Freestanding, substrate‐free organic field‐effect transistors and organic circuits with a nominal thickness of 320 nm are demonstrated by using a simple water‐floatation method. The devices work well in freestanding status, attached on banknotes, or bent over the blade of a knife. The ultralight devices with extreme bending stability indicate a bright future for organic electronics.

Hybridization of silicon integrated circuits (ICs) with compound semiconductor device arrays are crucial for making functional hybrid chips, which are found to have enormous applications in many areas. Although widely used in manufacturing hybrid chips, the flip-chip technology suffers from several limitations that are difficult to overcome, especially when the demand is raised to make functional hybrid chips with higher device array density without sacrificing the chip footprint. To address those issues, Beida Jade Bird Display Limited has developed its unique wafer-level monolithic hybrid integration technology and demonstrated its advantages in making large-scale hybrid integration of functional device arrays on Si IC wafers. Active matrix micro-light-emitting diode micro-displays with a resolution of 5000+ pixel per inch were successfully fabricated using Beida Jade Bird Display Limited's monolithic hybrid integration technology. The general fabrication method is described, and the result is presented in this paper. The fabricated monochromatic micro-light-emitting diode micro-displays exhibit improved device performance than do other micro-display technologies and have great potentials in applications such as portable projectors and near-to-eye projection for augmented reality. More importantly, the wafer-scale monolithic hybrid integration technology offers a clear path for low-cost mass production of hybrid optoelectronic IC chips.

Driven by an ever-expanding interest in new material systems with new functionality, the growth of atomic-scale electronic materials by molecular beam epitaxy (MBE) has evolved continuously since the 1950s. Here, a new MBE technique called hybrid-MBE (hMBE) is reviewed that has been proven a powerful approach for tackling the challenge of growing high-quality, multicomponent complex oxides, specifically the ABO 3 perovskites. The goal of this work is to (1) discuss the development of hMBE in a historical context, (2) review the advantageous surface kinetics and chemistry that enable the self-regulated growth of ABO 3 perovskites, (3) layout the key components and technical challenges associated with hMBE, (4) review the status of the field and the materials that have been successfully grown by hMBE which demonstrate its general applicability, and (5) discuss the future of hMBE in regards to technical innovations and expansion into new material classes, which are aimed at expanding into industrial realm and at tackling new scientific endeavors.

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Strain engineering of thin films is a conventionally employed approach to enhance material properties and to energetically prefer ground states that would otherwise not be attainable. Controlling strain states in perovskite oxide thin films is usually accomplished through coherent epitaxy by using lattice-mismatched substrates with similar crystal structures. However, the limited choice of suitable oxide substrates makes certain strain states experimentally inaccessible and a continuous tuning impossible. Here, we report a strategy to continuously tune epitaxial strains in perovskite films grown on Si(001) by utilizing the large difference of thermal expansion coefficients between the film and the substrate. By establishing an adsorption-controlled growth window for SrTiO thin films on Si using hybrid molecular beam epitaxy, the magnitude of strain can be solely attributed to thermal expansion mismatch, which only depends on the difference between growth and room temperature. Second-harmonic generation measurements revealed that structure properties of SrTiO films could be tuned by this method using films with different strain states. Our work provides a strategy to generate continuous strain states in oxide/semiconductor pseudomorphic buffer structures that could help achieve desired material functionalities.

Pd nanoparticles (NPs) were prepared by focused femtosecond laser irradiation of PdCl2 dissolved in ethanol. Transmission electron microscopy (TEM) analysis revealed that Pd NPs show certain crystalline microstructure, and the average diameter is 3.4 nm with narrow size distribution from 2.0 to 6.0 nm. The nonlinear optical absorption and refraction of Pd NPs solution were investigated with nanosecond laser pulses at 532 nm. The nonlinear absorption of Pd NPs is saturable at low intensity of 3.28×1011 W/m2 but it is changed to reverse saturable with the intensity increased to 7.96×1011 W/m2, which accordingly indicates the nonlinear refraction is changed from self-defocusing to self-focusing. The transition of the nonlinear absorption with the increase in pulse intensity is analyzed by an empirical model which includes mostly saturable absorption (SA) and two-photon absorption (TPA). The intensity of saturable Is is obtained, along with TPA coefficient β. SA and TPA are both originated from the interband transition between the d band and s-p conduction band. The SA possess less occupied density of states in the ground state and less unoccupied density of states in the excited state than that of TPA, so the TPA dominates the nonlinear absorption when the pulse intensity is high, leading to as-observed transition from SA to TPA. The refraction variation with increase in pulse intensity is attributed to the interband transition of electrons from d band to s-p conduction band in the Pd NPs.

Multiferroic BiFeO 3 (BFO) films with spontaneously formed periodic stripe domains can generate abovegap open circuit voltages under visible light illumination; nevertheless the underlying mechanism behind this intriguing optoelectronic response has not been understood to date. Here, we make contact-free measurements of light-induced currents in epitaxial BFO films via detecting terahertz radiation emanated by these currents, enabling a direct probe of the intrinsic charge separation mechanisms along with quantitative measurements of the current amplitudes and their directions. In the periodic stripe samples, we find that the net photocurrent is dominated by the charge separation across the domain walls, whereas in the monodomain samples the photovoltaic response arises from a bulk shift current associated with the non-centrosymmetry of the crystal. The peak current amplitude driven by the charge separation at the domain walls is found to be 2 orders of magnitude higher than the bulk shift current response, indicating the prominent role of domain walls acting as nanoscale junctions to efficiently separate photogenerated charges in the stripe domain BFO films. These findings show that domain-wall-engineered BFO thin films offer exciting prospects for ferroelectric-based optoelectronics, as well as bias-free strong terahertz emitters.

We propose and demonstrate an optical signal processor performing matrix-vector multiplication, which is composed of laser-modulator array, multiplexer, splitter, microring modulator matrix and photodetector array. 8 × 10⁷ multiplications and accumulations (MACs) per second is implemented at the clock at a clock frequency of 10 MHz. All functional units can be ultimately monolithically integrated on a chip with the development of silicon photonics and an efficient high-performance computing system is expected in the future.