Person:

Ham, Donhee

Highly stretchable and robust antennas are fabricated by injecting liquid metal into a microfluidic channel that consists of two types of silicone rubber with different stiffness. The resulting antennas exhibit high mechanical stability under strain, while retaining high stretchability; these antennas can be stretched by up to a tensile strain of 120% with little degradation in radiation efficiency.

In this study, we report the unequivocal demonstration of midinfrared mode-locked pulses from quantum cascade lasers. The train of short pulses was generated by actively modulating the current and hence the gain of an edge-emitting quantum cascade laser (QCL). Pulses with duration of about 3 ps at full-width-at-half-maxima and energy of 0.5 pJ were characterized using a second-order interferometric autocorrelation technique based on a nonlinear quantum well infrared photodetector. The mode-locking dynamics in the QCLs was modeled based on the Maxwell-Bloch equations in an open two-level system. Our model reproduces the overall shape of the measured autocorrelation traces and predicts that the short pulses are accompanied by substantial wings as a result of strong spatial hole burning. The range of parameters where short mode-locked pulses can be formed is found.

Individual electrons in graphene behave as massless quasiparticles1. Unexpectedly, it is inferred from plasmonic investigations that electrons in graphene must exhibit a non-zero mass when collectively excited. The inertial acceleration of the electron collective mass is essential to explain the behaviour of plasmons in this material, and may be directly measured by accelerating it with a time-varying voltage and quantifying the phase delay of the resulting current. This voltage–current phase relation would manifest as a kinetic inductance, representing the reluctance of the collective mass to accelerate. However, at optical (infrared) frequencies, phase measurements of current are generally difficult, and, at microwave frequencies, the inertial phase delay has been buried under electron scattering. Therefore, to date, the collective mass in graphene has defied unequivocal measurement. Here, we directly and precisely measure the kinetic inductance, and therefore the collective mass, by combining device engineering that reduces electron scattering and sensitive microwave phase measurements. Specifically, the encapsulation of graphene between hexagonal boron nitride layers, one-dimensional edge contacts and a proximate top gate configured as microwave ground together enable the inertial phase delay to be resolved from the electron scattering. Beside its fundamental importance, the kinetic inductance is found to be orders of magnitude larger than the magnetic inductance, which may be utilized to miniaturize radiofrequency integrated circuits. Moreover, its bias dependency heralds a solid-state voltage-controlled inductor to complement the prevalent voltage-controlled capacitor.

Network-wide parallelization of neuronal intracellular recording and quantification of synaptic connections and their strengths is a challenge still open in neuroscience, with a mapping limit of ~300 connections. Here, we report a 4,096 microhole electrode array on a semiconductor chip for parallel intracellular recording and synaptic connectivity mapping of rat neuronal cultures using electroporation. The microholes are etched from a complementary metal-oxide semiconductor chip, and the final surface is coated with platinum black to increase roughness and the neuronal interface. The microhole array allows up to 90% average intracellular coupling rate with high coupling fidelity, generating network-wide intracellular recording data containing synaptic signals, and allows regaining intracellular coupling on the same neurons. We extract 70,000+ plausible synaptic connections amongst 2,000+ neurons, and catalogue them into inhibitory, weak/uneventful excitatory, strong/eventful excitatory chemical synaptic connections, and electrical synaptic connections, with an estimated overall error rate of around 5%. The reported scale of chemical and electrical synaptic mapping combines the advantages of patch clamp and extracellular multi-electrode array recordings, providing valuable insights into large-scale neural connectivity.

Massive parallelization of neuronal intracellular recording, which can measure synaptic signals across a network and thus can enable the mapping and characterization of synaptic connections, is a challenge still open in neuroscience, with the state-of-the-art limited to a mapping of ~300 synaptic connections. Here, we report a 4,096 platinum/platinum-black microhole electrode array fabricated on a complementary metal-oxide semiconductor electronic chip that substantially advances parallel intracellular recording and synaptic connectivity mapping. The microhole-neuron interface, together with current-clamp electronics in the underlying semiconductor chip, allows 90% average intracellular coupling rate with rat neuronal cultures, generating network-wide intracellular recording data that abound with synaptic signals. From these data we extract 70,000+ plausible synaptic connections amongst 2,000+ neurons, and catalogue them into inhibitory, weak/uneventful excitatory, and strong/eventful excitatory chemical synaptic connections, and electrical synaptic connections, with an estimated overall error rate of around 5%. The reported scale of synaptic connection mapping, with the ability to characterize synaptic connections, provides a step toward functional connectivity mapping of a large-scale neuronal network.

Parallelized DNA synthesis across a dense array of sites is crucial to high-throughput synthetic biology and diagnostics, and could potentially be used for DNA-based data storage. Phosphoramidite synthesis can achieve substantial parallelism, but relies on harmful solvents and centralized facilities. Enzymatic DNA synthesis in mild aqueous solution is safer and could be more accessible, but parallel demonstrations remain modest at an early stage. Here, we show that a complementary metal–oxide–semiconductor (CMOS) chip can be used to perform parallel enzymatic DNA synthesis of up to 64 distinct 38–39-nucleotide sequences (10–11-nucleotide feature sequences). The chip controls an array of 256 ring-electrode pairs (each one a programmable synthesis site) that can create an arbitrary pattern of localized acidity to enable DNA deprotection and subsequent enzymatic nucleotide incorporation. We also illustrate this parallel synthesis for data storage by encoding a 169-byte text. Our mechanistic analysis shows that shifting from an indirect to a direct local-acid chemistry route could lead to higher-throughput enzymatic synthesis that can scale with the CMOS chip.