Quantum Engineering With Hybrid Magnonic Systems and Materials (Invited Paper)

Quantum technology has made tremendous strides over the past two decades with remarkable advances in materials engineering, circuit design, and dynamic operation. In particular, the integration of different quantum modules has benefited from hybrid quantum systems, which provide an important pathway for harnessing different natural advantages of complementary quantum systems and for engineering new functionalities. This review article focuses on the current frontiers with respect to utilizing magnons for novel quantum functionalities. Magnons are the fundamental excitations of magnetically ordered solid-state materials and provide great tunability and flexibility for interacting with various quantum modules for integration in diverse quantum systems. The concomitant-rich variety of physics and material selection enable exploration of novel quantum phenomena in materials science and engineering. In addition, the ease of generating strong coupling with other excitations makes hybrid magnonics a unique platform for quantum engineering. We start our discussion with circuit-based hybrid magnonic systems, which are coupled with microwave photons and acoustic phonons. Subsequently, we focus on the recent progress of magnon–magnon coupling within confined magnetic systems. Next, we highlight new opportunities for understanding the interactions between magnons and nitrogen-vacancy centers for quantum sensing and implementing quantum interconnects. Lastly, we focus on the spin excitations and magnon spectra of novel quantum materials investigated with advanced optical characterization

Oxidation behavior of graphene-coated copper at intrinsic graphene defects of different origins

The development of ultrathin barrier films is vital to the advanced semiconductor industry. Graphene appears to hold promise as a protective coating; however, the polycrystalline and defective nature of engineered graphene hinders its practical applications. Here, we investigate the oxidation behavior of graphene-coated Cu foils at intrinsic graphene defects of different origins. Macro-scale information regarding the spatial distribution and oxidation resistance of various graphene defects is readily obtained using optical and electron microscopies after the hot-plate annealing. The controlled oxidation experiments reveal that the degree of structural deficiency is strongly dependent on the origins of the structural defects, the crystallographic orientations of the underlying Cu grains, the growth conditions of graphene, and the kinetics of the graphene growth. The obtained experimental and theoretical results show that oxygen radicals, decomposed from water molecules in ambient air, are effectively inverted at Stone-Wales defects into the graphene/Cu interface with the assistance of facilitators

Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit

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Photoelectrical imaging and characterization of point contacts in pentacene thin-film transistors

We report the spatially resolved electrical response of bottom-contact pentacene thin-film transistors to a scanning, focused laser. We find that pentacene films make point-like electrical contacts to the underlying gold electrodes and are able to image them with diffraction-limited resolution. We can further estimate the interfacial resistance associated with hole-injection at an individual point contact, and show that optical activation of one alone increases device current significantly. © 2010 American Institute of Physics

Laser-based imaging of individual carbon nanostructures

Laser-based imaging and characterization of individual nanostructures provides significant advantages over other imaging techniques, such as scanning probe microscopy and electron microscopy, by allowing simultaneous imaging and spectroscopic measurements. Laser-based techniques also involve simpler sample preparation, cause minimal sample damage and provide high-throughput measurements over large sample areas. In this article, we review recent progress in this field focusing on applications in the study of individual carbon nanostructures, mainly carbon nanotubes and graphene. Absorption, Rayleigh, Raman and photoluminescence techniques will be discussed for optical-based detection, and photocurrent and photothermal current techniques will be discussed for electrical detection. Each optical technique relies on a different physical process, allowing spectroscopic investigation of the fundamental optical, thermal and optoelectronic processes for individual nanoscale carbon structures. In addition, we will compare the various advantages of wide-field and focused (confocal) laser excitation/detection geometries and discuss ongoing efforts to overcome the speed and resolution limitations of laser-based imaging.open1166sciescopu

Large scale metal-free synthesis of graphene on sapphire and transfer-free device fabrication

Metal catalyst-free growth of large scale single layer graphene film on a sapphire substrate by a chemical vapor deposition (CVD) process at 950 degrees C is demonstrated. A top-gated graphene field effect transistor (FET) device is successfully fabricated without any transfer process. The detailed growth process is investigated by the atomic force microscopy (AFM) studies.open1164sciescopu

High-mobility graphene on liquid p-block elements by ultra-low-loss CVD growth

The high-quality and low-cost of the graphene preparation method decide whether graphene is put into the applications finally. Enormous efforts have been devoted to understand and optimize the CVD process of graphene over various d-block transition metals (e.g. Cu, Ni and Pt). Here we report the growth of uniform high-quality single-layer, single-crystalline graphene flakes and their continuous films over p-block elements (e.g. Ga) liquid films using ambient-pressure chemical vapor deposition. The graphene shows high crystalline quality with electron mobility reaching levels as high as 7400 cm(2) V(−1)s(−1) under ambient conditions. Our employed growth strategy is ultra-low-loss. Only trace amounts of Ga are consumed in the production and transfer of the graphene and expensive film deposition or vacuum systems are not needed. We believe that our research will open up new territory in the field of graphene growth and thus promote its practical application

Formation of Graphene Grain Boundaries on Cu(100) Surface and a Route Towards Their Elimination in Chemical Vapor Deposition Growth

Grain boundaries (GBs) in graphene prepared by chemical vapor deposition (CVD) greatly degrade the electrical and mechanical properties of graphene and thus hinder the applications of graphene in electronic devices. The seamless stitching of graphene flakes can avoid GBs, wherein the identical orientation of graphene domain is required. In this letter, the graphene orientation on one of the most used catalyst surface - Cu(100) surface, is explored by density functional theory (DFT) calculations. Our calculation demonstrates that a zigzag edged hexagonal graphene domain on a Cu(100) surface has two equivalent energetically preferred orientations, which are 30 degree away from each other. Therefore, the fusion of graphene domains on Cu(100) surface during CVD growth will inevitably lead to densely distributed GBs in the synthesized graphene. Aiming to solve this problem, a simple route, that applies external strain to break the symmetry of the Cu(100) surface, was proposed and proved efficient