Search

We report the design and realization of the back focal plane (BFP) imaging for the light emission from a tunnel junction in a low-temperature ultrahigh-vacuum (UHV) scanning tunneling microscope (STM). To achieve the BFP imaging in a UHV environment, a compact "all-in-one" sample holder is designed and fabricated, which allows us to integrate the sample substrate with the photon collection units that include a hemisphere solid immersion lens and an aspherical collecting lens. Such a specially designed holder enables the characterization of light emission both within and beyond the critical angle and also facilitates the optical alignment inside a UHV chamber. To test the performance of the BFP imaging system, we first measure the photoluminescence from dye-doped polystyrene beads on a thin Ag film. A double-ring pattern is observed in the BFP image, arising from two kinds of emission channels: strong surface plasmon coupled emissions around the surface plasmon resonance angle and weak transmitted fluorescence maximized at the critical angle, respectively. Such an observation also helps to determine the emission angle for each image pixel in the BFP image and, more importantly, proves the feasibility of our BFP imaging system. Furthermore, as a proof-of-principle experiment, electrically driven plasmon emissions are used to demonstrate the capability of the constructed BFP imaging system for STM induced electroluminescence measurements. A single-ring pattern is obtained in the BFP image, which reveals the generation and detection of the leakage radiation from the surface plasmon propagating on the Ag surface. Further analyses of the BFP image provide valuable information on the emission angle of the leakage radiation, the orientation of the radiating dipole, and the plasmon wavevector. The UHV–BFP imaging technique demonstrated here opens new routes for future studies on the angular distributed emission and dipole orientation of individual quantum emitters in UHV. [ABSTRACT FROM AUTHOR]

Nonvolatile memories are in strong demand due to the desire for miniaturization, high-speed storage, and low energy consumption to fulfill the rapid developments of big data, the Internet of Things, and artificial intelligence. Hafnia (HfO2)-based materials have attracted significant interest due to the advantages of complementary-metal–oxide–semiconductor (CMOS) compatibility, large coercive voltage, and superior ferroelectricity at an ultra-thin thickness. The comparable ferroelectricity to that of traditional perovskite materials and size advantage of HfO2 result in fascinating storage performance, which can be readily applicable to the fields of integrated non-volatile memories. This Review provides a comprehensive overview of recent developments in HfO2-based ferroelectrics with attention to the origin of ferroelectricity, performance modulation, and recent achievements in the material. Moreover, potential solutions to existing challenges associated with the materials are discussed in detail, including the wake-up effect, long-term fatigue behavior, and imprint challenges, which pave the way for obtaining HfO2-based ferroelectric materials and devices with long service life and high stability. Finally, the range of potential applications for these fascinating new materials is presented and summarized, which include non-volatile memories and neuromorphic systems. This Review intends to present the state-of-the-art HfO2-based ferroelectrics and to highlight the current challenges, possible applications, and future opportunities and can act as an update for recent developments in these intriguing materials and provide guidance for future researchers in the design and optimization of HfO2-based ferroelectric materials and devices. [ABSTRACT FROM AUTHOR]

Piezoelectric fiber composites (PFCs) with interdigitated electrodes have attracted increasing interest in a variety of industrial, commercial, and aerospace markets due to their unique flexibility, adaptability, and improved transverse actuation performance. Viscous plastic processing technique was utilized for the fabrication of PFCs with customized feature sizes. The assembly parameters showed great influence on the performance of PFCs, which was verified by the finite element analysis. The cracks were identified in the fibers underneath the electrode finger after several millions cycles due to the stress and electric field concentration. The electrode finger width was an important structural parameter and showed great influence on the actuation performance and the stress distribution in the PFCs. The finite element analysis revealed that wider electrode finger would be beneficial for reducing the risk of materials failure with slight influence on the actuation performance. [ABSTRACT FROM AUTHOR]