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High packing density aligned arrays of semiconducting carbon nanotubes (CNTs) are required for many electronics applications. Past work has shown that the accumulation of CNTs at a water-solvent interface can drive array self-assembly. Previously, the confining interface was a large-area, macroscopic feature. Here, we report on the CNT assembly on microscopic water features. Water microdroplets are formed on 10-100 μm wide hydrophilic stripes patterned on a substrate. Exposure to CNTs dispersed in solvent accumulates CNTs at the microdroplet-solvent interface, driving their alignment and deposition at the microdroplet-solvent-substrate contact line. Compared with macroscopic methods in which the contact line uncontrollably moves across the substrate as it is pulled out of the liquids, the hydrophilic patterns and microdroplets allow pinning of the contact line. As CNTs deposit, the contact line self-translates, allowing for dense CNT packing. We realize monolayer CNT arrays aligned within ±3.9° at density of 250 μm -1 and field effect transistors with a high current density of 1.9 mA μm -1 and transconductance of 1.2 mS μm -1 at -0.6 V drain bias and 60 nm channel length.

Robust, high-yield integration of nanoscale components such as graphene nanoribbons, nanoparticles, or single-molecules with conventional electronic circuits has proven to be challenging. This difficulty arises because the contacts to these nanoscale devices must be precisely fabricated with angstrom-level resolution to make reliable connections, and at manufacturing scales this cannot be achieved with even the highest-resolution lithographic tools. Here we introduce an approach that circumvents this issue by precisely creating nanometer-scale gaps between metallic carbon electrodes by using a self-aligning, solution-phase process, which allows facile integration with conventional electronic systems with yields approaching 50%. The electrode separation is controlled by covalently binding metallic single-walled carbon nanotube (mCNT) electrodes to individual DNA duplexes to create mCNT-DNA-mCNT nanojunctions, where the gap is precisely matched to the DNA length. These junctions are then integrated with top-down lithographic techniques to create single-molecule circuits that have electronic properties dominated by the DNA in the junction, have reproducible conductance values with low dispersion, and are stable and robust enough to be utilized as active, high-specificity electronic biosensors for dynamic single-molecule detection of specific oligonucleotides, such as those related to the SARS-CoV-2 genome. This scalable approach for high-yield integration of nanometer-scale devices will enable opportunities for manufacturing of hybrid electronic systems for a wide range of applications.

The heteroepitaxial growth of crystal silicon thin films on sapphire, usually referred to as SoS, has been a key technology for high-speed mixed-signal integrated circuits and processors. Here, we report a novel nanoscale SoS heteroepitaxial growth that resembles the in-plane writing of self-aligned silicon nanowires (SiNWs) on R-plane sapphire. During a low-temperature growth at <350 °C, compared to that required for conventional SoS fabrication at >900 °C, the bottom heterointerface cultivates crystalline Si pyramid seeds within the catalyst droplet, while the vertical SiNW/catalyst interface subsequently threads the seeds into continuous nanowires, producing self-oriented in-plane SiNWs that follow a set of crystallographic directions of the sapphire substrate. Despite the low-temperature fabrication process, the field effect transistors built on the SoS-SiNWs demonstrate a high on/off ratio of >5 × 104 and a peak hole mobility of >50 cm2/V·s. These results indicate the novel potential of deploying in-plane SoS nanowire channels in places that require high-performance nanoelectronics and optoelectronics with a drastically reduced thermal budget and a simplified manufacturing procedure. [ABSTRACT FROM AUTHOR]

Two-dimensional semiconductors (2DSCs) such as molybdenum disulfide (MoS2) have attracted intense interest as an alternative electronic material in the postsilicon era. However, the ON-current density achieved in 2DSC transistors to date is considerably lower than that of silicon devices, and it remains an open question whether 2DSC transistors can offer competitive performance. A high current device requires simultaneous minimization of the contact resistance and channel length, which is a nontrivial challenge for atomically thin 2DSCs, since the typical low contact resistance approaches for 2DSCs either degrade the electronic properties of the channel or are incompatible with the fabrication process for short channel devices. Here, we report a new approach toward high-performance MoS2 transistors by using a physically assembled nanowire as a lift-off mask to create ultrashort channel devices with pristine MoS2 channel and self-aligned low resistance metal/graphene hybrid contact. With the optimized contact in short channel devices, we demonstrate sub-100 nm MoS2 transistor delivering a record high ON-current of 0.83 mA/μm at 300 K and 1.48 mA/μm at 20 K, which compares well with that of silicon devices. Our study, for the first time, demonstrates that the 2DSC transistors can offer comparable performance to the 2017 target for silicon transistors in International Technology Roadmap for Semiconductors (ITRS), marking an important milestone in 2DSC electronics. [ABSTRACT FROM AUTHOR]

The seamless coalescence of parallelly aligned 2D materials is the primary route toward the synthesis of wafer-scale single crystals (WSSCs) of 2D materials. The epitaxial growth of various 2D materials on a single-crystal substrate, which is an essential condition of the seamless coalescence approach, has been extensively explored in previous studies. Here, by using hexagonal boron nitride (hBN) growth on a liquid gold surface as an example, we demonstrate that growth of WSSCs of 2D materials via the seamless coalescence of self-aligned 2D islands on a liquid substrate is possible. Here we show that, in the presence of hydrogen, all the hBN edges tend to be hydrogen terminated and the coalescence of hBN islands occurs only if their crystallographic lattices of neighboring hBN islands are aligned parallelly. The mechanism of hBN self-alignment revealed in this study implies that, under the optimum experimental condition, the seamless coalescence of 2D materials on a liquid substrate is possible and thus provides guidance for synthesizing WSSCs of various 2D materials by using liquid phase substrates.

Quantum sciences are revolutionizing computing and communication technologies, in which single-photon emitters are the key components for creating strong quantum entanglement. Color centers in diamonds in coupled-cavity systems are considered great candidates for the efficient generation of quantum carriers over other solid-state emitters. Owing to the multi-mode nature of high quality factor ( Q) diamond cavities, however, it is a grand challenge to the achievement of single photon emission with high rate and indistinguishability. To this end, a single-mode high- Q diamond cavity is highly desired. Here, we report a diamond mesostructured nanomembrane microcavity of a discrete rotational symmetry that selectively produces the desired single-mode emission in a broad spectrum. The strategic rolling up of a flexible diamond nanomembrane with aligned holes effectively defines the designed symmetry while maintaining the high- Q resonance through the whispering-gallery mode supported in the central hollow microcavity. The demonstrated diamond mesostructured microcavity features a distinct and enhanced single-mode emission, a step toward efficient quantum sources with designed positions or bands for quantum information technology.

We demonstrate the realization of core-shell transformation-imprinted solder bumps to enable low-temperature chip assembly, while providing a route to high-temperature interconnects through transformation. The reported core-shell solder bump uses a lower melting point BiIn-based shell and a higher melting point Sn core in the initial stage. The bumps enable fluidic self-assembly and self-alignment at relatively low temperatures (60-80 °C). The bumps use the high surface free energy of the liquid shell during the self-assembly to capture freely suspended Si dies inside a heated (80 °C) water bath, leading to well-ordered defect-free chip arrays; the molten liquid shell wets the metal contact (binding site) on the chips and yields self-aligned and electrically connected devices. The solid core provides the anchor point to the substrate. After the completion of the assembly, a short reflow raises the melting point, yielding a solid electrical connection. The low melting point liquid diffuses into the high melting point core. The tuning of the material ratios leads to tailored transformation-imprinted solders with high melting points (160-206 °C) in the final structure.

The design and preparation of an excellent corrosion protection coating is still a grand challenge and is essential for large-scale practical application. Herein, a novel cationic reduced graphene oxide (denoted as RGO-ID + )-based epoxy coating was fabricated for corrosion protection. RGO-ID + was synthesized by in situ synthesis and salification reaction, which is stable dispersion in water and epoxy latex, and the self-aligned RGO-ID + -reinforced cathodic electrophoretic epoxy nanocomposite coating (denoted as RGO-ID + coating) at the surface of metal was prepared by electrodeposition. The self-alignment of RGO-ID + in the coatings is mainly attributed to the electric field force. The significantly enhanced anticorrosion performance of RGO-ID + coating is proved by a series of electrochemical measurements in different concentrated NaCl solutions and salt spray tests. This superior anticorrosion property benefits from the self-aligned RGO-ID + nanosheets and the quaternary-N groups present in the RGO-ID + nanocomposite coating. Interestingly, the RGO-ID + also exhibits a high antibacterial activity toward Escherichia coli with 83.4 ± 1.3% antibacterial efficiency, which is attributed to the synergetic effects of RGO-ID + and the electrostatic attraction and hydrogen bonding between RGO-ID + and E. coli. This work offers new opportunities for the successful development of effective corrosion protection and self-antibacterial coatings.

The heteroepitaxial growth of crystal silicon thin films on sapphire, usually referred to as SoS, has been a key technology for high-speed mixed-signal integrated circuits and processors. Here, we report a novel nanoscale SoS heteroepitaxial growth that resembles the in-plane writing of self-aligned silicon nanowires (SiNWs) on R-plane sapphire. During a low-temperature growth at <350 °C, compared to that required for conventional SoS fabrication at >900 °C, the bottom heterointerface cultivates crystalline Si pyramid seeds within the catalyst droplet, while the vertical SiNW/catalyst interface subsequently threads the seeds into continuous nanowires, producing self-oriented in-plane SiNWs that follow a set of crystallographic directions of the sapphire substrate. Despite the low-temperature fabrication process, the field effect transistors built on the SoS-SiNWs demonstrate a high on/off ratio of >5 × 10 4 and a peak hole mobility of >50 cm 2 /V·s. These results indicate the novel potential of deploying in-plane SoS nanowire channels in places that require high-performance nanoelectronics and optoelectronics with a drastically reduced thermal budget and a simplified manufacturing procedure.

Two-dimensional semiconductors (2DSCs) such as molybdenum disulfide (MoS 2 ) have attracted intense interest as an alternative electronic material in the postsilicon era. However, the ON-current density achieved in 2DSC transistors to date is considerably lower than that of silicon devices, and it remains an open question whether 2DSC transistors can offer competitive performance. A high current device requires simultaneous minimization of the contact resistance and channel length, which is a nontrivial challenge for atomically thin 2DSCs, since the typical low contact resistance approaches for 2DSCs either degrade the electronic properties of the channel or are incompatible with the fabrication process for short channel devices. Here, we report a new approach toward high-performance MoS 2 transistors by using a physically assembled nanowire as a lift-off mask to create ultrashort channel devices with pristine MoS 2 channel and self-aligned low resistance metal/graphene hybrid contact. With the optimized contact in short channel devices, we demonstrate sub-100 nm MoS 2 transistor delivering a record high ON-current of 0.83 mA/μm at 300 K and 1.48 mA/μm at 20 K, which compares well with that of silicon devices. Our study, for the first time, demonstrates that the 2DSC transistors can offer comparable performance to the 2017 target for silicon transistors in International Technology Roadmap for Semiconductors (ITRS), marking an important milestone in 2DSC electronics.

Electrospinning, a process that converts a solution or melt droplet into an ejected jet under a high electric field, is a well-established technique to produce one-dimensional (1D) fibers or two-dimensional (2D) randomly arranged fibrous meshes. Nevertheless, the direct electrospinning of fibers into controllable three-dimensional (3D) architectures is still a nascent technology. Here, we apply near-field electrospinning (NFES) to directly write arbitrarily shaped 3D structures through consistent and spatially controlled fiber-by-fiber stacking of polyvinylidene fluoride (PVDF) fibers. An element central to the success of this 3D electrospinning is the use of a printing paper placed on the grounded conductive plate and acting as a fiber collector. Once deposited on the paper, residual solvents from near-field electrospun fibers can infiltrate the paper substrate, enhancing the charge transfer between the deposited fibers and the ground plate via the fibrous network within the paper. Such charge transfer grounds the deposited fibers and turns them into locally fabricated electrical poles, which attract subsequent in-flight fibers to deposit in a self-aligned manner on top of each other. This process enables the design and controlled fabrication of electrospun 3D structures such as grids, walls, hollow cylinders, and other 3D logos. As such, this technique has the potential to advance the existing electrospinning technologies in constructing 3D structures for biomedical, microelectronics, and MEMS/NMES applications.

A comparative study of the electronic structure of methylammonium (CH3NH3) in organometallic lead triiodide perovskite (CH3NH3PbI3) thin films synthesized using either one- or two-step deposition protocols is performed using angle-resolved C K-edge soft X-ray absorption spectroscopy (XAS) and model calculations. We find that our XAS measurements can be accurately related to the ground-state unoccupied orbitals using a simple crystal field model. We further find that films made by the one-step deposition protocol exhibit angle-dependent features, indicating long-range alignment of the CH3NH3 molecules, although the angle-dependency decreases as the film thickness increases. No angle-dependency was observed in the films made via the two-step deposition method.