The morphology of doubly-clamped graphene nanoribbons

Understanding the response of micro/nano-patterned graphene to mechanical forces is instrumental for applications such as advanced graphene origami and kirigami. Here, we analyze free-standing nanoribbons milled into single-layer graphene by focused ion beam processing. Using transmission electron microscopy, we show that the length L of the structures determines their morphology. Nanoribbons with L below 300 nm remain mainly flat, whereas longer ribbons exhibit uni-axial crumpling or spontaneous scrolling, a trend that is well reproduced by molecular dynamics simulations. We measure the strain of the ribbons as well as their crystallinity by recording nanometer-resolved convergent beam electron diffraction maps, and show that the beam tails of the focused ion beam cause significant amorphization of the structures adjacent to the cuts. The expansive or compressive strain in the structures remains below 4%. Our measurements provide experimental constraints for the stability of free-standing graphene structures with respect to their geometry, providing guidelines for future applications of patterned graphene

MAxSIM: Multi-Angle-Crossing Structured Illumination Microscopy With Height-Controlled Mirror for 3D Topological Mapping of Live Cells

Mapping 3D plasma membrane topology in live cells can bring unprecedented insights into cell biology. Widefield-based super-resolution methods such as 3D-structured illumination microscopy (3D-SIM) can achieve twice the axial ( ~ 300 nm) and lateral ( ~ 100 nm) resolution of widefield microscopy in real time in live cells. However, twice-resolution enhancement cannot sufficiently visualize nanoscale fine structures of the plasma membrane. Axial interferometry methods including fluorescence light interference contrast microscopy and its derivatives (e.g., scanning angle interference microscopy) can determine nanoscale axial locations of proteins on and near the plasma membrane. Thus, by combining super-resolution lateral imaging of 2D-SIM with axial interferometry, we developed multi-angle-crossing structured illumination microscopy (MAxSIM) to generate multiple incident angles by fast, optoelectronic creation of diffraction patterns. Axial localization accuracy can be enhanced by placing cells on a bottom glass substrate, locating a custom height-controlled mirror (HCM) at a fixed axial position above the glass substrate, and optimizing the height reconstruction algorithm for noisy experimental data. The HCM also enables imaging of both the apical and basal surfaces of a cell. MAxSIM with HCM offers high-fidelity nanoscale 3D topological mapping of cell plasma membranes with near-real-time ( ~ 0.5 Hz) imaging of live cells and 3D single-molecule tracking

0.52 V mm ITO-based Mach-Zehnder modulator in silicon photonics

Electro-optic modulators transform electronic signals into the optical domain and are critical components in modern telecommunication networks, RF photonics, and emerging applications in quantum photonics, neuromorphic photonics, and beam steering. All these applications require integrated and voltage-efficient modulator solutions with compact form factors that are seamlessly integrable with silicon photonics platforms and feature near-CMOS material processing synergies. However, existing integrated modulators are challenged to meet these requirements. Conversely, emerging electro-optic materials heterogeneously and monolithically integrated with Si photonics open up a new avenue for device engineering. Indium tin oxide (ITO) is one such compelling material for heterogeneous integration in Si exhibiting formidable electro-optic effect characterized by unity-order index change at telecommunication frequencies. Here we overcome these limitations and demonstrate a monolithically integrated ITO electro-optic modulator based on a Mach Zehnder interferometer featuring a high-performance half-wave voltage and active device length product of VπL = 0.52 V mm. We show that the unity-strong index change enables a 30 μm-short π-phase shifter operating ITO in the index-dominated region away from the epsilon-near-zero point for reduced losses. This device experimentally confirms electrical phase shifting in ITO enabling its use in applications such as compact phase shifters, nonlinear activation functions in photonic neural networks, and phased array applications for LiDAR