protein Nanodrugs with Coordination‐ and Heating‐Enhanced Photothermal Effects for Antitumor Therapy

Supramolecular protein nanodrugs provide opportunities for improving antitumor therapeutic efficiency and lowering toxicity. However, protein nanodrugs that have robust structural stability and enhanced therapeutic efficiency are still in infancy. In this study, photothermal protein nanodrugs are constructed through a supramolecular approach along with heating by using proteins, photosensitizers, and metal ions as the building blocks. The metal coordination and heating improve not only the structural stability but also photothermal performance of the resulting nanodrugs. By virtue of the first integration of coordination‐ and heating‐enhanced photothermal effects, the nanodrugs show superior photothermal conversion efficiency, enhanced tumor accumulation, and improved tumor inhibition. Metal coordination and heating are versatile to be applied for various protein nanodrugs. Hence, this study provides insights for the construction of highly efficient photothermal nanodrugs and thus will be beneficial to precision theranostics.     

Self‐Assembly of Shaped Nanoparticles into Free‐Standing 2D and 3D Superlattices

This article describes a novel supramolecular assembly‐mediated strategy for the organization of Au nanoparticles (NPs) with different shapes (e.g., spheres, rods, and cubes) into large‐area, free‐standing 2D and 3D superlattices. This robust approach involves two major steps: (i) the organization of polymer‐tethered NPs within the assemblies of supramolecular comblike block copolymers (CBCPs), and (ii) the disassembly of the assembled CBCP structures to produce free‐standing NP superlattices. It is demonstrated that the crystal structures and lattice constants of the superlattices can be readily tailored by varying the molecular weight of tethered polymers, the volume fraction of NPs, and the matrix of CBCPs. This template‐free approach may open a new avenue for the assembly of NPs into 2D and 3D structures with a wide range of potential applications.     

Solid-phase epitaxial growth of (111)-oriented Si film on InGaO<Subscript>3</Subscript>(ZnO)<Subscript>5</Subscript> buffer layer

In this paper, the (0001) surface of an InGaO₃(ZnO)₅ (c-IGZO) single-crystal buffer layer was used as a seed layer to control the orientation of a Si film in solid-phase heteroepitaxial growth at 950 °C. Despite a large lattice misfit of 20%, electron backscattering diffraction (EBSD) and transmission electron microscope (TEM) measurements substantiated that the (111)-oriented Si layers are grown epitaxially on the c-IGZO (0001) surface, which is explained by domain-matched epitaxy. The process can be further developed for low temperature process by utilizing excimer laser annealing to produce highly uniform (111) oriented Si TFT over a large area.     

Self‐Healing of Polarizing Films via the Synergy between Gold Nanorods and Vitrimer

Conventional self‐healing is about the recovery of shape and mechanical properties. In contrast, recovery of functional properties is still a great challenge, especially for optical functional materials, as the known self‐healing methods are incompatible with optical properties. By utilizing the synergistic effect between Au nanorods and vitrimer, the alignment of Au nanorods can be achieved in the crosslinked polymer. The optical properties of the resulting polarizing film, such as light transmittance and polarization degree, can be fully recovered without an external repair agent. With simple laser irradiation to induce the photothermal effect of Au nanorods, the shape‐memory effect of vitrimer returns the Au nanorods to their initial orientation, and the plasticity achieves in situ self‐healing of the cutting area. The self‐healing of polarizing film provides a new research direction and reference for the application of self‐healing systems in functional materials.     

Damage threshold prediction of hafnia-silica multilayer coatings by nondestructive evaluation of fluence-limiting defects

A variety of microscopic techniques were employed to characterize fluence-limiting defects in hafnia-silica multilayer coatings manufactured for the National Ignition Facility, a fusion laser with a wavelength of 1.053 mum and a pulse width of 3 ns. Photothermal microscopy, with the surface thermal lens effect, was used to map the absorption and thermal characteristics of 3 mm x 3 mm areas of the coatings. High-resolution subaperture scans, with a 1-mum step size and a 3-mum pump-beam diameter, were conducted on the defects to characterize their photothermal properties. Optical and atomic force microscopy were used to identify defects and characterize their topography. The defects were then irradiated by a damage testing laser (1.06 mum and 3 ns) in single-shot mode until damage occurred. The results were analyzed to determine the role of nodular and nonnodular defects in limiting the damage thresholds of the multilayer coatings. It was found that, although different types of defect were present in these coatings, the fluence-limiting ones had the highest photothermal signals (up to 126x over the host coating). The implication of this study is that coating process improvements for hafnia-silica multilayer coatings should have a broader focus than just elimination of source ejection, since high photothermal signals frequently occur at nodule-free regions. The study also demonstrates that, for optics subject to absorption-induced thermal damage, photothermal microscopy is an appropriate tool for nondestructive identification of fluence-limiting defects.