Epitaxy of wafer-scale single-crystal MoS2 monolayer via buffer layer control.

Monolayer molybdenum disulfide (MoS2), an emergent two-dimensional (2D) semiconductor, holds great promise for transcending the fundamental limits of silicon electronics and continue the downscaling of field-effect transistors. To realize its full potential and high-end applications, controlled synthesis of wafer-scale monolayer MoS2 single crystals on general commercial substrates is highly desired yet challenging. Here, we demonstrate the successful epitaxial growth of 2-inch single-crystal MoS2 monolayers on industry-compatible substrates of c-plane sapphire by engineering the formation of a specific interfacial reconstructed layer through the S/MoO3 precursor ratio control. The unidirectional alignment and seamless stitching of MoS2 domains across the entire wafer are demonstrated through cross-dimensional characterizations ranging from atomic- to centimeter-scale. The epitaxial monolayer MoS2 single crystal shows good wafer-scale uniformity and state-of-the-art quality, as evidenced from the ~100% phonon circular dichroism, exciton valley polarization of ~70%, room-temperature mobility of ~140 cm2v-1s-1, and on/off ratio of ~109. Our work provides a simple strategy to produce wafer-scale single-crystal 2D semiconductors on commercial insulator substrates, paving the way towards the further extension of Moore's law and industrial applications of 2D electronic circuits.

Electron/infrared-phonon coupling in ABC trilayer graphene.

Stacking order plays a crucial role in determining the crystal symmetry and has significant impacts on electronic, optical, magnetic, and topological properties. Electron-phonon coupling, which is central to a wide range of intriguing quantum phenomena, is expected to be intricately connected with stacking order. Understanding the stacking order-dependent electron-phonon coupling is essential for understanding peculiar physical phenomena associated with electron-phonon coupling, such as superconductivity and charge density waves. In this study, we investigate the effect of stacking order on electron-infrared phonon coupling in graphene trilayers. By using gate-tunable Raman spectroscopy and excitation frequency-dependent near-field infrared nanoscopy, we show that rhombohedral ABC-stacked trilayer graphene has a significant electron-infrared phonon coupling strength. Our findings provide novel insights into the superconductivity and other fundamental physical properties of rhombohedral ABC-stacked trilayer graphene, and can enable nondestructive and high-throughput imaging of trilayer graphene stacking order using Raman scattering.

10× continuous optical zoom imaging using Alvarez lenses actuated by dielectric elastomers.

Optical zoom is an essential function for many imaging systems including consumer electronics, biomedical microscopes, telescopes, and projectors. However, most optical zoom imaging systems have discrete zoom rates or narrow zoom ranges. In this work, a continuous optical zoom imaging system with a wide zoom range is proposed. It consists of a solid lens, two Alvarez lenses, and a camera with an objective. Each Alvarez lens is composed of two cubic phase plates, which have inverted freeform surfaces concerning each other. The movement of the cubic phase masks perpendicular to the optical axis is realized by the actuation of the dielectric elastomer. By applying actuation voltages to the dielectric elastomer, cubic phase masks are moved laterally and then the focal lengths of the two Alvarez lenses are changed. By adjusting the focal lengths of these two Alvarez lenses, the optical magnification is tuned. The proposed continuous optical zoom imaging system is built and the validity is verified by the experiments. The experimental results demonstrate that the zoom ratio is up to 10×, i.e., the magnification continuously changes from 1.58× to 15.80× when the lateral displacements of the cubic phase masks are about 1.0 mm. The rise and fall response times are 150 ms and 210 ms, respectively. The imaging resolution can reach 114 lp/mm during the optical zoom process. The proposed continuous optical imaging system is expected to be used in the fields of microscopy, biomedicine, virtual reality, etc.

MoS2-Thin Film Transistor Based Flexible 2T1C Driving Circuits for Active-Matrix Displays.

Two-dimensional (2D) semiconductors offer great potential as high-performance materials for thin film transistors (TFTs) in displays. Their thin, stable, and flexible nature, along with excellent electrical properties, makes them suitable for flexible displays. However, previous demonstrations lacked clear superiority in pixel resolution and TFT performance. Here we present the flexible 2T1C pixel driving circuit for active-matrix displays based on high-quality large-scale monolayer MoS2. A gate-first fabrication process was developed for flexible MoS2-TFTs, showing a remarkable carrier mobility (average at 52.8 cm2 V-1 s-1), high on/off ratio (average at 1.5 × 108), and negligible hysteresis. The driving current can be modulated by pulsed input voltages and demonstrates a stable and prompt response to both frequency and amplitude. We also demonstrated a 10 × 10 active-matrix with high resolution of 508 pixels per inch, exhibiting 100% yield and high uniformity. The driving circuit works well under bending up to ∼0.91% strain, highlighting its normal functions in flexible displays.

Review of state-of-the-art artificial compound eye imaging systems.

The natural compound eye has received much attention in recent years due to its remarkable properties, such as its large field of view (FOV), compact structure, and high sensitivity to moving objects. Many studies have been devoted to mimicking the imaging system of the natural compound eye. The paper gives a review of state-of-the-art artificial compound eye imaging systems. Firstly, we introduce the imaging principle of three types of natural compound eye. Then, we divide current artificial compound eye imaging systems into four categories according to the difference of structural composition. Readers can easily grasp methods to build an artificial compound eye imaging system from the perspective of structural composition. Moreover, we compare the imaging performance of state-of-the-art artificial compound eye imaging systems, which provides a reference for readers to design system parameters of an artificial compound eye imaging system. Next, we present the applications of the artificial compound eye imaging system including imaging with a large FOV, imaging with high resolution, object distance detection, medical imaging, egomotion estimation, and navigation. Finally, an outlook of the artificial compound eye imaging system is highlighted.

Compound eye and retina-like combination sensor with a large field of view based on a space-variant curved micro lens array.

A compound eye and retina-like combination sensor based on a space-variant curved micro lens array (CMLA) is proposed to simultaneously offer the large FOV characteristic of a compound eye and retina-like feature of a single aperture eye. The mathematical models of the sensor are developed and the structure parameters of the space-variant CMLA are deduced. Modeling verification is carried out and the results show that the whole field of view (FOV) of the sensor is 105° and the optical information loss rate is 0.06 when the sector is 32. Imaging simulations illustrate that the sensor possesses the retina-like property, i.e., logarithmic-polar transformation. Meanwhile, the simulation results indicate that the overlapping angles between the two micro lenses on the adjacent rings can be reduced by decreasing the rings and the blind radius, and increasing the sectors. This work is beneficial for large FOV and time-efficient applications.