Abstract
Atomic-scale metal films exhibit intriguing size-dependent film stability, electrical conductivity, superconductivity, and chemical reactivity. With advancing methods for preparing ultra-thin and atomically smooth metal films, clear evidences of the quantum size effect have been experimentally collected in the past two decades. However, with the problems of small-area fabrication, film oxidation in air, and highly-sensitive interfaces between the metal, substrate, and capping layer, the uses of the quantized metallic films for further ex-situ investigations and applications have been seriously limited. To this end, we develop a large-area fabrication method for continuous atomic-scale aluminum film. The self-limited oxidation of aluminum protects and quantizes the metallic film and enables ex-situ characterizations and device processing in air. Structure analysis and electrical measurements on the prepared films imply the quantum size effect in the atomic-scale aluminum film. Our work opens the way for further physics studies and device applications using the quantized electronic states in metals.
Highlights
Electrical transport properties can be enhanced by using high-quality metals owing to the reduced loss,[6,7] which could benefit the fabrication of superconducting qubits.[1]
With film thickness reduced from the nanometer scale to the atomic scale, a metal exhibits intriguing properties, due to so-called quantum size effect, and opens a window for fundamental science exploration and novel device development.[8,9,10,11,12]
The continuous Al film of few atomic layers, observed in the cross-sectional TEM images, showing anomalous electrical properties in both normal and superconducting states, which could be explained with quantum size effect
Summary
High-quality nanoscale metal film is a key element in electronic, plasmonic, and nano-photonics devices and circuits.[1,2] For example, it has been demonstrated that the crystal quality of metal films plays an essential role in making high definition optical antennas as well as improving the performance and operating temperature of plasmonic nanolasers.[2,3,4,5] Electrical transport properties can be enhanced by using high-quality metals owing to the reduced loss,[6,7] which could benefit the fabrication of superconducting qubits.[1]. Driven by the huge potential of the quantized electronic/metallic states for various applications, searching for a practical and reliable method for preparing an atomic-scale metal film has been a long-standing challenge for material scientists and engineers.[13,14,15,16,17,18,19,20,21]. The Al films grown on GaAs (001) substrate were ex-situ characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), cross-sectional transmission electron microscopy (TEM), optical reflectivity and four-probe electrical measurements. The continuous Al film of few atomic layers, observed in the cross-sectional TEM images, showing anomalous electrical properties in both normal and superconducting states, which could be explained with quantum size effect. Our work builds a playground for ex-situ studies of the quantum size effect in metals and paves a way for future applications using atomic-scale metal films
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