Semiconducting ink based on 2D single‐crystal flakes with dangling‐bond‐free surfaces enables the implementation of high‐performance devices on form‐free substrates by cost‐effective and scalable printing processes. However, the lack of solution‐processed p‐type 2D semiconducting inks with high mobility is an obstacle to the development of complementary integrated circuits. Here, a versatile strategy of doping with Br2 is reported to enhance the hole mobility by orders of magnitude for p‐type transistors with 2D layered materials. Br2‐doped WSe2 transistors show a field‐effect hole mobility of more than 27 cm2 V−1 s−1, and a high on/off current ratio of ≈107, and exhibits excellent operational stability during the on‐off switching, cycling, and bias stressing testing. Moreover, complementary inverters composed of patterned p‐type WSe2 and n‐type MoS2 layered films are demonstrated with an ultra‐high gain of 1280 under a driving voltage (VDD) of 7 V. This work unveils the high potential of solution‐processed 2D semiconductors with low‐temperature processability for flexible devices and monolithic circuitry.

Crystalline films offer various physical properties based on the modulation of their thicknesses and atomic structures. The layer-by-layer assembly of atomically thin crystals provides a powerful means to arbitrarily design films at the atomic level, which are unattainable with existing growth technologies. However, atomically clean assembly of the materials with high scalability and reproducibility remains challenging. We report programmed crystal assembly of graphene and monolayer hexagonal boron nitride, assisted by van der Waals interactions, to form wafer-scale films of pristine interfaces with near-unity yield. The atomic configurations of the films are tailored with layer-resolved compositions and in-plane crystalline orientations. We demonstrate batch-fabricated tunnel device arrays with modulation of the resistance over orders of magnitude by thickness control of the hexagonal boron nitride barrier with single-atom precision and large-scale, twisted multilayer graphene with programmable electronic band structures and crystal symmetries. Our results constitute an important development in the artificial design of large-scale films.

To utilize the intrinsic properties of 2D materials, it is important to control both interlayer interfaces and intralayer dislocations. Significant efforts have been made mostly to suppress the formation of crystalline disorders by developing advanced material growths [10][11][12] and integration techniques, [13] resulting in single-crystalline materials with atomically clean interfaces. However, structural boundaries can provide exciting control knobs to program the material properties beyond what is available in the thermodynamically most stable forms if the boundaries are fabricated controllably. Prototypical examples are the electrical doping of materials by introducing impurities [14] and optimizing device performances for targeted functionalities by forming heterojunctions. [15] Furthermore, 2D materials of van der Waals (vdW) structures arbitrarily enable the control of their atomic configurations due to the weak interlayer interactions. Therefore, various types of structural boundaries with different crystalline symmetries and band structures have been reported even in a single material platform by atomic displacements, [16,17] crystalline misorientation, [18] and distortions of chemical bonding [19,20] without the introduction of foreign materials. They have provided testbeds to discover novel electrical properties, [21] which are inaccessible in perfect crystals. However, direct applications of the material properties are elusive due to the lack of techniques to precisely control the boundaries over technologically relevant scales.In this review, we discuss about the emerging properties of structural boundaries in vdW structures and the developments of techniques to control the boundaries at the atomic scale. We focus on boundary structures caused by atomic displacements within a single-crystalline material, rather than heterogeneous boundaries with chemical complexity, which have been summarized in detail elsewhere. [22] We discuss the remaining critical issues to reproduce functional boundaries by a designer approach for the discovery of properties and applications in electronics and provide our outlook on the directions in the field. Boundary Types and Related Properties in vdW SolidsA grain boundary is an interfacial plane that exists between two perfect crystallites. The boundaries are not randomly formed, and the resultant structures are restricted by the crystalline lattices, in which they are embedded. The structural defects emerge at the boundaries of misaligned crystalline domains, whose rotation axis most likely points to the out-of-plane Engineering the boundary structures in 2D materials provides an unprecedented opportunity to program the physical properties of the materials with extensive tunability and realize innovative devices with advanced functionalities. However, structural engineering technology is still in its infancy, and creating artificial boundary structures with high reproducibility remains difficult. In this review, various emergent properties of 2D materials with different ...

Nonlinear multiphoton absorption induced by focusing near infrared (NIR) femtosecond (fs) laser pulses into a transparent cornea allows surgery on neovascular structures with minimal collateral damage. In this report, we introduce an fs laser-based microsurgery for selective treatment of rat corneal neovascularizations (in vivo). Contiguous tissue effects are achieved by scanning a focused laser pulse below the corneal surface with a fluence range of 2.2–8.6 J/cm2. The minimal visible laser lesion (MVL) threshold determined over the corneal neovascular structures was found to be 4.3 J/cm2. Histological and optical coherence tomography examinations of the anterior segment after laser irradiations show localized degeneration of neovascular structures without any unexpected change in adjacent tissues. Furthermore, an approximately 30 % reduction in corneal neovascularizations was observed after 5 days of fs laser exposure. The femtosecond laser is thus a promising tool for minimally invasive intrastromal surgery with the aid of a significantly smaller and more deterministic photodisruptive energy threshold for the interaction between the fs laser pulse and corneal neovascular structures.