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Composite structures exhibiting a periodic arrangement of building blocks can be found in natural systems at different length scales. Recreating such systems in artificial composites using the principles of self-assembly has been a great challenge, especially for 1D microscale systems. Here, we present a purposely designed composite material consisting of gold nanoparticles and a nematic liquid crystal matrix that has the ability to self-create a periodic structure in the form of a one-dimensional photonic lattice through a phase separation process occurring in a confined space. Our strategy is based on the use of a thermoswitchable medium that reversibly and quickly responds to both heating and cooling. We find that the period of the structure is strongly related to the size of the confining space. We believe that our findings will allow us to not only better understand the phase separation process in multicomponent soft/colloid mixtures with useful optical properties but also improve our understanding of the precise assembly of advanced materials into one-dimensional periodic systems, with prospective applications in future photonic technologies.

The reaction of monolayer graphene with aryl diazonium salts is a popular approach for functionalizing graphene under ambient conditions. We here apply interference reflection microscopy (IRM), a label-free optical technique, to study the in situ reaction dynamics of the representative diazonium reaction of graphene with 4-nitrobenzenediazonium tetrafluoroborate (4-NBD) at high spatiotemporal resolution and further correlate results with atomic force microscopy, Raman spectroscopy, and infrared scattering scanning near-field optical microscopy. Interestingly, we find the reaction to be significantly promoted by a low (0.5 W/cm2) level of blue visible light, whereas at the same intensity level, red light has negligible effects on reaction rate. We further report rich spatial heterogeneities for the reaction, including enhanced reactivity at graphene edges and an unexpected flake-to-flake variation in reaction rate. Moreover, we demonstrate direct photopatterning for the 4-NBD functionalization, achieving 400 nm patterning resolution.

We unveil the reaction dynamics of monolayer graphene in electrochemical oxidation and reduction processes through interference reflection optical microscopy. At 300 nm spatial resolution and 200 ms temporal resolution, we reveal rapid electrochemical oxidation of graphene, as well as its efficient electrochemical reduction back to the unoxidized state. We identify 1.4 V (vs Ag/AgCl) as the onset voltage for oxidation and show that the process is driven by free radicals generated in the electrolysis of water and so fully suppressible by a radical-trapping molecule. Moreover, we find the oxidation process to be spatially heterogeneous at the nanoscale, defect- and history-dependent, and characterized by a self-limiting effect unique to the two-dimensional system. We further demonstrate that electrochemical reduction rapidly reverses the oxidized graphene back to the unoxidized state in a controlled manner and find strong dependency of reduction speed on the reduction voltage and pH, from which we conclude a one-to-one relationship between protons and electrons in the reduction process. Besides elucidating the electrochemical reaction mechanisms of graphene, our results point to new pathways to the controlled generation and fine-tuning of graphene derivatives through electrochemistry.

The potential of rising two-dimensional materials, such as graphene, can be substantially expanded through chemistry. However, it has been a challenge to study how chemical reactions of two-dimensional materials progress. Existing techniques offer limited signal contrast and/or spatial-temporal resolution and are difficult to apply to in situ studies. Here we employ an optical approach, namely interference reflection microscopy, to quantitatively monitor the redox reaction dynamics of graphene and graphene oxide (GO) in situ with diffraction-limited (∼300 nm) spatial resolution and video-rate time resolution. Remarkably, we found that the oxidation kinetics of graphene is characterized by a seeded, autocatalytic process that gives rise to unique, wave-like propagation of reaction in two dimensions. The reaction is initially slow and confined to highly localized, nanoscale hot spots associated with structural defects, but then self-accelerates while propagating outward, hence flower-like, micrometer-sized reaction patterns over the entire sample. In contrast, the reduction of GO is spatially homogeneous and temporally pseudo-first-order, and through in situ data, we further identify pH as a key reaction parameter.

Correlative microscopy, the integration of two or more microscopy techniques performed on the same sample, produces results that emphasize the strengths of each technique while offsetting their individual weaknesses. Light microscopy has historically been a central method in correlative microscopy due to its widespread availability, compatibility with hydrated and live biological samples, and excellent molecular specificity through fluorescence labeling. However, conventional light microscopy can only achieve a resolution of ∼300 nm, undercutting its advantages in correlations with higher-resolution methods. The rise of super-resolution microscopy (SRM) over the past decade has drastically improved the resolution of light microscopy to ∼10 nm, thus creating exciting new opportunities and challenges for correlative microscopy. Here we review how these challenges are addressed to effectively correlate SRM with other microscopy techniques, including light microscopy, electron microscopy, cryomicroscopy, atomic force microscopy, and various forms of spectroscopy. Though we emphasize biological studies, we also discuss the application of correlative SRM to materials characterization and single-molecule reactions. Finally, we point out current limitations and discuss possible future improvements and advances. We thus demonstrate how a correlative approach adds new dimensions of information and provides new opportunities in the fast-growing field of SRM.

The electronic, optical, and mechanical properties of bilayer and trilayer graphene vary with their structure, including the stacking order and relative twist, providing novel ways to realize useful characteristics not available to single layer graphene. However, developing controlled growth of bilayer and trilayer graphene requires efficient large-scale characterization of multilayer graphene structures. Here, we use dark-field transmission electron microscopy for rapid and accurate determination of key structural parameters (twist angle, stacking order, and interlayer spacing) of few-layer CVD graphene. We image the long-range atomic registry for oriented bilayer and trilayer graphene, find that it conforms exclusively to either Bernal or rhombohedral stacking, and determine their relative abundances. In contrast, our data on twisted multilayers suggest the absence of such long-range atomic registry. The atomic registry and its absence are consistent with the two different strain-induced deformations we observe; by tilting the samples to break mirror symmetry, we find a high density of twinned domains in oriented multilayer graphene, where multiple domains of two different stacking configurations coexist, connected by discrete twin boundaries. In contrast, individual layers in twisted regions continuously stretch and shear independently, forming elaborate Moiré patterns. These results, and the twist angle distribution in our CVD graphene, can be understood in terms of an angle-dependent interlayer potential model.