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Matrix nanotopographical cues are known to regulate the structure and function of somatic cells derived from human pluripotent stem cell (hPSC) sources. High-throughput electrophysiological analysis of excitable cells derived from hPSCs is possible via multielectrode arrays (MEAs), but conventional MEA platforms use flat substrates and do not reproduce physiologically-relevant tissue-specific architecture. To address this issue, we developed a high-throughput nanotopographically-patterned multielectrode array (nanoMEA) by integrating conductive, ion-permeable, nanotopographic patterns with 48-well MEA plates, and investigated the effect of substrate-mediated cytoskeletal organization on hPSC-derived cardiomyocyte and neuronal function at scale. Using our nanoMEA platform, we found patterned hPSC-derived cardiac monolayers exhibit both enhanced structural organization and greater sensitivity to treatment with calcium blocking or conduction inhibiting compounds when subjected to high-throughput dose-response studies. Similarly, hPSC-derived neurons grown on nanoMEA substrates exhibit faster migration and neurite outgrowth speeds, greater co-localization of pre- and post-synaptic markers, and enhanced cell-cell communication, only revealed through examination of data sets derived from multiple technical replicates. The presented data highlight the nanoMEA as a new tool to facilitate high-throughput, electrophysiological analysis of ordered cardiac and neuronal monolayers, which can have important implications for preclinical analysis of excitable cell function.

We propose dual resonant optical sum frequency generation (SFG), where the two most singular resonances could be selected, and report for the monolayer (1L-) WSe2 when one (ω1) of two excitation pu...

Friction and wear remain the primary cause of mechanical energy dissipation and system failure. Recent studies reveal graphene as a powerful solid lubricant to combat friction and wear. Most of these studies have focused on nanoscale tribology and have been limited to a few specific surfaces. Here, we uncover many unknown aspects of graphene's contact-sliding at micro- and macroscopic tribo-scales over a broader range of surfaces. We discover that graphene's performance reduces for surfaces with increasing roughness. To overcome this, we introduce a new type of graphene/silicon nitride (SiNx, 3 nm) bilayer overcoats that exhibit superior performance compared to native graphene sheets (mono and bilayer), that is, display the lowest microscale friction and wear on a range of tribologically poor flat surfaces. More importantly, two-layer graphene/SiNx bilayer lubricant (

We report on the thickness-dependent Raman spectroscopy of ultrathin silicon (Si) nanomembranes (NMs), whose thicknesses range from 2 to 18 nm, using several excitation energies. We observe that the Raman intensity depends on the thickness and the excitation energy due to the combined effects of interference and resonance from the band-structure modulation. Furthermore, confined acoustic phonon modes in the ultrathin Si NMs were observed in ultralow-frequency Raman spectra, and strong thickness dependence was observed near the quantum limit, which was explained by calculations based on a photoelastic model. Our results provide a reliable method with which to accurately determine the thickness of Si NMs with thicknesses of less than a few nanometers.

Enhancing the device performance of organic memory devices while providing high optical transparency and mechanical flexibility requires an optimized combination of functional materials and smart device architecture design. However, it remains a great challenge to realize fully functional transparent and mechanically durable nonvolatile memory because of the limitations of conventional rigid, opaque metal electrodes. Here, we demonstrate ferroelectric nonvolatile memory devices that use graphene electrodes as the epitaxial growth substrate for crystalline poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) polymer. The strong crystallographic interaction between PVDF-TrFE and graphene results in the orientation of the crystals with distinct symmetry, which is favorable for polarization switching upon the electric field. The epitaxial growth of PVDF-TrFE on a graphene layer thus provides excellent ferroelectric performance with high remnant polarization in metal/ferroelectric polymer/metal devices. Furthermore, a fully transparent and flexible array of ferroelectric field effect transistors was successfully realized by adopting transparent poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] semiconducting polymer.

High-performance, flexible all graphene-based thin film transistor (TFT) was fabricated on plastic substrates using a graphene active layer, graphene oxide (GO) dielectrics, and graphene electrodes. The GO dielectrics exhibit a dielectric constant (3.1 at 77 K), low leakage current (17 mA/cm(2)), breakdown bias (1.5 × 10(6) V/cm), and good mechanical flexibility. Graphene-based TFTs showed a hole and electron mobility of 300 and 250 cm(2)/(V·s), respectively, at a drain bias of -0.1 V. Moreover, graphene TFTs on the plastic substrates exhibited remarkably good mechanical flexibility and optical transmittance. This method explores a significant step for the application of graphene toward flexible and stretchable electronics.

We demonstrate high-performance, flexible, transparent heaters based on large-scale graphene films synthesized by chemical vapor deposition on Cu foils. After multiple transfers and chemical doping processes, the graphene films show sheet resistance as low as ∼43 Ohm/sq with ∼89% optical transmittance, which are ideal as low-voltage transparent heaters. Time-dependent temperature profiles and heat distribution analyses show that the performance of graphene-based heaters is superior to that of conventional transparent heaters based on indium tin oxide. In addition, we confirmed that mechanical strain as high as ∼4% did not substantially affect heater performance. Therefore, graphene-based, flexible, transparent heaters are expected to find uses in a broad range of applications, including automobile defogging/deicing systems and heatable smart windows.

With the emergence of human interface technology, the development of new applications based on stretchable electronics such as conformal biosensors and rollable displays are required. However, the difficulty in developing semiconducting materials with high stretchability required for such applications has restricted the range of applications of stretchable electronics. Here, we present stretchable, printable, and transparent transistors composed of monolithically patterned graphene films. This material offers excellent mechanical, electrical, and optical properties, capable of use as semiconducting channels as well as the source/drain electrodes. Such monolithic graphene transistors show hole and electron mobilities of 1188 ± 136 and 422 ± 52 cm(2)/(V s), respectively, with stable operation at stretching up to 5% even after 1000 or more cycles.

Nanoscale grating structure can be utilized in many practical applications in optics, flat-panel displays, and biosensors. We present a dynamic nanoinscribing (DNI) technique for directly creating large-area, truly continuous nanograting patterns in a variety of metal or polymer materials with feature size down to sub-50 nm and at very high speed (10 cm/sec). DNI is carried out under either ambient temperature or with a brief heating time on the order of 10 micros, which minimizes damage on UV or thermosensitive functional materials. We also demonstrated future applications of the DNI process into the simple, one-step fabrication of split-ring resonator (SRR) structures for negative index materials.

Scattering-type apertureless near-field microscopy (ANSOM) provides high-resolution dielectric maps of indium gallium nitride (InGaN) semiconductor nanoparticles at visible (633 nm) wavelengths. A specific size-dependent contrast reversal is observed in the ANSOM images of InGaN nanoparticles grown on a layer of gallium nitride (GaN). Model calculations demonstrate that the observed contrast reversal is the result of the competition between the tip-particle versus tip-substrate dipolar coupling.

The anomalous piezoresistance (a-PZR) effects, including giant PZR (GPZR) with large magnitude and inverse PZR of opposite, have exciting technological potentials for their integration into novel nanoelectromechanical systems. However, the nature of a-PZR effect and the associated kinetics have not been clearly determined yet. Even further, there are intense research debates whether the a-PZR effect actually exists or not; although numerous investigations have been conducted, the origin of the effect has not been clearly understood. This paper shows the existence of a-PZR and provides direct experimental evidence through the performance of well-established electrical measurements and terahertz spectroscopy on silicon nanomembranes (Si NMs). The clear inverse PZR behavior was observed in the Si NMs when the thickness was less than 40 nm and the magnitude of the PZR response linearly increased with the decreasing thickness. Observations combined with electrical and optical measurements strongly corroborate that the a-PZR effect originates from the carrier concentration changes via charge carrier trapping into strain-induced defect states.

Two dimensional (2D) semiconductors have attracted attention for a range of electronic applications, such as transparent, flexible field effect transistors and sensors owing to their good optical transparency and mechanical flexibility. Efforts to exploit 2D semiconductors in electronics are hampered, however, by the lack of efficient methods for their synthesis at levels of quality, uniformity, and reliability needed for practical applications. Here, as an alternative 2D semiconductor, we study single crystal Si nanomembranes (NMs), formed in large area sheets with precisely defined thicknesses ranging from 1.4 to 10 nm. These Si NMs exhibit electronic properties of two-dimensional quantum wells and offer exceptionally high optical transparency and low flexural rigidity. Deterministic assembly techniques allow integration of these materials into unusual device architectures, including field effect transistors with total thicknesses of less than 12 nm, for potential use in transparent, flexible, and stretchable forms of electronics.

A novel graphene-on-organic film fabrication method that is compatible with a batch microfabrication process was developed and used for electromechanically driven microactuators. A very thin layer of graphene sheets was monolithically integrated and the unique material characteristics of graphene including negative thermal expansion and high electrical conductivity were exploited to produce a bimorph actuation. A large displacement with rapid response was observed while maintaining the low power consumption. This enabled the successful demonstration of transparent graphene-based organic microactuators.

Micro/nanoscale periodic structures are widely used in display, optics and bio industries as key functional elements. We present a novel nanopatterning method, localized dynamic wrinkling (LDW), which creates micro/nanoscale metal gratings continuously by simply sliding a flat edge of a hard material over a thin metal surface coated on a polymer layer. The LDW process presented in this paper is an etching- and template-free nanopatterning technology based on nanoscale wrinkling phenomenon. This simple process enables spontaneous formation of large-area metal gratings with controllable periodicity from micrometer down to 120 nm.

A high-performance low-voltage graphene field-effect transistor (FET) array was fabricated on a flexible polymer substrate using solution-processable, high-capacitance ion gel gate dielectrics. The high capacitance of the ion gel, which originated from the formation of an electric double layer under the application of a gate voltage, yielded a high on-current and low voltage operation below 3 V. The graphene FETs fabricated on the plastic substrates showed a hole and electron mobility of 203 +/- 57 and 91 +/- 50 cm(2)/(V x s), respectively, at a drain bias of -1 V. Moreover, ion gel gated graphene FETs on the plastic substrates exhibited remarkably good mechanical flexibility. This method represents a significant step in the application of graphene to flexible and stretchable electronics.

We carried out the near-field optical imaging of isolated and dimerized gold nanocubes to directly investigate the strong coupling between two adjacent nanoparticles. The high-resolution (approximately 10 nm) local field maps (intensities and phases) of self-assembled nanocube dimers reveal antisymmetric plasmon modes that are starkly different from a simple superposition of two monomeric dipole plasmons, which is fully reproduced by the electrodynamics simulations. The result decisively proves that, for the closely spaced pair of nanoparticles (interparticle distance/particle size approximately 0.04), the strong Coulombic attraction between the charges at the interparticle gap dominates over the intraparticle charge oscillations, resulting in a hybridized dimer plasmon mode that is qualitatively different from those expected from a simple dipole-dipole coupling model.